A new perspective on the reaction and re-precipitation of calcium carbonate during ferrite carbonation

In this study, the synergistic hydration-carbonation mechanism of the C 4 AF system incorporating calcite or aragonite was systematically investigated. The results indicate that under coupled carbonation-hydration conditions, aragonite undergoes phase transformation to calcite via dissolution-recrystallization, increasing the regenerated calcite content. This process is facilitated by free Ca 2 + ions released from C 4 AF dissolution, which react with CO 3 2- . The presence of calcium carbonate significantly enhances the CO 2 uptake capacity of the C 4 AF system, with the aragonite group exhibiting approximately 2.8 times higher CO 2 absorption rate than the calcite group. Notably, this study reveals for the first time that the C 3 (A,F)H 6 phase undergoes decomposition in carbonation environments. This decomposition is primarily driven by H + ions generated during carbonation, which react with interlayer OH - in OH-AFm, disrupting the C 3 (A,F)H 6 crystal structure. The released ions initially form monocarbonate/hemicarbonate calcium aluminate phases (Mc/Hc). However, in increasingly acidic and CO₃²⁻-rich environments, progressive replacement of interlayer anions with CO 3 2- through ion exchange ultimately transforms them into a more stable CO 3 -AFt phase (calcium ferrite aluminate carbonate), forming characteristic clustered aggregates. • Aragonite changes to calcite via dissolution/recrystallization, boosting regenerated carbonate. • Aragonite addition increases CO 2 uptake ~2.8x vs calcite via phase transformation. • C 3 (A,F)H 6 decomposes under carbonation via H + attack on interlayer OH - in OH-AFm.