MIT researchers identify viable anode material for molten oxide electrolysis for lower CO2 steel production
Researchers at MIT have identified inexpensive metal alloy materials that can serve as anodes for molten oxide electrolysis (MOE)—an electrometallurgical technique that enables the direct production of metal in the liquid state from oxide feedstock. Compared with traditional methods of extractive metallurgy, MOE offers both a substantial simplification of the process and a significant reduction in energy consumption.
The principle of MOE is the dissolution of a metal oxide by a mixture of oxides, the corresponding ions being converted to metal and oxygen by the application of a voltage difference.
MOE is considered a promising route for mitigation of CO2 emissions in steelmaking, production of metals free of carbon, and generation of oxygen for extra-terrestrial exploration. A paper on their discovery is published in the journal Nature.
Until now, MOE has been demonstrated using anode materials that are consumable (graphite for use with ferro-alloys and titanium) or unaffordable for terrestrial applications (iridium for use with iron). To enable metal production without process carbon, MOE requires an anode material that resists depletion while sustaining oxygen evolution.
The challenges for iron production are threefold. First, the process temperature is in excess of 1,538 degrees Celsius. Second, under anodic polarization most metals inevitably corrode in such conditions. Third, iron oxide undergoes spontaneous reduction on contact with most refractory metals14 and even carbon.
Here we show that anodes comprising chromium-based alloys exhibit limited consumption during iron extraction and oxygen evolution by MOE. The anode stability is due to the formation of an electronically conductive solid solution of chromium(III) and aluminium oxides in the corundum structure.
These findings make practicable larger-scale evaluation of MOE for the production of steel, and potentially provide a key material component enabling mitigation of greenhouse-gas emissions while producing metal of superior metallurgical quality.—Allanore et al.
In addition to producing no emissions other than pure oxygen, the process lends itself to smaller-scale factories: Conventional steel plants are only economical if they can produce millions of tons of steel per year, but this new process could be viable for production of a few hundred thousand tons per year, he says.
Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT and senior author of the paper, Antoine Allanore, the Thomas B. King Assistant Professor of Metallurgy at MIT, and a former student have formed a company to develop the concept, which is still at the laboratory scale, to a commercially viable prototype electrolysis cell. They expect it could take about three years to design, build and test such a reactor.
Worldwide steel production currently totals about 1.5 billion tons per year. The prevailing process makes steel from iron ore—which is mostly iron oxide—by heating it with carbon; the process forms carbon dioxide as a byproduct. Production of a ton of steel generates almost two tons of CO2 emissions, according to steel industry figures, accounting for as much as 5% of the world’s total greenhouse-gas emissions.
The research was supported by the American Iron and Steel Institute and the US Department of Energy (DOE).
Antoine Allanore, Lan Yin & Donald R. Sadoway (2013) A new anode material for oxygen evolution in molten oxide electrolysis. Nature doi: 10.1038/nature12134