Synthesis of highly efficient CaO-based, self-stabilizing CO₂ sorbents via structure-reforming of steel slag

Capturing anthropogenic CO₂ in a cost-effective and highly efficient manner is one of the most challenging issues faced by scientists today. Herein, we report a novel structure-reforming approach to convert steel slag, a cheap, abundant, and nontoxic calcium-rich industrial waste, as the only feedstock into superior CaO-based, self-stabilizing CO₂ sorbents. The CO₂ capture capacity of all the steel slag-derived sorbents was improved more than 10-fold compared to the raw slag, with the maximum uptake of CO₂ achieving at 0.50 g_CO2 g_sorbent^–1. Additionally, the initial steel slag-derived sorbent could retain 0.25 g_CO2 g_sorbent^–1, that is, a decay rate of only 12% over 30 carbonation–calcination cycles, the excellent self-stabilizing property allowed it to significantly outperform conventional CaO, and match with most of the existing synthetic CaO-based sorbents. A synergistic effect that facilitated CO₂ capture by CaO-based sorbents was clearly recognized when Mg and Al, the most common elements in steel slag, coexisted with CaO in the forms of MgO and Al₂O₃, respectively. During the calcium looping process, MgO served as a well spacer to increase the porosity of sorbents together with Al₂O₃ serving as a durable stabilizer to coresist the sintering of CaCO₃ grains at high temperatures.