MIT scientists demonstrate carbon-free method for making cement

A team at the Massachusetts Institute of Technology (MIT) has developed a way to make cement without heating, potentially eliminating the carbon produced in the process.

Portland cement, the most widely used variety, is made by grinding up limestone then cooking it with sand and clay at temperatures of up to 1,500°C, releasing carbon from the fuel used to obtain the heat energy and the limestone itself.

Altogether, this accounts for an estimated 8% of global carbon emissions, and the development of low-carbon production is presently one of the most urgent challenges facing the industry (see Further reading, below).

The MIT team’s idea is to use electrochemical processes rather than heat. Limestone is first dissolved in acid, then placed in a tank with an electric current passing through it.

This splits water molecules into oxygen and hydrogen, creates an acid at the positive electrode and an alkali deposit of calcium hydroxide at the negative. This deposit, which forms in flakes, can then be used to produce Portland cement.

The findings were published yesterday in the Proceedings of the National Academy of Science, in a paper by Yet-Ming Chiang, professor of materials science, and researchers Leah Ellis, Andres Badel and others.

Chiang commented in MIT News: "About 1kg of carbon dioxide is released for 1kg of cement made. That adds up to 3-4 gigatons of cement and of carbon dioxide produced annually, and the number of buildings worldwide is expected to double by 2060, which is equivalent to building one new New York City every 30 days."

So far, the team has demonstrated the process at laboratory scale, with the process looking "a bit like shaking a snow-globe" as lime precipitates out of the solution.

The researchers said it could be scaled up to an industrial process, but warned it would be difficult to change such a basic process in such a large industry.

Researcher Leah Ellis said that a typical cement plant produced about 700,000 tons a year. "How do you penetrate an industry like that and get a foot in the door?"

Chiang says the team wants to "get people in the electrochemical sector to start thinking more about this" and come up with new ideas. "It’s an important first step, but not yet a fully developed solution," he adds.

Image: The MIT experiment, showing the separation of acid and alkali liquids (Felice Frankel/MIT News)

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