Ind. Eng. Chem. Res. 2008, 47, 7617–7622
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CO2 Sequestration by Aqueous Red Mud Carbonation at Ambient Pressure and Temperature Danielle Bonenfant,† Lynda Kharoune,‡ Se´bastien Sauve´,§ Robert Hausler,† Patrick Niquette,† Murielle Mimeault,| and Mourad Kharoune*,⊥ STEPPE, De´partement de Ge´nie de la Construction, De´partement de Ge´nie Me´canique, and De´partement de Ge´nie de la Production Automatise´e, E´cole de Technologie Supe´rieure, 1100, Notre-Dame Ouest, Montre´al, Que´bec, Canada H3C 1K3, De´partement de Chimie, UniVersite´ de Montre´al, P.O. 6128, Succursale CentreVille, Montre´al, Que´bec, Canada H3C 3J7, and Department of Biochemistry and Molecular Biology, College of Medicine, Eppley Cancer Institute, 7052 DRC, UniVersity of Nebraska Medical Center, Omaha, Nebraska 68198-5870
An analysis of carbonation was carried out with the aqueous fresh red mud suspension at a liquid-to-solid ratio of 10 kg/kg, as well as in the leached-hydrated matrixes and leachates isolated from this red mud suspension after three successive leachings, to evaluate their intrinsic carbonation potential at ambient conditions (temperature of 20 ( 1 °C and atmospheric pressure). The carbonation assays were performed at 20 °C using a CO2 concentration of 15.00 vol% at a flow rate of 5 mL/min. The red mud matrix has a great leaching capacity of Na-(hydr)oxide, which is the principal hydroxide that seems to be implicated in the carbonation of leachates that have half-carbonation capacity of red mud. Moreover, the carbonation of the red mud suspension also involves a portlandite-containing matrix. The carbonation of the red mud suspension and leachates implicates a complete neutralization of their content in Ca- and Na-(hydr)oxides. Although the leached hydrated-matrixes seem to be partially carbonated, it preserves a carbonation capacity near to that of leachate after three successive leachings. Moreover, three leached hydrated-matrixes and leachates have a carbonation capacity (7.09 g of CO2/100 g of red mud) higher than the carbonation capacity obtained for the red mud suspension, which is evaluated to 4.15 g of CO2/100 g of red mud. Taken together, these results suggest that the carbonation of the red mud may be enhanced by the use of leached hydrated-matrixes and leachates obtained from multiple leaching. 1. Introduction The aluminum manufacturers annually produce several million tons of alumina in the world through the Bayer chemical process.1 The Bayer process implicates the production of a large amount of a bauxite residue, the red mud.2 Generally, the production of 1 ton of alumina generates 1.0-1.5 tons of red mud, and thereby aluminum manufacturers generate over 66 million tons of red mud residues per year.3,4 The red mud is characterized by a high alkalinity (pH 13) that is associated with its composition in oxides including basic oxides (CaO, Na2O), amphoteric oxides (Al2O3, Fe2O3, TiO2), and acidic oxide (SiO2) (Table 1). These oxides are present in main phases such as portlandite (Ca(OH)2), sodium carbonate (Na2CO3), NaAl(OH)4, Na6[AlSiO4]6, crystalline hematite (Fe2O3), goethite (R-FeOOH), gibbsite (Al(OH)3), boehmite (γ-AlOOH), sodalite (Na4Al3Si3O12Cl), anastase (TiO2), rutile (TiO2), katoite (Ca3Al2SiO4(OH)12), gypsum (CaSO4 • 2H2O), and quartz (SiO2).1,2,5,10 The storage of red mud is a major environmental problem due to its caustic nature, which may enhance the alkalinity of the environment and may represent a risk for all living organisms.1,6 One of the solutions * To whom correspondence should be addressed. Phone: (514) 396 8640. Fax: (514) 396 8595. E-mail:
[email protected]. † STEPPE, De´partement de Ge´nie de la Construction, E´cole de Technologie Supe´rieure. ‡ De´partement de Ge´nie Me´canique, E´cole de Technologie Supe´rieure. § Universite´ de Montre´al. | University of Nebraska Medical Center. ⊥ De´partement de Ge´nie de la Production Automatise´e, E´cole de Technologie Supe´rieure.
to this environmental problem that is associated with the use of red mud is its valorization. The reuse of this bauxite residue was studied to remove the phosphorus and toxic heavy metals from wastewater, amendment of soil, and cement and brick production, as corrosion inhibitor of carbon steel, and for the elimination of volatile organic compounds.7-13 Moreover, the chemical composition of oxides and alkaline character of red mud may also contribute to make very good material for the CO2 sequestration by carbonation. The carbonation of alkaline material is an inexpensive and safe process that leads to the formation of thermodynamically stable products.14 The use of the carbonation can be an advantageous solution for overcoming problems associated with red mud storage and the emissions of several thousand tons of CO2 from aluminum manufacturers each year.3,4 Moreover, several benefits have been associated with the use of carbonated red mud including soil amendment, to remove nitrogen and Table 1. X-ray Fluorescence Analysis of Red Mud component Fe2O3 CaO SiO2 MgO Al2O3 P2O5 TiO2 Na2O K 2O LOIa a
LOI, loss on ignition.
10.1021/ie7017228 CCC: $40.75 2008 American Chemical Society Published on Web 09/26/2008
concentration (wt %)‘ 33.45 7.77 9.58 0.86 18.96 0.21 8.61 8.08 0.30 12.18
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phosphorus from sewage effluent, fertilizer additive in soils, in brick and tile manufacture, filler for plastics, and in the cement production.1 In spite of advantages to use the red mud for capture of CO2, a small number of studies were effectuated on the carbonation of red mud. Cooling et al.1 have notably conducted a pilot scale testing red mud slurry carbonation at a solid content of 48 wt %. This process implicated several CO2 reactions with the alkaline compounds within the liquor to form carbonate species as follows: NaAl(OH)4+CO2 T NaAlCO3(OH)2+H2O
(1)
NaOH + CO2 T NaHCO3
(2)
Na2CO3+CO2+H2O T 2NaHCO3
(3)
3Ca(OH)2 · 2Al(OH)3+3CO2 T 3CaCO3+Al2O3 · 3H2O + 3H2O (4) Na6[AlSiO4]6 · 2NaOH + 2CO2 T Na6[AlSiO4]6+2NaHCO3 (5) These authors have established that the carbonation process of bauxite residue slurry requires 33.7 kg of CO2/L to attain a pH of ∼8.3 (pH of a CaCO3 saturated solution in equilibrium with atmospheric air) and is principally dependent on the carbonation of the sodium and calcium oxides and hydroxides.1,15 The aim of this study is to evaluate the intrinsic carbonation potentials of the aqueous red mud suspension, matrixes, and leachates and leaching capacity of the red mud matrix in water at ambient conditions (temperature of 20 ( 1 °C and atmospheric pressure). Therefore, the measurements and comparison of the carbonation capacities will be carried out in an aqueous red mud suspension, the leached hydrated-matrixes, and leachates extracted from three successive leaching of this suspension. The aim of this study is to evaluate the carbonation capacity at ambient conditions (temperature of 20 ( 1 °C and atmospheric pressure) of aqueous fresh red mud suspension, their leachedhydrated matrixes, and their leachates. 2. Experimental Section 2.1. Materials. The concentrated dry red mud was provided by Alcan Inc. (Vaudreuil, QC, Canada). Concentrated nitric acid (trace metal grade 68-70 wt %) was purchased from Fisher Scientific Co. (Nepean, ON, Canada), and oxygen extra dry and a mixture of 15.00 vol % CO2 and 85.00 vol % N2 gas were from Praxair Production Inc. (Montre´al, QC, Canada). All these products were used without additional purification. 2.2. Materials Preparation. Fresh dry red mud was produced from the Bayer process and stored in containers hermetically closed at 22 °C. This bauxite residue possessed a particle size and a specific gravity of 0.1-1000 µm and 3.0-3.5 g/cm3, respectively. The red mud suspension was prepared by mixing 20.0 ( 0.1 g of fresh dry red mud (d ) 38-106 µm) and 200 mL of deionized water in 250-mL Pyrex Erlenmeyer flasks. The red mud suspension was stirred during 24 h at 20 ( 1 °C, at atmospheric pressure, and under an agitation of 300 rpm in an Innova 4230 Refrigerated-Incubator Shaker from New Brunswick Scientific Co. (Fischer, Ottawa, ON, Canada). The three consecutive leachates and leached hydrated-matrixes, designated as first, second, and third leachates, and the leached hydratedmatrixes of red mud were prepared with three consecutive leachings of red mud suspension. The leached hydrated-matrix and leachate were collected after a centrifugation during 10 min
Figure 1. Schematic diagram of the reactor for carbonation of the red mud suspension, and leachates.
at 10 000 rpm and 20 ( 1 °C and a filtration with Filtropur cellulose acetate sterile filters with a pore size of 0.45 µm from Sarstedt Aktlengesellschaft & Co. 2.3. Materials Characterization. The chemical composition of fresh red mud was measured by fluorescence X-ray using a sequential X-ray spectrometer Philips PW2400. The measures were made in triplicate. The acidic neutralizing capacities of suspensions, containing (1) 10.0 ( 0.1 g of fresh dry red mud and 100 mL of deionized water, (2) 10.0 ( 0.1 g of the first leached hydrated-matrix and 100 mL of deionized water, and (3) the first leachate prepared as indicated in section 2.2, were measured by titration with 1 N HNO3 using an automatic TIM865 Titration manager and the Titramaster 85 V.1.3.0. software from Radiometer Analytical (Lyon, France). The nitric acid was prepared by a dilution of concentrated nitric acid in deionized water. All the assays have been made in duplicate. The pH and electrolytical conductivities of the red mud suspension, prepared as indicated in section 2.2 and leached at intervals from 2 min to 24 h, were measured with a pH-meter PHM 250 Ion Analyzer and a CDM Conductivity Meter from MeterLab Co. (Radiometer Analytical). All the assays were made in triplicate. The concentrations of the different elements were measured in the first leachates of red mud obtained after 30, 60, 120, 360, 600, and 1440 min according to the material tested, by ICP-AES using an ICP-AES IRIS Advantage system (Thermo Scientific). The samples were previously filtered using Filtropur cellulose acetate sterile filters (0.45-µm pore size) from Sarstedt Aktlengesellschaft & Co. and acidified to 5 vol % HNO3 before each ICP-AES measurement. 2.4. Materials Carbonation. The carbonation was performed with a gas mixture containing 15.00 vol % CO2 and 85.00 vol % N2 at a gas flow rate of 5 mL/min in the following materials: fresh red mud suspension, the leached hydrated-matrixes, and the leachates collected from three consecutive leachings (section 2.2). The assays were realized at 20 ( 1 °C during 2, 10, 20, and 30 min and 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20, and 24 h according to the material tested, at atmospheric pressure and under an agitation of 200 rpm. The leached hydrated-matrixes extracted from three consecutive leaching steps, were dispersed at the bottom of Pyrex Erlenmeyer flasks to form a uniform layer before carbonation. The CO2 sequestration was made in 250-mL Pyrex Erlenmeyer flasks open to the atmosphere (Figure 1). The CO2 was injected from a gas mixture reservoir, and the gas flow rate was controlled by using a flowmeter with a stainless steel float from Cole-Parmer Instrument Co. (Vernon Hills, IL). The uniform repartition of gas in the aqueous red mud suspension, leachates, and hydrated-matrixes was assumed by using a porous diffuser located within each suspension and leachate or in the Erlenmeyer flasks for the leached hydratedmatrixes. The pH and electrolytical conductivity were measured
Ind. Eng. Chem. Res., Vol. 47, No. 20, 2008 7619 Table 2. Acidic Neutralizing Capacities of Red Mud Suspension, Leached Hydrated-Matrix, and Leachates
material
acidic neutralizing capacitya (mol of HNO3/kg of red mud)
fresh red mud suspension leached hydrated-matrix leachate
0.32 0.13 0.24
a The acidic neutralizing capacity was measured at pH 8.3 in 10.0 ( 0.1 g of fresh red mud suspension in 100 mL of deionized water; mixture of 10.0 ( 0.1 g of leached hydrated-matrix and 100 mL deionized water; 100 mL of leachate, after a titration with HNO3 1 N.
according to the techniques described in section 2.3, and the content of carbon was measured in each sample using an Apollo 9000 TOC Combustion Analyzer from Dohrmann Division Co. (Santa Clara, CA). The carbon analysis were made using a furnace with a continuous flux of oxygen at 800 °C for combustion and a tube containing cobalt oxide on alumina for catalysis. The analyzer was calibrated with a solution of potassium biphthalate at an organic carbon concentration of 2000 ppm. The concentrations in organic carbon of red mud suspension and leachates were measured after the injections of 20-40 µL while the values for hydrated-matrixes were measured after the injections of amounts of hydrated-matrixes corresponding to 10-40 µL of nonhydrated matrixes. The fresh red mud suspension and leachates were stirred with a magnetic stir-bar at 500 rpm before the measurements, and the amounts of hydrated-matrixes analyzed were weighed using an analytic balance. The concentrations in organic carbon of fresh red mud suspension, leachates, and leached hydrated-matrixes were evaluated by subtraction of the amounts of carbon measured before and after the carbonation of these samples. The samples were discarded after each analysis. 3. Results and Discussion 3.1. Determination of the Acidic Neutralizing Capacities of Fresh Red Mud and Its Leached Hydrated-Matrix and Leachate. The acidic neutralizing capacities of fresh red mud and its leached hydrated-matrix and leachate, which were measured by titration at pH 8.3 (pH of a CaCO3 saturated solution in equilibrium with atmospheric air), are indicated in Table 2.15 These results indicate that the acidic neutralizing capacity of the fresh red mud is 0.32 mol of HNO3/kg of red mud. According to these results, the red mud has a carbonation capacity of 0.007 kg of CO2/kg of red mud, which is low as compared to the total theoretical carbonation capacity based on the calcium total composition, and which is evaluated at 0.056 kg of CO2/kg of red mud (Table 1). This value indicates that the red mud contains a small amount of calcium (12.5 wt % of total calcium) leachable in water and for carbonation at ambient conditions (20 ( 1 °C and atmospheric pressure). Therefore, most of the portlandite remains in the matrix at the leaching. In addition, the results shown in Table 2 also indicate that the total acidic neutralizing capacity (leached hydrated-matrix + leachate) is comparable to that observed for fresh red mud. This suggests that the separation of matrix and leachate does not cause a loss of alkalinity in the red mud suspension. However, ∼75% of the acidic neutralizing capacity of the fresh red mud suspension was transferred to leachate during the leaching. 3.2. Determination of pH, Electrolytical Conductivity, and Concentrations of Reactive Elements Liberated during the Leaching of Red Mud. The variations of pH and conductivity of fresh red mud suspension and the maximal concentrations of elements released during the leaching are
Figure 2. Variation of pH (A), and electrolytical conductivity (B) as afunction of leaching time of aqueous fresh red mud suspension. The results were measured after the leaching of red mud suspension at an agitation of 300 rpm, atmospheric pressure, and 20 ( 1 °C. Table 3. Maximal Concentrations of Reactive Elements Leached in the Red Mud Suspension reactive element Ca Na K Mg Fe Mn Pb Zn Cu Al Cd Ni Cr
concentration (mg/L)a 10.23 330.6 8.47 0.0004 0.01 0 0.41 0.04 0.01 172.9 0 0.01 0.16
a The leaching was effectuated in deionized water at 20 ( 1 °C under an agitation of 300 rpm during 24 h at atmospheric pressure.
indicated in Figure 2 and Table 3. The curves presented in Figure 2 show a rapid leaching of elements where the pH and electrolytical conductivity reach maximal values at 120 min. These results, combined with those of Table 3, suggest that red mud matrix can easily leach a large part of its sodium, aluminum, and hydroxyl ions during the leaching in water at 20 ( 1 °C and atmospheric pressure. The sodium and aluminum (hydr)oxides, and probably other aluminum-containing mineral phases (reaction 5) leached, may also be responsible of the high pH and in part of the high
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Figure 3. Variation of carbonation (A), variation of pH (B), and electrolytical conductivity (C) in aqueous fresh red mud suspension effectuated with a 15.00 vol % CO2/N2 mixture and measured at a CO2 flow rate of 5 mL/min, an agitation of 200 rpm, atmospheric pressure, and 20 ( 1 °C.
electrolytical conductivity values that were measured after a leaching of 24 h (Figure 2, Table 3). 3.3. Determination of the Carbonation Capacities of Fresh Red Mud Suspension and Its Leached HydratedMatrixes and Leachates. The variations of CO2 captured, pH, and electrolytical conductivities that have been measured during the carbonation of fresh red mud suspension, three leachates, and three leached hydrated-matrixes are presented in Figures 3-5 and Table 4. The data shown in Figures 3A and 4A and Table 4 indicate that the carbonation of fresh red mud suspension, leachates, and leached hydrated-matrixes rapidly reach the maximal capacities of 4.15; 1.88, 0.75, and 0.40 (first, second, and third leachates) and 1.95, 1.46, and 0.65 g of CO2/100 g of red mud (first, second, and third leached hydrated-matrixes),
Figure 4. Variation of carbonation (A), variation of pH (B), and electrolytical conductivity (C) in first (b) and second (9) leachates of red mud effectuated with a 15.00 vol % CO2/N2 mixture and measured at a CO2 flow rate of 5 mL/min, an agitation of 200 rpm, atmospheric pressure, and 20 ( 1 °C.
respectively. These results may be attributed in large part to the carbonation of portlandite and Na-(hydr)oxide present in the matrix that may be responsible for the CO2 sequestration in the matrix, and which may produce the carbonate and bicarbonate species. However, the great leaching of Na-(hydr)oxide may also be associated with the lose of 53% of the carbonation capacity that occurred in the matrix during the leaching, as well as the carbonation capacities of leachates. The carbonation of red mud suspension, leachates, and leached hydrated-matrixes is accompanied by a rapid decrease of about 4, 5, and 2 pH units, respectively, and a reduction of their electrolytical conductivity values (Figures 3B and C and 4B and C, and Table 4). These effects may be explained by the
Ind. Eng. Chem. Res., Vol. 47, No. 20, 2008 7621 Table 4. Results for pH, Electrolytical Conductivity, and Carbonation Capacities of Suspension, Leached Hydrated-Matrixes, and Leachates of Red Mud electrolyticala conductivity (mS/cm)
pHa material
initial
final
initial
final
fresh red mud suspension 1st leachate 2nd leachate 3rd leachate 1st leached hydrated-matrix 2nd leached hydrated-matrix 3rd leached hydrated-matrix
11.92 12.62 12.10 10.09 12.32 12.20 12.14
7.57 7.60 7.25 7.18 9.44 9.78 9.76
5.07 4.75 1.93 1.30
4.74 2.68 1.09 0.63
carbonation capacitya (g of CO2/100 g of red mud) 4.15 1.88 0.75 0.40 1.95 1.46 0.65
a The carbonation was performed with a 15.00 vol % CO2/N2 mixture at a flow of 5 mL/min and 20 ( 1 °C under an agitation of 200 rpm at atmospheric pressure.
In parallel, the addition of carbonation capacities of three leachates and leached hydrated-matrixes from red mud give a carbonation capacity (7.09 g of CO2/100 g of red mud) that is 1.7 times higher than the value obtained for fresh red mud suspension (Table 4). This result suggests that leachates and matrixes from this red mud are more effective to uptake the CO2 when they are separated. This difference of carbonation capacities may be due to greater exposure of CO2 binding sites of the matrix when it is separated from the leachate. 4. Conclusions
Figure 5. Variation of carbonation (A) and variation of pH (B) in first (b) and second (9) leached hydrated-matrixes of red mud effectuated with a 15.00 vol % CO2/N2 mixture and measured at a CO2 flow rate of 5 mL/ min, an agitation of 200 rpm, atmospheric pressure, and 20 ( 1 °C.
formation of carbonate and bicarbonate species and HCO3-. The rapid decrease of pH and the neutral values reached during the carbonation of red mud suspension and leachates indicate that the majority of Ca- and Na-(hydr)oxides were rapidly neutralized to form carbonate and bicarbonate species. In the case of the leached hydrated-matrixes carbonation, the final values of pH >9 may be associated with an incomplete carbonation of the content in hydroxides. In this case, the formation of a carbonate layer at the surface of the matrixes and the dispersal of leached hydrated-matrixes at the bottom of Pyrex Erlenmeyer flasks, which may restrict the carbonation of the exposed surfaces of matrixes, can limit the accessibility to CO2 binding sites and decrease the carbonation potentials of hydrated-matrixes.16,17
This study has show that the aqueous red mud suspension at a liquid-to-solid ratio of 10 kg/kg has a carbonation capacity of 4 g of CO2/100 g of red mud at ambient conditions (temperature of 20 ( 1 °C and atmospheric pressure), which is attributed to a complete carbonation of its contents of Ca- and Na-(hydr)oxides. The red mud matrix has a great leaching capacity of Na-(hydr)oxide that seems to be the major hydroxide implicated in the complete carbonation of leachates. This great leaching capacity of Na-(hydr)oxide permits the the first leachate to have about half-carbonation capacity of the fresh red mud. However, the leached hydrated-matrixes also preserve about half-carbonation capacity of the aqueous red mud suspension, which be due to the carbonation of Na-(hydr)oxide and portlandite. Finally, the separation of three leachates and hydrated-matrixes from three successive leaching also may increase the carbonation capacity of the red mud as compared to its aqueous suspension. Altogether, the results from the present study have indicated that the red mud carbonation at ambient conditions (temperature of 20 ( 1 °C and atmospheric pressure) could present an effective option for the CO2 sequestration in aluminum manufacturers. More particularly, the alternated carbonation of the separated leached hydrated-matrixes and leachates from red mud could constitute a more effective method for the CO2 sequestration than the use of aqueous red mud suspension. In this context, the use of a cyclic system where the leachate is generated by the washing of red mud matrix in a first reactor followed by carbonation in a second reactor could increase the quantities of carbonate and bicarbonate and carbonated red mud. The use of this type of system could thus become a source of additional income for aluminum manufacturers and reduce environmental problems associated with red mud storage. Acknowledgment This work was supported by the grants from Natural Resources Canada in collaboration with Alcan Inc. Ste´phane Gauthier, Luc Fortin, and Johann Friedrich are also acknowl-
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edged for providing the red mud and information about aluminum processing. Literature Cited (1) Cooling, D. J. ; Hay, P. S.; Guilfoyle, L. Carbonation of bauxite residue In Proceeding of the 6th International Alumina Quality Workshop 2002, 185, 190. (2) Hind, A. R.; Bhargava, S. K.; Grocotte, S. C. The surface chemistry of Bayer process solids: a review. Colloids Surf., A: Physicochem. Eng. Aspects 1999, 146 (1-3), 359–374. (3) Agrawal, A.; Sahu, K. K.; Pandy, B. D. Solid waste management in non-ferrous industries in India. Resources ConserV. Recycl. 2004, 42 (2), 99–120. (4) Yang, J.; Xiao, B. Development of unsintered construction materials from red mud wastes produced in the sintering alumina process. Construct. Build. Mater. In press. (5) Forte´, G. Composition typique du sous-produit de l’extraction de l’alumine a` partir de la bauxite, commune´ment appele´ boue rouge. Alcan International Lte´e, CRDA. (6) Brunori, C.; Cremisini, C.; Massanisso, P.; Pinto, V.; Torricelli, L. Reuse of a treated red mud bauxite waste: studies on environmental compatibility. J. Hazard. Mater. B 2005, 117 (1), 55–63. (7) Roberge, G.; Blais, J. F.; Mercier, G. Enle`vement du phosphore des eaux use´es par traitement a` base de tourbe dope´e aux boues rouges. Can. J. Chem. Eng. 1999, 77, 1185–1194. (8) Genc¸, H.; Tjell, J. C.; McConchie, D.; Schuiling, O. Adsorption of arsenate from water using neutralized red mud. J. Colloid Interface Sci. 2003, 264 (2), 327–334.
(9) Zouboulis, A. I.; Kydros, K. A.; Matis, K. A. Removal of toxic metalions from solutions using industrial solid by-products. Water Sci. Technol. 1993, 27, 83–93. (10) Cabeza, M. ; Collazo, A.; No´voa, X. R.; Pe´rez, M. C. Red mud as a corrosion inhibitor for reinforced concrete JCSE: J. Corros. Sci. Eng. 2003, 6, Conference Paper C077, Preprint 32. (11) Wang, S.; Choueib, B. A.; Zhu, Z. H. Removal of dyes from aqueous solution using fly ash and red mud. Water Res. 2005, 39 (1), 129– 138. (12) Gupta, V. K.; Sharma, S. Removal of cadmium and zinc from aqueous solutions using red mud. EnViron. Sci. Technol. 2002, 36 (16), 3612–3617. (13) Lamonier, J. F.; Wyrwalski, F.; Laclerq, G.; Aboukaı¨s, A. Recyclage d’un de´chet, une boue rouge, comme catalyseur pour l′e´limination des compose´es organiques volatiles. Can. J. Chem. Eng. 2005, 83, 737–741. (14) Huijgen, W. J. J.; Witkamp, G.-J.; Comans, R. N. J. Mineral CO2 Sequestration by Steel Slag Carbonation. EnViron. Sci. Technol. 2005, 39 (24), 9676–9682. (15) Standard Methods for the Examination of Water and Wastewater, 16th ed.; American Public Health Association, American Water Works Association and Water Pollution Control Federation. Washington, DC, 1985. (16) Gupta, H.; Fan, L.-S. Carbonation-Calcination Cycle Using High Reactivity Calcium Oxide for Carbon Dioxide Separation from Flue Gas. Ind. Eng. Chem. Res. 2002, 41 (16), 4035–4042. (17) Oakeson, W. G.; Cutler, I. B. Effect of CO2 Pressure on the Reaction with CaO. J. Am. Ceram. Soc. 1979, 62 (11-12), 556–558.
ReceiVed for reView December 17, 2007 ReVised manuscript receiVed July 24, 2008 Accepted July 28, 2008 IE7017228
