Molten Oxide Electrolysis: Metal recovery and primary processing?

Abstract

Molten oxide electrolysis has the potential to be a more efficient method to produce metals with near zero CO$_2$ emissions compared to traditional methods. If metals can be produced from industrial by-products, such as slags, then the environmental and sustainability benefits are considerable. Our team uses thermodynamic predictions coupled with high-temperature molten oxide electrochemical experiments to explore the opportunities and limitations of this approach. In this talk, I’ll show how we used these methods to characterise the selective reduction of titanium from steelmaking slag. Due to the complex composition of the industrial material, we studied the reduction of titanium from model pseudo-quinary metal oxide melts. Co-reduction of silicon and titanium was achieved with sufficient ionic transport in the oxide melt such that salt-free electrolytes could be used, avoiding the environmental impact of halides. Model binary oxide systems were sought to simplify the electrolyte for titanium extraction and to reduce the operating temperature to about 1100˚C. We identified alkali metal oxides as candidates based on thermodynamic predictions. Our work on these simpler systems, illustrates the challenges of characterising electrochemical behaviour of transition metal molten oxides at elevated temperatures. In new work, we turn our attention to primary production of critical metals. We focus on Ta and Nd, two technology-critical metals. I’ll discuss the characteristics of high temperature electrolytic melts that allow for the extraction of metals, and the opportunities and challenges of molten oxide electrolysis to obtain selected metals from mixtures of chemically similar elements.