Sorption and filtration of metals using iron-oxide-coated sand

Iron oxides are good adsorbents for uncomplexed metals, some metal-ligand complexes, and many metal oxyanions. However, the adsorbent properties of these oxides are not fully exploited in wastewater treatment operations because of difficulties associated with their separation from the aqueous phase. This paper describes experiments in which iron oxides were coated onto the surface of ordinary filter sand, and this composite media was used in a fixed bed configuration for simultaneous filtration of particulate matter and sorption of dissolved metals. The process was successful in removing uncomplexed and ammonia-complexed cationic metals (Cu, Cd, Pb, Ni, Zn), as well as some oxyanionic metals (SeO3, AsO3), from simulated and actual waste streams over a wide range of metal concentrations. The adsorbent was stable during backwashing and regeneration operations, releasing most metals quantitatively; the exception was AsO3, which was not efficiently recovered by regeneration with either acid or base. The composite media is inexpensive to prepare and could serve as the basis of a useful metal removal and possibly metal recovery process in a variety of settings.