Evaluation of a Magnetite-based Adsorption Process for the Recovery of Metals from Industrial Wastewaters

The objectives of the research were to evaluate a magnetite-based adsorption process as an alternative treatment technique for removing metals from industrial wastewaters. A composite adsorbent was prepared b precipitating sorption, magnetic separation, and desorption process to recover Cr or Zn from solution The process was effective, but performance decreased when the adsorbent was recycled. The results suggest that the relationship between the adsorbed metal and the coated magnetite changed with reuse and an increasing fraction of the Cr or Zn removed in each adsorption step became more tightly bound to the surface. ferrihydrite in a suspension of magnetite to roduce a solid wit hy a greater adsorption capacity than magnetite only. TR e adsorbent was used in a combined Introduction Traditional wastewater treatment techniques for wastewaters in the metal finishing and electroplating industries involve some form of a recipitatioa process. Metals that occur as cations in aqueous solutions, are typicafy removed through preci itation as hydroxo, sulfide, or carbonate solids. Hexavalent chromium, trivalent form for removal by precipitation. Other metals that occur as anions in aqueous solutions are often removed through a combined coagulation/adso tion/coprecipitation process with aluminum or iron salts. There are sever disadvantages to these traditional treatment rocesses. For example, additional treatment ma be required to remove comp d n g agents which may inhibit precipitation. &en precipitation does occur, the minimum solubility of the various metals in a mixed waste stream generally occurs at different pH values. As a result, maximum removal of one metal ma occur at a mcreasingly strin ent treatment and disposal r e p P ations, a successfu recipitation process may not te the optimal solution to wastewater treatmenrtyems. m e options for sludge management are becoming more limited and e associated costs are increasing. Furthermore, the long-term liabilities associated with sludge disposal represent an ill-defined, growing concern. whic R usually occurs as an anion in aqueous solutions, is nonnally reduced to the