Large grain size ammonium paratungstate is an important intermediate product in the preparation of tungsten powder from tungsten concentrates. The physical properties of APT such as particle size, particle size distribution, and crystal morphology have an important influence on the physical and mechanical properties of its downstream products such as tungsten carbide, tungsten wire, and so on. Therefore, it is of great significance to study the influencing factors of grain size of APT.
In the crystallization of APT, there are many factors affecting its particle size, such as temperature, stirring rate, purity of ammonium tungstate solution (impurity content), relative supersaturation, evaporation rate, and common ion effect, etc. The influence of purity of ammonium tungstate solution, temperature, stirring rate, and relative supersaturation on the particle size of APT is studied as follows:
1. Purity of ammonium tungstate solution. The purity of the ammonium tungstate solution should be improved to reduce the crystal nucleus formed by impurities, and therefore increase the particle size of APT.
2. Temperature. A suitable temperature is selected so that the crystal growth rate exceeds the growth rate of crystal nucleus to obtain coarse crystals.
3. Stirring rate. Stirring is conducive to the escape of ammonia, prompting the reaction to proceed. At the same time, stirring helps APT molecules in the solution diffuse to the surface of crystal nucleus and promote crystal growth.
4. Relative supersaturation. The relative supersaturation of crystallization solution should be reduced to obtain large grain size crystals.
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