SORPTION AND FILTRATION OF METALS USING IRON-OXIDE-COATED SAND

Iron oxides are good adsorbents for uncomplexed metals, some metal-lig and complexes, and many metal oxyanions. However, the adsorbent proper ties of these oxides are not fully exploited in wastewater treatment o perations because of difficulties associated with their separation fro m the aqueous phase. This paper describes experiments in which iron ox ides were coated onto the surface of ordinary filter sand, and this co mposite media was used in a fixed bed configuration for simultaneous f iltration of particulate matter and sorption of dissolved metals. The process was successful in removing uncomplexed and ammonia-complexed c ationic metals (Cu, Cd, Pb, Ni, Zn), as well as some oxyanionic metals (SeO3, AsO3), from simulated and actual waste streams over a wide ran ge of metal concentrations. The adsorbent was stable during backwashin g and regeneration operations, releasing most metals quantitatively; t he exception was AsO3, which was not efficiently recovered by regenera tion with either acid or base. The composite media is inexpensive to p repare and could serve as the basis of a useful metal removal and poss ibly metal recovery process in a variety of settings. Copyright (C) 19 96 Elsevier Science Ltd