Producing Ammonium Metatungstate from Ammonium Paratungstate

A method is disclosed for producing ammonium metatungstate from ammonium paratungstate. The method involves first roasting the ammonium paratungstate at from about 275° C. to about 300° C. for from about 10 hours to about 20 hours to remove some ammonia and some water. The roasted ammonium paratungstate is then added to dilute solution of an ammonium metatungstate which is at a pH of from about 3.6 to about 4.2, the rate of addition being such that a slurry is produced having a pH of from about 3.6 to about 4.2. The pH of the resulting slurry is then adjusted to stabilize it at from about 3.6 to about 4.2 followed by evaporation to form a relatively concentrated solution of ammonium metatungstate which is separated from any insolubles. Ammonium metatungstate is then crystallized from the relatively concentrated ammonium metatungstate solution.

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