IL217176A - Polyhalite imi process of commercial quality potassium nitrate from polyhalite - Google Patents

Description

PROCESS FOR PRODUCTION OF COMMERCIAL QUALITY POTASSIUM Ni l RAIL FROM POL Y HA LITE o^NfT^non ηηηυη πΐ3'Ν- θΝΊΰ) y!wN TIIP!? - ^ππ IMI TAMI Institute lor Research and Development Ltd : nw no PROCESS FOR PRODUCTION OF COMMERCIAL QUALITY POTASSI UM NITRATE FROM POLYHAL1TE REFERENCE TO RELATED PUBLICATION This application claims priority from U.S. provisional application 61 /220,232, dated 25 June 2009, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION This invention concerns improved methods for the production of N03 and potassium and magnesium sulfates from polyhalite.

BACKGROUND OF THE INVENTION Potassium nitrate, KNO3, is an industrially important chemical with a variety of uses from fertilizers to explosives. It is primarily obtained either by mining of KNO3 deposits or by methods that ultimately derive from nitrogen fixation via the Flaber process.

Methods for production of .NO3 from syngenite (K2Ca(S04)2) are known in the literature. For example, Canadian Pat. No. 121 7027 to Worthington et al. and German patent 3525654 to Loblich et al. disclose methods for producing KNO3 from syngenite via reaction with CaN03'4H20.

Polyhalite, Ca2MgK2(S04)4-2H20, is widely distributed and readily available potassium-containing mineral. It has been known for some eight decades (see, for example, Partridge, E. P. Ind. Eng. Chem. 1932, 24, 895) that polyhalite can be a useful starting material for production of potash and potassium sulfate. Commercially viable methods that use polyhalite as a starling material for formation of KNO3 remain as yet unknown, however. A more efficient means for converting raw polyhalite into salts such as potassium nitrate, while increasing the quantity of gypsum relative to that in the raw polyhalite and controlling the relative quantity of KNO3 and potassium magnesium sulfates produced from the polyhalite, remains a long-felt need.

SUMMARY OF THE INVENTION The invention herein disclosed is designed to meet this long-felt need. The method herein disclosed recovers at least 45% to 75% of the potassium content of polyhalite, primarily as commercial-quality N03, with the remainder as potassium magnesium sulfate or as a mixture of sulfate salts.

It is therefore an object of the present invention to disclose a continuous method for producing NO3 from polyhalite, said method comprising steps of (a) washing polyhalite; (b) heating said washed polyhalite; (c) contacting said washed and heated polyhalite with sufficient water to produce decomposition products comprising K.2Ca(S04)2, gypsum, and a solution comprising K+, Mg2+, and S0 2" ions; (d) separating at least one solid product from said solution; (e) contacting solids obtained from said step of contacting said washed and heated polyhalite with water with a quantity of HNO3 at least sufficient to produce a slurry; (I) contacting said slurry with an alkaline Ca compound; (g) filtering said slurry; (h) washing gypsum obtained in said steps of contacting said washed and heated polyhalite with water and of treating said slurry with an alkaline Ca compound; (i) concentrating the filtrate obtained in said step of filtering the product of said step of treating said slurry with an alkaline Ca compound; (j) separating at least part of the CaS04 contained in said filtrate from the liquid; (k) separating NO3 from the solution recovered after said step of separating at least part of the CaS04 contained in said filtrate; (1) adding a basic Ca compound to the solution recovered after said step of separating KN03 from the solution recovered after said step of separating at least part of the CaSC^ contained in the filtrate; and (m) separating at least part of the Mg(OH)2 produced in said step of adding an alkaline Ca compound to the solution recovered after said step of separating K.NO3. It is within the essence of the invention wherein said method is adapted to produce commercial quality NO3 from raw polyhalite.

It is a further object of this invention to disclose such a method, wherein between 45% and 75%) of the K value of said polyhalite is recovered as KNO3, and further wherein substantially all of the remaining value of said polyhalite is recovered in a form chosen from the group consisting of (a) langbeinite, (b) a mixture of Mg and sulfate salts, and (c) any combination of the above.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of heating said washed polyhalite further comprises an additional step of heating said washed polyhalite to a temperature between about 400 °C and about 500 °C.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of heating said washed polyhalite Iurther comprises an additional step of heating said washed polyhalite to a temperature of about 450 °C.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of contacting said washed and heated polyhalite with sufficient water to produce decomposition products comprising K2Ca(S04)2, gypsum, and a solution comprising +, Mg2+, and S0 2" ions occurs at a temperature between about 20 °C and about 70 °C.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of contacting said washed and healed polyhalite with sufficient water to produce decomposition products comprising 2Ca(S04)2, gypsum, and a solution comprising ", Mg2+, and SO42" ions occurs at ambient temperature.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of contacting said washed and heated polyhalite with sufficient water to produce decomposition products comprising K2Ca(S04)2, gypsum, and a solution comprising +, Mg2+, and S042" ions further comprises an additional step of choosing a polyhalite/water ratio such that substantially all of the Mg2 ' and less than about 55% of the + originally present in the raw polyhalite remains in solution.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least one solid product from said solution further comprises an additional step of separating at least one solid chosen from the group consisting of (a) potassium sulfate salts; (b) magnesium sul fate salts; (c) potassium magnesium sulfate mixed salts.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least one solid product from said solution further comprises an additional step of precipitating a solid.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least one solid product from said solution further comprises an additional step of crystallizing said at least one solid product from said solution.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of contacting solids obtained from said step of contacting said washed and heated polyhalite with water with a quantity of I-I NO3 at least sufficient to produce a slurry further comprises an additional step of recycling at least part of the solution recovered after said step of separating at least part of the g(OH)2 produced in said step of said alkaline Ca compound to the sol ution recovered after said step of separating N03.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of contacting said slurry with said alkal ine Ca compound further comprises an additional step of contacting said slurry with a quantity of said alkaline Ca compound to reduce the sulfate content by at least 99% whi le maintaining a pH below 8. it is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least part of the CaS04 contained in said filtrate from the liquid further comprises an additional step of separating more than hal f of the CaSC»4 contained in said filtrate from the liquid.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least part of the CaS04 contained in said filtrate from the liquid further comprises an additional step of separating substantial ly all of the CaS04 contained in said filtrate from the liquid.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least part of the CaS04 contained in said filtrate from the liquid further comprises an additional step of separating said CaS04 by crystallization.

It is a further object of this invention to disclose such a method, further including an additional step of concentrating said filtrate.

It is a further object o f this invention to disclose such a method, further including an additional step of evaporating at least part of the liquid from said filtrate.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of evaporating is effected by a method chosen from the group consisting of (a) multiple effect evaporation; (b) mechanical vapor recompression; (c) solar evaporation.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating K.NO3 from the solution recovered after said step of separating at least part of the CaSC>4 contained in said filtrate further comprises an additional step of separating KNO3 from said solution by crystall ization.

It is a further object of this invention to disclose such a method, wherein said step of separating NO3 from said sol ution by crystal lization is carried our in a cooling crystaliizer.

It is a further object of this invention to disclose such a method as defined in any of the above, further comprising an additional step of puri ying the KNO3 recovered.

It is a further object of this invention to disclose such a method, further comprising an additional step of repulping with a substantially pure K.NO3 solution.

It is a further object of this invention to disclose such a method, further comprising an additional step of recrystallizing said KN03.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said step of separating at least part of the Mg(OH)2 produced in said step of adding Ca(OH)2 to the solution recovered after said step of separating K.NO3 further comprises an additional step of separating NO3 by crystallization.

It is a further object of this invention to disclose such a method as defined in any of the above, further including the additional step of recovering at least part of the gypsum produced during the process.

It is a further object of this invention to disclose such a method as defined in any of the above, wherein said alkal ine Ca compound is chosen from the group consisting of (a) Ca(OH)2, (b) CaO, (c) CaC03, and (d) any combination of the above.

BRI EF DESCRIPTION OF TH E FIGURE FIG. 1 shows a schematic flowchart of a combined process for treatment of polyhalite according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIM ENTS The present invention is described hereinafter with reference to the drawing, in which preferred embodiments are described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding o f the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that di ffer in details without affecting the essential nature thereof. Therefore the invention is not limited by that which is illustrated in the figures and described in the speciilcation, but only as indicated in the accompanying claims, with the proper scope determined only by the broadest interpretation of said claims.

Unless specifically indicated to the contrary, chemical formulas are given without regard to the presence or absence of water of hydration, or the stoichiometry of hydration of the salt.

As used herein, the generic term "sulfate salt" includes any salt that contains an anion of the general formula MaSbOc"", including anions where a = 0.

As used herein, the term "crystallizing" includes any technique known in the art for precipitating a solid from a solution.

The method disclosed herein for production of NO3 from polyhal ile involves the following two sequential chemical reactions, where x represents the fraction of polyhalite converted into syngenite (K2Ca(SO-!)2*I-l20); in preferred embodiments of the invention, x is between about 0.45 and about 0.85. 2K2 MgCa 2 (SOJ,( *: 2 H 20 ? (4 - JC)H 20 ? ( 1 ) ,v 2 Ca(SO,( )2 ?H 20 ? (4 ? j )CaSO., ?2H 20 ?2MgSO, ? (1 ? x)K2SO, ,rK2Ca(S04 )2 ? (4 7 .v)CaS04 ?2H 20 ? 2,rHNO? ? .vH 20 ? A-Ca(OH)2 ? (4 ? )CaSO, ?2H 20 ? 2JCKN03 In summary, in reaction ( 1 ). polyhalite is decomposed into syngenite, CaSC>4 (gypsum), and IVlgSO,). In reaction (2), the syngenite and gypsum react with nitric acid and calcium hydroxide (introduced separately into the reaction) to yield potassium nitrate.

As discussed in detail below, the reactions are carried out in a series of stages. Reference is now made to FIG. 1 , which presents a schematic flowchart of the stages involved in a preferred embodiment 10 of the method disclosed in the present invention for producing K.NO3 from polyhalite.

In the first stage 1010 of the method, polyhalite 101 is washed with sufficient water 102 to remove substantial ly al l of the NaCl contained within the polyhal ite. The polyhalite is separated from the supernatant liquid (step 1012), and the supernatant NaCl solution is then discharged from the system (step 1014).

In the second stage 1020 of the method, the polyhalite undergoes thermal treatment to dry it. In a preferred embodi ment, the polyhalite is dried by heating to 450 °C. As is well-known in the art, the effectiveness of the drying is demonstrated by the near-total decomposition of the polyhalite in its reaction in the following step of the process. In preferred embodiments, the heating is performed over a period of at least 20 minutes.

Polyhalite decomposition occurs in stage three (1030). In this stage, polyhalite is contacted with water 103. In preferred embodiments of the invention, the reaction takes place at a temperature between about 20 °C and 70 °C. In more preferred embodiments of the invention, the reaction mixture is not heated. In a most preferred embodiment of the invention, reaction takes place at ambient temperature. An amount of water sufficient to decompose the polyhalite is added. The polyhalite decomposes to yield as insoluble products syngenite and gypsum (CaS04*2H20). The polyhalite : water ratio and the temperature are chosen such that substantially all of the Mg + and less than about 55% of the + contained in the polyhalite is dissolved; in preferred embodiments, the polyhalite : water ratio (w/w) ranges from about 2:5 to 2:3. This reaction, and means for optimizing the polyhalile : water ratio, are well-known in the art. The syngenite is then separated from the supernatant liquid and washed (step 1032).

In stage 4 (1.040), the solution containing Mg2+, K.+, S042', and traces of Ca2 t' obtained in the previous stage is concentrated sufficiently to precipitate at least part of the dissolved material to provide solid product 204. In preferred embodiments, the concentration is performed by crystallization. In some embodiments of the invention, MgS04 solution recycled from stage 8 described below is added to the solution. In preferred embodiments, the solution is concentrated sufficiently to produce solid product 204 K.xMgy(S04)(x 2 + y> as a mixture of langbeinite ( 2Mg2(S04)3) and hydrated gS04. In some embodiments of the invention, the salts are crystallized separately, while in other embodiments, they are crystallized as a mixture. n stage 5a of the method (1050), the solids precipitated in stage 3 are treated with HNO3 (105) in order to obtain a solution containing K+, Ca2+, and NO3", along with small quantities of Mg2+ and SO42", as well as undissolved solids comprising primarily gypsum. In stage 5b (1052) the slurry obtained in stage 5a is further treated with Ca(OH)2 (106) to precipitate the sulfate as gypsum (205) and to bring the solution substantially to neutral pl-1. The gypsum precipitated in stages 5a and 5b (step 1054) is washed with water (in preferred embodiments, by counter-current washing on a tiller or by continuous washing in equipment) in order to reduce the nitrate content.

In stage 6 (1060), the supernatant liquid obtained in stage 5 is concentrated (in preferred embodiments, by evaporation by methods well-known in the art, e.g. in a multiple effect evaporator, by mechanical vapor recompression, or by solar evaporation). In some embodiments of the invention, the CaS04 precipitated (206) is separated from the solution (1062) at the exit from the evaporator (in preferred embodiments, by a polishing filter). In embodiments in which solar evaporation is performed, the CaS04 is left on the bottom of the pond.

In stage 7 (1070), KN03 (208) is separated from the solution. In preferred embodiments of the invention, the separation is accomplished by crystallization. In most preferred embodiments, the crystallization is carried out in a cooling crystallizer of any appropriate type known in the art, for example, a cooling disc crystallizer. In some embodiments of the invention, the KN03 produced in stage 7 is further purified by repulping with a pure KNO3 solution or by further recrystallization.

In stage 8 of the method (1080), a second stream comprising an alkaline Ca compound is added to the solution recovered from the crystallizer in order to precipitate the major part of the Mg2+ remaining in the solution. The solid Mg(OH)2 (207) thus precipitated can be used as obtained, or reacted with H2SO4 and the resulting solution added to the solution concentrated in stage 4, as described above. In preferred embodiments, the solution remaining after the crystallization step in stage 8 (107) is recycled into the solution used in stage 3, wherein at least a portion of the Ca(N03)2 in the solution reacts with at least a portion of the sul fate to precipitate gypsum.

EXAMPLES Example 1 Polyhalite was washed with water to remove NaCl and then dried at 450 °C. 200 g of washed and dried polyhalite were mixed with 500 g of water at 50 °C. After two hours, the slurry was filtered. The solution comprised 1 .7% K+, 1 .5 % Mg2 \ and 8.1 % S04= (w/w).

The solid was examined by XI D; the phases identi fied were gypsum and syngenite. The solid comprised 16.3% Ca2+, 1 1 .3% K+, 0.75% Mg2+ and 55% S04=. More than 70% of the potassium of the polyhalite remained in the solid phase, while about 85% of the Mg was dissolved.

Example 2 Polyhalite was washed with water to remove NaCI and then dried at 450 °C. 200 g of washed and dried polyhalite were mixed with 400 g of water at 50 °C. After two hours, the slurry was filtered. The solution comprised 2.2% K+, 1 .4 % Mg2'1', and 8.% S04=.

The solid comprised 19% Ca2+, 6.8% +, 0.8% Mg2+ and 57% S04=. About 45% of the potassium content of the polyhalite remained in the solid phase, while about 85% of the Mg was dissolved.

Reaction of 1 00 g of the wet solids with 23 g of HNO3 (60%) in presence of 900 g of water yielded a solution comprising 3.8% K+ and 0.5% Mg2+, while the solid residue contained less than 0.1 % o both Mg2+ and K+.

ABSTRACT A method for the production of N03 from poiyhalite is provided. The method comprises steps of decomposing said poiyhalite into syngenite, gypsum, and soluble components, treating the solid decomposition products sequential ly with HNO3 and Ca basic compound, precipitating the CaS04 thus formed, and crystallizing the K.NO3 from the solution remaining. The method recovers up to 75% of the potassium present in the raw poiyhalite as N03 and substantially all of the remainder as a potassium magnesium sul fate salt.

Claims (26)

CLAIMS We claim: 1. A continuous method for producing NO3 from polyhalite. said method comprising steps of: a. washing polyhalite; b. heating said washed polyhalite; c. contacting said washed and heated polyhalite with sufficient water to produce decomposition products comprising K2Ca(S04)2, gypsum, and a solution comprising +, Mg2+, and S042" ions; d. separating at least one solid product from said solution; e. contacting solids obtained from said step of contacting said washed and heated polyhaiite with water with a quantity 0ΙΊ-ΙΝΟ3 at least sufficient to produce a slurry; f. contacting said slurry with an alkaline Ca compound; g. filtering said slurry; h. washing gypsum obtained in said steps of contacting said washed and heated polyhalite with water and of treating said slurry with an alkaline Ca compound; i. concentrating the filtrate obtained in said step of fi ltering the product of said step of treating said slurry with an alkaline Ca compound; j . separating at least part of the CaS04 contained in said filtrate from the liquid; k. separating K.NO3 from the solution recovered after said step of separating at least part of the CaS04 contained in said filtrate;

1. adding a basic Ca compound to the solution recovered after said step of separating KNO3 from the solution recovered after said step of separating at least part of the CaS04 contained in the filtrate; and, m. separating at least part of the Mg(OH)2 produced in said step of adding an alkaline Ca compound to the solution recovered after said step of separating KN03; wherein said method is adapted to produce commercial quality KNO3 from raw polyhalite.

2. The method of claim 1 , wherein between 45% and 75% of the K value of said polyhalite is recovered as K.NO3, and further wherein substantially all of the remaining K value of said polyhalite is recovered in a form chosen from the group consisting of (a) langbeinite, (b) a mixture of Mg and K sul fate salts, and (c) any combination of the above.

3. The method of claim 1 , wherein said step of heating said washed polyhahte further comprises an additional step of heating said washed polyhahte to a temperature between about 400 °C and about 500 °C.

4. The method of claim 1 , wherein said step of heating said washed polyhahte further comprises an additional step of heating said washed polyhahte to a temperature of about 450 °C.

5. The method of claim 1 , wherein said step of contacting said washed and healed polyhahte with sufficient water to produce decomposition products comprising K2Ca(S04)2, gypsum, and a solution comprising +, Mg2+, and S042" ions occurs at a temperature between about 20 °C and 70 °C.

6. The method of claim 1 , wherein said step of contacting said washed and heated polyhahte with sufficient water to produce decomposition products comprising K2Ca(S04)2, gypsum, + 2 1" 2 and a sol ution comprising K. , Mg , and S04 " ions occurs at ambient temperature,

7. The method of claim 1 , wherein said step of contacting said washed and heated polyhahte with sufficient water to produce decomposition products comprising K^CafSCU , &ypsum) and a solution comprising +, Mg +, and S042" ions further comprises an additional step of choosing a polyhalite/water ratio such that substantially al l of the g2+ and less than about 55% of the K ' originally present in the raw polyhahte remains in solution.

8. The method of claim 1 , wherein said step of separating at least one solid product from said solution further comprises an additional step of separating at least one sol id chosen from the group consisting of (a) potassium sulfate salts; (b) magnesium sul fate salts; (c) potassium magnesium sulfate mixed salts.

9. The method of claim 1, wherein said step of separating at least one solid product from said solution further comprises an additional step of precipitating a solid.

10. The method of either one of claims 1 or 8, wherein said step of separating at least one solid product from said solution further comprises an additional step of crystal lizing said at least one solid product from said solution.

11. The method of claim 1, wherein said step of contacting solids obtained from said step of contacting said washed and heated polyhalite with water with a quantity o f HNO3 at least sufficient to produce a slurry further comprises an additional step of recycling at least part of the solution recovered after said step o separating at least part of the Mg(OH)2 produced in said step of said alkaline Ca compound to the solution recovered after said step of separating KNO3.

12. The method o f claim 1 , wherein said step of contacting said slurry with said alkaline Ca compound further comprises an additional step of contacting said slurry with a quantity of said alkaline Ca compound to reduce the sul fate content of the solution by at least 75% while maintaining a pH below 8.

13. The method of claim 1 , wherein said step of separating at least part of the CaS04 contained in said filtrate from the liquid further comprises an additional step of separating more than hal f of the CaSCX) contained in said filtrate from the liquid.

14. The method of claim 1. wherein said step o separating at least part of the CaS04 contained in said filtrate from the liquid further comprises an additional step of separating substantially all of the CaS04 contained in said filtrate from the liquid.

15. The method of any one of claims 1 , 12, or 13, wherein said step o separating at least part of the CaS0 contained in said filtrate from the liquid further comprises an additional step of separating said CaS04 by crystal lization.

16. The method of claim 15, further including an additional step of concentrating said filtrate.

17. The method of claim 16, further including an additional step of evaporating at least part of the liquid from said filtrate.

18. The method of claim 17, wherein said step of evaporating is effected by a method chosen from the group consisting of (a) multiple effect evaporation; (b) mechanical vapor recompression; (c) solar evaporation.

19. The method of claim 1 , wherein said step of separating N03 from the solution recovered alter said step of separating at least part of the CaS04 contained in said filtrate further comprises an additional step of separating K.NO3 from said solution by crystallization.

20. The method of claim 19, wherein said step of separating NO;¾ from said solution by crystal lization is carried our in a cooling crystal lizer.

21. The melhod of claim I , further comprising an additional step of purifying the NO.; recovered.

22. The melhod of claim 21 , further comprising an additional step of repulping with a substantial ly pure NO3 solution.

23. The method of either one of claims 21 or 22, further comprising an additional step of recrystal lizing said NO3.

24. The method of claim I , wherein said step of separating at least part of the Mg(OH)2 produced in said step of adding Ca(OH)2 to the solution recovered after said step of separating NO3 further comprises an additional step of separating NO3 by crystal l ization.

25. The method of claim 1 , further including the additional step of recovering at least part of the gypsum produced during the process.

26. The method of claim 1 , wherein said alkaline Ca compound is chosen from the group consisting of (a) Ca(OH)2, (b) CaO, (c) CaC03, and (d) any combination of the above. Uan-cWn Elwahu, ADV..