Influence of Glycerol Concentration on the Dissolution Mechanism of Calcium in Water.

The structural characteristics of dissolved calcium species in glycerol-water solutions were investigated, and the mechanism by which calcium solubility increased upon increasing the glycerol concentration was elucidated. Comparative dissolution experiments using CaO in various alcohol-water solutions with varying numbers of hydroxyl groups revealed that the calcium solubility increased with increasing number of hydroxyl groups; glycerol and erythritol promoted calcium dissolution to a significantly greater extent than methanol. Structural analysis confirmed the formation of calcium-glycerol complexes and the presence of hydrated species. Evaluation of the solution viscosity and calcium concentration as a function of the glycerol mole fraction identified a critical molar fraction (Xglyc ≈0.18) at which the hydrogen-bonding network of the solution structure underwent a pronounced transition. Chemical shifts observed via proton nuclear magnetic resonance spectroscopy and spin-lattice relaxation measurements suggested that increasing the glycerol content altered the local water arrangement and enhanced the stability of the calcium-glycerol complexes. At Xglyc >0.18, the calcium solubility increased sharply due to the preferential formation of stable glycerol-coordinated complexes. These findings establish a critical glycerol concentration threshold for efficient calcium dissolution and offer a new solvent design principle for selective calcium extraction and high-purity CaCO3 synthesis.