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Preparation of CaMgAl-LDHs and mesoporous silica sorbents derived from blast furnace slag for CO₂ capture

Jiang, Haojie, Guo, Hongwei, Li, Peng, Li, Yang, Yan, Bingji
RSC advances 2019 v.9 no.11 pp. 6054-6063
adsorption, aluminum, calcium, carbon dioxide, chemical bonding, chemical composition, desorption, furnaces, hydrochloric acid, hydroxides, leaching, magnesium, porous media, remediation, silica, slags, sorbents, temperature, texture, thermal stability, value-added products
High volume blast furnace slag (BFS) resulting from iron-making activities has long been considered a burden for the environment. Despite considerable research efforts, attempts to convert BFS into high value-added products for environmental remediation are still challenging. In this study, calcium–magnesium–aluminium layered double hydroxides (CaMgAl-LDHs) and ordered mesoporous silica material (MCM-41) sorbents were simultaneously synthesized from BFS, and their CO₂ adsorption performance was evaluated. Calcium (Ca), magnesium (Mg) and aluminium (Al) were selectively extracted from BFS using hydrochloric acid. Leaching conditions consisting of 2 mol L⁻¹ acid concentration, 100 °C leaching temperature, 90 min leaching time and a solid-to-liquid ratio of 40 g L⁻¹ achieved a high leaching ratio of Ca, Mg and Al at 88.08%, 88.59% and 82.27%, respectively. The silica-rich residue (SiO₂ > 98.6 wt%) generated from the leaching process could be used as a precursor for MCM-41 preparation. Chemical composition, surface chemical bonds, morphology and textural properties of the as-synthesized CaMgAl-LDHs and MCM-41 sorbents were determined. Both the CaMgAl-LDHs and MCM-41 sorbents were found to be thermally stable and exhibited comparable adsorption uptake and rates over 20 CO₂ adsorption/desorption cycles. This work demonstrated that a total solution for the utilisation of BFS can be achieved and the resulting valuable products, i.e. CaMgAl-LDHs and MCM-41 are promising sorbents for CO₂ capture.