Modeling geochemical and reactivity changes of different iron materials

Including declining reactivity of iron, resulting from precipitation of secondary minerals, into reactive transport models is a key component for better estimation of longevity of iron permeable reactive barriers (PRBs). In this study, the accumulation of secondary minerals and reactivity loss were coupled using an empirically-derived relationship that was incorporated into an existing multi-component reactive transport code. The simulation results were compared to the observations from column experiments, which were designed to evaluate the changes of the reactivity of different iron materials for cis-dichloroethene (cis-DCE) treatment in the presence of dissolved CaCO₃. The model provided a reasonable representation of the evolution of iron reactivity toward cis-DCE treatment and the changes in geochemical conditions for each material. The modeling results suggest that iron material having a high corrosion rate is not beneficial in the presence of a high concentration of dissolved CaCO ₃ because of a faster migration of cis-DCE profiles and greater porosity loss closer to the influent end. This study shows that declining reactivity of iron due to mineral precipitation should be considered at the design stage of iron PRB construction. Copyright ASCE 2008.