Towards Sustainable Metals Production By Molten Oxide Electrolysis

Abstract:

Marked by reliance on carbon as a reducing agent, modern metallurgy is intrinsically incapable of achieving sustainability. For example, in round numbers it takes ½ tonne of carbon to make a tonne of steel; in parallel it takes about ½ tonne of carbon to make a tonne of aluminium. Molten oxide electrolysis (MOE), which is the electrolytic decomposition of a metal oxide into molten metal and oxygen gas, is put forth as a low-carbon alternative. In its most advanced embodiment MOE avoids the use of consumable carbon anodes and halide electrolytes; this eliminates the need for energy-intensive anode manufacture and guarantees the absence of greenhouse-gas emissions as the by-product of the metal-recovery step. Instead, tonnage oxygen is the by-product of electrolytic metal production. In the author’s laboratory a variety of metals have been produced by MOE including iron, nickel, chromium, manganese, silicon, and titanium, each by electrolytic decomposition of the related metal oxide. So, for example, to produce iron by MOE, molten iron oxide is decomposed by the action of electric current into liquid iron and oxygen gas at a temperature of 1575ºC. What sets MOE apart from all other metal producing technologies is that in the extreme it is totally carbon-free and, hence, generates no greenhouse gases (GHGs). Promising results for a low-cost, oxygen-evolving anode have been obtained. Furthermore, MOE may even prove to be an enabling technology in human colonization of space, which must rely upon in situ resource utilization to the fullest extent. The extraction of iron and silicon with co-generation of oxygen has been demonstrated in laboratory-scale cells charged with lunar soil simulant NASA JSC1-A. Beyond sustainable metals production, MOE can serve as the inspiration for scalable electrical energy storage in stationary applications. Liquid-metal/molten-salt cells have been shown to operate as rechargeable batteries that have the potential to handle colossal currents thereby enabling us to store off-peak power from the grid for subsequent delivery on demand during high-usage periods.

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