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Electrodeposition of Iron in Aqueous Alkaline Solution: An Alternative to Carbothermic Reduction

Recent studies on global warming and climate change concluded that a substantial reduction in greenhouse gases (notably carbon dioxide (CO2)) emissions is necessary and urgent. This requires enormous technological innovations in, especially, electric power generation and heavy industries including steelmaking. In order to develop a new, efficient industrial process for producing high quality iron and steel without CO2 emissions, we investigated the electrodeposition of iron in aqueous alkaline solution containing iron oxide ore particles in suspension (electrolyte). As schematically illustrated in Figure 1, hematite (Fe2O3) particles suspended in concentrated aqueous sodium hydroxide (NaOH) solution were transferred to the cathode (rotating disk graphite electrode) and were reduced to iron metal by applying a constant current; and oxygen evolved on the inert anode (nickel screen). Figure 2 shows (a) the experimental set-up for the electrodeposition of iron in the alkaline solution containing Fe2O3 particles in suspension (electrolyte) and (b) the mechanical sketch of the rotating disk graphite electrode (cathode). The average particle size and purity of the Fe2O3 powder were 10 μm and 99.5% by mass, respectively. A heating circulator (Julabo) filled with thermal oil was used to raise and maintain the cell operation temperature at 110 °C. An electrochemical workstation (IM6, Zahner) was employed to perform the galvanostatic electrolysis. As shown in Figure 3, cathode current efficiency (calculated according to Faraday’s law using the weight of obtained iron) of 90 ~ 96% was successfully obtained under the determined cell operation conditions, and the energy consumption was 2.6 ~ 3.0 kWh·kg iron produced. Figure 4 shows a scanning electron microscopic image of the electrodeposited iron. The deposited iron crystals was oriented cluster of stacked six–fold twins in tetrahedron-shape grew layer-by-layer in the direction perpendicular to the cathode surface. Influences of rotation rate of the cathode, cathode current density, weight percentage of Fe2O3 particles in electrolyte, and concentration of NaOH on current efficiency and morphology of the deposit were studied.