The performance of an electrocoagulation system with aluminium electrodes for removing heavy metal ions (Zn2+, Cu2+, Ni2+, Ag+, Cr2O72-) on laboratory scale was studied systematically. Several parameters - such as initial metal concentration, numbers of metals present, charge loading and current density - and their influence on the electrocoagulation process were investigated. Initial concentrations from 50 to 5000mgL(-1) Zn, Cu, Ni and Ag did not influence the removal rates, whereas higher initial concentrations caused higher removal rates of Cr. Increasing the current density accelerated the electrocoagulation process but made it less efficient. Zn, Cu and Ni showed similar removal rates indicating a uniform electrochemical behavior. The study gave indications on the removal mechanisms of the investigated metals. Zn, Cu, Ni and Ag ions are hydrolyzed and co-precipitated as hydroxides. Cr(VI) was proposed to be reduced first to Cr(HI) at the cathode before precipitating as hydroxide. (C) 2007 Elsevier B.V. All rights reserved.