Removal of low concentrations of nickel ions in electroplating wastewater using capacitive deionization technology

The capacitive deionization (CDI) technology was adopted to reduce the low concentrations of nickel in electroplating wastewater to meet the discharge standard. The composite anode and the composite cathode (Resin-CGA) were prepared by incorporating anion-exchange resin (AR-CGA) and cation exchange resin (CR-CGA) into the titanium mesh by the conductive graphite adhesive, respectively. The electrolytic performances of the Resin-CGA electrodes at different cell voltages, initial electrolyte pH and initial nickel concentrations were investigated. The adsorbed amount of nickel on the CR-CGA electrodes and the removal percentage of nickel were 0.095 mg g^-1 and 95%, respectively. The Ni²⁺ concentrations were reduced to 0.005 mg L^-1 and the electricity consumption was 1.6 kWh per ton of the electroplating wastewater at the initial Ni²⁺ concentrations of 1.0 mg L^-1 under the optimal conditions, exhibiting better electrolytic performance than the cation-exchange resin and the electrodes prepared by the conductivity graphite adhesive (CGA). In addition, the spent electrodes were electrochemically regenerated and the electrolytic performance of the Resin-CGA electrodes kept stable during the cycles. This study provided a promising method to reduce the low concentrations of Ni²⁺ to less than 0.1 mg L^-1 in the treatment of electroplating wastewater.