Title: Experimental study of pyrite oxidation at pH 6-9 and 30 degrees C
Abstract: Experimental studies of pyrite oxidation over the pH range 6-9 were carried out at 30°C in 0.1 M KC1 under conditions of fixed pH and p02 .Rate of addition of base necessary to maintain a fixed pH was monitored.Samples were withdrawn periodically and analyzed for total sulfur in solution, thiosulfate, polythionates, and sulfide.The results demonstrate an increase in rate of hydrogen-ion production with increase in pH.Metastable sulfur oxyanions were detected as intermediates in the sulfur oxidation pathway.For short-term (less than 2 day) runs, the proportion of these sulfur oxyanions was less sensitive to the length of a run than to the pH of the run.At the lower pH values (6-7), tetrathionate and sulfate were the major observed species.As pH is increased, these ions diminish with respect to thiosulfate and sulfite.The short-term data are consistent with a rate-controlling step involving the pH-dependent oxygenation of the ferrous-iron component of the pyrite and subsequent rapid oxidation of the sulfur component to an intermediate oxidation state dictated by pH-dependent reactions.Ultimately, all sulfur is oxidized to sulfate.