Recycling coal gangue into advanced CO₂ sorbents: metal-doped Li₄SiO₄ for enhanced capture efficiency

Abstract

Coal-gangue backfilling offers potential for mineral-based CO₂ sequestration, as gangue can react with injected CO₂ to form stable carbonates. A stable CO₂ supply requires efficient capture technologies, for which lithium orthosilicate (Li₄SiO₄) is a promising high-temperature sorbent. Its broader use is limited by the cost of conventional silica, so in this study, amorphous SiO₂ from coal gangue was used as a sustainable precursor for solid-state synthesis of Li₄SiO₄. Targeted K⁺ and Nd³⁺ doping were employed to improve performance. K⁺ doping promotes LiKCO₃ formation and accelerates surface reactions, achieving high initial CO₂ uptake (36.15 wt%) but lower cyclic stability. In contrast, Nd³⁺ doping preserves the Li₄SiO₄ phase, enhances internal diffusion, and maintains stable uptake (34–36 wt%) over 20 cycles, with LiNd-0.10 showing the best multi-cycle performance. This approach provides a cost-effective, environmentally friendly route to high-performance CO₂ sorbents from waste silica, combining carbon capture and solid waste valorization.