Patent ID: 8871170

Claim:
A process for producing solid KNO 3 of at least 98.5% purity from polyhalite, said polyhalite containing NaCl as an impurity, wherein said process comprises: contacting polyhalite with a substance comprising NO 3 − ; adding at least one inorganic base to the solution obtained in the step of contacting polyhalite with a substance comprising NO 3 − , thereby precipitating as a solid at least part of the sulfate present in said solution; precipitating as Mg(OH) 2 at least part of the Mg 2+ remaining in said solution by adding at least one basic compound to the remaining solution; concentrating a solution obtained after said step of precipitating at least part of the Mg 2+ remaining in said solution; precipitating at least part of said NaCl from the solution obtained after said concentrating; separating solid NaCl obtained in said step of precipitating at least part of said NaCl; separating as a quantity of solid KNO 3 at least part of K + and NO 3 − contained in the solution remaining after the step of precipitating at least part of said NaCl; and, recycling into the reaction vessel at least part of the solution remaining after said separating as a quantity of solid KNO 3 at least part of said K + and NO 3 − .