Within the electrochemical regime, molten oxides are an attractive medium for extraction of iron for a number of reasons [2]. Their high solubilizing power allows iron ore to be directly fed to the electrolytic cells, while their low vapor pressure allows electrolysis to be conducted above the melting point of iron, which greatly improves throughput, and most importantly, oxide ions in the melt can be discharged as environmentally benign oxygen gas if anode materials are inert. Consequently, there has been considerable effort to develop a molten oxide electrolysis process for iron [3]. However, there remain fundamental uncertainties regarding the electrochemistry of iron in molten oxides [4], thus the process has not yet been commercialized.
In this work, we present recent fundamental and experimental investigations into the electrochemical behaviour of iron in molten oxides, with the aim of understanding mechanisms that govern electrolysis. Attention is given to the design and testing of supporting electrolytes to minimize electronic conduction in the melt and improve the current efficiency of the process. At the same time, the performance of supporting electrolytes with respect to viscosity, surface tension, diffusivity, ionic conductivity, and liquidus temperature are considered. The results of fundamental investigations were used to strategically direct experimental investigations.
[1] Energy Technology Perspectives 2017. International Energy Agency: Paris (2017): 76-79.
[2] D.R. Sadoway. "New Opportunities for Metal Extraction and Waste Treatment by Electrochemical Processing in Molten Salts." J. Mater. Res. 10 (1995): 487-492.
[3] A. Allanore. "Features and Challenges of Molten Oxide Electrolytes for Metal Extraction." J. Electrochem. Soc. 162 (2015): E13-E22.
[4] W.D. Judge, A. Allanore, D.R. Sadoway, and G. Azimi. "E-logpO2 diagrams for ironmaking by molten oxide electrolysis." Electrochim. Acta 247 (2017): 1088-1094.