METHOD OF PRODUCTION OF POLYPHOSPHATES OF THE ALKALI METALS FROM THE PURIFIED EXTRACTION PHOSPHORIC ACID Russian patent published in 2006 - IPC C01B25/41 C01B25/234 

FIELD: chemical industry; pharmaceutical industry; food industry; textile industry; methods of production of polyphosphates of alkali metals from the purified extraction phosphoric acid.

SUBSTANCE: the invention is pertaining to the field of production of polyphosphates of alkali metals from the purified extraction phosphoric acid, in particular, to the method of production of the pure potassium and sodium polyphosphates used in food, pharmaceutical, chemical and textile industry. The method of production of polyphosphates of alkali metals includes desulfitation of the acid with the help of calcium compounds, further purification from cations, deep defluorination of the acid. The concentrated phosphoric acid, which before its concentrating is introduced with the compounds containing cations NH₄ ⁺ in amount ensuring the ratio in the acid N: P₂O₅ equal to 0.005-0.01/1 is neutralized by alkali or soda salt within one stage without the intermediate separation of the phases. Before neutralization the acid is discolored with the help of the oxidized activated charcoal having pH of the water extract of not exceeding 5.0, up to the optical density, equal to 0.05 - 0.005. The neutralized fine pulp is subjected to dehydration with production of the end-product. In the capacity of the compound containing cations_{NH4 ⁺ use the solution of ammonium nitrate. The result is production the product containing 95.5-98.5 % of the main substance; 6-8 % of the first form of sodium tripolyphosphate; 88-96 % of the brightness degree; 0.001-0.003 % of iron; 0.001-0.0015 % of fluorine; 0.005-0.001 % of sulfate-ion; less than 0.0001 % of arsenic and less than 0.0002 % of lead.}

EFFECT: the invention ensures production of more than 95-98 % of the main substance; 6-8 % of the first form of sodium tripolyphosphate; 88-96 % of the brightness degree; less than three thousandth of % of iron; two thousandth of % of fluorine; one thousandth of % of sulfate-ion; less than one thousandth of % of arsenic and less than two thouthandth of % of lead.

2 cl, 2 ex, 1 tbl