High-gravity intensified electrodeposition for efficient removal of Cd2+ from heavy metal wastewater

Abstract

Efficiently treating heavy metal wastewater are the goal that industries pursuit. A novel Multi-concentric Cylindrical Electrodes-Rotating Bed (MCCE-RB) which could provide high-gravity fields was proposed to enhance electrodeposition for efficient treatment of Cd-containing wastewater in this paper. Under the optimal operating conditions covering current density of 53.1 A m−2, wastewater circulation flowrate of 64 L h−1, high-gravity factor of 15, NaCl concentration of 0.2 mol L−1, initial pH value of 2, and initial Cd2+ concentration of 800 mg L−1, the removal efficiency of Cd2+ reached 99.4% after 120 min electrodeposition. Compared with the results of electrodeposition in normal gravity field, the removal efficiency of Cd2+, current efficiency and the mass of deposits were increased by 18.4%, 15.7% and 35.4%, respectively. The cell voltage, electrodeposition time and total energy consumption (ETotal) were decreased by 21.7%, 42% and 21.2%, respectively. SEM, EDS, XRD and XPS analyses showed that the deposits were flaky and layered structure in high-gravity fields, avoiding the formation of dendrite in normal gravity field. The deposits were comprised of the mixture of Cd and Cd(OH)2, and the percent weight of elemental Cd was 91.29% in the high-gravity field which was 19.17% higher than that in normal gravity field. The purity of Cd was improved in the high-gravity field. These was ascribed to the depressed hydrogen evolution reaction, the removal of gas bubbles from the electrodes and the improvement in mass transport in the optimal high-gravity field. High-gravity intensified electrodeposition could serve as a clean, high efficient and low energy consumption method for treating heavy metal wastewater.