For safe and efficient geologic CO2 sequestration (GCS), we need a better understanding of the effects of organic ligands on scCO2 saturated brine-biotite interactions. This work investigated biotite dissolution and secondary precipitation in the presence of acetate and oxalate under GCS relevant conditions of 95 oC and 102 atm CO2. We used inductively coupled plasma optical emission spectrometry (ICP-OES) to measure the evolution of aqueous ion concentrations, and atomic force microscopy (AFM) to characterize biotite surface morphology changes. Acetate was found to slightly inhibit biotite dissolution and promote secondary precipitation, while oxalate strongly enhanced biotite dissolution and induced faster and more significant evolution of surface morphology changes by forming cracks and dissolution channels. Anisotropic dissolution of biotite was strengthened by oxalate. Oxalate preferentially formed complexes with metal sites on edge surfaces, increasing the relative reactivity ratio of biotite edge surfaces to basal surfaces. The enhancement effect of oxalate on biotite dissolution is caused by oxalate attacking edge surface sites. However, acetate did not impact the relative reactivity ratio of biotite edge surfaces to basal surfaces. The effects of acetate were mainly pH-induced: acetate buffers the pH drop caused by injection of supercritical CO2, and acetate exists as acetic acid. A layer of acetic acid molecules adsorbed to biotite surfaces, reducing biotite dissolution, especially interactions with surface Si and Al sites, and thus reducing the release of tetrahedral Si and Al cations. The organic ligands, acetate and oxalate in this study, affected biotite dissolution and secondary precipitation, which might potentially lead to changes in biotite properties, such as porosity, permeability, and wettability, which are all related to the sealing property of caprocks. Therefore, information provided in this study can benefit CO2 storage in organic-rich sites.

Effects of organic ligands on scCO2 saturated brine-biotite interactions: Implications for organic-rich geologic CO2 sequestration

249th National Meeting (2015)

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