Ammonium Paratungstate Prepared by Neutralization Crystallization Feasibility

Ammonium paratungstate prepared by the neutralization crystallization method is one of the main methods of industrial production of ammonium paratungstate. Ammonium paratungstate, which is fine in grain size, is a necessary condition for the production of subsequent high-performance tungsten products.

Therefore, pentahydrate ammonium paratungstate compaction density, less crystal defects and thermal stability, is the production of high-performance tungsten products, a very good raw material. In contrast to the ammonium paratungstate neutralization crystallization method, the ammonium paratungstate evaporation crystallization method is currently one of the methods for industrially producing ammonium paratungstate. Due to the evaporation crystallization process requires conventional heating conditions, resulting in the existence of temperature gradient, the product size is difficult to control at the same time prone to produce ammonium paratungstate heptahydrate. The thermal stability of ammonium paratungstate heptahydrate is not good, resulting in poor performance of the overall ammonium paratungstate.

Because ammonium paratungstate neutralization crystallization method is to use hydrochloric acid to neutralize the ammonium tungstate solution, and by stirring constantly and the solution compared with the evaporation crystallization easier to achieve saturation, the solution concentration is more uniform. Therefore, according to lamer monodisperse model crystallization can nucleate rapidly, the concentration of the reaction solution is rapidly reduced, which can avoid the grain growth region. Thus, under the same crystallization conditions, neutralization of the crystals results in finer grains of ammonium paratungstate. Therefore, in order to produce finer Ammonium paratungstate, it is one of the feasible ways to prepare Ammonium paratungstate by neutralization crystallization.

Neutralization crystallization of ammonium paratungstate at low temperatures to obtain a small particle size of ammonium paratungstate. However, because of the low crystallization temperature during the reaction, the final product is ammonium tungstate monohydrate. At the same time a long crystallization lead to the entire production time becomes longer. According to the thermodynamics of crystallization in aqueous solution, it can be seen that under the condition of low temperature, the formation of nuclei is favorable and the growth of crystal grains is suppressed. Therefore, the lower crystallization temperature is favorable for obtaining fine crystals. However, from the crystallization kinetics to analyze the crystal nucleation, lattice rearrangement, dehydration, growth and other processes require a lot of energy to promote. Therefore, low temperature crystallization water can not be removed only 11 water ammonium paratungstate, at the same time crystal form and dispersion is not good enough. Based on these two aspects of analysis, in order to use neutralization crystallization method to meet the preparation of small particles with complete crystal form, good dispersion of ammonium paratungstate is not possible.

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