Effects of radioactive by-products along the extraction of rare ...

Effects of radioactive by-products along the extraction of rare earth elements on

aquatic and terrestrial organisms

Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der RWTH Aachen University zur Erlangung des akademischen Grades eines

Doktors der Naturwissenschaften genehmigte Dissertation

vorgelegt von

Matthias Findeiß, Diplom Biologe aus Erlangen, Deutschland

Berichter: Universitätsprofessor Dr. Andreas Schäffer

Universitätsprofessor Dr. Henner Hollert

Tag der mündlichen Prüfung: 13.12.2016

Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar

Erklärung:

Ich versichere, dass ich diese Doktorarbeit selbständig und nur unter

Verwendung der angegebenen Hilfsmittel angefertigt habe. Weiterhin

versichere ich, die genutzten Quellen als solche kenntlich gemacht zu haben.

Matthias Findeiß

Aachen, am 4. Oktober 2016

Funding

This research was financially supported by the SIEMENS AG under the SIEMENS

Forschungsbereich (S-FB) “Rare earth: Green Mining & Separation”.

Acknowledgements

First and foremost, I would like to thank Andreas Schäffer for giving me the opportunity to pursue my

Ph.D. in Aachen. I am grateful for your excellent guidance, input and instruction but more

importantly for the immense patience you showed to me throughout my Ph.D.

Thanks to Dr. Burkhard Schmidt, Dr. Thomas Preuß, Prof. Dr. Henner Hollert and Dr. Martina Roß-

Nickoll for being there whenever I needed help. Furthermore I wish to thank Prof. Hollert for being

my second referee.

I am thankful to Prof. Dr. Wegener and Dr. Thomas to make it possible to join this project and Dr.

Stanzel for supervising me.

Many thanks to the Oceans 9, Karoline Raulf, Stefanie Kruse, Theresa Stark, Kilian Neubert, Hanno

Vogel, Nico Stoltz, Daniel Voßenkaul and Patrick Friedrichs, it was a pleasure to work with you and I

hope we will stay together as friends.

For being not only excellent colleagues but especially wonderful friends over all these years, I wish to

thank Felix Stibany, Benjamin Daniels, Anne Wyrwoll, Björn Deutschmann, Anne Simon, Jochen

Kuckelkorn, Eva Penssler, Hanna Maes, Andrzej Schiwy and Stefan Rhiem. For their valuable advices

and helping hands in and next to the laboratory, I like to thank Brigitta Goffart, Anne Schoer, PD. Dr.

Sven Sindern, Irene Knisch, Brigitte Thiede, Hilde Patti, Claudia Poßberg, Dennis Goebele and Telse

Bauer.

I loved to be connected within the institute (UBC & ESA) so my gratitude goes to all the friends I have

forgotten to mention. It was a great time! Thanks to Peggy Heine, Jea-gyn Byun, Jonas Hausen, Ann-

Katrin Luk and Michael Hennig it was always fun with you.

Thanks to Kadda Graf for supporting me during all the ups and downs, and especially the time of

hardest work - my writing.

I wish to thank my family for their never-ending support and patience.

Zusammenfassung

i

Zusammenfassung

Lanthanide, auch Seltene Erd Elemente (SEE) genannt, sind Schüsselelemente in vielen modernen

Technologien mit einem besonderen Fokus auf grüne Technologien wie zum Beispiel die

Energieerzeugung durch Windkraftanlagen. Daher sind sie von großer wirtschaftlicher Bedeutung

und werden jährlich in Mengen von mehr als 120 000 t produziert. Eine ausführliche

Umweltbewertung, die alle möglichen Risiken identifiziert, ist die Grundlage, um die Nachhaltigkeit

der Bergbau-, Aufbereitungs-, und Separationsprozesse zu bewerten.

Seltene Erd Elemente liegen meist vergesellschaftet mit Actiniden wie Uran und Thorium vor.

Während der Anreicherung und Aufbereitung der SEE werden daher gleichzeitig auch Actiniden und

deren Zerfallsprodukte angereichert. Neben den klassischen Abbaumineralien wie Bastnasit oder

Monazit kann auch das Mineral Eudialyt zur SEE-Gewinnung abgebaut werden. Dessen Gesamtanteil

an SEE ist zwar geringer, enthält aber für die Industrie besonders wichtige SEE. Des Weiteren ist der

Anteil von radioaktiven Begleitstoffen sehr gering. Derzeit wird Eudialyt nicht als Wertstoffmineral

genutzt, wird aber wahrscheinlich in der Zukunft an Bedeutung gewinnen.

Über die Umweltauswirkungen der SEE–Gewinnung sind nur wenige Informationen öffentlich

zugänglich, insbesondere in Bezug auf die radioaktiven Begleitprodukte. Thorium ist das

prominenteste Abfallelement in der SEE Gewinnung. Ein erstes Ziel dieser Arbeit war es, den

α-Strahler Thorium und dessen Einfluss auf die Umwelt zu untersuchen. Dazu wurde zunächst eine

intensive Literaturrecherche durchgeführt und deren Inhalte aufbereitet. Darin wird besonders auch

auf die gut dokumentierten Langzeit-Effekte von Thorium-Stäuben und gasförmigen Emissionen

eingegangen. Deshalb und weil eine ökotoxikologische Untersuchung der gasförmigen Emissionen

aus technischen Gründen nicht möglich war, wurden bislang unbekannte Effekte wie die aquatische

und terrestrische Toxikologie untersucht. Daher bieten die gewonnenen Erkenntnisse eine Ergänzung

der fehlenden Daten für eine umfassende Bewertung von Thorium. Es wurde eine Analyse von

Thorium Stoffflüssen entlang der Prozesskette der SEE-Gewinnung durchgeführt, sowie die Effekte

Zusammenfassung

ii

von Abgängen und beteiligten Produkten anhand von ökotoxischen Tests mit aquatischen und

terrestrischen Organismen bestimmt.

In Experimenten mit Thorium wurde vornehmlich die Schwermetalleigenschaft betrachtet, da die

Strahlungseigenschaft bei reinem Thorium 232 mit einer Halbwertszeit von ca. 14 Milliarden Jahren

eine untergeordnete Rolle in den bei ökotoxikologischen Tests üblichen Zeiträumen spielt. Darüber

hinaus ist zu berücksichtigen, dass Thorium in der Natur zusammen mit seinen Zerfallsprodukten

auftritt. Thorium (Th(OH)4 bei pH 6,5 - 8) zeigte bei allen untersuchten aquatischen (Bakterien, Algen

und Daphnien) wie terrestrischen (Springschwänze, Regenwürmer) Organismen keine toxischen

Effekte. Es scheint somit als Schwermetall in den Bereichen der Wasserlöslichkeit und in typischen

Bodenkonzentrationen unproblematisch für die untersuchten Organismen zu sein.

Die Auswirkungen von Abwässern der verschiedenen Prozessschritte der Gewinnung von SEE wurden

anhand von Eudialyt als ein Beispiel für ein SEE- Mineral untersucht. Abbildung I zeigt die

Prozesskette: das Mineral wird zuerst aufbereitet und dabei gemahlenen und flotiert, es folgt ein

physikalischer Anreicherungsprozess und ein chemischer Aufbereitungsprozess. Abwässer all dieser

Prozessschritte wurden durch ökotoxikologische Tests mit aquatischen (Algen und Daphnien) und

terrestrischen (Springschwänze) Organismen untersucht. Gemahlener und flotierter Eudialyt weist

keine oder nur sehr geringe ökotoxikologische Effekte auf. Dagegen zeigt sich, dass die

Laugungsrückstände in Konzentrationen, die an den Produktionsstätten und Bodenablagerungen

anfallen, einen negativen Einfluss auf alle getesteten Organismen haben (siehe Abbildung 1).

Zusammenfassung

iii

Abbildung 1: Ökotoxikologische Untersuchung der S-FB Prozess-Abfallströme

Aufgrund der Mischtoxizität der Metalle ist es jedoch schwer zu abzuschätzen, welchen Anteil ein

bestimmtes Metall an der gesamten Toxizität hat. Es ist bekannt, dass sich die Toxizität von Metallen

in verschiedenen Organismen unterscheidet. Ein allgemeiner Trend zeigt folgende

Toxizitätsreihenfolge: Hg > Ag > Cu > Cd > Zn > Ni > Pb > Cr > Sn (Luoma & Rainbow 2011; Merian et

al. 2004; F. Scheffer & Schachtschabel 2010). Im Boden hat der pH-Wert (Bodenacidität) den größten

Einfluss auf die Metallverfügbarkeit, während höhere pH-Werte die Schwermetallverfügbarkeit

vermindern. Nimmt der pH-Wert zu, sinkt die Schwermetallmobilität und damit ihre biologische

Verfügbarkeit.

Es konnte gezeigt werden, dass Rückstände aus dem SEE- Abbau so gelagert werden sollten, dass sie

keinen Auswaschungsprozessen durch Regen oder Überschwemmungen ausgesetzt sind. Auch sollte

eine reine Aufschüttung der Rückstände vermieden werden, da es sonst zu Auswaschungen kommen

und zum anderen terrestrische Organismen negativ beeinflusst werden könnten. Abschließend ist

festzuhalten, dass die Deponierung der Laugungsrückstände überwacht (Monitoring) werden muss,

da diese nicht frei auf Halden gelangen dürfen. Auf Halden ist vor allem darauf zu achten, dass sich

der Feinstaub, der durch das Mahlen entsteht, nicht ausbreitet, was durch eine kontinuierliche

Befeuchtung der Halden erzielt werden kann.

Zusammenfassung

iv

Summary

v

Summary

Lanthanides, also called rare earth elements (REE) are key elements in modern technologies and

especially in green technologies such as energy generation through wind power. Thus, they are of

considerable economic importance with a global production of around 124 000 t REE per year. A

detailed environmental assessment with identification of all risks is the foundation to assess the

sustainability of mining, processing and separation processes. Rare earth elements usually are found

together with actinides such as uranium and thorium. Therefore, actinides and their decay products

are simultaneously enriched during the processing of REE. In addition to conventional REE minerals

such as monazite or bastnasite, the mineral eudialyte can be used as a REE source. Even though, the

total share of REE is low, the most important REE needed for industrial usages are strongly

represented in eudialyte. Furthermore, the proportion of radioactive impurities is very low. Eudialyte

is currently not used as source mineral, but might play a bigger role on the global market in the

future.

Little information about the environmental impacts of REE-production is available to the public, in

particular with regard to its radioactive by-products. Thorium is the most prominent of these and has

therefore been characterized in detail for its ecotoxicity. A first goal of this work was to evaluate the

α- emitter thorium and its impact on the environment. To this aim, an intensive literature search was

conducted and results were prepared including the long-term effects of thorium dust and gaseous

emissions. Therefore and because ecotoxicological testing of gaseous emissions was technically

difficult and environmentally less relevant – unlike its immense impact for exposed industrial workers

and bystanders – the water effluent und solid waste streams were investigated with aquatic and

terrestrial toxicological experiments. The knowledge gained is meant to supplement the missing data

for thorium. A throughout analysis of thorium fluxes along the process of SEE recovery was carried

out, and the effects of disposals and other products involved were measured based on

ecotoxicological tests with aquatic and terrestrial organisms.

In experiments with thorium exclusively the heavy metal property was regarded since radiation

effects with a radioactivity half-life of approximately 14 billion years play a subordinate role in typical

Summary

vi

ecotoxicological testing periods. Moreover, it should be noted that thorium occurs in nature

alongside its decay products. Th(OH)4 at pH 6.5 to 8 showed no toxic effects in all organisms studied,

aquatic (bacteria, algae and daphnia) and terrestrial (springtails, earthworms). Thorium thus does not

appear to be a problem in the range of water solubility and in soil concentrations typical found.

The effects of process wastewater from various process steps in the production of REE were

evaluated based on eudialyte, which was investigated as an example for REE minerals. Figure 1

shows the investigated process steps of eudialyte: after mining, drill, blast and load haul operation,

the ore is milled and grinded. In order to enrich it, the wanted mineral is flotated. Afterwards

chemicals (acids) are added to dissolve the minerals. Impurities are removed by pH adjustment and

precipitation which is also used for REE separation later. Stronger REE separation is achieved by

solvent extraction and finally pure REE are obtained by electrolysis. Ground and flotated eudialyte

had no or very little ecotoxicological effects. By contrast, leaching residues showed that

concentrations which arise during production have a negative impact on all tested organisms (see

figure 1).

Figure 1: Ecotoxicological investigation of S-FB process-waste streams

Summary

vii

Due to mixture toxicity, it is difficult to estimate which compound is responsible for the total toxicity.

It is known that the toxicity of metals differs in various organisms. A general trend shows the

following toxicity sequence: Hg> Ag> Cu> Cd> Zn> Ni> Pb> Cr> Sn (Luoma & Rainbow 2011; Merian et

al. 2004; F. Scheffer & Schachtschabel 2010). In soil the pH value (soil acidity) has the greatest impact

on the metal availability. If the pH value increases, the mobility of heavy metals decreases and thus

their availability is reduced.

The current study showed that residues from rare earth mining should be stored in a way that

ensures that wash-out processes do not affect the water or soil systems. Even tailing dams should be

avoided, since otherwise leaching residues can still be washed out, and, on the other hand, terrestrial

organisms may be adversely affected. In conclusion, the dumping of leaching residues should be

monitored so that they will not pass freely to stockpiles. Additionally, it is important to avoid fine

dust which is produced by grinding processes and must not drift. This can be achieved by continuous

humidification of stockpiles.

List of abbreviations


µg micro gram

µm micro meter

a year

AMD acid mine drainages

Bq Bequerel

BRK long time fluid culture for algae after Bringmann & Kühn

CL confidential limit

d day

DIN German Institute of Standardization (Deutsches Institut für Normierung)

ECx Effect concentration causing X% effect

EDTA Ethylenediaminetetraacetic acid

EU eudialyte

FGD Flue Gas Desulphurisation

g unit of gravitational force

h hour

HCl hydrochloric acid

HDPE high density polyethylene

HREE heavy rare earth elements

ICP-MS Inductively coupled plasma mass spectrometry

ISO International Organization for Standardization

Kd Liquid solid partition coefficient

kg kilogram

l litre

LCx Lethal concentration causing X% mortality

LOEC Lowest observed effect concentration

LREE light rare earth elements

m meter

mg miligram

min minutes

ml milliliter

mol amount of substances

NOEC No observed effect concentration

NORM naturally-occurring radioactive material

NUF Neutralization Underflow

OECD Organisation for Economic Cooperation and Development

pH negative of the logarithm to base 10 of the molar concentration of hydrogen ions (mol/L)

PP polypropylene

ppm parts per million

RE rare earth

RECl rare earth chloride

REE Rare earth elements

REO rare earth oxids

s second

SEE Seltene Erd Elemente


S-FB Siemens Forschungsbereich

SSD species sensitivity distribution

t ton

TENORM technical enhanced naturally-occurring radioactive material

Th(OH)4 Thorium hydroxide

ThNS thorium nitrate standard solution

ThO2 thorium oxide

ThP2O7 thorium pyrophosphate

WLP water leached purification

INDEX

I

INDEX

1. Chapter: Background and scope ................................................................... 1

1.1 Background and scope of the thesis ....................................................................................... 2

1.2 Structure of the thesis ............................................................................................................. 3

2. Chapter: Introduction ....................................................................................... 5

2.1 General introduction ............................................................................................................... 6

2.1.1 Rare earth –nomenclature and occurrence .................................................................... 6

2.1.2 Health effects of thorium and uranium......................................................................... 10

2.1.3 Ecotoxic effects of thorium and uranium ...................................................................... 11

2.1.4 Environmental behavior of thorium and uranium ........................................................ 12

2.1.5 Summary of ecotoxic effects and calculation of SSDs ................................................... 13

2.2 References ............................................................................................................................. 16

3. Chapter: Fate and environmental impact of thorium residues along

rare earth processing ........................................................................................... 19

3.1 Abstract ................................................................................................................................. 20

3.2 Introduction ........................................................................................................................... 21

3.3 Production processes from ore to metal .............................................................................. 23

3.3.1 Rare Earth Ores ............................................................................................................. 23

3.3.2 From ore to RE concentrate .......................................................................................... 24

3.3.3 From RE concentrate to RE elements ............................................................................ 26

3.4 Waste treatment and storage ............................................................................................... 28

3.4.1 USA (Mountain Pass) ..................................................................................................... 29

3.4.2 China (Bayan Obo) ......................................................................................................... 29

3.4.3 Australia/Malysia (Mt Weld/ Kuantan) ......................................................................... 30

3.5 The impact of thorium release to the environment and regulatory approaches ................. 31

3.5.1 Mining ............................................................................................................................ 33

3.5.2 Beneficiation .................................................................................................................. 33

3.5.3 Leaching ......................................................................................................................... 33

3.5.4 Regulatory approaches .................................................................................................. 34

3.6 Improving waste management ............................................................................................. 35

3.7 Conclusion ............................................................................................................................. 39

3.8 References ............................................................................................................................. 41

4. Chapter: Toxicity of thorium to aquatic and terrestrial organisms:

algae, daphnia and collembola .......................................................................... 47

INDEX

II

4.1 Abstract ................................................................................................................................. 48

4.2 Introduction ........................................................................................................................... 49

4.3 Material and Methods ........................................................................................................... 52

4.3.1 Sample preparation and analytical measurement of thorium solution ........................ 52

4.3.2 Aquatic biotesting with algae (Desmodesmus subspicatus/ Pseudokirchneriella

subcapitata) ................................................................................................................................... 53

4.3.3 Aquatic biotesting with daphnids (Daphnia magna) .................................................... 54

4.3.4 Terrestrial biotesting with collembola (Folsomia candida) ........................................... 54

4.3.5 Terrestrial biotesting with earthworm (Eisenia fetida) ................................................. 55

4.3.6 Statistics ......................................................................................................................... 55

4.4 Results ................................................................................................................................... 56

4.4.1 Aquatic toxicity .............................................................................................................. 56

4.4.2 Terrestrial toxicity.......................................................................................................... 57

4.5 Discussion .............................................................................................................................. 59

4.6 Conclusion ............................................................................................................................. 61

4.7 References ............................................................................................................................. 62

5. Chapter: Environmental consequence arising from eudialyte

processing ................................................................................................................ 67

5.1 Abstract ................................................................................................................................. 68

5.2 Introduction ........................................................................................................................... 69

5.3 Material and Methods ........................................................................................................... 72

5.3.1 Preparation of process waste streams .......................................................................... 72

5.3.2 Algae (Desmodesmus subspicatus) ................................................................................ 73

5.3.3 Daphnids (Daphnia magna) ........................................................................................... 73

5.3.4 Collembola (Folsomia candida) ..................................................................................... 74

5.3.5 Statistics ......................................................................................................................... 74

5.4 Results ................................................................................................................................... 74

5.5 Discussion .............................................................................................................................. 78

5.6 Conclusion ............................................................................................................................. 81

5.7 References ............................................................................................................................. 82

6. Chapter: Conclusion ....................................................................................... 86

6.1 General conclusion ................................................................................................................ 87

6.2 References ............................................................................................................................. 92

ANNEX ........................................................................................................................ 94

INDEX

III

1. ANNEX: Toxicity of thorium to aquatic and terrestrial organisms: algae, daphnia and

collembola ......................................................................................................................................... 95

2. ANNEX: Environmental consequence arising from eudialyte processing ................................. 96

3. ANNEX: Preparation of eudialyte mineral ................................................................................ 97

Flotation ........................................................................................................................................ 97

Acidified eudialyte ......................................................................................................................... 98

4. ANNEX: Decay chain of thorium ............................................................................................... 99

5. ANNEX: Decay chain of uranium ............................................................................................ 100

6. ANNEX: Endpoints used to determine the SSD ...................................................................... 102

7. ANNEX: References ................................................................................................................. 104

INDEX

IV

List of figures

Figure 1: Periodic system of elements .................................................................................................... 6

Figure 2: Rare earth usage by application ............................................................................................... 7

Figure 3: Global distribution of REE mines .............................................................................................. 9

Figure 4: Short-term SSD representing the toxicity of a) lanthanum, b) cerium and c) uranium ......... 14

Figure 5: Rare earth elements, thorium and uranium effect concentrations ....................................... 15

Figure 6: Sketch of thorium enrichment during REE processing ........................................................... 23

Figure 7: From ore to RE concentrate: monazite, bastnasite................................................................ 25

Figure 8: From concentrate to REE: Monazite, Bastnasite .................................................................... 28

Figure 9: Growth rate inhibition of Desmodesmus sp. exposed to Th .................................................. 56

Figure 10: Mobility of Daphnia magna neonates exposed to Th .......................................................... 57

Figure 11: Folsomia candida: number of survived adults (a) and number of offspring (b) .................. 58

Figure 12: Eudialyte process chain as developed in the project. ......................................................... 71

Figure 13: Biotests with milled weathered EU eluate ........................................................................... 75

Figure 14: Biotests with EU Flotation solution ...................................................................................... 76

Figure 15: Biotests with EU leachates and leached EU ......................................................................... 77

Figure 16: Pseudokirchneriella subcapitata growth rate at pH 5 .......................................................... 95

Figure 17: Eisenia fetida reproduction test ........................................................................................... 95

Figure 18: Control experiments. ............................................................................................................ 96

Figure 19: Flotation of eudialyte mineral .............................................................................................. 97

Figure 20: Acidified eudialyte mineral - Preparation of eluates and solids for ecotoxic experiments . 98

Figure 21: Thorium-232 decay chain ..................................................................................................... 99

Figure 22: Uranium 238 decay chain ................................................................................................... 100

Figure 23: Uranium 235 decay chain ................................................................................................... 101

INDEX

V

List of tables

Table 1: Applications of rare earth elements, thorium and uranium ..................................................... 8

Table 2: Thorium & uranium content of important minerals and deposits .......................................... 24

Table 3: Radiation risk and waste management of REE mining ............................................................ 37

Table 4: Literature data for thorium toxicity in aquatic and terrestrial organisms .............................. 51

Table 5: Summarized results for all biotest performed with thorium .................................................. 58

Table 6: Metal content of eudialyte, leaching residues and leaching residues eluates ........................ 73

Table 7: Effects of leached EU residues on all organisms tested .......................................................... 78

Table 8: Environmental impact of treated eudialyte ............................................................................ 89

Table 9: Endpoints used to determine the SSD for uranium ............................................................... 102

Table 10: Endpoints used to determine the SSD for lanthanum ......................................................... 103

Table 11: Endpoints used to determine the SSD for cerium ............................................................... 103

1

1. Chapter:

Background and scope

Chapter 1

2

1.1 Background and scope of the thesis

Lanthanides are key elements in modern technologies, especially in green technologies such as

energy generation through wind power. In the past the production of REE was located predominantly

in China because of its large deposits and low environmental standards. In recent years countries and

companies outside of China were harshly reminded on how much they depend on the Chinese

goodwill when purchasing REE. China carefully protects its own interests and regulates the REE

market accordingly. In 2010 Japan was banned from import of REE from China, which lead to global

outcry. This incident was the trigger for western countries to disengage from Chinas REE monopole

market and invest in old and new REE mining and processing projects.

China has leading edge technologies in processing REE and even set up universities with strong

emphasis on REE mining, processing and associated technologies. Research outputs are publicized in

mandarin, both about technologies and environmental issues. So, knowledge is present but not

always accessible for non-mandarin speakers. Huge disadvantages of technologies based on REE are

the environmental and health risks which mining and processing of REE cause. Chinese residents are

so strongly burdened that civil society action and protest against the government is forming. One

environmental impact of REE processing is radiation, caused by thorium, uranium and their daughter

radionuclides. These elements are enriched when REE minerals are processed because of their

physico-chemical similarity to REE. Thorium is rarely examined for its behavior towards aquatic and

soil organisms. Within this scope, a SIEMENS project “Rare Erath: Green Mining & Separation (S-FB)

was launched by SIEMENS AG, RWTH Aachen and FZ Jülich. The main purpose of this project is to

develop environmentally friendly and efficient methods and procedures to source REE (Anon 2011).

Therefore, a total REE process chain was evaluated to investigate alternative REE deposits, to analyze

mining, physical, metallurgical and recycling processes of REE, as well as to determine the

sustainability of existing REE process chains via life cycle assessment.

Chapter 1

3

The thesis was embedded in the sustainability assessment of S-FB, with particular focus on the

environmental behavior of thorium and produced waste streams during rare earth processing. The

thesis provides an overview of thorium effects to the ecosystem as well as ecotoxicological effects of

rare earth waste streams, which were produced by an alternative rare earth mineral (eudialyte). The

objectives are:

To identify the fate and environmental impact of thorium residues along rare earth

processing with an exhaustive literature review. The thorium accumulation and enrichment

steps were identified in order to analyze the relevant waste streams.

To conduct ecotoxicological experiments with thorium on organisms in order to assess its

risks.

To determine effects of potential hazardous waste streams of eudialyte processing on the

environment.

1.2 Structure of the thesis

The thesis is divided into 6 chapters including this chapter. Each following chapter is structured like a

publication with including abstract, introduction, methods, results, discussion and references so that

each chapter could stand alone. All aforementioned objectives were achieved during the SIEMENS

framework “Rare Erath: Green Mining & Separation”:

Chapter 2 General introduction

This chapter describes general characteristics of lanthanides and actinides, their applications as well

as their toxicological effects on the environment. Additionally, a short historical outline describes

China’s role as a leader in rare earth processing.

Chapter 3 Fate and environmental impact of thorium residues along rare earth processing

In this chapter the various REE processing steps and streams are described from ore to pure element

with a focus on thorium waste streams. Furthermore, waste treatment and storage, which are

applied by various REE companies, are described. The impact of thorium release to the environment

Chapter 1

4

and its regulatory approaches are mentioned, focusing on known processes established for a number

of years. At last, the state of the art is outlined considering environmental impacts, status, costs,

effectiveness of waste management on thorium and other radiation sources.

Chapter 4 Toxicity of thorium to aquatic and terrestrial organisms; algae, daphnia,

collembolan and earthworms

This chapter describes the element thorium and its ecotoxicological effects. Standard

ecotoxicological test systems were chosen to investigate effects of the heavy element thorium on

different organisms. Since thorium has a long decay half live, the radioactive hazardous effects were

not considered in this analysis.

Chapter 5 Environmental consequence arising from eudialyte processing

This chapter describes the methodological approach to identify potential hazardous risk of mined

eudialyte (EU) tailings with the help of ecotoxicological test systems. Representative soil and water

samples from tailings were prepared in three different EU processing steps and are characterized by

chemical and ecotoxicity investigations for their environmental impacts. Eudialyte could be an

alternative source of heavy rare earth elements. In addition, EU has less radioactive elements which

makes it more attractive.

Chapter 6 General conclusions

This chapter discusses and summarizes the achievements of the preceding chapters and gives a main

résumé of the thesis. Finally, future research needs which arise from the proceeding of this thesis are

identified.

5

2. Chapter:

Introduction

Chapter 2

6

2.1 General introduction

2.1.1 Rare earth –nomenclature and occurrence

Rare earth elements (REE) are a group of 17 metals (Figure 1), including the lanthanides lanthanum

(La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium

(Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),

ytterbium (Yb) lutetium (Lu) as well as yttrium (Y) and scandium (Sc). These elements can be further

divided into light rare earth elements (LREEs) and heavy rare earth elements (HREEs). Sc, Gd, Tb, Dy,

Ho, Er, Tm, Yb, Lu and Y, because of their close chemical similarity, belong to the HREE. Promethium

is a short lived radioactive element and does not occur in nature (Gupta & Krishnamurthy 2005;

Evans 1996). Rare earth elements are widespread over the world and not entirely rare like their

name suggests. Due to their similar chemical and physical characteristics they mostly occur together

within one mineral. Thorium and uranium are components of several minerals mined for their rare

earth components, e.g. monazite, xenotime, and bastnaesite. When pure metals are mined this

similarity between elements leads to a huge effort and environmental burden during beneficiation

processes.

Figure 1: Periodic system of elements

Lanthanides, scandium and yttrium (all named under the term rare earth elements) are highlighted blue; actinides:

thorium and uranium in red

Chapter 2

7

Applications of REE reach from technical applications as constituents of lasers or metal alloys to

agriculture uses such as fertilizer (Val’kov et al. 2010; Sabiha-Javied et al. 2010; Pang et al. 2002) or

food additives (Redling 2006; He & Rambeck 2000) (Figure 2, Table 1).

Figure 2: Rare earth usage by application

(U.S. Geological Survey 2013).

Chapter 2

8

Table 1: Applications of rare earth elements, thorium and uranium

(Data compiled from BGS 2011; Castor and Hedrick 2006; U.S. Geological Survey 2013).

Chapter 2

9

Since the 1980’s, when rare earth processing first begun, China has become the world producer of

REE covering around 95% of the total REE production. In 1992, Deng Xiaoping´s proclamation “there

is oil in the Middle East, there is rare earth in China” has proven true (Hurst 2010; Evans 1996). Less

strict environmental regulations and subventions from the Chinese government until recently

enhanced industrial REE processing in China, while western countries have stopped the mining of

REEs altogether, despite existing deposits (Figure 3). The US was the biggest producer of REE until

2002 but closed its last mine inter alia because of China’s foreseeable dominance and competitive

advantage on the market. Rare earth elements in natural ores are commonly associated with

radioactive metals such as uranium and thorium which are often used as indicators for REE deposits.

The environment at mining and processing sites of these regions in China has suffered huge damage

due to the usual processing steps and radioactive contamination caused by thorium and its daughter

radionuclides.

Figure 3: Global distribution of REE mines

Adopted from Castor SB, Hedrick JB (2006)

Chapter 2

10

Lately, Chinas politics have changed notably by establishing stronger regulations for the processing of

REE and more requirements concerning environmental compatibility. In succession, prices of REE

have exploded over the last years and the export rates of REEs decreased. Several efforts have been

taken by western countries to regain control over the REE market and initiate countermeasures to

the Chinese monopole in REE production. For example, the US Company Molycorp has reopened its

REE mine at Mountain Pass or the Lynas company has opened a REE mine at Mount Weld, Australia

(Figure 3). As already stated, rare earth elements are processed from ores and minerals that naturally

contain uranium and thorium. However, insecurity regarding the environmental effects of thorium

persists. A fundamental precautionary principle of radioactive waste management is to guarantee

the safety of humans and nature. Waste rock and tailings from the extraction of REE which contain

these radionuclides are under special surveillance.

2.1.2 Health effects of thorium and uranium

Thorium and uranium emit α-radiation while their daughter-nuclides decay with α- ß- and very

slightly γ-radiation. Alpha radiation has short travel distances (cm in air) in comparison with ß- and γ-

radiation. Therefore, α emitters release their energy very concentrated and physically located if

ingested or inhaled and thus have stronger radio-biological effects than ß- and γ- emitters (decay

chains of 232 Th, 238 U and 235 U are displayed in Figure 21, Figure 22, Figure 23, in ANNEX).

Inhalation of thorium and uranium containing material is harmful, because the heavy metals are

incorporated into the Ca-phosphate structures of bones. This may lead to cancer in the bone tissues.

Other tissues may also accumulate the two heavy metals but to a minor degree. Ingestion of

thorium- and uranium oxide containing material is more or less negligible when assessing human

toxicity since they are not resorbed in the intestinal tract because of their very low solubility but are

eliminated through the faeces (Keith & Wohlers 1990; Peterson et al. 2007).

Thorotrast is the most investigated thorium exposure scenario. It was used as a contrast agent for

radiography between 1930 and 1964 and consists of a colloidal solution of thorium dioxide (Harrist et

al., 1979; Lipshutz et al., 2002). When injected intravascularly, thorotrast exposure leads to a

Chapter 2

11

deposition of 72% 232 Th in the liver, 12% in the spleen and 8% in the bone marrow. After 16 to 45

years of latency (Lipshutz et al. 2002) malignancies were observed in several forms such as

angiosarcomas, plasmacytomas or carcinomas (Becker et al., 2008; Harrist et al., 1979; Jones et al.,

1999; Lipshutz et al., 2002; Mays et al., 1979). Animal experiments with thorotrast affected the

humoral antibody production and enhanced virus growth (Monath et al., 1971).

Mice which were exposed with thorium nitrate (10 mg/kg/day) for 30 days showed an accumulation

of thorium in liver > femur > spleen, while the body and liver weight of the animals decreased and

oxidative stress was measured (Kumar et al. 2008; Kumar et al. 2009; Ishikawa et al. 1999).

2.1.3 Ecotoxic effects of thorium and uranium

Ecotoxicology describes effects of toxic substances on the environment, starting on a cellular level,

continuing to organisms, populations, communities and eventually entire ecosystems. It helps to

predict the effects on an ecosystem level, so that the most efficient and effective action to prevent or

remediate detrimental effects can be identified. All toxic events can be broken down into the

following three steps: exposure, toxicokinetics and toxicodynamics, i.e. exposure, accumulation, and

toxicity. For exposure, a number of physical, chemical, and biological factors act to determine the

bioavailability of the substance (McCarty et al. 2011). Characteristics such as pH, presence of organic

matter, amount of suspended solids, alkalinity, water hardness and other factors determine how

effective the metal uptake is. Consequently, the same exposure concentration of a metal will cause

different lethal concentrations (LC) or effect concentrations (EC) at different pH, dissolved organic

compounds, etc. (van Dam et al. 2012; Wilde et al. 2006; Franklin et al. 2000). If the sediment has a

low level of contamination by 234 U and 235 U the predicted no effect concentration (PNEC) of the

toxic metal will most likely surpass the radiological effect (Mathews et al. 2009). Effect data of α-

emitters thorium and uranium, i.e., LC50, EC50 and LOEC, are summarized in Table 9 (in ANNEX) and

Table 4 (in chapter 4), while more data was available for uranium. The data show that higher

amounts of thorium are nominally applied at the start of experiments than can be measured at the

end. For example, the crustacea Hyalella azteca was exposed with a nominal concentration of

Chapter 2

12

thorium in a factor ~100 higher than the values measured during the experiments (Borgmann et al.

2005). In comparison, uranium concentrations measured were generally higher than thorium, while

the applied nominal concentrations were lower (Table 4, in chapter 4, Table 9, in ANNEX). The

different environmental factors like pH or water hardness also influence the toxicological effects

which should also impact the thorium toxicology (Table 9, in ANNEX).

2.1.4 Environmental behavior of thorium and uranium

Thorium is extremely insoluble in water but will become soluble under acidic conditions and only

precipitates at a pH above 4. Complexes of thorium with carbonates and organic substances like

EDTA enhance its solubility under conditions above pH 4 (Higashi et al., 1959; Langmuir et al., 1980;

Östhols et al., 1994; Grenthe et al. 2004). Thorium is to be found only in the tetravalent oxidation

state (Th4+), in contrast to uranium which is found in both the U4+ and U6+ states. Under anaerobic

conditions, U6+ is reduced to the less soluble U4+ form (Abdelouas et al. 2000). The water

concentrations of thorium in fresh water is estimated to be around 0.01 to 1 µg/L (Langmuir &

Herman 1980). Th4+ ions strongly adsorb on soil, although this depends on the soil type: sandy soil

0.03 – 2 200 L/kg; silty soil 0.2 – 4 500 L/kg; clayey soil 46 – 395 000 L/kg; soil with high organic

matter content 1 578-13 000 000 L/kg) (Thibault et al. 1990). Organic Th-complexes are more soluble

in water and can be washed out at mining sites. A general assumption is that only low thorium

amounts enter the food chain via plants. The transport factor of thorium from root to shoot is only

0.12 which indicates roughly no thorium transport (Sheppard et al. 1980). For uranium there is a

wide range of mobility within plants transfer factors ranging from 0.0001 to 0.02 in herbs, shrubs and

trees and 0.6 to 325 for mosses and peat (Sheppard et al. 1980). The thorium soil-to-plant transfer

factor (kg kg-1 dry weight) is around 3.5 10-3 geometric mean and fluctuates between different soil

and plant types in a dimension of 10-2 to 10-6 (Vandenhove et al. 2009).

Chapter 2

13

2.1.5 Summary of ecotoxic effects and calculation of SSDs

As previously mentioned, environmental toxicity data for thorium (Table 4, in chapter 4) is scarce.

This is probably due to its chemical and physical characteristics, i.e. its very low mobility (Torstenfel

1986) and insolubility at neutral pH. Poston (1982) showed that size and exposure time correlate

positively with the bioconcentration factors of thorium in rainbow trout. Yet, they found that most of

the thorium is excreted after the termination of exposure. Effect and lethal concentrations were

collected for acute (EC50 & LC50) toxicity of actinides (Th and U) and lanthanides. A species sensitivity

distribution (SSD) was performed and is presented in Figure 4. The selected data were calculated for

proportions by ranking data from lowest to highest effect concentration and subsequently converted

from ranks into proportion (proportion=[rank - 0.5]/ number of species). Additionally, the

distribution was fitted to taxa proportion vs metal concentration (Posthuma et al. 2002; Neter et al.

1990; EPA 2005). In order to reduce confounding factors as much as possible, the effect

concentration determined under low CO32- content (soft water) was chosen whenever possible. For

thorium alone no SSD could be calculated because of the limited data available (see Table 9, Table

10, Table 11, in ANNEX).

Additionally, the chemical effect concentrations of Chlorella vulgaris, Danio rerio and Hyalella Azteca

against REE and actinides are shown in Figure 5 demonstrating the narrow interval in which these

elements affect the same organism.

Chapter 2

14

Figure 4: Short-term SSD representing the toxicity of a) lanthanum, b) cerium and c) uranium

in fresh water, consisting of acceptable short-term LC50s of aquatic species versus proportion of species affected

Chapter 2

15

Figure 5: Rare earth elements, thorium and uranium effect concentrations

on a) Chlorella vulgaris, b) Hyalella azteca and c) Danio rerio

Chapter 2

16

2.2 References Abdelouas, A. et al., 2000. Biological reduction of uranium in groundwater and subsurface soil.

Science of The Total Environment, 250(1–3), pp.21–35. Available at: http://www.sciencedirect.com/science/article/pii/S0048969799005495.

Becker, N. et al., 2008. Mortality among thorotrast-exposed patients and an unexposed comparison group in the German thorotrast study. European Journal of Cancer, 44(9), pp.1259–1268. Available at: http://www.sciencedirect.com/science/article/pii/S0959804908001743.

BGS, B. geological S., 2011. Rare earth elements. www.MineralsUK.com, (NERC), pp.1–54. Available at: http://www.bgs.ac.uk/downloads/start.cfm?id=1638.

Borgmann, U. et al., 2005. Toxicity of sixty-three metals and metalloids to Hyalella azteca at two levels of water hardness. Environmental Toxicology and Chemistry, 24(3), pp.641–652. Available at: http://dx.doi.org/10.1897/04-177R.1.

Castor, S.B. & Hedrick, J.B., 2006. Rare earth elements. Industrial Minerals and Rocks, (in Kogel, et al., 7th edition Society for Mining, Metallurgy and Exploration), pp.769–792. Available at: http://www.fieldexexploration.com/images/property/1_RareEarths_FLX_02.pdf.

van Dam, R.A. et al., 2012. Reanalysis of uranium toxicity data for selected freshwater organisms and the influence of dissolved organic carbon. Environmental Toxicology and Chemistry, 31(11), pp.2606–2614. Available at: http://dx.doi.org/10.1002/etc.1987.

EPA, U.S.E.P.A., 2005. Methods/ indicators for determining when metals are the cause of biological impairments of rivers and streams: Species sensitivity distributions and chronic exposure-response relationships from laboratory data. Environmental Protection, (July), p.49.

Evans, C.H., 1996. Episodes from the history of the rare earth elements (chemists and chemistry), Springer Netherlands.

Franklin, N.M. et al., 2000. pH-dependent toxicity of copper and uranium to a tropical freshwater alga (Chlorella sp.). Aquatic Toxicology, 48(2â€“3), pp.275–289. Available at: http://www.sciencedirect.com/science/article/pii/S0166445X99000429.

Grenthe, I. et al., 2004. Chemical thermodynamics of Uranium H. Wanner & I. Forest, eds., Available at: https://www.oecd-nea.org/dbtdb/pubs/uranium.pdf.

Gupta, C.K. & Krishnamurthy, N., 2005. Extractive Metallurgy of Rare Earths. CRC PRESS, (ISBN 0-415-33340-7).

Harrist, T.J. et al., 1979. Thorotrast-associated sarcoma of bone. A case report and review of the literature. Cancer, 44(6), pp.2049–2058. Available at: http://dx.doi.org/10.1002/1097-0142(197912)44:6<2049::AID-CNCR2820440615>3.0.CO.

He, M.L. & Rambeck, W. a., 2000. Rare earth elements - a new generation of growth promoters for pigs? Archiv für Tierernaehrung, 53(4), pp.323–334. Available at: http://www.tandfonline.com/doi/abs/10.1080/17450390009381956.

Higashi, S., 1959. Determination of the solubility of thorium hydroxide. Bulletin of the Institute for Chemical Research, Kyoto University, 37(3), pp.200–206.

Hurst, C., 2010. China’s rare earth elements industry: What can the west learn? IAGS. Institute for the Analysis of Global Security, pp.1–42. Available at: http://www.iags.org/rareearth0310hurst.pdf.

Ishikawa, Y. et al., 1999. Revised organ partition of Thorium-232 in thorotrast patients. Radiation

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research, 152(6), pp.102–106.

Jones, M., Malveiro, F. & Swerdlow, A., 1999. Mortality in the Portuguese thorotrast study. Radiation Research, 152(6s), pp.S88–S92. Available at: http://www.rrjournal.org/doi/abs/10.2307/3580121.

Keith, S. & Wohlers, D.W., 1990. Toxicological profile for thorium. Agency for Toxic Substances and Disease Registry, (Atlanta (GA): Agency for Toxic Substances and Disease Registry (US)), pp.1–186. Available at: http://www.atsdr.cdc.gov/toxprofiles/tp.asp?id=660&tid=121.

Krupka, K.M. et al., 1999. Understanding variation in partitom coefficient, Kd values - review of geochemistry and available Kd values for cadmium, cesium, chromium, lead, plutonium, radon, strontium, thorium, tritium (3H), and uranium. U.S. Environmental Protection Agency, 2(EPA 402-R-99-004B), p.341.

Kumar, A. et al., 2009. Thorium-induced neurobehavioural and neurochemical alterations in Swiss mice. International journal of radiation biology, 85(4), pp.338–47. Available at: http://www.ncbi.nlm.nih.gov/pubmed/19399679 [Accessed November 19, 2014].

Kumar, A. et al., 2008. Thorium-induced oxidative stress mediated toxicity in mice and its abrogation by diethylenetriamine pentaacetate. International journal of radiation biology, 84(4), pp.337–49. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18386198 [Accessed November 19, 2014].

Langmuir, D. & Herman, J.S., 1980. The mobility of thorium in natural waters at low temperatures. Geochimica Et Cosmochimica Acta, 44(11), pp.1753–1766. Available at: <Go to ISI>://WOS:A1980KT66800011.

Lipshutz, G.S., Brennan, T. V & Warren, R.S., 2002. Thorotrast-induced liver neoplasia: A collective review. Journal of the American College of Surgeons, 195(5), pp.713–718. Available at: http://www.sciencedirect.com/science/article/pii/S1072751502012875.

Mathews, T. et al., 2009. A probabilistic assessment of the chemical and radiological risks of chronic exposure to uranium in freshwater ecosystems. Environmental Science & Technology, 43(17), pp.6684–6690. Available at: <Go to ISI>://WOS:000269258000042.

Mays, C.W. & Spiess, H., 1979. Bone tumors in thorotrast patients. Environmental Research, 18(1), pp.88–93. Available at: http://www.sciencedirect.com/science/article/pii/0013935179901415.

McCarty, L.S. et al., 2011. Advancing environmental toxicology through chemical dosimetry: External exposures versus tissue residues. Integrated Environmental Assessment and Management, 7(1), pp.7–27. Available at: http://dx.doi.org/10.1002/ieam.98.

Monath, T.P.C. & Borden, E.C., 1971. Effects of thorotrast on humoral antibody, viral multiplication, and interferon during infection with St. Louis encephalitis virus in mice. Journal of Infectious Diseases, 123(3), pp.297–300. Available at: http://jid.oxfordjournals.org/lookup/doi/10.1093/infdis/123.3.297.

Neter, J., Wasserman, W. & Kutner, M.H., 1990. Applied linear statistical models 3rd ed., CRC Press.

Östhols, E., Bruno, J. & Grenthe, I., 1994. On the influence of carbonate on mineral dissolution: III. The solubility of microcrystalline ThO2 in CO2-H2O media. Geochimica et Cosmochimica Acta, 58(2), pp.613–623. Available at: http://www.sciencedirect.com/science/article/pii/0016703794904928.

Pang, X., Li, D. & Peng, A., 2002. Application of rare-earth elements in the agriculture of China and its

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environmental behavior in soil. Environmental science and pollution research international, 9(2), pp.143–148.

Peterson, J. et al., 2007. Radiological and chemical fact sheets to support health risk analyses for contaminated areas. Argonne National Laboratory Environmental Science Division, p.133.

Posthuma, L., Suter II, G.W. & Traas, T.P., 2002. Species sensitivity distributions in ecotoxicology, CRC press.

Poston, T.M., 1982. Observations on the bioaccumulation potential of thorium and uranium in rainbow trout (Salmo gairdneri). Bulletin of Environmental Contamination and Toxicology, 28(6), pp.682–690. Available at: http://dx.doi.org/10.1007/BF01605636.

Redling, K., 2006. Rare earth elements in agriculture with emphasis on animal husbandry,. , (Dissertation statement: Munchen, Univ., Diss.,). Available at: oai:d-nb.de/dnb/98212497X.

Sabiha-Javied et al., 2010. Measurement of rare earths elements in Kakul phosphorite deposits of Pakistan using instrumental neutron activation analysis. Journal of Radioanalytical and Nuclear Chemistry, 284(2), pp.397–403. Available at: http://link.springer.com/10.1007/s10967-010-0469-9.

Sheppard, M.I. et al., 1980. The environment behaviour of uranium and thorium. Atomic Energy of Canada Limited, (Whiteshell Nuclear Research Establishment - AECL-6795), p.51.

Thibault, D.H., Sheppard, M.I. & Smith, P.A., 1990. A critical compilation and review of default soil solid/liquid partition coefficients, Kd, for Use in environmental assessments. Whiteshell Nuclear Research Establishment Pinawa,, (AECL- 10125).

Torstenfel, B., 1986. Migration of the actinides thorium, protactinium, uranium, neptunium, plutonium and americium in clay. Radiochimica Acta, 39, pp.105–112.

U.S. Geological Survey, 2013. Mineral commodity summaries. U.S. Geological Survey, p.198.

Val’kov, a. V. et al., 2010. Monazite raw material for the production of highly effective fertilizers. Theoretical Foundations of Chemical Engineering, 44(4), pp.497–499. Available at: http://link.springer.com/10.1134/S0040579510040238.

Vandenhove, H. et al., 2009. Proposal for new best estimates of the soil-to-plant transfer factor of U, Th, Ra, Pb and Po. Journal of Environmental Radioactivity, 100(9), pp.721–732. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0265931X08001823.

Wilde, K.L. et al., 2006. The effect of pH on the uptake and toxicity of copper and zinc in a tropical freshwater alga (Chlorella sp.). Archives of Environmental Contamination and Toxicology, 51(2), pp.174–185. Available at: <Go to ISI>://WOS:000238362100003.

19

3. Chapter: Fate and environmental

impact of thorium residues

along rare earth processing

Matthias Findeiß, Andreas Schäffer

RWTH Aachen University, Institute for Environmental Research, Department of Environmental

Biology and Chemodynamics, Worringerweg 1, 52074 Aachen, Germany

Published in Journal of Sustainable Metallurgy, slightly modified; manuscript number: SUME-D-16-

00052R1

Chapter 3

20

3.1 Abstract

Rare earth (RE) processing is an environmental hazardous operation. Processed minerals often

contain radioactive elements like thorium which occur together with the precious rare earth

elements due to their chemical and physical similarities. Environmental contamination with thorium

around rare earth mining and processing sites is an issue of concern and many examples of health

impact have been reported. Thorium is enriched during different processing steps like flotation or

leaching activities. Therefore, torium containing waste arising during RE processing needs a careful

waste management since contamination, e.g., by dust drift or tailing dam bursts are severe threats

for exposed organisms in the environment. Aim of the paper is to summarize the routes of thorium

enrichment along rare earth mining processes along with the environmental impact and to provide

suggestions how to manage thorium enriched waste.

Keywords: thorium, rare earths, environmental impact, waste management

Chapter 3

21

3.2 Introduction

Rare earth elements (REE) are a group of 17 metals and can be divided into light rare earth elements

(LREE) and heavy REE (HREE). Rare earth elements are ubiquituos in the environment and not

uncommon unlike their name suggests. Due to their similar chemical and physical characteristics they

are mostly found associated with other minerals such as monazite, xenotime, and bastnaesite which

may contain low amounts of thorium and uranium. When pure metals are produced the similarity

between the elements leads to huge efforts and environmental costs during beneficiation and

separation processes. Rare earth elements in natural ores are commonly associated with radioactive

metals such as uranium and thorium which are also used as indicators for REE deposits. During

production of REE metals various inorganic and organic additives are used often in large quantities,

e.g., hydrochloric acid, sulphuric acid, sodium hydroxide, flocculants, acidic organic phosphorus

compounds like di-(2-ethylhexyl)phosphoric acid, polychlorinated biphenyls, tertiary amines, iso-

octyl alcohol or kerosene (Environmental Protection Acency 2012; Jordens et al. 2013; Xie et al. 2014;

Weng et al. 2013; Yang et al. 2013). It is obvious that these chemicals may lead to ecotoxicological

effects if they were released to the environment. The level of contamination depends on the mined

mineral, the used extraction methods and the laws and regulations in force. Furthermore, many

environmental and health risks have been identified for years for mining operation. Groundwater,

surface water, soil and air are the environmental compartments mainly affected through tailing dam

bursts, pipe leakages, lacking of proper waste treatments, or by airborn particulate matter, which can

be transported over long distances (Öko-institut e.V. 2011; Environmental Protection Acency 2012;

European Commission 2009; Weng et al. 2013). In China, the environment at mining and processing

sites of the regions has suffered from radioactive contamination caused by thorium and its daughter

radionuclides as well as from the processed waste water and sludge (Li et al. 2012; Qifan et al. 2010).

Thorium is one of the waste products in rare earth mining which is mainly eliminated during the

leaching process of the desired metals. The waste product thorium, which stands for the radioactive

impact of RE mining besides uranium and their decay products (Figure 21, Figure 22, Figure 23, in

Chapter 3

22

ANNEX), has given rise to concern for the last years. Besides the radiation of thorium of course the

ten times higher radioactivity (in Bq) of its ten decay products has to be considered as well. Because

of the different radiation types of the decay products, i.e., α-, ß- and γ- emission, toxic health effects

are multifold, e.g., by the α- emitters 232 thorium, 228 thorium, 224 radium or 220 radon which

severely impact biological tissue if incorporated (Ragheb 2011; Pillai 2005). In our review we focus on

thorium concentrations but this very important issue has to be kept in mind. Environmental toxicity

data for thorium are scarce. This is probably due to its chemical and physical characteristics, i.e. its

strong sorption to solid matrices (Thibault et al. 1990) resulting in a very low bioavailability and

mobility (Torstenfel 1986). Thorium (Th4+) is highly insoluble in water. Under acidic conditions below

pH 4 the solubility increases and complexation with carbonates, sulphates or organic substances

enhance its solubility (Langmuir & Herman 1980; Östhols et al. 1994; Higashi 1959; Wanner & Forest

2004; Sapsford et al. 2012). During physical beneficiation thorium is mostly available as an insoluble

material, but it is transformed within the chemical processes into more soluble Th(NO3)4, Th(OH)4,

Th-oxalate and other species.

Purpose of this article is to point to the enrichment of thorium from the original ore through several

REE processing steps to the final storage of the waste materials from which emissions to the

environment occur (Figure 6). Beside contamination sources from other byproducts in REE mining it

is shown that thorium due to its radioactive nature (and that of the decay products) is one of the

pollutants that needs thorough planning of the waste management. Some suggestions and

constraints addressing waste handling are finally presented.

Chapter 3

23

Figure 6: Sketch of thorium enrichment during REE processing

3.3 Production processes from ore to metal

3.3.1 Rare Earth Ores

Four minerals are mainly used for processing REE. Each of the minerals, i.e., bastnaesite, monazite,

xenotime (hard rock minerals) and ion adsorbed clays are mined and extracted in China. Bastnaesite

(a carbonate mineral) is the most commonly processed mineral due to its relatively high amount of

REE but relatively low amounts of thorium (≤ 28,000 ppm ThO2) and uranium (Yang et al. 2013)

whereas monazite and xenotime (phosphate minerals) contain a relatively high amount of thorium

and uranium in the range of 5,000 to 200,000 and 100 to 160,000 ppm, respectively (Gupta &

Krishnamurthy 2005; BGS 2011; Castor & Hedrick 2006; Chakhmouradian & Wall 2012). In the US, the

Mountain Pass mine has been reopened in order to process REE from a bastnaesite ore. At Mount

Weld in Australia, REE are mainly processed from monazite ore. The ion-adsorption clay deposits in

Longnan, Xunwu, China, have a lower amount of REE in comparison to bastnaesite or monazite. They

can be processed without physical beneficiation and are characterized by very low thorium and

uranium concentrations (typically about 50 ppm) (IAEA 2011) and rich HREE contents. Processing of

Chapter 3

24

heavy mineral sand (monazite) has been stopped in most countries, because of the resulting

environmental radioactive contamination.

Rare earth elements are generally mined as open pit mines with standard drill, blast, load, and haul

operations, and milled for further processing like froth flotation (Gupta & Krishnamurthy 2005). Rare

earth elements are also processed as main products for example at Mountain Pass and Mount Weld,

but in the biggest RE mine, the Bayan Obo mine in China, REE have been mined as a by-product of

iron mining for years. Differences of mineral types lead to various physical beneficiation processes.

Table 2: Thorium & uranium content of important minerals and deposits 1 (Gupta & Krishnamurthy 2005), 2 adopted from (Jordens et al. 2013), 3 (Qifan et al. 2010), 4 (IAEA 2011)

Minerals ThO2

[ppm]

U3O8

[ppm]

Monazite2 0-200,000 0-160,000

Bastnasite2 30,000 900

Xenotime1 0-50,000 0-50,000

Deposit

Bayan Obo3 100-500 5-20

Mount Weld4 750 30

Mountain

Pass4 200 20

3.3.2 From ore to RE concentrate

After mining, a physical beneficiation process is applied to the crude ore of bastnaesite, monazite,

xenotime or other REE minerals in order to produce an appropriate RE concentrate. The mined ore

has to be crushed (into mm sized aggregates) and milled (forming µm sized particles) followed by

magnetic separation (only at Bayan obo) and froth flotation (Gupta & Krishnamurthy 2005; Castor &

Hedrick 2006; BGS 2011; Koltun & Tharumarajah 2014). Most tailings are produced along these

Chapter 3

25

separation steps because the REE amount of the crude ore is just in the low percentage range.

Usually the tailings of physical beneficiation are stored in impoundment areas. Upon closure these

tailings are seldom used as backfill material of a mine; rather, the heavy sand accumulating during

the processes and resulting in huge amounts is used for backfill.

Froth flotation is an important step in rare earth processing where the milled minerals are selectively

separated and concentrated. Chemicals are added to enhance different physical-chemical properties

of the various minerals, i.e., mineral particles are hydrophobized while others remain hydrophilic.

The bubbles formed by air purging stick to the hydrophobic particles concentrating them in the foam

on the water surface, where they can be mechanically removed and afterwards dewatered. The

remainders are concentrated as pulp which is discharged. The pulp therefore contains the applied

reagents, water and huge volumes of crude ore. Usually the process water is then recycled and

reused. In a series of flotation cells the RE minerals are concentrated to amounts between around

10 % (Bayan Obo) (Yu et al. 2012; Ding et al. 2013; Tharumarajah & Koltun 2011) up to 40 – 60 %

(Lynas & Molycorp). Bastnasite concentrate from Mountain Pass is further concentrated by leaching

with hydrochloric acid which dissolves the carbonate gangue (County of San Bernadino Public Works

Group 1996).

Figure 7: From ore to RE concentrate: monazite, bastnasite

(Gupta & Krishnamurthy 2005; Castor & Hedrick 2006)

Chapter 3

26

3.3.3 From RE concentrate to RE elements

Rare earth mining and processing is a much more environmentally hazardous process than other

mining activities since radioactive waste is formed. Especially during the chemical separation of REE

into single elements huge amounts of toxic substances are produced. The efficiency needed to

separate REE depends on the quality of the ore, on the availability of a competent supplier industry,

and of course on the customers. Bastnaesite, monazite or xenotime concentrates are further

processed with chemicals in order to produce rare earth chlorides (RECl), rare earth oxides (REO),

and REE or other rare earth products which can be sold to industrial sectors. During chemical

separation a lot of toxic compounds are produced and the involved radionuclides thorium and

uranium become separated in different processing steps or may be even released into the

environment if conducted improvidently (Öko-institut e.V. 2011).

Rare earth concentrates can be decomposed by sulfurizing roasting with concentrated sulphuric acid

(Figure 8) as for instance in China (monazite and bastnaesite concentrate; Bayan

Obo/Sichuan)(Xiaowei et al. 2005; BGS 2011; Gupta & Krishnamurthy 2005) and Malaysia (monazite

concentrate; Lynas) (BGS 2011; Det-Norske-Veritas DNV 2011). When bastnaesite and monazite are

treated with sulphuric acid in a single step, REE precipitate as double sulphates, while thorium and

other impurities stay in solution (Gupta & Krishnamurthy 2005; Murthy & Mukherjee 2001). In order

to separate the heavy REE, solvent extraction is applied to recover thorium from the organic phase

along with other impurities (Xie et al. 2014; Yan et al. 2006); this solvent extraction is considered as a

rather eco-friendly separation process.

Another commonly used digestion technique is the treatment with sodium hydroxide. REE and

thorium are converted by sodium hydroxide decomposition of monazite into hydroxides which can

be separated by controlling the pH with hydrochloric acid and transformed into RECl at a pH around

3.2. RECl are soluble whereas thorium hydroxides remain insoluble under such conditions. Uranium

and radium is selectively precipitated by barium chloride and sodium sulphate addition. The

Chapter 3

27

remaining impurities of the RECl solution can be further separated by solvent extraction and the

purified RECl are either sold directly or further transformed to REO (Gupta & Krishnamurthy 2005).

At Mountain Pass, bastnaesite concentrate is leached with high amounts of hydrochloric acid. In the

past the concentrate was roasted achieving an oxide feed which can be further processed with

selective hydrochloric acid leaching (County of San Bernadino Public Works Group 1996; Gupta &

Krishnamurthy 2005). In another approach (the Phoenix project at Mountain Pass), the roasting step

is removed from the process (Environmental Audit 2010) and only hydrochloric acid is applied to

transfer REE into solution (Figure 8). The leaching of bastnaesite concentrate with 10 % HCl leads to

dissolved uranium and REO while thorium remains in solid form. Uranium and radium is selectively

precipitated by barium chloride and sodium sulphate addition and thus separated from the REO

during further leaching steps. At Mountain Pass the non-dissolved thorium and the precipitated

uranium are disposed together with tailings of the milling (REITA 2012; Lucas et al. 2015).

After the inorganic pre-separation, a liquid–liquid (water–organic) solvent extraction is carried out

based on differences in the solubility of REE. Actinium is separated from REE by solvent extraction

because of its similar properties compared to REE (Lucas et al. 2015). The REE ions transfer from the

aqueous phase into the organic phase enhanced by complexing agents and solvents within a

counterflow process (Chunhua et al. 2006; Xie et al. 2014). After solvent extraction a final

precipitation step with oxalic acid or sodium hydroxide is carried out. The resulting oxalates and

carbonates are then converted to REO in a tunnel furnace at 900°C. The single REO are sold or

reduced via electrolysis to the pure REE metal.

The final RE products, e.g. REE, RECl or REO, are uncontaminated by thorium. But Qifan et al. also

reported relevant thorium concentrations of 40 – 240 ppm for RE alloys, 45 ppm for RECl and

6.9 ppm for REO, but the source of this information was not provided (Qifan et al. 2010).

Chapter 3

28

Figure 8: From concentrate to REE: Monazite, Bastnasite

a) Sulphuric acid digestion used for Monazite concentrates (or mixed Monazite/Bastnasite concentrates) at Mt.

Weld/Kuantan or Bayan obo. b) Hydrochloric acid digestion used for Bastnasite at Mountain. Pass(Zhu et al. 2015;

Det-Norske-Veritas DNV 2011; Gupta & Krishnamurthy 2005; Environ Consulting Services 2008; Environmental

Audit 2010; Qifan et al. 2010; County of San Bernadino Public Works Group 1996; Kim & Osseo-Asare 2012)

3.4 Waste treatment and storage

According to OECD mining wastes are by-products of extraction, dressing and beneficiating from ores

and related processed material (OECD 2001). Many countries define “mining waste” as material from

several operations including extraction, beneficiation, and processing of mineral resources

(Environmental Protection Acency 2016). However, laws and regulations differ from country to

country including mining legislations, environmental standards, occupational health and safety

regulations (BRGM 2001). The geology, hydrology and hydrogeology of a site are important factors

for an efficient storage of the waste. Both, weathering and wrong management may lead to

mobilization of contaminants with potential environmental impact. The variability of crude ore, i.e.

the composition of elements, the grain size etc., affects the build-up of waste rocks, ore stockpiles

and processed waste streams at the mine and processing plant. Several options are possible for

Chapter 3

29

managing tailings, especially tailings with radioactive compounds which are under special

surveillance and stored separately.

Waste rock is either managed on heaps or on occasion dumped on existing hillsides (European

Commission 2004; Environmental Protection Acency 2012). Milling material is stored correspondingly

until further processing. Installed sprinkler, which receive recycled water from other beneficiation

processes, are installed to avoid distribution of thorium containing dust. Flotation slurries are

pumped to impoundment areas in order to collect surplus water or to dry out. Thorium containing

leaching wastes (filter cakes) are generally neutralized, e.g., with limestone, and stored also at

impoundment facilities, which are built with waterproof material like high density polyethylene

(HDPE) cover. In addition, radioactive tailings are mixed with BaOH2 to precipitate radioactive

elements. Especially during chemical beneficiation hazardous gases are released and directed into

gas filters reducing the toxic compounds. In the following different waste treatments and storage of

radioactive tailings are summarized.

3.4.1 USA (Mountain Pass)

At the Mountain Pass mine, tailings from milling operations are co-disposed with radioactive waste

streams for simple dilution resulting in slightly increased Th and U contents compared to the crude

ore (Th 200 ppm to 220 ppm; U 20 ppm to 22 ppm) (REITA 2012). Molycorp changed the way of

waste storage. In the past the waste was transported via pipelines to the nearby lake Ivanpah but

nowadays they attempt to recycle most of water producing a cement-like material, which is stored in

dry form for long term disposal (Molycorp 2012).

3.4.2 China (Bayan Obo)

In the Baotou Region of Inner Mongolia at the Bayan Obo mine ten million tons of waste rock is

produced per year for both ferrous and REE mining. The produced effluent is about 69 million tons

per year containing thorium, fluorine, nitrogen, sulphate, chlorines and other toxic substances (Qifan

et al. 2010). The toxic waste of 6.55 million t/a with a thorium content of 480 ppm is stored in

Baogang tailings pond forming a so called “second mine”: it is planned to re-process the tailings

Chapter 3

30

because of their rather high rare earth content of 30,000 ppm (Hurst 2010; Lee 2012; Li et al. 2012;

IAEA 2010; Qifan et al. 2010). 60000 t/a REE slurries are disposed with a thorium content between 70

to 2400 ppm at Baotou radioactive waste storage facilities (Qifan et al. 2010). The water

concentrations of thorium in fresh water at remote sites is estimated to be around 0.01 to 1 µg/ L

(Langmuir & Herman 1980)., In comparison, leaching pond concentrations are up to about 5 mg/L

which was detected in pond waters (Huang et al. 2014).

3.4.3 Australia/Malysia (Mt Weld/ Kuantan)

In Malaysia, the Lynas Company (RE producer) produces residues by Flue Gas Desulphurisation (FGD),

Neutralisation Underflow (NUF) and Water Leaching Purification (WLP), which contain thorium

compounds. WLP represents the main thorium containing residue with a production of about 32,000

tonnes per year containing 1655 ppm thorium and 22 ppm uranium (Malaysia Nuclear Agency 2010;

WorleyParsons 2008). Thus, about 53 tons of thorium per year accrue in the WLP process (Al-Areqi et

al. 2014). The radioactive solutions are stored in retention ponds, which are built with impermeable

soil and are lined with a HDPE (high density polyethylene) cover to prevent any seepage (Environ

Consulting Services 2008). The runoff water and supernatant effluent of WLP is collected and

recycled at a nearby waste water facility and afterwards returned into the cracking and separation

process (Environ Consulting Services 2008). The treated effluent was analyzed for its thorium

radionuclide content, Ra-226 and Ra-228, but concentrations did not reach the detection limit of

< 0.5 Bq/L during a test run (Malaysia Nuclear Agency 2010). It is speculated that thorium is

completely precipitated as thorium pyrophosphate (ThP2O7) during the separation with MgO at pH of

3.5 (Malaysia Nuclear Agency 2010) and discharged in WLP. The WLP residues contain a lot of

compounds beside ThP2O7 like iron, barium, calcium or silica species (Al-Areqi et al. 2014). Another

consideration of the company has been to dilute the waste to a Th concentration of less than

500 ppm, which is the maximum concentration allowed under international standards for the

material to be disposed without restrictions. Annually, 220 000 tonnes of waste are foreseen to be

processed by this “solution by dilution” concept (Lee 2011) which environmental scientists consider a

Chapter 3

31

bad solution. However, there the extraction of thorium from the WLP for future nuclear fuel usage is

already envisaged (Al-Areqi et al. 2014).

3.5 The impact of thorium release to the environment and regulatory

approaches

As mentioned before, REE mining holds environmental issues due to the required use of high

amounts of chemicals: besides the here referred thorium and other radioactive residues containing

waste, corrosive fluorine-bearing gases and the manifold organic process chemicals in liquid and solid

waste can have an environmental and public health impact if no proper management is obeyed

(Weng et al. 2013). As with any environmental pollutant, also for thorium the environmental

relevance is sometimes controversially discussed since the causative factors for observed health

effects in mining areas are difficult to differentiate as discussed below.

Negative health effects have been reported for people living or working close to thorium waste

disposals or to REE plants. Birth defects, liver disease or lung burden occurred in the exposed

population at high rates (Najem & Voyce 1990; Environmental Protection Acency 2012; Xing-An et al.

2005; Terry et al. 1997; Xing-an et al. 2004; Polednak et al. 1983; Liu et al. 1991; Furuoka & Lo 2005;

Ichihara & Harding 1995). In 1992, a REE refinery was closed after birth defects were correlated with

emissions from the processing plants and came to the public awareness of the Malaysian population

(Furuoka & Lo 2005). Thus, when the Lynas Company came up with a concept to store radioactive

tailings at its plant in Malaysia, the Malaysians formed resistance against this plan. However, to the

authors’ knowledge, Lynas has still no strategy how to improve the handling of Water Leaching

Purification residues in the future. Currently, Lynas has the permission to produce REE in Malaysia, as

long as the radioactive solid waste is disposed outside of the country (Environmental Protection

Acency 2012).

In monazite processing areas, it is known that monazite dust is deposited in the lung which then

results in long-term α- particle irradiation of lung tissue (Terry & Hewson 1995; Terry et al. 1997).

Chapter 3

32

However, in the past, burdens caused by smoking could not be distinguished from exposure to

radiation of thorium, uranium and their daughter radionuclides (Polednak et al. 1983). At the yellow

river, China, thorium concentrations in water in the vicinity of the Baotou plant are generally below

the detection limit of 0.002 μg/L but thorium found to be increased in leachates with about

0.064 μg/L (Huang et al. 2016) and it is strongly contaminated with chemicals used for processing at

Baotou which affect fish population and people in that area (Hurst 2010). Studies from the Bayan

Obo mine in China were published in which the long-term exposure to ore dusts was assessed. The

authors took into account that workers smoked and worked in different low or high dust exposed

areas. Workers in the high dust exposed mining parts had a higher risk for lung burden, even though

a differentiation between the carcinogens ThO2, SiO2 of dust particles and enhanced effect of chronic

γ- exposure was not possible (Xing-an et al. 2004; Xing-An et al. 2005). Furthermore, due to improper

waste management and missing protection against emission around the Bayan obo mine, analysis of

sheep bones, pasture, grassland soil samples and different soil depth samples of surrounding tailings

revealed radioactive contamination (Li et al. 2012; Li et al. 2014). Once an area is contaminated it is a

long and expensive operation of cleaning up. Mountain Pass, Molycorp, had to pay a high penalty

and processing was temporarily suspended until the pollution case was cleaned (Nystrom 2003). In

order to get an impression of air pollution, the IAEA concluded that the best way of assessing

radioactivity doses is air monitoring rather than biological or body sampling (IAEA 2011) although the

concept of body burden is well accepted in ecotoxicology.

The decay products of thorium, radium, the gaseous radon and lead are important components of

radiation pollution. Radium and lead are precipitated and separated using sodium sulphate, barium

chloride and sodium sulphide during chemical beneficiation. Gaseous radon is emitted during the

grinding process, from solid wastes and from thorium slag (IAEA 2011)(Pillai 2005). The radioactive

containing residues are drained to storage facilities, thereby used equipment become contaminated

by accumulation of radium, lead or bismuth inside the drainages.

Chapter 3

33

3.5.1 Mining

At open pits care must be taken that regularly exposed workers are protected against inhaling

particulate matter which can contain thorium and other cancer promoting elements. Such toxic dust

stirs up by blasting and crushing activities and so produced stockpiles. Radon, which becomes also

released during grinding process, can cause lung cancer. Ventilation and shielding are effective

protection methods. A standard avoidance is to sprinkle the stockpiles preventing dust formation

which is the major exposure pathway for organisms living in that area. The inhaled particle size

seems to play a role in determining which isotope is responsible for the observed damages. Smaller

particles have a higher 230 Th content, while bigger particles contain more 232 Th (Wrenn et al.

1981). Dust particles also content thorium decay products as 228 radium which is ingested into the

body, where it is stored in tissues and will decay into 228 Th. Thorium is mostly enriched in lymph

nodes, followed by lung and bone tissue (228 Th, 230 Th, 232 Th) (Wrenn et al. 1981).

3.5.2 Beneficiation

After froth floatation of the milled ore the produced slurry and concentrate are stocked until further

processing trying to avoid dust erosion. The concentrate is enriched in thorium, uranium, and their

daughter radionuclides containing hundreds to thousands ppm in comparison with the crude ore,

e.g. 750 ppm, 320 ppm or 200 ppm ThO2 and 30 ppm, 5-20 pm, 20 ppm U3O8 (IAEA 2011; Qifan et al.

2010; Environ Consulting Services 2008). The slurries are drained to a tailing pond for drying.

Seepage water of tailing ponds can be formed even if acid mine drainage is not a main issue in REE

processing because of the carbonate und phosphorous minerals. However, the composition of

seepage water is only rarely investigated.

3.5.3 Leaching

99 % of thorium is separated from the concentrate during the leaching step (Gupta & Krishnamurthy

2005) producing a thorium filter cake with high thorium concentration. Radium and uranium become

precipitated by addition of sodium sulphate and barium chloride producing other filter cakes which

are stored together with thorium containing wastes (1655 ppm ThO2 and 22.5 ppm U3O8 in the WLP

Chapter 3

34

at Kuantan) (Environ Consulting Services 2008). In Malaysia thorium was dumped at areas close to

the public as well as to streams causing high radiation risk in the past (Ichihara & Harding 1995).

Radioactive waste is sometimes mixed with other residues which results in lower thorium

concentration than in the concentrate which is disposed onsite, e.g. 220 ppm (22 ppm U3O8) at

Mountain Pass or 480 ppm at Bayan obo. Between 1984 and 1998 radioactive slag leaked into Lake

Ivanpah from a hole in the pipe which transported the tailing waste to the tailing dam (Juettten

2011). The uranium and thorium tailing solids contain < 40 ppm and < 100 ppm with a radiation of

232 Th of around 0.44 – 0.46 Bq/g (CWQCBLR 2010). In general it can be assumed that the strongest

enrichment of thorium, uranium, radium and lead occur by leaching separation processes. These

technologically-enhanced naturally-occurring radioactive materials (TENORM) are under special

surveillance by different agencies.

3.5.4 Regulatory approaches

Different regulatory approaches exist to handle radioactive materials which are not further

processed for uranium enrichment depending on their origin. If naturally-occurring radioactive

materials (NORM) are concentrated or released by human activities, they are classified as TENORM.

The scientific community uses the terms uniformly and NORM waste describes mostly TENORM in

the relevant literature (Hua & Pan 2012; Department of Mines and Petroleum Resources Safety

2010a; Sahoo et al. 2010; Pillai 2005; Ault et al. 2015; IAEA 2011). Produced concentrates and

leached waste streams are under special surveillance and belong surely to TENORM.

The International Atomic Energy Agency IAEA has developed guidelines for these materials which are

used by countries as a basis of their own legislation and regulations. International standards consider

materials as not radioactive if activities are below 1 Bq/g for 232 Th and 238 U or 10 Bq/g for 39 K.

Exemptions are possible if the dose of 1 mSv for an exposed person per year is not exceeded (IAEA

1996; IAEA 2009). TENORM waste with an activity concentration of less than 1 Bq/g is internationally

classified as exempt waste (IAEA 2006; IAEA 2004). This also involves all decay products of 232 Th,

238 U and 39 K in secular equilibrium, and it is assumed, that the radioactivity of the material does

Chapter 3

35

not exceed 10 times that of the exempt material (IAEA 2006; IAEA 2004; IAEA 1996; IAEA 2009). If

material is physically processed, secular equilibrium is assumed. In case of chemical or thermal

treatments the different process streams must be analyzed to identify interruptions of the secular

equilibrium estimating the activity of each material (Department of Mines and Petroleum Resources

Safety 2010a; Resources Safety 2010; Department of Mines and Petroleum Resources Safety 2010b).

Furthermore, radioactive materials with less than 50 ppm of uranium and thorium or any

combination of the two are legally regarded as not radioactive by the U.S. NRC (10 CFR Part 40). The

European Commission stated exemption values at 1 Bq/g for 238 U, 1 Bq/g for 232 Th and 10 Bq/g

for 39 K in secular equilibrium (2013/59/Euratom 2014). In China an environmental impact

assessment is requested at non-uranium mining sites containing natural radioactive nuclides which

needs to be approved by the Environmental Protection Agency (Hua & Pan 2012). After a long way of

TENORM implementation, China accepted that ores, intermediate products or tailings of new mining

projects with a radiation > 1 Bq/g of uranium, thorium or any decay radionuclide need to be

regulated (Ma 2013; Ault et al. 2015). In Malaysia 1 Bq/g is the clearance limit of TENORM, i.e.,

materials with lower radioactivity can be stored without restrictions by the Atomic Energy Licensing

Board (AELB). Effluent limits of 1 Bq/L for 226 radium and 1 Bq/L of 228 radium have to be fulfilled

which is stipulated by AELB (Lin 2012; Ault et al. 2015).

3.6 Improving waste management

Soil and water contaminants may be released by natural processes, e.g., weathering or human

mismanagement when constructing defective impoundment areas which may break or leak. Natural

consequences (e.g., strong rain events or earthquakes) should be taken into account using suitable

models to assess the probability and consequences of dam bursts, flooding and further scenarios. In

order to avoid air emission several state of the art prevention methods exist, like the use of

sprinklers against dust, cooling systems or gas filters to collect volatile components formed during

processing (European Commission 2009). Also, there are techniques at hand to protect soil and

water ecosystems, for example the use of limestone to neutralize acidic waste effluents and to

Chapter 3

36

precipitate heavy metals from these effluents, which can also act as a buffer system to avoid acid

mine drainages (AMD). In

Table 3 existing waste handling strategies, their environmental impacts and possibilities for an

improved waste management are listed.

Chapter 3

37

Table 3: Radiation risk and waste management of REE mining

Particulate matter/ dust

Environmental

impact

1. Thorium

accumulation in

surrounded areas

2. Rn gas lung

cancer

3. Particulate

matter cancer

(Waste)

Management

Sprinkler HDPE cover NaOH scrubber Shielding of crushing

and grinding facilities

Supply of respiratory

masks

supply of individual

dosimeters and

portable ratemeters

Status Well established Well established Well established In progress In progress

Advantage Effective usage Environmental

protection

Environmental

protection

Avoidance of

uncontrolled dust

release

Early warning system

Disadvantage High water

consumption

Fragility seepage

Rain cause run off

water

Rn accumulation of

equipment after time - -

Costs

Additional

information -

HDPE top cover for

leaching residues

avoidance of drift of

particular matter

Exchange of

equipment

Exchange of old

technology -

Thorium containing leaching residues/ fine grinded bulk material enriched with radionuclides

Environmental

impact

1. Accumulation in

surrounded areas

2. (Ground) water

contamination

3. Rn gas lung

cancer

(Waste)

Management

Sealed storage

facilities

solid foundation:

(cement and HDPE

cover)

Buffering with BaCl2/

Na2SO4

Covering with top soil Phytoremediation Supply of respiratory

masks, individual

dosimeters and

portable ratemeters

Status In progress Well established Well established In progress In progress

Advantage Safe temporary

storage

Buffering for potential

radioactive leaching

residues

Avoidance of drift Stabilization of top soil,

extraction of heavy

metals from polluted

areas

Early warning system

Disadvantage No permanent storage - Unnoticed release of

radionuclides into

(ground or) surface

waters

High water consumption -

Costs

Additional

information

Deactivation of Rn

Avoidance of seepage

water

- - - -

Generic management should comprise the transparent information of workers and the public about the safety management

and any accidental incidents, shielding of resident properties, support for renovation of residents households, and increased

monitoring stations for analyzing dust, soil, sediment, water

Chapter 3

38

Management of mining wastes should start during the operation of the mine and should continue

after mine closure. During operation, it is important to minimize dust development after blasting,

hauling, drilling, crushing and grinding using sprinklers to wet the ore and the soil. The sprinkling

water containing the contaminated dust could be drained into a pond avoiding the release of

thorium containing particulate matter over the surrounding area. Gaseous radon could be collected

by NaOH scrubbers. After froth floatation, fine ground waste and the produced concentrate enriched

with thorium should be kept wet to minimize dust formation (Li et al. 2016; Li et al. 2013). Vacuum

cleaner, gas filters and ventilation are good practice to avoid the release of thorium containing

material by indoor operations which mostly occur during chemical beneficiation steps. Tailing heaps

are not suited to store radioactive waste because of emission by wind erosion. Installing trees will

reduce wind and water erosion in such areas by stabilizing the soils and at the same time will resorb

part of the contaminants, a process called phytoremediation (Chibuike & Obiora 2014). Pipes

transporting liquid waste must regularly be controlled for leakages and for radiation contamination

due to inside radionuclide accumulation. A good managing practice of radioactive waste is to dilute

the slag with wastes from the physical beneficiation tailings in order to only slightly increase the

radioactive content in comparison with the crude ore content (REITA 2012) and to cover the tailings

with top soil in the end.

After closure of the mine, waste management comprises standard techniques such as covering

tailings with top soil although still years after closure weathered material has been detected in

nearby waters or even groundwater. Leachates and seepage effluents from covered heaps have to be

monitored for radioactive residues (European Commission 2009; Environmental Protection Acency

2012). One way to avoid such emissions could be to install drainages deep into the heaps and create

stockpiles which steer the weathered water into nearby impoundment basins for surveillance.

Precipitation of radioactive residues is an important technique by mixing BaCl2 /Na2SO4 with the

thorium containing leaching tailings and in the tailings ponds. The use of radioactive slag as additive

for agriculture or for brick production is a bad option, because of the permanent radioactivity the

Chapter 3

39

public is exposed to (Qifan 2011). Indoor storage of thorium tailings is a good practice to avoid

contamination through dust erosion but that is not a permanent solution.

3.7 Conclusion

The radioactive byproduct thorium in rare earth ores is enriched during the beneficiation steps

(Figure 6) and significant amounts will end up in the waste streams of REE processing. Contamination

with radioactive material containing thorium, uranium and the decay products has increased over

many years of mining activity and consequently mines had to be closed due to environmental

problems (Hurst 2010; Lee 2012; Li et al. 2012; IAEA 2010). The thorium containing waste is stocked

as solid heaps whose handling and management need most careful consideration because of

environmental and health effects in case that men and other environmental organisms become

exposed to such material. If proper management is applied, thorium contents of the annually

produced sludge can be decreased such as at Bayan Obo, the largest RE producer (Qifan 2011). New

environmental legislation, for instance implemented recently in China, promoted the development of

proper radioactive disposal techniques (Li et al. 2012). Usually, leaching residues, which contain

thorium filter cake material as well as thorium containing dust have the main hazardous potential at

different RE processing steps. It is unclear whether economic restrictions will hamper the ecological

improvement of current mining methods and equipment especially in countries with low gross

national product. New research needs to address:

Improved life cycle assessment studies with collected data especially from the main

producers in China to assess potential risks and possible improvements in handling

thorium and its daughter radionuclides.

Improvement of processing ores with repect to the separation of hazardous radioactive

metals

Recycling of thorium in waste streams for use in new, inventive technologies

Chapter 3

40

Beside the research needs old mining technology must be improved by using the information of

recent research projects, as summarized in the special issue of this journal. Furthermore, the public

must be informed to become aware of positive and negative aspects in rare earth mining comprising

Full concept for radiation protection already during the exploration phases involving

waste management

Detailed storage information for exploration, operation and closure time, exposure and

protection of workers and the public

Handling of thorium residues after mine closure

Responsibilities in case of disaster

Recycling of thorium for use in nuclear power plants (atomic fuel cycle) will stimulate intensive

research, as for example in China. Also in such developing techniques “green processing” has to

become a standard to keep the environmental consequences as low as possible.

Chapter 3

41

3.8 References

2013/59/Euratom, 2014. COUNCIL DIRECTIVE 2013/59/EURATOM. Journal of the European Union, (December 2003), pp.1–73.

Al-Areqi, W.M., Majid, A.A. & Sarmani, S., 2014. Digestion Study of Water Leach Purification Residue for Possibility of Thorium Extraction. The Malaysian Journal of Analytical Sciences, 18(1), pp.221–225.

Ault, T., Krahn, S. & Croff, A., 2015. Radiological impacts and regulation of rare earth elements in non-nuclear energy production. Energies, 8(3), pp.2066–2081.

BGS, B. geological S., 2011. Rare Earth Elements. www.MineralsUK.com, pp.1–54. Available at: http://www.bgs.ac.uk/downloads/start.cfm?id=1638.

BRGM, 2001. Management of mining, quarrying, and ore-processing waste in the European Union. , (79 p., 7 Figs., 17 Tables, 7 annexes, 1 CD-ROM (Collected data)), pp.1–88. Available at: http://ec.europa.eu/environment/waste/studies/mining/0204finalreportbrgm.pdf.

Castor, S.B. & Hedrick, J.B., 2006. Rare Earth Elements. Industrial Minerals and Rocks, (in Kogel, et al., 7th edition Society for Mining, Metallurgy and Exploration), pp.769–792. Available at: http://www.fieldexexploration.com/images/property/1_RareEarths_FLX_02.pdf.

Chakhmouradian, a. R. & Wall, F., 2012. Rare Earth Elements: Minerals, Mines, Magnets (and More). Elements, 8(5), pp.333–340. Available at: http://elements.geoscienceworld.org/cgi/doi/10.2113/gselements.8.5.333 [Accessed August 12, 2014].

Chibuike, G.U. & Obiora, S.C., 2014. Heavy metal polluted soils: Effect on plants and bioremediation methods. Applied and Environmental Soil Science, 2014.

Chunhua, Y.A.N., Jiangtao, J.I.A. & Chunsheng, L., 2006. Rare Earth Separation in China *. , 11(2).

County of San Bernadino Public Works Group, 1996. Transmittal of Draft EIR for Molycorp Mountain Pass Mine Expansion, for review and comment. , (Accession No. ML032180283).

CWQCBLR, 2010. Revised Waste Discharge Requirements for Molycorp Minerals LLC, Mountain Pass Mine and Mill, San Bernardino County. California Water Quality Control Board Lathontan Region, (Board Order NO. R6V-2010-(Proposed)), p.124.

Department of Mines and Petroleum Resources Safety, 2010a. Managing naturally occurring radioactive material (NORM) in mining and mineral processing - guideline. , NORM 4.1, p.37.

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4. Chapter: Toxicity of thorium to

aquatic and terrestrial

organisms: algae, daphnia

and collembola

Matthias Findeiß, Andreas Schaeffer

RWTH Aachen University, Institute for Environmental Research, Department of Environmental

Biology and Chemodynamics, Worringerweg 1, D-52074 Aachen, Germany

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4.1 Abstract

Due to rare earth mining and its usage in nuclear reactors, thorium receives more and more public

and economic attention. Despite growing awareness for elevated thorium concentrations in the

environment, only limited ecotoxicological data are available for aquatic as well as terrestrial

organisms. In this study, standard biotesting protocols for Desmodesmus sp., Pseudokirchneriella

subcapitata, Daphnia magna, Folsomia candida and Eisenia fetida were used to evaluate the acute

and chronic toxicology of thorium. Exposure of algae showed a low growth rate inhibition of about

9 % whereas daphnids were mobile i.e. unaffected through all exposure scenarios. Different

exposure scenarios of collembola also showed no effects.

Keywords: Algae, Daphnids, Collembola, Earthworm, Thorium, Toxicity

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4.2 Introduction

A large number of studies have found that heavy metals may be toxic to soil-living species, including

microorganisms, plants and invertebrates. Thorium is three to four times more abundant in the

environment than uranium and as often found as magnesium, calcium or iron (Rudnick 2005). It is a

naturally occurring element with around 99% as 232 Th isotopes. Along with uranium, thorium is

responsible for most of the radiation from geogenic sources. Thorium is soluble under acidic

conditions and precipitates if the pH of aqueous solutions increases. Above a pH of 4, thorium forms

complexes primarily with carbonates and organic substances like EDTA, which themselves enhance

its solubility (Higashi et al., 1959; Langmuir et al., 1980; Östhols et al., 1994). Reported environmental

concentrations of thorium range between 0.009 μg/L (<0.002 μg/L to 0.37 μg/L) in stream water,

8 mg/kg (<0.1 to 71. mg/kg) in subsoil, 7 mg/kg (0.3 to 75.9 mg/kg) in topsoil and 10 mg/kg (<1 to

253 mg/kg) in stream sediment (Salminen et al. 2006). These concentrations cause no harm to

organisms while elevated concentrations from depositions of mining and processing sites like rare

earth mining are suspected to have an environmental impact. Around rare earth mines studies have

demonstrated that grass, water, soil and animals show higher concentrations and are therefore

contaminated with thorium residues of mining waste (Li et al. 2012). For example, Langmuir and

Herman, (1980) reported highly acidic groundwater and concentrations of 38 mg/L thorium close to

an uranium mine. Around the rare earth mine Bayan obo an enriched thorium concentration of

about 4 to 60 mg/kg in the upper soil layer has been reported (Li et al. 2014).

It is assumed that humans are mainly exposed to thorium matter through inhalation of contaminated

dust. The inhaled particle size seems to play a role in determining which isotope is responsible for the

observed damages. As a further thorium source 228 radium is ingested into the body, where it is

stored in tissues and will decay into 228 Th (half-life: ~1.9 years). Thorium is enriched mostly in

lymph nodes, followed by lung and bone tissue (228 Th, 230 Th, 232 Th) (Wrenn et al. 1981). Based

on data for uranium the absorption rate from contaminated dust will be between 1 and 5 % for the

human body. Gastrointestinal absorption of thorium and uranium differ, 0.02 % for thorium and

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between < 0.1 to 6 % for uranium depending on the solubility of the uranium ion(s) (Keith et al. 2013;

Keith & Wohlers 1990). Rats which were exposed to thorium containing monazite dust (particle size

< 5µm) for 180 days remained without visible effects, although they showed slight enzymatic

(succinic dehydrogenase and adenosine triphosphatase) changes in the kidney, which might be

triggered by a dislocation of monazite compounds from the lung to other organs of the body (Tandon

et al, 1977). Once inside the body, thorium is transported via transferrin in the blood stream (Peter &

Lehmann 1981). Mice which were exposed with thorium nitrate (10 mg/kg/day) for 30 days showed

an accumulation of thorium in liver > femur > spleen, while the body and liver weight of the animals

decreased and oxidative stress was measured (Kumar et al. 2008; Kumar et al. 2009; Ishikawa et al.

1999). As mentioned before, thorium has been investigated for its health effects on mice and rats

(Kumar et al. 2008; Kumar et al. 2009; Ishikawa et al. 1999; Wrenn et al. 1981; Tandon et al. 1977;

Peter & Lehmann 1981; Keith & Wohlers 1990) but studies on the ecotoxic impact on aquatic and

terrestrial organisms are rare (Table 4).

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Table 4: Literature data for thorium toxicity in aquatic and terrestrial organisms

Species Concentration Exposure Time

Effect References

Chlorella vulgaris - green agae 1.2 0.8

mg/l mg/l

3-4 m LOEC NOEC

De Jong et al. 1965

Daphnia Magna - crustacea 1,000 mg/l 48 h no Bringmann & Kuhn, 1959*

Microregma sp. - ciliated protozoa 25 mg/l 28 h no Bringmann & Kuhn, 1959b*

Scenedesmus quadricauda - green algae

4 d no Bringmann & Kuhn, 1959*

Monoraphidium sp.- green algae 50 25

mg/l mg/l

30 d LOEC NOEC

de Queiroz et al. 2012

Scenedesmus sp .- green algae <25 mg/l 30 d supporting

growth

50 25

mg/l mg/l

30 d LOEC NOEC

Hyalella azteca - crustacea 473 µg/l

(nominal) 7 d

LC50 (soft water) Borgmann et al.

2005 5.2 µg/l

(measured)

Hyalella azteca - crustacea >3,150 µg/l (nominal)

7 d LC50

(tap water)

Tadpole – frog 1-5 mg/l 1 m

arrested germination of the ovum

Dilling et al. 1925

Thiobacillus ferrooxidans – bacteria (several strains)

0.232 – 0.928

ng/l 100 h

inhibition of ferrous iron

oxidation Leduc et al., 1997

*data adopted from http://cfpub.epa.gov/ecotox/

Incorporated thorium can cause long time effects on humans which is shown by the application of

the radiocontrast agent “thorotrast” between 1930 and 1964 (Becker et al. 2008; Mays & Spiess

1979; E. Glover et al. 2001; Lipshutz et al. 2002). When injected intravascularly, thorotrast exposure

leads to a deposition of 72% of the applied 232 Th in the liver, 12% in the spleen and 8% in the bone

marrow. After 16 to 45 years of latency (Lipshutz et al. 2002) malignancies were observed in several

forms like angiosarcomas, plasmacytomas or carcinomas (Becker et al., 2008; Harrist et al., 1979;

Jones et al., 1999; Lipshutz et al., 2002; Mays et al., 1979). Animal experiments with thorotrast

showed effects on the humoral antibody production and enhanced virus growth (Monath et al.,

1971). Nevertheless, no genetic effect was observed for thorium in the rec-assay using Bacillus

subtilis strain H17 and M54 (Nishioka 1975), which reflects that the exposure time interval was

probably too short for the manifestation of genetic effects.

Chapter 4

52

In the future, thorium will increase in importance due to intensive investment in nuclear reactors

(World Nuclear Association 2015). Thus, there is a strong need for a better insight into thorium’s

environmental impact as well as the environmental fate and behavior of the heavy metal.

Algae and daphnids are important organisms in the aquatic ecosystem due to their respective roles

as primary producers and primary consumers. Collembola and earthworms play an important role in

soil formation and the terrestrial food chain and are often used to determine the terrestrial toxicity

of substances.

In this study, tests with aquatic organisms (Desmodesmus sp. and Daphnia magna) and terrestrial

organisms (Folsomia candida and Eisenia fetida) were performed to assess the ecotoxicological

potential of thorium. Additionally, algae tests were performed at low pH (pH 5) to simulate the acidic

conditions of common mining effluents and potential acidic basins (Langmuir & Herman 1980). Our

data add to a more comprehensive assessment of the environmental and ecotoxicological impact of

thorium contamination at mining sites. Because health impacts caused by radioactive radiation are

difficult to investigate in such a short time (half-life of thorium of 14 x 109 years), we focused on the

metal toxicity of thorium.

4.3 Material and Methods

4.3.1 Sample preparation and analytical measurement of thorium solution

Thorium standard solution (AccuTraceTM Reference Standard: 1000 µg/ mL) was used to prepare

test media. Several sample preparation steps were performed prior to the biotests: thorium nitrate

solution (ThNS) was neutralized with sodium hydroxide (10 M NaOH) and the precipitated thorium

was centrifuged for 10 min at 900 g. Afterwards, the thorium pellet was resuspended in double

distilled water and centrifuged again (900 g; 10 min). This procedure was repeated seven times until

no nitrate was detected in the supernatant using a rapid nitrate test (EM Water QuantTM nitrate test

stripes). The thorium pellet was again resuspended in double distilled water and shaken for 24 h

(200 rpm). After 24 h the suspension was centrifuged at 900 g for 10 minutes and the supernatant

Chapter 4

53

was immediately used for aquatic ecotoxicological tests; for the terrestrial tests the pellet was dried

prior to application. These preparatory steps were done to avoid toxic effects of the high nitrate

content of the ThNS (containing 2-5% HNO3) which were observed in pretests (data not shown).

Furthermore, algae experiments were performed with thorium nitrate salt to achieve higher solved

thorium (generously provided by the Institute of Nuclear Waste Management and Reactor Safety, FZ-

Jülich). Algae and daphnia solutions were filtered before analytical preparation (< 0.5 µm) at the end

of each biotest. Final thorium concentrations were measured at the end of each test using ICP-MS

(PerkinElmer DRCe quadrupole ICP-MS) and a thorium nitrate standard solution for calibration

(AccuTraceTM Reference Standard: 1000 µg/ mL). Rubidium (RbNO3, Merck, Darmstadt) was used as

internal standard.

4.3.2 Aquatic biotesting with algae (Desmodesmus subspicatus/ Pseudokirchneriella subcapitata)

Desmodesmus subspicatus/ Pseudokirchneriella subcapitata were cultured in-house in BRK medium

(long time fluid culture for algae after Bringmann & Kuehn 1980). 5000 cells per mL were chosen for

the experiments according to OECD 201 and DIN 8692 guidelines (OECD 201 2011; DIN EN ISO 8692

2012). It was confirmed that exponential growth of the algae was maintained for 72 h (test period)

under continuous light conditions. All experiments were performed in 24 well plates. Plates were

measured with the SPECTRA Fluor Plus’ (Tecan AG, Hombrechtikon, Switzerland) every 24 h over the

72 h test period (excitation wavelength: 485 nm with a bandwidth of 20 nm, emission wavelength:

685 nm with a band width of 9 nm). ThNS experiments were performed with Desmodesmus

subspicatus.

The low pH experiments with Pseudokirchneriella subcapitata were conducted at pH 5. The BRK

growth medium was adjusted to pH 5 using HCl, and algae were subsequently cultured in the

medium for one to two month of adaptation. The medium for the algae exposure tests was also

adjusted to pH 5. Preliminary experiments were done to confirm that exponential growth of the

algae was maintained throughout the test period of 72 h under these conditions.

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54

4.3.3 Aquatic biotesting with daphnids (Daphnia magna)

Acute toxicity for Daphnia magna was evaluated by determining the 48 h LC50 of ThNS according to

guidelines (OECD 202 2004). Daphnids were held in in-house cultures at a constant temperature

(20±2°C) and light/dark conditions (16/8 day light cycle). Neonates were sieved 24 h prior to testing,

so to ensure all animals used for the biotest were less than 24 h old. Five organisms were placed into

each test unit containing 10 mL medium and kept during the test without renewal. For the test

medium, ISO test water (CaCl2*2H2O, MgSO4*7H2O, NaHCO3, KCl) at pH 7 was used, in which the

respective ThNS solution was dissolved. At least 3 replicates per treatment and 5 replicates per

control were tested under continuous dark conditions at 20°C. After 24 h, 48 h and 72 h exposure

time, the number of mobile daphnia in each unit was recorded, considering that animals without

reaction to soft agitation after 15 s were immobile.

4.3.4 Terrestrial biotesting with collembola (Folsomia candida)

The collembolan toxicity tests were conducted with Folsomia candida (gently provided by Prof. Dr.

Filser, Institute of Ecology, University of Bremen UFT). Collembola are cultured and synchronized on

activated carbon plates in-house. Reproduction tests were performed according to guidelines OECD

232 2009. Ten synchronized (9-12 d old) organisms were placed into each test vessel (VWR

Laboratory bottles, round, 50 ml with screw cap), with 5 replicate vessels per concentration,

additional vessels were used as pH and water control respectively. After 28 d adults and juveniles

were floated by addition of tap water and subsequently alive adults and juveniles produced were

counted. A feeding experiment was conducted with dried bran, finely ground together with dried

thorium hydroxide pellet (see above) for 15 min producing a homogenous distribution. For this, 10

synchronized (9-12 d old) collembola were added to an active coal plate and fed with dried bran

(0.1 g Th(OH)4 / g bran). During the test period, it was ensured that the plates did not dry out and

that the bran did not mold. After 28 d coal plates were photographed and adults and juveniles were

counted. All toxicity tests were performed with 8/16 h light/dark rhythm and temperature kept at 20

± 2°C.

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4.3.5 Terrestrial biotesting with earthworm (Eisenia fetida)

Synchronized, 3-12 month old, worms were generously provided by Ibacon GmbH, Roßdorf,

Germany. The compost worm, Eisenia fetida, was used for earthworm reproduction toxicity test

according to guidelines (OECD 222 2004). The reproduction test was conducted as a limit test. Four

replicates with 10 mature adults were selected for each treatment. Experimental conditions included

16/8 h (light/dark) photoperiod and temperature at 20 ± 2°C. The testing period was 56 days.

Measured endpoints for limit reproduction test were adult mortality and their weight loss on day 28,

when the adults were removed from the test units; the number of juveniles was counted on day 56.

4.3.6 Statistics

In order to determine NOEC, LOEC and ECx values results were analyzed using the statistical program

ToxRat®Professional XT (ToxRat®Professional XT 2.10, ToxRat®Solutions GmbH 2001-2010) for their

statistical toxic effects as defined by OECD. NOEC values were determined from single replicate

values. First, normal distribution was tested with a Shapiro-Wilk´s test. If variances were

homogeneous, NOEC values were determined by Bartlett´s test (p< 0.05). If variances were

inhomogeneous NOEC values were determined using Welch-t test with Bonferroni-Holm Adjustment

(p< 0.05). Significant differences to the control (p< 0.05) were determined using Fisher's Exact

Binominal test with Bonferroni Correction. Concentration response functions were fitted to the data

using probit analysis with a linear maximum likelihood regression. The median effective

concentration (EC50) was calculated from this function.

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4.4 Results

4.4.1 Aquatic toxicity

Algae tests

Algae tests were initiated under a pH of 8.1, but the pH changed during the experiment (see below).

The growth rate for Desmodesmus subspicatus at concentrations above 145 µg Th/L was about 9.6 %

lower than in the control (Figure 9). It was not possible to determine a 50 % effect concentration

(EC50) because of the low thorium solubility at this elevated pH. Especially for the OECD/DIN medium,

higher concentration of thorium led to precipitation.

Another algae strain, Pseudokirchneriella subcapitata, was chosen for the simulation of acidic

conditions, because it showed better growth rates at a low pH. After 72 h growth rate at

1.5 mg Th(NO3)4 aq /L (95 %-CL: 1.3 - 1.7) was inhibited by 50 % compared to controls (Figure 16, in

ANNEX). However, the growth rate of control algae at pH 5 was around~0.9, which is generally lower

than the growth rate of ~1.4 at pH 8 (Figure 16, ANNEX).

Figure 9: Growth rate inhibition of Desmodesmus sp. exposed to Th

for 72 h at pH 8. Data represent the growth rate mean±SM. NOEC: 93 µg/L, LOEC: 145 µg/L, test was repeated

thrice

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57

Tests with daphnids

In comparison with algae medium, higher thorium concentrations were achieved in daphnid

experiments where ISO minimal medium was used. Accordingly, an immobilization tendency was

observed for daphnia exposed to 5 mg/L thorium after 72 h. No effects were observed at

concentrations below 5 mg/L thorium. A NOEC of 2.5 g Th/L was determined after 72 h (Figure 10).

The acute immobilization test showed no significant effects after 48 h.

Figure 10: Mobility of Daphnia magna neonates exposed to Th

for 48 h at pH 7. Data represent the mean± SM, test was repeated thrice

4.4.2 Terrestrial toxicity

For collembolan feeding tests dried thorium-bran pellets were added to soil (Figure 11) at a nominal

concentration of 0.1 g Th(OH)4 / g bran. No differences in survival or reproduction were observed

after 28 d compared to control animals. Also, tests with thorium contaminated OECD soil showed no

effects on survival or reproduction after 28 d in comparison with the control group, neither when the

soil was loaded with thorium dissolved in water (1,000 mg/L [nominal], pH 6.9) nor when it was

loaded with dried thorium-pellets mixed with the soil. Soil pH was constant during of experiments

(pH 6.5).

Furthermore, an earthworm experiment was performed as a limit test with OECD soil contaminated

with dried thorium pellets at a constant pH of 6.5 during the 56 d test period. After 28 d 100 % of all

adult animals survived with no weight changes compared to the control up to the highest thorium

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concentration of 1 590 µg/kg soil. No alteration in the reproduction was observed after 56 d (Figure

16, in ANNEX,Table 5).

Figure 11: Folsomia candida: number of survived adults (a) and number of offspring (b)

(mean±SM) per microcosm after 28 days; test was performed twice

Table 5: Summarized results for all biotest performed with thorium

EC: effect concentration; NOEC: no observed effect concentration; LOEC: Lowest observed effect concentration;

CL: confidence level

Organism Experiment Time Effect Thorium Concentration

(ICP-MS)

pH CO32-

(mg/l)

Algae Desmodesmus sp.

Growth inhibition test OECD 201

72 h NOEC LOEC

93 µg/l 145 µg/l

6.5-8 35.7

Algae Pseudkirchnella subspicata

Growth inhibition test OECD 201

72 h EC50 1.5 mg/l (95% CL 1.3-1.7)

5 35.7

Daphnid Daphnia magna

Acute test OECD 211

48 h no effect ≤ 4750 µg/l 6-7 46

Collembola Folsomia candida

Reproduction test OECD 232

28 d no effect ≤ 1590 µg/l 6-7 -

Compost worms Eisenia fetida

Reproduction test OECD 222

46 d no effect ≤ 890 mg Th /kg soil

6.5 -

a) b)

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4.5 Discussion

Algae tests

The pH of the algae media fluctuated highly during experiments. It is well known that metabolic

activity of algae strongly affect the pH of the medium (Dubinsky et al. 1974) which then affects the

solubility of thorium (Langmuir & Herman 1980; Östhols et al. 1994). Thus, the major difficulty when

assessing the toxicity of thorium in an aquatic environment is its low solubility at pH 5-8 (Wiberg &

Holleman 2007). According to the literature, a LOEC of around 1.2 mg Th/L was determined for the

green algae Chlorella vulgaris, however, the authors reported a LOEC of around 1.2 mg/L nominal

concentrations only anticipating constant concentrations during the exposure time of one month.

Other green algae showed growth inhibition only at a concentration around 50 mg/L. Thus, the

measured effect concentration for Desmodesmus subspicatus of 145 µg/L is much lower than

reported in the literature. This difference is most likely resulting from the fact that for the first time

measured final concentrations which varied considerably from the initial (nominal) concentrations

were used to calculate effect concentrations.

Data from the literature illustrate that algae react differently to different heavy metals. For example,

the green algae Chlorella vulgaris showed an EC50 of 15.4 mg/L for thorium (Bringmann & Kuhn

1959a), while for uranium it was 100 to 1000-fold lower (1.4 - 270 µg/L) (Franklin et al. 2000; Charles

et al. 2002). Uranium occurs in different oxidations states with U4+ and is much less soluble than U6+,

which is why the latter is mostly used for assessing aquatic ecotoxicity (Massarin et al. 2010; Herlory

et al. 2013). Other EC50 values for cadmium, zinc, manganese, aluminum or chromium are 0.3, 1.4,

15.3, 16.5 or 0.84 mg/L respectively (Eisentraeger et al. 2003; DIN EN ISO 8692 2012; Baścik-

Remisiewicz et al. 2011).

Thorium ecotoxicity results are strongly influenced by experimental parameters like pH, hardness,

and dissolved organic carbon. A phenomenon also observed for other elements. Cadmium, copper

and nickel are well investigated examples for showing how the effect concentration is influenced by

these parameters (Borgmann et al. 1991; Meyer et al. 2002; Meyer et al. 1999). We chose acidic

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conditions for the algae tests referring to OECD 201 for increasing thorium solubility and derived an

EC50 of 1.5 mg Th/l (analytically verified). It has to be taken into account, however, that acidic

conditions (pH 5 in our experiment) inhibit the general algae growth slightly. Nevertheless, a

significant reduction of algae growth was reported for organisms exposed to thorium in comparison

to the acidic pH control organisms. This underlines the robustness of the effect.

Tests with daphnids

Daphnia magna is known to react rapidly to heavy metals (in the µg/L - mg/L range) (Attar & Maly

1982; Fargasova 1994; Sankaramanachi & Qasim 1999; Tisler & Zagorc-Koncan 2002; DIN EN ISO

6341 2010). In the literature D. magna tests with uranium revealed an EC50 between 6 to 55 mg/L

depending on the water hardness, which affects the bioavailability of metals (Franklin et al. 2000;

Charles et al. 2002). Experiments with daphnids were performed at pH 7 and no pH shift occurred

during the experiment. Immobilization was not observed in the experiments (Figure 17, in ANNEX). In

comparison with the literature (Bringmann & Kuhn 1959a) lower concentrations were tested but it

was not possible to dissolve more thorium. Whenever more thorium was dissolved in water, it

precipitated during pH adjustment.

Collembola and earthworm tests

Although toxic effects of various metals have been reported for collembola and earth/ compost

worms (Lock & Janssen 2003; Lock et al. 2000) this report is the first to present effects of thorium on

springtails and compost worms. Folsomia candida was exposed to thorium using different scenarios.

However, none of the scenarios led to any effect on survival or reproduction (Figure 11) even at

concentrations higher than those found in the environment (Salminen et al. 2006).

Eisenia fetida was not affected by thorium when testing survival, weight change or reproduction

which in a way has also been concluded by others: thorium contaminated mining sites such as Bayan

obo (Li et al. 2014; Li et al. 2013) exert no toxicity against terrestrial organisms. For other heavy

metals, like uranium, Sheppard et al. (2005) concluded that terrestrial organisms are not impaired by

concentrations up to 100 - 350 mg U/kg soil. The radioactive effects of thorium in the environment

Chapter 4

61

were not considered in these studies, since the whole toxic potential of thorium, the radioactive

toxicity and heavy metal, cannot be assessed simultaneously under the rather short incubation

conditions.

4.6 Conclusion

The tested aquatic and terrestrial organisms were exposed to thorium at concentrations higher than

those reported in the environment. None of tested organisms were strongly affected and most did

not show any symptoms. Only under conditions of a constantly low pH where thorium solubility is

increased, algae showed a significant inhibition in their growth rate resulting in an EC50 of

1.5 mg Th/l. These results are in line with other reports (Table 4) although several of the toxicity data

found in the literature were based on nominal rather than measured concentrations.

For a comprehensive hazard potential of thorium the dominating radioactivity effects have to be

addressed: long-term damage of exposed men and animals has been reported repeatedly. Birth

defects, liver disease or lung burden occurred in exposed population living close to thorium waste

disposals or to REE plants (Najem & Voyce 1990; EPA 2012; Chen et al. 2005; Terry et al. 1997; Chen

et al. 2004; Polednak et al. 1983; Liu et al. 1991; Furuoka & Lo 2005; Ichihara & Harding 1995).

Analysis of sheep bones, pasture, soil samples at different soil depth and samples of surrounding

tailings revealed radioactive thorium contamination (Li et al. 2012; Li et al. 2014). In laboratory tests

like those reported here only the metal toxicity can be investigated which according to our results is

of no environmental concern, but should not be regarded isolated from radioactivity assessments.

ACKNOWLEDGMENTS

This work was funded by the SIEMENS AG. Special thanks to Prof. Mayer and Dr. Sindern, department

of mineralogy, inorganic reservoirs and geochemistry at RWTH Aachen for the possibility to perform

ICP-MS analyses.

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62

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5. Chapter: Environmental consequence

arising from eudialyte

processing

Matthias Findeiß1, Mariola Gschwendtner2 #, Daniel Voßenkaul3 #, Theresa Stark4 #, Volker

Linnemann2 #, Andreas Schaeffer1

1RWTH Aachen University, Institute for Environmental Research, Department of Environmental

Biology and Chemodynamics, Worringerweg 1, 52074 Aachen, Germany

2RWTH Aachen University, Institute of Environmental Engineering, Mies-van-der-Rohe-Str. 1, 52074

Aachen, Germany

3RWTH Aachen University, Institute of Process Metallurgy and Metal Recycling, Intzestr. 3, 52056

Aachen, Germany

4RWTH Aachen University, Unit of Mineral Processing, Lochnerstr. 4-20, 52064 Aachen, Germany

# In case of publication, this chapter must be shown to the co-authors for improvement.

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5.1 Abstract

Mining activities cause severe environmental contamination with high risks for water, soil and biota.

A methodological approach was developed to identify potential hazardous risk of mined eudialyte

(EU) tailings with the help of ecotoxicological testing systems. Representative soil and water samples

from tailings were prepared in three different EU processing steps and characterized by chemical and

ecotoxicicological investigations for their environmental impacts. The processing steps can be divided

into physical, including milling and flotation, and chemical processes such as acid treatment. Extracts

of milled EU showed no effects on the organisms tested. EU flotation solution showed a slightly

inhibited growth rate for algae. Yet, after chemical treatment for disintegration of EU, the processing

solution revealed significant effects in all tested organisms. Algae showed an EC50 at 40 % of EU

leachates (growth rate inhibition), daphnids an EC50 at 83 % of EU leachates (immobility) while

collembola had an EC50 at 48 % of EU residues (reproduction); percentages refer to the original

leachate after dilution with water (no absolute concentrations is given due to the complex mixture of

components eluted from EU; see table 6). Special attention needs to be paid to the leaching

eudialyte residues which are eventually disposed and have hazardous potential due to low pH

(increase of metal mobility), seepage or dust drift.

Keywords: Alga, Daphnia, Collembolan, Eudialyte, Rare earth, Toxicity, Process chain, Risk

assessment

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5.2 Introduction

The mining industry is increasingly confronted with economic, social and environmental aspects of

sustainability. This includes topics like cost reduction, bribery and corruption, human rights and

business ethics, child labor, but also loss of biodiversity, global warming, noise pollution or chemical

contamination of surrounded areas, to name but a few (Shen et al. 2015). Contamination of

groundwater, surface water and soils is an known impact of mining activities and difficult to manage

even today (Concas et al. 2006). Mining and processing sites enhance contamination of their

surroundings because of milled ores which enlarge the mineral surface providing a greater scope for

weathering or chemical treatment. This leads to the gradual dissolution of metals. Dust drift of

particulate matter, dam bursts, tailing pond overflows, uncontrolled treatment of waste water or

acid mine drainages (AMD) are the main sources of spreading soil and water contamination (Courtin-

Nomade et al. 2012) from mining activities. In the end of 2015, one of the most hazardous dam

disasters happened at Bento Rodrigues in Brazil and once again showed the impact of catastrophic

waste and tailing management (AFP and Reuters 2015). Another example for environmental and

occupational health issues is the Bayan obo mine in China which became widely known for its by-

products of rare earth elements (Qifan et al. 2010; Lee 2012; Huang et al. 2014).

In the environment, metals are natural components of waters and soils. They are important

constituent of daily life, whether within the steel production or for the health of humans, fauna and

flora as trace minerals. However, metals can reach concentrations where they affect organisms in a

toxic way. Essential metals have adverse effects on organisms when they reach too low

concentrations and again at very high concentrations. On the other hand non-essential metals, called

heavy metals, are even toxic at low concentrations and become more toxic with increasing doses

(Connell et al. 1999; Hopkin 1989; Walker et al. 1996). Once in the environment, metals persist in

aquatic and terrestrial ecosystems for long periods. Redox potential, decrease of pH or organic

matter are important factors influencing the mobility and bioconcentration of metals (García-Gómez

et al. 2014; Gupta et al. 1996; Hattori 1996). Due to weathering, metals are transported from soil to

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70

water systems and eventually into our food chain (Boularbah et al. 2006; Dang et al. 2002; Fanfani et

al. 1997). Once contamination of waters or soils took place, it is difficult to manage for years on end

(Concas et al. 2006; Malik & Husain 2006). In the past, hazardous capacity of soils was characterized

by chemical analysis of soil samples. In recent years ecotoxicological test systems were developed to

measure the biological effect concentrations of contaminated soil samples. In order to evaluate the

potential risk of contaminated areas, soil and water samples can be investigated in different ways:

native samples can be used for ecotoxicological tests directly, eluates from soil samples can be tested

or artificial soil samples can be spiked with different concentrations of the contaminant and used for

testing (Bierkens et al. 1998). In order to assess the fate and behavior of potential contaminants in

the environment it is necessary to investigate different trophic levels. For that reason, different

bioassays were used alongside to assess the ecotoxicological effects: in particular daphnids, algae

and collembola were used (Fernandez et al. 2005; García-Gómez et al. 2014; De Zwart & Slooff 1983;

Bierkens et al. 1998).

Eudialyte is a cyclosilicate mineral which has a low rare earth content but is enriched with heavy rare

earths that are demanded increasingly (Johnsen et al. 2001). It can be easily dissolved by acid which

makes eudialyte interesting as a future rare earth source. Up to date the state of the art for

beneficiation is less accessible for silicate minerals than for carbonates or phosphates like Bastnasite

or Monazite (Sukumaran 2012). In this study, eudialyte mineral (chemical composition: Table 6) was

processed as follows: first it was milled, followed by froth flotation and finally pre-separated by

hydrochloric acid and water (Figure 12). Milled eudialyte, residues of flotation and residues of

leaching were investigated using biotests with algae, daphnids and collembola. The present study

anticipates and discloses possible hazardous potential of the waste streams produced.

Chapter 5

71

Figure 12: Eudialyte process chain as developed in the project.

Section I: Boxes show an abstracted process chain; the aggregate state of the sample in the respective process step is

shown in light green. Process description is as follows: Mining: extraction of valuable minerals. Crushing/ Milling:

mineral is crushed and grinded for the optimal particle size needed in the following processes. Flotation: hydrophobic

materials are selectively separated from hydrophilic ones. This is the first enrichment step which then results in a

solid concentrate. The leftover sludge is passed into tailing ponds (see section II), where it is stored. Leaching pre-

separation: The concentrate is treated with HCl and most of the rare earth elements (REE) are dissolved. This is

essential for the further enrichment and purification steps. The HCl leached solution is separated from undissolved

solids with filters. The remaining filter cake is neutralized with limestone or CaCO3 and stored in an impoundment

area. The components of the leached solution are purified and separated by pH adjustment. Solvent Extraction: a

more specific method to separate rare earth oxides (REO) with liquid–liquid (water–organic) extraction based on

differences in the solubility of REO. Electrolysis: REO are converted into REE. Section II: Waste streams produced

and their disposal areas. Section III: boxes outlined in red show the process sample analyzed in this study.

The different test organisms which were used for the various samples are highlighted in dark green (A: algae; D:

daphnids; C: collembola).

Chapter 5

72

5.3 Material and Methods

5.3.1 Preparation of process waste streams

5.3.1.1 Treatment of milled eudialyte

Ten gram milled eudialyte were shaken with 100 ml bidest. water for 48 h. Afterwards, pH was

measured (pH 6.53) and the solution was centrifuged for 6 min at 700 g. The resulting supernatant

was used for the aquatic ecotoxicological tests.

5.3.1.2 Treatment of residues of flotation

Air-dried eudialyte was treated according to a developing patent by the institute of RWTH Aachen,

Unit of Mineral Processing, Aachen, Germany and SIEMENS AG. Therefore, this manual will not give

any further explanation about compounds and treatment. The sludge was analyzed by OECD

standard ecotoxicity biotests (terrestrial biotests: 579 g flotation solution / 1 kg OECD soil) (Figure 19,

in ANNEX).

5.3.1.3 Treatment of residues of leaching

Milled eudialyte was treated according to patent EP2995692 A1 (Friedrich et al. 2016). Briefly, the

eudialyte was treated with conc. HCl and subsequently leached with water. The leaching residues

had a pH around 1 and were consequently neutralized with CaCO3 until the pH reached 6.

Afterwards, the two phases (solid phase = cake; liquid phase = water) were separated by

centrifugation (22400 g for 10 min). Cake and water were investigated by OECD standard aquatic and

soil biotests (Figure 20, in ANNEX).

Chapter 5

73

Table 6: Metal content of eudialyte, leaching residues and leaching residues eluates

La Ce Nd Y Sr Nb Ta SiO2 TiO2 Al2O3 Fe2O3 Mn3O4 MgO CaO Na2O K2O Zr2O3 Th

ppm ppm ppm % ppm % ppm % % % % % % % % % % ppm

Milled EU1 2200 5500 2900 0.67 491 0.21 138 54.7 0.14 14.9 4.67 0.66 0.49 3.51 10.1 3.59 3.73

Leached

EU2

residues

268 811 418 0.14 178 0.23 184 67.3 0.1 11.9 4.7 0.19 0.33 1.39 5.91 3.54 2.17

La Ce Nd Y Sr Nb Ta Si Ti Al Fe Mn Mg Ca Na K Zr Th

mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l

Leached

EU eluate 0.266 0.508 0.148 0.077 1.48 n/a n/a n/a 0.063

0.60

9 0.09 12.9

35.1

5 670.5 219 18.3 n/a 0.02

1,2 data were gently provided by Daniel Voßenkaul, Institute of Process Metallurgy and Metal Recycling

5.3.2 Algae (Desmodesmus subspicatus)

Desmodesmus subspicatus are cultured in-house in BRK medium (long time fluid culture for algae

after Bringmann & Kuehn 1980). 5 000 cells per mL were chosen for the experiments according to

OECD 201 and DIN 8692 guidelines (OECD/OCDE 201 2011; DIN EN ISO 8692 2012). It was confirmed

that an exponential growth of the algae was maintained for the 72 h test period. All experiments

were performed in 24 well plates (TPP®tissue culture plates). Plates were measured with the Tecan

Infinite 200 (Tecan AG, Hombrechtikon, Switzerland). The settings of the fluorescence reader were as

follows: excitation wavelength: 485 nm, emission wavelength: 685 nm.

5.3.3 Daphnids (Daphnia magna)

Daphnids were held in in-house cultures at constant temperature (20±2°C) and light conditions (16/8

day light cycle). Acute toxicity was evaluated in ISO test water (CaCl2*2H2O, MgSO4*7H2O, NaHCO3,

KCl) at-pH 7 by determining the 48 h LC50 according to the OECD 202/ DIN 6341 methodology

(OECD/OCDE 202 2004; DIN EN ISO 15088 2009). Five neonates were placed into each test unit

containing 10 mL medium, without renewal during the test. At least 3 replicate units per treatment

and 5 replicates per negative control were tested. After 24 h and 48 h exposure time, the number of

mobile daphnids in each unit was recorded considering that animals without reaction to soft

agitation after 15 s were immobile.

Chapter 5

74

5.3.4 Collembola (Folsomia candida)

The collembolan toxicity tests were conducted with Folsomia candida (gently provided by Prof. Dr.

Filser, Institute of Ecology, University of Bremen UFT). Collembola were cultured and synchronized

on activated carbon plates in-house. Reproduction tests were performed according to OECD 232 and

DIN 11267 (OECD 232 2009; DIN EN ISO 11267 2012). Ten synchronized (9-12 d old) organisms were

placed into each test polypropylene (PP) vessel. Five replicate vessels per concentration, plus 1

additional vessel as pH and water control were tested. All toxicity tests were performed with 8/16 h

light/dark rhythm and temperature at 20 ± 2°C.

5.3.5 Statistics

In order to determine NOEC, LOEC and ECx values the collected data were analyzed with the

statistical program ToxRat®Professional XT (ToxRat®Professional XT 2.10, ToxRat®Solutions GmbH

2001-2010) according to OECD. Concentration response functions were fitted to the data using probit

analysis with a linear maximum likelihood regression. The median effective concentration (EC50) was

calculated from this function. Significant differences to the control (p< 0.05) were determined using

Fisher's Exact Binominal Test with Bonferroni Correction. NOEC values were derived from single

replicate values. First, normal distribution was tested applying Shapiro-Wilk´s Test. If variances were

homogeneous, NOEC values were determined by analysis Bartlett´s Test (p< 0.05). If variances were

inhomogeneous, NOEC values were determined using Welch-t test with Bonferroni-Holm Adjustment

(p< 0.05).

5.4 Results

The weathered milled eudialyte was tested for its ecotoxic effects on algae and daphnids (Figure 13).

The produced extract of the milled EU had a pH of 6.8 and could be used without further pH

adjustment for testing. The exposed algae, D. subspicatus, showed a normal growth rate after 72 h

like the unexposed control groups. Furthermore, the crustaceae D. magna showed no effects on

mobility when it was exposed with weathered eudialyte after 48 h.

Chapter 5

75

Figure 13: Biotests with milled weathered EU eluate

a) Growth rate inhibition of Desmodesmus sp. exposed for 72 h according to OECD 201. b) Mobility of Daphnia

magna neonates exposed for 48 h according OECD 202. [%] represent weathered EU eluate diluted with medium.

Data represent the mean± SD.

Algae exposed to residues of flotation (5.3.1.2) showed an inhibition of the growth rate even though

it never ceased entirely. The growth inhibition is indicative of the chemical composition used in the

floatation process (5.3.1.2). A dilution of the residues of floatation diminished the inhibition effect

(Figure 14) until a normal growth rate was reached at a dilution of 12.5 % when compared to the

control. Daphnids showed no loss of mobility after 48 h when exposed to the flotation solution

(Figure 14). Furthermore, OECD soil spiked with the floatation solution had no effect on collembolan

reproduction. After 28 d all exposed adults were alive and showed normal reproduction.

a) b)

Chapter 5

76

Figure 14: Biotests with EU Flotation solution

a) Growth rate inhibition of Desmodesmus sp. exposed for 72 h. NOEC: 12.5 % of EU Flotation solution, LOEC: 25 %

of EU Flotation solutionb. ) Mobility of Daphnia magna neonates exposed for 48 h. c) Number of offspring and d)

survival rate of adult Folsomia candida per microcosm to EU Flotation solution dilution series for 28 d. Data

represent the mean± SD. Biotest according to OECD 201, OECD 202 and OECD 232

Leaching samples of the metallurgical pretreatment were neutralized with CaCO3 and aquatic

organisms were exposed with the receiving water (EU leachate, also see Figure 12; section III). Algae,

Desmodesmus sp., exposed to EU leachate for 72 h showed an EC10 inhibition in growth rate at 9.2 %

dilution as well as EC50 inhibition at 43.5 % of the EU leachate (Figure 15Table 7). Furthermore,

significant immobility of D. magna of EC10 was observed at 40.5 % of EU leachate and an EC50

(immobility) at 83.2 % of EU leachate after 48 h, respectively (Figure 15Table 7). In the negative

control, algae and daphnids exposed with a hydrochloric acid and CaCO3 composition (pH 6.2)

showed no effects on their growth rate or on their mobility (Figure 18, in ANNEX).

a)

c)

b)

d)

Chapter 5

77

The dried and neutralized leached EU residues (Figure 12; section III) were used for terrestrial

biotesting. Experiments with collembola and soil (0.1, 0.5, 1.0, 1.5, and 2 kg leached EU residues/ kg

soil) indicated negative effects on collembola reproduction at high amounts of leaching EU residue.

F. candida showed a reduction in reproduction with an EC10 at 0.38 and an EC50 at 1.10 kg leached EU

residues/ kg soil after 28 d (Figure 15, Table 7). Thus, the leached EU residues mixed with soil in a 1:1

ratio affected the reproduction of around 50 %.

co

ntr

ol

0.1

0.5

1.0

1.5

2.0

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

k g le a c h e d E U re s id u e s /

k g s o il

Nu

mb

er o

f O

ffs

prin

g

100

0

20

40

60

80

Re

du

ctio

n o

f Offs

prin

g

[%

]

co

ntr

ol

0.1

0.5

1.0

1.5

2.0

0

2 0

4 0

6 0

8 0

1 0 0

k g le a c h e d E U re s id u e s /

k g s o il

Su

rv

iva

l ra

te [

%]

Figure 15: Biotests with EU leachates and leached EU

a) Growth rate inhibition of Desmodesmus sp. exposed for 72 h according to OECD 201. Data represent the growth

rate mean±SD. EC10: 12 % and EC50: 40 % of EU leachates; b) Mobility of Daphnia magna neonates exposed for 48 h

according to OECD 202. Data represent the mean± SD EC10: 64 % and EC50: 83 % of EU leachates;{%] represent EU

leachate diluted with test medium c) Number of offspring and survival rate of adult Folsomia candida per microcosm

to a leached EU residues dilution series for 28 d according to OECD 232, EC10: 0.38 and EC50: 1.10 kg leached EU

residues/ kg soil. For better understanding see Figure 12, section III.

a) b)

c) d)

Chapter 5

78

Table 7: Effects of leached EU residues on all organisms tested

Each line represent an independent experiment. Percentages describe EU leachates diluted with test medium.

EU eudialyte; EC: effect concentration; 95 CL: 95 % confidence limits.

Leached EU residues EC50 pH

Algae

(Desmodesmus sp.)

56.7 % (95%-CL 52.4 – 61.6)

28.1 % (95%-CL 24.1 – 32.7)

49.7 % (95%-CL 45.8 - 53.5)

39.5 % (95%-CL 36.4 – 42.6)

EC50(mean): 43.5 %

5.75

6.00

6.00

5.75

Daphnids

(Daphnia magna)

82.7 % (95%-CL 75.5 – 89.6)

78.3 % (95%-CL 75.7 – 80.9)

88.6 % (95%-CL 85.9 – 91.2)

EC50(mean): 83.2 %

5.75

6.00

5.75

Collembola

(Folsomia candida)

0.92 kg leached EU residues/

kg soil (95%-CL 0.81 - 1.01)

1.27 kg leached EU residues/

kg soil (95%-CL 0.95- 1.95)

EC50(mean): 1.10 kg leached

EU residues/ kg soil

5.63

6.12

5.5 Discussion

EU mineral was analyzed for its ecotoxicological effects using fine grinded EU, but no aquatic effects,

i.e. on algae and daphnids, were observed even in undiluted doses. The fine grinded mineral was

chosen because of the surface expansion and, hence, to simulate the solubility of minerals. In

addition, the pH potential of EU for acidification is low because EU is a silicate mineral which was

shown to display a buffer potential (White 2003). Other rare earth minerals such as bastnaesite

(carbonate mineral) and monazite (phosphorus mineral) also show pH buffer effects (EPA 2012)

Chapter 5

79

which facilitates the waste management to a certain extent. However, it is important to know the

mineral composition of a deposit since sulphurous minerals are responsible for AMD (Akcil & Koldas

2006).

After the first enrichment step, froth flotation, the EU flotation solution showed slight effects on

algae with a growth rate inhibition of about 23 % for undiluted slurry. Daphnids as well as collembola

showed no adverse effects toward the flotation slurry. Flotation water is generally recycled and re-

used in manufacturing processes. Slurries are channeled into tailing ponds with associated

sedimentation. The flotation solution had a neutral pH of about 6.9, so no limestone or other buffer

chemicals were added to prevent acidification. The slight inhibition of algae growth could be caused

by the organic substances added, which are needed for the beneficiation process. It was not possible

to investigate the organic products for difficulties in detection and analysis. However, onsite the

plant pH surveillance is a must to AMD prevention. Taking this into account, the impact analyses of

the flotation solution analysis suggest that it is not hazardous and after mine closure remediation

programs can be conducted easily.

Several factors make it difficult to investigate and evaluate weathered soils. For once, heavy metals

are washed out in their ionic forms, metalloids or bound to natural organic chemicals. Also, the metal

content of pore water is usually higher than the content of extracts (Friege et al. 1990). In order to

counteract these effects we modified the DIN EN 12457-4 and used 3 L of bidest. water leaching

around 800 mg leached EU residues, to increase the ionic strength. The most concentrated,

undiluted EU leachate showed a significant algae growth rate inhibition and daphnid immobility as

well as leached EU residues a reduction in collembola reproduction (Figure 12, section III). When the

EU leachate is diluted, negative effects decrease and eventually cease completely. At first, pH values

were thought to cause the observed effects, but a dilution of the analyzed probes raised the pH to

biologically reasonable values which was also observed by others authors (Artal et al. 2013). All

tested dilutions were in the pH range between 5.75 (undiluted) and 7.94 (most diluted probe). The

metal mixture complicates the argument as to which compound is responsible for the observed

Chapter 5

80

effects but it shows that a good management of the waste solids as well as of the effluent water is

necessary. Organic compounds can be neglected since leaching processes were conducted without

organic additives. CaCO3 which was added for neutralization could be responsible especially for the

aquatic effects. However, control experiments with algae and daphnids showed no effects towards

CaCO3 at the same concentration and neither hydrochloric acid. Collembola also showed effects on

reproduction when exposed to the neutralized leaching EU residues. Here it also seems that not a

single metal is causing the observed effect, but rather the mixture.

Effect concentrations of single metals were collected in order to find the most toxic compound of the

metal mixture (Table 6) using the EPA ECOTOX database. Assessing the individual metal effect

concentration that have the greatest impact suggest that the most important might be manganese

(Fargasová et al. 1999; Kimball 1978; Kuperman et al. 2004) and calcium (De Jong 1965; Mount et al.

1997; Xu et al. 2009; Deventer & Zipperle 2004). Rare earth metals are known to enhance the

development of organisms at low concentrations and to be toxic at higher concentrations. However,

rare earth metal concentrations of the EU leachates were below the effect concentrations reported

(De Jong 1965; Barry & Meehan 2000; Rodea-Palomares et al. 2011; Khangarot & Das 2009; Gonzalez

et al. 2014; González et al. 2015; Sneller et al. 2000). This shows that the impact of the analyzed

process chain on the environment makes it necessary to keep this waste under special surveillance

and to implements monitoring systems.

Mining is one of the greatest environmental, economic and political challenges of our times. It is

essential for many industrial applications, while nobody wants to take responsibility for its negative

effects on health and the environment. Bad waste management is the biggest thread for the

surrounding environment. A good and sustainable management means to recover most of the mined

material so to minimize tailings and relying on waste disposal as a last resort. Failures in waste water

treatment can lead to metal accumulation in agricultural areas or fishing grounds (Hu et al. 2014). In

order to analyze the produced waste streams we used standard ecotoxicological test systems which

can be easily performed and thus used by mining companies onsite. Other biological test systems like

Chapter 5

81

the activity of dehydrogenase or microbial biomass carbon are strongly sensitive to the toxicity of

heavy metals and could be additionally used as eco-indicators for soil pollution (Hu et al. 2014). At

the same they these are more costly.

5.6 Conclusion

From the data presented it can be concluded that weathered and floated Eudialyt is not a burden for

the aquatic and terrestrial fauna. However, the leaching EU residues tell a different story (Figure 12,

section III). Here, it must be ensured that no effluent water is released into the environment and

water clarification is strongly required. Storage facilities should be created, which prevent water

seepage and ensure the collection of waste water. In order to determine the actual impact of the

effluent discharge into receiving waters, both the flow of the effluent and river should be considered.

Nevertheless, chronic toxicity tests should be included in a monitoring program to provide more

information about the long-term impact of the discharge. Aside from ecotoxicological test systems,

bioavailability, bioaccumulation and trophic transfer are import monitoring factors. However,

monitoring with biotests could be a cheap and early warning system for mining companies on-site.

ACKNOWLEDGMENTS

This work was funded by the SIEMENS AG. Special thanks to Anne Schoer and Katharina Graf.

Chapter 5

82

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Kuperman, R.. et al., 2004. Manganese toxicity in soil for Eisenia fetida, Enchytraeus crypticus (Oligochaeta), and Folsomia candida (Collembola). Ecotoxicology and Environmental Safety, 57(1), pp.48–53. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0147651303001544 [Accessed December 4, 2013].

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Malik, R.N. & Husain, S.Z., 2006. Classification and ordination of vegetation communities of the lohibehr reserve forest and its surrounding areas, Rawalpindi, Pakistan. Pakistan Journal of Botany, 38(3), pp.543–558.

Mount, D.R. et al., 1997. Statistical models to predict the toxicity of major ions to Ceriodaphnia dubia, Daphnia magna and Pimephales promelas (fathead minnows). Environmental Toxicology and Chemistry, 16(10), pp.2009–2019.

OECD/OCDE 201, 2011. Guidline for testing chemicals - freshwater alga and cyanobacteria, growth inhibition test. OECD Guidelines for the Testing of Chemicals.

OECD/OCDE 202, 2004. Daphnia sp., acute immobilisation test. OECD Guidelines for the Testing of Chemicals. Available at: http://www.oecd-ilibrary.org/docserver/download/9720201e.pdf?expires=1354882795&id=id&accname=guest&checksum=F4906FC77D036502C9CFB3AE3E1E2EF2.

OECD/OCDE 232, 2009. Collembolan Reproduction Test in Soil. OECD Guidelines for the Testing of Chemicals.

Qifan, W. et al., 2010. The use and management of NORM residues in processing Bayan Obo ores in China. Natural Occuring Radioactive Material (NORM VI) Proceedings of an International Symposium Marrakesh, Morocco, 22–26 March 2010, (page 65 - 78), p.13. Available at: http://www-pub.iaea.org/MTCD/Publications/PDF/Pub1497_web.pdf.

Rodea-Palomares, I. et al., 2011. Physicochemical characterization and ecotoxicological assessment of CeO2 nanoparticles using two aquatic microorganisms. Toxicological Sciences, 119(1), pp.135–145.

Shen, L., Muduli, K. & Barve, A., 2015. Developing a sustainable development framework in the context of mining industries: AHP approach. Resources Policy, 46, pp.15–26. Available at: http://dx.doi.org/10.1016/j.resourpol.2013.10.006.

Sneller, F.E.C. et al., 2000. Maximum permissible concentrations and negligible concentrations for rare earth elements (REEs). , Report(601501), p.66.

Sukumaran, P. V, 2012. The need to explore for rare earth minerals. , 102(6), pp.839–841.

Walker, C.H. et al., 1996. Principles of Ecotoxicology, London: Taylor & Francis.

White, a F., 2003. Natural weathering rates of silicate minerals. Treatise on Geochemistry (Second

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Edition), 5(5.05), pp.133–168. Available at: http://www.sciencedirect.com/science/article/pii/B9780080959757005040.

Xu, J. et al., 2009. Effects of copper, lead and zinc in soil on egg development and hatching of Folsomia candida. Insect Science, 16(1), pp.51–55. Available at: http://doi.wiley.com/10.1111/j.1744-7917.2009.00253.x.

De Zwart, D. & Slooff, W., 1983. The microtox as an alternative assay in the acute toxicity assessment of water pollutants. Aquatic Toxicology, 4(2), pp.129–138.

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6. Chapter: Conclusion

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6.1 General conclusion

Ecotoxicological assessment of mining residues is often carried out after mine closure or when a

disaster occurs. Yet, remediation potential could be done much more easily in a prospective way with

pretests showing the potential hazards of solid wastes or effluents. Environmental risk assessment of

mining sites generally includes all steps from processed elements, reagents used for processing,

potential for natural disasters or man-made catastrophes to happen. Biotests like the ones used in

this study and other standard ecotoxicological test system can be used as an effective prospective

risk assessment as they are indicators for a toxic burden on the surrounding environment. In the total

cost analysis of a mining site the cost are negligible for an ecotoxicological assessment. It

nevertheless needs to be taken into account that such data are single tested endpoints and thus have

their limitations in prediction. Substance mixtures which are usually released from mining sites can

affect the environment in different ways, which was often shown when closed mining sites and their

surrounded areas were analyzed (Johnson et al. 2016; García-Gómez et al. 2014; Romero-Freire et al.

2016). This is why the results from biotests should not stand-alone, but be embedded in a more

farsighted risk assessment scheme. For example, impairment of the environment is usually indicated

by various signals which are all important. Absence of vegetation, change of water color, change in

soil/ water pH and high concentration of metals are warning signs (Romero-Freire et al. 2016). This is

why ecotoxicological data, analysis of physico-chemical water and soil properties and chemical

analysis should be used for a comprehensive environmental risk assessment. Investigation of soil and

water can detect the most hazardous metals, but only when the metal contamination is already

difficult to remove (Luoma & Rainbow 2011; Li et al. 2014; Johnson et al. 2016; Wilson & Pyatt 2007).

This is why it would be most cost-efficient for operators of mining sites to analyze the produced

residues and effluents in the proposed manner during their exploration time.

The results of this study seem to indicate that thorium does not pose an immediate threat to the

environment. Nevertheless, it should be considered that this study only aimed at investigating the

ecotoxicological effect of thorium viewed as heavy metal. It is a radioactive material which means

Chapter 6

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that all radionuclides of the Th decay chain must be considered. Analysis of thorium is difficult

because of its low water solubility and precipitation above a pH of 3-4 and its tendency to adsorb to

organic matter. This is reflected by the difficulty to measure analytical thorium concentrations which

fluctuated with only minor differences in pH or CO32- content of the media. However, OECD standard

biotests revealed no hazard potential of the heavy metal thorium. The radioactivity of thorium must

be looked at separately but could not be analyzed due to the short incubation times in

ecotoxicological tests and the long half life time of 232 Th of about 14 billion years (Keith & Wohlers

1990; Wiberg & Holleman 2007). Thorium and its daughter radionuclides emit α-, ß- and γ-radiation

which may all arise during separation processes when the decay chain is disrupted (EPA 2012; IAEA

2011; Gupta & Krishnamurthy 2005). Although these waste streams are thereafter mostly drained

and stored together, each radionuclide has its own decay chain. This causes a higher radiation level

which is about 5 times higher after ~50 years than it would be without interruption (Pillai 2007).

For future research it would be interesting to investigate thorium waste streams which contain

thorium in different states of the decay chain. Applying the experiments performed in this study to

such a mixture would mean that all effects from the different heavy metals and radioactive

properties all captured. This would be a more comprehensive risk assessment which is closer to the

real situation. When doing so, it would be very important to obtain knowledge of the total 232 Th

decay chain in order to interpret the results correctly and be able to make definite conclusion about

which compound has the strongest ecotoxic effect.

The investigation of eudialyte was used as an example of REE processing without thorium influence,

since the analyzed eudialyte contains only negligible amounts of thorium. Therefore, in the second

part of the thesis, the focus shifted from thorium to a general assessment of the environmental

impact of artificially produced mining wastes. Results showed unpredicted ecotoxic effects which are

summarized in Table 8.

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Table 8: Environmental impact of treated eudialyte

Milled eudialyte showed no effects on all organisms tested which was conceivable because the

metals are still in a crystalline structure which is almost not solvable in water (Rastsvetaeva 2007).

Furthermore, eudialyte is a silica mineral which does not cause acidification on its own (Sukumaran

2012). Flotation residues showed minor effects on test organisms. Only algae showed a slight growth

rate inhibition which is most likely caused by the reagents used for flotation. However, it seems that

the chemicals used were diluted low enough concentrations as not to affect the other test

organisms. Finally, all organisms were affected by effluents of the last processing step, the leaching.

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Leaching processes cause the crystalline structure of the eudialyte to break down. Thus, the

components are becoming accessible and consequently more readily bioavailable. Additionally, the

acid or alkaline reagents used in prior processing steps are likely to persist and are therefore also

made bioavailable. These effects make the results of this study plausible. Consequently, it is

advisable to keep leaching wastes under strong surveillance because of their high hazardous

potential (Table 8). Also, leaching processes show a high potential for improvement. More cleaning

steps should be conducted to reduce the amount of HCl from wastes. Also effluent water from the

leaching residue stockpiles should be collected for further treatment (e.g. precipitation of dissolved

heavy metals).

Metals and associated mining processes are indispensable for modern life. Also, technological

progress is an important motor for development. Minerals from which REE are mined always contain

radioactive elements varying only in the amounts. This means that as long as REE are used in

technologies mining sites have to deal with thorium challenges. Eudialyte contains thorium as well,

meaning that the results for thorium from this study are relevant, too. Only the amount will be lower

than when processing bastnasite or monazite, meaning that different processes need to be applied.

Different research is needed for REE processing. The most important need is to develop recycling

systems which saves resources and avoids further production of radioactive wastes (Binnemans et al.

2013). An example for recycling of REE gives OSRAM who developed a patent for fluorescent light

tubes using acid treatment for dissolving rare-earth fluorescent substances (Otto & Wojtalewicz-

Kasprzak 2011; Binnemans & Jones 2014). Another approach is to investigate technologies without

REE as key elements (Massari & Ruberti 2013; Aston 2010; Physorg Inc. 2011; Bourzac 2011). Many

view thorium nuclear power plants as a solution for thorium wastes from REE mining. But ultimately

this only just shifts the problem from the REE mining sector to the energy sector. However, also the

most advanced thorium power plants need fissile uranium to start the decay and most certainly

radioactive waste will be produced alongside this process. Meanwhile, other radionuclides separated

from the minerals would still need to be stored at REE mining sites causing most of the radiation.

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Another opportunity to meet the global REE demand would be to process old wastes, so called

second mines, for their still profitable elements. This way no additional thorium wastes would be

produced; however, there is still a big research gap for processing low grade ores in an economic and

environmentally friendly way.

The economic question behind this thesis was electricity generation for green energy. While nuclear

power plants have the advantage of no CO2 emission the unsolved question of the final nuclear

disposal remains probably for the next centuries (Rashad & Hammad 2000). Coal-fired power plants

are old and ineffective. Also, coal must be imported from developing countries leading to enormous

environmental degradation and climate issues resulting from the CO2 produced. Moreover, coal

power plants emit radioactivity and high levels of toxic mercury into the environment via dust. Gas

power plants seem to be a good alternative due to their high efficiency, which is only maintained

when methane loss is not reckoned into the equation. The methane which is emitted during

extraction, promotes the greenhouse effect enormously (Gagnon et al. 2002).

Finally, three types of power plants are left: wind, water and solar plants. For an effective energy

production from wind power REE minerals are needed for production of superconducting magnets.

This study, along with other studies from the research project, helped to reveal the environmental

problems of REE production is (Elshkaki & Graedel 2014; Saidur et al. 2011; Leung & Yang 2012;

Evans et al. 2009; Varun et al. 2009). Water power plants seem to be an alternative to wind power

but they also have an immense impact on the aquatic ecosystems. Solar plants should be the power

plant of choice but the production process needs to be improved to make it more effective. In my

opinion the renewable energy sources, wind, water, sun should be chosen whenever possible, while

keeping in mind how the expensive production affects the environment and humans across national

borders.

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6.2 References

Aston, A., 2010. China’s Rare-Earth Monopoly. Technology Review, (October 15. MIT), p.(accessed 22.08.16). Available at: http://adamaston.com/?p=178.

Binnemans, K. et al., 2013. Recycling of rare earths: A critical review. Journal of Cleaner Production, 51, pp.1–22. Available at: http://dx.doi.org/10.1016/j.jclepro.2012.12.037.

Binnemans, K. & Jones, P.T., 2014. Perspectives for the recovery of rare earths from end-of-life fluorescent lamps. Journal of Rare Earths, 32(3), pp.195–200. Available at: http://linkinghub.elsevier.com/retrieve/pii/S100207211460051X.

Bourzac, K., 2011. New magnets could solve our rare-earth problems. Technology Review, (January 20 MIT), p.(accessed 22.08.16). Available at: https://www.technologyreview.com/s/422459/new-magnets-could-solve-our-rare-earth-problems/.

Elshkaki, A. & Graedel, T.E., 2014. Dysprosium, the balance problem, and wind power technology. Applied Energy, 136, pp.548–559. Available at: http://dx.doi.org/10.1016/j.apenergy.2014.09.064.


Evans, A., Strezov, V. & Evans, T.J., 2009. Assessment of sustainability indicators for renewable energy technologies. Renewable and Sustainable Energy Reviews, 13(5), pp.1082–1088.

Gagnon, L., Bélanger, C. & Uchiyama, Y., 2002. Life-cycle assessment of electricity generation options: The status of research in year 2001. Energy Policy, 30(14), pp.1267–1278.

García-Gómez, C. et al., 2014. Risk assessment of an abandoned pyrite mine in Spain based on direct toxicity assays. Science of the Total Environment, 470-471, pp.390–399. Available at: http://dx.doi.org/10.1016/j.scitotenv.2013.09.101.


IAEA, I.A.E.A., 2011. Radiation protection and NORM residue management in the production of rare earths from thorium containing minerals. Safety Reports Series, 68, p.259. Available at: http://www-ns.iaea.org/standards/.

Johnson, A.W. et al., 2016. State of remediation and metal toxicity in the Tri-State Mining District, USA. Chemosphere, 144, pp.1132–1141.


Leung, D.Y.C. & Yang, Y., 2012. Wind energy development and its environmental impact: A review. Renewable and Sustainable Energy Reviews, 16(1), pp.1031–1039. Available at: http://dx.doi.org/10.1016/j.rser.2011.09.024.

Li, Z. et al., 2014. A review of soil heavy metal pollution from mines in China: Pollution and health risk assessment. Science of the Total Environment, 468-469, pp.843–853. Available at: http://dx.doi.org/10.1016/j.scitotenv.2013.08.090.

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Luoma, S.N. & Rainbow, P.S., 2011. Metal Contamination in Aquatic Environments, Cambridge University Press.

Massari, S. & Ruberti, M., 2013. Rare earth elements as critical raw materials: Focus on international markets and future strategies. Resources Policy, 38(1), pp.36–43. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0301420712000530 [Accessed August 7, 2014].

Otto, R. & Wojtalewicz-Kasprzak, A., 2011. Method for recovery of rare earths from fluorescent lamps. , US 7976798, p.11. Available at: https://www.google.com/patents/US7976798.

Physorg Inc., 2011. Japan nano-tech team creates palladium-like alloy: report. , p.(accessed 22.08.16). Available at: http://phys.org/news/2010-12-japan-nano-tech-team-palladium-like-alloy.html.

Pillai, P.M.B., 2007. Naturally occurring radioactive materials (NORM) in the extraction and processing of rare earths. , (Proceedings of an international symposium Seville, Spain, 19–22 March 2007), p.17.

Rashad, S.M. & Hammad, F.H., 2000. Nuclear power and environment: comparative assessment of enviornmental and health impacts of electricity-generating systems. Applied Energy, 65, pp.211–229.

Rastsvetaeva, R.K., 2007. Structural mineralogy of the eudialyte group: A review. Crystallography Reports, 52(1), pp.47–64.

Romero-Freire, a. et al., 2016. Long-term toxicity assessment of soils in a recovered area affected by a mining spill. Environmental Pollution, 208, pp.553–561. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0269749115301305.

Saidur, R. et al., 2011. Environmental impact of wind energy. Renewable and Sustainable Energy Reviews, 15(5), pp.2423–2430. Available at: http://dx.doi.org/10.1016/j.rser.2011.02.024.

Sukumaran, P. V, 2012. The need to explore for rare earth minerals. , 102(6), pp.839–841.

Varun, Bhat, I.K. & Prakash, R., 2009. LCA of renewable energy for electricity generation systems - a review. Renewable and Sustainable Energy Reviews, 13(5), pp.1067–1073.

Wiberg, E. & Holleman, A.F., 2007. Lehrbuch der Anorganischen Chemie. Gruyter, 102, p.2149.

Wilson, B. & Pyatt, F.B., 2007. Heavy metal dispersion, persistance, and bioccumulation around an ancient copper mine situated in Anglesey, UK. Ecotoxicology and Environmental Safety, 66(2), pp.224–231.

94

ANNEX

ANNEX

95

1. ANNEX: Toxicity of thorium to aquatic and terrestrial organisms: algae,

daphnia and collembola

Figure 16: Pseudokirchneriella subcapitata growth rate at pH 5

a) comparison of growth rate at pH 8 and pH 5 significant lower by Student-t test and b) growth inhibition curve of

P. subcapitata exposed to Th for 72 h at pH 5. EC50: 1.5 (95% CL 1.3-1.7 mg/L), Probit analysis using linear max.

likelihood regression.

Figure 17: Eisenia fetida reproduction test

a) Number of offspring and b) weight measurement (mean±SM) after 56 days; test was performed once.

a) b)

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2. ANNEX: Environmental consequence arising from eudialyte processing

Figure 18: Control experiments.

a) Growth rate inhibition of Desmodesmus sp. exposed to CaCO3 for 72 h. b) Daphnia magna immobilization exposed

to CaCO3 after 48 h.

cont

rol

CaC

O3

contr

ol0.0

0.5

1.0

1.5

2.0

gro

wth

rate

in

hib

itio

n

contr

ol

CaC

O3

cont

rol

0

20

40

60

80

100

mo

bile d

ap

hn

ids

a) b)

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3. ANNEX: Preparation of eudialyte mineral Preparations of eudialyte mineral were conducted by other institutes.

Flotation

RWTH Aachen University, Unit of Mineral Processing, Lochnerstr. 4-20, 52064 Aachen, Germany

Grinding and acidic treatment

RWTH Aachen University, Institute of Process Metallurgy and Metal Recycling, Intzestr. 3, 52056

Aachen, Germany

Flotation

Air dried eudialyte mineral was flotated. The applied chemicals are shown in Figure 19. The sludge

had a pH of 7.34 and could be used directly for ecotoxic experimetns.

Figure 19: Flotation of eudialyte mineral

eudilayte 10 g

30 min treatment

Na3PO4 (6 kg/t)

Oxalic acid (2kg/t) H

2SO

4 (kg/t)

Flotinor SM15 (750 g/t) Na

2CO

3 (2kg/t)

NaOH (4kg/t) AERO 845 (500g/t)

decantation

enriched rare earth compounds

sludge

ANNEX

98

Acidified eudialyte

Acidified eudialyte mineral was dried and mixed with double distilled water, 10 g mineral /1 L H2O.

Afterwards, pH was adjusted to circa 6 with calcium carbonate (CaCO3) and the mixture was shaken

for 24 h. Phases were separated by centrifugation into the solid and the water phase which both

were analyzed by ecotoxic test systems (Figure 20).

Figure 20: Acidified eudialyte mineral - Preparation of eluates and solids for ecotoxic experiments

acidified eudialyte

treatment 10g/ 100ml double dist. H

2O

neutralize with CaCO

3

(pH ~6)

centrifugation

solids eluate

sh

akin

g

for 2

4 h

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4. ANNEX: Decay chain of thorium The thorium decay chain is represented, with increasing mass number from right to left as well as

increasing order number from the bottom up (Figure 21).

Figure 21: Thorium-232 decay chain

Th thorium; Ra radium; Ac actinium; Rn radon; Po polonium; Pb lead; Bi bismuth; Tl thallium.

ANNEX

100

5. ANNEX: Decay chain of uranium The uranium decay chains are represented, with increasing mass number increases from right to left

as well as increasing order number from the bottom up

The primordial radionuclides 238 U (Figure 22) occur with a frequency of 99.27 %, 235 U (Figure 23)

with a frequency of 0.72 %.

Figure 22: Uranium 238 decay chain

U uranium; Th thorium; Pa protactinium; Ra radium; Ac actinium; Rn radon; Po polonium; Pb lead; Bi bismuth.

ANNEX

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Figure 23: Uranium 235 decay chain

U uranium; Th thorium; Pa protactinium; Ra radium; Ac actinium; Rn radon; Po polonium; Pb lead; Bi bismuth.

ANNEX

102

6. ANNEX: Endpoints used to determine the SSD

Table 9: Endpoints used to determine the SSD for uranium

Species Endpoint Concentration

uranium [mg/L] References

Scenedesmus subspicatus 120 h LC50 36.3 (Vinot & Larpent 1984) Ptychocheilus lucius 96 h LC50 46 (Hamilton 1995) Gila elegans 96 h LC50 46 (Hamilton 1995) Xyrauchen texanus 96 h LC50 46 (Hamilton 1995) Salvelinus fontinalis 96 h LC50 5.5 (Parkhurst et al. 1984) Salvelinus fontinalis 96 h LC50 8 (Davies 1980) Salvelinus fontinalis 96 h LC50 23 (Parkhurst et al. 1984) Hyalella azteca 72 h LC50 0.02 (Borgmann et al. 2005) Lemna aequinoctialis 96 h LC50 0.76 (Charles et al. 2006) Melanotaenia splendida 96 h LC50 1.57 (Holdway 1992) Melanotaenia splendida 96 h LC50 1.39 (Holdway 1992) Mogurnda mogurnda 168 h LC50 3.29 (Holdway 1992) Mogurnda mogurnda 168 h LC50 2.69 (Holdway 1992) Mogurnda mogurnda 168 h LC50 1.59 (Holdway 1992) Oncorhynchus mykiss 96 h LC50 6.2 (Davies 1980) Pimephales promelas 96 h LC50 2.8 (Tarzwell & Henderson 1960) Pimephales promelas 96 h LC50 135 (Tarzwell & Henderson 1960) Melanotaenia splendida 96 h LC50 1.57 (Holdway 1992) Melanotaenia splendida 96 h LC50 1.39 (Holdway 1992) Lepomis macrochirus 96 h LC50 1.67 (Trapp 1986) Daphnia pulex 48 h LC50 0.22 (Trapp 1986) Daphnia magna 48 h LC50 6.19 (Poston et al. 1984) Cypris subglobosa 48 h EC50 62.72 (Khangarot & Das 2009) Corbicula sp. 96 1.87 (Labrot et al. 1999) Chironomus crassiforceps 72 h LC50 36 (Peck et al. 2002) Ceriodaphnia dubia 48 0.05 (Pickett et al. 1993) Ceriodaphnia dubia 48 0.12 (Pickett et al. 1993) Ceriodaphnia dubia 48 h LC50 0.07 (Pickett et al. 1993) Catostomus latipinnis 24 h LC50 43.5 (Hamilton & Buhl 1997) Brachydanio rerio 96 3.05 (Labrot et al. 1999) Brachydanio rerio 24 h LC50 6.4 (Vinot & Larpent 1984)

ANNEX

103

Table 10: Endpoints used to determine the SSD for lanthanum

Species Endpoint Concentration

Lanthanum [mg/L] References

Vibrio fischer 30 min EC10 1.21 (González et al. 2015) Tubifex tubifex 96 h EC50 29.38 (Khangarot 1991) Pseudokirchneriella subcapitata 72 h EC50 2.22 (González et al. 2015) Poecilia reticuiata 96 h LC50 47 (Maas & Botterweg 1993) Hyalella azteca 72 h LC50 229 (Borgmann et al. 2005) goldfish 60.4 Daphnia 48 h EC50 0.05 (Barry & Meehan 2000) Danio rerio 96 h LC50 156.33 (Mácová et al. 2010) Danio rerio 96 h LC50 152.98 (Mácová et al. 2010) Cypris subglobosa 48 h EC50 50.75 (Khangarot & Das 2009) Chlorella vulgaris 10 (De Jong 1965) Caenorhabditis elegans 24 h LC50 1.35 (Tatara et al. 1998) Brachydanio rerio 96 h LC50 23 (Sneller et al. 2000) Acartia tonsa 48 h 1.04 (Maas & Botterweg 1993)

Table 11: Endpoints used to determine the SSD for cerium

Species Endpoint Concentration cerium [mg/L]

References

Vibrio fischeri 30 min EC10 6.32 (González et al. 2015)

Poecilia reticuiata 96 h LC50 11.2 (Maas & Botterweg 1993)

Hyalella azteca 72 h LC50 32 (Borgmann et al. 2005)

Daphnia 48 h 22 (Sneller et al. 2000)

Chlorella vulgaris 4 (De Jong 1965)

Brachydanio rerio 96 h LC50 22 (Sneller et al. 2000)

Acartia tonsa 48 h 0.15 (Maas & Botterweg 1993)

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7. ANNEX: References Barry, M.J. & Meehan, B.J., 2000. The acute and chronic toxicity of lanthanum to Daphnia carinata.

Chemosphere, 41(10), pp.1669–74. Available at: http://www.ncbi.nlm.nih.gov/pubmed/11057695.


Charles, A.L., Markich, S.J. & Ralph, P., 2006. Toxicity of uranium and copper individually, and in combination, to a tropical freshwater macrophyte (Lemna aequinoctialis). Chemosphere, 62(8), pp.1224–1233. Available at: http://www.sciencedirect.com/science/article/pii/S0045653505006776.

Davies, P.H., 1980. Acute toxicity of uranium to brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) in soft water. , (Fort Collins, CO, Colorado Division of Wildlife. F-33-R-15).

González, V. et al., 2015. Lanthanide ecotoxicity: First attempt to measure environmental risk for aquatic organisms. Environmental Pollution, 199, pp.139–147. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0269749115000391.

Hamilton, S.J., 1995. Hazard assessment of inorganics to three endangered fish in the Green River, Utah. Ecotoxicology and Environmental Safety, 30(2), pp.134–142. Available at: http://www.sciencedirect.com/science/article/pii/S0147651385710172.

Hamilton, S.J. & Buhl, K.J., 1997. Hazard evaluation of inorganics, singly and in mixtures, to flannelmouth sucker Catostomus latipinnisin the San Juan River, New Mexico. Ecotoxicology and Environmental Safety, 38(3), pp.296–308. Available at: http://www.sciencedirect.com/science/article/pii/S0147651397916006.

Holdway, D.A., 1992. Uranium toxicity to two species of Australian tropical fish. Science of The Total Environment, 125(0), pp.137–158. Available at: http://www.sciencedirect.com/science/article/pii/0048969792903878.


Khangarot, B.S., 1991. Toxicity of metals to a freshwater tubificid worm,Tubifex tubifex (Muller). Bulletin of Environmental Contamination and Toxicology, 46(6), pp.906–912. Available at: http://dx.doi.org/10.1007/BF01689737.

Khangarot, B.S. & Das, S., 2009. Acute toxicity of metals and reference toxicants to a freshwater ostracod, Cypris subglobosa Sowerby, 1840 and correlation to EC50 values of other test models. Journal of Hazardous Materials, 172(2-3), pp.641–649.

Labrot, F. et al., 1999. Acute toxicity, toxicokinetics, and tissue target of lead and uranium in the clam Corbicula fluminea and the worm Eisenia fetida: comparison with the fish Brachydanio rerio. Archives of Environmental Contamination and Toxicology, 36((2)), pp.167–178.

Maas, J.L. & Botterweg, J., 1993. Milieubezwaarlljkheid van zeldzame aardmetalen (lanthaniden, yttrium, scandium) in oppervlaktewater. , (RIZAnota 93.018).

Mácová, S. et al., 2010. Acute toxicity of lanthanum to fish Danio rerio and Poecilia reticulata. Journal of Biochem Tech, 2(5), pp.46–47.

Parkhurst, B.R. et al., 1984. An environmental hazard evaluation of uranium in a rocky mountain

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ANNEX

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Publications

Article

Findeiß M, Schaeffer A (2016) Fate and environmental impact of thorium residues during rare earth processing. Journal of Sustainable Metallurgy, August DOI: 10.1007/s40831-016-0083-3

Presentation:

Matthias Findeiß, Andreas Schaeffer (2015): Analysis of the environmental consequence arising from eudialyte processing, 11th International Rare Earth Conference, Singapur

Poster:

Findeiß M, Schmidt B, Schaeffer A (2014): Toxicity of thorium to various aquatic and terrestrial organisms. 24th SETAC Europe Annual Meeting, Basel, Schweiz.

Findeiß M, Schaeffer A (2016) Analysis of the environmental consequence arising from eudialyte processing. 11th International Rare Earth Conference, Singapur

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CURRICULUM VITAE Personal data

Name: Matthias Findeiß

Address: Mariabrunnstraße 34, 52064 Aachen

Contact: +49 151 54854989,

[email protected]

Birth day: 30. Mai 1982, Erlangen

Marital status: single

Nationality: german

Education

February 2012 - PhD Studies at the RWTH Aachen University

SIEMENS framwork: Rare earth: Green Mining & Separation

August 2010 Diploma of Biology

Diploma work: „Antigen presenting cells in P.berghei ANKA infected CB2-/- mice “

2004 - 2010 Study of Biology, Diploma Rheinische Friedrich-Wilhelms-Universität Bonn

2003 – 2004 Study of Chemistry Diploma Friedrich-Alexander-Universität Erlangen-Nürnberg

Employment

2015 - 2016 Employee at RWTH Aachen, Institute for environmental Research

2012 - 2014 Freelancer at SIEMENS AG

2007 - 2009 University of Bonn – Scientific library

2008 Internship at Bayer AG India, Environmental Science

before 2000 Part-time work

Aachen, 4. October 2016

Matthias Findeiß

Effects of radioactive by-products along the extraction of rare ...

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