Simultaneous removal of Zn2+ and Mn2+ ions from synthetic and real smelting wastewater using electrocoagulation process: Influence of pulse current parameters and anions

- Iron material as anode favored zinc and manganese removal during ARP-EC process.
- Sulfate lead to lower removal rate of Mn2+ when large quantity of Ca2+ and Mg2+ are present.
- A certain proportion of chloride to sulfate can decrease the negative effect of passivation.
- The energy consumption and the actual dry sludge mass of real smelting wastewater were calculated.

In present work, alternating rectangular pulse electrocoagulation (ARP-EC) system was constructed to simultaneously remove zinc (Zn2+) and manganese (Mn2+) ions from synthetic and real high salinity smelting wastewater using hybrid Fe-Al electrodes. Effects parameters of reversal time ratio of anode material (TFe:Al), frequency (f), duty cycle (r), current density (javg), initial pH (pHi) and anions concentration (Cl−, SO42− and their mass ratios) were examined to determine the optimal ARP-EC operation parameters. The results indicated that the anode reversal time ratios, frequency, current density, initial pH and Cl− ions concentration are conducive to the removal of two heavy metal ions. After 180 min treatment, almost all Zn2+ were removed in all experiments. However, high concentration of SO42− ions have an dramatically negative effect on Mn2+ removal due to the severe passivation of electrodes. Interestingly, moderate concentration of Cl− ions can decrease the negative effect passivation by dissolving passive film. The optimal parameters were obtained with anode reversal time ratio of 25s: 5s (Fe: Al), frequency of 5000 Hz, duty cycle of 40%, at a initial pH 7.0 and current density of 8 mA/cm2 (400 mA). Finally, real smelting wastewater was treated using ARP-EC under these optimum conditions (not alter pHi and anions concentration). The highest removal efficiency of Zn2+ and Mn2+ ions respectively reached 99.16% and 70.37% with an electrical energy consumption (EEC) of 18.3 kWh/m3 and a dry sludge mass of 3.15 kg/m3.