Process for the preparation of alkali metal phosphate solutions

Details Process for the preparation of alkali metal phosphate solutions Process for the preparation of alkali metal phosphate solutions

1991-03-28

1992-06-23

Morris, Theodore

Chemistry of inorganic compounds

Phosphorus or compound thereof

Oxygen containing

423167, 423309, 423313, 423166, 423312, 423321R, 423555, C01B 2516

Patent

active

051241374

ABSTRACT:
Alkali metal phosphate solutions having a fluorine content of less than 20 ppm, based on P.sub.2 O.sub.5, are prepared by first digesting crude phosphate using sulfuric acid, and separating the calcium sulfate from the crude phosphoric acid. An alkali metal compound is then added to the crude phosphoric acid, and the precipitated solid is filtered off. The prepurified crude phosphoric acid is neutralized to a pH of at least 7, and the solid produced during this operation is separated off. The resultant alkali metal phosphate solutions having a P.sub.2 O.sub.5 content of from 10 to 30% by weight are adjusted to a pH of between 4.8 and 6.0 using phosphoric acid. The solutions are heated to from 60.degree. to 120.degree. C., and from 1 to 6% by weight, based on the weight of the solution, of an alkaline earth metal oxygen compound are added to the alkali metal phosphate solutions with stirring. Finally, the precipitated solid is filtered off from the alkali metal phosphate solutions after a residence time of from 0.5 to 4 hours.

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