Geochemical Modeling And Experimental Studies On Mineral Carbonation Of Primary Silicates For Long-Term Immobilization Of Co2 In Basalt From The Eastern Deccan Volcanic Province

Deccan flood basalt records immense accumulation (1.5 X 10(6) km(2) area) of tholeiitic magma in a relatively short time span. For mineral carbonation study and long-term storage of CO2, massive tholeiitic basalt from the Mandla lobe of the eastern Deccan volcanic province was considered as it contains a high amount of reactant minerals such as Ca, Mg and Fe rich silicates. Main objective of the present study is to understand effects of CO2 concentration on conversion of Ca, Mg and Fe bearing silicate minerals in to stable carbonate minerals such as calcite, dolomite, magnesite and siderite. Computer based computation details of chemistry of basalt-water-CO2 interaction, under laboratory induced hydrothermal-like conditions, form the basis of the treatment of basalt specimens. Grain surface area value = 23,000 cm(2)/g was maintained throughout the experiments. A series of experiments were performed at accelerated conditions of 5 and 10 bars pCO(2), while vessel pressures were maintained at 10 and 20 bars at 100 and 200 degrees C temperatures for 50, 60, 70 and 80 hours, respectively. XRD and SEM-EDS results show presence of calcite (Ca-0.29 C-0.79 O-6), aragonite (Ca-0.43 C-1.19 O-9), siderite (Fe-0.45 C-0.79 O-6) and magnesite (Mg0.11C0.79 O-6) in the treated samples. It is also observed that mineral carbonation accompanied by dissolution reactions led to rise in the pH (7.42) of the solution, when treated for 80 hours at 100 degrees C temperature and 5 bar pCO(2) pressure. A sudden decrease in the pH (6.85) is also noticed in case of a specimen treated similarly, but at elevated (10 bar) pCO(2). Bulk of the neo-formed secondary product is mainly composed of clay minerals. Present experimental results correspond largely to those obtained from kinetic modelling of basalt-water-CO2 interaction. Results indicate presence of similar carbonate minerals such as calcite, aragonite, siderite and magnesite. Details pertaining to mineral carbonation related phase transformations are discussed in the paper.