METHOD OF PRODUCING SODIUM TRIPOLYPHOSPHATE Russian patent published in 2009 - IPC C01B25/40 

FIELD: chemistry.

SUBSTANCE: method of producing sodium tripolyphosphate from wet process phosphoric acid and calcined soda involves desulfation with calcium compounds and defluorination with soda to 0.4 - 0.8% CaO and 0.1 - 0.2% F content in the solution, separation of calcium sulphate and sodium silicofluoride, deep desulfation with barium hydroxide or carbonate to 0.05-0.1% SO₃ content in the solution without separating barium sulphate, neutralisation of the obtained phosphoric acid with soda to molar ratio Na/P at the first stage of 1.05 - 1.08 with 14 - 20% P₂O₅ content in the solution, addition of ammonium nitrate to molar ratio NH₃:MgO in the solution equal to 1.1 - 1.5, dividing the obtained suspension into two parts with mass ratio 1.55-1.9:1, neutralisation of the larger part of the suspension with soda at temperature ranging from 90 to 95°C to molar ratio Na/P equal to 1.95 - 2.05, and its subsequent mixing at the third stage with the smaller part of the suspension to molar ratio Na/P equal to 1.65 - 1.67, where mixing is done for 2-2.5 hours at each stage, separation of sludge of impurities, evaporation of the obtained solution of sodium phosphates, drying and calcination of the dried product.

EFFECT: increased efficiency of filtration by 1,5-3 times, reduced content of magnesium, calcium and aluminium depending on process parameters and quality of the material by 3-30 times.

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