Recovery of Tungsten Disulfide

Recovery of tungsten disulfide is extremely significant. It mainly refers to the recovery of tungsten-containing residue, acid-containing liquor, and hydrogen sulfide together with other gases produced in tungsten disulfide preparation.

Tungsten disulfide is often prepared from ammonium tetrathiotungstate in industry. In the process, the raw material is firstly dissolved with HCl hydrochloric acid to form tungstic acid. Then tungstic acid is mixed with ammonia water to form ammonium tungstate. Next, ammonium tungstate is added to hydrogen sulfide to form tetrathiotungstate. Finally, tungsten disulfide is prepared by the reduction reaction of tetrathiotungstate by hydrogen in high temperature reflector. Tungsten-containing residue produced in the preparation process may be a waste of resource while acid-containing liquor and hydrogen sulfide may do harm to the environment. They should be recycled.

With the example of a plant, the recovery of tungsten disulfide is as follows:

1. Recovery of tungsten-containing residue

The plant’s annual output of ammonia dissolved filter residue was 8.58 t, containing 0.79 t tungsten oxide; the annual concentrated filter residue was 14.28 t and about 9.28 t of tungsten oxide contained in it. The residue can be made into tungsten salt and the tungsten salt can be returned to production. The recovery of tungsten-containing residue not only increases the recovery rate of tungsten, but also increases the economic benefit.

2. Recovery of acid-containing liquor

The plant’s annual output of acid-soluble filtrate was 450 m³, containing 500 g/m³ WO₃ and 2.5 mol/L HCl. It is recycled to form CaWO₄ and then be returned as raw material. 230 kg tungsten oxide can be recycled annually in this way. In addition, tungsten acid solution annual output was 1350 m³, containing a small amount of calcium ions. To treat sewage, HCl can be neutralized with alkaline waste solution. Besides, sodium sulfate concentrate containing NaSO₄ can be recovered by the condensing crystallization.

3. Recovery of hydrogen sulfide and other gases

The harmful hydrogen sulfide, together with HCl gas and NH₃ were discharged in production. HCl and NH₃ can be discharged into the atmosphere with a strong exhaust device. And hydrogen sulfide can be repeatedly absorbed by dilute NaOH solution, so that most of it can be converted into Na₂S and returned for production. The remaining small amount of hydrogen sulfide can be discharged through the chimney with a height of 30 m.

Recovery of tungsten disulfide treats the waste substances into raw materials and increases the economic benefits. It is worthy of our attention.

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