Electrochemical Production of Magnetite Nanoparticles for Sulfide Control in Sewers

Recently, naturally occurring magnetite (Fe₃O₄) has emerged as a new material for sulfide control in sewers. However, unrefined magnetite could have high heavy metal contents (e.g., Cr, Zn, Ni, Sn, etc.) and the capacity to remove dissolved sulfide is reasonably limited due to relatively large particle sizes. To overcome the drawbacks of unrefined magnetite we used an electrochemical system with mild steel as sacrificial electrodes to in-situ generate high strength solutions of plate-like magnetite nanoparticles (MNP). MNP with a size range between 120 and 160 nm were electrochemically generated at 9.35 ± 0.28 g Fe₃O₄-Fe/L, resulting in a Coulombic efficiency (CE) for iron oxidation of 93.5 ± 2.8%. The produced MNP were found to effectively reduce sulfide levels in sewage from 12.7 ± 0.3 to 0.2 ± 0.0 mg S/L at a sulfide-to-MNP ratio of 0.26 g S/g Fe₃O₄-Fe. Subsequently, MNP were continuously generated with polarity switching at stable cell voltage for 31 days at 4.53 ± 0.35 g Fe₃O₄-Fe/L with a CE for iron oxidation of 92.4 ± 7.2%. The continuously produced MNP reduced sulfide at similar levels to around 0.2 mg S/L at a ratio of 0.28 g S/g Fe₃O₄-Fe.