Metallurgical processes for smelting and refining sulphide ores, such as copper, lead, zinc, nickel, etc., produce a waste gas containing dust, metallic vapours and sulphur dioxide that must be treated before discharge into the environment. The most common method for treating the gas is a sulphuric acid plant with upstream gas cleaning.
In this process, the purified SO2 in the gas is catalytically oxidised to SO3 by means of the contact process and subsequently converted to sulphuric acid.