A method for the production of phorphorsaeure and calcium sulfate hemihydrate

摘要

In the wet process for the production of phosphoric acid and calcium sulphate hemihydrate, natural phosphates are treated with a mixture of sulphoric and phosphoric acids. The mash of gypsum (CaSO42H2O) formed is then treated with concentrated sulphuric acid and heated to a temperature between 70 DEG and 90 DEG C., other conditions being P2O5 concentration in liquid 15-35% by weight, H2SO4 concentration in liquid 2-25% by weight and rate of flow of gypsum sludge between 0.5 and 1.5 times the volume of the recrystallization tank per hour. CaSO4. 1/2 H2 is precipitated and is filtered off. The phosphoric acid may be extracted before or after the gypsum treatment. The liquid from the hemihydrate separation may be recycled in total or in part to the initial stage of attack on the natural phosphates.