Basalt Could Make Cement Without the CO2

A new paper argues that swapping limestone for volcanic rock eliminates cement's hardest-to-cut emissions—if the energy math can work out.

By The energy-climate Desk

Cement production accounts for about 8 percent of global CO2 emissions, and the nastiest slice isn't the kilns—it's the chemistry. When limestone converts to lime, it releases CO2 as an inescapable byproduct, and those "direct process emissions" are actually slightly larger than the emissions from burning fuel to run the kilns. [1]

A new paper in Communications Sustainability proposes a fix: ditch limestone entirely. The authors—including the CEO and an engineer from a company that says it has made Portland cement from silicate rocks like basalt at the lab scale—argue that basalt can supply the calcium oxide that cement needs, with no carbon in the feedstock and only water vapor released from the kiln. [1]

The process looks more like refining than baking: acid leaches calcium from the rock, a chemical step precipitates calcium hydroxide, and that goes into the kiln with less heating than limestone requires. [1] The catch is efficiency—current techniques demand a little more than double the energy of conventional production, even though thermodynamics says the conversion should need only around half as much. [1]

Even with that energy penalty, running the process on a fossil-fuel-dominated grid would cut emissions by almost 30 percent; clean electricity would eliminate most of what remains. [1] The economics get more interesting when you count the byproducts: iron, magnesium, and aluminum can be separated and sold, while leftover silicate material substitutes for coal ash as a cement additive. [1]

The path from lab curiosity to quarry-scale operation is long, and cost has a habit of outlasting good intentions. But in a sector where structural emissions have resisted every other approach, a credible thermodynamic shortcut is worth the scrutiny.

The researchers acknowledge that efficiency improvements proven in the lab would need to survive industrial scale before the numbers truly close—but the analysis maps, concretely, what would have to happen to make it viable. [1]

The trade-off, obviously, would be cost, which generally wins out over the sustainability of a livable environment.Ars Technica