Polyhalite IMI process for KNO3 production

摘要

A process for producing KNO3 from polyhalite is disclosed. In a preferred embodiment, the process comprises steps of (a) contacting polyhalite with HNO3; (b) adding Ca(OH)2 to the solution, thereby precipitating as CaSO4 at least part of the sulfate present in said solution; (c) precipitating as Mg(OH)2 at least part of the Mg2+ remaining in said solution by further addition of Ca(OH)2 to the remaining solution; (d) concentrating the solution, thereby precipitating as a sulfate compound at least part of the sulfate remaining in solution; (e) separating at least part of the NaCl from the solution remaining; and (f) crystallizing as solid KNO3 at least part of the K+ and NO3- contained in the solution. The process enables direct conversion of polyhalite to KNO3 of purity exceeding 98.5% and that is essentially free of magnesium and sulfate impurities.