MOBILIZATION OF ELEMENTS BY CO2-MINERAL INTERACTIONS

CO₂ injected into saline aquifers is trapped as a supercritical phase below sealing cap-rocks or sealing faults, as a residual phase in small pores, dissolved in the aquifer solution, and as secondary carbonate minerals. Increased reservoir pressures may however pollute nearby aquifers if the CO₂ leaks into the groundwater reservoir or if the saline aquifer water is mobilized and mixed with potable groundwater.

The intrusion of CO₂ into the groundwater leads to an acidification which induces a range of reactions associated with mineral dissolution and growth, and sorption and cation exchange. Dissolution of primary aquifer minerals release cations, and dependent on the physical conditions various secondary phases may form. Generally, the acidification might lead to the release and mobilization of heavy metals.

In this study we have evaluated the various processes that may mobilize elements by running 1D column simulations with varying mineral contents, sorption, cation exchange capacities, organic content, and initial aquifer formation water composition. The carbonate system with its capability to immobilize elements has also been given special attention.