Studies of pH buffer systems to promote carbonate formation for CO2 sequestration in brines

Carbon dioxide (CO2) sequestration using brines is significantly dependent on pH for the formation of carbonates. This study evaluated a series of buffer solutions and then selected the optimal one to promote the precipitation of mineral carbonates (mainly calcium carbonates) for above-ground and to help to understand the pH effect on both above-ground and underground carbonation. Five organic or inorganic buffer solutions (pH > 9.0) were selected in this study. pH stability studies were conducted to compare the buffering ability amongst those five buffer solutions for 15 days in both closed and open atmospheres. Buffer solution Bf 1 (boric buffer solution, pH = 10.0) and Bf 2 (0.3 M Tris buffer solution) were selected as the optimal buffers to conduct carbonation experiments due to their strong buffering ability to maintain the pH above 9.0. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis showed that the concentration of Ca decreased considerably after each carbonation experiments with buffer Bf 1 or Bf 2. The results from X-ray diffraction (XRD) analysis of the precipitates formed from carbonation reactions confirmed the predominant presence of calcite (CaCO3). Finally, the buffers studied here were compared to biocatalysts previously reported for rising pH of brines.