Carbonate Mineralization of Volcanic Province Basalts
Flood basalts are receiving increasing attention as possible host formations for geologic sequestration of anthropogenic CO2, with studies underway in the United States, India, Iceland, and Canada. As an extension of our previous experiments with Columbia River basalt, basalts from the eastern United States, India, and South Africa were reacted with aqueous dissolved CO2 and aqueous dissolved CO2-H2S mixtures under supercritical CO2 (scCO2) conditions to study the geochemical reactions resulting from injection of CO2 in such formations. The results of these studies are consistent with cation release behavior measured in our previous experiments (in press) for basalt samples tested in single pass flow through dissolution experiments under dilute solution and mildly acidic conditions. Despite the basalt samples having similar bulk chemistry, mineralogy and apparent dissolution kinetics, long-term static experiments show significant differences in rates of mineralization as well as compositions and morphologies of precipitates that form when the basalts are reacted with CO2-saturated water. For example, basalt from the Newark Basin in the United States was by far the most reactive of any basalt tested to date. Carbonate reaction products for the Newark Basin basalt were globular in form and contained significantly more Fe than the secondary carbonates that precipitated on the other basalt samples. In comparison, the post-reacted samples associated with the Columbia River basalts from the United States contained calcite grains with classic dogtooth spar morphology and trace cation substitution (Mg and Mn). Carbonation of the other basalts produced precipitates with compositions that varied chemically throughout the entire testing period. Examination of polished cross sections of the reacted grains by scanning electron microscopy and energy dispersive x-ray spectroscopy show precipitate overgrowths with varying chemical compositions. Compositional differences in the precipitates suggest changes in fluid chemistry unique to the dissolution behavior of each basalt sample reacted with CO2-saturated water. The Karoo basalt from South Africa appeared the least reactive, with very limited mineralization occurring during the testing with CO2-saturated water. The relative reactivity of different basalt samples were unexpectedly different in the experiments conducted using aqueous dissolved CO2-H2S mixtures versus those reacted with aqueous dissolved CO2 mixtures. For example, the Karoo basalt was highly reactive in the presence of aqueous dissolved CO2-H2S, as evident by small nodules of carbonate coating the basalt grains after 181 days of testing. However the most reactive basalt in CO2-H2O, Newark Basin, formed limited amounts of carbonate precipitates in the presence of aqueous dissolved CO2-H2S mixture. Basalt reactivity in CO2-H2O mixtures appears to be controlled by the composition of the glassy mesostasis, which is the most reactive component in the basalt rock. With the addition of H2S to the CO2-H2O system, basalt reactivity appears to be controlled by precipitation of coatings of insoluble Fe sulfides.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 979485
- Report Number(s):
- PNNL-SA-65778; AA3010000; TRN: US201010%%711
- Journal Information:
- International Journal of Greenhouse Gas Control, 4(2 ):249-261, Vol. 4, Issue 2
- Country of Publication:
- United States
- Language:
- English
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