Co-carbonation behaviors of blast furnace ferronickel slag-cement in aqueous conditions and the associated mechanisms

Blast furnace ferronickel slag (BFNS) has the potential to sequester CO2 for building materials. This study used cement to enhance reactivity of BFNS and found that cement can not only improve the CO2 capture ability of BFNS via stimulating the carbonation of Mg, but also stabilize the formed carbonation products. Co-carbonation of 70 % BFNS and 30 % cement (B70C30) shows higher CO2 uptake capacity (20.57 %) than the theoretical value (16.93 %). The main reason is the formation of the relatively more stable low-Mg calcite in the carbonated B70C30, compared to formed metastable monohydrocalcite in carbonated BFNS. Carbonation kinetics showed that pure BFNS and cement reached almost complete carbonation after 7 h, while B70C30 took 20 h to reach a stable state, resulting from the fact that Mg calcite forms in B70C30 at a low rate, due to incorporation of Mg and calcite crystal structure during growth. This study provides theoretical guidance for BFNS-cement CO2 capture to make building materials. •Blast furnace ferronickel slag (BFNS) is applied in CO2 capture for the first time.•Metastable monohydrocalcite is formed in carbonated BFNS.•Co-carbonation of BFNS and cement enhances their CO2 capture abilities.•Adding cement helps to improve the stability of the BFNS carbonation products.