[M-IS18] Interface- and nano-phenomena on crystal growth and dissolution

[MIS18-P01] Analysis of the dissolution reaction of calcium carbonate by simultaneous visualization of local pH and calcium ion concentration.

Kosei Miki², *Jun Kawano¹, Makoto Yazaki², Takashi Toyofuku^3,4, Yukiko Nagai³, Takaya Nagai¹ (1.Faculty of Science, Hokkaido University, 2.Graduate School of Science, Hokkaido University, 3.JAMSTEC, 4.TUMSAT)

Keywords:imaging, calcium carbonate, pH, dissolution

Recent developments in experimental and simulation techniques have revealed that the growth or dissolution mechanism of minerals in an aqueous solution is more complicated than we had imagined. To understand these mechanisms, the analysis of local conditions of the solution around the dissolving or forming minerals is critical. Recently, we succeeded in simultaneously visualizing the distribution of pH and calcium concentration around a calcium carbonate crystal dissolving in an aqueous solution using a fluorescent probe. In the present study, more precise calibration between pH/calcium ion concentration and the intensity of fluorescence which probes emitted at these conditions was performed, and the dissolution reaction of calcium carbonate crystal in aqueous solution was analyzed based on it.
pH and calcium ion concentration could be measured and their distributions around calcite dissolving in an aqueous solution were successfully visualized by simultaneously using HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid) and Rhod-5N as pH and calcium concentration probes, respectively. Tendencies of change in calcium ion concentration could be explained by the diffusion equation with the reasonable values of the dissolution rate of calcite and the diffusion constant of calcium ion. When considered simultaneously with changes in pH, bicarbonate ions are suggested to play an important role in the dissolution of calcium carbonate.