Comparative performance of aerobic and anaerobic environments on simultaneous removal of Cd2+ and Mn2+ by Fe–electrocoagulation

In the this work, the performance of Fe–electrocoagulation in anaerobic (ANA) and aerobic (AER) environments for simultaneous removal of Cd2+ and Mn2+ from synthetic wastewater were investigated. Detailed experiments were carried out to evaluate the effects of oxidants and reductants, initial pH (pHi), current density (j), nature of the anions, and initial concentration ([anions]0) on electrocoagulation performance. The results showed that ANA process was superior to AER process due to the formation of high proportion of Fe(II)/Fe(III) hydroxide species (green rust). These results were supported by X-ray photoelectron spectroscopy analysis. A high current density favored the heavy metal removal, especially in the ANA process and an RCd of 95.21% and an RMn of 93.83% were obtained at a current density of 100 A/m2. A significant difference was also observed between chloride and sulfate for the heavy metal removal; chloride was more suitable for Mn2+ removal than sulfate but the opposite was true for Cd2+ when the initial anion concentration was 50 mmol/L. However, excess concentrations of chloride and sulfate had an adverse influence on the Cd2+ and Mn2+ removal in the AER and ANA processes, although the increase in Cl– (from 10 to 50 mmol/L) and SO42– (from 10 to 30 mmol/L) contributed to the removal of Cd2+. Finally, kinetic isotherm and thermodynamic studies were conducted to illustrate the removal mechanisms.