Patent ID: 8388916

Claim:
A continuous method for producing KNO 3 from raw polyhalite, said method comprising steps of: washing raw polyhalite; heating said washed polyhalite; contacting said washed and heated polyhalite with water to produce decomposition products comprising K 2 Ca(SO 4 ) 2 , gypsum, and a first solution comprising K + , Mg 2+ , and SO 4 2− ions; separating at least one solid product from said first solution; contacting at least a portion of said at least one solid product separated from said first solution with a quantity of HNO 3 at least sufficient to produce a slurry; contacting said slurry with an alkaline Ca compound to precipitate sulfate as gypsum; filtering said contacted slurry to obtain a filtrate; washing gypsum obtained in the preceding steps; concentrating the filtrate obtained in said step of filtering the product of said step of contacted said slurry with an alkaline Ca compound; separating at least part of any CaSO 4 from said filtrate to yield a second solution; separating KNO 3 from the second solution to yield a third solution recovered; adding an alkaline Ca compound to the third solution; and, separating at least part of any Mg(OH) 2 produced in said step of adding an alkaline Ca compound to the third solution.