Copper cation transport and scaling of ionic exchange membranes using electrodialysis under electroconvection conditions

Here we report on the removal efficiency of copper cations from model Cu²⁺ ion wastewater by electrodialysis (ED) under electroconvection conditions. Experiments were conducted on commercial ionic exchange membranes (IEMs). Results are presented on the copper cation transport properties through a cation exchange membrane (CEM) showing that Cu²⁺ ions can penetrate a copper-saturated CEM and still maintain a stable cation removal efficiency rate. We use field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) to analyze the scale formed on the IEMs after ED treatment. XRD results show that the scaling on the IEMs is Cu(OH)₂ and/or CuO potentially formed from the reaction of Cu²⁺ ions with hydrolysis products. In particular, results show that the anion exchange membranes (AEMs) are the most prone to scaling which results in a decrease in the overall ion removal efficiency of the ED system. Under electroconvection conditions, hydrolysis of water causes the formation of H⁺ and OH^- ions which penetrate the IEMs leading to a lowering of the pH in both the treated and concentrated model Cu²⁺ ion wastewater. Finally we show that a stronger field is necessary to drive ion transport through the CEM due to scaling and that transport is heterogeneous in comparison to that of a CEM with no scaling.