The Reduction of Tungsten Powder by Using Zinc Tungstate

There are two ways of tungsten smelting: hydrometallurgy and pyrometallurgy. However, the most important smelting method at present is to go for hydrometallurgy because of its shorter process, shorter production cycles, better production environment, and relatively stable product quality.

The hydrometallurgy of tungsten is divided into ion exchange process, extraction process, classic process and acid process. Among them, the mainstream process is ion exchange process and extraction process. Both of these processes need to convert tungsten from sodium tungstate system to ammonium tungstate system to obtain the desired tungsten powder through calcination to tungsten oxide and hydrogen reduction. The disadvantage of ion exchange process lies in not only the complex process and the need of lots of water resulting large emission of waste water but also hydrochloric acid consumption and easy to cause environmental pollution. Therefore, for many years, China's smelting experts have continued to try to improve the ion exchange process.

To this end, some scholars have proposed a process to prepare tungsten powder, which is simple and has little pollution to the environment. The main principle of this method is to reduce tungsten tungstate with hydrogen. The main principle is: zinc has a relatively low a boiling point (900 ° C.) and melting point (420 ° C.) which is the lowest melting point of all transition metals except mercury and cadmium. At the same time, it can be seen that the zinc tungstate is insoluble in water and has a solubility product of 1.2 * 10-8. The tungsten enters the sodium tungstate system and is transformed into the zinc tungstate system by the zinc salt, and then the hydrogen tungstate Zinc is reduced to obtain the desired tungsten powder. Specific steps are as follows:

(1) Using glacial acetic acid (acetic acid) to make the pH of sodium tungstate concentrate acid from 8 to 10.

(2) Add zinc acetate to the acidified sodium tungstate concentrated solution; heat it to 180 °C in a water bath for 5 hours and detect the composition of the tungsten trioxide and the filter residue in the filtrate; judge whether the reaction is finished or not, if not, keep adding zinc acetate to continue to the reaction, and then we can finally get 10g of zinc tungstate precipitates which is amorphous state.

(3) Under the condition of a temperature of 950 °C and a hydrogen atmosphere, reduce 10g of zinc tungstate in water bath kettle for 2 hours to obtain a tungsten powder which has a gray-black color and a loose texture weighing 5.492g. Through X-ray diffraction detection and fluorescence analysis of the tungsten powder, we can find that it is amorphous state, with a high purity which contains as high as 98.6% of tungsten.

The preparation of tungsten in this way can not only obtain tungsten powder and control suitable reduction conditions, but also to collect zinc. The process is simple, low labor costs, energy saving and environmental protection, good production efficiency and it can significantly reduce wastewater emissions and hydrochloric acid consumption.

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