A rotating ring (Pt)-disc (FeS2) electrode was used to investigate the surface oxidation process of pyrite in the hydrochloric solutions. It is reported for the first time that the oxidation intermediates of pyrite were formed on the disc electrode and then oxidized on the ring electrode. The results indicate that at a rotation rate of 20 Hz, when the disc electrode potential was in the region of 0.43 to 0.62 V and the ring electrode potential was at 1 V vs a standard calomel electrode (SCE), approximately 50% of the reacted pyrite was oxidized to ferric and sulfate ions and the other 50% was oxidized to sulfur and ferrous ions on the disc electrode. The latter was further oxidized to ferric ions on the ring electrode. As the disc electrode potential increased to 1.22 V vs SCE, more than 90% of the reacted pyrite was oxidized to ferric and sulfate ions on the disc electrode and less than 10% formed ferrous ions, which were further oxidized to ferric ions on the ring electrode. Copyright 1999 Academic Press.