In this paper, the electrodialysis technique is tested as a possible treatment of smelter wastewater containing mainly copper and arsenic. The results show that it is not feasible to treat the raw wastewater, because the highly acidic pH favours the proton electro migration compared to copper. However, when adjusting the pH of the wastewater to 2 and 3, the copper could be removed entirely into a copper concentration section. Less than 2.5% of the total arsenic migrated into the copper concentration section, indicating the possibility to separate copper from arsenic. At higher pH values and current density, copper is removed faster but at pH values greater than 3 precipitates start to form. (C) 2015 Elsevier Ltd. All rights reserved.