1. Absorption method:
The hydrogen sulphide gas is absorbed by a solution of sulfide (or caustic soda). Because hydrogen sulfide gas is poisonous, absorption reaction should be under negative pressure. In order to prevent the excessive pollution of hydrogen sulfide in the exhaust gas, several absorbers are operated in series, and the content of hydrogen sulphide has been reduced to a lower degree by multiple absorption. The absorption liquid is concentrated and made of sodium hydrogenated sodium. Its chemical equation:
H2S + NaOH - NaHS + H2O
H2S + Na2S - > 2 nahs [1]