The fate and transport of the injected CO2 and the integrity of caprocks at geologic CO2 sites depend greatly on brine−mineral interactions, including dissolution and secondary precipitation. While phosphate can exist naturally in subsurface environments and can be introduced during engineered subsurface processes, our understanding of the influence of phosphate on brine−mica interactions is limited, especially under GCS relevant conditions. In this study, biotite (Fe-containing mica) dissolution experiments were conducted with different phosphate concentrations (0, 1, and 10 mM) at 95 °C and 102 atm CO2. We found that the effects of phosphate were concentration-dependent and element-specific. Similar levels of biotite dissolution were observed in the control and 1 mM phosphate experiments, however, 10 mM phosphate significantly promoted biotite dissolution. Additionally, phosphate complexed with surface Al or Fe sites and precipitated as Al- or Fe-bearing minerals, either on surfaces or in solutions, leading to lower aqueous Al and Fe concentrations with phosphate than those in control experiments without phosphate. Furthermore, 10 mM phosphate enhanced secondary surface precipitation, resulting in at least 4 times higher surface roughness than that in the control system. As a result, the biotite basal surfaces became more hydrophilic and supercritical CO2 wetting on biotite decreased. This study offers new fundamental information on the effects of phosphate on the geochemical reactions under GCS conditions and the consequent wettability changes of minerals, which has important implications for subsurface CO2 storage.

Brine−biotite interactions under Geologic CO2 Sequestration (GCS) conditions: Effects of phosphate

253rd National Meeting (2017)

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