The arsenic content in wastewater is of major concern in copper mineral processing. Typically, a complex wastewater treatment is needed with a combination of chemical and physical processes. Electrocoagulation (EC) has shown its potential for arsenic removal due to the formation of ferric hydroxide-arsenate precipitates but the acidic conditions in the wastewater disfavours the hydroxide formation. This work evaluates the feasibility of EC combined with addition of zero valent iron nanoparticles in the treatment process. The results showed that copper smelter wastewater could be treated efficiently with EC and presence of nanoparticles. The treatment with EC or nanoparticles alone was less efficient. Increasing the concentration of nanoparticles during EC did not increase the efficiency accordingly. The arsenic removal was favoured by an increase of the current density during EC but only until a limiting current density; thereafter the anodes got partly passivated. (C) 2011 Elsevier B.V. All rights reserved.