In situ redeposition of trace metals mobilized by CO sub(2)-charged brines

Mobilization of contaminants by CO sub(2)-charged brines is one concern relating to injection of CO sub(2) as part of carbon capture and storage projects. This study monitors the mobility of trace metals in an exhumed CO sub(2)-charged aquifer near the town of Green River, Utah (USA), where CO sub(2)-charged brines have bleached red sandstones, and concentrated trace metals at the bleaching reaction front. Mass balance calculations on the trace metal enrichments are used to calculate time-integrated fluid fluxes and show that a significant fraction of the metals mobilized by the CO sub(2)-rich brines are redeposited locally. A sequential extraction procedure on metal-enriched samples shows that these metals are incorporated into secondary carbonate and oxide phases which have been shown to grow at the CO sub(2)-promoted bleaching reaction front. We argue that while CO sub(2)-charged brines are capable of mobilizing trace metals, local metal redeposition implies that the potential for contamination of overlying freshwater aquifers is low. Key Points * Trace metals mobilized by CO2 are enriched at CO2-promoted reaction fronts * Within error, all of the mobilized metals are re-deposited in secondary phases * Calculated metal concentrations in the fluid remain below guideline values