OXIDATION OF PYRITE BY CHLORINE

Although many studies have been conducted on pyrite oxidation by oxygen and dissolved iron, there is very little information in the literature on pyrite oxidation by chlorine. As chlorine is used as a bacterial disinfectant both in wells and in water treatment systems, understanding how pyrite and other sulfides are affected by chlorine has environmental relevance. This study examined the rates of oxidation of pyrite by chlorine. Ten grams of 250-500um size pyrite was reacted with 500ml of water, 60 mg/l free chlorine or 1200 mg/l free chlorine at pH 7 or 8.5. Samples collected from solutions over the 24 hour period were analyzed for sulfate, which was used as the reaction progress variable. Results demonstrate that pyrite oxidation rates were fastest in solutions with the highest concentrations of chlorine held at pH 7. The difference in the rate of oxidation at pH 7 and 8.5 is likely connected to the different free chlorine species present (hypochlorite and hypochlorous acid).