Effect of the heterotrophic bacterium Pseudomonas reactans on olivine dissolution kinetics and implications for CO2 storage in basalts

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This work is aimed at quantification of forsteritic olivine (Fo92) dissolution kinetics in batch and mixed-flow reactors in the presence of aerobic gram-negative bacteria (Pseudomonas reactans HK 31.3) isolated from an instrumented well located within a basaltic aquifer in Iceland. The release rate of mineral constituents was measured as a function of time in the presence of live and dead cells in constant-pH (4–9), bicarbonate-buffered (0.001–0.05M), nutrient-rich and nutrient-free media in batch reactors at 0–30atm of CO2 partial pressure (pCO2). In batch reactors at 30atm pCO2, 0.1M NaCl and 0.05M NaHCO3 the rates were weakly affected by the presence of bacteria. In nutrient media, the SEM observation of reacted grains revealed the presence of biofilm-like surface coverage that does not modify Mg and Si release rate at the earlier stages of reaction but significantly decreased the dissolution after prolonged exposure.Olivine dissolution rates measured in flow-through reactors are not affected by the presence of dead and live bacteria at pH ⩾9 in 0.01M NaHCO3 solutions. In circumneutral, CO2-free solutions at pH close to 6, both live and dead bacteria increase the dissolution rate, probably due to surface complexation of exudates and lysis products. In most studied conditions, the dissolution was stoichiometric with respect to Mg and Si release and no formation of secondary phases was evidenced by microscopic examination of post-reacted grains. Obtained results are consistent with known molecular mechanism of olivine dissolution and its surface chemistry. Overall, this work demonstrates negligible effect of P. reactans on olivine reactivity under conditions of CO2 storage in the wide range of aqueous fluid composition.