The surface changes of synthetic hexagonal pyrrhotite Fe[10]S[11] during laboratory wetting-drying treatment at 45°C were investigated using FTIR (DRIFT) spectroscopy, FTIR Raman microscopy, and scanning electron microscopy. α-FeO(OH) (goethite) and elemental sulphur were the main products of the surface pyrrhotite oxidation. The formation of goethite and elemental sulphur was studied on the basis of the corrosion theory and using a potential-pH (Pourbaix) diagram. The appearance of oxidation products on the surface of pyrrhotite grains was detected between 10 and 20 h of treatment. The obtained results can be used for comparison of oxidation processes of synthetic pyrrhotite with that of natural sulphide minerals in dumps.