PROCESS FOR PREPARING TRISODIUM POLYPHOSPHATE Russian patent published in 1994 - IPC

FIELD: inorganic chemistry. SUBSTANCE: solution of orthophosphoric acid is neutralized with sodium carbonate to adjust pH 6.3-6.7. Thereafter, admixture of calcium carbonate and sulfur-containing agent such as alkaline metal sulfides is added to the resulting reaction solution in weight mixture ratio of (0.002-0.2): 1, respectively, the resulting mixture is allowed to stay for 25-30 min. The resulting suspension is filtered, and the filtrate is thermally treated to give the end product, with weight mixture-to-filtrate ratio being (0.005-0.015): 1. During purification of solutions of wet-process phosphoric acid admixture of alkaline metal sulfides and sodium carbonate is added to such solutions at the secondary stage of their neutralization, pH 6,3-6,7, removing the main part of contaminating impurities at the first stage, pH 4.5-5.0. EFFECT: allows total content of trace contaminants to decrease by a factor of 1.5-2. 1 cl, 2 tbl