In situ redeposition of trace metals mobilized by CO2‐charged brines

Abstract

Mobilization of contaminants by CO2‐charged brines is one concern relating to injection of CO2 as part of carbon capture and storage projects. This study monitors the mobility of trace metals in an exhumed CO2‐charged aquifer near the town of Green River, Utah (USA), where CO2‐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 CO2‐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 CO2‐promoted bleaching reaction front. We argue that while CO2‐charged brines are capable of mobilizing trace metals, local metal redeposition implies that the potential for contamination of overlying freshwater aquifers is low.