ALKALI METAL POLYPHOSPHATE SALT PRODUCTION PROCESS Russian patent published in 2006 - IPC C01B25/41 

FIELD: industrial inorganic synthesis.

SUBSTANCE: invention provides a process for producing double sodium-potassium tripolyphosphates used in chemical industry and related industrial fields, primarily in household chemical goods production industry. Process comprises (i) preparing mixture of alkali metal orthophosphates using phosphoric acid and neutralizing alkali agent, in particular mixture of double sodium-potassium carbonate and potassium carbonate in 1:(0.15-0.40) molar ratio, respectively; (ii) forming sodium-potassium tripolyphosphates going from Na_2.2K_2.8P₃O₁₀ to Na_1.8K_3.2P₃O₁₀; and (iii) drying resulting solution by spraying it into rotating drum onto a hot phosphate salt mixture followed by calcination at 350-600°C to form particles of solid solution of desired product, cooling and disintegration of double polyphosphate. Above-mentioned double sodium-potassium carbonate and potassium carbonate mixture is obtained in the process of integrated processing of nepheline into alumina and co-products using extraction phosphoric acid, which was preliminarily desulfatized to 0.15-0.35% SO₃ by treatment chiefly with naturally occurring phosphate and defluorinated to 0.15-0.25% fluorine using solutions and alkali metal salts. Neutralization is effected until molar ratio Na₂O/P₂O₅ attains value of 1.60-1.700, preferably 1.66-1.68, after which appearing precipitate of impurity salts is separated, e.g. by pressure filtration, impurity salt mixture is repulped with 1-3 wt parts of water per 1 wt part precipitate, and resulting slurry is filtered. Wash filtrate is combined with mother liquor and resulting liquid is concentrated until dry and calcined. Washed precipitate is dried at 105-140°C and is ready to be used as phosphorus-potassium fertilizer.

EFFECT: reduced in price process and increased solubility of product tripolyphosphates.

4 cl, 1 tbl, 4 ex