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Mechanism of Pyrite Oxidation in Aqueous Mixtures

Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521-0424;

J. J. Jurinak

Dep. of Soil Science and Biometeorology, Utah State Univ., Logan, UT, 84322-4840.

^* Corresponding author.

ABSTRACT

The rate of pyrite oxidation in aqueous mixtures was studied at 25 °C for periods up to 3 wk. Dissolved plus citrate-dithionite-extractable Fe was used to measure the extent of reaction. Pyriteoxidation rate was independent of time (zero order) in the presence of NaClO₄, CaCO₃, and NaHCO₃. Oxidation rate was a linear function of substrate concentration. Oxidation rates increased with pH. Solutions of Cl^–, SO^2–₄, and diethylenetriamine pentaacetic acid (DTPA) inhibited pyrite oxidation. The data are consistent with a surface-controlled reaction with Fe³⁺ as the rate-controlling oxidant. The effect of OH^–, Cl^–, SO^2–₄, and DTPA on oxidation rates is explained by the relative reactivity of each of these in ligand exchange during an inner-sphere electron transfer. It is suggested that OH^– is the rate-determining bridging ligand between Fe³⁺ and the pyrite surface. This reaction is compatible with recently proposed surface-reaction mechanisms.

Published as Journal Paper no. 3191 of the Utah State Agric. Exp. Stn., Logan, Utah.

Received for publication January 20, 1989.

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