Removal of chelated Cu(II) from aqueous solution by adsorption–coprecipitation with iron hydroxides prepared from microelectrolysis process

Iron hydroxides prepared from microelectrolysis process were applied to remove EDTA-chelated copper from aqueous solution through adsorption–coprecipitation. To eliminate the occurrence of adverse reactions, Fe(II)-rich effluent of microelectrolysis was pretreated by continuously flushing N2 for 15 min to eliminate dissolved oxygen, then iron hydroxides were generated in less than 30 s. The experimental results showed that Fe(II) yields could achieve 530.00–748.00 mg/L after 60-min operation of microelectrolysis process at the initial pH of 2.0–2.3. The uptake rate of Cu(II) by iron(II) hydroxides was so rapid under nitrogen-aerated condition that 100% of Cu(II) was removed within only 5 min at an initial Fe(II) concentration of 374.0 mg/L. However, Cu(II) would desorb from iron hydroxides when iron(II) hydroxides were gradually oxidized into iron(III) hydroxides by oxygen, indicating that iron(II) hydroxide had much higher adsorptive capacity for chelated Cu(II) than iron(III) hydroxide. In addition, iron(II)/(III) hydroxides prepared from microelectrolysis process exhibited a higher removal efficiency of Cu(II) than iron hydroxides prepared from FeSO4·7H2O, especially under air-aerated condition. This research provided a novel method for efficient removal of both Cu(II) and EDTA from Cu(II)-chelated wastewater.

Research highlights
► Iron hydroxides are prepared from Fe(II)-rich effluent of microelectrolysis.
► Chelated Cu(II) can be efficiently removed by iron(II) hydroxides.
► Fe(II) concentration, aeration and Fe(II) source affect Cu(II) removal.
► Fe(OH)2 has much higher adsorptive capacity for chelated Cu(II) than Fe(OH)3.
► Fe(II)-rich effluent of microelectrolysis shows superior properties.