Evaluation of carbon dioxide sequestration via interaction with peridotite and peridotite-hosted groundwaters: an experimental case study with Bay of Islands Ophiolite rocks, western Newfoundland, Canada

This study measured the CO2 gas flux into various aqueous media (i.e., simulated ultra-basic and basic groundwater, and deionized water) containing ultramafic rock. Basic and ultra-basic waters simulated the aqueous chemistry and ion concentrations of distinct groundwaters found within terrestrial ultramafic bodies. Experiments were performed in a closed chamber in-line with a CO2 analyzer, which measured the gaseous CO2 concentration in the chamber every second. Total inorganic carbon, as well as aqueous species Ca, Mg, and Si were monitored in the reaction fluids. All three fluid types sequestered CO2. The addition of crushed peridotite to deionized water reduced the CO2 concentration in the headspace by 70 ppm (+/- 9 ppm, 1 sigma, n = 3) and had a calculated CO2 flux of -2.5 x 104 mol/m2min (+/- 9 x 105 mol/m2min, 1 sigma, n = 3), while the greatest CO2 flux was observed in ultra-basic Ca-rich waters of -1.40 x 103 mol/m2min (+/- 3 x 105 mol/m2min, 1 sigma, n = 3), which reduced the headspace CO2 concentration by 323 ppm (+/- 4 ppm, 1 sigma, n = 3). The presence of calcite was detected using FTIR in ultra-basic waters in the presence and absence of ultramafic rock. A carbon mass balance model indicated that solid carbonates were precipitated in the ultra-basic water experiments, converting up to 59% of the CO2 removed from the chamber headspace in 4 h. Extrapolating the data collected in these experiments, it was estimated that at surface conditions, with an adequate residence time, the mass of ultramafic rock in the Bay of Islands Complex in Newfoundland could sequester up to 4 million tonnes of atmospheric CO2.