Environmental Controls of Cadmium Desorption during CO2 Leakage

Geologic carbon sequestration represents a promising option for carbon mitigation. Injected CO2, however, can potentially leak into water systems, increase water acidity, and mobilize metals. This study used column experiments to quantify the effects of environmental controls on cadmium desorption during CO2 leakage in subsurface systems without ambient flow. Results show that fast leakage rates are responsible for earlier and larger amounts of Cd desorption. Long weathering time of Cd laden clay leads to low Cd desorption. Calcite content as low as 10% can mitigate the effect of pH reduction and result in zero Cd desorption. Increasing the salinity of the leaking fluid has a relatively minor effect, primarily due to the offsetting impacts of an increased extent of ion exchange and the decrease in CO2 solubility (and therefore acidity). This work systematically quantifies, for the first time, the effects of environmental controls on Cd desorption and points to key parameters for risk assessment associated with metal mobilization during CO2 leakage.