Structure-dependent interactions between alkali feldspars and organic compounds: Implications for reactions in geologic carbon sequestration

Organic compounds in deep saline aquifers may change supercritical CO ₂ (scCO₂)-induced geochemical processes by attacking specific components in a mineral's crystal structure. Here we investigate effects of acetate and oxalate on alkali feldspar-brine interactions in a simulated geologic carbon sequestration (GCS) environment at 100 atm of CO ₂ and 90 C. We show that both organics enhance the net extent of feldspar's dissolution, with oxalate showing a more prominent effect than acetate. Further, we demonstrate that the increased reactivity of Al-O-Si linkages due to the presence of oxalate results in the promotion of both Al and Si release from feldspars. As a consequence, the degree of Al-Si order may affect the effect of oxalate on feldspar dissolution: a promotion of ∼500% in terms of cumulative Si concentration was observed after 75 h of dissolution for sanidine (a highly disordered feldspar) owing to oxalate, while the corresponding increase for albite (a highly ordered feldspar) was ∼90%. These results provide new insights into the dependence of feldspar dissolution kinetics on the crystallographic properties of the mineral under GCS conditions.