Ammonium Paratungstate Evaporation Crystallization Defects

Ammonium paratungstate evaporation crystallization process due to the continuous process, it has a large production capacity, uniform particle size and quality and stability and so on. At the same time, ammonia is easy to recycle. At present, this method has replaced the traditional neutralization crystallization method in industrial production and has become the mainstream method for the preparation of ammonium paratungstate.

However, ammonium paratungstate evaporation crystallization methods exist such as long production time, energy consumption, long production cycle, product purity level is inversely proportional to the size of the crystallization rate, the purity of the product and the crystallization rate is difficult to control at the same time and other issues. Therefore, the use of this method of APT morphology and particle size control, is still a more complex issue. Some scholars on the use of third-generation tungsten smelting conventional evaporation crystallization of ammonium paratungstate, the average particle size of 35.28μm. However, the flaw of this method makes the crystal form of the crystal particles not perfect, the crystal defects and crushed crystal more, the difference of the size of the larger and local agglomeration is more serious.

There are also scholars at 45 ℃ low temperature by adding a large amount of surfactant in the reaction, can be prepared micron ultra-fine ammonium paratungstate. The results showed that when 1000 mg. (Kg) -1 of surfactant A was added, the resulting crystal had a particle size of 13.2 μm. Due to the addition of the surfactant, a large amount of active agent is adsorbed on the specific crystal plane of ammonium paratungstate so as to inhibit the growth of the crystal plane. Its shape by the strip into a cubic shape. APT particle size can be refined to 5μm when the amount of surfactant A is increased to 7000 ~ 10000 mg. (Kg) -1. With the increase of the amount of surfactant used in the crystallization at low temperature, although the control of the grain size can be achieved, the control of the morphology is not ideal. And the addition of active agent can increase the production cost and also affect the purity of ammonium paratungstate.

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