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Electrolysis method described for making ‘green’ iron

Posted May 9, 2013

Anyone who has seen pictures of the giant, red-hot cauldrons in which steel is made—fed by vast amounts of carbon, and belching flame and smoke—would not be surprised to learn that steelmaking is one of the world’s leading industrial sources of greenhouse gases. But remarkably, a new process developed by MIT researchers could change all that.

The new process even carries a couple of nice side benefits: The resulting steel should be of higher purity, and eventually, once the process is scaled up, cheaper. Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT and senior author of a new paper describing the process, says this could be a significant “win, win, win” proposition.

The paper, co-authored by Antoine Allanore, the Thomas B. King Assistant Professor of Metallurgy at MIT, and former postdoc Lan Yin (now a postdoc at the University of Illinois at Urbana-Champaign), has just been published in the journal Nature.

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 percent of the world’s total greenhouse-gas emissions.

The industry has met little success in its search for carbon-free methods of manufacturing steel. The idea for the new method, Sadoway says, arose when he 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.

It wasn’t an easy problem to solve, Sadoway explains, because a vat of molten iron oxide, which must be kept at about 1600 degrees Celsius, “is a really challenging environment. The melt is extremely aggressive. Oxygen is quick to attack the metal.”

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