Reduction of iron sulphates during coal liquefaction

The transformation of pyrite to pyrrhotite and gypsum to anhydrite is well known during coal liquefaction. Most coals, except extremely fresh ones, contain various iron sulphates resulting from the oxidation of pyrite and marcasite. The reduction of iron sulphates to pyrrhotite during liquefaction is shown with the degree of reduction being temperature dependent. The formation of pyrrhotite from the iron sulphates is important because pyrrhotite is considered to catalyse hydrogénation reactions.