Method for removing cadmium in the manufacture of phosphoric acid

A method for manufacturing phosphoric acid from a calcium- and cadmium-containing phosphate ore, comprising the steps of:

• (a) digesting the calcium- and cadmium-containing phosphate ore with sulfuric acid to give an aqueous mixture of calcium sulfate, phosphoric acid, and cadmium impurities, wherein the content of calcium sulfate in the aqueous mixture is from about 20 to about 40% (w/w);
• (b) removing the calcium sulfate from the aqueous mixture to give a wet-process phosphoric acid solution containing from about 20 to about 45% (w/w) P2O5 and having a pre-treated cadmium content more than about 10 mg Cd/kg P2O5;
• (c) treating the wet-process phosphoric acid solution with from about 0.5 to about 10% (w/w) of a solid adsorbing material and from about 150 to about 900 ppm (by weight on a 100% basis with respect to the volume of the wet-process phosphoric acid solution) of a complex reagent to form a cadmium complex-contaminated solid adsorbing material;
• and
• (d) removing the cadmium complex-contaminated solid adsorbing material from the phosphoric acid solution to yield a treated phosphoric acid solution having a post-treated cadmium content at least about 10% lower than the pre-treated cadmium content;
• and
• (e) collecting the calcium sulfate removed from the step (b), cleaning the collected calcium sulfate, and adding the cleaned calcium sulfate into the wet-process phosphoric acid solution of step (c) as the solid adsorbing material.