Use of ultrafiltration membranes and aluminosilicate minerals for nickel removal from industrial wastewater

This work investigated the removal of nickel ions from aqueous solutions and activated sludge by employing ultrafiltration (UF) membranes together with natural aluminosilicate minerals (bentonite, zeolite and vermiculite). The performance of the system was examined with respect to different parameters including the membrane nominal pore size, the temperature and pH of aqueous solution and sludge, the mineral type and concentration, the sludge MLSS concentration, the Ni(II) initial concentration and the metal-mineral contact time. The experiments were conducted in a batch ultrafiltration unit with constant initial Ni(II) concentration of 320 mg/l. The addition of 15 g/l of bentonite and 15 g/l of vermiculite at pH 6 resulted in Ni(II) removal efficiencies of 65.3% and 80.0% respectively due to sorption induced by minerals and sludge. The addition of 10 g/l vermiculite at pH 8 resulted in the production of a final effluent with Ni(II) concentration that met the EPA short-term effluent reuse limit of 2.0 mg/l. The processes involved in the removal of nickel consisted of biosorption onto sludge flocs, adsorption onto the mineral, retention of insoluble metal ions by the UF membranes and chemical precipitation. High temperatures, sludge MLSS concentrations and pH values favoured the nickel removal process. Film diffusion was important at the early stages of the process, while intraparticle diffusion was dominant at the later stages. The equilibrium isotherms for the minerals followed the Langmuir model, while sludge followed the Freundlich model. (C) 2010 Elsevier B.V. All rights reserved.