Purification of Ammonium Para Tungstate Solution after Ion Exchange by Molybdenum Removal

Before crystallization of ammonium para tungstate (APT), it is necessary to further remove molybdenum from the crystallization process of APT to obtain a more pure APT crystal product. The impurity removal rate in the crystallization process is directly related to the crystallization rate of APT. With the increase of the crystallization rate of APT, the precipitation rate of impurity increases rapidly. For the same concentration solution, when the crystallization rate of tungsten is increased from 60% to 80%, the crystallization rate of molybdenum will be increased by nearly 3 times. It is difficult to break through 80% of the crystallization rate.

In order to improve the evaporation crystallization rate of APT, researchers in China continue to explore new technologies, for example, by inhibiting the co precipitation of molybdenum in ammonium tungstate solution during the crystallization of APT, some scholars have achieved the purpose of producing APT products with high purity and low molybdenum content while improving the crystallization rate of the solution.

Ion exchange: ammonium tungstate solution with WO₃ content of 170g/L and Mo impurity content of 0.09 g/L. Under the condition that the pH value of the solution is less than 12, it is put into the vacuum stirred reactor. At the stirring speed of 80 r/min, a certain amount of NH₄Cl reagent is slowly added to the solution, and the concentration of the solution Cl- is 12 g/L, and the crystallization reaction is carried out at 65~85°C. Under such crystallization conditions, the APT crystallization rate of ammonium tungstate solution is more than 96% under the condition that the content of Mo is not more than 2 * 10-5 in the APT product, and most of the APT products are hexahedron with regular shape.

Through this method, under the condition that the control of Mo content in the product is not more than 2.0×10‑5, the first crystallization rate of APT is above 96%, and the high efficiency production of APT-0 grade products is realized. The purity of the produced APT products is high, with the regular shape of the six face shape and the good particle size distribution.

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