Activated carbon fiber for adsorption/electrodeposition of Cu (II) and the recovery of Cu (0) by controlling the applied voltage during membrane capacitive deionization

Membrane capacitive deionization (MCDI) as a promising approach was developed to simultaneously conduct water desalination and metal recovery by using activated carbon fiber (ACF) as electrodes. The removal performance of two metal ions (Cu2+, Zn2+) was firstly investigated at different voltages. Experiments showed that the adsorption amount of Cu2+ was higher than that of Zn2+ under the voltage of 0.4-0.6 V. However, inverse result was obtained at the voltage of 0.8-1.2 V that the adsorption amount of Cu2+ was lower than that of Zn2+. The analysis of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) showed that Cu2+ removal involved the adsorption and electrodeposition, and the reduction potential of Cu2+ was found to be 0.6 V. At a higher voltage, Cu2+ was reduced and the reduction product consisting of Cu/Cu2O would decrease the effective surface area and cause serious degradation of electrode properties, which inhibited Cu2+ adsorption. Comparatively, Zn2+ reduction was only observed at the voltage of 1.2 V. FTIR showed that the difference of the reduction potential was partly attributed to the type of functional groups of ACF and its affinity towards ions. Considering the gap of the reduction potential, the feasibility of selective reduction and recovery of Cu(0) from CuCl2/ZnCl2 mixed solution was studied by controlling the applied voltage and the optimal voltage was determined to be 0.8 V. The recovery efficiency of Cu(0) in the competitive environment could reach to 42.8% at the voltage of 0.8 V. Moreover, the electrode regeneration was investigated and it was found that the performance of fouled electrode could be effectively recovered for further reuse via cleaning methods. (C) 2019 Elsevier Inc. All rights reserved.