Selective extraction of potassium chloride employing tartaric acid as safe, benign and recyclable extractant

Patent metadata

Field	Value
Publication number	US-9540248-B2
Application number	US-201314379215-A
Country	US
Kind code	B2
Filing date	Apr 2, 2013
Priority date	Apr 2, 2012
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

Although U.S. Pat. No. 8,182,784 teaches the recovery of potassium chloride from schoenite end liquor (SEL) using dipicrylamine as extractant, and consequently simplifies the recovery of sulphate of potash (SOP) from kainite mixed salt employing the scheme disclosed in U.S. Pat. No. 7,041,268, the hazards associated with this extractant have thwarted practical utilization of the invention. Many other extractants for potash recovery have been disclosed in the prior art but none has been found suitable so far for practical exploitation. It is disclosed herein that the bitartrate ion, and particularly L-bitartrate, precipitates out potassium bitartrate very efficiently from SEL with ca. 90% utilization of the extractant. In contrast, recovery of potassium bi-tartrate from sea bittern directly is relatively much lower. It is further disclosed that this precipitate can be treated with magnesium hydroxide and magnesium chloride to throw out magnesium tartrate with ca. 90% recovery while yielding a nearly saturated solution of potassium chloride which can be utilized for the reaction with schoenite to obtain SOP. It is further demonstrated that the magnesium tartrate can be treated with an appropriate amount of aqueous HCl and added into a subsequent batch of SEL to throw out potassium bitartrate once again which demonstrates the recyclability of the extractant. The overall loss of tartrate over a cycle was ca. 20% but the dissolved tartrate remaining in the K-depleted SEL and KCl solutions can be precipitated out as calcium tartrate from which tartaric acid can be recovered by known methods, curtailing thereby the loss of tartaric acid per kg of KCl to <5 g. It is also demonstrated that through a similar approach, seaweed sap containing ca. 4% KCl can be concentrated to 20-22% KCl, with excellent utilization efficiency of tartaric acid, and this solution can similarly be utilized for SOP preparation. Potassium salts bearing other anions such as sulphate, nitrate, phosphate and carbonate can also be prepared from the isolated potassium bitartrate.

First claim

We claim:

1. A safe and efficient extraction process for recovery of a solution of potassium chloride, free of impurities, wherein said process comprises the steps of:
i. providing a) a schoenite end liquor containing 4.0-5.5% w/v K + obtained from decomposition of kainite mixed salt into schoenite, b) seaweed sap from Kappaphycus alvarezi containing 3.0-4.5% w/v potassium chloride, or c) sea bittern having 3.25% w/v potassium chloride;
ii. treating the schoenite end liquor, the seaweed sap, or the sea bittern obtained in step (i) with tartaric acid or a salt thereof and Mg(OH) 2 , to obtain precipitated potassium bi-tartrate and a potassium depleted residue, wherein the tartaric acid or a salt thereof is in a sub-stoichiometric amount, and a molar ratio of the tartaric acid or a salt thereof to the Mg(OH) 2 is 2:1;
iii. separating out the precipitated potassium bi-tartrate obtained in step (ii), and washing the precipitated potassium bi-tartrate obtained in step (ii) after separation with water to generate washings and washed potassium bi-tartrate;
iv. adding the washings obtained in step (iii) into the potassium-depleted residue obtained in step (ii);
v. treating the washed potassium bi-tartrate obtained in step (iii) with a stoichiometric amount of MgCl 2 and a stoichiometric amount of Mg(OH) 2 to convert the washed potassium bi-tartrate to magnesium tartrate while generating a potassium chloride solution;
vi. separating the magnesium tartrate obtained in step (v) from the potassium chloride solution obtained in step (v), washing the magnesium tartrate after separation to give washings and washed magnesium tartrate;
vii. treating the K-depleted residue obtained in step (iv) and the potassium chloride solution obtained in step (vi) with calcium carbonate and calcium chloride to precipitate out residual tartaric acid in a form of insoluble calcium tartrate;
viii. adding the washed magnesium tartrate of step (vi) into a second schoenite end liquor along with a stoichiometric amount of aqueous HCl to precipitate out potassium bi-tartrate;
ix. adding the potassium bi-tartrate from step (viii) into the washings of step (vi) and an additional amount of water followed by treating with a stoichiometric amounts of MgCl 2 and a stoichiometric amount of Mg(OH) 2 to precipitate out magnesium tartrate and obtaining a solution of Potassium chloride followed by regenerating tartaric acid from calcium tartrate obtained in step (vii).

2. The process as claimed in claim 1 , wherein in step (ii) the tartaric acid or a salt thereof is in DL, D, or L form.

3. The process as claimed in claim 2 , wherein recovery of potassium bi-tartrate is 85-95 mol % with respect to L-tartaric acid or a salt thereof and magnesium L-tartrate used in steps (ii) and (viii), respectively.

4. The process as claimed in claim 2 , wherein the washings of magnesium tartrate obtained in step (vi), contained 7-9% KCl in case of L-tartaric acid and 14-16% KCl in case of DL tartaric acid.

5. The process as claimed in claim 2 , wherein the tartaric acid or a salt thereof is L-tartaric acid or a salt thereof.

6. The process as claimed in claim 5 , wherein amounts of L-tartaric acid and magnesium L-tartrate in steps (ii) and (viii), respectively, are in the range of 85-95 mol % of the amount of K+ in the schoenite end liquor, the seaweed sap, or the sea bittern.

7. The process as claimed in claim 1 , wherein in step (ii), the schoenite end liquor, the seaweed sap, or the sea bittern is treated with tartaric acid and Mg(OH) 2 , at a temperature of 20 to 35° C.

8. The process as claimed in claim 1 , wherein in step (i), seaweed sap from Kappaphycus alvarezi containing 3.0-4.5% w/v potassium chloride is used.

9. The process as claimed in claim 1 , wherein in step (i), sea bittern having 3.25% w/v potassium chloride is used.

10. The process as claimed in claim 9 , wherein L-tartaric acid or a salt thereof is used in step (ii), and recovery of potassium L-bitartrate from sea bittern having 3.25% w/v KCl is 54-58 mol %.

11. The process as claimed in claim 1 , wherein in step (vii) the residual tartaric acid is reduced to 200-400 ppm.

12. The process as claimed in claim 1 , wherein Mg(OH) 2 required in the process of steps (ii) and (v) is generated as part of an integrated processes for sulphate of potash recovery from kainite mixed salt.

13. The process as claimed in claim 1 , wherein the calcium carbonate in step (vii) is obtained from an integrated production of sulphate of potash and ammonium sulphate from kainite mixed salt.

14. The process as claimed in claim 1 , wherein the potassium chloride solution of step (v) produces sulphate of potash on reaction with schoenite.

15. The process as claimed in claim 1 , wherein recovery of magnesium tartrate obtained in step (vi) with respect to potassium bi-tartrate is 85-95 mol %.

Assignees

• Council Scient Ind Res

Inventors

• Maiti Pratyush
• Ghosh Pushpito K
• Ghara Krishna K
• Solanki Jignesh
• Brahmbhatt Harshad R
• Chunawala Jatin R
• Eringathodi Suresh
• Paul Parimal

Classifications

• C01D3/08 Primary

  Preparation by working up natural or industrial salt mixtures or siliceous minerals · CPC title

• C01D3/06 Primary

  Preparation by working up brines; seawater or spent lyes · CPC title

• C22B26/10

  Obtaining alkali metals · CPC title