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.

 

Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). 

Leaching (chemistry), the process of extracting minerals from a solid by dissolving them in a liquid

 

Dissociation (in the wide sense of the word) is an act of disuniting or separating a complex object into parts. 

Dissociation (chemistry), general process in which molecules or ionic compounds (complexes, or salts) split into smaller particles, usually in a reversible manner

 

The research on ammonia dissolving after thermal dissociation and direct ammonia dissolving shows that APT solid is thermally dissociated for 50 minutes at temperature of 280±5℃,and then 1:3 ammonia solution of 200 mL is added to dissolve for 6 hours at temperature of 95℃,leaching efficiency is 85.1%. Dissociation time has a little influence on S(Fe)/WO3. Leaching efficiency of ammonia dissolving after thermal dissociation is higher than that of direct ammonia dissolving,but amounts of S(Fe)/WO3 are basically similar.