Molten Salt Electrolysis for Sustainable Iron Metal Production
Authors: Badalbayli Anar , Sinclair Nicholas Scott , Akolkar Rohan 
Published: December 2024

Iron and steel production, comprising approximately 95% of the global metal output annually1, are integral to modern industrialization, with steel serving as a critical material across various sectors, including construction and automotive industries. However, the industry's significant environmental impact is evident in the escalating CO2 emissions observed over the last decade. Due to this massive environmental burden, efforts to develop cleaner alternatives that benefit from advantages of electrochemistry have grown.

Existing and emerging electrochemical processes ideally aim for emission-free operations by utilizing energy extracted from renewable sources. While processes operating at high temperatures (using molten oxides at 1600°C) show promise, they face some challenges related to complex materials choices2, resulting in increased production costs. Conversely, processes operating at low temperatures using aqueous electrolytes (60-100°C) suffer from significantly lower production rates and efficiency3,4.

In this study, we present a novel approach—moderate temperature, chloride-based molten salt electrolysis (MSE) of iron—under development at CWRU. This method combines the advantages of both high and low-temperature electrolytic processes, offering a clean, cost-effective, and practical solution for sustainable iron metal production. During chloride MSE, iron is electrodeposited from a binary (NaCl+FeCl3) or ternary (LiCl+KCl+FeCl3) chloride mixture at moderate temperatures ranging from 300-500°C. Electrowinning in these molten salts capitalizes on their several attractive properties, including low viscosity, high ionic conductivity, high diffusivity, high solubility for electroactive species, electrochemical stability over a wide potential range, and fast electrochemical kinetics.5

Figure 1 illustrates the overall process flow of iron production via chloride MSE, including the upstream non-carbothermic chlorination of ore to FeCl3 resulting in the separation of ore impurities and the subsequent electrolytic deposition process. Initial findings indicate promising outcomes for sustainable iron electrowinning at lower operational costs, attributed to the moderate temperatures, high electrolyte conductivity (1-2 S/cm), and adequate FeCl3 concentrations (>2 M), allowing for high current efficiencies (>85%) at high electrodeposition rates (approaching 1 A/cm2). Furthermore, the chloride MSE process enables the incorporation of a proprietary dimensionally stable anode (DSA) to catalyze the chlorine evolution reaction at the anode. This innovation significantly reduces cell voltage, thereby enhancing the overall process energy efficiency.

Figure 1. Iron metal production from ore via chloride-based Molten Salt Electrolysis (MSE) process.

References:

Iron and Steel Statistics and Information | U.S. Geological Survey. www.usgs.gov. https://www.usgs.gov/centers/national-minerals-information-center/iron-and-steel-statistics-and-information.

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Figure 1