Recovery of Waste Gases from Tungsten Disulfide

Waste gases from tungsten disulfide are toxic hydrogen sulfide and some other gases. Among them, hydrogen sulfide poses a serious threat to the human health and environment. Therefore, we have to recycle the waste gases from tungsten disulfide.

Tungsten disulfide is often prepared from ammonium tetrathiotungstate in industry. In the preparation 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. A small amount of HCl and NH₃ gas, together with a certain amount of H₂S are produced in this preparation process. And the hydrogen sulfide is a dangerous gas throughout the preparation.

Hydrogen sulfide, with a molecular weight of 34.076, is an acidic colorless gas. It has a rotten egg smell at low concentrations and a sulfur odor at very low concentrations. It is soluble in water, alcohol, petroleum solvents and crude oil. Its aqueous solution is hydrosulphuric acid. Hydrogen sulfide gas is dangerous in three aspects:

1. Hydrogen sulfide a flammable and dangerous chemical with a ignition point of 292°C. When mixed with air, it can form explosive mixture, which can cause combustion and explosion when exposed to naked fire and high heat energy.

2. When hydrogen sulfide burns, blue flame and toxic sulfur dioxide occur, damaging the human health.

3. Hydrogen sulfide is an extremely toxic gas, posing a serious or even fatal threat to human health. Even thin hydrogen sulfide can irritate the airways and eyes and cause headaches. Even more, it can be life-threatening at concentrations of 1 mg/L or higher. Therefore, both preparation and use of hydrogen sulfide should be done in a fume hood.

Hydrogen sulfide not only causes serious air pollution, but also produces unimaginable harm to human body. Therefore, we can take the following measures to recycle and purify the waste gases from tungsten disulfide.

1. The small amount of HCL and NH₃ gases produced in the preparation can be discharged into the atmosphere with a strong exhaust device.

2. Harmful H₂S gas can be repeatedly absorbed by dilute NaOH solution, so that most of it is converted into Na₂S and returned to production. The remaining small number of H₂S can be discharged with the chimney up to 30 m high without affecting the environment.

Tungsten disulfide gas contains highly toxic hydrogen sulfide gas which poses a serious threat to human health and environmental hygiene. We have to recycle it.

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