Hybrid Capacitive Deionization with Ag-coated Activated Carbon Electrodes for Nickel Treatment

Nickel (Ni) is an essential resource in many industries. However, as the industrial use of Ni increases, its impact as an environmental pollutant has also increased. Accordingly, effective Ni treatment processes are required. In this study, hybrid capacitive deionization (HCDI) with an Ag-coated activated carbon (AC) electrode was proposed as a Ni treatment. The deionization capacity of the HCDI system with Ag coating was 66% higher than that of the membrane capacitive deionization system. In addition, as the applied potential increased from 0.5 V to 1.1 V, the deionization capacity also increased from 10 mg/g to 18 mg/g, although the charge efficiency decreased from 84.6% to 77.2%. However, when the applied potential was 0.9 V or more, the pH of the effluent exceeded the drinking water range, which appeared to be caused by the electron transfer reaction of Ni ions under a high applied potential (0.9 V or more). In terms of energy consumption, HCDI with Ag-coated electrodes achieved 0.24 Wh/g-NiCl2 as a minimum value. The results of this study demonstrate the potential of capacitive deionization (CDI) for Ni treatment.