Crystalline ammonium paratungstate may be prepared by evaporative crystallization, which has been favored in industrial production as this method has the characteristics of simple operation, low cost, uniform particle size and stable quality.
The purity of ammonium paratungstate can be guaranteed by controlling the evaporative crystallization rate. To obtain high purity APT, the crystallization rate must be controlled to be low as the evaporative crystallization process requires long production cycle and consumes a lot of energy.
Certainly, there are a lot of methods for preparing ammonium paratungstate. And each has its own advantages and disadvantages. The main problem in the preparation of APT is to remove impurities and control crystalline morphology to meet the requirements of final tungsten products.
Evaporative Crystallization to Prepare Ammonium Paratungstate
The ammonium tungstate solution was heated, the ammonia concentration decreased, the concentration of the (NH4)2WO4 solution gradually increased, and ammonium paratungstate precipitated.
12(NH4)2WO4=5(NH4)2O•12WO3•5H2O+14NH3↑+2H2O
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