CA2926356C - Production of high strength hydrochloric acid from calcium chloride feed streams by crystallization - Google Patents
Production of high strength hydrochloric acid from calcium chloride feed streams by crystallization Download PDFInfo
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- CA2926356C CA2926356C CA2926356A CA2926356A CA2926356C CA 2926356 C CA2926356 C CA 2926356C CA 2926356 A CA2926356 A CA 2926356A CA 2926356 A CA2926356 A CA 2926356A CA 2926356 C CA2926356 C CA 2926356C
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- calcium chloride
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- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 title claims abstract description 167
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 title claims abstract description 102
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 21
- 239000001110 calcium chloride Substances 0.000 title abstract description 71
- 229910001628 calcium chloride Inorganic materials 0.000 title abstract description 71
- 238000002425 crystallisation Methods 0.000 title description 25
- 230000008025 crystallization Effects 0.000 title description 25
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 claims abstract description 90
- 239000013078 crystal Substances 0.000 claims abstract description 89
- 238000000034 method Methods 0.000 claims abstract description 77
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 55
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 47
- 239000007787 solid Substances 0.000 claims abstract description 32
- 238000002156 mixing Methods 0.000 claims abstract description 13
- 229910052751 metal Inorganic materials 0.000 claims abstract description 12
- 239000002184 metal Substances 0.000 claims abstract description 12
- 150000002739 metals Chemical class 0.000 claims abstract description 12
- 238000012545 processing Methods 0.000 claims abstract description 6
- 229910052761 rare earth metal Inorganic materials 0.000 claims abstract description 4
- 230000008569 process Effects 0.000 claims description 59
- 239000000203 mixture Substances 0.000 claims description 22
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 16
- 229910052791 calcium Inorganic materials 0.000 claims description 16
- 239000011575 calcium Substances 0.000 claims description 16
- 238000002386 leaching Methods 0.000 claims description 10
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 3
- 238000010276 construction Methods 0.000 claims description 3
- 238000004064 recycling Methods 0.000 claims description 3
- 150000002910 rare earth metals Chemical class 0.000 claims description 2
- 235000011148 calcium chloride Nutrition 0.000 abstract description 70
- 230000001172 regenerating effect Effects 0.000 abstract description 3
- 239000000243 solution Substances 0.000 description 51
- 150000004683 dihydrates Chemical class 0.000 description 45
- 238000002474 experimental method Methods 0.000 description 37
- 230000000694 effects Effects 0.000 description 33
- 239000012071 phase Substances 0.000 description 28
- 235000011132 calcium sulphate Nutrition 0.000 description 24
- 239000002253 acid Substances 0.000 description 20
- 238000006243 chemical reaction Methods 0.000 description 18
- 229910052925 anhydrite Inorganic materials 0.000 description 15
- 230000008929 regeneration Effects 0.000 description 14
- 238000011069 regeneration method Methods 0.000 description 14
- 239000000047 product Substances 0.000 description 13
- 238000009826 distribution Methods 0.000 description 12
- 239000002245 particle Substances 0.000 description 11
- 238000000113 differential scanning calorimetry Methods 0.000 description 10
- 239000002002 slurry Substances 0.000 description 9
- 238000012360 testing method Methods 0.000 description 8
- 239000003153 chemical reaction reagent Substances 0.000 description 7
- 230000014759 maintenance of location Effects 0.000 description 7
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 6
- 239000008367 deionised water Substances 0.000 description 6
- 229910021641 deionized water Inorganic materials 0.000 description 6
- 238000001878 scanning electron micrograph Methods 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 4
- 238000010924 continuous production Methods 0.000 description 4
- 238000000605 extraction Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 239000012266 salt solution Substances 0.000 description 4
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 238000013459 approach Methods 0.000 description 3
- 229910001424 calcium ion Inorganic materials 0.000 description 3
- 239000012527 feed solution Substances 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 239000011435 rock Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 102100034323 Disintegrin and metalloproteinase domain-containing protein 2 Human genes 0.000 description 2
- 101000780288 Homo sapiens Disintegrin and metalloproteinase domain-containing protein 2 Proteins 0.000 description 2
- 101000821981 Homo sapiens Sarcoma antigen 1 Proteins 0.000 description 2
- 102100021466 Sarcoma antigen 1 Human genes 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 239000010440 gypsum Substances 0.000 description 2
- 229910052602 gypsum Inorganic materials 0.000 description 2
- 238000009854 hydrometallurgy Methods 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 238000010310 metallurgical process Methods 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 235000010755 mineral Nutrition 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 230000002572 peristaltic effect Effects 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 239000012925 reference material Substances 0.000 description 2
- 238000004626 scanning electron microscopy Methods 0.000 description 2
- 239000007790 solid phase Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- 229910021532 Calcite Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910002483 Cu Ka Inorganic materials 0.000 description 1
- 235000019738 Limestone Nutrition 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052586 apatite Inorganic materials 0.000 description 1
- 238000011074 autoclave method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 239000008364 bulk solution Substances 0.000 description 1
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000004035 construction material Substances 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000012470 diluted sample Substances 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000010459 dolomite Substances 0.000 description 1
- 229910000514 dolomite Inorganic materials 0.000 description 1
- 238000000445 field-emission scanning electron microscopy Methods 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 239000010436 fluorite Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- FBAFATDZDUQKNH-UHFFFAOYSA-M iron chloride Chemical compound [Cl-].[Fe] FBAFATDZDUQKNH-UHFFFAOYSA-M 0.000 description 1
- 239000006028 limestone Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- VSIIXMUUUJUKCM-UHFFFAOYSA-D pentacalcium;fluoride;triphosphate Chemical compound [F-].[Ca+2].[Ca+2].[Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O VSIIXMUUUJUKCM-UHFFFAOYSA-D 0.000 description 1
- 239000011505 plaster Substances 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- -1 rare earth elements Chemical class 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000013341 scale-up Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000008247 solid mixture Substances 0.000 description 1
- 239000012265 solid product Substances 0.000 description 1
- 230000008685 targeting Effects 0.000 description 1
- 238000001757 thermogravimetry curve Methods 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
- 238000000844 transformation Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B7/00—Halogens; Halogen acids
- C01B7/01—Chlorine; Hydrogen chloride
- C01B7/03—Preparation from chlorides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
- C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
- C22B3/10—Hydrochloric acid, other halogenated acids or salts thereof
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/46—Sulfur-, selenium- or tellurium-containing compounds
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
- C30B7/14—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions the crystallising materials being formed by chemical reactions in the solution
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The present relates to a method for producing calcium sulfate solid crystals and hydrochloric acid (HCI) from a calcium chloride solution comprising the steps of feeding a continuous stirred-tank reactor with a calcium chloride solution, sulfuric acid and water; mixing the calcium chloride solution, sulfuric acid and water in the reactor; and maintaining the reactor a temperature of less than about 70°C, converting the calcium chloride solution, sulfuric acid and water into HCI and calcium sulfate solid crystals. The method described herein can be incorporated as a means for regenerating HCI from CaCl2 solutions which are generated in the metallurgical industry when processing calcium- bearing ores for recovering metals like rare earth elements.
Description
PRODUCTION OF HIGH STRENGTH HYDROCHLORIC ACID FROM
CALCIUM CHLORIDE FEED STREAMS BY CRYSTALLIZATION
TECHNICAL FIELD
[0001] The present relates to a process for the production of high strength hydrochloric acid from calcium chloride feed streams.
BACKGROUND ART
CALCIUM CHLORIDE FEED STREAMS BY CRYSTALLIZATION
TECHNICAL FIELD
[0001] The present relates to a process for the production of high strength hydrochloric acid from calcium chloride feed streams.
BACKGROUND ART
[0002] Hydrochloric acid (HCI)-based leaching of calcium-based rock, with the goal of extracting valuable metals such as rare earth elements, can produce a CaCl2 solution by-product. The extraction of these metals relies on the use of concentrated HCI, typically of azeotropic strength. The CaCl2 solutions cannot be released into the environment due to their high concentration of chloride ions and have to be processed further. This is ideally done in a way that offers the possibility to reclaim the HCI used by the process (acid recycling).
Therefore, in order to enable the leaching of minerals with HCI on an industrial scale, the acid needs to be recovered. Conventional HCI recovery techniques, such as pyrohydrolysis for iron chloride solutions, are used at industrial scale, but are not economically feasible for the treatment of CaCl2 solution for fundamental thermodynamic reasons. The pyrohydrolysis of CaCl2 requires temperatures of up to 1000 C to recover the HCI.
Therefore, in order to enable the leaching of minerals with HCI on an industrial scale, the acid needs to be recovered. Conventional HCI recovery techniques, such as pyrohydrolysis for iron chloride solutions, are used at industrial scale, but are not economically feasible for the treatment of CaCl2 solution for fundamental thermodynamic reasons. The pyrohydrolysis of CaCl2 requires temperatures of up to 1000 C to recover the HCI.
[0003] It is thus desirable to have a means to treat the concentrated calcium chloride solutions generated from the processing of calcium-based rock, thereby allowing recovery of the chloride units as high strength HCI for re-use.
SUMMARY
SUMMARY
[0004] In accordance with the present disclosure there is now provided a method for producing calcium sulfate solid crystals and hydrochloric acid (HCI) from a calcium chloride solution comprising the steps of feeding a continuous-stirred tank reactor with a calcium chloride solution, sulfuric acid and water;
mixing the calcium chloride solution, sulfuric acid and water in the reactor;
and maintaining the reactor at a temperature of less than about 70 C, converting the calcium chloride solution, sulfuric acid and water into HCI and calcium sulfate solid crystals.
mixing the calcium chloride solution, sulfuric acid and water in the reactor;
and maintaining the reactor at a temperature of less than about 70 C, converting the calcium chloride solution, sulfuric acid and water into HCI and calcium sulfate solid crystals.
[0005] In an embodiment, the calcium sulfate solid crystals are crystals of at least one of calcium sulfate dihydrate, calcium sulfate a-hemihydrate and mixture thereof.
[0006] In another embodiment, the azeotropic HCI is obtained with calcium sulfate solid crystals.
[0007] In another embodiment, up to 30 wt% (9.5 mol/L) of super-azeotropic HCI is obtained.
[0008] In an additional embodiment, the ratio of sulfate to calcium in the reactor is 0.90 to 0.98.
[0009] In a further embodiment, the temperature of the reactor is about less than 60 C.
[0010] In another embodiment, the temperature of the reactor is about 40 C-70 C.
[0011] In an embodiment, the temperature of the reactor is about 40 C or less.
[0012] In another embodiment, the reactor is continuously fed with calcium chloride solution, sulfuric acid and water, continuously producing HCI and calcium sulfate solid crystals.
[0013] In an embodiment, the calcium chloride solution is a feed stream from the processing of calcium-bearing ores.
[0014] In another embodiment, calcium chloride solution, sulfuric acid and water are fed in multiple parallel reactors.
[0015] Also encompassed is a process of extracting metals from calcium-bearing ores comprising the steps of leaching the ores with HCI, producing a leachate containing a calcium chloride solution and metals; separating the metals from the calcium chloride solution; feeding a continuous-stirred tank reactor with the calcium chloride solution, sulfuric acid and water; mixing the calcium chloride solution, sulfuric acid and water in the reactor; maintaining the reactor at a temperature of less than about 70 C, converting the calcium chloride solution, sulfuric acid and water into HCI and calcium sulfate solid crystals; and recycling the HCI to the leaching of the ores.
[0016] In an embodiment, the metals are rare earths.
[0017] It is also provided a construction board comprising calcium sulfate a-hemihydrate produced by the method or process described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Reference will now be made to the accompanying drawings.
[0019] Fig. 1 illustrates an experimental set-up for a continuous process as encompassed herein.
[0020] Fig. 2A illustrates the evolution of HCI and CaCl2 concentration over operating time for experiments run at 30 C (CT4) and 60 C (CT6) under different start-up modes.
[0021] Fig. 2B illustrates the evolution of HCI concentration over time for experiments producing azeotropic and super-azeotropic strength HCI.
[0022] Fig. 3A illustrates a model-based estimation of water activity aw as a function of CaCl2 concentration and HCI concentration at 40 C, wherein (*) indicates the steady state composition, the solid observed to form experimentally is given in ( ); - - - - (dashed line) signifies the water activity line at which DH and HH have the same metastability; above the line HH is relatively more stable than DH and below the line the reverse is true.
[0023] Fig. 3B illustrates a model-based estimation of water activity aw as a function of CaCl2 concentration and HCI concentration at 60 C, wherein (*) indicates the steady state composition, the solid observed to form experimentally is given in ( ); - - - - (dashed line) signifies the water activity line at which DH and HH have the same metastability; above the line HH is relatively more stable than DH and below the line the reverse is true.
[0024] Fig. 4 illustrates a comparison of particle size distributions obtained from experiments CT1, CT2 and CT3 after 8 h of experiment.
[0025] Fig. 5A illustrates the crystal morphologies of steady-state products (after 8 h) from experiment CT2 calcium sulfate hemihydrate.
[0026] Fig. 5B illustrates the crystal morphologies of steady-state products (after 8 h) from experiment CT3 calcium sulfate dihydrate.
[0027] Fig. 6A illustrates a scanning electron microscope (SEM) image showing the crystal morphology and size of a-HH crystals produced at a steady-state concentration of 3.4 mol/L (CT2) of CaCl2.
[0028] Fig. 6B illustrates a SEM image showing the crystal morphology and size of a-HH crystals produced at a steady-state concentration of 1.2 mol/L
(CT7) of CaCl2.
(CT7) of CaCl2.
[0029] Fig. 6C illustrates a SEM image showing the crystal morphology and size of a-HH crystals produced at a steady-state concentration of 0.8 mol/L
(CT6) of CaCl2.
(CT6) of CaCl2.
[0030] Fig. 6D illustrates a SEM image showing the crystal morphology and size of a-HH crystals produced at a steady-state concentration of 0.1 mol/L
(CT12) of CaCl2.
(CT12) of CaCl2.
[0031] Fig. 7A illustrates the effect of steady-state crystallization conditions on a-HH crystal size distributions at CT2 conditions and CT12 conditions.
[0032] Fig. 7B illustrates the effect of steady-state crystallization conditions on a-HH crystal size quality as characterized by differential scanning calorimetry (DSC) at CT2 conditions and CT12 conditions.
[0033] Fig. 8A illustrates the relationship between the amount of fine particles and the exothermic peak in a DSC scan.
[0034] Fig. 8B illustrates the relationship between the amount of fine particles and the steady-state CaCl2 content.
[0035] Fig. 9 illustrates the comparison of x-ray diffraction (XRD) patterns of solid produced in the continuous process as encompassed herein (t=8 h) (CT12: 2; CT10: 3; CT9: 4; and CT6: 5) with a-HH reference material produced in the autoclave process.
[0036] Fig. 10 illustrates a comparison of DSC patterns of solid produced in the continuous process (t=8 h) (CT12: 2; CT10: 3; CT9: 4; and CT6: 5) with a-HH reference material produced in the autoclave process.
[0037] Fig. 11A illustrates the crystal morphology of a-HH produced by the process described herein according to one embodiment under CT6 conditions (t=8 h).
[0038] Fig. 11B illustrates the crystal morphology of a-HH produced by the process described herein according to one embodiment under CT9 conditions (t=8 h).
[0039] Fig. 11C illustrates the crystal morphology of a-HH produced by the process described herein according to one embodiment under CT10 conditions (t=8 h).
[0040] Fig. 11D illustrates the crystal morphology of a-HH produced by the process described herein according to one embodiment under CT12 conditions (t=8 h).
[0041] Fig. 11E illustrates the crystal morphology of a-HH produced with a process according to current commercially-available material.
[0042] Fig. 12 illustrates a flow sheet of the acid regeneration process described herein incorporated in a metallurgical process.
[0043] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
DETAILED DESCRIPTION
DETAILED DESCRIPTION
[0044] It is provided a process for the production of high strength (sub-azeotropic, azeotropic or super-azeotropic) hydrochloric acid from calcium chloride feed streams.
[0045] Using a low temperature (40-70 C) hydrochemical process, the process described herein produces a solid calcium sulfate product (calcium sulfate a-hemihydrate; a-HH or calcium sulfate dihydrate; DH). Especially, a-HH
is currently only produced by an energy intensive and labor intensive autoclave process that operates at approximately 115 C.
is currently only produced by an energy intensive and labor intensive autoclave process that operates at approximately 115 C.
[0046] It is demonstrated that the process described herein resulted in a production rate of approximately 0.5 kg /h and 0.9 kg conc. HCI solution/h. The process described herein can be embedded in any hydrometallurgical/chemical operation that generates a concentrated CaCl2 solution as a by-product of its processes and where such solution cannot be used/treated internally or sold externally and HCI needs to be regenerated. The regenerated HCI can be reused internally in the production process or sold on the external market.
[0047] Also encompassed herein is the use of the solid product (a-HH) described herein in the production of plaster board used in the drywall construction industry for example.
[0048] It is provided a process for regenerating HCI from CaCl2 solutions, which has not been previously economically feasible and hence not been practiced on an industrial scale so far. Furthermore, it is provided a means for the metallurgical industry to recycle CaCl2 waste solution streams and hence make these operations more environmentally-friendly.
[0049] The process described herein provides a significant improvement over the commercially-existing autoclave-based production of a-HH, a construction material that is already in use. The process described herein utilizes a continuous mode of operation and uses much lower temperatures, such as at room temperature for example, preferably at 40-70 C compared to known processes (115-130 C for conventional processes). In addition, the processing time is reduced from several hours for known conventional processes to less than 3 h, preferably 1-2 h.
[0050] Contrary to the salt solution method, which uses concentrated CaCl2 solutions or mixtures of CaCl2-MgC12-KCI to convert calcium sulfate dihydrate from flue gas desulfurization operations into a-HH, the temperature used in the present process is lower and the processing time is shorter. Furthermore, the salt solution process cannot be integrated into the larger context of a hydrometallurgical extraction process that continuously produces CaCl2 solution. This is because the salt solution is not transformed/consumed during the process of calcium sulfate dihydrate to a-HH conversion. Hence, the salt solution method does not provide an answer to the problem of spent CaCl2 solution treatment and acid regeneration in the same way as the present process does.
[0051] Laboratory crystallization studies are carried out in batch or semi-batch reactors. The latter has been the system of choice as it allows operation in constant composition mode. This concept achieves a constant supersaturation level via regulated reagent addition. This technique has proven particularly successful with relatively dilute reagent solutions when precipitation of sparingly soluble compounds at a controlled pH level is practiced. As such, the semi-batch constant composition crystallization system can also simulate steady-state crystallization as encountered in continuous stirred-tank crystallizers that are widely used in large-scale industrial operations.
However, in many cases the semi-batch crystallization results may not be entirely transferable to the continuous crystallizer operation mainly because of differences in the residence time distribution and mixing effects. It has been discovered that crystallization of metastable phases in concentrated acidic solutions not amenable to pH control, due to excessive acidity levels for pH
probes, constitutes another case where employment of a continuous stirred-tank reactor (CSTR) during the development stage offers distinct superiority over the semi-batch precipitation approach.
However, in many cases the semi-batch crystallization results may not be entirely transferable to the continuous crystallizer operation mainly because of differences in the residence time distribution and mixing effects. It has been discovered that crystallization of metastable phases in concentrated acidic solutions not amenable to pH control, due to excessive acidity levels for pH
probes, constitutes another case where employment of a continuous stirred-tank reactor (CSTR) during the development stage offers distinct superiority over the semi-batch precipitation approach.
[0052] It is provided herein the results of continuous crystallization experiments in the context of HCI regeneration from concentrated calcium chloride solutions. Such solutions are generated in chloride-based hydrometallurgical processes. One example is the HCI leaching of calcium-based ores for rare earth extraction. However, regeneration of HCI via pyrohydrolysis of CaCl2 solutions is not feasible due to the very high temperatures (-800-1000 C) required. This has prompted exploration of alternative HCI regeneration routes. To this end, a reactive crystallization process involving stage-wise reaction of concentrated calcium chloride solution (up to 5 mol/L) with concentrated sulfuric acid (up to 18 mol/L) at temperatures below 100 C in a semi-batch configuration has been investigated previously, based on the following equation CaCl2 + H2SO4 + xH20 2HCI + CaSO4.xH20 (1)
[0053] In principle, depending on the process operating window defined in terms of temperature, solution composition, {HCI] and [CaCl2], and time, the reaction can be controlled to produce metastable calcium sulfate dihydrate (DH, x=2) or metastable calcium sulfate a-hemihydrate (a-HH, x0.5), while avoiding formation of the thermodynamically stable, but undesirable, calcium sulfate anhydrite (AH, x=0). The process is feasible due to the low solubility of calcium sulfates, especially if a small amount of calcium chloride is still present in solution. In order to obtain high strength HCI, both reagents (CaCl2, H2SO4) need to be used at high concentration, which causes the water activity of the solution to be significantly reduced. It has been shown that the availability of free water, reflected by the magnitude of water activity, is a key parameter controlling calcium sulfate phase (meta-)stability in addition to the effect of temperature. Over the temperature range 55 C-95 C, a-HH was found to be the favored metastable phase while DH is the metastable phase at lower temperature. AH is always the stable phase in the relevant composition range.
It has been shown that the lifetime of DH and ct-HH primarily depends on the level of HCI concentration, which has the greatest impact on the water activity in the system by lowering it. This makes the production of the metastable phases very challenging, as their conversion to the undesirable stable AH phase is a constant threat.
It has been shown that the lifetime of DH and ct-HH primarily depends on the level of HCI concentration, which has the greatest impact on the water activity in the system by lowering it. This makes the production of the metastable phases very challenging, as their conversion to the undesirable stable AH phase is a constant threat.
[0054] So far, nothing exists showing a successfully operating continuous HCI regeneration process from concentrated CaCl2 solutions. Up to now, the production of DH and/or a-HH in a continuous crystallization reactor cascade via adaptation of a semi-batch staged crystallization scheme failed to generate super-azeotropic strength HCI without forming the undesirable anhydrite (AH) phase. The present provides a newly-developed continuous process that yields high strength HCI (up to 9.5 mol/L, ==30% super-azeotropic strength) by reactive crystallization of a-HH without forming anhydrite. The present process was designed on the basis of water activity calculations made with the OLI Stream Analyzer software. It was demonstrated using a single-stage CSTR crystallizer (see Figure 12), which can be implemented in a parallel reactor scheme upon industrial scale up, rather than the more conventional in-series approach.
[0055] Accordingly, the process described herein consists of a single, continuous, stirred tank reactor (CSTR) in which the following reaction is performed:
CaCl2 + H2SO4 + xH20 2HCI + CaSO4.xH20 (2) where x=0.5 or 2.
CaCl2 + H2SO4 + xH20 2HCI + CaSO4.xH20 (2) where x=0.5 or 2.
[0056] This reaction is performed at a stoichiometric sulfate to calcium ratio of the inflow solutions of 0.90 to 0.98 in a single step and in continuous fashion.
It results in the generation of super-azeotropic HCI with up to 30 wt.%
(9.5 mol/L). The temperature of the reaction inside the stirred reactor can be about 60 C for the production of a-HH crystals or 5 40 C for the production of DH crystals. The nominal residence time of the crystals in the reaction tank is preferably 1 h. CaCl2 and H2SO4 solution is constantly fed by pumps to the reactor and the reaction product (slurry consisting of HCI acid and a-HH or DH
solid) is continuously removed.
It results in the generation of super-azeotropic HCI with up to 30 wt.%
(9.5 mol/L). The temperature of the reaction inside the stirred reactor can be about 60 C for the production of a-HH crystals or 5 40 C for the production of DH crystals. The nominal residence time of the crystals in the reaction tank is preferably 1 h. CaCl2 and H2SO4 solution is constantly fed by pumps to the reactor and the reaction product (slurry consisting of HCI acid and a-HH or DH
solid) is continuously removed.
[0057] Depending on the concentration of the inflow solutions and the stoichiometric ratio, as summarized in Table 1, it can be seen that different HCI
concentrations can be obtained in a stable manner for several hours.
Table 1 Summary of experimental parameters and properties Experimental parameter and solution compositions Steady-state product properties Exp. Temper Reaction extent, Feed solution Feed CaCI0 flow H2S0. flow Steady state Steady state Solid Solid Median no. ature (S0.27Ce ratio)* CaCI, conc. solution rate, actual rate (target) NCI conc. CaCI, conc. content produced at particle H2S0. (target) standard dev standard steady state size conc. dev - mol/L mol/L mo l/h mo l/h mol/L
mol/L pm Experiments with target product DH
CT2 40 33.3, (0.95) 5.06 12.54 3.99 (4.00) 1_25 (1.25) 2.8 0.1 3.4 0.2 17 HH 16 CT3 40 100, (0.90) 3.03 5.40 1.79 (1.80) 1.63 (1.62) 4.0 0.1 0.4 0.0 24 DH 97 CT4 30 100, (0.90) 5.04 7.71 2.94 (3.00) 2.65 (2.70) 6.7 0.2 0.5 0,0 35 DH & HH 40 traces Experiments with target product HH
CT6 60 100, (0.90) 4.94 7.71 2.97 (3.00) 2.49 (2.70) 5.9 0.1 0.8 0.1 31 HH 25 CT9 60 100, (0.95) 5.06 17.87 3.95 (3.95) 3.95 (3.75) 8.9 0.1 0.5 0.1 36 HH 27 CT10 60 100, (0.95) 5.11 17,87 3.89 (3.95) 3.88 (3,75) 9.0 0,2 0.3 0.1 36 HH 33 CT12 5631- 100, (0.95) 5.11 17.87 3.61 (3.95) 3.95 (3.75) 9.530.2 0.130.0 n.a. HH 61
concentrations can be obtained in a stable manner for several hours.
Table 1 Summary of experimental parameters and properties Experimental parameter and solution compositions Steady-state product properties Exp. Temper Reaction extent, Feed solution Feed CaCI0 flow H2S0. flow Steady state Steady state Solid Solid Median no. ature (S0.27Ce ratio)* CaCI, conc. solution rate, actual rate (target) NCI conc. CaCI, conc. content produced at particle H2S0. (target) standard dev standard steady state size conc. dev - mol/L mol/L mo l/h mo l/h mol/L
mol/L pm Experiments with target product DH
CT2 40 33.3, (0.95) 5.06 12.54 3.99 (4.00) 1_25 (1.25) 2.8 0.1 3.4 0.2 17 HH 16 CT3 40 100, (0.90) 3.03 5.40 1.79 (1.80) 1.63 (1.62) 4.0 0.1 0.4 0.0 24 DH 97 CT4 30 100, (0.90) 5.04 7.71 2.94 (3.00) 2.65 (2.70) 6.7 0.2 0.5 0,0 35 DH & HH 40 traces Experiments with target product HH
CT6 60 100, (0.90) 4.94 7.71 2.97 (3.00) 2.49 (2.70) 5.9 0.1 0.8 0.1 31 HH 25 CT9 60 100, (0.95) 5.06 17.87 3.95 (3.95) 3.95 (3.75) 8.9 0.1 0.5 0.1 36 HH 27 CT10 60 100, (0.95) 5.11 17,87 3.89 (3.95) 3.88 (3,75) 9.0 0,2 0.3 0.1 36 HH 33 CT12 5631- 100, (0.95) 5.11 17.87 3.61 (3.95) 3.95 (3.75) 9.530.2 0.130.0 n.a. HH 61
[0058] The process encompassed herein was tested on a lab scale using a temperature-controlled reactor with a working volume of 1 L over a period of h, during which the process was operated at stable steady state conditions for 6.5 h. An example of an experimental set up can be seen in Fig. 1.
[0059] The crystallization experiments as described herein were carried out in a continuous-stirred tank reactor 5. Encompassed herein is the use of multiple reactors in parallel. The working volume of the reactor 5 was 1 L, which was maintained by the overflow of the slurry through a 1 cm diameter tube at the side of the reactor. A turbulent mixing regime was achieved with a two-level pitched blade impeller with 3 blades at each level, having a hydrodynamic diameter of 6 cm (3 cm apart vertically) controlled by a speed motor 3. The stirrer speed was adjusted as necessary to maintain good mixing and slurry flow inside the reactor 5; it was set to 300 rpm at the beginning of the experiment (low solids content) and subsequently increased up to 700 rpm at steady state condition. The sulfuric acid and calcium chloride solutions 1 were fed drop-wise with peristaltic pumps 2 at different flow rates in order to maintain a residence time of 60 min and account for the stoichiometry of the experiment. The temperature was maintained by either heating the reactor with a temperature controlled hot-plate 4 or by cooling the reactor with compressed air to stabilize it at a certain temperature (in the case of DH experiments only). The latter was necessary to offset the heat released from acid (H2SO4) mixing and the reaction. All solutions were prepared with deionized water (DIW), and ACS
reagent grade chemicals. The produced HCI-solid mixture was collected in a receiving container 6.
reagent grade chemicals. The produced HCI-solid mixture was collected in a receiving container 6.
[0060] Since a continuous reactor goes through a start-up phase before it reaches steady state conditions, the effect of different starting solution compositions was tested. In some experiments, the start-up was done with water and in some experiments a synthetic solution with a composition closer to the expected steady-state composition was used (Table 2).
Table 2 Detailed experimental results Experimental parameter and solution compositions Steady-state product properties Start-up condition Exp. Tempe Reaction extent Feed Feed CaCl2 flow H2SO4 flow Retention Steady state Steady Solid Solid produced Seed type Start-up no. rature target (S0427Ca solution solution rate, rate (target) time HCI conc. state CaCl2 content at steady state used solution ratio) CaCl2 H2SO4 actual standard conc.
(Median type conc. conc. (target) dev standard particle size) dev C %, _ mol/L mol/L mol/h mol/h min mol/L
mol/L % pm Experiments with DH as target CT1 40 133.3, (0.95) 5.32 12.54 3.94 (4.0) 1.19 (1.25) 61 2.88 0.07 3.55 0.07 14 HH lab made DH synthetic (12) o n.) CT2 40 133.3, (0.95) 5.06 12.54 3.99 (4.0) 1.25 (1.25) 60 2.75 0.12 3.41+0.19 117 HH lab made DH DI
water l0 n.) (16) (3) w CT3 40 1100, (0.90) 3.03 5.40 1.79 (1.8) 1.63 (1.62) 60 4.02 0.10 0.38 0.02 ' 24 DH lab made DH DI
water cri (97) cn CT4 30 100, (0.90) 5.04 7.71 2.94 (3.0) 2.65 (2.70) 64 6.74 0.19 0.48 0.02 ' 35 DH, HH traces lab made DH DI water n.) o (40) cn oI
CT5 13 100, (0.90) 5.00 18.00 3.98 (4.0) 3.42 (3.60) 64 8.13 0.18 0.92 0.04 36 DH/HH mix lab made DH
DI water (9) o.
i Experiments with a-HH as target CT6 60 100, (0.90) 4.94 7.71 2.97 (3.0) 2.49 (2.70) 66 5.94 0.12 0.77 0.05 ' 31 HH lab made a-HH synthetic cn (25) CT7 60 ' 100, (0.90) 4.96 18.00 3.90(4.0) 3.05(3.60) 64 6.74 0.17 1.22 0.08 132 HH lab made a-HH synthetic (7) CT9 60 100, (0.95) 5.06 17.87 3.95 3.95 (3.75) 56 8.88 0.12 0.45 0.04 136 HH lab made a-HH synthetic (3.95) (27) -CT10 60 100, (0.95) 5.11 17.87 3.89 3.88 (3.75) 56 8.97 0.2 0.33 0.07 ' 36 HH Knauf FGD" a- synthetic (3.95) (33) HH
CT12 56 1"" 100, (0.95) 5.11 17.87 3.61 3.95 (3.75) 60 9.52 0.21 0.11 0.04 n.a. HH lab made a-HH synthetic (3.95)
Table 2 Detailed experimental results Experimental parameter and solution compositions Steady-state product properties Start-up condition Exp. Tempe Reaction extent Feed Feed CaCl2 flow H2SO4 flow Retention Steady state Steady Solid Solid produced Seed type Start-up no. rature target (S0427Ca solution solution rate, rate (target) time HCI conc. state CaCl2 content at steady state used solution ratio) CaCl2 H2SO4 actual standard conc.
(Median type conc. conc. (target) dev standard particle size) dev C %, _ mol/L mol/L mol/h mol/h min mol/L
mol/L % pm Experiments with DH as target CT1 40 133.3, (0.95) 5.32 12.54 3.94 (4.0) 1.19 (1.25) 61 2.88 0.07 3.55 0.07 14 HH lab made DH synthetic (12) o n.) CT2 40 133.3, (0.95) 5.06 12.54 3.99 (4.0) 1.25 (1.25) 60 2.75 0.12 3.41+0.19 117 HH lab made DH DI
water l0 n.) (16) (3) w CT3 40 1100, (0.90) 3.03 5.40 1.79 (1.8) 1.63 (1.62) 60 4.02 0.10 0.38 0.02 ' 24 DH lab made DH DI
water cri (97) cn CT4 30 100, (0.90) 5.04 7.71 2.94 (3.0) 2.65 (2.70) 64 6.74 0.19 0.48 0.02 ' 35 DH, HH traces lab made DH DI water n.) o (40) cn oI
CT5 13 100, (0.90) 5.00 18.00 3.98 (4.0) 3.42 (3.60) 64 8.13 0.18 0.92 0.04 36 DH/HH mix lab made DH
DI water (9) o.
i Experiments with a-HH as target CT6 60 100, (0.90) 4.94 7.71 2.97 (3.0) 2.49 (2.70) 66 5.94 0.12 0.77 0.05 ' 31 HH lab made a-HH synthetic cn (25) CT7 60 ' 100, (0.90) 4.96 18.00 3.90(4.0) 3.05(3.60) 64 6.74 0.17 1.22 0.08 132 HH lab made a-HH synthetic (7) CT9 60 100, (0.95) 5.06 17.87 3.95 3.95 (3.75) 56 8.88 0.12 0.45 0.04 136 HH lab made a-HH synthetic (3.95) (27) -CT10 60 100, (0.95) 5.11 17.87 3.89 3.88 (3.75) 56 8.97 0.2 0.33 0.07 ' 36 HH Knauf FGD" a- synthetic (3.95) (33) HH
CT12 56 1"" 100, (0.95) 5.11 17.87 3.61 3.95 (3.75) 60 9.52 0.21 0.11 0.04 n.a. HH lab made a-HH synthetic (3.95)
(61) [0061] The reason for this investigation was to determine if the time to reach steady state or if the stability of the seed crystals would be affected. With reference to the latter, emphasis was placed on ensuring that the DH or HH
crystals used as seed would not undergo phase transformations during the start-up period. In other words, the strategy was to have the right crystal phase (DH or HH depending on the desired end product) present during the unsteady-state start-up of the process.
crystals used as seed would not undergo phase transformations during the start-up period. In other words, the strategy was to have the right crystal phase (DH or HH depending on the desired end product) present during the unsteady-state start-up of the process.
[0062] Fig. 2A shows the evolution of acid concentration and CaCl2 concentration over time for two typical experiments (CT4, CT6). It can be seen that steady state was reached after approximately 3.5 h in both cases and that the process is reasonably stable. As can be seen in the experiment that was started with deionized water (CT4), a fast build-up of acid concentration within the first few hours was observed. On the other hand, in an experiment started with a synthetic solution of near steady-state composition (CT6), steady-state was also reached after 3-3.5 h.
[0063] The choice of the start-up mode is dictated by the targeted product, DH or a-HH. This is because it is important to avoid phase transformation of the seed crystals during start-up. For example, if a-HH seed crystals are added to DIVV at the beginning of a test targeting a-HH as product, this will not work as after the ramp-up phase a-HH will have converted to DH as the latter is the thermodynamically stable phase in water at temperatures below 42 C. These results allow the selection of suitable start-up conditions, thus avoiding complications.
[0064] It has been shown previously that apart from the activity of water (governed by solution composition), the temperature at which the crystallization-based acid regeneration process is performed influences the crystal phase that is formed. The heat released by the reaction system needs to be taken into account in the process design as it is significant, especially with high reactant stream concentrations. For example, a calculation with OLI Stream Analyzer showed that the heat released from mixing and the reaction between the reagents was 310 kJ/h. This calculation was done for experiment CT5 (5 mol/L
CaCl2 at 3.98 mol/h and 18 mol/L H2SO4 at 3.42 mol/h). As a result of the high level of heat released, a steady-state temperature was attained in the non-insulated, single-walled glass reactor in the case of experiment CT12. A
temperature of 56 C was measured while the ambient temperature was 23 C
during the experiment, which was run without any temperature control. This means that the process can essentially run autogenously if concentrated feed solutions are used.
CaCl2 at 3.98 mol/h and 18 mol/L H2SO4 at 3.42 mol/h). As a result of the high level of heat released, a steady-state temperature was attained in the non-insulated, single-walled glass reactor in the case of experiment CT12. A
temperature of 56 C was measured while the ambient temperature was 23 C
during the experiment, which was run without any temperature control. This means that the process can essentially run autogenously if concentrated feed solutions are used.
[0065] Previous semi-batch crystallization work with a similar system showed that calcium sulfate dihydrate (DH) could exist in a solution with a composition of -2.8 mol/L HCI and -3.5 mol/L CaCl2 at 40 C, as was the case in CT1 and CT2, for a time sufficiently longer than the residence time of 60 min.
Surprisingly, DH was not obtained as the steady state product, but rather a-HH
(see Table 2). This underlines the importance of performing continuous crystallization tests in the case of metastable crystal phases.
Surprisingly, DH was not obtained as the steady state product, but rather a-HH
(see Table 2). This underlines the importance of performing continuous crystallization tests in the case of metastable crystal phases.
[0066] The observed behavior is explained with the help of Fig. 3, which shows estimations of the water activity (aw) as a function of HCI and CaCl2 concentration. The calculations were made with OLI Stream Analyzer. A value for aw close to 1 means that the "lifetime" of the metastable phase in contact with the solution will be significantly extended. From Equation 2 and Fig. 3, a concentrated CaCl2 feed solution, for example 5 mol/L, will be converted to a certain HCI concentration (approximately two times the CaCl2 concentration).
Therefore, the steady state condition will always be diagonally (left and up) from the initial calcium chloride concentration in such a diagram, since calcium is consumed/precipitated as calcium sulfate and HCI is left in solution.
Therefore, the steady state condition will always be diagonally (left and up) from the initial calcium chloride concentration in such a diagram, since calcium is consumed/precipitated as calcium sulfate and HCI is left in solution.
[0067] This situation is illustrated with the results of experiments CT1, and CT3 conducted at 40 C (Fig. 3A). Although CT1 and CT2 should have formed DH (as CT3 did), a-HH was formed instead. The reason for the formation of a-HH is that the steady state composition of CT1 and CT2 in comparison to CT3 was in a less favorable region in terms of water activity despite the lower acid concentration (2.75 mol/L HCI in 012 vs. 4 mol/L HCI in CT3). This realization, that it is the water activity that governs the crystal production process, prompted the idea to opt for a single CSTR operating at low steady-state CaCl2 concentration that is associated with a relatively higher water activity. In this way, the relative metastability of the target phase is enhanced, allowing for high HCI concentrations to be achieved. The dashed line in Fig. 3 denotes the change of relative metastability, i.e., below the line DH is relatively more stable than a-HH and above the line a-HH is relatively more stable than DH. In all conditions investigated, calcium sulfate anhydrite is the thermodynamically stable phase.
[0068] This water activity-based single-stage crystallization approach also proved to have beneficial effects on crystal growth as reflected by the particle size distribution data in Table 1, Figs. 4 and 5. Thus the DH crystals produced at the relatively high acid concentration of 4 mol/L HCI but low (0.38 mol/L) CaCl2 concentration (CT3 test) were much larger than the HH crystals produced at the same temperature (40 C) but lower HCI concentration (2.75 mol/L HCI) and correspondingly higher (3.4 mol/L) CaCl2 concentration (CT2 test). There are two influences to distinguish, namely that of water activity and that of calcium chloride/calcium ion concentration in solution. The water activity in the former case (CT3) was higher than the corresponding one in the latter case.
This caused a different phase to form DH, which has a higher relative metastability.
This caused a different phase to form DH, which has a higher relative metastability.
[0069] A comparison of the particle size data shows in the case of CT2 the fraction of crystals being smaller than 10 pm was 43% while in the case of CT3 it was only 6%. It is proposed that this difference is due to high CaCl2 concentration in CT2. In this situation, homogeneous nucleation prevails as a result of high supersaturation, hence the smaller crystal size. By contrast, crystallization at low CaCl2 concentration favors crystal growth of existing crystals over nucleation, due to lower supersaturation. It should be noted that large crystals have better filtration characteristics than small ones.
[0070] In essence, it is demonstrated that water activity will determine the crystal phase that is formed, while the residual CaCl2 concentration will influence the particle growth/size characteristics of that solid phase.
[0071] Experiments CT1 and CT2, which were run at 40 C, yielded a-HH
crystals as a result of operating at low water activity. In both experiments, the a-HH crystals were rather fine and of poor quality as evident by their SEM
morphology (see Fig. 5A), particle size distribution (Fig, 6A), and differential scanning calorimetry scans (DSC in Fig. 6B). Furthermore, the obtained acid concentration in this case (CT2) was quite low and not of interest from an industrial process point of view (only - 2.7 mol/L, see Table 1). However, by increasing the temperature to 60 C and lowering the steady-state CaCl2 concentration below 1 mol/L, larger a-HH crystals were produced (see Table 1, CT6) at a higher HCI concentration of roughly azeotropic strength of -5.9 mol/L.
The crystal size of a-HH was observed to be very dependent on the steady-state CaCl2 concentration level. For example, the size distribution of CT7 (median particle size given in Table 2) that was run at 1.2 mol/L CaCl2 showed the presence of a significant amount of fines. By reducing the level of CaCl2, the generation of fines was eliminated and crystal growth was promoted as demonstrated by the size distribution data of CT9, CT10 and CT12. It can be seen in the case of the CT12 test that the a-HH had grown to large, elongated prismatic shape crystals (Fig. 6D) while the generated HCI acid concentration was of super-azeotropic strength, -9 mol/L (or 30%), while at higher CaCl2 concentrations much finer HH crystals were produced (Figs. 6A-C).
crystals as a result of operating at low water activity. In both experiments, the a-HH crystals were rather fine and of poor quality as evident by their SEM
morphology (see Fig. 5A), particle size distribution (Fig, 6A), and differential scanning calorimetry scans (DSC in Fig. 6B). Furthermore, the obtained acid concentration in this case (CT2) was quite low and not of interest from an industrial process point of view (only - 2.7 mol/L, see Table 1). However, by increasing the temperature to 60 C and lowering the steady-state CaCl2 concentration below 1 mol/L, larger a-HH crystals were produced (see Table 1, CT6) at a higher HCI concentration of roughly azeotropic strength of -5.9 mol/L.
The crystal size of a-HH was observed to be very dependent on the steady-state CaCl2 concentration level. For example, the size distribution of CT7 (median particle size given in Table 2) that was run at 1.2 mol/L CaCl2 showed the presence of a significant amount of fines. By reducing the level of CaCl2, the generation of fines was eliminated and crystal growth was promoted as demonstrated by the size distribution data of CT9, CT10 and CT12. It can be seen in the case of the CT12 test that the a-HH had grown to large, elongated prismatic shape crystals (Fig. 6D) while the generated HCI acid concentration was of super-azeotropic strength, -9 mol/L (or 30%), while at higher CaCl2 concentrations much finer HH crystals were produced (Figs. 6A-C).
[0072] DSC measurements further confirmed the high quality of the a-HH
crystals, as revealed by the sharp endothermic/exothermic peaks (Fig. 7B).
High quality a-HH provides for a better binder material than the more commonly used 13-HH phase.
crystals, as revealed by the sharp endothermic/exothermic peaks (Fig. 7B).
High quality a-HH provides for a better binder material than the more commonly used 13-HH phase.
[0073] Further analysis shows a direct relationship between the fraction of very fine crystals (<1 pm) and the exothermic peak signal in the DSC
measurements (see Fig. 8A). The latter was quantified by measuring the area underneath the peak to the baseline of the signal. In addition, there is a direct relationship between the amount of fines and the concentration of CaCl2 at steady-state (see Fig. 8B). The differently-sized crystals and the relationship to the steady-state CaCl2 concentration were also confirmed by the SEM images presented in Fig. 6. It can be clearly seen that a-HH crystals produced under conditions of lower steady-state calcium chloride concentration are much larger than those produced at much higher CaCl2 concentration. This behavior relates to the prevailing supersaturation condition, which is directly influenced by the magnitude of the CaCl2 concentration.
measurements (see Fig. 8A). The latter was quantified by measuring the area underneath the peak to the baseline of the signal. In addition, there is a direct relationship between the amount of fines and the concentration of CaCl2 at steady-state (see Fig. 8B). The differently-sized crystals and the relationship to the steady-state CaCl2 concentration were also confirmed by the SEM images presented in Fig. 6. It can be clearly seen that a-HH crystals produced under conditions of lower steady-state calcium chloride concentration are much larger than those produced at much higher CaCl2 concentration. This behavior relates to the prevailing supersaturation condition, which is directly influenced by the magnitude of the CaCl2 concentration.
[0074] The effect of CaCl2 on crystal growth - as contrasted between CT2 ("high" CaCl2 concentration, fine crystals) and CT12 ("low" CaCl2 concentration, large crystals) tests - can be explained by considering the local supersaturation generated upon the entry of a droplet of concentrated sulfuric acid into the receiving solution in the reactor. Although the reactor was well and turbulently mixed, some short finite amount of time is necessary to evenly distribute the viscous H2SO4 drop. Since the crystallization reaction of calcium sulfates proceeds without any noticeable induction time, it is apparent that calcium sulfate crystals nucleate instantaneously in the immediate vicinity around the droplet, before they have the chance to be dispersed into the bulk solution.
[0075] Thus, the process described herein provides a means for the efficient regeneration of high strength HCI (up to -9 mol/L, -30% super-azeotropic) that is critically needed in the implementation of modern chloride hydrometallurgical processes and which was not possible until the present disclosure from calcium chloride solutions. By making use of water activity and supersaturation control concepts, a novel acid regeneration process is provided featuring the crystallization of well-grown a-HH or DH crystals in a single CSTR without formation of the undesirable AH. The process described herein involves reaction of concentrated CaCl2 solution with concentrated sulfuric acid which is flexible with respect to the concentration of the regenerated HCI as well as the type of calcium sulfate phase (a-HH or DH) that is produced.
(0076] The selective production of DH or a-HH crystals with simultaneous regeneration of HCI in a continuous reactor is demonstrated for the first time.
The production of DH is possible only at sub-azeotropic HCI concentration (6 5_mol/L) and a preferred temperature 40 C. The regeneration of >9 mol/L
HCI with simultaneous production of a-HH was achieved with little to no heating at 60 C, due to the strongly exothermic nature of the dilution of the H2SO4 feed and the reaction itself. The concentration of CaCl2 at steady-state influenced the crystal size distribution of a-HH. Lower concentrations, e.g., 0.5 mol/L or below, led to larger crystals with narrower particle size distribution, effectively lowering the fraction of fines (crystals of <10 pm). This behavior is attributed to a lower local supersaturation environment. In contrast, the high calcium chloride concentration and low water activity that is encountered in multistage reactor set¨ups severely reduces the life-time of a-HH crystals, making the regeneration of high-concentration acid unfeasible.
The production of DH is possible only at sub-azeotropic HCI concentration (6 5_mol/L) and a preferred temperature 40 C. The regeneration of >9 mol/L
HCI with simultaneous production of a-HH was achieved with little to no heating at 60 C, due to the strongly exothermic nature of the dilution of the H2SO4 feed and the reaction itself. The concentration of CaCl2 at steady-state influenced the crystal size distribution of a-HH. Lower concentrations, e.g., 0.5 mol/L or below, led to larger crystals with narrower particle size distribution, effectively lowering the fraction of fines (crystals of <10 pm). This behavior is attributed to a lower local supersaturation environment. In contrast, the high calcium chloride concentration and low water activity that is encountered in multistage reactor set¨ups severely reduces the life-time of a-HH crystals, making the regeneration of high-concentration acid unfeasible.
[0077] When solid a-HH is produced by the process described herein, characterization by X-ray diffraction, Differential Scanning Calorimetry and Scanning Electron Microscopy compared to commercially available a-HH
produced with the state of the art autoclave method (Figs. 9-11) respectively, demonstrates that the solid produced by the process described herein produces crystals that are similar in size and crystal shape.
produced with the state of the art autoclave method (Figs. 9-11) respectively, demonstrates that the solid produced by the process described herein produces crystals that are similar in size and crystal shape.
[0078] The process described herein provides a means for regenerating HCI
from CaCl2 solutions which are generated in the metallurgical industry when leaching calcium-bearing ores to extract rare earths, for example.
Accordingly, it is provided a means to recycle CaCl2 waste solution streams and hence make these operations more environmentally-friendly.
from CaCl2 solutions which are generated in the metallurgical industry when leaching calcium-bearing ores to extract rare earths, for example.
Accordingly, it is provided a means to recycle CaCl2 waste solution streams and hence make these operations more environmentally-friendly.
[0079] Calcium bearing ores are, for example, sedimentary rock deposits of gypsum, limestone, skarn and shale. Some common calcium-bearing minerals include apatite, calcite, dolomite, fluorite, and gypsum (calcium sulfate).
[0080] As depicted in Fig. 12, normal extraction metallurgical processes incorporating the process described herein consist in leaching 12 using HCI
ores, preferably calcium-bearing ores 10 in order to produce a leachate containing metals and a calcium chloride solution. After separation/purification 14, the calcium solution collected can be integrated in the process (HCI
regeneration process described herein 16) in a reactor in order to extract calcium sulfate crystals and HCI which is recycled back to the leaching step 12.
ores, preferably calcium-bearing ores 10 in order to produce a leachate containing metals and a calcium chloride solution. After separation/purification 14, the calcium solution collected can be integrated in the process (HCI
regeneration process described herein 16) in a reactor in order to extract calcium sulfate crystals and HCI which is recycled back to the leaching step 12.
[0081] The present disclosure will be more readily understood by referring to the following examples which are given to illustrate embodiments rather than to limit its scope.
EXAMPLE I
Crystallization experiments
EXAMPLE I
Crystallization experiments
[0082] The crystallization experiments were carried out in a continuous stirred-tank reactor. The working volume of the reactor was 1 L, which was maintained by the overflow of the slurry through a 1 cm diameter tube at the side of the reactor. A turbulent mixing regime was achieved with a two-level pitched blade impeller with 3 blades at each level, having a hydrodynamic diameter of 6 cm (3 cm apart vertically). The stirrer speed was adjusted as necessary to maintain good mixing and slurry flow inside the reactor; it was set to 300 rpm at the beginning of the experiment (low solids content) and subsequently increased up to 700 rpm at steady state condition. A nearly ideal residence time distribution was achieved in all tests.
[0083] The sulfuric acid and calcium chloride solutions were fed drop-wise with peristaltic pumps at different flow rates in order to maintain a residence time of 60 min and account for the stoichiometry of the experiment. The temperature was maintained by either heating the reactor with a temperature controlled hot-plate or by cooling the reactor with compressed air to stabilize it at a certain temperature (in the case of DH experiments only). The latter was necessary to offset the heat released from acid (H2SO4) mixing and the reaction. All solutions were prepared with deionized water (DIW), and reagent grade chemicals.
[0084] Slurry samples were taken from the reactor every 30 min and immediately filtered through 0.22 pm Millipore Swinnex filters. The recovered crystals (-1-1.5 g) were immediately washed with isopropanol after filtration and stored in test tubes covered by a layer of isopropanol before further analysis.
This procedure successfully prevents any potential phase transformation of the crystals, especially a-HH, which is a metastable phase and might otherwise be susceptible to reaction with ambient moisture.
This procedure successfully prevents any potential phase transformation of the crystals, especially a-HH, which is a metastable phase and might otherwise be susceptible to reaction with ambient moisture.
[0085] Liquid samples taken during the experiment were immediately diluted with deionized water by a factor of 10, in order to avoid any further precipitation of calcium sulfates due to temperature change. The solutions were analyzed for acid concentration and Ca2+ concentration via titration of 1 mL of the diluted sample.
[0086] The solids were characterized by X-ray powder diffraction performed with a Cu Ka Philips PVV 1710 diffractometer. Additionally, crystal size distributions were measured in isopropanol with a Horiba Laser Scattering Particle Size Distribution Analyzer LA-920. Scanning electron microscopy was performed with a Philips XL30 FEG-SEM; samples were coated with carbon in order to avoid charging effects during imaging. In addition, differential scanning calorimetry (DSC) was carried out on a TGA Instruments 02000 apparatus, with a heating rate of 10 K/min and a nitrogen gas flow of 50 mL/min in closed aluminum crucibles. The latter two types of measurements were performed on selected samples to obtain information about the crystal morphology and the type of calcium sulfate hemihydrate produced, respectively. Especially, DSC is capable of identifying a-HH, due to a sharp exothermic peak found in the thermograms.
[0087] In order to characterize the slurry properties during steady state conditions, its solid content was determined on the basis of dry weight of produced solid to slurry weight at the end of the experiment.
EXAMPLE II
Effect of temperature on dihydrate production at high HCI concentration
EXAMPLE II
Effect of temperature on dihydrate production at high HCI concentration
[0088] Reduction of the temperature at which the crystallization is performed (from 40 C to 30 C to 13 C) helped to increase the steady state HCI
concentration, while DH with only a minor a-HH content was produced at 30 C
or a mix of DH/a-HH at 13 C. This shows that a water activity of 0.5 is required to operate in the window of DH "life-time" allowing for the precipitation of a pure solid phase., In the case of CT5, it appears that the temperature was not low enough to stabilize DH for a sufficiently long time, i. e., longer than the retention time in the reactor. This is due to the fact that the steady-state composition of the solution was in a region with a water activity value that was too low. Therefore, it can be seen that in order to obtain pure DH crystals at high acid concentration (>7 mol/L HCI), it will be necessary to cool the reactor to temperatures well below 13 C.
EXAMPLE III
Effect of seed material on product morphology
concentration, while DH with only a minor a-HH content was produced at 30 C
or a mix of DH/a-HH at 13 C. This shows that a water activity of 0.5 is required to operate in the window of DH "life-time" allowing for the precipitation of a pure solid phase., In the case of CT5, it appears that the temperature was not low enough to stabilize DH for a sufficiently long time, i. e., longer than the retention time in the reactor. This is due to the fact that the steady-state composition of the solution was in a region with a water activity value that was too low. Therefore, it can be seen that in order to obtain pure DH crystals at high acid concentration (>7 mol/L HCI), it will be necessary to cool the reactor to temperatures well below 13 C.
EXAMPLE III
Effect of seed material on product morphology
[0089] A comparison between a situation in which commercial seed crystals of a-HH (CT10) were used in the process during start-up with an experiment where lab-made a-HH (CT9) crystals were used showed no difference in particle size of the steady-state product after 8 h. A comparison of the seed material with SEM images of process product shows that even after 0.5 h almost no compact commercially-available a-HH crystals are left. It appears that these crystals would have dissolved and re-precipitated in the more elongated (rod-shaped) form, which is typical of a-HH produced under the conditions of discussing HCI regeneration process. Further support for this explanation is given by the fact that calcium sulfates experience higher solubility at high HCI
content when only low concentrations of calcium ions are present.
EXAMPLE IV
Influence of nominal retention time on process
content when only low concentrations of calcium ions are present.
EXAMPLE IV
Influence of nominal retention time on process
[0090] As shown by experiments CT9, CT10 and CT12, it was possible to produce a-HH and simultaneously recover high-strength HCI. In all cases the nominal retention time, defined by reactor volume divided by reagent flow rate, was -60 min. In order to investigate the effect of a shorter residence time of -30 min, two experiments were conducted with 5 mol/L CaCl2 and 11.1 mol/L
(CT15) or 18.2 mol/L (CT14) H2SO4 solution. The volumetric flow rates were adjusted to obtain the target nominal retention time. In both cases, no steady state conditions were achieved. In the case of CT14, the slurry became impossible to mix after 30 min and in the case of CT15 this happened after 1 h.
XRD results confirmed the presence of calcium sulfate anhydrite (at least partially). It is known that the morphology of this phase's crystals is very fine and fibrous. Therefore, under these conditions a phase transformation of a-HH
to AH occurred. The reason for this is that the increased molar flow rate, which delivers more sulfuric acid per time to the same point in the reactor than in the 60 min retention time experiments, caused a zone of high acid concentration resulting in local low water activity. This created a favorable environment for the formation of AH. Therefore, it can be concluded that the nominal retention time of the reactor should be at least one hour and preferably below 2-3 h, which showed that especially at high acid strength the metastable life-time of a-HH
is only a few hours, before transformation to the thermodynamically stable AH
phase starts.
(CT15) or 18.2 mol/L (CT14) H2SO4 solution. The volumetric flow rates were adjusted to obtain the target nominal retention time. In both cases, no steady state conditions were achieved. In the case of CT14, the slurry became impossible to mix after 30 min and in the case of CT15 this happened after 1 h.
XRD results confirmed the presence of calcium sulfate anhydrite (at least partially). It is known that the morphology of this phase's crystals is very fine and fibrous. Therefore, under these conditions a phase transformation of a-HH
to AH occurred. The reason for this is that the increased molar flow rate, which delivers more sulfuric acid per time to the same point in the reactor than in the 60 min retention time experiments, caused a zone of high acid concentration resulting in local low water activity. This created a favorable environment for the formation of AH. Therefore, it can be concluded that the nominal retention time of the reactor should be at least one hour and preferably below 2-3 h, which showed that especially at high acid strength the metastable life-time of a-HH
is only a few hours, before transformation to the thermodynamically stable AH
phase starts.
[0091] While the present disclosure has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as illustrative and not in a limiting sense.
[0092] While the disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations, including such departures from the present disclosure as come within known or customary practice within the art and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.
Claims (16)
1. A method for producing calcium sulfate solid crystals and azeotropic hydrochloric acid (HCI) from a calcium chloride solution comprising the steps of:
feeding a continuous-stirred tank reactor with a calcium chloride solution, sulfuric acid and water;
mixing the calcium chloride solution, sulfuric acid and water in the reactor;
and maintaining the reactor at a temperature of less than about 70°C, converting the calcium chloride solution, sulfuric acid and water into azeotropic HCI and calcium sulfate solid crystals.
feeding a continuous-stirred tank reactor with a calcium chloride solution, sulfuric acid and water;
mixing the calcium chloride solution, sulfuric acid and water in the reactor;
and maintaining the reactor at a temperature of less than about 70°C, converting the calcium chloride solution, sulfuric acid and water into azeotropic HCI and calcium sulfate solid crystals.
2. The method of claim 1, wherein the calcium sulfate solid crystals are crystals of at least one of calcium sulfate dihydrate, calcium sulfate a-hemihydrate and mixture thereof.
3. The method of claim 1 or 2, wherein up to 30 wt% (9.5 mon) of super-azeotropic HCI
is obtained.
is obtained.
4. The method of any one of claims 1-3, wherein the ratio of sulfate to calcium in the reactor is 0.90 to 0.98.
5. The method of any one of claims 1-4, wherein the temperature of the reactor is about less than 60°C.
6. The method of any one of claims 1-4, wherein the temperature of the reactor is about 40°C-70°C.
7. The method of any one of claims 1-4, wherein the temperature of the reactor is about 40°C or less.
8. The method of any one of claims 1-7, wherein the reactor is continuously fed with calcium chloride solution, sulfuric acid and water, continuously producing the azeotropic HCI and the calcium sulfate solid crystals.
9. The method of any one of claims 1-8, wherein the calcium chloride solution is a feed stream from processing of calcium-bearing ores.
10. The method of any one of claims 1-9, wherein the continuous-stirred tank reactor is a single continuous-stirred tank reactor not in series.
11. The method of any one of claims 1-10, wherein the calcium chloride solution, sulfuric acid and water are fed in multiple parallel reactors.
12. A process of extracting metals from calcium-bearing ores comprising the steps of:
leaching the ores with HCI. producing a leachate containing a calcium chloride solution and metals;
separating the metals from the calcium chloride solution;
feeding a continuous-stirred tank reactor with the calcium chloride solution, sulfuric acid and water;
mixing the calcium chloride solution, sulfuric acid and water in the reactor;
maintaining the reactor at a temperature of less than about 70°C, converting the calcium chloride solution, sulfuric acid and water into azeotropic HCI and calcium sulfate solid crystals; and recycling the HCI to the leaching of the ores.
leaching the ores with HCI. producing a leachate containing a calcium chloride solution and metals;
separating the metals from the calcium chloride solution;
feeding a continuous-stirred tank reactor with the calcium chloride solution, sulfuric acid and water;
mixing the calcium chloride solution, sulfuric acid and water in the reactor;
maintaining the reactor at a temperature of less than about 70°C, converting the calcium chloride solution, sulfuric acid and water into azeotropic HCI and calcium sulfate solid crystals; and recycling the HCI to the leaching of the ores.
13. The process of claim 12, wherein the calcium sulfate solid crystals are crystals of at least one of calcium sulfate dihydrate, calcium sulfate a-hemihydrate and mixture thereof.
14. The process of claim 12 or 13 wherein the metals are rare earth metals.
15. The process of any one of claims 12-14, wherein the continuous-stirred tank reactor is a single continuous-stirred tank reactor not in series or is in multiple parallel reactors.
16. A construction board comprising calcium sulfate solid crystals produced by the method of any one of claims 1-15.
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