Recovery of Monoclinic Tungsten Trioxide from Waste Tungsten Slag

In the process of preparation of tungsten products and elimination of waste products, a large number of secondary resources containing tungsten will be formed. Recovering tungsten from secondary resources will not only improve the quality of tungsten, but also realize resource recycling. At present, the recovery and utilization of tungsten slag is mainly divided into three parts: (1) recovering valuable metals; (2) using tungsten slag as mineral material to produce wear-resistant materials; (3) producing tungsten slag glass-ceramics.

Some scholars have designed a process for producing monoclinic tungsten trioxide using waste tungsten slag. The crystalline tungsten oxide has good photocatalytic activity, simple process, low production cost and is suitable for industrial production. The process is as follows:

(1)Tungsten-copper alloy scrap is used as raw material to remove copper from copper-tungsten alloy by nitric acid leaching, and tungsten slag is obtained. The content of copper in tungsten slag is at least 0.5%. Tungsten trioxide is obtained by calcining tungsten slag at 400-600 ℃.

(2)Tungsten trioxide is dissolved in alkali solution and ammoniated to obtain ammonium paratungstate or ammonium tungstate.

(3)Ammonium paratungstate or ammonium tungstate were prepared into 1-2 mol/L aqueous solution, and then acidified slowly in 3-4 mol/L reducing acid, and yellow tungstic acid colloid was obtained by stirring.

(4) The yellow tungstic acid colloid was aged at 20-35 ("room temperature") for 16-24 hours, then dried at 100 ("room temperature") for 6 hours to obtain monoclinic tungsten trioxide. After grinding, the yellow monoclinic tungsten trioxide powder was obtained.

The experimental results show that the degradation rate of 10mg/L/methylene blue solution can reach 98.74% when 0.10g monoclinic tungsten trioxide powder is irradiated by 500 W xenon lamp for 3 hours. The monoclinic tungsten trioxide with photocatalytic degradation of organic matter is prepared by using tungsten-copper alloy scrap as raw material in the process, and the resource cycle of scrap metal is realized. It is in line with the national energy-saving and environmental protection strategy that recycled products can be used for environmental pollution control by environmental utilization and renewable energy solar energy.

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