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Journal of Hazardous Materials 176 (2010) 1044–1050

Contents lists available at ScienceDirect

Journal of Hazardous Materials

journa l homepage: www.e lsev ier .com/ locate / jhazmat

equestration of carbon dioxide (CO2) using red mud

ishwajeet S. Yadav, Murari Prasad ∗, Jeeshan Khan, S.S. Amritphale, M. Singh, C.B. Rajunvironmental Chemistry Division, Advanced Materials & Processes Research Institute, (C.S.I.R.), Hoshangabad Road, Bhopal 462064, M.P., India

r t i c l e i n f o

rticle history:eceived 28 July 2009eceived in revised form5 November 2009ccepted 27 November 2009vailable online 4 December 2009

a b s t r a c t

Red mud, an aluminium industry hazardous waste, has been reported to be an inexpensive and effectiveadsorbent. In the present work applicability of red mud for the sequestration of green house gases withreference to carbon dioxide has been studied. Red mud sample was separated into three different sizefractions (RM I, RM II, RM III) of varying densities (1.5–2.2 g cm−3). Carbonation of each fraction of red mudwas carried out separately at room temperature using a stainless steel reaction chamber at a fixed pressureof 3.5 bar. Effects of reaction time (0.5–12 h) and liquid to solid ratio (0.2–0.6) were studied for carbonation

eywords:ed mudreen house gasesarbon dioxidearbonation

of red mud. Different instrumental techniques such as X-ray diffraction, FTIR and scanning electronmicroscope (SEM) were used to ascertain the different mineral phases before and after carbonation of eachfraction of red mud. Characterization studies revealed the presence of boehmite, cancrinite, chantalite,hematite, gibbsite, anatase, rutile and quartz. Calcium bearing mineral phases (cancrinite and chantalite)were found responsible for carbonation of red mud. Maximum carbonation was observed for the fractionRM II having higher concentration of cancrinite. The carbonation capacity is evaluated to be 5.3 g of

CO2/100 g of RM II.

. Introduction

Growing concern over increased levels of atmospheric carbonioxide has prompted new interests in development of techniquesor its removal to mitigate the global climate change problem. Largeuantities of carbon dioxide are released in the atmosphere fromeveral important industries, like electricity generation, steel man-facturing, cement manufacturing, around the globe every day.oreover, carbon dioxide is the main gas that contributes greatly

o the greenhouse effect, therefore its removal from the industrialue gases is very important [1]. The most direct way of capturingnd sequestering carbon dioxide from power plants is separatingt from the flue gas using conventional techniques [2]. There areeveral methods like geological sequestration, physical and chem-cal adsorption, membrane separation, CO2 sequestration etc. toemove the carbon dioxide. The existing methods available for thearbon dioxide sequestration include adsorption by physical andhemical wet scrubbing, adsorption by solid using pressure and

emperature swing modes, cryogenic distillation and mineraliza-ion process, i.e. mineral carbonation [3,4]. Mineral carbonation isne of the best method for the removal of carbon dioxide becauset results permanent storage of carbon dioxide as mineral carbon-

∗ Corresponding author. Tel.: +91 755 2457105;ax: +91 755 2457042x2488985x2488323.

E-mail addresses: prasadmurari56@yahoo.co.in, drmprasad56@gmail.comM. Prasad).

304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.jhazmat.2009.11.146

© 2009 Elsevier B.V. All rights reserved.

ates. Direct carbonation, using liquid carbon dioxide, is used for theremediation of aqueous streams or slurries while sequestering car-bon dioxide in the form of metal carbonates [5]. The carbonationprocess is exothermic and therefore has the potential to becomeeconomically viable. Advantages of mineral carbonation includevast storage capacity and exothermal reaction.

To date, all commercial CO2 capture plants use processes basedon chemical absorption with an aqueous alkanolamine solvent[6–8]; monoethanolamine (MEA) is the most popular solvent [9].However, they have a number of shortcomings for treating fluegases, which manifest themselves in the form of high capital andoperating costs. The development of a low-cost means (processesand materials) of capturing CO2 is therefore crucial to the realisa-tion of the goal of sequestering CO2 emissions on large/industrialscale.

The aluminium manufacturing industries annually produce sev-eral million tons of alumina in the world through the Bayer process[1]. The Bayer process implicates the production of a large amountof a bauxite residue, the red mud [2]. Generally, the productionof 1 ton of alumina generates 1.0–1.5 tons of red mud, and therebyaluminium manufacturers generate over 66 million tons of red mudresidues per year [10,11]. The disposal of such a large quantityof this alkaline waste sludge is expensive [12]. Red mud is cur-

rently being used in the manufacture of building materials andceramics. Studies on the use of red mud for making inexpensiveand efficient adsorbent for removal of lead, chromium and arsenic[13,14], fluoride [15], cadmium, zinc [16] from aqueous solutionshave also been reported recently. So far, the various uses of red

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ud developed include, as acidic amender [17], in making build-ng materials namely bricks [18], ceramics, tiles [19], glazes [20]nd red mud–polymer composites panels as wood substitute [21],ron rich cement [22], radiopaque materials [23], CO2 sequestra-ion using liquid carbon dioxide [24], etc. Moreover, the chemicalomposition of oxides and alkaline character of red mud may alsoontribute to make very good material for the carbon dioxideequestration by carbonation. The carbonation of alkaline mate-ial is an inexpensive and safe process that leads to the formation ofhermodynamically stable products [25]. The use of the carbonationan be an advantageous solution for overcoming problems associ-ted with red mud storage and the emissions of several thousandons of carbon dioxide from aluminium manufacturers each year26,11]. Moreover, several benefits have been associated with these of carbonated red mud including soil amendment, to removeitrogen and phosphorus from sewage effluent, fertilizer additive

n soils, in brick and tile manufacture, filler for plastics, and in theement production [13,27].

The aim of this study is to characterize different size fractionsf red mud to ascertain main mineral phases responsible for itsarbonation and to evaluate the CO2 uptake capacity of differentractions of red mud. For this purpose red mud was separatedravity wise into different size fractions and was subjected for car-onation in a stainless steel reaction chamber at optimum reactionime and liquid to solid ratio. Phases which are responsible for car-onation were characterized by X-ray diffraction and carbonationapacity of red mud fractions were determined by gain in weightf all the three fractions. FTIR and scanning electron microscopeSEM) studies were also used to verify the results.

. Experimental

Representative samples of red mud were used for experimentaltudies to sequester carbon dioxide gas. Prior to experimental stud-es, red mud samples procured from aluminium industries wereharacterized using X-ray diffraction, FTIR techniques and scanninglectron microscope. The chemical analysis was carried out usinget chemical method.

.1. Materials

The red mud procured from Hindustan Aluminium CompanyHINDALCO), Renukoot, India was in the form of clay-type wasteesidue composed of fine fraction (mud) and a relatively coarseraction (sand) with small granules. Representative sample of red

ud was prepared by the method of coning and quartering.

.2. Preparation of the adsorbents

Different sized lumps of red mud sample were pulverized andeparated into three fractions using a large perspex column ofength, 228 cm and diameter, 15 cm. The separation of red mudnto three different size fractions was based on density. Low den-

ity material (Fraction I) was recovered from upper portion of theolumn and high density material (Fraction III) was recovered fromottom portion of the column. All the three fractions were dried inhe oven and grinded. Weight percent of low, medium and highensity red mud samples were 0.34, 4.57 and 95.08 respectively

able 1elative density of different fractions of red mud.

S. no. Red mud fraction Weight % A

1 Fraction I 0.34 52 Fraction II 4.57 33 Fraction III 95.08 5

aterials 176 (2010) 1044–1050 1045

and their relative densities were 1.5, 1.8 and 2.2 g cm−3 respectivelyand their pH were 7–8, 7 and 8 as shown in Table 1.

2.2.1. Optimum fraction of adsorbentEach fractions of red mud sample were dried and kept in air

oven at 100 ◦C for 2 h to expel the remaining moisture. They werekept further in the carbon dioxide atmosphere by adding knownquantity of alkali (NaOH) as described elsewhere [28]. Percentweight gain in the all fractions was determined gravimetrically.It was observed that the carbonation capacity of red mud fractionII (medium density) is maximum. The effects of reaction time, liq-uid to solid ratios on carbonation were studied further for eachfractions of red mud.

2.3. Experimental method

Different instrumental techniques such as X-ray diffraction, FTIRand SEM were used to characterize the red mud samples. Qualita-tive analysis of the finely ground samples of RM I, RM II and RMIII was done with help of a Philips X-ray diffractometer (Model PW1710) using Cu-K� radiation and operated at 40 kV and 20 mA. TheXRD patterns were recorded from 6 to 70 2�◦ with a scanning speedof 0.02 2�◦ per second. Infra red spectrophotometer (Perkin Elmer,983 G) was used in the frequency range 4000–180 cm−1 using KBrpellet method. In order to examine the surface and morphology ofred mud samples and confirmation of mineralogical characteristicsat an enhanced resolution, a scanning electron microscope (JEOL,Model JSM 5600) was used.

All the three fractions of red mud were carbonated in the stain-less steel chamber by exposing them in a CO2 atmosphere at apressure of 3.5 bar. Reaction chamber was equipped with an ana-logue pressure gage to monitor the reaction chamber pressure.CO2 gas was generated by mixing oxalic acid solution into sodiumbicarbonate powder and was introduced into the chamber usingpressure pump. Before exposing red mud to CO2, they were mixedthoroughly with alkaline in 50 ml Petri dishes of 90 mm internaldiameter at predetermined liquid to solid ratios in the range from0.2 to 0.6 and then placed in reaction chamber. For each set ofexperiments, samples were prepared in the manner as describedabove.

The reaction chambers were flashed with CO2 three times priorto experiments to ensure that all the air was expelled. The extentof the carbonation was assessed by measuring the gain in weightbefore and after carbonation of the sample. After carbonation, sam-ples were dried at 105 ◦C to constant weight. The gain in weight ofcarbonated sample indicates about reaction of carbon dioxide withred mud sample.

Effects of parameters like reaction time, liquid to solid ratio werestudied to check the maximum carbonation capacity of all threefractions of red mud.

3. Results and discussion

3.1. Characterization of materials

The chemical analysis of representative sample of red mudwas determined by wet chemical method. The chemical analy-sis revealed the presence of various metal oxides (Fe2O3 = 31.88;

vg. size, micron pH Relative density (g cm−3)

�m 7–8 1.50 �m 7 1.80 �m 8 2.2

1046 V.S. Yadav et al. / Journal of Hazardous Materials 176 (2010) 1044–1050

Table 2Mineral phases present in red mud and in its fractions (RM I, RM II, RM III).

S. no. Red mud RM I RM II RM III

1 Anatase Anatase Anatase Anatase2 Rutile Rutile Rutile Rutile3 Quartz Quartz4 Hematite Hematite Hematite Hematite5 Boehmite Boehmite Boehmite Boehmite6 Gibbsite Gibbsite7 Bayerite Bayerite

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8 Na5Al3CSi3O15 Na5Al3CSi3O15 Na5Al3CSi3O15 Na5Al3CSi3O15

9 Cancrinite Cancrinite Cancrinite Cancrinite10 Chantalite Chantalite Chantalite Chantalite

iO2 = 21.20; Al2O3 = 20.10; SiO2 = 8.50; CaO = 2.99; Na2O = 6.0% andoss on ignition = 10.0.). The results of chemical analysis of red mudample especially alumina content and loss on ignition appear veryimilar to the chemical analysis of red mud as described elsewhere29]. The wet sieve analysis of red mud sample has indicated thathe 78% of the samples are below 48 �m size [23]. The density andorosity of red mud sample were 2.0 g cm−3 and 0.45%. The mea-urement of surface area by the Brunauer–Emmette–Teller methodas reported 10.8 m2 g−1. Characterization studies of represen-

ative sample of red mud and its fractions carried out by X-rayiffraction and I.R. suggested the presence of boehmite, cancrinite,ematite, gibbsite, anatase, rutile, and quartz as shown in Table 2.ancrinite and chantalite were the two calcium bearing mineralhases present in all the three fractions.

The dominance of cancrinite phase in RM II is evident from the-ray diffractogram of three fractions shown in Fig. 1.

.2. Effect of reaction time

All the three fractions (RM I, RM II and RM III) of red mud werearbonated in the stainless steel chamber by exposing them in a CO2tmosphere for reaction time of 0.5–12 h at an average pressure of.5 bar. The CO2 uptake by three different fractions of red mud forifferent time intervals is shown in Fig. 2. Initially a steep rise inhe consumption of the gas was observed. Thereafter it was lower-

ng gradually till the adsorbent was saturated. While carbonatinghe red mud fraction I, II and III for 12 h, a larger portion (77%, 82%,nd 76%) of CO2 capture takes place in the first 3.5 h, respectively.urther to this reaction time (3.5 h) a small percentage of carbona-ion takes place for a comparatively very longer time of reaction, i.e.

Fig. 1. X-ray diffraction patterns for different fractions (RM

Fig. 2. Effect of reaction time on carbonation of different fractions of red mud.

12 h. Therefore, 3.5 h has been selected as reaction time for furtherexperiments.

The carbonation pattern of red mud fractions clearly indicatedthat the consumption of CO2 is higher for RM II than for RM III andRM I. This is believed mainly due to higher percentage of weightgain (5.3%) of RM II fraction at optimum time of 3.5 h in comparisonto relatively less percentage of weight gain of other two fractions(3.5% and 0.7% for RM III and RM I respectively). The higher percent-age of weight gain of RM II fraction may be assigned to the strongpresence of cancrinite phases (Fig. 1) responsible for carbonationin RM II with respect to RM III and RM I. X-ray diffraction analysis(Figs. 1 and 3) of RM I, RM II and RM III fractions before and aftercarbonation has well supported the above result.

Particle size of the reactant plays an important role for any

reaction. Generally finer size particles enhance the reaction ratesignificantly. Higher carbonation was expected for RM I fraction ofred mud because it has finer particles (average particle size, 5 �m)than RM II and RM III. But RM II fraction of red mud reported highercarbonation than other two fractions. This may be attributed to

I, RM II and RM III) of red mud before carbonation.

V.S. Yadav et al. / Journal of Hazardous Materials 176 (2010) 1044–1050 1047

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Fig. 3. X-ray diffraction patterns for different fraction

he presence of higher concentration of chantalite and cancrinitehases in RM II which are responsible for carbonation of red mud.

.3. Effect of liquid to solid ratio

Water is necessary for the carbonation reaction to proceed, butoo much water hinders the diffusion of CO2 into the pores of aolid. Pore water hydrates and solvates the CO2 and dissolves thea2+ ions from the solid phase to react and form calcium carbonate.o it was inevitable to study the influence of the water content onhe carbonation reaction. The carbonation experiment was carriedut for all the three fractions over a period of 3.5 h at different l/satios ranging from 0 to 0.6. The gain in weight was determined forhe three fractions of red mud. These experiments indicated (Fig. 4)hat for maximum carbonation, the l/s ratio should be 0.5, 0.35 and.3 for RM I, RM II and RM III respectively.

Carbonation capacity (5.3 g of CO /100 g) of RM II at l/s ratio 0.35

2hen compared to the results (4.15 g of CO2/100 g at l/s ratio 10.0)

f other investigator [30], it was found that higher l/s ratio did notield higher CO2 capture efficiency.

ig. 4. Effect of liquid to solid ratio on carbonation of different fractions of red mud.

I, TRM II and TRM III) of red mud after carbonation.

3.4. X-ray diffraction study

In the present studies the identification of various mineralphases responsible for sequestration of carbon dioxide in the redmud as well as in the three different fractions of the processedred mud have been studied using X-ray powder diffraction tech-nique. The X-ray diffractogram of all the three fractions of redmud before and after carbonation has been shown in Fig. 1 andFig. 3 respectively. Boehmite, hematite and cancrinite are themajor phases identified in each fraction of red mud. They wereobserved at corresponding ‘d’ values 2.345, 2.68 and 2.034 Å respec-tively.

The intense peak of boehmite was observed at 2� (38.33◦) inboth RM II and TRM II at ‘d’ value 2.346 Å. Higher concentrations ofcancrinite, chantalite and sodium aluminosilicate mineral phaseswere present in RM II. These three mineral phases may be respon-sible for carbonation of red mud by reacting with CO2 to formcarbonates. The formation of calcite (CaCO3) is confirmed by thepresence of its peak corresponding to ‘d’ values 3.032 and 1.89 Å. It isalso validated by 20% decrease in intensities of cancrinite and chan-talite in TRM II with respect to intensities of these mineral phases inRM II. The peaks of calcite were observed at corresponding ‘d’ val-ues of 3.025 and 1.88 Å with percent intensity 28.9 and 29.6 in TRMI, at 3.032 and 1.890 Å with percent intensity 54.3 and 55.1 in TRMII and at 3.0260 and 1.889 Å with percent intensity 40.2 and 41.6respectively in TRM III. These finding suggest about comparativelymore carbonation of RM II followed by RM III and RM I.

This is to clarify that our raw red mud sample did contain cal-cium hydroxide. But, three fractions (RM I, RM II and RM III) ofred mud did not show any presence of alkalis as observed by

pH and X-ray studies. This may be due to excessive washing ofred mud sample while separating three fractions. After treatmentof fractionated red mud samples with CO2, calcite peaks wereobserved in all three fractions of red mud with intense peak in RM

Table 3Percentage transmittance of CO3

2− group of carbonated and noncarbonated red mudfractions I, II and III.

S. no. Different fraction of red mud % Transmittance

1 RM I 882 TRM I 823 RM II 734 TRM II 455 RM III 576 TRM III 45

RM, noncarbonated red mud fractions; TRM, carbonated red mud fractions.

1048 V.S. Yadav et al. / Journal of Hazardous Materials 176 (2010) 1044–1050

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Fig. 5. FTIR spectra of different fractions (RM

I fraction as discussed above. Formation of calcium carbonate (cal-ite) might be due to reaction of cancranite with high dosage ofO2. This corroborates the observations of earlier investigator [31]hich experimentally described about the break-up of cancrinite

o nepheline + calcite + nH2O.

.5. FTIR spectroscopy

The IR spectra study of carbonated and noncarbonated redud fractions helps to understand their CO2 sequestration

bility. The changes in % transmittance of CO32− group have

een observed in each fraction of red mud and shown inable 3.

In all the spectra of different fractions of untreated red mudFig. 5) and treated red mud (Fig. 6), a strong band was observedn the hydroxyl stretching region 3300–3400 cm−1. This may be

Fig. 6. FTIR spectra of different fractions (TRM I, TRM

II and RM III) of red mud before carbonation.

due to the presence of H2O in the red mud [32,33,34]. The peaks at1630 and 463 cm−1 represent the stretching vibration of Fe O bond[33,29]. The presence of calcium carbonate is confirmed by strongasymmetric C O stretching vibration at 1420 cm−1 and mediumand sharp C O bending at 874 cm−1 [35]. Additional peaks werealso observed in the region 680–600 cm−1 due to the symmetricstretching of the Si O Al framework. The peaks at 100–1120 cm−1

are for asymmetric stretching of Si O Al framework [36]. Thepeaks at 980–995 cm−1 are due to SiO2 [29]. These results are con-sistent with the results obtained from the XRD analysis of the redmud.

It is evident from the spectra and data that there is a significantchange in % transmittance of CO3

2− group for RM II in comparisonto RM I and RM III. So it can be concluded that RM II has higheraffinity towards for carbon dioxide sequestration than RM I andRM III.

II and TRM III) of red mud after carbonation.

V.S. Yadav et al. / Journal of Hazardous Materials 176 (2010) 1044–1050 1049

Fig. 7. SEM micrographs of untreated red mud RM I (A) and treated red mud TRM I (B).

Fig. 8. SEM micrographs of untreated red mud RM II (A) and treated red mud TRM II (B).

Fig. 9. SEM micrographs of untreated red mud RM III (A) and treated red mud TRM III (B).

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.6. Morphological study

The morphological study of all fractions of carbonated (TRM I,RM II and TRM III) and noncarbonated (RM I, RM II and RM III)ed mud was carried out using SEM. Notable are the changes inorphology of particle surfaces when compared micrographs A and

, C and D and E and F shown in Figs. 7–9 for three fractions ofed mud. The carbonated particles contain a porous coating thatas absent in noncarbonated particles as described elsewhere [25].

he composition of this coating was identified as calcite (CaCO3) byEM/EDX analysis.

. Conclusions

The following points can be summarized from the above studies;

(I) Red mud can be effectively utilised for sequestration of carbondioxide (CO2).

(II) Chantalite and cancrinite are mineral phases responsible forcarbonation of red mud.

(III) Out of three fractions of red mud, RM II was found more effec-tive to capture CO2.

IV) Carbonation capacity was evaluated to be 5.3 g of CO2/100 g ofRM II.

cknowledgement

The authors are grateful to the Director, A.M.P.R.I., Bhopal forncouragement of the present research work and kind permissiono publish this paper.

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