Toward a Model for Mineral Dissolution Kinetics

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The objective of this study is to compare the acid-base surface chemistry and dissolution kinetics of a series of minerals of similar composition and increasing structural complexity. This series includes bromellite (corundum, quartz), phenakite, chrysoberyl (and beryl). This study is intended to establish a link between models for dissolution of simple oxides, which are easily studied, and rock-forming minerals containing several potential sites for dissolution. The research entails determining the dissolution rate laws for phenakite, chrysoberyl and beryl as a function of pH and temperature in the range of 15-80 degrees C. Data already exist for the other minerals. An essential part of the research is comparison of the dissolution activation energies with the enthalpies of hydrogen- and hydroxyl-ion adsorption. This comparison will determine the extent that variations in equilibrium adsorption enthalpies with pH account for the reported variation in dissolution activation energies with solution pH. The proposed minerals have properties which are uniquely suited to establish the aforementioned link. All dissolve sufficiently slowly that solute diffusion does not affect the reaction rate. Thus the acid-base surface chemistry, which controls the pH-dependence of the reaction rate, can be easily characterized. Most importantly, the coordination chemistry of cations to oxygens is consistent in the entire series of minerals. This research involves fundamental understanding of the kinetics of dissolution in common rock-forming minerals necessary to get at the basics of rock weathering are metamorphism.