Electrochemical treatment of heavy metals (Cu2+, Cr6+, Ni2+) from industrial effluent and modeling of copper reduction

An electrochemical technique was tested in a laboratory scale to treat heavy metals (Cu2+, Cr6+ and Ni2+) from plating industrial effluent. The experiments were performed in a membrane reactor having a capacity of 1 l. Stainless-steel sheets with surface area of 0.011 m2 and titanium coated with ruthenium oxide were used as cathode and anode, respectively. The electrolyte was circulated at a constant flow rate (0.42 l/min) and the pH was kept constant at 1. Applied current densities were 10 and 90 A/m2. According to the experiment, it was found that a membrane reactor with plane electrode was capable for treating plating wastewater with low energy consumption (42.30 kWh/kg metal) and low operating cost (5.43 US$/m3). More than 99% of metal reduction was achieved and the final concentrations of copper, chromium and nickel in treated water were 0.10–0.13, 0.19–0.20 and 0.05–0.13 ppm, respectively. The brightener had no effect on copper reduction whereas hexavalent chromium had strong effect. The kinetic of copper reduction in the presence of hexavalent chromium was modeled as a two-step process with respect to copper concentration.