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 materials, 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% 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 partial 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.