Ind. Eng. Chem. Res. 2006, 45, 1551-1556
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APPLIED CHEMISTRY Efficient Recovery of Potassium Chloride from Liquid Effluent Generated during Preparation of Schoenite from Kainite Mixed Salt and Its Reuse in Production of Potassium Sulfate Rohit H. Dave and Pushpito K. Ghosh* Salt & Marine Chemicals Discipline, Central Salt and Marine Chemicals Research Institute, BhaVnagar - 364002, Gujarat, India
Although bittern of oceanic origin can be utilized for the production of K2SO4 via kainite (KCl‚MgSO4‚ 2.75H2O) and schoenite (K2SO4‚MgSO4‚6H2O) double salts, certain limitations are encountered in practice. These include (i) difficulties in obtaining pure schoenite from crude kainite and (ii) the requirement of KCl in the K2SO4 forming process. When schoenite is prepared from kainite through a simple reaction-cumleaching process and the liquid effluent is desulfated with CaCl2 as part of a scheme to coproduce magnesia (Ghosh et al. U.S. Patent Publication No. 2005/0220698 A1, 2005 (Notice of Allowance); International Patent Publication No. WO 2005/063626 A1, July 14, 2005), the composition of the resultant effluent is found to be ideally positioned in the phase diagram for direct recovery of sylvinite (NaCl/KCl). The intermediate steps of carnallite crystallization and decomposition, encountered during sylvinite preparation from Dead Sea brine and desulfated oceanic bittern, are avoided as a result. In this manner, 70-80% of the KCl in the effluent can be recovered, which largely fulfils the requirement for K2SO4 preparation. The amount of water that must be evaporated is 6.5-7.5 kg per kg of KCl in the form of sylvinite. 1. Introduction We report here an efficient scheme for the recovery of KCl from the liquid effluent obtained during schoenite (K2SO4‚ MgSO4‚6H2O) preparation from a kainite (KCl‚MgSO4‚2.75H2O)containing mixed salt. The composition of this liquor, after removal of sulfate, is shown to be attractively positioned in the phase diagram of the Na2Cl2-saturated K2Cl2/MgCl2/H2O system, allowing direct and efficient recovery of up to 80% of the KCl in the form of sylvinite (NaCl/KCl), which can be processed further to obtain pure KCl. Potassium is an essential plant nutrient.1 The most common potassium-containing fertilizer is KCl (sylvite), known as MOP (muriate of potash) in the agriculture sector. Production of KCl from sylvinite ore is especially attractive, e.g., as practiced in New Brunswick, Canada, wherein the high-quality sylvinite seam contains 25-30% K2O.2 The sylvinite can be purified by the process of flotation or hot leaching,3 although in many cases, solution mining is employed, and KCl is subsequently recovered from the solution.4 An alternative source of KCl is carnallite double salt (KCl‚MgCl2‚6H2O), either obtained as ore or recovered from brine that favors carnallite formation.5 Such recovery is based on an understanding of the composition and solubility relationships of the various salts that can be obtained from seawater, both under ambient conditions and as a function of temperature.6,7 Carnallite formation is promoted when the ratios of Mg2+ to K+ and Cl- to SO42- are both high,8 as evident * To whom correspondence should be addressed. E-mail: pkghosh@ csmcri.org. Fax: +91-278-2567562.
from the phase diagram of Figure 1. The KCl concentration in Dead Sea brine is ca. 1.2% (w/v) vs 0.08% in oceanic water.9 The Mg2+/K+ molar ratio is as high as 9.5 for the former, and the brine is virtually free of sulfate. As a result, Dead Sea brine is well suited to carnallite production, which explains the dominance of this region in global KCl production from brine sources.2,10 The recovered carnallite is converted into sylvinite through decomposition with water (eq 1), followed by separation of the solid from the MgCl2-rich mother liquor.7,11
KCl‚MgCl2‚6H2O + xH2O ) yK2Cl2 + z(1000H2O + 5.5K2Cl2 + 72.5MgCl2) (1) K2SO4 (commonly known as sulfate of potash, or SOP, in the fertilizer industry) is a dual fertilizer, typically containing 50.0-52.0% K2O and 17.0-18.0% S and having low salt index. This makes it a superior fertilizer to KCl, although the latter is used more extensively, except in those cases where plants are sensitive to chloride. This is mainly due to the higher cost of K2SO4.1,12 Apart from its application as a fertilizer, K2SO4 has industrial uses as well.9 It can be produced from KCl and H2SO4 by the well-known Mannheim process.13 Less direct methods of production include reaction of KCl with MgSO4 [in the form of epsomite (MgSO4‚7H2O), kieserite (MgSO4‚ H2O), langbeinite (K2SO4‚2MgSO4), or schoenite].9 Production of K2SO4 via schoenite is of particular interest to us, as the latter can be obtained from kainite double salt, which, in turn, is obtained through evaporation of oceanic bittern (eq 2). The schoenite is then reacted with KCl to produce K2SO4 (eq 3),3,5,14 or alternatively, it can be decomposed with hot water and
10.1021/ie050433g CCC: $33.50 © 2006 American Chemical Society Published on Web 02/07/2006
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the lowest possible level by careful fractional crystallization during kainite formation from bittern. Thereafter, the kainite is subjected to flotation to eliminate all NaCl and subsequently treated with water or an appropriate liquor to obtain schoenite. The liquid effluent or schoenite end liquor (SEL) is normally recycled back into evaporation ponds for kainite preparation.14i,16 In the case of difficulty ii, KCl is required for the production of K2SO4 from schoenite under ambient conditions. KCl can be outsourced provided that it is economical and accessible easily, as in the case of SOP production at Great Salt Lakes.14i Unfortunately, there are several situations, including that in India, where this is not a viable option. Moreover, production of KCl directly from oceanic bittern for this purpose would not be very economical. Although the decomposition reaction in eq 4 apparently eliminates the requirement for KCl, the process is more energy intensive. There is also considerable loss of K+ in the mother liquor, and if this K+ is to be recovered, it would necessarily involve reaction with KCl. Thus, KCl usage can be minimized but not eliminated.14i We have recently devised a scheme wherein both reactants required for eq 3 are obtained from kainite mixed salt.17 The scheme is made viable through integration with magnesia production. The direct recovery of sylvinite from desulfated SEL reported in the present work eliminates the intermediate steps of carnallite formation, thereby enhancing further the attractiveness of K2SO4 production. 2. Experimental Section
Figure 1. Phase diagram of oceanic salt system at 25 °C (concentrations expressed in moles per 1000 mol of H2O).7 Compositions of Dead Sea brine (b), oceanic bittern [before (2) and after (∆) desulfation] and SEL [before (9) and after (0) desulfation] are also shown. Compositions are provided in Table 1 for Dead Sea brine (1), SEL (2), desulfated SEL (3), oceanic bittern of specific gravity 1.263 (5), and desulfated oceanic bittern of specific gravity 1.221 (6).
fractionally crystallized to obtain K2SO4 and a mother liquor rich in MgSO4 (eq 4).14i room temperature
2(KCl‚MgSO4‚2.75 H2O) + H2O 98 K2SO4‚MgSO4‚6H2O + MgCl2 (2) room temperature
K2SO4‚MgSO4‚6H2O + KCl 98 2K2SO4 + MgCl2 (aq) (3) 105-115 °C
K2SO4‚MgSO4‚6H2O 98 K2SO4V + MgSO4 + 6H2O (4) Compositional factors of brine that promote kainite formation are evident from Figure 1. Its formation over carnallite is favored when the sulfate content of brine increases, there is an optimum balance between the concentrations of Cl- and SO42-, and an adequate Mg2+/K+ ratio is maintained. Bittern sources of oceanic origin exhibit the desired composition for kainite formation.15 Moreover, their composition is fairly constant. However, despite the apparent simplicity of K2SO4 preparation from kainite mixed salt, there are several difficulties. These include (i) the cocrystallization of NaCl along with kainite and (ii) the requirement for KCl in the reaction of eq 3. Regarding difficulty i above, NaCl in kainite is generally maintained at
2.1. Materials. The mixed salt used was obtained from sea bittern, and the KCl used was of commercial grade (95% purity). The hydrated lime used was of laboratory reagent grade (95% available lime). The SEL used in the present work was obtained as described below. Tap water was used in all experiments, except for analytical measurements, for which doubly distilled water was used. Standard glassware was used in all experiments. Wherever heating was required, a hot plate was used. 2.2. Analytical Measurements. The ionic compositions of the liquid and solid phases were determined using wellestablished literature procedures.18 Ca2+ and Mg2+ were estimated by complexometric titration with EDTA, K+ and Na+ were estimated by flame photometry, SO42- was estimated by the gravimetric method, and Cl- was estimated using Mohr’s method. 2.3. Chemical Processing. 2.3.1. Preparation of Schoenite and Schoenite End Liquor (SEL) from Kainite. The kainitetype mixed salt used in this work was prepared from sea bittern through solar evaporation and had the following composition ranges: KCl, 13-16%; NaCl, 14-19%; MgSO4, 32-42%; MgCl2, 3-5%. The end bittern from mixed salt preparation contained ca. 40-44% MgCl2. A 2-5-kg portion of the mixed salt was treated under mechanical stirring for 3 h at room temperature (25-35 °C) with all of the mother liquor from K2SO4 preparation (Mg2+, 2.5-3.0%; Na+, 0.3-0.6%; K+, 8-9%; Cl-, 10-11%; SO42-, 8-9%) formed during K2SO4 production from a previous batch, along with an appropriate quantity of water, to convert it into schoenite and at the same time leach out the NaCl impurity. The schoenite was then filtered, typically giving the following composition: K2SO4, 30-35%; MgSO4, 29-31%; NaCl, 1-3%; MgCl2, 0.5-1%. The filtrate (SEL) had the following ionic composition: Mg2+, 4-5%; Na+, 4-5%; K+, 4.5-5.8%; Cl-, 18-20%; SO42-, 7.5-14%. Approximately 0.35 kg of schoenite and 1.5-2.0 L of SEL were obtained per kilogram of the kainite mixed salt.17 The following illustrates a specific example: One kilogram of mixed salt containing 14.1%
Ind. Eng. Chem. Res., Vol. 45, No. 5, 2006 1553 Table 1. Composition of Different Brine Systems
1 2 3 4 5 6
a
component
sp gr
Ca2+ a
Mg2+ a
Cl- a
SO42- a
Na+ a
K+ a
[K2Cl2]b
[MgCl2]b
[MgSO4]b
Dead Sea brine SELc desulfated SELc concentrated desulfated SELc oceanic bittern desulfated oceanic bittern
1.228 1.286 1.224 1.270
1.37 0.04 0.15 0.18
3.65 4.22 3.65 7.89
18.0 19.29 21.90 28.07
7.50 0.51 0.59
2.83 4.79 4.12 1.66
0.617 5.78 4.96 2.32
1.48 15.31 13.05 6.15
28.07 19.66 30.56 66.98
16.03 0.34 0.34
1.263 1.221 1.236 1.243 1.275 1.292
trace 0.04 0.04 0.04 0.04 0.04
5.25 4.77 5.44 6.07 7.86 8.76
19.25 20.63 23.26 24.38 26.15 27.03
6.16 1.19 1.32 1.44 1.74 1.62
4.64 4.01 3.70 2.99 1.50 1.02
1.78 1.26 1.47 1.63 2.10 1.94
4.60 3.21 3.77 4.20 5.46 5.07
30.46 36.74 42.34 47.49 62.34 70.32
13.02 -
Units: % w/v. b Units: mol/1000 mol of H2O. c Average of three batches.
KCl, 16.5% NaCl, and 41.6% MgSO4 was reacted with 0.96 L of K2SO4 mother liquor containing 13.9% K2SO4, 2.8% NaCl, and 11.6% MgCl2 and 0.39 L of water for 2 h. The slurry was centrifuged to obtain 0.34 kg of schoenite containing 37.0% K2SO4, 30.3% MgSO4, and 4.9% NaCl and 1.83 L of filtrate (SEL) containing as 9.5% KCl, 13.0% NaCl, 15.1% MgSO4, and 8.0% MgCl2. 2.3.2. Preparation of Potassium Sulfate from Schoenite and KCl. A 0.335-kg sample of schoenite containing 37.0% K2SO4, 30.3% MgSO4, and 4.9% NaCl was reacted with a solution of 0.125 kg of KCl in 0.44 L of water for 3.5 h in a vessel with continuous stirring at room temperature (ca. 30 °C) to yield 0.168 kg of K2SO4 that analyzed as containing 97.3% K2SO4, 0.2% NaCl, and 3.0% MgSO4. The filtrate (K2SO4 mother liquor) measured 0.769 L and was found to contain 15.8% K2SO4, 1.3% NaCl, and 11.4% MgCl2. 2.3.3. Preparation of Calcium Chloride from Concentrated Desulfated SEL. The mother liquor obtained after separation of sylvinite (see section 2.3.6 below), which is enriched in MgCl2, was treated with hydrated lime (80-90% of the stoichiometric requirement) to obtain CaCl2 and Mg(OH)2 under ambient conditions as described previously.17,19 Only the initial concentrated filtrate (containing ca. 30-50% of total CaCl2 generated) was collected, and the rest of the washings were discarded. The composition of the filtrate was: 27-31% CaCl2, 2.5-5.0% KCl, 3.0-4.2% NaCl, and 3.5-4.2% MgCl2 (w/v). If required, the CaCl2 concentration was raised to 34-40% with solid CaCl2 to provide the requirement for complete desulfation of SEL. In larger-scale batches, the washings were recycled, which helped conserve water and also increased the CaCl2 concentration. 2.3.4. Desulfation of SEL. Experiments were conducted with 0.25 L of SEL generated above. Its sulfate content was determined, and CaCl2 solution prepared as described above was added in stoichiometric quantity.17,19,20 The resulting desulfated bittern was vacuum filtered, and its composition was in the following ranges: KCl, 9-11%; NaCl, 10-11%; MgCl2, 14-15% (w/v). 2.3.5. Preparation of Sylvinite from Desulfated SEL via Carnallite Route. Desulfated SEL (0.250 L) was mixed with 0.038 L of desulfated end bittern containing ca. 40% MgCl2. The resultant solution was subjected to forced evaporation until the solution attained a boiling point of 125-126 °C. The solution was then allowed to cool to room temperature (30-35 °C) to crystallize out carnallite. The slurry was then filtered to obtain 0.096 kg of carnallite containing 14.3% KCl, 12.7% NaCl, 31.9% MgCl2, and 1.9% CaSO4. The carnallite was decomposed with 0.041 L of water to give 0.029 kg of wet sylvinite containing 33.9% KCl and 46.3% NaCl. The yield of KCl in the form of sylvinite was 71.5% with respect to the KCl in desulfated SEL.
2.3.6. Preparation of Sylvinite from Desulfated SEL via Direct Evaporation. Desulfated SEL (0.270 L) containing 0.0254 kg of KCl was directly subjected to forced evaporation in the temperature range of 105-110 °C and then left to cool to room temperature (30-35 °C) to crystallize out 0.0457 kg of sylvinite containing 0.0194 kg of KCl. The yield of KCl in the form of sylvinite was 76.4% with respect to the KCl in desulfated SEL. The mother liquor after separation of sylvinite had the following composition: MgCl2, 30-31%; K2Cl2, 4.44.6%. 3. Results and Discussion As reported by us in a recent patent application, kainite mixed salt prepared from oceanic bittern can be converted in one step into NaCl-free schoenite through a simple reaction-cum-leaching process, while utilizing the K+ lost in the aqueous leachate (schoenite end liquor, abbreviated as SEL) for preparation of KCl in more-or-less the required quantity.17 This has been found to be a more cost-effective option than outsourcing KCl and helps in the near-complete utilization of K+ in kainite mixed salt, provided that the latter can be produced consistently with similar composition. Moreover, the process of obtaining pure schoenite is greatly simplified as a result because there is no longer a need to minimize K+ loss in SEL, but rather, there is a need to ensure optimum balance between K+ in the form of schoenite and SEL. KCl recovered from the SEL was almost adequate when the yield with respect to the KCl in SEL was ca. 75% and the KCl/schoenite mole ratio was 1.13:1 for K2SO4 production through eq 4.17 SEL contains as much as 5% K+, in addition to other constituents (Table 1). This concentration is more than twice that found at the onset point of carnallite production from ordinary oceanic bittern. Also as can be seen in the table, the SO42- concentration in SEL is ca. 7.5%, i.e., similar to that in oceanic bittern. Because the SO42-/K+ ratio of SEL is less than one-half the value for oceanic bittern, and its absolute K+ concentration is substantially higher, desulfation of SEL for KCl recovery is an attractive proposition. The cost of desulfation with CaCl2 can be offset by the production of Mg(OH)2 as a byproduct, which can be converted into refractory-grade MgO.17,19,21 Moreover, the KCl lost in end bittern/carnallite decomposed liquor used for CaCl2 preparation is also recovered in the process. By integrating desulfation with Mg(OH)2 production, its cost is distributed over three products, namely, gypsum, KCl, and Mg(OH)2, while simultaneously minimizing effluent load. Our initial efforts focused on recovery of carnallite from desulfated SEL, which is the conventional approach to KCl production from brines. Because the composition of SEL is lacking in Mg2+ for this purpose, we increased the Mg2+/K+
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Cl2. The diagram is plotted using the well-known van’t Hoff coordinates, i.e., moles per 1000 mol of H2O, and expressing KCl in the form of K2Cl2.9,22 The last three columns of Table 1 present the data in the above units of concentration. It can be seen from Figure 2 that evaporation of Dead Sea brine leads to carnallite formation, as observed experimentally. In the case of desulfated oceanic bittern, the resultant composition upon evaporation moves along a path that initially leads to minor formation of sylvinite. As the solution composition moves toward the carnallite field, the precipitated KCl is transformed into carnallite as per the phase rule, and thereafter, carnallite crystallizes directly from solution.7 In the case of desulfated SEL, it can be seen that, for the composition indicated in Table 2, the system is poised at the saturation point (region A) and yields sylvinite upon evaporation. The solution was heated to ca. 105 °C on a hot plate, and water was boiled off. Forced evaporation was continued to the point (typically ca. 110 °C) that, upon cooling, the maximum extent of KCl crystallized as sylvinite, and the mother liquor was at point B. Data obtained for experiments conducted in triplicate are shown. Further evaporation beyond point B would lead to carnallite formation, and we therefore confined our recoveries to point 4 in Figure 2 to ensure that carnallite formation was fully avoided. At this point, the concentrated desulfated SEL contained 30-31% MgCl2 and 4.4-4.6% K2Cl2. The yield of KCl obtained through this simplified route was in the range of 75-80% (Table 2), which compares well with the yield obtained through intermediate carnallite formation.17 Because the desulfated SEL solution is at the saturation point, the need for water evaporation is minimized. Moreover, as can be seen from Figure 2, the presence of MgCl2 in SEL greatly suppresses the sylvinite solubility in the solution as the MgCl2 concentration rises. The evaporation requirement was found to be ca. 6.5 L of water per kilogram of KCl in the form of sylvinite. The sylvinite can be treated further by well-established processes to obtain KCl (reported yields are >95%) of required purity,7,9,23 and accounting for losses, the overall yield of KCl recovery from SEL would be in excess of 70% when conducted on a large scale, i.e., the scheme of K2SO4 formation from kainite mixed salt is selfsustaining. Because the KCl obtained after hot leaching can be used directly, costs involving drying, granulation, packaging, and shipping are avoided, making this competitive vis-a`-vis other options. The only operations required are desulfation, evaporation of water, and hot leaching. The scheme for K2SO4 production, with integration of the sylvinite-forming process, is shown in Figure 3. It can be seen that the K2SO4 mother liquor, KCl, and CaCl2 required in the process are also generated in the process, and therefore, these are required from outside only for initialization of the process. As can be seen in Table 3, the input-output analysis for the total scheme is satisfactory, although fine-tuning will be required of the individual steps. Nevertheless, it can be seen that the KCl generated via the present scheme is close to the requirement for KCl in the reaction with schoenite to form K2SO4. Similarly, the amount of KCl in the form of K2SO4 mother liquor used
Figure 2. Phase diagram of the K2Cl2/MgCl2/H2O saturated with NaCl.9 The compositions of Dead Sea brine (b), desulfated oceanic bittern (2), and SEL (9) and the trajectories these follow upon evaporation of water are also shown. Points 1 and 6 represent the initial compositions of Dead Sea brine and desulfated oceanic bittern, respectively, and points 3 and 4 represent the initial and final compositions, respectively, of desulfated SEL (Table 1).
ratio by adding MgCl2 into desulfated SEL, as described in the Experimental Section.8,17 Hildebrand has shown that, for pure carnallite, the decomposition reaction in eq 1 is optimum when the stoichiometry of eq 1 is followed, wherein the values of x, y, and z are 7.8, 0.425, and 0.0138, respectively.7 It has been further established that the amount of water required for decomposition is small, i.e., only one-half the weight of carnallite. Even so, the fraction of KCl lost in the liquor upon decomposition is ca. 16%.7 When carnallite is contaminated with NaCl, as in the case of sea brine, losses in the liquor are higher, i.e., in the range of 25-30% for a KCl/NaCl weight ratio of ca. 2:1. In our case, the recovery was ca. 72% in the form of carnallite decomposed product, which primarily comprises a mixture of NaCl and KCl (sylvinite). With a view toward simplifying the process of KCl recovery from desulfated SEL, we began exploring more direct means of obtaining sylvinite, especially to short circuit the process of producing carnallite and then decomposing it and also to avoid the addition of Mg2+. An additional consideration was that carnallite recovery by forced evaporation requires heating of the desulfated SEL to temperatures as high as 125 °C, which can lead to partial hydrolysis/decomposition of MgCl2. We examined the compositions of Dead Sea brine, desulfated oceanic bittern, and desulfated SEL in relation to the reported phase diagram of these systems.9 Figure 2 shows the phase diagram of the K2Cl2/MgCl2/H2O system saturated with Na2-
Table 2. KCl Mass Balance for the Process of Direct Recovery of Sylvinite from SEL
batch
vol of SEL taken (L)
KCl in SEL taken (g)
vol of dSEL/ total KCl in dSELa (L/g)
vol of dSEL taken (L)
KCl in dSEL taken (g)
vol of H2O evaporated (L)
total KCl in sylvinite (g)
yield of KCl wrt dSEL taken (%)
H2O evaporated per kg of KCl (L)
1 2 3
0.250 0.250 0.250
27.65 27.50 27.50
0.270/(26.98)b 0.285/26.79c 0.300/27.00c
0.250 0.270 0.280
25.0 25.4 25.2
0.123 0.144 0.137
19.18 19.41 20.00
76.7 76.4 79.4
6.41 7.42 6.85
a dSEL ) desulfated SEL (composition as in entry 3 of Table 1). b Desulfation with pure CaCl solution for initialization. c Desulfation with CaCl 2 2 generated from concentrated desulfated SEL and topped off with small quantity (20% of total) of externally added CaCl2.
Ind. Eng. Chem. Res., Vol. 45, No. 5, 2006 1555
Figure 3. Scheme for the preparation of K2SO4 from kainite-type mixed salt with direct recovery of sylvinite from desulfated SEL. In the integrated scheme, kainite mixed salt and lime would be the only raw materials, and K2SO4 and MgO would be the final products. Table 3. Mass Balance of Potassium (Expressed as KCl) for the Scheme of Figure 3 weight/volume taken kainite mixed salt K2SO4 mother liquor KCl total input
Input of K 153.7 g 153 mL 21.5 g
Output of K K2SO4 23.9 g K2SO4 mother liquor 127.6 mL concentrated desulfated SEL 118 mL sylvinite 45.5 g total output
K content expressed as weight of KCl (g) 21.4 18.1 21.0 60.5 19.8 15.6 5.1 19.5 60.0
and the amount produced in the process are in reasonable accord. It is also evident from the composition of SEL in Table 1 that, mole for mole, the Mg2+ content in SEL is higher than that of sulfate (ca. 1.1-1.2:1). Because almost all of this Mg2+ ends up in the concentrated desulfated SEL, the reaction of this MgCl2 with lime would generate more or less the desired amount of CaCl2 required for desulfation of SEL.21 As already mentioned, this would further enable the recycling of K+ that would otherwise be lost in the latter. 4. Conclusion The need to develop indigenous potassium fertilizer from seawater, and the special importance of K2SO4 as a premium fertilizer, motivated us to explore its cost-effective production from kainite mixed salt. Schoenite and KCl required for this purpose can both be generated from kainite mixed salt, as a result of which K+ utilization is nearly quantitative. The crucial step of the process is the recovery of KCl from schoenite end liquor (SEL). The unique composition of SEL lends itself to cost-effective desulfation with CaCl2 generated in the process, with desulfated SEL being located conveniently in the roomtemperature phase diagram of the K2Cl2/MgCl2/H2O system, saturated with Na2Cl2. As a result, sylvinite is obtained directly with the least amount of water evaporation, while the mother liquor is recycled for desulfation after reaction with lime to obtain CaCl2 and Mg(OH)2. The sylvinite can be hot leached
to obtain KCl of adequate purity that can be used directly in the reaction of eq 3. Because of the simplification in the preparation of KCl and the further savings due to its direct use in wet form, it is advantageous to recover KCl from SEL, which eliminates the need for the outsourcing of KCl and yields pure gypsum, Mg(OH)2, and NaCl as byproducts. Acknowledgment The authors are grateful to Dr. K. J. Langalia for providing schoenite end liquor and to Mr. M. R. Gandhi and Dr. H. L. Joshi for bench-scale data on the SOP process. We also acknowledge valuable discussions with Dr. V. R. K. S. Susarla and Dr. V. P. Mohandas on phase diagrams of brine systems and thank the referees for their valuable comments. This work was undertaken as part of a project (GAP 0048 sponsored to Mr. S. L. Daga) on KCl development supported by the Department of Ocean Development, New Delhi, India. Literature Cited (1) Collings, G. H. Commercial Fertilizers; Blakiston Co.: Philadelphia, PA, 1950; pp 255-256. (2) (a) World SurVey of Potash Resources; The British Sulphur Corporation: London, 1985; pp 62-64. (b) Zharkov, M. A. Paleozoic Salt Bearing Formations of the World; Springer-Verlag, Berlin, 1984. (c) BrongersmaSanders, M. Origin of major cyclicity of evaporites and bituminous rocks: An actualistic model. Mar. Geol. 1972, 11 (2), 123-144. (3) (a) Udwadia, N. N.; Saraiya, U. P.; Sanghavi, J. R. Potassium sulfate from mixed salt. Salt Res. Ind. 1979, 15 (1), 1-5. (b) Jackson, D. Eng. Min. J. 1973, 174 (7), 59-68. (c) Phosphorus Potassium 1985, 138, 3233. (4) (a) Bakr, M. Y.; Zatout, A. A. Minerals from the sea: Recovery of potassium salts from Egyptian bittern. Chem. Age India 1975, 26 (3), 197199; Chem. Abstr. 1975, 83 (18), 151954d. (b) Dahms, J. B.; Edmonds, B. P. (Pittsburgh Plate Glass Co.). Solution mining of potassium chloride from subterranean deposits. U.S. Patent 3,058,729, 1962; Chem. Abstr. 1963, 58, 3127g. Goldsmith, E. L. Preferential solution mining process. U.S. Patent 4,007,964, 1977. Edmonds, B. P.; Dahms, J. B. Solution mining of potassium chloride. U.S. Patent 3,262,741, 1966. Dahms, J. B.; Edmonds, B. P. Method of solution mining potassium chloride. U.S. Patent 3,433,530, 1969. Goldsmith, E. L. Solution mining potassium chloride from heated subterranean cavities. U.S. Patent 4,239,287, 1980. (5) Braitsch, O. Entstehung und Stoffbestand der Salzlagersta¨tten; Springer-Verlag: Berlin, 1962. (6) van’t Hoff, J. H. Untersuchungen u¨ber die BildungsVerha¨ltnisse der ozeanischen Salzablagerungen; Akademische Verlagsges: Leipzig, Germany, 1912.
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ReceiVed for reView April 8, 2005 ReVised manuscript receiVed January 1, 2006 Accepted January 2, 2006 IE050433G
