Elucidating the differences in the carbon mineralization behaviors of calcium and magnesium bearing alumino-silicates and magnesium silicates for CO2 storage

Engineering the permanent storage of CO2 in earth-abundant Ca- and Mg-bearing silicate and alumino-silicate rocks and minerals as carbonates requires a fundamental understanding of the extents of carbonate conversion that can be achieved at conditions relevant to geologic formations. While many studies have reported the reaction rates and the carbonation extents of specific minerals, the data is limited in terms of reaction conditions and the mineral samples were relatively pure to start with. Thus, understanding of the effect of the chemical and mineralogical heterogeneity on the carbon mineralization behaviors of various minerals and rocks in geologic conditions is lacking. Therefore, this study investigated the reactivities of a selection of minerals and rocks such as (a) Mg-rich olivine (Mg1.74Fe0.26SiO4) as previously reported by Gadikota and co-workers (2014), [1] labradorite (plagioclase feldspar with Ca0.53Na0.47Al1.53Si O-8), (b) anorthosite (a mixture of plagioclase (Ca0.98Na0.02Al1.98Si2.02O8), olivine (Mg1.32Fe0.68SiO4) and magnetite (Fe3O4)), and (c) basalt (a fine-grained volcanic rock containing a mixture of plagioclase (Ca0.6Na0.4Al1.6Si2.4O8), calcic pyroxene (similar to Mg0.48Fe0.52CaSi2O6) and low Ca pyroxene (similar to Mg0.48Fe0.52SiO3)), that are relevant to CO2 storage. The reaction conditions were also selected to mimic the conditions relevant to geologic CO2 storage sites (T-max = 185 degrees C, P-max = 164 bar, 0-1 M NaHCO3, 0-1 M NaCl, 1.0 M NaCl + 0.64 M NaHCO3). Our studies show that the extents of carbonation of olivine, labradorite, anorthosite, and basalt are 85, 35, 19 and 9%, respectively, when reacted for three hours at 185 degrees C, P-CO2 of 139 atm in 1.0 M NaCl + 0.64 M NaHCO3 with 15 wt% solid reactant and a stirring rate of 800 rpm. Further, our results indicate that increasing the reaction temperature over the range of 90 to 185 degrees C, and increasing the concentration of NaHCO3 over the range of 0 to 1 M, both enhance the extent of carbon mineralization. On the other hand, increasing the partial pressure of CO2 from 64 atm to 169 atm and raising the concentration of NaCl to 1.0 M have no significant effects within the time-scale of these experimental studies. Comparison of our results with previous studies suggests that the reactivity of Ca- and Mg-bearing alumino-silicates is lower compared to Ca- and Mg-bearing silicates.