Precipitation of synthetic scheelite
AssigneeAmax Inc.
InventorsLeo W. Beckstead, Paul B. Queneau
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Abstract
Synthetic scheelite (calcium tungstate) having a low sulfur content is produced in high yield from an aqueous solution of sodium tungstate, that can be contaminated with sulfate ion dissolved therein, by digesting the solution with solid calcium sulfate whereby low-sulfur calcium tungstate precipitates. The solution remaining after filtration of the calcium tungstate product can be treated with calcium sulfate to precipitate additional purified calcium tungstate or to generate a calcium tungstate-calcium sulfate mixture that can be recycled for digestion with additional sulfate-contaminated sodium tungstate solution.
Claims11
A process for producing low-sulfur calcium tungstate from an aqueous feed solution of alkali tungstate, comprising
- (a) slurrying in said solution a precipitant comprising finely divided calcium sulfate in an amount up to the stoichiometric amount based on the tungstate in the solution,
- (b) digesting the slurry formed in step (a) while maintaining the pH value of the slurry between about 9 and about 12 and under conditions such that essentially all the calcium sulfate reacts with alkali tungstate, thereby forming low-sulfur calcium tungstate which is slurried in a pregnant solution containing dissolved therein alkali sulfate, and
- separating the low-sulfur calcium tungstate from the pregnant solution.
Dependencies are inferred from the claim text.