Alkalinity Generation Constraints on Basalt Carbonation for Carbon Dioxide Removal at the Gigaton-per-Year Scale

Parts-Per-Million Carbonate Mineral Quantification with Thermogravimetric Analysis-Mass Spectrometry

Mitigating the deleterious effects of climate change requires the development and implementation of carbon capture and storage technologies. To expand the monitoring, verification, and reporting (MRV) capabilities of geologic carbon mineralization projects, we developed a thermogravimetric analysis-mass spectrometry (TGA-MS) methodology to enable quantification of <100 ppm calcite (CaCO3) in complex samples. We extended TGA-MS calcite calibration curves to enable a higher measurement resolution and lower limits of quantification for evolved CO2 from a calcite-corundum mixture. We demonstrated <100 ppm carbonate mineral quantification with TGA-MS for the first time, an outcome applicable across earth, environmental, and materials science fields. We applied this carbonate quantification method to a suite of Columbia River Basalt Group (CRBG) well cuttings recovered in 2009 from Pacific Northwest National Laboratory's Wallula #1 Well. Our execution of this new combined calcite and calcite-corundum calibration curve TGA-MS method on our CRBG sample suite indicated average carbonate contents of 0.050 wt % in flow interiors (caprocks) and 0.400 wt % in interflow zones (reservoirs) in the upper 1250 m of the Wallula #1 Well. By advancing our knowledge of continental flood basalt-hosted carbonates in the mafic subsurface and reaching new TGA-MS quantification limits for carbonate minerals, we expand MRV capabilities and support the commercial-scale deployment of carbon mineralization projects in the Pacific Northwest United States and beyond.

Reactivity and Dissolution Characteristics of Naturally Altered Basalt in CO2-Rich Brine: Implications for CO2 Mineralization

Hydrothermally altered basaltic rocks are widely distributed and more accessible than fresh basaltic rocks, making them attractive feedstocks for permanent CO2 storage through mineralization. This study investigates the reactivity and dissolution behaviors of altered basalt during the reaction with CO2-rich fluids and compares it with unaltered basalt through batch hydrothermal experiments using a brine that simulates reservoir conditions with 5 MPa CO2 gas at 100 °C. When using basalt powders to evaluate reactivity, results show that although the leaching rates of elements (Mg, Al, Si, K, and Fe) from altered basalt were generally an order of magnitude lower than those from unaltered basalt in a CO2-saturated acidic environment, similar elemental leaching behavior was observed for the two basalt samples, with Ca and Mg having the highest leaching rates. However, in a more realistic environment simulated by block experiments, different leaching behaviors were observed. When the CO2-rich fluid reacts with altered basalt, rapid and preferential dissolution of smectite occurs, providing a significant amount of Mg to the solution, while Ca dissolution lags. This implies that when altered basalt is utilized for CO2 mineralization, the carbonation step may differ from that of fresh basalt, with predominant Mg carbonation followed by Ca carbonation. This rapid dissolution of Mg suggests that altered basalt is a promising feedstock for CO2 mineralization. This study provides theoretical support for developing technologies to utilize altered basalt for carbon storage.

Exotic Carbonate Mineralization Recovered from a Deep Basalt Carbon Storage Demonstration

Mitigating climate change requires transformational advances for carbon dioxide removal, including geologic carbon sequestration in reactive subsurface environments. The Wallula Basalt Carbon Storage Pilot Project demonstrated that CO₂ injected into >800 m deep Columbia River Basalt Group flow top reservoirs mineralizes on month-year timescales. Herein, we present new optical petrography, micro-computed X-ray tomography, and electron microscopy results obtained from sidewall cores collected two years after CO₂ injection. As no other anthropogenic carbonates from geologic carbon storage field studies have been recovered, this world-unique sample suite provides unparalleled insight for subsurface carbon mineralization products and paragenesis. Chemically zoned nodules with Ca/Mn-rich cores and Fe-dominant outer rims are prominent examples of the neoformed carbonate assemblages with ankerite-siderite compositions and exotic divalent cation correlations. Paragenetic insights for the timing of aragonite, silica, and fibrous zeolites are clarified based on mineral texture and spatial relationships, along with time-resolved downhole fluid sampling. Collectively, these results clarify the mineralogy, chemistry, and paragenesis of carbon mineralization, providing insight into the ultimate fate and transport of CO₂ in reactive mafic-ultramafic reservoirs.