Ammonium paratungstate is normally prepared by any one of several well known techniques. One technique involves the dissolution of tungstic acid in ammonium hydroxide to produce ammonium tungstate followed by filtration and evaporation to crystallize ammonium paratungstate. Another technique involves addition of ammonium chloride to sodium tungstate solution to precipitate ammonium paratungstate and leave sodium chloride in solution. Still another technique involves the extraction of a metatungstate species with an organic extracting agent followed by stripping with ammonium hydroxide to produce ammonium tungstate which is evaporated to produce ammonium paratungstate crystals. Another technique involves addition of ammonium hydroxide to ammonium metatungstate solution to precipitate ammonium paratungstate crystals.

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Ammonium paratungstate hydrates (hereinafter referred to as APTs) are known intermediates for producing tungsten metal, tungsten-containing catalysts or hard materials based on tungsten, for example tungsten carbides.

A process for the continuous preparation of ammonium paratungstate hydrate directly in the reextraction of a tungsten-laden organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus, which comprises carrying out the reextraction at an NH3:W molar ratio of from 0.83 to 1.30, and a volume feed ratio of the tungsten-laden organic phase to the ammonia-containing aqueous solution of from 5 to 25. Directing ammonium paratungstate decahydrate containing at least 75% of crystals having a length of at least 200 μm and having a ratio of length to width of less than 4.5:1.

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Cobalt doped ammonium paratungstate (Co-doped APT) precursors for the fabrication of cemented carbides were synthesized by co-precipitation, where W and Co are mixed on the atomic scale. The effect of cobalt content on the reduction of W–Co precursor was studied. W–Co precursors with different ratios of tungsten to cobalt were prepared and calcined at 220 °C for 5 h in air, followed by a reduction in hydrogen gas at 600 and 650 °C for different times. The resulting powders were characterized with respect to phase constituent, specific surface area, particle size, density, and morphology of the reduced powders. It has been found that the addition of cobalt results in a higher reduction rate toward the metallic phases. However, the particle size of the reduced powders increases with increasing cobalt content, while its relative density decreases. The specific surface area of reduced powders at 650 °C increases for short reduction times, due to reduction of oxides to metal powder, and decreases for long reduction time due to agglomeration of metal powder. Cobalt plays the role as a catalyst during the reduction processing. On the other hand, it promotes the agglomeration of small particles. However, the completely reduced powders were well nanostructured with an average particle size between 20–50 nm.

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The possibility of mechanochemical decomposition of ammonium paratungstate (APT) has been studied, and compared with thermal decomposition method. For this purpose, APT powders were milled using a planetary ball mill up to 36 h and under air atmosphere. For thermal decomposition, APT powders were heated for 30 minutes at 300 and 450 °C in air atmosphere. X-ray diffraction (XRD), differential scanning calorimeter (DSC), and thermo gravimetric analyzer (TGA) were used to study the decomposition progress, and products. The XRD results showed that APT completely decomposed to WO₃ by thermal decomposition, while the final product of mechanochemical decomposition was WO₃ (H₂O)_0.5. According to DSC and TGA results, during thermal decomposition, ammonia and water released in four steps, and leaved WO₃. By mechanochemical decomposition crystal water and ammonia liberated from APT structure, but structural water of APT remained. In both methods, an X-ray amorphous phase was the intermediate product of APT decomposition.

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