R2: Crystal structure, crystal chemistry, physical properties of minerals, crystal growth and applied mineralogy

[R2-10] Mechanism of calcium carbonate formation from portlandite Ca(OH)₂

*Atsushi Kyono¹, Hiroki Hasegawa¹, Satoru Okada¹ (1. Life & Environmental Sci, Univ of Tsukuba)

Keywords:Carbon dioxide Capture and Storage, Portlandite, Calcite, Aragonite, Vaterite

Portlandite synthesized was placed in a CO₂ gas-filled desiccator with relative humidity (RH) = 0%, 30%, 60%, and 99%. The results of XRD showed that no calcium carbonate was formed at RH = 0% for 3 weeks. At RH = 30%, on the other hand, calcite was formed after 2 days, and at RH = 99%, portlandite was completely converted to calcite after 24 hours. At RH = 60%, however, not only calcite but also aragonite and vaterite were formed after 12 hours and persisted at least until 14 days. The results confirm that carbonation of portlandite may have a different reaction path at RH = 60% than at RH = 30% and 99%.