Date of Award
Doctor of Philosophy (PhD)
Geologic carbon sequestration (GCS) is an effective method to mitigate environmental problems due to excessive anthropogenic CO2 emissions. It involves injecting supercritical CO2 into deep geologic formations in which CO2 will ultimately be converted to solid carbonate minerals. Basalt is a promising host rock that is rich in the divalent cations Ca, Mg and Fe that are important for mineral trapping of CO2. Fractures and pores in basalt reservoirs provide substantial surface area for geochemical reactions during carbon sequestration. The transport in fractures and pores is controlled by diffusion. The coupling of diffusive transport and geochemical reactions leads to carbonate mineral formation in these fractures. This research studied the effect of diffusive transport on mineral carbonation in basalt and olivine powder packed bed systems and in systems with fractured basalts at conditions relevant to GCS. Carbonate minerals can form rapidly in basalt within weeks of reaction. For olivine, carbonate minerals precipitated within one day. Carbonate mineral formation is unevenly distributed along diffusion-limited zones as a result of opposing chemical gradients driven by concentration differences between inner part of the zones and the outside bulk solution. Certain regions in the fracture have maximum amount of carbonate mineral. Carbonate mineral spatial distribution is influenced by a series of factors including mineral composition, mineral grain size, basalt type, temperature and reaction time. Different carbonation products occur in different experiments. Hydromagnesite formed at early reaction times in forsteritic olivine powder packed bed experiments, and magnesite became the only carbonate mineral type after 8 days of reaction. Mg- and Ca-bearing siderite was observed in fractured flood basalt and serpentinized basalt within 6 weeks of reaction. Calcium carbonate minerals that were predominantly aragonite were found in fractured and porous Grand Ronde basalt. The formation of carbonate minerals did not block the transport pathway and end the overall reaction. Though in different extent, carbonation happened in the entire fracture within the longest experimental time in this research.
Daniel E. Giammar
John D. Fortner, Sophia E. Hayes, Young-Shin Jun, Philip Skemer,