Pyrrhotite used in this study was provided by an iron sulphur mine in Tonglin City, Anhui In the laboratory, pyrrhotite was broken to fine particles. Pyrrhotite particles were added in 0.5 mol/L sulphuric acid solution for 2 h, and washed with deionized water repeatedly until water was clear. The clean pyrrhotite particles were dried in a draught cupboard. The dried pyrrhotite particles were then stored in airtight bags, which were flushed with nitrogen gas to prevent oxidation of pyrrhotite.