Role of Fe(II) Content in Olivine Carbonation in Wet Supercritical CO2

摘要

Basalt geologic reservoirs are targeted for carbon storage because they are abundant in divalent silicates such as olivine [(Mg,Fe)(2)SiO4] that can carbonate to permanently trap CO2. Under reservoir conditions, CO2 is a supercritical fluid that contains dissolved H2O, which adsorbs to minerals as nanometer thin films. In this study, the role of Fe(II) in the thin H2O film carbonation of olivine was investigated using in situ high-pressure infrared spectroscopy and ab initio thermodynamic calculations. Experiments were performed at 50 degrees C and 90 bar in both supercritical CO2 and supercritical CO2 with 1% H-2 at a relative humidity of 79% on synthetic forsterite, fayalite, and two Mg/Fe mixture olivines, (MgxFe1-x)(2)SiO4 (x = 0.33 and 0.66). Carbonation rates and extents are lower with increasing concentrations of Fe(II) in the olivine, but the addition of 1% H-2 increases the level of carbonation in Fe(II)-rich olivines. These trends are explained according to the dependencies of olivipe acidic solubilities, carbonate precipitation equilibria, and dissolution/growth kinetics on Fe(II) content and by considering that Fe(II)-rich olivines can undergo competing oxidation reactions by O-2 and H2O to form Fe(III)-containing oxides. Given that CO2 injected into the subsurface will be relatively oxic, the oxidation of Fe(II)-rich olivines could impact their carbonation potential.