Long-term CO2 capture-induced calcite crystallographic changes in Deccan basalt, India

Previous basalt carbonation studies under hydrothermal-like conditions suggested high amount of calcite formation in a shorter period which is related to the andesine dissolution. However, CO2 capture-induced structural changes in neo-formed minerals have not been studied in detail. To understand these changes, Rietveld refinement and crystallographic characterization were performed for andesine and calcite residue obtained after basalt-water-CO2 interaction experiments. These results indicate large spontaneous strain within calcite which led to contraction along the c-axis and expansion along a-axis. Thus, contraction/expansion along the c-axes is inversely proportional to a-axis of the calcite and andesine, respectively. Interatomic Ca-O and C-O bond lengths show changes with the experimental run time, signifying mutually inverse relationship. Observed crystal structure distortion is due to variation in the O-M-O bond angle. Ionic bond length between Ca and O atoms decreased after 70h of experiment run that enabled Ca-O ligand to enter in the phyllosilicates. The Ca-O bond length weakening along c-axis caused shrinkage of calcite crystals. Increased bond length together with the weakened covalent bond between C and O atoms led to calcite degeneration after 80h of experiments; therefore, no calcite persisted in the system. Thus, basalt carbonation is time-dependent process, where, pCO(2) plays sub-ordinate role, but, at a constant temperature.