Biogenic calcium waste as CaO adsorbents for CO2 capture: Progress and future outlook.

This article reviews current developments and applications of biogenic calcium waste as a sustainable CaCO3 source, aiming to eradicate waste while providing a competitive way for CO2 capture in a calcium looping system. A broad overview of the carbonation performances of various bio-derived CaO sorbents is assessed based on their unique morphologies, crystal structures, and polymorphic forms. Eggshells and Mactra veneriformis shells achieved initial carbonation conversions of up to 86 %, significantly outperforming limestone at 21 %, however suffer sharp cyclic adsorption decay due to sintering. To address the issue of severe sintering during calcination and to improve the cyclic performance of bio-based sorbents, this work discusses modification techniques for enhanced capture performance and sintering resistance. Bauxite-tailings containing 37 wt % of Al2O3 and 25.48 wt% of SiO2, achieved 55 % conversion after 40 cycles, nearly doubling that of unmodified eggshells. A Life Cycle Analysis highlights the reduced environmental footprint the calcium looping process, and techno-economic data confirm lower costs per ton of CO2 captured compared to conventional systems. A review of CO2 capture kinetics is also included. The article concludes with recommendations for advancing waste shell utilization in industrial-scale carbon capture.