Recycling Tungsten and Ammonia from Ammonium Paratungstate Mother Liquid Effectively

Ion exchange process has become China's chief tungsten smelting process. With the advancement of technology and the improvement of environmental-friendly awareness, most tungsten smelting enterprises have already attached importance to the treatment of effluent wastewater and the improvement of the total recovery of tungsten, especially for the recycling of tungsten in the crystallizing mother liquor and the treatment of ammonia nitrogen. In general, the recovery of tungsten and ammonia in the crystallizing mother liquor treated by independent process respectively.

The principal recovery and treatment of ammonia nitrogen are stripping, precipitation and ion-exchange technique, etc., but the more mature technique applied in the industrial is stripping which is applied widely in the treatment of high concentrations of ammonia nitrogen solution. In order to dissociate ammonium radical in ammonium chloride to ammonia molecules, sodium hydroxide is usually added during stripping and the cost is relatively high. Therefore, based on the stripping, some scholars have made corresponding improvements to the technological process.

After the evaporation and crystallization of APT is completed, the mother liquor was pumped to the reactor which is stripping. The mother liquor is added with calcium oxide of over 90% or calcium hydroxide of over 95% and the added-amount takes the concentration of ammonium chloride of the mother liquor as calculated basis. The actual added-amount is based on excess coefficient of 1.1 to 1.3 of its theoretical molar ratio. Using stripping which is widely used in crystallizing mother liquor of the APT process to recycle ammonia. The reaction temperature ranges from 25 ℃ to 90 ℃. Ammonia separates by condensation gas-liquid, sprays by hydrochloric acid, prepared as ammonium chloride and return to the main process to match with the analytical solution and white tungsten slag return to the pressurizing and boiling process. When the pH of reaction system maintains from 9 to 11, the concentration of ammonia nitrogen in the water is reduced to about 30 mg / L, and after the reaction is completed, after exchanging the waste liquid of the removing ammonia nitrogen with the ion produced in the main process, the mixed liquid is to be processed.

After the evaporation and crystallization of APT is completed, the mother liquor was pumped to the reactor which is stripping, while APT solution containing tungsten trioxide 20g / L, ammonium ions 20 g / L, the solution volume of 500mL. By adding solid calcium oxide 17.2 grams of the main component of over 90%, the excess coefficient of theoretical molar ratio is 1.11. In the stripping reactor for stripping ammonia and precipitated tungsten, the blowing-off ammonia gas separates by condensation gas-liquid, sprays by hydrochloric to be made of ammonium chloride. Ammonium chloride returns to match with the analytical solution, white tungsten slag return to the pressurizing and boiling process. Analysis after stripping the liquid contains tungsten trioxide 1 mg / L, ammonium ion 30 mg / L. The residue contains tungsten trioxide 63.32%.

Compared with stripping, the traditional method of APT preparation industry, the above method to replace the sodium hydroxide with calcium oxide or calcium hydroxide greatly reduces the production cost. Therefore, the method greatly simplifies the process and has high tungsten deposition rate. The method is a simple, easy-to-operate and low-cost method for recovering tungsten and ammonia from APT crystallizing mother liquor.

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