Insights into silicate carbonation processes in water-bearing supercritical CO2 fluids

Abstract

Subsurface injection of CO2 is commonplace in certain industries, yet deployment at the scale required for emission reduction is unprecedented and therefore requires a high degree of predictability. Accurate modeling of subsurface geochemical processes related to geologic carbon sequestration requires experimentally derived data for mineral reactions. Most work in this area has focused on aqueous-dominated systems in which dissolved CO2 reacts to form crystalline carbonate minerals. Comparatively little laboratory research has been conducted on reactions occurring between minerals in the host rock and the wet supercritical fluid phase. We studied the carbonation of wollastonite [CaSiO3] exposed to variably hydrated supercritical CO2 (scCO2) at 50, 55 and 70°C and 90, 120 and 160bar. Reactions were followed by three novel in situ high pressure techniques, which demonstrated increased dissolved water concentrations in the scCO2 resulted in increased wollastonite carbonation approaching ∼50wt.%. Overall, the X-ray diffraction and infrared and magic angle nuclear magnetic resonance spectroscopies experiments conducted in this study allow detailed examination of mechanisms impacting carbonation rates. These include the development of amorphous passivating layers, thin liquid water films, and amorphous hydrated carbonate phases. Collectively, these results emphasize the importance of understanding geochemical processes occurring in wet scCO2 fluids.