The Effect of Calcium and Magnesium Ions on CO2 Convective Dissolution and Carbonate Precipitation

The reduction of carbon dioxide concentration in the atmosphere has become an important objective to diminish the predicted exponential increase in global temperatures. A promising long-term solution is carbon capture, and sequestration (CCS), whereby CO₂ is injected into saline aquifers containing high concentrations of divalent cations leading to the mineralization of carbonate salts. These precipitation reactions provide a potential long-term solution for storing and preventing reentry of this greenhouse gas into the atmosphere. Our study aims to understand the influence of the initial host solution composition on CCS. Using two glass plates separated by a thin gap (~1 mm), we steadily inject CO₂ gas above an alkaline aqueous solution of either calcium chloride and/or magnesium chloride and monitor the convective uptake of CO₂ and subsequent mineralization into calcium carbonate (e.g., calcite, aragonite, and vaterite), magnesium carbonate (e.g., hydromagnesite), or calcium magnesium carbonate (e.g., dolomite). The buoyancy-driven convective dynamics from the dissolution of CO₂ is monitored using schlieren imaging techniques. In addition, a pH indicator in the initial metal salt solution shows its acidification from the continuous uptake of CO₂. The mineral products are analyzed using X-ray diffraction, Raman spectroscopy and scanning electron microscopy to determine the composition, crystal structure, and crystal habit.