Original Article

Assessment of the natural absorption of CO₂ performed by steelmaking slag

¹ Dipartimento di Meccanica - Politecnico di Milano, Via La Masa 1, 20156 Milano, Italy
² Fassa Bortolo S.r.l., via Lazzaris 3, 31027 Spresiano (TV), Italy

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Received: 22 September 2025
Accepted: 8 April 2026

Abstract

This study aims to evaluate the direct natural wet CO₂ absorption potential of steelmaking slag, with a specific focus on the behavior of black and white slag, respectively, collected after the steel production by electric arc furnace and molten steel refining in a ladle furnace. Slag contains significant amounts of calcium and magnesium compounds capable of reacting with atmospheric CO₂ through carbonation, forming stable carbonates and thereby enabling permanent carbon sequestration. Representative samples of black and white slag were monitored to assess their physicochemical properties, mineral composition, and carbonation behavior under natural environmental conditions over time. The investigation seeks to characterize and quantify the tendency and rate of CO₂ uptake for each slag type, highlighting differences in carbonation efficiency. Preliminary findings contribute to understanding the role of steel slag as potential carbon sinks within the steel industry, supporting sustainability goals. Furthermore, the study discusses the main factors influencing carbonation, such as particle size, exposure time, and ambient conditions, thereby providing insights into slag management optimization and the parallel enhancement of CO₂ sequestration during slag-yard stockpiling. This research represents a step forward in incorporating natural carbonation processes of steelmaking by-products into carbon accounting frameworks and promoting their beneficial reuse in climate change mitigation strategies.