An Electrochemical Investigation of Surface Reactions of Coal- and Mineral-Pyrite in Aqueous Solutions

Abstract

Oxidation and reduction processes occurring on polished and freshly fractured coal- and mineral-pyrite have been studied using electrochemical techniques with the aim of understanding the reactions that control its hydrophobicity and flotation. Ring-disc studies show that 1) the kinetics of oxygen reduction on pyrite depends on its source; 2) two distinct soluble reduction products (ferrous hydroxide and HS - ) are generated on pyrite in alkaline solutions (pH 9.2) during cathodic sweeps; and (3) one distinct soluble oxidation product (also ferrous hydroxide) is produced during anodic sweeps (pH 9.2). The voltammetry behavior of polished pyrite at moderate overpotentials is dominated by the oxidation and reduction of ferrous and ferric hydroxides, respectively, and not by the oxidation and reduction of pyrite. To study the initial oxidation processes occurring on pyrite itself, fresh surfaces were created by fracturing electrodes under the electrolyte. This procedure avoided complications from the iron oxides and hydroxides present on polished electrodes. Chronoamperometry immediately after fracture and subsequent cyclic voltammetry were used to elucidate the initial oxidation reaction producing hydrophobic sulfur species on pyrite.