Kinetic and mechanistic insights into the simultaneous fluoride removal and <scp> CaF ₂ </scp> recovery from aqueous solutions

Abstract The simultaneous defluorination and recovery of calcium fluoride (CaF 2 ) from fluoride‐containing wastewater is of practical significance. This study compared the reaction characteristics of synthesized polycrystalline calcium carbonate (CaCO 3 ) and calcium sulfate dihydrate (CaSO 4 ·2H 2 O). The results indicate that CaCO 3 more readily undergoes morphology‐preserving transformation to CaF 2 , following a shrinking core mechanism. At low temperatures, the process is surface‐reaction controlled, while higher temperatures shift it to mixed control involving internal diffusion, with regressed apparent reaction orders ranging from 0 to nearly 4. Initial surface cracking and pore formation were gradually repaired by Ostwald ripening, stabilizing the final product structure. Molecular dynamics simulations revealed that the interfacial distribution and diffusion of fluoride species are concentration‐dependent, which, together with temperature, drive the dynamic transition of controlling regimes and the variation in the apparent reaction order. These multi‐scale insights provide theoretical guidance for designing controllable defluorination processes and fluoride resource recovery with preserved particle morphology.