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.