GB818117A - Improvements in the extracting of tungsten compounds from tungsten ores - Google Patents

Abstract

In a process for obtaining ammonium tungstate from tungstate ores or calcium tungstate, an aqueous mixture of said materials with oxalic acid or a soluble oxalate is treated with ammonia. Calcium tungstate may be mixed with an aqueous solution of oxalic acid (whereby some insoluble yellow tungstic acid is formed), digested at 50-100 DEG C. and aqueous ammonia added. After further digestion the residue may be removed and filtered hot to avoid precipitation of ammonium paratungstate. Preferably 3-4 mols. of oxalic acid and 5-10 mols. of ammonia are employed per gram atom of tungsten in the ore. Alternatively the ore may be extracted with ammonium or other soluble oxalate, followed by addition of ammonia. Thereafter tungstic oxide may be precipitated, e.g. by adding to the filtrate hot hydrochloric acid containing a small amount of nitric acid. It is said to be known to extract tungsten with hydrochloric acid and with alkali metal hydroxides and carbonates. A process wherein after extraction with oxalic acid the resultant solution is separated and ammonium paratungstate precipitated therefrom with ammonia, and Japanese Specification 172,961, which describes the extraction of scheelite with oxalic acid, are referred to.