A process used to produce sulphuric acid from calcium sulphate. It uses calcium sulphide to produce lime (CaO) and sulphur dioxide in the so-called Müller–Kühne reaction, which takes place in a kiln operated at 1,150ºC:
It is named after German chemist inventors W. S. Müller and Hans Kühne (1880–1969) who developed the process in the First World War (1914–18) when Germany was unable to obtain imported supplies of iron pyrites used for making sulphuric acid.