Neutralization of Red Mud Using Inorganic Acids

Research Research Journal of Chemistry Chemistry and Environment Environment

___________________________________ ___________________________________Vol. Vol.17 (7) July (2013) Res. J. Chem. Environ. Environ.

Neutralization of Red Mud using Inorganic Acids 1

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Rai S.B., Wasewar K.L., * Mishra R. S., Puttewar S. P. and Chaddha M. J., 1 3 Mukhopadhyay Mukhopadhyay J. and Chang Kyoo Yoo *

1. Jawaharlal Nehru Aluminium Research Development and Design Centre, Wadi, Amravati Road, Nagpur, INDIA 2. Advanced Separation and Analytical Laboratory, Department of Chemical Engineering, Visvesvaraya National Institute of Technology (VNIT), Nagpur, Maharashtra, INDIA INDIA 3. Environmental Management & Systems Engineering Lab., Dept. of Environmental Science and Engineering, Kyung Hee University, KOREA * [email protected]; [email protected]

Abstract

Red mud’ or ‘bauxite residue’ is a waste generated from alumina refinery in an an enormous quantity posing posing a very serious and alarming environmental problem due to its high causticity. Red mud is highly alkaline in nature with a pH of 10.5-12.5 due to caustic soda solution used in extraction of alumina from bauxite ore using Bayer process. It can be made less hazardous and capable for utilization by ameliorating the caustic properties of red mud. One of the options may be neutralization of red mud using inorganic acid. To see the feasibility of using acid for the treatment of red mud, a systematic, methodological and comparative study of pH was carried out using three different inorganic acids (HCl, H 2SO4 , HNO3 ) for neutralizing red mud from two different Indian alumina refineries having different composition.

2NaOH + Al2O3.3H2O Red Mud

Na2O.Al2O3 + 4H2O+ (1)

About 1 ton of alumina is produced from 3 tons of bauxite and about 1 ton aluminium is produced from 2 ton of 1 alumina . Depending on the raw material processed, 1- 2.5 tons of red mud is generated per ton of alumina produced 10 . Bauxite ore mined globally amounts to be around 205 14 million tons per year . This indicates an enormous quantity of red mud is generated world wide every year posing a very serious serious and alarming environmental environmental problem. Red mud is disposed as dry or semi dry material in red mud pond or abandoned bauxite mines and as slurry having a high solid concentration of 30-60% with a high ionic strength. Chemical analysis shows that red mud contains silicon, aluminium, iron, calcium, titanium, sodium as well as an array of minor elements namely K, Cr, V, Ba, Cu, Mn, Pb, Zn, P, F, S, As etc. The variation in chemical composition between red mud worldwide is high. Typical composition of red mud contains Al 2O3 (10-20%), Fe2O3 (30-60%), SiO 2 (3-50%), Na2Oc (2-10%), CaO (212 8%), TiO2 (trace-25%) . Environmental concerns relate to two aspects: very large quantity of the red mud generated and its causticity. Problems associated with with the disposal of red mud waste include its high pH, alkali seepage into underground water, safety in storage, impact on plant life due to alkaline dust in the air and vast area of land required. Up to 2 tons of liquor with a significant alkalinity of 5- 20 g/L caustic (as Na 2CO3) accompany every ton of dry mud.

The work describes the chemical characterization of red mud before and after neutralization at different pH values with all the three acids. Parameters such as weight of red mud and volume of acid are optimized. Phases of different constituents in neutralized red mud have also been studied. It has been observed that nearly 35- 40% of the total caustic soda can be reduced reduced by acid treatment. Keywords : Bauxite residue, red mud, acid neutralization, inorganic acids, pH.

Introduction

Safe treatment and storage of high volume industrial waste streams pose unique waste management challenges. Land disposal of these materials often has negative environmental impacts such as contamination of soil and groundwater and consumes vast areas of land. Revegetation of dewatered red mud is not possible without addition of amendments because of the high pH, high salinity and absence of nutrients and organic constituents. Conventional thickener, high solids thickeners, vacuum filters, hyperbaric filters are the equipments used for dewatering the red mud.

The Bayer process of extraction of alumina from bauxite remains the most economical process till till date. In the Bayer process, the insoluble product generated after bauxite digestion (containing 40-60% A1203) with sodium hydroxide at elevated temperature (106-240°C) and pressure (1-6 atm.) to produce alumina is known as „red mud‟ or „bauxite residue‟. The waste product gets its name as red mud due to the oxidized iron content present in it. Red mud is a mixture of compounds originally present in the bauxite which is the parent mineral and of compounds formed during the Bayer cycle. As the bauxite has been subjected to sodium hydroxide treatment, red mud is highly caustic with a pH in the range of 10.5-12.5. The main reaction that occurs in the Bayer process (the conversion of bauxite to sodium aluminate) can be schematized as follows:

Neutralization of red mud will help to reduce the environmental impact caused due to storage activities of the residue and also lessen significantly the ongoing management of the deposits after closure. It will also open (10)

Research Journal of Chemistry and Environment

___________________________________Vol.17 (7) July (2013) Res. J. Chem. Environ.

opportunities for re-use of the residue which to date have been prevented because of the high pH. Long-term management of the residue deposits will reduce due to neutralization. Instead of accruing funds to deal with a future liability, the funds can be invested in process improvements which will reduce or remove the liability.

the red mud samples has been carried out in the paper. Neutralization studies using various inorganic acids such as HCl, HNO 3 and H2SO4 have been carried out for the treatment of red mud.

Material and Methods Materials: Red mud from two Indian alumina plants, one located at the eastern coast and the other located in the Central part of India have been used for the study. Let the two red muds be referred as Red Mud-1 and Red Mud-2 respectively. Three inorganic acids HCl, HNO 3, H2SO4 (Merck, India) having 0.1 M concentration and distilled water were used for experimentation.

Neutralization will cause reduced risk to clay and synthetic seals of red mud pond. Studies have been carried out by Alcoa World Alumina, Australia to investigate the potential impact of residue leachates on clay seal material. This test work indicated that as the pH (and hence alkalinity) of the leachate in contact with the clay seal increases, the clay itself is increasingly susceptible to dissolution reactions which alter the chemical and mineralogical composition of the clay seal and probably its sealing properties. By reducing the pH of residue leachate, the potential risk of long-term degradation to clay or synthetic liners will reduce. Also, any leachate which does escape from the impoundment will have a reduced impact on the receiving waters, hence the overall risk of groundwater contamination would be reduced significantly.

Red mud: Chemical composition of Red mud-1 and Red Mud-2 are given in table 1. Though the same chemical constituents occur in both the red mud, they differ quantitatively as the bauxites used in the two refineries differ from each other. Hence the technological parameters required for processing of these bauxites are different. East coast bauxite used for alumina production is highly gibbsitic in nature and hence uses atmospheric digestion technology (106°C) for alumina production while the alumina refinery situated in Central India uses high temperature digestion technology (240°C) for processing of mixed bauxite (gibbsitic + boehmetic). Gibbsite, boehmite and diaspore are the three phases of alumina present in bauxite.

Efforts to ameliorate red mud typically and possibly incorporate a pH-reduction processing step. These are CO 2 treatment, seawater neutralization, bioleaching, sintering and acid leaching being one of them. A comparison of all 3 the neutralization processes has been made by Cooling .

Mineralogically, these red muds have phases of undigested alumina, aluminosilicates, phases of iron and titania. These phases are hematite (Fe2O3), goethite Fe(1x)AlxOOH(x=0.33), gibbsite Al(OH) 3, boehmite AlO(OH), calcite (CaCO3), calcium aluminium hydrate (x.CaO.yAl2O3.zH2O), rutile (TiO2), anatase (TiO2), CaTiO3, Na2TiO3, kaolinite Al2O3.2SiO2.2H2O, sodalites, aluminum silicates, cancrinite (NaAlSiO 4)6CaCO3 and hydrogarnet Ca3Al2(SiO4)n(OH)12-4n.

The feasibility of treating red mud with acid has been 2, 5 studied by researchers . Various aqueous acidic solutions have been considered for this application including acidic 15 industrial wastewater . The use of carbonic acid has also been considered. A number of studies have been done for the feasibility of treating bauxite residue with acid on Kwinana red mud slurry. Treating red mud with acidic spent pickling solutions (SPSs), derived from the steelmaking process, provides a coagulant – a mixture of 11 aluminium and iron salts- for waste water treatment . Neutralization using acids is reasonably cheap if sufficiently large quantities of waste acid are available. Red mud has been treated with hydrochloric acid to 6 dissolve only the sodium content and the treated material is mixed with kaolinitic clay and formed into construction bricks.

Sodium is present in red mud in two forms: free soda and bound soda. Free sodium is the caustic soda in the entrained liquor of red mud slurry which gets incorporated during digestion process and remains with red mud in spite of repeated washings. Free sodium is in the form of NaOH, Na2CO3, NaAlO2 etc. The pH of the red mud is due to the presence of these alkaline solids in red mud. Inclusion of caustic soda in bound form in the red mud is due to the desilication step carried out in the Bayer process for removal of kaolinitic silica in bauxite. Bound soda is in the

Vice-a-versa, it has been proposed to use red mud that is 8, 9 very alkaline to neutralize acidic tailings . Red mud can be used to neutralize acid forming gases produced during coal combustion. Studies have been carried out on absorption of SO2 on red mud (Sumitomo scrubbing 4 process) . The feasibility of using red mud for the 13 treatment of acid leachates was studied by Rubinos et al .

form of sodalite complex which can be stated as “NAS” 2-

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phases: 3(Na2OAl2O32SiO 2)Na2X (X=CO2 , 2OH , SO4 , - 7 2Cl ) . In red muds, about 20-25 % is the free sodium while the rest is in the form of sodalite complex. Though red mud appears to be consolidated, it has a muddy consistency because of the fineness of the material involved and their colloidal nature due to the caustic soda present in it. Red mud is a very fine material in terms of

In the present study, acid neutralization studies have been carried out on red mud from two different Indian alumina refineries. Detailed chemical and mineralogical analysis of (11)



particle size distribution. Red mud is a very fine material in terms of particle size distribution. Average particle size of red mud is less than 10 microns. The specific surface area 2 -1 (BET) of red mud is between 10 and 30 m g depending on the degree of grinding of bauxite.

Effect of volume of acid used : Figs. 2, 3 and 4 show the pH of the two red muds (10 g) obtained after treatment with different volumes of 0.1 M HCl, H 2SO4 and HNO 3 respectively.

It can be seen from fig. 2 that for the same volume of acid (HCl) used, the higher pH is seen with Red mud-2 as compared to that of Red mud-1. Alternatively, it can be said that more amount of acid is required to neutralize Red mud-2 to an end point of pH 7.

Methods: Red mud from the refineries were ground to 100 mesh size and used for the study. Magnetic stirrer (Eltek M S 204, India) was used for stirring of red mud slurry mixed with different acids. The pH was measured on calibrated pH meter (Orion EA940, Thermo Electron Corporation, India). Analysis of chemical constituents of red muds has been carried by Wet Chemical method in which the caustic soda has been determined by using Flame photometer (Systronic, Ahmedabad, India). Mineralogy of red muds for determination of phases present in it has been studied using XRD (Philips X‟pert_Pro, Holland).

The standard enthalpy of neutralization is the heat absorbed per mole when an acid and a base react to form water under standard conditions. Neutralization is the formation of water from hydrogen and hydroxide ions. H3O+ (aq) + OH-(aq)

2H 20(aq)

Experiments were carried out to study the effect of weight of red mud taken for neutralization and acid volume added on the pH values of red mud slurry. Different quantities of each red mud (5, 10, 20 and 50 g) were taken and thoroughly mixed with 100 mL of 0.1 M HCl. After filtration, pH value was noted to decide the quantity of red mud to be taken for experimentation.

According to Arrhenius' theory, neutralization occurs because equal moles of hydrogen ions in the acid are equal to the moles of hydroxide ions in the base so the two react completely to form water. Neutralization of HCl and NaOH: NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

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10 g sample of each red mud was leached with acids keeping stirring time as 10 min. Leaching was carried out using different volumes of acid (50, 75, 100, 125 and 150 mL) and the slurry was filtered. pH of the supernatant liquor was measured. The filtered mud was dried and analyzed chemically and mineralogically. Both the red mud were also treated with excess amount of acid (H 2SO4) to see its effect on pH value and other components of red mud.

Neutralization of HNO3 and NaOH: NaOH(aq) + HNO3(aq) NaNO 3(aq) + H 20(l)

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Neutralization of H2SO4 and NaOH: NaOH(aq) + H2SO4 Na2SO4(aq) + H 20(l)

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The enthalpy of neutralization for strong acids is similar because strong acids fully disassociate in water therefore all hydrogen ions and all hydroxide ions react to from water molecules. However enthalpy of neutralization for H2SO4 would be different compared to the enthalpy of neutralization for the other two acids. This is because H2SO4 is a dibasic acid which means for every mol of + H2SO4 which dissolves 2 mols of H are disassociated. For every molecule of H 2SO4 it will contain 2 hydrogens compared to HCl and HNO3 which contain only 1. This + means twice as many H will be dissolved in a given volume compared to HCl and HNO 3. The enthalpy of neutralization, should therefore be different for H 2SO4 as in neutralization, energy is released when

Results and Discussion When an acidic solution is mixed with a basic solution in suitable amounts, both the solutions neutralize the effect of each other. The acidic nature of the acid and basic nature of the base is destroyed in the process of neutralization and the resulting solution is neither basic nor acidic. This important property of acid and bases to cancel each other out when mixed together in the right proportions called as the neutralization reaction can be an exothermic reaction. This phenomenon has been applied to destroy the alkaline nature of red mud by adding different acids to it and the suitable quantity of acid required to neutralize red mud has been studied.

+

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H + OH

H2O

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Hence H2SO4 should release around twice the amount of energy in neutralization compared to HCl and HNO 3. This is seen from fig. 3 in which a much less quantity of H 2SO4 (about 50 mL) is required to neutralize both the muds. If more amount of acid (125-150 mL) is added, much less value of pH (3-4) is achieved.

Effect of quantity of red mud: Fig. 1 shows the variation of pH value with respect to quantity of red mud. It can be seen that a higher values of pH is obtained with Red mud-2 owing to the presence of higher sodium content in it. 10 g of Red mud-1 and 5 g of Red mud-2 are the optimized value of red mud that can be neutralized with 100 mL of HCl to get a pH value of about 7.0.

Fig. 4 shows that the amount of acid (HNO 3) needed to neutralize Red mud-1 are between 75-100 mL while a (12)



much more quantity of acid (more than 150 mL) is required to neutralize Red mud-2. With a volume of 125150 mL of acid, the value of pH obtained is between 6.5 and 7 for Red mud-2.

from coal combustion can also be used for neutralization of red mud.

Conclusion The study shows that a large quantity of acid (10 g of red mud needs about 100 mL of 0.1 M acid) is required to neutralize the red mud. This volume may reduce by using acids of higher concentration. About 25% more quantity of acid is required in case of Red mud-2 to neutralize it to nearly a neutral value of pH in comparison to Red mud-1. Nearly same quantity of HCl and HNO3 are required to achieve the pH of the red mud slurry to a neutral value but it can be seen that only about half the quantity of H 2SO4 is needed to achieve the same value of pH. About 40% of the total sodium content (leachable and non-leachable) reduces in both the red mud after treatment with acids.

Chemical and mineralogical composition of neutralized red muds: Chemical composition of Red mud-1 and Red mud-2 treated with HCl, H2SO4, HNO3 to a nearly neutral value of pH is given in table 2 and table 3 respectively. Effect of excess use of acid was seen by adding higher quantity of H 2SO4 (125 ml) to both the red mud. A much lower pH is obtained with nearly 75-80% of the sodium content reducing in both the red muds. Reduction in silicon and calcium content of red muds has also been observed. The chemical composition of the red mud after treatment with more quantity of H 2SO4 is given in table 4. The mineralogical phases obtained in nearly all the neutralized red mud are shown in table 5. Iron oxides, aluminium hydroxides, alumininosilicates, calcium silicates, titanates dominate the composition of both the neutralized red muds.

Large volumes of reagent are required to fully neutralize the residue at a relatively high cost even if spent (waste) acid could be used. The study shows that neutralization using acids would be reasonably cheap if sufficiently large quantities of waste acid are available and need to be disposed off. Contaminated waste acids are produced during scrubbing of acid forming gases and pickling liquor may be used to destroy the alkaline nature of red mud. However, waste acids are rarely available in sufficient quantities to neutralize all the red mud generated at a bauxite refinery. Also the use of acid may introduce large volumes of impurities to the process water stream (sulphate in the case of sulfuric acid, chloride in the case of hydrochloric acid). It is therefore likely that the return of any water from the residue deposits will be unacceptable to process without further treatment to remove these added impurities.

Comparison of caustic soda content in neutralized red mud: The composition of Red mud 1 and Red mud 2 varies in soda content due to the type of bauxite used and the technology applied. Red mud 2 contains 25-30% more of caustic soda in it as compared to that of Red mud 1. Fig. 5 and Fig. 6 show the comparison of the soda content of the original and treated red mud. Caustic soda reduction of about 41% with HCl, 43% with H 2SO4 and 38% with HNO3 is observed with Red mud-1 and soda reduction of about 46% with HCl, 41% with H 2SO4 and 38% with HNO3 is observed with Red mud-2. It means that on neutralization of red mud at pH 7, apart from neutralizing the caustic soda present in the liquor phase, the sodalite complex (sodium aluminosilicates) are also being attacked by the acid releasing the caustic soda present in it. About 5-25% alumina, 10-15% silica and 20-40% of caustic soda dissolution from the sodalite complex of solid phase is taking place. Iron and titanium remaining the same, calcium is also being dissolved. A conceptual flow chart of neutralization process is given in fig.7.

Nevertheless acid neutralization would definitely help in reducing the sodium content in the red mud and the red mud can be subsequently utilized for making construction bricks. This would also render red mud less hazardous for disposal which can be subsequently re-vegetated.

References 1. Annual report, Chapter V, Department of Ministry of Mines, India, http: //mines.nic.in/archp5.html http: // www.portal. gsi. gov.in/gsiDoc/pub/DID_Bauxite_WM.pdf (1999-2000)

It can be seen from the results that acids can be used to reduce the alkaline nature of red mud. The wastes of many industries contain acids. One such example is the pickling liquor waste which is highly acidic and having a very low pH (less than 2) utilized to neutralize red mud. This may also subsequently generate a waste which would be much less hazardous than the individual wastes. Acid pickle liquors (HCl and H2SO4) are used in cold rolling mills and galvanizing mills to clean iron and steel surfaces. If they are allowed to flow into the water bodies, the acids will kill the aquatic life. Hence it may be mixed with red mud rendering both the wastes as non- hazardous. Also contaminated waste acids produced during scrubbing of acid forming gases (primarily sulphur dioxide) arising

2. Colombera P.M. and LePage G.P., Acid neutralisation of Kwinana Red Mud Slurry, Alcoa internal report (1982) 3. Cooling D.J., Paste, Improving the sustainability of residue management practices, Alcoa World Alumina Australia, Fourie A. and Jewell R.J., eds., Australian Centre of Geomechanics, Perth, Australia, 3 (2007) 4. Fois E., Lallai A. and Mura G., Sulfur dioxide absorption in a bubbling reactor with suspensions of Bayer red mud, Ind. Eng. Chem. Res., 46 (21), 6770 (2007) 5. Hughes C.A. and Thornber M.R., Treatment of refinery waste red mud with acid, CSIRO Division of Mineral products (1991)

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Table 1 Chemical Composition Red Mud

Constituents Al2O3,% Fe2O3,% SiO2,% TiO2,% Na2O,% CaO,%

Red mud-1 16.29 54.30 6.24 5.00 4.64 2.36

Red mud-2 19.36 36.40 7.12 17.23 6.36 1.68

Table 2 Chemical Composition of Neutralized Red Mud-1 after Treatment with different Acids

Constituents Al2O3,% Fe2O3,% SiO2,% TiO2,% Na2O,% CaO,% pH of red mud slurry

HCl 16.83 56.70 5.92 5.94 2.74 1.37 7.27

H 2SO4 16.71 56.82 6.07 5.65 2.67 1.25 7.88

HNO3 16.44 56.89 5.98 6.06 2.88 1.17 6.98

Table 3 Chemical Composition of Neutralized Red Mud-2 after Treatment with different Acids

Constituents Al2O3,% Fe2O3,% SiO2,% TiO2,% Na2O,% CaO,% pH of red mud slurry

HCl 20.50 38.60 6.85 18.74 3.47 1.12 7.12

H 2SO4 20.40 38.38 6.97 18.13 3.78 1.22 7.76

HNO3 19.83 38.04 6.99 18.09 4.00 1.18 7.46

Table 4 Chemical Composition of Red Muds at Lower pH value (Treatment with excess H 2SO4) Constituents

Red mud-1

Red mud- 2

Al2O3,% Fe2O3,% SiO2,% TiO2,% Na2O,% CaO,% pH of red mud slurry

16.56 59.89 3.91 5.68 0.97 0.55 3.49

21.05 39.54 5.20 18.84 1.60 1.10 5.24

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Table 5 Mineralogy of Neutralized Red Mud-1 and Red Mud-2

Constituents

Phases

Red mud-1

Red mud-2

Chemical formula

Alumina as

Silica as

Titania as

Iron as

Na2O as Calcium as

Gibbsite Diaspore Alumogoethite Bsodalite CanB hydrogrossular Bsodalite CanB hydrogrossular Anatase Rutile Ileminite Hematite Alumogoethite Ileminite Bsodalite CanB hydrogrossular Calcite

Al(OH)3 AlOOH FeAlOOH Na2OAl2O32SiO2 (NaAlSiO4)6CaCO3 Ca3Al2(SiO4)3-x(OH)4x Na2OAl2O32SiO2 (NaAlSiO4)6CaCO3 Ca3Al2(SiO4)3-x(OH)4x TiO2 TiO2 FeTiO3 Fe2O3 FeAlOOH FeTiO3 Na2OAl2O32SiO2 (NaAlSiO4)6CaCO3 Ca3Al2(SiO4)3-x(OH)4x CaCO3

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Fig. 1: Treatment of different quantities of red mud with 100 mL 0.1 M HCl

Fig. 2: Neutralization of red mud with 0.1 M HCl (15)



Fig. 3: Neutralization of red mud with 0.1 M H 2SO4

Fig. 4: Neutralization of red mud with 0.1 M HNO3

Fig. 5: Comparison of caustic soda content of original and neutralized Red mud-1 7

pH 11.5

6 5 % , O 2 a N

pH 7.44

pH 7.76

pH 7.46

4 3 2 1 0 Original

HCl

H2SO4

HNO3

Fig. 6: Comparison of caustic soda content of original and neutralized Red mud-2

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Acids: HNO3, H2SO4, HCl

Red mud

Liquor (pH 7-8)

Mixing of red mud and acid

Separation of entrained liquor and red mud

Safe disposal pH: 10.5-12.5 Chemical constituents: Al2O3, Fe2O3, SiO2, TiO2, Na2O, CaO Particle size: Average particle size < 10 microns. 2 Surface area (BET):10 -30 m /g

Neutralized red mud

Fig. 7: Conceptual flowchart for neutralization of red mud using inorganic acids 6. Iwu. Gregory Onyemauwa, Method of treating bauxite waste red mud with acid and making construction bricks from the treated material, United States Patent, 3985567 (1976)

11. Piga L., Pochetti F. and Stoppa L., Recovering metals from red mud generated during Alumina Production, JOM, 54 (1993) 12. Red mud Project, http: //www.redmud.org Characteristics, html

7. Kurdowski W. and Sorrentino F., Waste materials used in concrete manufacturing, Satish C., ed., William Andrew Publishing/ Noyes, 290 (1997)

13. Rubinos D., Fierros F.D. and Barral M. T., Neutralization and decontamination of Acid leachates using Bauxite Red mud, IMWA -2011, Mine water- Managing the challenges, at Aachen, Germany, 441 (2011)

8. Paradis M., Duchesne J., Lamontagne A. and Isabel D., Using red mud bauxite for the neutralization of acid mine tailings: a column leaching test, Can. Geotech. J., 43 (11), 1167 (2006)

14. U.S. Geological Survey, Mineral Commodity Summaries http: //minerals. usgs.gov/ minerals/pubs /mcs/2010.pdf (2010)

9. Paradis M., Duchesne J., Lamontagne A. and Isabel D., Longterm neutralization potential of red mud bauxite with brine amendment for the neutralization of acidic mine tailings, Applied Geochemistry 22 (11), 2326 (2007)

15. Wong J.W.C. and Ho G.E., Effectiveness of acidic industrial wastes for reclaiming fine bauxite refining residue (Red Mud), Soil Science, 158(2), 115 (1994).

10. Paramguru R.K., Rath P.C. and Misra V.N., Trends in red mud utilization-A Review, Mineral Processing & Extractive Metall, Rev., 26, 1 (2005)

th

th

(Received 20 February 2013, accepted 25 April 2013)

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Neutralization of Red Mud Using Inorganic Acids

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