Trace element mobility during the injection of water-dissolved CO₂ into basalts

In-situ carbon mineralization in basalts has been identified as a permanent and scalable method to sequester CO₂ in the subsurface. The extent of potentially toxic trace element mobilization during basalt dissolution, however, remains poorly constrained. The Jizan carbon sequestration pilot was undertaken to assess the potential for carbon disposal through the mineralization of water-dissolved CO₂ injected into subsurface basalts in arid regions. The temporal evolution of trace element and potentially toxic metal concentrations in the Jizan groundwater during and following the injection of CO₂-charged water and its recirculation has been assessed. Twenty-eight representative production well fluid samples were selected and analyzed by ICP-MS. Element mobility was quantified by comparing the increase in concentration of the selected elements in the aqueous phase to the corresponding increase in sodium concentration. Results indicate that the mobility of trace elements in the Jizan system is limited, with the average mobility of most trace elements remaining below 20% of that of sodium. Furthermore, the maximum measured concentrations of most trace elements are significantly below the acceptable levels in drinking water before, during, and after the CO₂ injection. These observations suggest the risk of groundwater pollution during in-situ carbon mineralization efforts in basalt is likely minimal.