Thermodynamic Modelling and Experimental Validation of CO2 Mineral Sequestration in Mandla Basalt of the Eastern Deccan Volcanic Province, India

Abstract

Deccan basalt contains primary silicates rich in Ca, Mg, and Fe ions, suitable for CO2 sequestration. Previous, basalt-water-CO2 interaction studies were focused on other than Deccan basalt types. However, such studies on the Deccan basalt are rare. Thus, present basalt-CO2 water saturated interaction modelling under hydrothermal-like conditions was carried out on the Deccan basalt of the Mandla area to understand apposite pCO2 and time parameters. Modelling results were further validated by experiments run in a laboratory time framework. Present results show negative entropy (ΔS) and enthalpy (ΔfH) that suggest feasibility of plagioclase, pyroxene and magnetite dissolution. Obtained negative Gibb’s free energy (ΔfG), ΔfH and ΔS values for calcite, dolomite and magnesite indicate spontaneous reaction, whereas, positive ΔfG and negative ΔfH and ΔS values of the siderite suggest non-spontaneous and opposing reactions. Calcite is the first carbonate mineral to form, but, at a faster rate. Magnetite dissolution begins after a time lag (not initiated along with the plagioclase and pyroxene). X-ray Powder Diffraction results of post-experiment residues revealed formation of calcite, aragonite, ankerite, huntite, siderite, smectite, chlorite, smectite/chlorite mixed layers and chabazite. Scanning electron microscopic images show tiny calcite crystal growth over the larger calcite crystal and incipient-disordered calcite with imperfections on crystal faces. Thus, basalt carbonation is mainly controlled by time, but temperature, pCO2 and pH played sub-ordinate role. Largely, thermodynamic models do not agree well with the experimental results as numerical models indicate larger carbonate growth. Additionally, transition state theory based models work well to predict dissolution rates for most of the minerals, but, they overpredict growth of the secondary minerals.