Influence of cadmium sorption on FeS2 oxidation

Pyrite oxidation leads to the formation of acid-mine drainage and the relea se of associated trace metals. A better understanding of the processes that influence pyrite oxidation will help to determine the rate of acid and cat ion evolution from pyritic mine tailings. The oxidation process is surface- controlled and may be influenced by cadmium sorption, which forms surface p recipitates and complexes that may limit pyrite oxidation. The purpose of t his research is to investigate the effect of cadmium sorption on the rate o f FeS2 oxidation by molecular oxygen. Raman spectroscopy was used to track the evolution of oxidized sulfur products, and X-ray absorption spectroscop y was used to quantify iron oxidation rates. Cadmium concentrations as low as 50 mu M depressed pyrite oxidation rates. Oxygenation of amorphous FeS2 (1 g/L) is described by a pseudo-first-order reaction with a rate constant of 6.85 x 10(-5) s(-1); FeS2 sorbed with 500 mu mol of Cd g(-1) prior to ox ygenation exhibited an oxidation rate 5.15-fold lower with a rate constant of 1.33 x 10-5 s(-1). Raman and XANES data indicate that cadmium sorption i nfluences FeS2 oxidation. In natural systems, suppression of FeS2 oxidation by Cd and other soft Lewis acids may retard the release of acidity and tra ce metals to the environment.