Ammonium Paratungstate Converts to Ammonium Metatungstate

Before beginning the process to convert APT to AMT, a conventional pH, probe was calibrated using standard solutions at pH 4 and 7. 3000 mL of double distilled water was heated to 90-95° C. Approximately 250 g of APT powder was added to the hot water, and the mixture was stirred using a stir bar. Cation exchange resin was added incrementally in portions of approximately 10 g until the pH of the liquid portion of the APT/water mixture was between 3 and 4. The total volume of resin necessary to reach a pH between 3 and 4 was approximately 675 mL resin/Kg APT. As the APT dissolved in the acidified water, it reacted to form AMT, thereby allowing more APT to dissolve in the solution and drive the conversion of the APT toward completion.

The dissolution and reaction of the APT initially occurred relatively quickly. As the reaction proceeded the reaction mixture changed from an opaque white slurry to a clear, slightly yellow or amber solution. When the solution appeared clear, indicating that substantially all of the APT had been converted, additional APT was added in two 250 g increments until the solution contained 750 g APT (250 g/L). The 750 g of APT reacted in the process (250 g initially+500 g added) was dissolved and converted to AMT in approximately 90 minutes. 



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