Iron Production By Molten Sulfide Electrolysis

Abstract

With urgency and incentives to cut CO2 emissions, alongside increasing demand for steel, there is a need for technologies that use solely electricity for iron ore reduction, eliminating the role of carbon as a reductant. Herein, we propose the electrolytic production of liquid cast iron using a novel sulfide route, molten sulfide electrolysis (MSE). The process operates using sulfide chemistry and an inert anode. Sulfides are well known from non-ferrous metallurgy1 and the exclusion of oxygen supports a virtual elimination of green-house gases(GHG) emissions from the reduction step. The electrolytic decomposition of iron sulfide into iron and elemental sulfur gas operates in a multi-component molten sulfide electrolyte. The underlying thermodynamics suggests the absence of trivalent iron species (Fe3+) in such conditions, supporting the reduction of only divalent iron (Fe2+) and reducing the energy need proportionally, as compared to other oxide-based routes. Iron sulfide deposits or tailings, as well as conventional iron oxide ores after sulfidation2 are some of the suitable feedstocks for MSE.Both thermal only, and galvanostatic electrochemical experiments were carried out on electrolyte droplets (~200mg) in a thermal imaging furnace, to confirm the electrolytic deposition of Fe and the evolution of sulfur in a 2-electrode set-up. Faradaic efficiency estimates based on mass-loss measurements – i.e. with respect to gaseous sulfur anodic evolution – are of the order of 90%. Key electrochemical attributes of MSE to be reported include impedance measurement at various fixed DC potentials, measurements at various current densities up to 2A/cm2, and the role of the total charge passed, to highlight the potential limitations observed in such an experimental set up. Characterization of the electrochemical deposits are also presented.