Impurity Sodium in Ammonium Paratungstate

Ammonium paratungstate (APT) is an important intermediate product in tungsten metallurgical process, the characteristics and quality of the final tungsten products directly affect by impurities in APT, and the size of tungsten powder related to content of sodium (Na) . Ammonium paratungstate with high sodium calcined to produce WO₃ powder with high sodium which is the raw material for preparing coarse tungsten powder. On the contrary, tungsten powder with fine particles generated fromAPT with low sodium. Therefore,for producing fine particles of tungsten powder, the necessary to control content of sodium in APT in a lower state is self-evident.


Sodium ions (Na⁺) exists in APT crystallization solution mainly in the form of sodium tungstate, and because of the similarity in composition and structure between APT and sodium paratungstate, sodium may enter APT lattice in the form of alternative or impurity ions or surface chemical adsorption. There are two sources of impurity sodium in ammonium paratungstate:
1. The water
Using single stage double bed purification process, the average electrical resistance of pure water can controlled in 8*10⁴Ω*cm, and no impact on the quality of tungsten products because of the low sodium in water.
2. The ammonium chloride in the desorption agent
The content of sodium is really large in APT produced ion exchange method, generally reach (3-7) *10^-2%, far more than the highest value-0.01 [According to fine tungsten powder metal elements analysis table], and therefore will affect the fine tungsten powder. In this case, the sodium content not only related to its concentration, but also factors of over-saturation, nucleation rate, crystal growth rate, size of generated crystal, morphology and surface and solution viscosity and so on, and these factors listed are influenced by the concentration of WO₃.

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