Magnetic magnetite (Fe3O4) nanoparticles synthesized by chemical co-precipitation were characterized using XRD, TEM, SEM-EDX, FT-IR, ED-XRF, PPMS, point of zero charge (pH(pzc)) and surface area measurements. As-prepared Fe3O4 nanoparticles were successful for aqueous Cr6+ and Pb2+ removal. Batch adsorption experiments systematically investigated the influence of pH, temperature, contact time and adsorbate/adsorbent concentration on Cr6+ and Pb2+ adsorption. Maximum Cr6+ and Pb2+ removal occurred at pH 2.0 and 5.0, respectively. Sorption data fit pseudo-second order kinetics, indicating a chemical adsorption. The Freundlich, Langmuir, Redlich-Peterson, Toth, Radke and Sips adsorption isotherm models were applied to describe equilibrium data. The Sips and Langmuir models best described Cr6+ and Pb2+ adsorption on magnetite nanoparticles, respectively. The maximum Langmuir adsorption capacities were 34.87 (Cr6+ and 53.11 (Pb2+) mg/g at 45 degrees C, respectively. Fe3O4 nanoparticles are promising potential adsorbents and exhibited remarkable reusability for metal ions removal in water and wastewater treatment. (C) 2015 Elsevier Inc. All rights reserved.