Combined synthesis of Li4SiO4 sorbent with high CO2 uptake in the indirect carbonation of blast furnace slag process

Abstract

Carbon capture, utilization and storage (CCUS) is one of the most important technological options to mitigate the effect of greenhouse gases on the global climate. A process for indirect mineral carbonation of blast furnace slag (BFS) with (NH4)2SO4 as a recyclable reagent has been proposed recently. Preparation of high-performance and high-value-added products from its by-products would further improve economy of the process. In this study, Li4SiO4, a lithium-based high temperature CO2 sorbent, was prepared using Li2CO3 or LiOH·H2O and the silica gel derived from the indirect carbonation process. As a comparison, two other silicon sources were also used in the synthesis. The sorbents thus-prepared were compared for their CO2 uptake performances. The results show that the sorbent synthesized with Li2CO3 and the BFS-derived silica gel at Li/Si molar ratio of 4 (Li2CO3-BFS-4) possesses the best CO2 uptake performance with a sorption capacity of 0.329 (g CO2/g sorbent) within 20 min. The replacement of Li+ in the Li4SiO4 crystal lattice by the impurity metal ions, Ti4+ and Al3+, entrained in the silica gel through co-precipitation during the mineralization process, enhanced the diffusion of Li+ and O2−, which might be responsible for the excellent CO2 uptake performance. The effect of absorption temperature, Li/Si ratio, CO2 concentration and the CO2 sorption/desorption cycling stability were also investigated systematically. Compared with other existing synthesis methods, the method presented in this work for high temperature CO2 sorbent of Li4SiO4 through mineral carbonation of blast furnace slag is more environment-friendly and economically attractive, thus with promise in industrial application.