Towards in situ electro-generation of ferrate for drinking water treatment: A comparison of three low-cost sacrificial iron electrodes

This work studied the mechanisms governing the electrode processes along with the structure and impact of the passivation layer on the electro-generation of ferrate using three low-cost sacrificial iron materials: mild steel (MS), grey cast iron (GCI) and white cast iron (WCI) electrodes in highly alkaline media. Cyclic voltammetry studies showed that the mechanisms controlling the electrode reactions depend on its alloy composition as it influences the iron species formed in the passivation layer. The presence of silicon in the GCI electrode reduced the stability of the latter, significantly enhancing the ferrate electro-generation due to the persistence of γ-FeOOH in the passivation layer. The instability/dissolution of this layer contributed to a 54%-higher generation of ferrate with GCI when compared to the other electrodes, reaching a maximum titre of 37 mM of ferrate in 10 M NaOH solution with a current efficiency of 45% and the lowest specific energy consumption of 8 kWh kg−1.