About
Dr. Daniel Giammar of Washington University in St. Louis will lecture.
ABSTRACT:
Geologic carbon sequestration (GCS) is a potential strategy for mitigating the impacts of anthropogenic CO2 emissions on climate change. Fractured basalts are one of the geologic formations being considered for GCS. These formations have iron(II)-, calcium-, and magnesium-rich silicate minerals that can result in extensive trapping of CO2 in stable carbonate minerals. The pore space available for storage and fluid transport in such formations resides primarily in fractures. A series of laboratory experiments was performed to fill knowledge gaps regarding the location, mechanisms, and extents of mineral trapping in fractured basalts. Experiments were performed with natural basalts and with olivine, which is the most reactive mineral present in basalts. The solids were loaded into bench-scale reactors as either fractured core samples or packed beds of powdered solids and then immersed in CO2-rich aqueous solutions. While only limited magnesium, iron, and silicon were released from the solids to the aqueous solutions outside of the pore space, the conditions within the fractures and packed beds were favorable for the precipitation of magnesium and calcium carbonates. Geochemical gradients caused by diffusion of inorganic carbon and magnesium led to spatial localization of carbonate mineral precipitation, and the timing and location of precipitation could be predicted with reactive transport models. Carbonate minerals were observed using electron microscopy and identified using Raman spectroscopy. In situ measurements with forsterite using 13C nuclear magnetic resonance (NMR) spectroscopy were able to track the chemical speciation of the added inorganic carbon over time. The evolution of the pore space during reaction of the basalts and mineral powders was observed using X-ray computed tomography (CT). Collectively the observations indicate that mineral trapping within fractured basalts can be rapid and extensive.