Electric recycling of Portland cement at scale

Allwood, Julian M; Dunant, Cyrille Francois; Joseph, Shiju; Prajapati, Rohit

Electric recycling of Portland cement at scale

Authors

Allwood, Julian M

Dunant, Cyrille Francois

Joseph, Shiju

Prajapati, Rohit

Publisher

Nature Research
Department of Engineering
http://dx.doi.org/10.1038/s41586-024-07338-8

Description

Cement production causes 7.5 % of global anthropogenic CO2 emissions, due to both limestone decarbonation and fossil-fuel combustion. Current decarbonation efforts involve either partly substituting Portland clinker with supplementary materials or developing alternative binders. However most supplementary materials are the products of emitting processes, no alternative binder promises scale, and even if carbon capture and storage were deployed, some emissions would still be released. Producing cement with zero emissions requires a source of decarbonated calcium and large-scale, electrical, industrial equipment that can produce temperatures above 1450 °C. Here we show that cement can be recycled in electric arc furnaces when recovered cement paste is partially substituted for the lime-dolomite flux used in today’s steel recycling. Our results reveal that the paste can be re-clinkered over molten iron and the resulting slag can meet existing specifications for Portland clinker. In addition, we have demonstrated that these slags can be blended effectively with calcined clay and limestone. The process is sensitive to the silica content of the recovered cement paste, and silica and alumina which may come from the scrap, but this can be adjusted easily. We show that the proposed process will probably be economically competitive, and if powered by emissions-free electricity, can lead to zero emissions cement while also reducing the emissions of steel-recycling by reducing lime flux requirements. In the event of increasing coal prices and/or reducing electricity tariffs, this approach may even be an economically viable route to produce cement regardless of steel production. The global supply of scrap steel for recycling is expected to treble by 1 2050, and it is likely that more slag can be made per unit of steel recycled. With material efficiency in construction, future global cement requirements could be met by this route.