Ammonium paratungstate tetrahydrate or APT?4H2O may be prepared by crystallization process from pure ammonium tungstate solution by batch process and continuous process. But APT?4H2O will lose part of crystal water in the drying process of this industrial production. Therefore, repeated crystallization is usually used to improve product quality. However, this method is limited by the slow dissolution of APT?4H2O.
Ammonia Dissolves Ammonium Paratungstate Tetrahydrate
At room temperature, APT?4H2O dissolves very slowly in aqueous ammonia. The dissolution temperature can be increased for accelerating dissolution rate. But, at higher temperature, the total amount of dissolved APT?4H20 is reduced because the solubility of aqueous ammonia decreases leading to the decrease of the pH value of solution. Since the dissolution rate of APT?4H2O in aqueous ammonia was found to be independent of its particle size, it is therefore concluded that the control method for the rate of decomposition of APT?4H2O in ammonia water is dissolution. The highest solubility can be obtained by calcining APT?4H2O in air or nitrogen at temperatures ranging from 250°C to 310°C for approximately 2h.
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