Abstract:
Dissolution experiments using augite (Mg0.87Ca0.85Fe0.19Na0.09Al0.03Si2O6) and diopside (Mg0.91Ca0.93Fe0.07Na0.03Al0.03Si2O6) 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 25oC. 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.