METHOD OF PREPARATION OF EXTRACTION PHOSPHORIC ACID Russian patent published in 2008 - IPC C01B25/18 

FIELD: technological processes; chemistry.

SUBSTANCE: invention is related to method of preparation of extraction phosphoric acid (EPA) from apatite concentrate, and also of high quality phosphorites (P₂O₅ content - no less than 36%). Method includes treatment of phosphate raw materials with sulfuric and phosphoric acids with crystallisation of calcium sulfate dihydrate, separation of production dihydrate pulp into two parts, preparation of production acid from one part of pulp, counterflow water flushing of calcium sulfate dihydrate cake and return of flushing solutions to the stage of decomposition, treatment of second part of dihydrate pulp with sulfuric acid at mass ratios in liquid phase of pulp P₂O₅ : H₂SO₄ = (2.5 - 6.0) : 1 and H₂SO₄ : F = (2.0 - 9.4) : 1 in the presence of live steam with preparation of semi-hydrate of calcium sulfate, separation of semi-hydrate pulp with filtration, counterflow water flushing of calcium sulfate semi-hydrate with its usage for preparation of gypsum binder and return of filtrate and flushing waters to decomposition stage. Crystallization of calcium sulfate dihydrate is carried out at contents of P₂O₅ 25.0 - 28.5% and H₂SO₄ 0.5 - 2.4%, dihydrate pulp is treated with sulfuric acid of concentration 93.0 - 98.5%, and semi-hydrate of calcium sulfate at stage of filtration is exposed to additional flushing with water on the basis of 0.2 - 0.6 m³/t of α-semi-hydrate of calcium sulfate with disposal of prepared filtrate at the stage of calcium sulfate dihydrate flushing.

EFFECT: reduction of steam consumption in semi-hydrate stage.

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