Zinc removal from model wastewater by electrocoagulation: Processing, kinetics and mechanism

In this work, the research focused on the Zn2+ removal from the synthetic wastewater by electrocoagulation (EC) with aluminum electrodes. The effects of current density (2.1-12.5 mA/cm2), initial concentration (50-2000 mg/L), solution pH (2.9-7.4) and conductivity (0.15-14.11 mS/cm) on the removal efficiency and energy consumption were systematically investigated. It indicated that Zn2+ removal efficiency increased with the increasing of current density and residence time. With a relatively low energy consumption of 0.35 kWh/m3, all of Zn2+ (50 mg/L) was removed in 20 min EC treatment, 8.3 mA/cm2 for current density, and 5.3 for pH. With an energy consumption of 0.88 kWh/m3, all of Zn2+ (250 mg/L) were removed in 50 min. In addition, kinetic study was applied to analyze Zn2+ removal rate at different current densities and initial concentrations. Different mechanisms of Zn2+ removal were implied by comparing the results of low initial concentration (≤250 mg/L) and high one (≥500 mg/L). It was reasonable to conclude that, besides the precipitation effect of aluminum hydroxide flocculation, electrochemical reduction of Zn2+ at the cathode also contributed to Zn2+ removal, especially at a high initial concentration.