Predicting Silicate Mineral Dissolution Rates

We have developed a model that allows us to predict dissolution rates for some silicate minerals as a function of pH, temperature, connectedness of the mineral structure, and rate of water exchange around the dissolved cation (k_solv). Such a model can be used for rate prediction when data is unavailable as well as to elucidate inconsistencies among published data for mineral dissolution kinetics.

Previous experiments have identified several factors affecting silicate dissolution rates and have been included in an empirical model. Casey and Westrich (1992) showed that the rate of water exchange around an octahedral cation is correlated to the mineral dissolution rates in orthosilicates. It has also been suggested that minerals with a lower connectedness (the number of bridging oxygens per tetrahedron) dissolve more quickly than minerals with a higher degree of polymerization. Additionally, we know from numerous previous silicate dissolution studies that rates are generally a function of pH and temperature. We have developed a model that uses these four parameters (pH, k_solv, connectedness, and temperature) to predict silicate dissolution rates for many orthosilicate, pyroxene, amphibole, sorosilicate, and some phyllosilicate minerals.

In order to do this, we have gathered dissolution kinetics data from almost 70 laboratory studies of silicate dissolution for forsterite, fayalite, willemite, tephroite, phenacite, liebenbergite, kirschsteinite, monticellite, Ca-olivine, Co-olivine, epidote, augite, diopside, enstatite, wollastonite, anthophyllite, hornblende, tremolite, chrysotile, and talc. This data will be housed on ChemXSeer (http://chemxseer.ist.psu.edu/), an online cyberinfrastructure that emphasizes chemical kinetics data. We observe a strong correlation between log r and pH, k_solv, connectedness, and temperature.