The effect of iron content and dissolved O₂ on dissolution rates of clinopyroxene at pH 5.8 and 25°C: Preliminary results

Dissolution experiments using augite (Mg_0.87Ca_0.85Fe_0.19Na_0.09Al_0.03Si₂O₆) and diopside (Mg_0.91Ca_0.93Fe_0.07Na_0.03Al_0.03Si₂O₆) were conducted in flow-through reactors (5-ml/h flow rate). A pH of 5.8 was maintained by bubbling pure CO₂ through a solution of 0.01 M KHCO₃ at 25°C. Two experiments were run for each pyroxene type. In one experiment dissolved O₂ concentration in reactors was 0.6 (±0.1) ppm and in the second dissolved O₂ was 1.5 (±0.1) ppm. After 60 days, augite dissolution rates (based on Si release) were approximately three times greater in the 1.5 ppm. dissolved O₂ experiments than in the sealed experiments. In contrast, diopside dissolution rates were independent of dissolved O₂ concentrations. Preliminary results from the augite experiments suggest that dissolution rate is directly related to oxidation of iron. This effect was not observed in experiments performed on iron-poor diopside. Additionally, dissolution rates of diopside were much slower than those of augite, again suggesting a relationship between Fe content, Fe oxidation and dissolution rates.