[B-CG03] Earth and Planetary Science Frontiers for Life and Global Environment

[BCG03-P02] Formation conditions of calcium carbonate hemihydrate

*Suyama Mai¹, Keisuke Fukushi² (1.kanazawa University, 2.Institute of Nature and Environmental Technology Kanazawa University)

Keywords:Calcium carbonate , Calcium carbonate hemihydrate, Formation conditions , solubility, alkaline lakes

Calcium carbonates are classified into 6 mineral species: calcite, aragonite and vaterite of anhydrous calcium carbonate, monohydrocalcite (MHC, CaCO₃･H₂O) and ikaite (CaCO₃･6H₂O) of hydrous calcium carbonate and amorphous calcium carbonate (ACC). In addition to these, calcium carbonate hemi hydrate (CCHH, CaCO₃･1/2H₂O) was synthesized for the first time by Zou et al. (2019). They reported that when CaCl₂, MgCl₂, and Na₂CO₃ solutions are mixed, CCHH is produced after ACC formation as a precursor of MHC. Because Ca, Mg and CO₃ are abundant in nature, it is considered that CCHH formation is possible even in the natural environment. If a new type of calcium carbonate will be discovered, some geochemical processes which have been overlooked so far may be revealed. Therefore, the purpose of this study is to clarify the formation conditions for CCHH by attempting to synthesize calcium carbonates from the initial solution containing Ca, Mg, and CO₃ under various concentration conditions. In addition, we will compare the composition of the reacted solutions after the syntheses with the natural water to deduce the possible formation environment in nature.