Introducing the latest carbon offsetting solution: Slag — solid industrial waste containing calcium magnesium silicate, aluminate, ferrite, and oxides — produced from the iron and steel industry’s operations can help store CO2 for thousands of years, The Guardian writes, referencing initial research presented at the Goldschmidt conference in France earlier this month.

An ongoing study: University of Cambridge researcher Jahmaine Yambing is analyzing some 20 mn tons of discarded slag by the former Consett steelworks in the UK to ascertain how much carbon the heap had stored since the steel manufacturing plant shuttered four decades ago, according to the news outlet.

How does it work? The multi-state calcium silicate, free calcium oxide and magnesium oxide found in steel slag can react rapidly with CO2 to form stable calcium carbonate and calcium silicate hydrate, which can significantly absorb carbon from the atmosphere, according to research published by Science Direct.

Slag could also benefit the green cement sector: Some 400 mn tons of slag are produced annually, and while some of it is used in construction as road aggregates, for example, a majority of global slag volumes are discarded, the news outlet notes. The research notes that slag’s reaction to CO2 and the subsequent creation of stable calcium carbonate and calcium silicate hydrate also enhance the mechanical properties and durability of steel slag as a cement aggregate, potentially pushing down reliance on carbon-intensive Portland cement and helping decarbonize the global cement industry, which accounts for 8% of the world’s total carbon emissions.

And Emirates Steel is already repurposing theirs: Back in 2019, Emirates Steel — which produces c. 800k tons of slag annually — signed a 10-year agreement with Finnish supplier of steel slag processing solutions Ecofer to repurpose the slag generated from its operations. Emirates Steel’s slag will be crushed and turned into raw materials for the construction sector.

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