Optimization and assessment of Fe-electrocoagulation for the removal of potentially toxic metals from real smelting wastewater

This study evaluates the performance of a continuous electrocoagulation system (batch recirculation mode) on the simultaneous removal of Zn²⁺, Cd²⁺, and Mn²⁺ from real smelting wastewater by using Fe-Fe electrodes. Several parameters are evaluated to determine the optimal operating conditions. These conditions include the type of power supply (p), current density (j), aeration intensity (v), flow rate (u), and anions (SO₄^2- and SO₃^2-). At current density = 10-20 mA/cm², the DC power supply performs better than the APC power supply in treating wastewater. Current density positively affects the removal of heavy metals by increasing the production of Fe hydroxides. However, a lower aeration intensity of 0.5-1 L/min and a flow rate of 1 L/min are considerable because of flotation and turbulence, respectively. Moreover, adding SO₄^2- and SO₃^2- contributes to the precipitation of metal hydroxides. Lastly, the optimal parameters for the DC power supply used to treat smelting wastewater are as follows: pH_i, 6.9; current density, 15 mA/cm²; aeration intensity, 0.5 L/min; flow rate, 1 L/min; SO₄^2-, 25 mmol/L; and time, 120 min. The highest removal efficiency for each of Zn²⁺, Cd²⁺, and Mn²⁺ reached 99.93%, 97.15%, and 85.46%, with electrical energy consumption = 14.76 kWh/m³ (42 kWh/kg), electrode consumption = 2.09 kg/m³ (5.88 kg/kg), and operational cost = 2.2 US$/m³ (6.21 US$/kg), respectively.