Electrochemical Reaction Mechanisms at Pyrite in Acidic Perchlorate Solutions

Potentiodynamic sweeps, cyclic voltammetry, and the rotating ring‐disk technique were used to study the anodic dissolution of pyrite. Pyrite behaves as a metal in the potential region investigated. The dissolution was shown to be kinetically controlled. At low overpotentials a total of three electrons were transferred and selective dissolution of occurs with the formation of a metal‐deficient sulfide layer. At large overpotentials this passivating sulfide layer is oxidized in an overall 15 electron‐transfer reaction. Oxygen reduction at pyrite was studied in the pH range 1 to 3 using the rotating ring‐disk technique. Hydrogen peroxide was detected at the ring and mechanistic analyses of the data show that the reaction can proceed by two paths, one involving solution‐soluble hydrogen peroxide and one involving only adsorbed intermediates. The amount of hydrogen peroxide formed during the course of reaction diminishes as the pH decreases.