METHOD OF PREPARING PHOSPHORIC ACID Russian patent published in 2000 - IPC

FIELD: preparation of extracting phosphoric acid from natural phosphates. SUBSTANCE: method comprises sulfuric phosphoric acid decomposition of phosphate stock, defluorination of the resulting suspension with sodium-containing reactants, separation and washing off precipitate of calcium sulfate, sodium silicon fluoride and calcium fluoride from phosphoric acid, desulfurization of the latter with precipitate of dicalcium phosphate and calcium fluoride which result from treatment of circulating water with calcium oxide or hydroxide to pH values of 6-8, and separation of said precipitate from circulating water, filtration of precipitate of calcium sulfate and fluoride recovered from desulfurization of precipitate of calcium sulfate and fluoride and recycling said precipitate to decomposition stage, additional washing of precipitate of calcium sulfate, sodium silicon fluoride and calcium fluoride with 5-10 parts of circulating water per 1 part of calcium sulfate to leach sodium silicon fluoride, remove precipitate of calcium sulfate and calcium fluoride for processing or storage. EFFECT: reduced specific consumption of stock for phosphoric acid production and no discharge of toxic water soluble fluorine-containing compounds into environment. 3 cl, 3 ex, 1 dwg