Quantifying particle size effects on CO2 evolution at solid–liquid interfaces of calcium carbonate in acidic media

Environmental interfacial processes, from acid rain to acidic wastewaters, drive dissolution of carbonate-rich solids and CO₂ release. In this study, we investigate particle size effects on CO₂ emission kinetics in reaction between eggshell, a model porous bioceramic, with acetic acid (CH₃COOH). Five particle size fractions of eggshells, including dimensions above and below the natural shell thickness, were tested. Time-resolved CH₃COOH concentration measurements revealed that there are two regimes in dependence of CO₂ emission rates on the particle sizes. Simply breaking the shells does not lead to a clear enhancement in the reaction rate. However, finer particles, particularly those approaching or smaller than the shell thickness, exhibited markedly higher initial rates due to exposure of internal pore networks upon fracture. For all particle sizes, the reaction rates decrease with acid depletion and reduced reactive surface availability with time. No noticeable difference was observed by the presence of CO₂ bubbles on the reaction kinetics. These results highlight the role of particle size, morphology, and internal porosity in governing acid–carbonate interfacial reaction kinetics, with implications for porous carbonate dissolution in natural and engineered systems.