Mechanisms of nonbiological pyritic sulfur oxidation under alkaline conditions

Abstract

Pyrite oxidation was studied at 25°C in aqueous solutions at several pH levels for periods of 10 days to 2 weeks to determine the distribution of water‐soluble S products in this reaction. The extent of reaction was measured in terms of total oxidized Fe and compared with total SO₄ ²⁻. Sulfate measurements underestimate the extent of oxidation, especially above pH 8. This is due to the production of relatively unreactive reduced S compounds such as S₂O₃ ²⁻ and S₄O₆ ²⁻ in intermediate reactions. Excess S₂O₃ ²⁻ inhibits pyrite oxidation by reducing Fe³⁺, the principal pyrite oxidant. Mixing of pyrite and CaCO₃ in columns was used to model different management strategies for burial of pyritic wastes. The production of reduced S compounds should be considered in disposal plans.