Crystallisation and Processing of Ammonium Paratungstate (APT)

Crystallisation and processing of ammonium paratungstate (APT)
 

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.

This paper starts with the chemistry of tungsten in aqueous solutions. Various aspects of the crystallisation of the hydrates of ammonium paratungstate (APT) will be discussed in addition. This is then followed by the chemistry of the first pyrometallurgical treatment in non-sag (NS) tungsten manufacturing, the processing of APT into tungsten blue oxide. The section is mainly devoted to the chemistry of the thermal decomposition of APT in various atmospheres. Finally, parameters controlling tungsten blue oxide quality will be discussed.

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