| Description |
Storing carbon dioxide generated by fossil fuel utilization will provide means of reducing CO2 emissions into the atmosphere as the transition to carbon-neutral energy technologies unfolds. The brine-rock-CO2 interactions that govern the long-term fate of CO2 under conditions relevant to the geologic storage of CO2 are largely unknown. Batch experiments were conducted in high-temperature, high-pressure reactors to establish the types of brine-rock-CO2 reactions, including mineral precipitations. The solids were analyzed using X-Ray Diffraction (XRD), Scanning Electron Microscope/ Back Scattered Electron images (SEM/BSE) and Energy Dispersive X-Ray Spectroscopy analysis (EDS). The brine compositions were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for cations and Ion Chromatography (IC) for anions. The three formations, limestone, sandstone, and arkose, were chosen because of their common occurrence and their proximity to coal fire power plants. Peridotite was chosen because of its high reactivity. The experiments with synthetic arkose and CO2 yielded precipitation of calcite, analcime, kaolinite, and ankerite. In experiments with limestone, extensive dissolution was observed in limestone-brine-CO2 experiments with no precipitation. Precipitation of calcite and kaolinite (products of feldspar carbonation) were observed in sandstone experiments. Peridotite experiments yielded growth of orthorhombic crystals of magnesite. Growth of hollow Ca-zeolite crystals, alteration of clays, and trace amounts of dolomite precipitates were the principal observations in the experiments with retorted shale. In experiments with CO2+SO2 as the feed gas, pronounced dissolution of all minerals and precipitation of kaolinite and anhydrite were observed. Precipitation of ammonium zeolites and calcite were observed in experiments with CO2+NH3. Increase in brine-to-rock ratio increases the pace of the reactions. Modeling was performed by using the Geochemists WorkBench (GWB). The degassing simulations capture quenching and the secondary reactions that might occur during the de-pressurizing of the reactor. There was good agreement between the modeling and experimental results in all the cases and for all the ions barring calcium. A full factorial parameter sensitivity analysis was carried out to determine the principal kinetic factors affecting the behavior of a mineral species in the brine-arkose-CO2 reaction system. This study shows that permanent sequestration of CO2 in saline aquifers through mineral carbonation is highly dependent on the resident mineral composition and on the composition of the injected gas. |
