Aqueous matrix and limiting factors in steel slag carbonation under elevated CO2 at ambient conditions

[Geoengineering News]

https://www.nature.com/articles/s44296-026-00116-9

Authors: Reinaldy Poetra, Jens Hartmann, Mathilde Hagens, Ina Sophia Nipper, Lukas Rieder & Charly A. Moras 

15 July 2026

Abstract

Alkaline industrial by-products have significant potential for permanent CO2 sequestration, but their reaction kinetics and controlling factors are often overlooked. This study examined the direct aqueous carbonation of basic oxygen furnace (BOF) slag in a slurry setup with continuous mechanical mixing and CO2-enriched air bubbling in ultrapure water and natural seawater, at 25% pCO2 under ambient temperature and 1 atm for 24 h. CO2 sequestration into carbonate minerals was higher in the ultrapure water (105 ± 5 kg CO2 t−1 slag; 90% CO2 capture efficiency) than in seawater (78 ± 4 kg CO2 t−1 slag; 70% CO2 capture efficiency). Carbonation proceeded in two distinct stages: an initial rapid carbonation phase (4–12 h), dominated by reactive Ca-(hydr)oxides, silicates and aluminates (e.g. wollastonite), followed by slower reactions involving less-reactive phases as the system gradually approached equilibrium with the pCO2 in the gas phase. Ionic inhibitors (e.g. Mg2+) affected the overall carbonation rate throughout the process. These findings highlight the importance of considering multi-stage kinetics and the influence of the aqueous matrix on reaction-inhibiting factors when evaluating the achievable extent of CO2 sequestration potential and the time required to reach it.

Source: Npj