Ammonium paratungstate tetrahydrate, or APT·4H2O, is an important intermediate product in the production of tungsten powder. It has been reported that it is a key process to crystallize APT·4H2O from an aqueous solution of ammonium tungstate in the current preparation method of tungsten powder.
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According to the literatures, ammonium paratungstate tetrahydrate is an intermediate for the production of metal tungsten, tungsten-containing catalysts or hard materials based on tungsten (such as tungsten carbide) or sputtering targets. Generally, sputtering target is fabricated using high-purity APT as a raw material. And high-purity APT can be prepared by the following steps: Acid or alkali of tungsten-containing concentrate or tungsten waste is melted and then purified. The purification stage includes precipitation process and liquid-liquid extraction. The purified solution is usually concentrated by evaporation to finally crystallize APT. In other words, APT crystals are available by processing ammonium paratungstate tetrahydrate through a certain production process.