CO2 Mineralization of Deccan Trap Basalts

Banks, Finlay; Lacinska, Alicja; Bateman, Keith; Pearce, Jonathan; Williams, John; Vedanti, Nimisha. 2024 CO2 Mineralization of Deccan Trap Basalts. [Lecture] In: Society of Exploration Geophysicists. Role of Geosciences in Carbon Storage., Mumbai, India, 19-21 Mar 2024. (Unpublished)

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Introduction Many of India’s large emission sources are located far from sedimentary basin settings where CO2 storage might otherwise be considered. Continental flood basalts of the Deccan Traps cover an estimated 500,000 km3 in west-central India, and there is much interest in their potential to permanently store and trap CO2 through mineral carbonation processes. The Deccan Traps consist of layers of solidified flood basalt more than 2,000 m in thickness. The volume of basalt exceeds 1,000,000 km3 and provides a significant theoretical potential for high-volume storage of CO2. Carbon capture and storage by mineralization (CCSM) has been studied in several regions, including the Wallula Basalt Project in Columbia River, USA, and the Carbfix project in Iceland. Although some previous studies on the trapping potential of basalts have shown promising results, there remains significant uncertainty as to the practicality of storing CO2 volumes at industrial scale in the Deccan Traps. Theory and/or Method To gain a preliminary insight into the types of reactions that may be expected during CCSM in Deccan Trap basalts, a core sample taken from the Killari borehole was reacted with CO2-rich water. Prior to reaction the sample was crushed to produce a 125 to 250 μm fraction, which increases the mineral surface area and enhances the rate at which the reactions occur. Future experiments using whole-rock samples will provide more realistic reaction rates, requiring the experiments to be run over a longer period of time to produce detectable mineralogical reactions. To produce basalt-equilibrated fluid for the experiment, this powder was placed in a 1 liter container of deionized water at 70°C for one week. A preliminary study was conducted using three batch vessels containing crushed starting material and the equilibrated fluid pressurized first with nitrogen, and then with CO2 to 90 bar. Each vessel was subjected to a different temperature (50, 100, and 150°C), and reacted for up to 43 days. The selected temperature range reflects the significant variation in geothermal gradient across the Deccan Volcanic Province. Fluid samples were collected at regular intervals for geochemical analysis, while post-reaction solids were examined using Scanning Electron Microscopy (SEM) to provide evidence for mineral dissolution and precipitation. Example Little evidence of mineral dissolution or precipitation was observed in the 50˚C experiment, whereas notable dissolution of plagioclase was observed in the 100˚C experiment. There was no clear evidence of carbonate precipitation in either experiment. In contrast, the 150˚C experiment resulted in significant dissolution of plagioclase and precipitation of secondary phases, including rhombohedral crystals of siderite (40-50 μm) and silicate minerals, likely smectite and phases belonging to the zeolite mineral group based on SEM qualitative analysis. Figure 1 shows evidence of the rhombohedral siderite crystals and Figure 2 shows fibrous silicate minerals formed during the 150˚C experiment. Platy silicate minerals were also observed which may be smectite. A significant amount of calcium carbonate and amorphous silica precipitate eventually blocked the fluid sampling tube. Conclusions The preliminary data indicates that while dissolution and carbonate mineral precipitation occurred during experiments at 150˚C, the reaction rates were significantly reduced at lower temperatures resulting in less CO2 trapped in mineral form. This indicates that targeting of regions with higher geothermal gradients might be worthwhile for future laboratory and field studies. Ongoing work continues to analyze the fluid geochemistry data, which provide a sensitive analytical means of determining the relative timing and rates of reactions.

Item Type: Publication - Conference Item (Lecture)
Additional Keywords: IGRD
Date made live: 03 Apr 2024 14:37 +0 (UTC)

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