Process of refining sodium hexafluorosilicate
AssigneeCentral Glass Company, Limited
InventorsYoshiro Shiraki, Hiroshi Haraoka, Hiromichi Arai
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Abstract
Crude sodium hexafluorosilicate containing gypsum and various metal phosphates is refined into highly pure and sufficiently large crystals. First, the crude fluorosilicate is treated with a sodium chloride solution to dissolve gypsum. Then the solid phase is reconstituted into an aqueous slurry in which the concentration of Na is limited. This slurry is acidified and maintained at temperatures not lower than 80.degree. C. with continued stirring to cause recrystallization of sodium hexafluorosilicate.
Claims8
A process of refining a crude sodium hexafluorosilicate containing gypsum as an impurity, comprising the steps of:
- (a) dispersing the crude sodium hexafluorosilicate in an aqueous solution of sodium chloride to form a first slurry and allow the gypsum to dissolve in said solution;
- (b) removing at least a portion of the liquid component of said slurry thereby to accomplish the removal of a substantial amount of the dissolved gypsum;
- (c) reconstituting an aqueous second slurry of the solid component of said first slurry such that the concentration of Na in the liquid phase of said second slurry is not greater than 80 g/l;
- (d) adding a mineral acid to said second slurry so as to give an acid concentration of at least 0.1 N;
- (e) maintaining the acidified slurry at temperatures not lower than 80.degree. C. with continued stirring to cause recrystallization of sodium hexafluorosilicate;
- and
- (f) recovering crystalline sodium hexafluorosilicate from the product of step (e).
Dependencies are inferred from the claim text.