Method of making high purity alkali metal phosphates from wet-process phosphoric acid

Claim 1

Method of preparing high-purity alkali-metal phosphate comprising: a. extracting a portion of the P 2 O 5 in a wet-process phosphoric acid containing 40 - 58% P 2 O 5 with an essentially water-immiscible alcohol selected from the group consisting of n-hexanol, n-heptanol, n-octanol, iso-octanol and mixtures thereof in an amount from about one-half to about four parts by weight for each part by weight of wet-process phosphoric acid, b. recovering P 2 O 5 in a stripping process comprising the steps of i. scrubbing the P 2 O 5 -loaded alcohol extract with a portion of the aqueous phosphoric acid solution from water stripping step (b) ii, ii. thereafter stripping the P 2 O 5 -loaded alcohol extract from the scrubbing step with water to form an aqueous phosphoric acid solution, and iii. thereafter stripping the P 2 O 5 -loaded alcohol from the water stripping step (b) ii, with an alkali metal phosphate solution having a molar ratio of alkali metal to phosphorus of from 1.3 to 1 to 3.0 to 1, to form a product solution of alkali metal phosphate having a molar ratio of alkali metal to phosphate of from 1:1 to 1.67:1, c. neutralizing a portion of the aqueous phosphoric acid solution formed in water stripping step (b) ii, with sodium hydroxide or sodium carbonate to form a precipitate and an alkali metal phosphate solution having a molar ratio of alkali metal to phosphorus of 1.3 to 1 to 3 to 1, d. removing the precipitate formed during neutralizing step (c), e. recycling the alkali metal phosphate solution from step (c) for use in step (b) iii. as a stripping solution, f. recycling the stripped water-immiscible alcohol from the base stripping step (b) iii. to the extraction step (a), and g. adjusting the ratio of alkali metal to phosphorus in the alkali metal phosphate solution of step (b) iii. to a desired ratio by adding alkali metal hydroxide or alkali metal carbonate thereto.