Process for the removal of lead and cadmium from phosphoric acid

摘要

To remove lead and cadmium from phosphoric acid, alkali solution and aqueous sulfide solution are simultaneously introduced with thorough mixing into a phosphoric acid having a P2O5 content of up to 32% by weight, an iron content of up to 0.3% by weight and an alkali/P ratio of up to 0.30. The temperature of the phosphoric acid which is thoroughly mixed with alkali solution and sulfide solution is adjusted to temperatures of 58 DEG to 72 DEG C. with escape of the excess hydrogen sulfide. To complete the sulfide precipitation, the temperature is lowered to below 45 DEG C. Finally, the precipitated sulfides of the lead and cadmium are separated off from the phosphoric acid.