O in the Fe(II) + Mg + Ca + K + Cl + H - American Chemical Society

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Solubility of AlCl3•6H2O in the Fe(II)+Mg+Ca+K+Cl+H2O System and Its Salting-out Crystallization with FeCl2 Wencheng Gao, Zhibao Li, and Edouard Asselin Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie401850a • Publication Date (Web): 11 Sep 2013 Downloaded from http://pubs.acs.org on September 12, 2013

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Industrial & Engineering Chemistry Research

Solubility of AlCl3·6H2O in the Fe(II)+Mg+Ca+K+Cl+H2O System and Its Salting-out Crystallization with FeCl2 Wencheng Gao and Zhibao Li*

Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China

Edouard Asselin

Department of Materials Engineering, The University of British Columbia, Vancouver, B.C., Canada V6T 1Z4

ABSTRACT: Phase equilibria determination for the Al+Fe(II)+Mg+Ca+K+Cl+H2O system showed that FeCl2 is effective to promote the salting-out crystallization of AlCl3·6H2O. A novel process to recover AlCl3·6H2O from fly ash by salting-out crystallization with FeCl2 is proposed and proven feasible. This novel process includes leaching of fly ash by hydrochloric acid; reduction of Fe3+ to Formatted: Font color: Auto

Fe2+; salting-out crystallization of AlCl3·6H2O with FeCl2 and filtering followed by washing. The solubility of AlCl3·6H2O in the Fe(II)+Mg+Ca+K+Cl+H2O system was determined over the entire practical concentration range and from 283.2 to 363.2 K using a dynamic method. The experimental solubilities were regressed to obtain new mixed solvent electrolyte (MSE) model parameters. These new parameters were capable of accurately representing the experimental data of the system from 283.2 to 343.2 K. The phase diagram of the ternary AlCl3-FeCl2-H2O system at 298.2 and 333.2 K was successfully constructed with the aid of the new MSE model parameters. Based on the phase 1

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diagram, a promising route to recover AlCl3·6H2O by salting-out crystallization with FeCl2 was generated and verified feasible in laboratory experiments. All the results generated from this study will provide fundamental data for industrial applications aimed at the recovery of alumina from fly ash resources.

1. INTRODUCTION There is a growing interest in recovering alumina from the abundant industrial by-product fly ash1 Formatted: Font color: Auto

(about 10 billion tons produced per annum in China) due to an imminent shortage of high-grade bauxite around the world. Fly ash is a pollutant generated during the combustion of coal for energy production and it causes several environmental problems2-4 especially related to its fine particle content, which is ~10% by mass (EPA designated PM2.5)5-7. Among the major phases typically contained in fly ash are 15-40% Al2O3, 34-66% SiO2, 1.5-6% Fe2O3, 0.2-4% MgO, 0.4-3.0% CaO and 0.2-2.5% K2O. In an attempt to convert fly ash into value added products, thus substituting utilization

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for disposal, a considerable amount of research has looked at extracting its alumina content.8-15 The

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recovery of alumina from fly ash occurs through hydrometallurgical processes involving acid or alkali


leaching, precipitation, solvent extraction, crystallization and re-crystallization.15-17 Hydrochloric acid leaching of low grade aluminum resources for the production of alumina has a long history of development18-21. For example, the U.S. Bureau of Mines conducted a series of studies to recover alumina by calcination of AlCl3·6H2O obtained from HCl acid leaching of clay.22-27 In their process, Formatted: Font color: Auto

calcined clay is leached with 8-12 mol·L-1 HCl and the clarified liquor is treated by oxidation (Fe2+→ Fe3+) and solvent extraction to remove iron. The purified pregnant liquor is then evaporated to increase the AlCl3 concentration. To facilitate its precipitation as the hexahydrate, the activity of

2


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AlCl3 is increased by injection of HCl gas. As an alternative, the AlCl3 solution can be used directly to produce high-quality Mg-Al spinel.28 However, this process is not without challenges.

For

example, there are environmental and capital cost concerns surrounding the use of concentrated HCl in the AlCl3·6H2O crystallization step and there are also extra costs related to the use of the organic phase in the solvent extraction step. To overcome these drawbacks, a novel process to recover AlCl3·6H2O from fly ash by salting-out crystallization with FeCl2 is thus proposed herein, as shown in Figure 1. This process would consist of: (1) Leaching. The fly ash is leached by hydrochloric acid; (2) Reduction. After leaching, the clarified liquor is treated by reduction (Fe3+→Fe2+) with the addition of iron filings; (3) Salting-out crystallization. The purified pregnant leach solution is evaporated and AlCl3·6H2O is crystallized by salting-out crystallization in a controlled range of Fe2+ concentration (< ~2.0 mol·kg-1 at 333.2 K). When Fe2+ has accumulated to a certain amount, a bleed stream of liquor is removed and diluted for FeCl2·4H2O separation through cooling and crystallization; (4) Filtering and Formatted: Font color: Auto

washing. The obtained AlCl3·6H2O is separated from the liquor by filtering and washing. The wash solutions are adjusted to give the correct amount of HCl for leaching in the next cycle. It is well known that the solubility of crystals in aqueous solutions plays a significant role in the Formatted: Font color: Auto

development, design, optimization, and operation of crystallization processes29-31. The main impurities existing in the above-described leaching system are FeCl2, MgCl2, CaCl2 and KCl. For a better understanding of the salting-out crystallization of AlCl3·6H2O, it is necessary to further study the phase equilibria in the Al+Fe(II)+Mg+Ca+K+Cl+H2O system. Limited solubility data for this system have been reported in the literature. Christov32 measured the solubility of the AlCl3-MgCl2H2O system at 298.15 K, and we have previously determined the solubility of the AlCl3-MgCl2-H2O

3



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system from 283.2 to 343.2 K28 – neither of these studies sufficiently describes the system at issue in this work. In this article, the determination and modeling of phase equilibria for the Al+Fe(II)+Mg+Ca+K+Cl +H2O system were performed over the entire practical concentration range from 283.2 to 363.2 K. The mixed solvent electrolyte (MSE) model was used to regress new middle-range parameters of ionFormatted: Font color: Auto

ion interactions. The phase diagram of the system was then constructed through comprehensive experimental measurements and the newly established chemical model. The resulting phase diagram


was used to demonstrate how best to operate the salting-out crystallization process. Finally, the feasibility of the proposed process was verified through laboratory tests. All the results generated from this study provide the fundamental information necessary for the recovery of alumina from fly ash resources. 2. EXPERIMENTAL 2.1. Materials. Aluminum chloride hexahydrate (≥ 97.0%, Sinopharm Chemical Reagent Co., Ltd.), iron(II) chloride tetrahydrate (≥ 98.0%, Xilong Chemical Group), magnesium chloride hexahydrate (≥ 98.0%, Xilong Chemical Group), calcium chloride (≥ 96.0%, Beijing Chemical Plant) and potassium chloride (≥ 99.8%, Beijing Chemical Plant) were used without further purification. Distilled water with specific conductivity < 0.1 μS·cm-1 was used. 2.2. Determination of Phase Equilibria. The phase equilibria for the Al+Fe(II)+Mg+Ca+K+Cl+H2O system were determined using the dynamic method from 283.2 to 363.2 K. A similar procedure to that used in the literature28 was adopted and a brief description is given as follows. A 250-mL jacketed glass vessel with a condenser was used. The Fe(II)+Mg+Ca+K+Cl+H2O solution of known


composition was poured into the vessel, and the system was brought to- and maintained at a desired 4


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temperature to within ± 0.1 K using a thermostat. A known mass of AlCl3·6H2O was added into the solvent while magnetic stirring provided agitation. Some time later, if the last trace of solid was observed to disappear, more salt of known mass was added to the vessel. All the chemical reagents were prepared by weighing the pure components with an uncertainly of ± 0.001g. An equilibrium method was employed to determine the multiple points of saturation for the AlCl3FeCl2-H2O system. A known mass of water (~100 g) was introduced to the vessel and preheated to the


desired temperature. Excess AlCl3·6H2O and FeCl2·4H2O were then added to the vessel while magnetic stirring provided agitation. After solid-liquid equilibrium was achieved (the standard equilibrium time was 2 h), stirring was stopped for about 0.5 h to allow any remaining solids to settle. The supernatant solutions were withdrawn with a preheated syringe and immediately filtered into previously weighed 25 mL volumetric flasks, which were kept in the water bath and maintained at the same temperature as the test vessel in order to determine the density of the co-saturated solution. The concentrations of Al3+ and Fe2+ in the co-saturated solution were determined by ICP-AES and the potassium chromate method, respectively. Each reported experimental point is an average of at least three different measurements to reduce the error. 3. CHEMICAL MODELING FRAMEWORK 3.1. Speciation of the Al+Fe(II)+Mg+Ca+K+Cl+H2O System. For the Al+Fe(II)+Mg+Ca+K+


Cl+H2O system there exist a variety of chemical equilibria. For a given chlorinated salt MCl x ⋅ nH 2 O(s) , the equilibrium of dissociation is given by: MCl x ⋅ nH 2 O(s) = M x + + xCl − + nH 2 O

(1)

For reaction (1), the equilibrium constant (KSP) of the dissociation reaction is given as follows: K SP (MCl x ⋅nH 2O) = aM x+ ⋅ aClx − ⋅ aHn 2O = γM x+ ⋅ mM x+ ⋅ γClx − ⋅ mClx − ⋅ aHn 2O

(2) 5



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where ai , mi , γ i represent the activity, concentration in molality and activity coefficient of species i for the dissociation reaction, respectively. In this paper molality-based equilibrium constants for the various species of interest are calculated. 3.2. Equilibrium Constants. The equilibrium constants, calculated from the standard-state thermodynamic data of the equilibrium species, can be written with the following equation: lnK = −

∆RG RT

0

(3) Formatted: Font color: Auto

0

where ∆ R G represents the partial molal, standard-state Gibbs free energy change of reaction at temperature T (in Kelvin), and R denotes the gas constant (8.3145 J·mol-1·K-1).


There are two alternative methods in the OLI software that can be used to calculate equilibrium constants, including the HKF model and an empirical equation. Herein, the HKF model33-35 was used to calculate the standard properties of aqueous species. The alternative empirical equation was adopted to calculate the solubility products of solids in cases where no, or inaccurate, thermodynamic data existed: log K = A +

B + CT + DT 2 T

(4)

where A, B, C, and D are empirical parameters. T represents the temperature (K). Eq. (4) may be Formatted: Font color: Auto

applied to calculate the solubility product, and the four empirical parameters can be obtained via


fitting to experimentally measured solubility data of a pure salt in water. 3.2. Activity Coefficient Model. In this work, the more recently developed mixed solvent electrolyte (MSE) model36-38, included in the OLI platform, was used to calculate activity coefficients


of aqueous species. This model has already been proven accurate in calculating the properties of multi-component solutions generated from hydrometallurgical processes.39-42 6


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The MSE model is constructed on the basis of an excess Gibbs energy model for a mixed-solvent electrolyte, which is expressed as follows37: E GE GE G E GLR = + MR + SR RT RT RT RT

(5)

E where GLR denotes the contribution of long-range electrostatic interactions expressed by the Pitzer-

E represents the short-range contribution resulting from moleculeDebye-Hückel equation; GSR

molecule, molecule-ion, and ion-ion interaction calculated by the UNIQUAC model; and an E additional middle-range term GMR accounts for ionic interactions that are not included in the long-

E range term. GMR is calculated from a symmetrical second-virial coefficient-type expression: E GMR   = —  ∑ ni ∑∑ xi x j Bij (I x ) RT  i  i j

(6)

where x is the mole fraction of the species, I x represents the ionic strength, Bij is a binary interaction parameter between the species i and j (ion or molecule), and Bij ( I x ) = B ji ( I x ) , Bii ( I x ) = B jj ( I x ) = 0 . Bij is a function of ionic strength represented by the following empirical expression: Bij ( I x ) = bij + cij exp( — I x + a1 )

(7)

where bij and cij account for binary interaction. a1 is set equal to 0.01 according to Gruszkiewicz et al.43, bij and cij are calculated as functions of temperature by bij = b0,ij + b1,ij T + b2,ij /T + b3,ij T 2 + b4,ij lnT

(8)

cij = c0,ij + c1,ij T + c 2,ij /T + c3,ij T 2 + c 4,ij lnT

(9)

where bk ,ij and c k ,ij (k=0-4) are adjustable interaction parameters between species i and j that can be obtained by the regression of experimental results. In the MSE model, the middle-range parameters are used primarily for ion-ion and ion-neutral molecule interaction and the short-range parameters are for neutral-neutral interaction. Ions dominate in 7



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the Al+Fe(II)+Mg+Ca+K+Cl+H2O system of interest, so only the middle-range parameters were used


for regression. 4. RESULTS AND DISCUSSION 4.1. Solubility in the Al+Fe(II)+Mg+Ca+K+Cl+H2O System. The solubility of the ternary AlCl3-FeCl2-H2O system was experimentally measured from 283.2 to 343.2 K and throughout the full concentration range. The solubility data are tabulated in Table 1 and shown in Figure 2. It is clear that the solubility of AlCl3·6H2O increases a little with temperature and decreases gradually with an Formatted: Font color: Auto

increase in FeCl2 molality. The FeCl2·4H2O solubility increases with temperature over the investigated range, and decreases gradually with increasing AlCl3 molality across the entire concentration range. For the ternary AlCl3-MgCl2-H2O system, the AlCl3 solubility data reported in


our previous work28 are displayed in Figure 3. These data were used in model parameter regression,


which is discussed in the following section.


For the ternary AlCl3-CaCl2-H2O system, the measured solubility of AlCl3 in CaCl2 solution from 283.2 to 343.2 K is listed in Table 2 and shown in Figure 4. It is obvious that the solubility of AlCl3 decreases gradually with the concentration of CaCl2, which has the same trend in variation as the FeCl2 solution. For the ternary AlCl3-KCl-H2O system, the KCl solubility in AlCl3 solution from


283.2 to 363.2 K are presented in Table 3 and shown in Figure 5. It is found that the common ion effect decreases the solubility of KCl with AlCl3 molality up to 3.0 mol·kg-1. 4.2. Model Parameterization. The capability of the existing MSE model parameters for predicting


the system solubility should be tested before usage39-42. The solubility data of the AlCl3-HCl-H2O44-45,


FeCl2-H2O45, MgCl2-H2O45, CaCl2-H2O45 and KCl-H2O45 systems from 283.2 to 363.2 K are compared with model predictions in Figures 6–7. It is found that the MSE default parameters 8


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reasonably reproduce the solubility of AlCl3, FeCl2, MgCl2, CaCl2 and KCl. However, the solubility of the Al+Fe(II)+Mg+Ca+K+Cl+H2O system cannot be predicted because the Al3+-Fe2+, Al3+-Mg2+, Al3+-Ca2+ and Al3+-K+ interactions are not currently parameterized in the MSE default database. Therefore, to improve the default databank, new MSE model parameters for these interactions (as well as for the Fe2+-Cl- interaction) were determined via regression of the solubility of the ternary Formatted: Font color: Auto 44, 45

systems obtained in this work and from the literature

.

The new MSE ion interaction parameters are presented in Table 4, and the regressed results are also shown in Figures 3–7, respectively. All the regressed solubility data agree well with the experimental values. Figures 8–11 show that most of the deviations for the ternary AlCl3-FeCl2-H2O, AlCl3-MgCl2H2O, AlCl3-CaCl2-H2O, and AlCl3-KCl-H2O systems are less than 10%, indicating that the newly obtained parameters are capable of accurately representing experimental data. The multiple points of saturation for the ternary AlCl3-FeCl2-H2O system were then predicted from 283.2 to 333.2 K using the new parameters. As can be seen from Figure 8, the predictions are in good agreement with experimental values, and the largest deviations are less than 5%. 4.3. Conceptual Process for AlCl3·6H2O Salting-out Crystallization with FeCl2. With the newly established model, the phase diagram of the ternary AlCl3-FeCl2-H2O system can be constructed. The isothermal mutual solubility of AlCl3 and FeCl2 is plotted in Figure 12. All the solution compositions in equilibrium with solid AlCl3·6H2O at 333.2 K are shown on line AB.

All the solution Formatted: Font color: Auto

compositions in equilibrium with solid FeCl2·4H2O at 333.2 K are shown on line BC. If both solid phases, AlCl3·6H2O and FeCl2·4H2O, are present the solution composition at equilibrium can only be represented by point B, which is the point of co-saturation or the invariant point (at constant pressure). The isotherms show a marked decrease in solubility for each component as the amount of the other is 9



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increased. By connecting all the co-saturated points together from 283.2 to 333.2 K, the mixed-salt line, EB, is obtained. The locus of line EB is an important consideration in subsequent FeCl2·4H2O separations. A typical separation of FeCl2·4H2O from AlCl3·6H2O by salting-out crystallization can be represented as follows. Starting with an AlCl3 solution at 298.2 K, a small amount of FeCl2·4H2O is added and dissolved (at point G, area ODE) to ensure that the initially precipitated solids are AlCl3·6H2O. The solution is then concentrated by heating to- and evaporation at 333.2 K. During this process, the solution will increase in concentration with respect to both components until point H is reached. AlCl3·6H2O will then crystallize and the solution will become more concentrated in FeCl2, as indicated by line HI (point I is very close to point B), until point B is reached. After that, the AlCl3·6H2O crystals can be harvested from the liquor by filtering and washing. After solid/liquid separation at point B, a certain amount of water is added to dissolve any traces of solid phase that may be present. Evaporative cooling along line JE results in the crystallization of


FeCl2·4H2O. During this evaporative cooling, part of the water evaporated must be added back to the solution to prevent the co-precipitation of AlCl3·6H2O. After this, the solution is diluted by the feed AlCl3 solution until the original point G is reached for the next cycle. 4.4. Preliminary Testing of AlCl3·6H2O Salting-out Crystallization with FeCl2. AlCl3·6H2O crystallization was successfully carried out in batch operation using a 2-L jacketed stirred glass reactor. A typical experimental procedure follows. A 3.0 mol·kg-1 AlCl3 solution at 298.2 K was first introduced into the vessel with stirring at 200 rpm. FeCl2·4H2O was then added to the solution until the FeCl2 concentration reached about 0.20~1.0 mol·kg-1. The solution was then heated to 333.2 K by circulating water through the reactor’s jacket. Through the resulting evaporation the solution was 10



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concentrated and AlCl3·6H2O was crystallized using the salting-out effect generated by FeCl2 addition. When the co-saturation point (AlCl3 3.28 mol·kg-1; FeCl2 1.90 mol·kg-1) was reached the solid was collected, immediately filtered at 333.2 K, washed at least three times to remove any solution remnants and dried at 363.2 K for about 12 h. The filtrate was then poured back into the vessel and some water (about 8.64% wt/wt of the water in the filtrate) was added to the solution. The solution was then slowly cooled by circulating water at 298.2 K through the reactor’s jacket. When the temperature reached 298.2 K the FeCl2·4H2O was crystallized. X-Ray diffractograms and images of the particles are shown in Figures 13–14, respectively. The chemical composition of the AlCl3·6H2O obtained through the above procedure was determined by titration with standard EDTA solutions and ICP-AES. The purity of the AlCl3·6H2O sample was ~97.3%, which satisfies the requirement for calcination to alumina. 4.5. Use of the Model. The evaporation process was simulated with the newly parameterized model and the calculated results are given as follows. 0.20 kg FeCl2·4H2O was added to an initial solution of 3.0 mol·kg-1 AlCl3, containing 0.40 kg AlCl3 and 1.0 kg H2O at 298.2 K. Heating to 333.2 K resulted in the evaporation of 0.17 kg of H2O whereupon the AlCl3·6H2O began to crystallize. A further 0.29 kg of H2O was evaporated up until the moment that FeCl2·4H2O began to form. At the end of this single cycle, ~0.42 kg AlCl3·6H2O was obtained, yielding a recovery 57.3%. The mass balances for the main components were also calculated. For a plant producing 10,000 t per year of alumina (net), the mass of required feed solution would be 158,000 t and the evaporated water would be approximately 52,000 t. The amount of AlCl3·6H2O produced would be close to 47,000 tons. 5. CONCLUSIONS 11





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The solubility of AlCl3·6H2O in the Fe(II)+Mg+Ca+K+Cl+H2O system was determined from 283.2 to 343.2 K throughout the entire concentration range. Based on these solubility data, a chemical model for the Al+Fe(II)+Mg+Ca+K+Cl+H2O system was developed with a new parameterization for the MSE model in the OLI platform. The new model was found to accurately represent phase equilibria in the Al+Fe(II)+Mg+Ca+K+Cl+H2O system and was used to construct the phase diagram for the ternary AlCl3-FeCl2-H2O system from 283.2 to 333.2 K. Based on this phase diagram, a novel process to recover AlCl3·6H2O through salting-out crystallization with FeCl2 was proposed. This novel separation process was validated by batch experiments and may provide an efficient means to separate pure AlCl3·6H2O from fly ash leach solutions. AUTHOR INFORMATION Corresponding Author *

Tel./Fax: +86-10-62551557. E-mail: [email protected].

ACKNOWLEDGEMENTS The authors are grateful for the support of the National Natural Science Foundation of China (Grant No. 21146006 and 21206165) and the National Basic Research Development Program of China (973 Program with Grant No. 2013CB632605). NOTATIONS a = the activity; parameter for eq. 7 A = empirical parameter of log K b = parameter for eq. 7 B = empirical parameter of log K

Bij = a binary interaction parameter between the species i and j c = parameter for eq. 7 12


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C= empirical parameter of log K D = empirical parameter of log K 0

∆ R G = the partial molal, standard-state Gibbs free energy change G E = excess Gibbs energy E GLR = the contribution of long-range electrostatic interactions

E = the short-range contribution resulting from molecule-molecule, molecule-ion, and ion-ion GSR

interaction E GMR = middle-range term accounts for ionic interactions

I x = the ionic strength

m = concentration in molality, mol·kg-1 R = universal gas constant, 8.3145 J·mol-1·K-1 T = absolute temperature, K γ = activity coefficient of species x = the mole fraction of the species

Subscripts and Superscripts i, j = species(ion or molecule) cal = the calculated data exp = the experimental data lit = the literature data 0 = standard state REFERENCES (1) Zhang, D.; Zhou, C. H.; Lin, C. X.; Tong D. S.; Yu, W. H. Synthesis of clay minerals. Appl. Clay Sci. 2010, 50, 1−11. (2) Ahmaruzzaman, M. A review on the utilization of fly ash. Prog. Energy Combust. Sci. 2010, 36, 327−363. (3) Blissett, R. S.; Rowson, N. A. A review of the multi-component utilization of coal fly ash. Fuel 13



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2012, 97, 1−23. (4) Izquierdo, M.; Querol, X. Leaching behavior of elements from coal combustion fly ash: an overview. Int. J. Coal Geol. 2011, 94, 54−66. (5) Zheng, M.; Salmon, L. G.; Schauer, J. J.; Zeng, L.; Kiang, C. S.; Zhang Y.; Cass, G. R. Seasonal trends in PM2.5 source contributions in Beijing, China. Atmos. Environ. 2005, 39, 3967−3976. (6) Gu, J.; Bai, Z.; Li, W.; Wu, L.; Liu, A.; Dong, H.; Xie, Y. Chemical composition of PM2.5 during winter in Tianjin, China. Particuology 2011, 9, 215-221. (7) Wang, J.; Hu, Z.; Chen, Y.; Chen, Z.; Xu, S. Contamination characteristics and possible sources of PM10 and PM2.5 in different functional areas of Shanghai, China. Atmos. Environ. 2013, 38, 221−229. (8) Seidel, A.; Sluszny, A.; Zimmels, S. Y. Self inhibition of aluminum leaching from coal fly ash by sulfuric acid. Chem. Eng. J. 1999, 72, 195−207. (9) Balanco, F.; Garcia, M. P.; Ayala, J. Variation in fly ash properties with milling and acid leaching. Fuel 2005, 84, 89−96. (10) Ngagib, S.; Inoue, K. Recovery of lead and zinc from fly ash generated from municipal incineration plants by means of acid and /or alkaline leaching. Hydrometallurgy 2000, 56, 269−292. (11) Zhang, F. S.; Itoh, H. Extraction of metals from municipal solid waste incinerator fly ash by hydrothermal process. J. Hazard. Mater. 2006, B136, 663−670. (12) Iyer, R. S.; Scott, J. A. Power station fly ash – review of value-added utilization outside of the construction industry. Resour. Conserv. Recy. 2001, 31, 217−228. (13) Jackson, E. Hydrometallurgical Extraction and Reclamation. Ellis Horwood Ltd., John Wiley and sons, New York, 1986, pp 29−70, 109−137, 145−169. (14) Shemi, A.; Mpana, R. N.; Ndlovu, S.; van Dyk, L. D.; Sibanda, V.; Seepe, L. Alternative techniques for extracting alumina from coal fly ash. Miner. Eng. 2012, 34, 30−37. (15) Matjie, R. H.; Bunt. J. R.; van Heerden, J. H. P. Extraction of alumina from coal fly ash generated from a selected low rank bituminous South African coal. Miner. Eng. 2005, 18, 299−310. (16) Phillips, C. V.; Wills, K. J. Laboratory study of the extraction of Al2O3 of Smelter grade from China clay micaceous residues by a nitric acid route. Hydrometallurgy 1982, 9, 15−28. 14


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(17) Alquacil, F. J.; Amer, S.; Luis, A. The application of Primene 81R for the purification of concentrated aluminum sulphate solution from leaching of clay minerals. Hydrometallurgy 1987, 18, 75−92. (18) Hoffman, J. I.; Leslie, R. T.; Caul, H. J.; Clark, L. J.; Hoffman, J. D. Development of a Hydrochloric acid process for the production of alumina from clay. J. Res. NBS. 1946, 37, 409−428. (19) Clark, L. J.; Hubbard, W. D.; Hoffman, J. I. Crystallization of aluminum chloride in the hydrochloric acid process for production of alumina from clay. J. Res. NBS. 1951, 4, 269−271. (20) Golden, D. M.; Wilder, R. P. High value products from fly ash: new metal recovery. Marketing opportunities, US department Energy, Morgantown Energy Technology Center (Report) DOE METC 85−6018, vol. 2. Morgantown, WV, USA, 1985, 733−752. (21) Kim, A. G.; Hesbach, P. Comparison of fly ash leaching methods. Fuel 2009, 88, 926−937. (22) Bengston, K. B.; Chaberka, P.; Nunn, R. F.; San Jose, A. V.; Manarolls, G. M.; Malm, L. E. Alumina process feasibility study and preliminary pilot plant design. Task 3 report: Preliminary design of 25 ton per day pilot plant, vol. 1, Process Technology and Costs. BuMines Open File Rept. PB81-125301. 1979, p231. (23) Eisele, J. A. Producing alumina from clay by the hydrochloric acid process, a bench-scale study. BuMines RI 8476. 1980, p20. (24) Maysilles, J. H.; Traut, D. E.; Sawyer, D. L. Jr. Aluminum chloride hexahydrate crystallization by HCl gas sparging, Alumina recovery by the clay/hydrochloric acid process. BuMines RI 8590. 1984, p20. (25) Poppleton, H. O.; Sawyer, D. L. Hydrochloric acid leaching of calcined kaolin to produce alumina. In: Light Metals. Warrendale, PA: TMS Light Metals Committee. Metallurgical Society of AIME, 1977, pp103−114. (26) Shanks, D. E.; Eisele, J. A.; Bauer, D. J. Hydrogen chloride sparging crystallization of aluminum chloride hexahydrate. BuMines RI 8593. 1981, p15. (27) Eiseie, J. A.; Bauer, D. J.; Shanks, D.E. Bench-scale studies to recover alumina from clay by a hydrochloric acid process. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 105−110. (28) Gao, W.; Li, Z. A practical approach to produce Mg-Al spinel based on the modeling of phase equilibria for NH4Cl−MgCl2−AlCl3−H2O system. AIChE J. 2013, 59, 1855−1867. 15



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(29) Sangwal, K. Recent developments in understanding of the metastable zone width of different solute-solvent systems. J. Cryst. Growth 2011, 318, 103−109. (30) Rabesiaka, M.; Porte, C.; Bonnin-Paris, J.; Havet, J-L. An automatic method for the determination of saturation curve and metastable zone width of lysine monohydrochloride. J. Cryst. Growth 2011, 332, 75−80. (31) Mahoney, L.; Rapko, B.; Schonewill, P. Modeling the sodium recovery resulting from using concentrated caustic for boehmite dissolution. Ind. Eng. Chem. Res. 2011, 50, 11570–11575. (32) Christov, C. Thermodynamic study of the K-Mg-Al-Cl-SO4-H2O system at the temperature 298.15 K. Calphad. 2001, 25, 445−454. (33) Helgeson, H. C.; Kirkham, D. H.; Flowers, G. C. Theoretical prediction of the thermodynamic behavior of aqueous electrolytes at high pressures and temperatures. IV. Calculation of activity coefficients, osmotic coefficients, and apparent molar and standard and relative partial molar properties to 600oC and 5 kb. Am. J. Sci. 1981, 281, 1249−1516. (34) Tanger, J. C.; Helgeson, H. C. Calculation of thermodynamic and transport properties of aqueous species at high pressures and temperatures; Revised Equations of state for the standard partial molal properties of ions and electrolytes. Am. J. Sci. 1988, 288, 19−98. (35) Shock, E. L.; Helgeson, H. C. Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: Correlation algorithms for ionic species and equation of state predictions to 5 kb and 1000oC. Geochim. Cosmochim. Acta 1988, 52, 2009−2036. (36) Wang, P.; Anderko, A.; Young, R. D. A speciation-based model for mixed-solvent electrolyte systems. Fluid Phase Equilib. 2002, 203, 141–176. (37) Wang, P.; Anderko, A.; Young, R. D. Modeling viscosity of concentrated and mixed-solvent electrolyte systems. Fluid Phase Equilib. 2004, 226, 71–82. (38) Kosinski, J. J.; Wang, P. M.; Springer, R. D.; Anderko, A. Modeling acid-base equilibria and phase behavior in mixed-solvent electrolyte systems. Fluid Phase Equilib. 2007, 256, 34–41. (39) Liu, H.; Papangelakis, V. G. Thermodynamic equilibrium of the O2–ZnSO4–H2SO4–H2O system from 25 to 250 oC. Fluid Phase Equilib. 2005, 234, 122-130. (40) Liu, H.; Papangelakis, V. G. Solubility of Pb(II) and Ni(II) in mixed sulfate–chloride solutions with the mixed solvent electrolyte model. Ind. Eng. Chem. Res. 2006, 45, 39–47. 16


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(41) Azimi, G.; Papangelakis, V. G.; Dutrizac J. E. Modeling of calcium sulphate solubility in concentrated multi-component sulphate solutions. Fluid Phase Equilib. 2007, 260, 300–315. (42) Zeng, L.; Li, Z. Solubility and modeling of sodium aluminosilicate in NaOH–NaAl(OH)4 solutions and its application to desilication. Ind. Eng. Chem. Res. 2012, 51, 15193–15206. (43) Gruszkiewicz, M. S.; Palmer, D. A.; Springer R. D.; Wang, P. M.; Anderko, A. Phase behavior of aqueous Na-K-Mg-Ca-Cl-NO3 mixtures: isopiestic measurements and thermodynamic modeling. J. Solution Chem. 2007, 36, 723–765. (44) Lide, D. R. CRC Handbook of Chemistry and Physics, 89th ed. Boca Ration: CRC Press, 2009. (45) Brown, R. R.; Daut, G. E.; Mrazek, R. V.; Gokcen, N. A. Solubility and activity of aluminum chloride in aqueous hydrochloric acid solutions. BuMines RI 8379. 1979.

17



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Page 18 of 31

Figure Captions Figure 1. Illustrative flowsheet of the proposed process to recover AlCl3·6H2O from fly ash by


salting-out crystallization with FeCl2. Formatted: Font color: Auto

Figure 2. Phase equilibria in the AlCl3-FeCl2-H2O system from 283.2 to 333.2 K. Figure 3. Phase equilibria in the AlCl3(s)-MgCl2-H2O system from 283.2 to 343.2 K. Figure 4. Phase equilibria in the AlCl3(s)-CaCl2-H2O system from 283.2 to 343.2 K. Figure 5. Phase equilibria in the AlCl3-KCl(s)-H2O system from 283.2 to 363.2 K. Figure 6. Solubility of AlCl3 in the HCl-H2O system. Figure 7. Solubility of AlCl3, FeCl2, MgCl2, CaCl2 and KCl in the AlCl3-H2O, FeCl2-H2O, MgCl2H2O, CaCl2-H2O and KCl-H2O binary system, respectively. Figure 8. Relative deviation of the calculated values for the phase equilibria in the AlCl3-FeCl2-H2O system. × denotes the relative deviation of the multiple points of saturation. Figure 9. Relative deviation of the calculated values for the phase equilibria in the AlCl3(s)-MgCl2-


H2O system. Figure 10. Relative deviation of the calculated values for the phase equilibria in the AlCl3(s)-CaCl2H2O system. Figure 11. Relative deviation of the calculated values for the phase equilibria in the AlCl3-KCl(s)H2O system. Figure 12. Phase diagram and operation of AlCl3·6H2O salting-out crystallization for the AlCl3FeCl2-H2O system. Figure 13. X-Ray diffractograms of crystallized AlCl3·6H2O and FeCl2·4H2O solids. Figure 14. Crystallized (a) AlCl3·6H2O and (b) FeCl2·4H2O.

18



Page 19 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fly ash

Tailing

Leaching AlCl3·6H2O HCl solution

Iron filings

Fe3+ Reduction

Filtering and Washing

HCl

Solid FeCl2 Salting-out Crystallization

Evaporation

Liquor

Liquor

Dilution and Cooling Crystallization

FeCl2·4H2O

Figure 1.

19



4.0

283.2 K 293.2 K 298.2 K 303.2 K 313.2 K 323.2 K 333.2 K Cal.

3.5

AlCl3, mol⋅kg-1

3.0 2.5 2.0 1.5 1.0 0.5 0.0 0

1

2

3

4

5

6

7

8

-1

FeCl2, mol⋅kg Figure 2.

4.0

283.2 K 293.2 K 298.2 K 303.2 K 313.2 K 323.2 K 333.2 K 343.2 K Cal.

3.5 3.0

AlCl3, mol⋅kg-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 31

2.5 2.0 1.5 1.0 0.5 0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

-1

MgCl2, mol⋅kg Figure 3.

20


Page 21 of 31

4.0

283.2 K 293.2 K 298.2 K 303.2 K 323.2 K 343.2 K Cal.

3.5

AlCl3, mol⋅kg-1

3.0 2.5 2.0 1.5 1.0 0.5 0.0 1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-1

CaCl2, mol⋅kg Figure 4.

6

T=283.2 K T=298.2 K T=323.2 K T=343.2 K T=363.2 K Cal.

5

KCl, mol⋅kg-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4 3 2 1 0

0.5

1.0

1.5

2.0

2.5

3.0

-1

AlCl3, mol⋅kg Figure 5.

21



4.0 3.5

298.2 K 358.2 K Cal.

AlCl3, mol⋅kg-1

3.0 2.5 2.0 1.5 1.0 0.5 0

2

4

6

8

10

-1

HCl, mol⋅kg Figure 6. 14 12

Solubility, mol⋅kg-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 31

10 8

KCl AlCl3 MgCl2 FeCl2 CaCl2 Cal.

6 4 2 280

300

320

340

360

Temperature, K Figure 7.

22


Page 23 of 31

30

Relative deviation, %

25 20 15 10 5 0 -5 -10 -15 270

280

290

300

310

320

330

340

350

330

340

350


10


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5

0

-5

-10 270

280

290

300

310

320


23



14 12


10 8 6 4 2 0 -2 -4 -6 -8 -10 270

280

290

300

310

320

330

340

350


10 8


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 31

6 4 2 0 -2 -4 -6 -8

-10 280

300

320

340

360


24


Page 25 of 31

4.0 3.5

AlCl3, mol⋅kg-1

3.0

AlCl3⋅6H2O

AH

I

D E

B J

2.5 2.0

FeCl2⋅4H2O

1.5 G

C 1.0

333.2 K 298.2 K

0.5

F

0.0 0

1

2

3

4

5

6

7

-1

FeCl2, mol⋅kg Figure 12.

∇

∇ ∇

∇ ∇∇∇ ∇∇∇∇∇ ∇ ∇ ∇ ∇

∇∇

•

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


• •

0

20

• AlCl3⋅6H2O

•

• ••

∇ FeCl2⋅4H2O

•

••

•

•• • • • • • • •• • •

40

60

80

100

2Theta, degrees Figure 13.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

(a) AlCl3·6H2O

(b) FeCl2·4H2O Figure 14.

26


Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Experimental Solubilities in the AlCl3-FeCl2-H2O System m(FeCl2), mol·kg-1

m(AlCl3), mol·kg-1

Solid

m(AlCl3), mol·kg-1

Solid

0

3.4306

A

0.1752

3.3978

A

0

3.4492

A

0.4056

3.3681

0.4995

3.3349

A+F

A

0.6095

3.3269

A+F

1.7434

2.0387

2.3387

1.5472

F

1.2512

2.6422

F

F

1.7962

2.1328

3.1618

F

0.9348

F

2.6330

1.4346

4.3945

F

0.2076

F

3.6052

0.8312

F

4.2763

0.4272

F

4.5897

0.2194

F

A

T=283.2 K

m(FeCl2), mol·kg-1 T=293.2 K

T=298.2 K

T=303.2 K

0

3.4627

A

0

3.4776

0.5360 0.7214

3.3579

A

0.6992

3.3436

A

3.3181

A+F

0.8686

3.3095

A+F

1.3935

2.6147

F

1.6614

2.4981

F

1.6868

2.3431

F

2.5361

1.7509

F

2.0200

2.0364

F

2.9065

1.4897

F

2.5713

1.5760

F

3.6819

0.9895

F

3.5273

0.9729

F

4.1818

0.6614

F

4.2312

0.5499

F

4.8344

0.2234

F

4.6935

0.2369

F

A

T=313.2 K

T=323.2 K

0

3.5063

A

0

3.5228

0.7057

3.3787

A

0.7042

3.4120

A

1.0008

3.3309

A

1.5922

3.2869

A+F

1.2376

3.2955

A+F

2.6222

2.2079

F

1.5732

2.9427

F

3.2014

1.6919

F

2.4027

2.0889

F

3.8728

1.1868

F

3.2623

1.3743

F

4.4529

0.8222

F

4.0308

0.8890

F

5.5473

0.2058

F

5.1838

0.2147

F

A

T=333.2 K 0

3.5385

0.7002

3.4349

A

1.8980

3.2801

A+F

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2.8517

2.2325

F

3.4937

1.6869

F

4.1791

1.2373

F

4.9363

0.780

F

6.0536

0.1021

F

Page 28 of 31

Solid: A-AlCl3·6H2O(s), F-FeCl2·4H2O(s).

28


Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Table 2. Experimental Solubilities in the AlCl3(s)-CaCl2-H2O System m(CaCl2), mol·kg

-1

m(AlCl3), mol·kg

-1

Solid

T=283.2 K

m(CaCl2), mol·kg

-1

m(AlCl3), mol·kg-1

Solid

T=293.2 K

1.5235

2.6325

A

1.5151

2.6689

A

2.3348

2.2608

A

2.3213

2.3162

A

3.5492

1.7021

A

3.5368

1.7285

A

3.9411

1.5136

A

3.9146

1.5656

A

4.8212

1.1059

A

4.7709

1.1909

A

T=298.2 K

T=303.2 K

1.5068

2.7049

A

1.4981

2.7499

A

2.3001

2.3705

A

2.2958

2.4104

A

3.5162

1.7722

A

3.503

1.8111

A

3.8958

1.6025

A

3.8716

1.6500

A

4.7457

1.2333

A

4.7078

1.2974

A

1.4872

2.7903

A

1.4731

2.8513

A

2.2753

2.4535

A

2.2482

2.5346

A

3.4743

1.8613

A

3.4300

1.9555

A

3.8526

1.7089

A

3.7980

1.7945

A

4.6691

1.3867

A

4.5763

1.5194

A

1.4458

2.9143

A

2.2257

2.6018

A

3.3811

2.0595

A

3.7459

1.8966

A

4.509

1.6332

A

T=323.2 K

T=343.2 K

T=363.2 K

Solid: A-AlCl3·6H2O(s)

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31


Table 3. Experimental Solubilities in the AlCl3-KCl(s)-H2O System. m(AlCl3),

m(KCl), mol·kg-1

mol·kg-1

Solid

T=283.2 K

T=298.2 K

T=323.2 K

T=343.2 K

T=363.2 K

0.5016

3.0180

3.7015

4.5526

5.2324

5.8480

K

0.9990

1.9802

2.5240

3.2914

3.9946

4.4812

K

1.5179

1.1236

1.5709

2.2708

2.8345

3.4303

K

2.0005

0.7132

1.0291

1.6343

2.0876

2.5861

K

2.5066

0.3972

0.6558

1.1037

1.5222

1.9754

K

2.9997

0.2575

0.4457

0.8567

1.1823

1.5506

K

Solid: K-KCl(s)

30


Page 31 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 4. Newly Obtained MSE Model Parameters for Al3+-Fe2+, Fe2+-Cl-, Al3+-Mg2+, Al3+-Ca2+ and Al3+-K+ Interactions. Interactions Parameters

Al3+-Fe2+

Fe2+-Cl-

Al3+-Mg2+

Al3+-Ca2+

Al3+-K+

BMD0

0.1754057

-31.29317

0.6566769

-65.70246

-5.027065

BMD1

7.9085816E-03

4.8513956E-02

-1.1000809E-02

-0.2969792

1.6429923E-03

BMD2

-371.3868

6.477843

158.4011

-7958.720

-1565.874

BMD3

3.6998711E-05

0

-8.3887478E-05

-1.1526489E-03

-4.2273123E-05

BMD4

0.2358802

0

0.1159998

0

-0.4069523

CMD0

0.4267249

-4.934725

5.977986

119.6769

12.31360

CMD1

1.9887956E-02

7.6997626E-02

1.3290623E-02

0.4336690

5.9149192E-02

CMD2

-253.2308

183.6842

1549.160

36922.15

3729.442

CMD3

8.7821033E-05

-1.2532278E-07

-3.6638302E-06

1.7289382E-03

1.0212998E-04

CMD4

0.6011321

3.7275607E-02

1.009940

0

2.650125

31


O in the Fe(II) + Mg + Ca + K + Cl + H - American Chemical Society

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