Coarse grain size ammonium paratungstate may be prepared by using ammonium tungstate solution (produced by ion exchange method) as raw material, controlling certain process conditions and adopting specific operating systems. The coarse APT produced by this method has average particle size of 40μm or above.
The purity of ammonium tungstate (abbreviated as AT) solution is one of the factors affecting the particle size of APT. The AT solution prepared by ion exchange method contains a large amount of impurity - NH4Cl. The impurity makes the preparation of coarse APT more difficult. Particle size of APT can be increased from about 29μm to 40~53μm through the following optimization measures:
1. Control concentration, purity and ammonia content of AT solution;
2. In the process of evaporative crystallization, by adding seed crystals and AT solution, changing the stirring speed, washing APT with high-purity water, and avoiding grown crystals of APT breaking by machinery.
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