MANUFACTURE OF CRYSTALLINE AMMONIUM METHATUNGSTATE

摘要

A method is disclosed for producing crystalline ammonium metatungstate from ammonium paratungstate. The method involves heating the ammonium paratungstate at from about 100 DEG C. to about 250 DEG C. for from about 1 hour to about 8 hours to remove some ammonia and water, digesting a solution of the heated ammonium paratungstate in water at from about 80 DEG C. to about 100 DEG C. for from about 2 hours to about 6 hours at relatively constant volume while maintaining the pH of the slurry at from about 4.2 to about 3.0 by addition of ammonia as necessary to form a solution of ammonium metatungstate in water. The ammonium metatungstate solution is then evaporated to concentrate it. Any insoluble material is separated from the solution. Ammonium metatungstate is then crystallized from the resulting concentrated ammonium metatungstate solution.