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Paper No. 26-7
Presentation Time: 8:00 AM-5:30 PM
DECIPHERING COUPLED DISSOLUTION AND PRECIPITATION REACTION KINETICS USING MULTIPLE ISOTOPE TRACERS
Our current knowledge of geochemical kinetics is largely based on single mineral dissolution rates far from equilibrium. However, geologic systems that store CO2, e.g., soils and aquifers, are multi-mineral systems. There is a lack of experimental data on the multi-mineral kinetics of such systems. Here we show geochemical modeling results and experimental data on coupled plagioclase dissolution and calcite and clayey mineral precipitation in experiments using multiple isotope tracers. In this study, plagioclase was chosen as the reactant because it is both a major component and among the most reactive minerals in basalts. Following our isotope doping studies of single minerals in the last ten years [1-7], initial solutions in the multi-mineral experiments are doped with multiple isotopes (e.g., Ca and Si). Geochemical modeling results show that the use of isotope tracers gives us orders of magnitude more sensitivity than the conventional method based on concentrations and allows us to decouple dissolution and precipitation reactions. The simulations show that the precise unidirectional dissolution rates will likely inform us which rate laws that plagioclase dissolution has followed. Calcite precipitation likely occurs very near equilibrium and the multiple isotope tracer experiments will give us near-equilibrium precipitation rates, which was a challenge for the conventional concentration-based experiments. Experimental data will also likely reveal whether the precipitation of clayey phases will be the rate-limiting step in some multi-mineral systems. Overall, the results of multi-mineral reaction kinetics will improve the understanding of the coupled dissolution-precipitation in the multi-mineral systems and the quality of geochemical modeling prediction of CO2 removal and storage efficacy in the basalt systems.
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