Highly efficient removal of Cu-organic chelate complexes by flow-electrode capacitive deionization-self enhanced oxidation (FCDI-SEO): Dissociation, migration and degradation

Abstract

It is generally difficult to remove copper (Cu) from industrial wastewaters through traditional processes because Cu can form stable complexes with organic chelating agent. Here, the flow-electrode capacitive deionization-self enhanced oxidation (FCDI-SEO) system was applied to achieve highly efficient removal of two typical Cu-organic complexes (ethylenediaminetetraacetic acid-Cu (EDTA-Cu) and citric acid-Cu (CA-Cu)), and the underlying mechanism was also investigated. At the initial concentration of 1 mmol L−1, Cu removal efficiency reached 99.3% and approximately 100.0% respectively in FCDI-SEO treated EDTA-Cu and CA-Cu containing wastewaters after 75 min. Stable EDTA-Cu mainly migrated into the anode chamber as chelated Cu, while CA-Cu was easily dissociated and migrated into the cathode chamber as free Cu2+. After entering the anode chamber, the degradation rate of EDTA and CA was respectively 66.1% and 60.2%. Compared with the isolated closed-cycle mode, the short-circuited closed-cycle mode showed insignificant difference in Cu removal efficiency but higher energy efficiency. With pH increasing from 3.5 to 5.5, Cu removal efficiency showed little difference between the EDTA-Cu and CA-Cu system. With the addition of 180 mg L−1 extra Na+, Cu removal efficiency was about 80% and 90% in the EDTA-Cu and CA-Cu system, respectively. After operation for five cycles and regeneration of electrode, FCDI-SEO could still achieve stable removal efficiency. This work provides a new pathway for the removal of aqueous Cu-organic complexes.