The possible intrusion of CO2 into a given freshwater aquifer due to
leakage from deep geological storage involves a decrease in pH, which
has been directly associated with the remobilization of hazardous trace
elements via mineral dissolution and/or via desorption processes. In an
effort to evaluate the potential risks to potable water quality, the
present study is devoted to experimental investigation of the effects of
CO2 intrusion on the mobility of toxic ions in simplified equilibrated
aquifers. We demonstrate that remobilization of trace elements by CO2
intrusion is not a universal physicochemical effect. In fact goethite
and calcite, two minerals frequently found in aquifers, could
successfully prevent the remobilization of adsorbed Cu(II), Cd(II),
Se(IV), and As(V) if CO2 is intruded into a drinking water aquifer.
Furthermore, a decrease in pH resulting from CO2 intrusion could
reactivate the adsorption of Se(IV) and As(V) if goethite and calcite
are sufficiently available in underground layers. Our results also
suggest that adsorption of cadmium and copper could be promoted by
calcite dissolution. These adsorbed ions on calcite are not remobilized
when CO2 is intruded into the system, but it intensifies calcite
dissolution. On the other hand, arsenite As(III) is significantly
adsorbed on goethite, but is partially remobilized by CO2 intrusion.