Steel from the new process should be of higher purity, and — once the process is scaled up — cheaper, according to a paper that was published this week in the journal Nature.
Worldwide steel production 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 CO2 as a byproduct. Production of a ton of steel generates almost 2 tons of CO2 emissions, according to steel industry figures, accounting for as much as 5 percent of the world’s total GHG emissions, according to MIT.
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, researchers say.
The industry has met little success in its search for carbon-free methods of manufacturing steel. The idea for the new method arose when Donald Sadoway, the John F. Elliott professor of materials chemistry at MIT, received a grant from NASA to look for ways of producing oxygen on the moon — a key step toward future lunar bases.
Sadoway found that a process called molten oxide electrolysis could use iron oxide from the lunar soil to make oxygen in abundance, with no special chemistry. He tested the process using lunar-like soil from Meteor Crater in Arizona — which contains iron oxide from an asteroid impact thousands of years ago — finding that it produced steel as a byproduct.
Sadoway’s method used an iridium anode, but since iridium is expensive and supplies are limited, that’s not a viable approach for bulk steel production on Earth. But after more research and input from Allanore, the MIT team identified an inexpensive metal alloy that can replace the iridium anode in molten oxide electrolysis.
In addition to eliminating GHG emissions, the process yields metal of exceptional purity, Sadoway says. It could also be adapted to carbon-free production of metals and alloys including nickel, titanium and ferromanganese with similar advantages.
Steel company ArcelorMittal USA’s normalized carbon emissions increased 18.6 percent from 2010 to 2011, according to the company’s latest corporate sustainability report, released in late 2012. In 2010, the steel giant emitted 1.5 tons of CO2 for every ton of steel it produced. In 2011 this figure increased to 1.78 tons of CO2 per ton of steel. The company says that, despite the year-on-year increase, its normalized carbon emissions remain lower than the industry average of 1.8 tons of CO2 per ton of steel in both 2010 and 2011.