Study on the carbon mineralization mechanism of ultrafine steel slag slurry during the DAC process and its application in foam concrete - Preprint

[Geoengineering News]

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=6410690

Authors: Ying Su, Tianliang Ni, Zhengqi Zheng, Xingyang He, Zhou Zhang, Yingbin Wang, Jin Yang, Can Mei

13 March 2026

Abstract

Direct Air Capture (DAC) has become an indispensable solution for future atmospheric CO2 removal, with innovations in methodologies and materials serving as the cornerstone of its advancement. This study for the first time achieved the synergistic coupling of DAC technology with solid waste carbon mineralization, successfully preparing sub-micron carbon mineralized steel slag slurry, and applying it as a functional additive in the foam concrete system. During the DAC-mediated carbon mineralization process, the particle size of ultrafine steel slag remained highly stable with a median particle size (D50) of 0.46–0.55 μm, whereas the D50 of ordinary steel slag decreased significantly from 17.90 μm to 8.00 μm. XRD and SEM analysis confirmed that the carbonation products of both steel slag types were dominated by calcite, with trace amounts of aragonite. Under 1 d carbonation conditions, the carbon capture capacity of ultrafine steel slag reached 60.0 kg CO2/t, approximately 1.9 times that of ordinary steel slag (31.2 kg CO2/t). This significant enhancement was attributed to two key advantages induced by ultrafine grinding: (i) an obvious increment in specific surface area and enrichment of lattice defects, which markedly accelerated Ca2+ leaching kinetics; and (ii) a higher and more uniform content of hydrated calcium hydroxide, which provided abundant and stable alkaline reaction sites for in-situ CO2 mineralization. At a mass dosage of 4% carbon-mineralized steel slag, after 7 and 28 days of curing, the foam concrete attained compressive strengths of 4.3 MPa and 6.1 MPa, corresponding to gains of 19.4% and 24.5% over the control group. This strengthening effect was mainly derived from the physical stabilization of bubble walls by ultrafine carbon-mineralized particles and the densification of hydration products in the interfacial transition zone. Combining DAC and solid waste carbon mineralization to fabricate low-carbon building materials is anticipated to emerge as a feasible strategy for atmospheric carbon dioxide removal in the future.

Source: SSRN