Preparation Of Ammonium Paratungstate Using Low Grade Tungsten Concentrate

Low grade tungsten concentrate has such characteristics as a high content of calcium and impurities, and a low content of WO3. But it has a lower price than standard tungsten concentrate.

For example, the ratio of impurities to WO3 in particular low grade tungsten concentrate sample are 15%~20% Ca/WO3, 2%~5% As/WO3, 2%~3% P/WO3, 50%~60% SiO2/WO3 and 0.5% Mo/WO3. These values are 4 ~4.5, 15~30, 15~20, 4~8 and 5~8 times of that in standard tungsten concentrate respectively. Since its price is only 60%~70% of standard tungsten concentrate (according to the content of WO3). If low grade tungsten concentrate can be efficiently utilized for ammonium paratungstate (APT) preparation, the cost for material would decrease.

Thus, an effectual method to obtain APT from low-grade tungsten concentrate has been introduced. The experiment procedures are:

the first step is decomposing low grade tungsten concentrate by mechanical activiting cuastic decomposition method to dissolve tungsten into solution and to keep most impurities remaining in residue.

The second step is recovering NaOH and removing a part of impurities (P, As, Si, etc. ) by evaporation and crystallization of impure Na2WO4 solution.

In the third step Na2WO4 crystal is dissolved in water and prepared into ion exchange raw solution. Na2WO4 solution is purified (removing P, As, Si etc.) and changed to (NH4)2WO4 solution by traditional ion exchange method. Then molybdenum is removed from (NH4)2WO4 solution by the new ion exchange method. APT of high purity is produced by evaporation and crystallization of (NH4)2WO4 solution.

In conclusion, mechanical activating caustic decomposition and removing molybdenum from tungstate solution by ion exchange method are used in this technological process for treating low grade tungsten concentrate with a low concentration of WO3 and a high concentration of calcium and impurities to produce APT of high purity. The process has the advantages of shorter flowsheet, high recovery of tungsten and high purity of product.

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