Eco-Friendly Steelmaking

Conventional steelmaking may be the world’s leading industrial source of greenhouse gases. But a new process developed by MIT researchers could change all that—and produce stronger (and ultimately cheaper) steel.

Worldwide steel production currently totals about 1.5 billion tons per year, and each ton produced generates almost two tons of carbon dioxide, according to industry data. This accounts for about 5 percent of the world’s greenhouse-gas emissions.

The idea for the new method, which was developed by materials chemistry professor Donald Sadoway, assistant professor of metallurgy Antoine ­Allanore, and Lan Yin, PhD ’12, arose when ­Sadoway received a grant from NASA to look for ways of producing oxygen on the moon—a key step toward future lunar bases. He found that a process he invented called molten oxide electrolysis could use iron oxide from the lunar soil to make oxygen in abundance.

This 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. Finding an alternative wasn’t easy, because molten iron oxide, at about 1,600 °C, “is a really challenging environment,” Sadoway explains. “The melt is extremely aggressive. Oxygen is quick to attack the metal.”

But Allanore managed to solve the problem. The answer was an alloy that naturally forms a thin film of metallic oxide on its surface—thick enough to prevent further attack by oxygen but thin enough for electric current to flow freely through it. The alloy’s constituents, iron and chromium, are “abundant and cheap,” Sadoway says.

In addition to producing no emissions other than pure oxygen, the process lends itself to smaller-scale factories. Conventional steel plants are profitable only 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.

The process also yields metal of exceptional purity, Sadoway says. And it could be adapted for carbon-free production of other metals and alloys, including nickel, titanium, and ferromanganese.

The technology is still at the laboratory scale, but Sadoway, Allanore, and a former student have formed a company to develop a commercially viable prototype plant. They expect that designing, building, and testing such a facility could take about three years.