The use of manganese oxide-coated sand for the removal of trace metal ions from stormwater†
The large-scale, systematic introduction of urban stormwater into the subsurface could contaminate groundwater with metals including cadmium, copper, lead and zinc. To assess the potential for using manganese oxide-coated sand to remove metal ions during stormwater infiltration, batch and column tests were used to simulate conditions encountered in treatment systems. The geomedia exhibited a relatively high affinity for Zn, Cd and Pb at environmentally relevant conditions in batch tests. In column tests conducted in the absence of natural organic matter (NOM), dissolved Cu and Pb were removed for over 2000 pore volumes, whereas Zn and Cd were removed for several hundred pore volumes. In the presence of NOM, Cu and Pb removal diminished, but the adsorption of Zn and Cd decreased only slightly. Treating manganese oxide-coated sands with pH 3 hydrochloric acid after column tests recovered over 90% of the adsorbed Cd, Cu and Zn. It also restored the adsorptive capacity of the geomedia with minimal loss of the surface coating. Neither acids nor organic ligands removed significant amounts of adsorbed Pb from the geomedia. The results of this study imply that manganese oxide-coated sand can remove metal ions from stormwater, and that saturated geomedia can be regenerated with a mild acid solution.