Nickel is produced from ores that include oxides of nickel and nickel sulfides. Various chemical processes can be used to break these compounds of nickel to release free nickel. In the processing of nickel sulfides there is a release of sulfur oxides that reacts with water to form acidic compounds. Once nickel has been extracted it has to be purified which again requires the use of sulfuric acid in most cases.
The gaseous effluents in nickel extraction include a large quantity of compounds of sulfur; if these are mixed with water and the resulting sludge released into a water source like a lake it leads to acidification of the lake that presents a serious environmental concern. To reduce the acidity of the lake it is essential to treat the smoke stack of the smelter so that it is able to absorb more of the sulfur compounds and a reduced amount of acid is present in the sludge that is finally formed.