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 70 h 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 80 h of experiments; therefore, no calcite persisted in the system. Thus, basalt carbonation is time-dependent process, where, pCO₂ plays sub-ordinate role, but, at a constant temperature.