Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH4)10(H2W12O42)·4H2O.

 

Ammonium paratungstate is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO3, tungsten(VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.

The study shows that the precipitation and the distribution ratio (C S/C L) of Si, P, As in solid and liquid phases decrease with the increase of the concentration of WO3 in the crystallization process of APT. With the increase of crystallization ratio of tungsten, the C S/C L ratio of Si, P, As increases first and decreases afterwards. The order of the amount of decrease is SiPAs. The Si, P As contents in APT decreases with the increase of the temperature and shortening of the crystallization time. The reduction of the relative surface area of crystallization tank benefits the decrease of As. The distributions ratio measured in the experiment were: As 0.11~0.37, P 0.10~0.26, Si 0.012~0.15. The theoretical analysis and experimental results showed that the entrainment of Si, P, As in APT in the first stage is possibly a replacement and the possibility of arsenate forms heteropolyacid with tungstate is higher than silicate and phosphorate in the middle stage of the crystallization of APT.