Galena Oxidation in Oxygen-Bearing Acidic Solutions

The oxidation of galena (PbS) by oxygen-bearing acidic solutions was investigated over the pH range of 2-3.5 at two different oxygen concentrations (7.0 x 10(-5) and 2.2 x 10(-4) M) and a temperature of 25 degrees C using a potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS), aqueous batch experiments, and Fourier transforms infrared spectroscopy. EIS results indicate that the aqueous oxidation of galena is controlled by a surface reaction. At 25 degrees C and [O-2] = 2.2 x 10(-4) M, the reaction order with respect to the proton concentration is virtually zero (n(H) = -0.02 +/- 0.08), indicating that hydrogen is not involved in the rate-determining step of the reaction. At pH 2 and 25 degrees C, the reaction order with respect to the oxygen concentration is 0.96 +/- 0.06, showing that oxygen is an important component of the activated complex. The experimental results can be reasonably explained by the mixed potential theory. The aqueous oxidation rates evaluated by electrochemical measurements are not affected by the non-oxidative dissolution or the solid phases precipitated on the mineral surface and offer reliable information for the understanding of lead and sulfur mobility in the environment.