Valorisation of exhausted lime from industrial flue gas treatment for CO₂ capture and storage

The valorisation of hazardous alkaline residues and the mitigation of carbon dioxide (CO₂) emissions represent key challenges for sustainable industrial development. In this study, exhausted lime derived from ceramic industry flue gas treatment was investigated as a feedstock for CO₂ mineralization in a semi-continuous gas-liquid-solid system operating under mild conditions. The different batches, characterized by Ca(OH)₂ contents between 21 and 65 wt%, were directly used without pre-treatment. Batch experiments showed rapid carbonation kinetics, achieving up to 99 % CO₂ conversion at low slurry concentrations, while higher solid loadings were limited by mass transfer constraints. A semi-continuous process was developed to evaluate the effects of CO₂ concentration, gas flow rate, and slurry composition. The results indicated that CO₂ removal is complete and that the overall reaction time is primarily governed by the CO₂ molar flow rate. The system demonstrated stable performance across a range of operating conditions and allowed efficient CO₂ capture from diluted streams. Preliminary tests on the carbonated product showed its suitability as a substitute for limestone in cementitious binders, with mechanical properties comparable to reference materials. These findings highlight the potential of exhausted lime valorisation as a viable strategy for coupling CO₂ capture with hazardous waste treatment, supporting circular economy approaches in industrial systems.