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

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.

Automated summary

In this study, a FCDI-SEO system was used to efficiently remove EDTA-Cu and CA-Cu complexes from wastewaters. The results showed that stable EDTA-Cu migrated as chelated Cu to the anode chamber, while CA-Cu dissociated and migrated as free Cu2+ to the cathode chamber. The short-circuited closed-cycle mode exhibited similar Cu removal efficiency but higher energy efficiency compared to the isolated closed-cycle mode.