Artisanal and Small-Scale Gold Production - planetGOLD
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Transcript of Artisanal and Small-Scale Gold Production - planetGOLD
Artisanal and Small-Scale Gold Production: Technology Without Mercury
Virtual Exhibition
6 October 2021
Supported by:
Led by: In partnership with:
Considerations for Alternatives to Mercury
Consider the context of targeted mining communities, from remote individual operators to more centralized approachesDemonstrating higher gold recovery can be truly difficult to prove to minersBarriers to financing equipment for mercury free processing can be substantial depending on the context and are not easily overcome through traditional financial mechanismsReplacement or Alternative? To date, there is no direct replacement for mercury. Does the alternative technology produce a concentrate that requires another step to get the gold? If so, how can miners do this?
Orongo Ouma, Technician AssistantNANSIO
Artisanal and Small-Scale
Gold Production:
Technology Without Mercury
6 & 7 October 2021
Supported by: Led by: In partnership with:A GEF GOLD Supply Chain Approach to Eliminating Mercury in Guyana’s Artisanal and Small-Scale Gold Mining (ASGM) Sector: El Dorado Gold Jewellery - Made in Guyana
Ore types at project sites and technologies in operation in the areas
Location of Project Site Type of Ore Technology and Mining Practices
Tiger Creek- Puruni,Region 7 (Cuyuni – Mazaruni)
Hard Rock and alluvial. This is at a ratio of 30:70.
Small scale miners generally use Dredges and Sluice Boxes. Medium and Large Scale uses cyanide as an option.
Mahdia, Region 8 (Potaro – Siparuni)
Hard Rock and alluvial. This is at a ratio of 10:90.
Small scale miners generally use Dredges and Sluice Boxes. Medium and Large-Scale miners would incorporate cyanidation in circuit.
Soil type encountered
Laterite
Crusher
Trommel
Gold Kacha
Shaking Table
Gold Cube
Blue Bowl
Types of mercury-free technologies proposed for project sites
Gemeni Shaking Table
Gold Kacha
Gold Cube or Gold Konka
RG30 Trommel
Blue Bowl
Stock Pile Sluice Sump Pit
Crusher
Trommel
Gold MastaGold Kacha
Shaking Table
Water Testing Sluice Box in Action work
Estimated gold yield for the mercury-free technologies, compared to mercury-based technology
Name of Technology Recovery Rate
Gold Kacha 70% - 75%
Gemeni Shaking Table 99%
Blue Bowl 85% - 95%
Gold Cube 80% - 90%
Costs of the technologies
This is a list of the equipment likely to be used at each demonstration site.
These are dependent on the Ore composition at a specific site.
Name of Equipment Amount per Site Unit Cost (USD) Total Cost (USD)Gold Konka 1 2,170.00$ 2,170.00$ Gold Kacha 2 2,869.00$ 5,738.00$ Gemeni Shaking Table 1 8,700.00$ 8,700.00$ RG30 Trommel 1 25,678.00$ 25,678.00$ GOLD Masta 1 500.00$ 500.00$ Generator 1 13,954.00$ 13,954.00$ 2 inch Pumps 2 159.00$ 318.00$ 4 inch Pumps 1 316.00$ 316.00$ Blue Bowl 1 500.00$ 500.00$ Crusher 1 2,967.00$ 2,967.00$ Total 60,841.00$
Thank You!
Gold Katcha and Direct Smelting20Winifrida Kanwa, Solidaridad Eastern and Central Africa
Umoja Lwangasa
Mercury pond
21
Gold Katcha Centrifugal concentrator
➔ A successful Gravity separation depends on the liberation of Gold from other minerals.➔ Good Liberation + Good concentration=Mercury free extraction
Avoiding Mercury usageGravity concentration
Shaking table (secondary concentrator)
23
Mercury Free ExtractionsDirect Smelting
What you need to do direct smelting
1. High grade Concentrate2. Crucible3. Source of heat (Oxygen gas preferable)
Temperature 1200 degrees.4. Borax and Lime.
Direct Smelting Method - Smelt Gold purity of up to 98%- Borax and Siliceous flux- Smelting of high grade
concentration - 50-100gms - Efficiency depends on concentration.
Photos: Wikipedia
• To combat the dangers mercury poses, new equipment and techniques have been deployed to make mining safer for the environment, and Commodity Monitor, a logistics, trading and research company, seeks to promote these practices in Ghana and other West African countries.
• The technology is for: (i) hard rock gold deposits, (ii) eluvial gold deposits, and (iii) alluvial gold deposits.
• For all the forms of gold deposits, the combined technology has gravity-recoverable rate of 90%+. This is based on field engagements with different miners.
STEP 1PRIMARY CRUSH MATERIAL
Jaw Crusher (JC)• The JC allows for hard rock material larger than
40mm to be crushed down to smaller size (3mm).
• The JC is powered by either electric or diesel motor.
• It has a throughput of 2-3tph.
STEP 2IMPACT FINES GRINDER• The impact grinder crushes hard rocks to size
(100-400 microns) and passed through to the concentrator.
• We adjust screen sizes based on the nature of ore of a mining district or community.
• It is powered by either electric or diesel motor (18kW).
• The feed rate is between 1.5-3tph and requires 2-3 m3/h of water.
STEP 3CONCENTRATOR• A centrifugal concentrator is key in gold recovery
and it is fast becoming popular among miners in Ghana.
• The GoldKacha, which we’ve deployed, is suited to the recovery of precious metals from dump tailings, rubble beds and alluvial sands.
• The novel centrifugal riffle principle results in high recovery of both coarse and fine precious metals.
• It is 1-3tph feed rate and runs on 0.75kW electric motor.
STEP 4SLUICE• The sluice ensures enhanced production of a
higher-grade concentrate and maximise recoveries.
• The surface matting of the sluice is easy to clean, making for a quick harvest cycle.
• No power outlet is required. • The sluice is attached to the concentrator for
gold recovery.
STEP 5CONCENTRATE UPGRADE• The GoldKonka upgrader was designed as a
mercury free solution for concentrate upgrades. It is able to recover the finest gold particles for small scale mining.
• The recirculative water system enables miners to conserve water and reduces pollution.
• It has 0.5tph feed rate capacity.
STEP 6DIRECT SMELTING
• Commodity Monitor uses a small induction kettle furnace. It can be used to smelt gold from the upgrader.
• It is a direct smelt system and is easy to operate for artisanal and small scale miners.
• We are introducing cupellation system this year to miners, the first to happen. This will enhance the purity of gold produced by small scale miners.
THANK YOUFOR YOUR ATTENTION
Pact Mines to MarketandMount Baker Mining and Metals
Daniel Stapper, Manager, Pact Jason Gaber, Owner, MBMM
42
Direct Smelting and CupellationCritical skills for Hg free doré production
43
Hummingbird MaliSupport development of LSM / ASM strategy
US-DOS MaliMercury abatement
US-DOS GhanaMercury abatement
GIZ Sierra LeoneNAP implementation
EPRM MauritaniaASGM formalization & market access
Pact Gold Projects, West Africa
Producing gold doré
STEP 1: Ore extraction (extract and collect the ore rocks)
STEP 2: Gold liberation (crush and mill the ore rocks)
STEP 3: Mineral Concentration (concentrate the heavy minerals)
STEP 4: Process the concentrate to produce a gold ‘dore’
This can be done in 2 ways:(i.) Amalgamate or Leach (mercury, cyanide, etc.)(ii.) Direct smelting
IMPROVE / OPTIMIZE
IMPROVE / OPTIMIZE
& FOLLOW BY DIRECT
SMELTING
Pact Hg-free Interventions: from improving sluicing through concentrators, and MBMM shaking table
Pact training on Direct Smelting in Nigeria, inspired by Jason’s instructional videos
All of these technologies produce a mineral concentrate..
Direct Smelting vs Cupellation
“Direct Smelting” is the term used for melting down a mineral concentrate in order to separate the precious metal
It is an energy intensive process because you must bring the mineral concentrate past the melting point of gold (1,064°C)
For direct smelting to be effective (for most ASGMs)o maximum mass of mineral concentrate which can realistically be smelted in a single batch by
ASGMs is 100 - 500 g (requires approx. 30 minutes - 1 hour)o mineral concentrate should have minimum 2% gold
Pb melts at 327°CAg melts at 960°CAu melts at 1,064 °C
100 g 250 g 500 g2% 2 5 105% 5 10 2010% 10 20 40
Table 1. Direct Smelting: gold doré result (in grams) based on Au grade and size of mineral concentrate.
Direct Smelting vs Cupellation
“Cupellation” is a metallurgical process of refining - to separate precious metals from base metals (lead, zinc, and copper)
Cupellation is used in the process of assaying, but the method can also be used to produce clean gold doré
For cupellation to be effective (for most ASGMs) o final step of the direct smelting process, to purify gold buttono used with high grade concentrates (e.g. snuffer bottle, ~75%) to produce clean gold button doréo Small amount of lead or bismuth is added which helps separate impurities from the gold
Pb melts at 327°CAg melts at 960°CAu melts at 1,064 °C
48
Recap: Direct Smelting vs Cupellation
2 – 100 g of concentrate containing >75% Au
• Add concentrate to cupel & add lead or bismuth (~2:1). • Subject cupel to heat until melted• As the “charge” melts (starting with lead), it turns to
litharge (a type of lead oxide) which is absorbed into the porous cupel, taking the other base metals with it
100 – 500 grams of mineral concentrate containing >2% Au
• Add fluxes to crucible, based on compositiono to deal with sulfides: roasting can be used OR add iron
bar to the smelt which acts as oxidizer during smelt o If low gold content, consider adding small amount of
collector metal (lead, copper or bismuth)• Subject crucible to heat until fully melted• Pour the “charge” into a steel cone mold• Separate the metallic phase from the slag
o want to see good metal separation with the slag;o do not want to see a matte phase b/c this robs metals
from the metallic phase;• Once you have metal button, refine using cupellation
Direct Smelting is sometimes called the “Borax Method” but this can be confusing because all gold shops use borax when melting Au.
Cost Analysiso Lead cost 5 USD / kg (0.5 cents/gr.)o Copper cost 10 USD / kg (1 cents/gr.)o Bismuth cost 50 USD / kg (5 cents/gr.)o Mercury cost b/w 100 and 250 USD / kg (b/w 10 and 25 cents/gr.)
Cost item USDsilica crucibles 0.33borax 0.32soda ash 0.50butane/propane 2.50total 3.65
Cost item USDHg @ 7.5 grams 1.88detergent soap 0.15butane/propane 0.25total 2.03
Hardware Costs USDtongs 10forge/furnace 20leather gloves, PPE 5torch and cylinder 20steel mould 12total 67
Operating Cost Comparison : Direct Smelting vs. Hg amalgamation (based on sample work in Nigeria, using 5 grams Au in 100 grams concentrate)
Direct Smelting setup costs
Direct Smelting, cost per 5 grams of Au
Hg amalgamation, cost per 5 grams of Au
= 1.3% of value of the gold = 0.7% of value of the gold
planetGOLD Mercury-Free Technology FairSixto AgueroChief Mineral Processing Engineer
6 October 2021
Image: A woman pans crushed ore mixed with mercury to extract gold in a small processing facility located at the foothills of the Minahang Bayan of Paracale, Camarines Norte, one of the staging sites for the planetGOLD Philippines project | Lyka Cabatay | May 2021
Санхүүжүүлэгч: Үндсэн хэрэгжүүлэгч: Хамтран хэрэгжүүлэгчид:
Vibration Mills
Vibration Mill at Manufacturer (AGC, 2021)
Vibration Mill Schematic (AGC, 2021)
In the US, grinding represents:• 0.5% primary energy use
• 3.8% total electricity
• 40% mining industry energy use
• Ball mill, 15% energy efficient
• Vibration mill, 40% energy efficient
The Stress Forces of Rock Mechanics
(Metso, 2015)
A- Tensile
B- Compression
D-ShearingC- Impaction
E- Attrition
Grinding Is?A powdering or pulverizing process.
The two main PURPOSES for a grinding process are:
1. To liberate individual minerals trapped in rock crystals
2. To produce fines from mineral fractions by increasing the specific surface
(Metso, 2015)
A - Tumbling B - Stirring C - Vibration
Grinding Methods
(General Kinematics, 2015)
More Uniform Particle Shape (5 – 3,000 microns)Generates a high degree of impact energy
Low Initial Cost and Maintenance CostLower foundation requirements and 5-10 longer media life
Proven Energy SavingsRange from 35-50% reductions in kW hours per ton of processed material
Reduced Maintenance CostsThere are no expensive drive reducers or mill support bearings to maintain Only 60% of the grinding chamber requires liners
Increased FlexibilityWet or dry process
Easy to Use/Train
Technology Features
https://youtu.be/oHOl_pOuiyQ
Process Flow Sheet
Mid-Tailings(Leaching)
Vibration Mill(Game Changer) Sluice/Table
Concentrate(Daily Cash)
Jaw Crusher & Screen
Tailings
Specifications ValuePower (kW) 14
Feed size (mm) 100% pass 5 mm
Vibrating frequency (Hz) 980 rpm
Grinding type Dry
Liner/media material Manganese steel
Machine material Carbon Steel
Cost (USD) 20,000
Thank you.
Kristina Shafer, Cleangold LLCwww.cleangold.com
Director, Institute for Sustainable Mining AKA Artminers.org
[email protected], USA
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John Richmond, CEOSluice Goose
Artisanal and Small-Scale Gold Production: Technology Without Mercury
Virtual Exhibition
7 October 2021
Supported by: Led by: In partnership with:
Technologies for a mercury-free Colombia
October 6-7, 2021
Supported by: Led by: In partnership with:
Three technological proposals
Mobile plantsfor the benefitof alluvial gold
Mobile plants forprimary gold
MetallurgicalLaboratory
Focused on training, on pilot trials
and on small production.
Mercury-free, transportable,
autonomous and scalable
equipment.
Supported by knowledge and
technical control.
Alluvial deposits with difficulties in the recovery of fine gold
Miners who use mercury in the riverbedInstallation of a mobile plant for the benefit of alluvial gold in Caucasia, Antioquia
Plants for the gravitational separation of gold to increase the productivity of current processes without the use of mercury
Mobile plants for the benefit of alluvial gold
Difficulties that are solved
Primary gold deposits in need of comminution and concentration processes
Difficulty recovering fine gold
Miners using mercury to recover goldMobile plant for primary gold in Suárez, Cauca
Plants with processes for the comminution of the material and gravitational separation of gold in stages without the use of mercury
Mobile plants for primary gold
Difficulties that are solved
Laboratory techniques for analysis of quantity of gold, content, clean benefit methods.
The laboratory accompanies the intervened plants during the monitoring of the transfer processes to clean production
Mobile laboratories to monitor processes that ensure efficient and clean mineral production
Metallurgical laboratory for mineral characterization
Benefits and uses
Mobile Plant
Miner Testimonials
Supported by: Led by: In partnership with:
Thank you!
planetGOLD Mercury-Free Technology FairDouglas KaoMineral Processing Engineer, EIT
7 October 2021
Image: A woman pans crushed ore mixed with mercury to extract gold in a small processing facility located at the foothills of the Minahang Bayan of Paracale, Camarines Norte, one of the staging sites for the planetGOLD Philippines project | Lyka Cabatay | May 2021
Technical DesignPhilosophy
• Firm understanding of existing ASGM ecosystem
• Identify technology appropriateness Socio-economically feasible? Politically suitable? Environmentally acceptable? What are some potential
unintended consequences?• No "one-size-fits all" solution
(AGC, 2016)
Process Control & Fundamentals
“SOFTWARE” IMPROVEMENTS
FEATURES
Deciphering the “black box”
● Grain size control Improved gold liberation
● Reagent optimization Dosage control, cost savings pH control, safety
● Leaching kinetics optimization Increased throughput
● Understanding of assaying/ mass balancing (Nadolski, 2015)
“HARDWARE” IMPROVEMENTS
FEATURES
● Gravimetric options: Shaking table, concentrating spiral, centrifuge
● Leaching options: Cyanidation, alternative cyanidation methods
● Physical separation options: Agglomeration method, flotation
AGC Back-End Circuits/System
Gold Smelting (AGC, 2019)
Concentrating Spiral (AGC, 2021)
Amino Acid-AssistedLeaching
• Reduces CN consumption up to 75%
• Amino acid substitute is environmentally benign
• Minimal change to miners’ operations
• Upwards recoveries of 80%
Amino Acid-Produced Gold Bead (AGC, 2019)
Carbon Agglomeration Method
• Experimental stages Bench scale testing in
Canada Field trials in Peru and
Honduras• Utilizes hydrophobicity of gold• Recoveries of 60-80%
Gold Recovery Agglomerates (AGC, 2021)
IMPROVEMENTS
● Improvement of existing gravity concentration techniques of miners
● Secondary recovery from intermediate tailings of miners
● Higher overall throughput and gold production
TRAININGS NEEDED
● Metallurgy 101● Hands-on equipment operation● Metallurgical accounting● Lab analytical techniques● OHS training● Tailings management
MINERS’ UPTAKE ON PROPOSED
TECH
● As long as no Hg and CN use● As long as higher recovery than current
process● Fewer legal run-ins
Outcomes & Uptake
Thank you.
planetGOLD PresentationOctober 2021
Management Executive ChairmanRoger Pettman, PhD DSC.Founder of CycladexCo-Founder of Revolymer raising £40m including an AIM IPOCo-founder Chirex with $147m NASDAQ IPO
Executive Vice President sales and marketingA serial entrepreneur who was a NASCAR Professional driver who has owned several car body shops before inventing and developing a novel insect control machine. Owner of Triple 7 Mining and an expert in the design of Cycladex facilities. Responsible for Sales & Marketing worldwide
Independent Non-Executive DirectorProfessor Adrian Boyce Leader in Applied Geoscience research 4 decades of Scientific Research into Mineral DepositsPublished over 300 peer-reviewed papersFellow of the Society of Economic Geologists (SEG) and Geology Applied to Mineral Deposits (SGA)
Indepentdent AdviserSir Fraser Stoddart, Nobel LaureateDirector for the Chemistry of Integrated Systems at Northwestern UniversityKnighted by the Queen for his work in nanotechnologyAwards include; the King Faisal International Prize, the Albert Einstein World Award, the Feynman Prize in Nanotechnology and the Tetrahedron Prize for Creativity in Organic Chemistry. Over 1000 publications in the most prestigious scientific journalsBurning ambition to make an impact on society
Chief Financial OfficerChristine Betts ACAFormer CFO of Microsoft UK with 2000+ employeesJoined Microsoft with 4 UK employeesResponsible for the building of Microsoft Reading Campus.
Executive VP, Technology TransferDale Arnold CCHEMDuPont Chemical Engineer with 35 yrs experience in plant design, build and commissioningEngineered titanium dioxide plant in Taiwan from inception to productionDeveloped and scaled up Cycladex process development
Founded on Nobel Prize winning Chemistry and Funded by the National Science Foundation.
Key FactsLixiviantThe ProcessWhere is Cycladex?Types of Ore
Works Well
Oxide Ores
Refractory Ores
High Copper
High Ironj
Mercury Contaminated
Difficult
High Carbon
High Carbonates
Arizona – Commercial Facility (100MT per day)
Utah – Pilot
South Dakota - Pilot
Honduras – Being built
Mexico – Being built
Chile – Pilot
Mauritania – Being Built
VAT leaching
Trapping gold and silver on cartridges
Heap Leaching of low grade materials
Artisanal can use existing mercury equipment
Environmentally friendly chemicals
Chemicals are commodities available worldwide
Large Companies will pre-pack for us
Artisanal just have to add reagent A and reagent B.
Cycladex can formulate locally
Low Cost
CHEMTURA CONFIDENTIAL
Stir ore and Leach Separate ore and liquid
Trap gold and silver
Recycle lixiviate
Crushedore
FilterDecantTip liquid out
Gold
Silver
© Cycladex 2021
How Does it Work For Artisanal Miners
1h reaction timeAny stirred tankRotating 50 gallon drumBath and a paddle
Flow through columnAdd teabag of resinPour through pipe containing resin
Crushed not powderedAdd pre-packed leach
Ash resinSwap cartridge
Some More Key FactsScaleWasteElectricityWater
Any water
200L per 100 Kg of ore
15% loss due to adsorption by tails
Room temperature
No water waste
Everything recycled
Can be carried out by hand
Power to crush and stir
1-2 hp motor
Everything recycled
Tailings washed with lime water to make neutral
Centralized processing plant
Small scale with 50 gallon drum
Even wheelbarrow and paddle
Cycladex Community Mining Processing Facility
Artisanal Miner truck in ore
Analyze ore on each truck, agree content pay immediately Crush Ore
Process gold using CycladexEnvironmentally friendly process. Sell gold and silver.
Convert tailings into bricks, rooftilesArtisanal miner trucks bricks back to community
Artisanal and Small-Scale Gold Production: Technology Without Mercury Presenters: Kristina KazakoffPrincipal Chemical & Process Engineer
Nicole Looney Environmental & Technical Executive
A part of the Clean Earth Technologies group, Clean Mining Pty Ltd owns the technology to the award-winning, non-toxic gold recovery process using thiosulfate, developed by Australia’s national science agency, CSIRO.
With more than a decade of development and an in-field validation, results have proven this solution to be the mineral processing technology of the future. Through commercialization, this technology will set “a new gold standard” for mining production worldwide.
Clean Mining’s (thiosulfate) technology is being further developed in collaboration with CSIRO for implementation at gold operations around the world.
Cleaner Planet, Healthier Communities
WHAT IS OUR SOLUTION?• Award-winning, non-toxic solution, developed alongside CSIRO
• Widely applicable / scalable to broad range of ores / operations
• Potential to eliminate hazardous tailings dams entirely
• Only genuine solution for replacing mercury in ASGM
• Our blended reagent is classified as not dangerous goods of class 9 and contains no toxic elements
• Recent environmental test work on 2-year-old tailings from demonstration plant did not indicate any acidification of soils
GOLD EXTRACTION
RATE OF
We have conducted over 150 tests globally onthe rate of gold extraction using our non-toxic solution and here are some of our results
USA
• Sample Head Grade: 43.9g/t Au• Ore Type: Refractory Sulfide
• Sample Head Grade: 17.25g/t Au• Ore Type: Carbonaceous Artisanal
PHILIPPINES AUSTRALIA
• Sample Head Grade: 706/t Au• Ore Type: Concentrate
Crush/Grind Dewatering Batch Leaching Screening Resin Elution
Resin
Precipitate
Drying Oven
Furnace
Dore
Solids to tails asdry as possible
Solution
ARTISANAL HUBFLOWSHEET
GRA1
GRA2
• Ore prepared as normal – crushing and/or grinding
• Visible gold (nuggets) removed as per standard concentration methods such as;
CRUSHING/GRINDING
o Panningo Sluicingo Shaking Tableso Concentrators
DEWATERING• Ore to be leached/dissolved with Clean Mining Reagent
should be as dry as possible• Can be left in the sun to dry• Dewatering equipment such as centrifuge or filter press
• Clean Mining Reagent (powder) added to water to dissolve
REAGENT MIXING
• Ore• Solution• Resin• Agitate for period of time• Can be done in tanks
BATCH LEACHING
Resin
• Screen and collect Resin• Filter liquid from ore
SCREENING
• Recovered solution can be topped up with more Clean Mining Reagent and used for new leach batch
• Solids to tailings
GRA1
GRA2
• Add Resin to Elution vessel• Add Elution chemicals and stir to create Elution solution• Remove Resin and re-use in next leaching batch
RESIN ELUTION
Drying Oven
Furnace
Dore
• Add Precipitate reagent to Eluate Solution
• Recover ‘Black Precipitate’• Dry precipitate
• Add to furnace with normal smelting fluxes
• Pour Dore Bar
PRECIPITATE
R&D TEST DEMONSTRATION:
THANK YOUFor more information, please contact Kristina Kazakoff or Nicole Looney at:
• SINGAPORE 112 Robinson Road, #05-04, Singapore 068902
• AUSTRALIA Office 3, 10 Eastbrook Terrace, East Perth, WA, 6004
• T +65 9382 6401 E [email protected] W www.cleanmining.co
Marcello VeigaPariya Torkaman
Alternatives to Eliminate the Use of Mercury in Artisanal Gold Mining
Primary OreSecondary
Ore
Concentration
Amalgamation
Cyanidation
Amalgam
Concentrate
Ore
Grinding
Burning Hg to the Air
Tailing with Hg
How Artisanal Gold Miners Use Mercury
Tailings with Hg(CN)2 Tailings with Hg
Tailings
Tailings with Cyanide
Whole OreAmalgamation
MAIN PROBELMS
Ore
The Technological Approach Has Also Been Tried but…
• Changes in technology need SKILLS and MONEY• Amalgamation of the whole ore and cyanidation of Hg-
contaminated tailings are the main problems• Adequate concentration (gravity + flotation) and
amalgamation of concentrates reduce Hg use and losses• Alternative gold extraction processes from concentrates
require good amount of $
Gold from Alluvial Operations Does Not Need Mercury
• Alluvial Gold is usually LIBERATED• Direct Smelting has been used for
centuries in Canada and elsewhere• But in many other types of ores
GOLD IS NOT LIBERATED• It can be concentrated but NOT
AMALGAMATED
Gold from Alluvial Operations Does Not Need Mercury
Indonesia
All gold particles mustcoalesce… get together, to sink in the melted mixture
If the concentrate is notVERY RICH, gold is lost in the slag
goldconcentrateborax
Direct Smelting of Concentrates
Slag
Gold
Concentrate Grade
Recovery
Mass of concentrate
Very yellow concentrate = low Au recovery
More mass of concentrate = low grade but high Au recovery
Gravity Concentration is Not a Panacea
The higher the gold grade in
concentrates the lower in the gold
recovery
Who Are the Main Hg Polluters?(out of 20 million AGMs)
Processing Center in Zimbabwe
Laos
Cost of a Decent Processing Plant
CAPEX 50 tpd = $ 34000 per tonne processed per dayCAPEX 10 tpd = $ 65400 per tonne processed per day
Note: 300 days/a of operation, tpa = tonnes processed per annumr
tonnes processed per day
(tpd)
Cost of a Processing Plant
0
100
200
300
400
500
600
0102030405060708090
100
2 5 10 25 50 100 200
CA
PEX (US$/tpa)O
PEX
(US$
/tpa)
Processing Rate(tpd)
OPEX/tpa CAPEX/tpa
How about the Processing Centers?
• They must CHANGE or BE ELIMINATED• How? • Transforming these Centers into real processing
companies to co-exist with AGM• They should BUY the ores from miners and stop
exploiting them using amalgamation to extract the easy free Au and retaining rich tailings to be leached with CN
• Pay FAIR price for the gold in the ores
Advantages of Co-existence• Processing companies provide assistance to
artisanal miners in the mines and process the ores sold by them
• No investment or operating costs for miners• Miners receive more $ (more for the Au content)• No mercury or cyanide in the hands of miners• Miners do not need to obtain environmental
permits (use subcontracts)
Advantages of Co-existence• Many examples in Colombia, Peru, Nicaragua and
now in Costa Rica• Miners mine and Companies process the ore• Different types of co-existence: 1. Companies buy ore and process in a plant2. Share results of the processing with miners• Disadvantage: long process of create trust
Newlox Model
• Operating in Costa Rica since 2014 buying Hg-contaminated tailings (85 tonnes/day)
• Remove Hg, concentrate and leach concentrates with cyanide
• Now starting a 150 tonnes/day plant in partnership with the artisanal mining cooperative
• After paying the operating costs, the profit is shared 50-50%
Plant for Re-processing ASGM Tailings
Costa Rica
Plant for Re-processing ASGM Tailings
Costa Rica
Plant for Re-processing ASGM Tailings
concentrate
tailings
UF
Centrifuge
Agitator
Tailings85 tpd
Flotation
Mill
Ag
Plates
OF
Intensive Cyanidationwater
Au & AgHg
Smelting
conc.
tailings - bricks ?- roads ?
Cement + Sulphur
Costa Rica
What Technologies NERD is developing for Newlox plants?
• Methods for leaching gravity and flotation concentrates
• Extract Hg before leaching• Using Cassava• Using DMSO• Using Cyanide + Zn in a modified Merrill-Crowe
Tailing with 63 g Hg/t
1.2 m
Tailings3 g Hg/t
Ag-covered Plates
0.5 m
3 times
0.3 m
Removing Hg from Contaminated Tailings
Lab prototype
Removing Hg from Contaminated Tailings
• More than 2000 plants contain glycosides that can be converted to cyanide by hydrolysis (e.g. Bamboo, Sorghum, Lima Beans, Cassava, etc.)
• Some bamboo can have as much as 7.7 g of cyanide/kg of plant
• Some bitter cassava can have 2.4 g of cyanide/kg of plant
Cyanogenic Plants
• Around 98 species of cassava with different levels of the cyanogenic glycosides in which Linamarin is the main one
• Free cyanide is produced by reaction of the Linamarin with Linamarase (enzyme)
Cassava
Flour Production
Peeling cassava in Brazil
• World cassava production is around 300 million tonnes annually
• Brazil produces 6.5% of world’s cassava• 1.5 million people involved in Brazil alone• Bitter cassava is the main raw material• Main cassava use is to make flour or starch
Manipueira• The liquid extracted from cassava (“manipueira”), 30% of the
root weight, is rich in cyanide, reaching up to 2000 mg/L Free CN• The cassava we eat has <20 mg of cyanide per kg of cassava• Manipueira can be used to leach gold in small-scale
Bitter Cassava To Dissolve Gold• Preliminary results in the UBC laboratory using a cassava
with 267 mg/L free CN in 24 h resulted in 50-60% gold recovery from an artisanal gold sample
• Same conditions with pure NaCN reached 70% extraction• Some preg-rob condition was observed, then the starch
must be removed by flotation before using the manipueira
DMSO (in collaboration with Dr. Akihiro Yoshimura from Chiba Univ., Japan)
• DMSO (dimethyl sulfoxide) is used for cosmetics and paints
• A product with very low toxicity and a price compatible with sodium cyanide
• With a catalyst (copper salt) and sodium chloride • Once gold is dissolved, it is precipitated with water or
vinegar or lemon juice… no need of activated carbon• DMSO can be recycled• Main disadvantage: Not too many producers of DMSO
DMSO (in collaboration with Dr. Akihiro Yoshimura from Chiba Univ., Japan)
• Results with amalgamation tailings from Costa Rica:
More than 90% Au extraction in 2 h at 40 oC
Temp (°C) Time (h) % Au extracted 20 24 92.6330 8 95.5840 8 96.5150 4 93.5650 6 96.7260 8 95.94 0
20
40
60
80
100
0 2 4 6 8 10Time (h)
Au Extracted (%) @ 40 oC
Modified Merrill-Crowe• Main problem of the Merrill-Crowe process to precipitate
gold from cyanide solution (including cassava) is the need of clear (filtration) and de-aerated solution
• The idea is not to filter and not to use vacuum • Tests using some socks with Zinc shavings and very low
agitation of the pulp• Results with material from Costa Rica:• 99.6% of gold removal from solution in 2 h from Hg-
tailings (Hg was also removed)• 99.3% of gold removed from Newlox ore
Conclusion• Technology is only a piece of the complex actions to
eliminate Hg from AGM• Technology is not a universal solution, it depends on the
ore, the site, the skills, the capital, etc.• Co-existence provides the best solution to remove the
processing steps from the artisanal miners’ hands• Processing Centers and small companies can use Hg-
free techniques which are more efficient and cleaner
