METHOD FOR PREPARING PHOSPHORIC ACID BY CRYSTALLIZATION OF PHOSPHORIC ACID SEMIHYDRATE Russian patent published in 2004 - IPC

FIELD: inorganic chemistry, chemical technology. SUBSTANCE: invention relates to method for simultaneous preparing phosphoric acid with the nutritive quality by crystallization of phosphoric acid semihydrate of the formula H₃PO₄•H₂O from preliminary purified raw acid which is purified and crystallized by the following stages: a) after stage of foam flotation of phosphate concentrate the indicated concentrate is fed to the stage of intensive magnetic separation to diminish amount of magnesium ions; b) phosphate concentrate is leached out in mixture of sulfuric acid and phosphoric acid according to the wetting method, precipitated ions of SO2-4

and As are removed from medium and silicon source is added in order to bright about the molar ratio F/Si to the value less 6; c) phosphoric acid is concentrated, solid precipitate is removed and fluoride ions are evaporated; d) feeding acid obtained on the stage (c) with the concentration of P₂O₅ above 58%, the concentration of dry matter less 0.05%, the concentration of magnesium ions less 1.5%, the concentration of ions SO2-4 less 1%, the concentration of arsenic ions less 8 pro mille, and the concentration of fluoride ions less 0.2% is crystallized at the constant rate of crystals growth less 10 mcm/min and in the difference of temperatures in the process of the first crystallization less 17 C, and crystals are washed out in non-saturated mother liquor of the following stage of crystallization; e) phosphoric acid crystallized on the stage (d) is melted, diluted to the concentration of P₂O₅ less 63%, seed charges are added and crystallization is carried out as on the stage (d) in the difference between temperatures less 8 C, crystals are washed out with non-saturated phosphoric acid solution, and f) if necessary, phosphoric acid crystallized on the stage (e) is melted, diluted to the concentration of P₂O₅ less 63%, seed charges are added and crystallization is carried out as on the stage (d) in the difference between temperature less 6 C, crystals are washed out with non-saturated washing out solution prepared from the final crystals. Invention provides simplifying process for preparing phosphoric acid both of the nutritive quality and useful for preparing fodders for animals, and reducing exploitation consumptions also. EFFECT: improved preparing method. 12 cl, 6 tbl, 2 dwg, 7 ex