Membrane capacitive deionization (MCDI) for removal of chromium complexes with AC@SiO2-NH2 electrode

Considering the stability and hazard of chromium complexes, their removal and recovery from industrial wastewater is a worthy goal. Membrane capacitive deionization (MCDI) can effectively reduce co-ion adsorption compared with CDI technology and has been demonstrated to be a promising deionization technology. In this study, functionalized activated carbon (AC@SiO 2 -NH 2 ) was applied as a MCDI eletrode. The AC@SiO 2 -NH 2 adsorbs chromium complexes (Cr(Ⅲ)-EDTA) through electrostatic gravitation of protonated amino groups (-NH 3 + ). With applied voltage of 1.2 V, solution flow rate of 20 mL min −1 and initial concentration of 300 mg L −1 , the electrosorption capacity of the AC@SiO 2 -NH 2 electrode for Cr(Ⅲ)-EDTA was 17.70 mg g −1 . The Ragone curves verified that the electrosorption rate (SER) of the AC@SiO 2 -NH 2 electrode was positively correlated with voltage and initial concentration. Moreover, the effects of competing ions (K + , Na + , and Mg 2+ ) in a series of single electrolyte solution by the AC@SiO 2 -NH 2 electrode were investigated. It was also verified that the optimum pH was 3 for electrostatic attraction. The energy consumption of the MCDI process is calculated as 0.251 kWh m 3 and 0.039 kWh g −1 Cr at 1.2 V. We envisage that the use of AC@SiO 2 -NH 2 electrodes will pave the way for efficient operation of MCDI as well as the preferential recovery of Cr(Ⅲ)-EDTA.