Casio3

GLDA tetrasodium salt (GLDA-4Na, C₉H₉NNa₄O₈) solutions with different concentrations were prepared by mixing the initial GLDA-4Na solution (40 wt% in water, Tokyo Chemical Industry, Japan) with Milli-Q water, and pH was adjusted from an initial value of 13.8–~9.0 through the addition of aqueous HNO₃ (60–61%, Kanto Chemical, Japan). This weakly alkaline pH was used at the beginning of the Ca extraction process to minimize the cost of pH regulation, as subsequent CaCO₃ precipitation requires alkaline environments (pH > 8)^{32 (link),33 (link)}. High-purity commercial calcium silicate powders (Fig. 2, < 30 µm) with a general composition of CaSiO₃ (Wako Pure Chemical Industries, Japan) were used as a Ca source to represent silicate minerals. Na₂CO₃ (>99.0%, Kanto Chemical, Japan), NaHCO₃ (> 99.0%, Kanto Chemical, Japan), and CO₂ gas (> 99.995 vol.%, Taiyo Nippon Sanso, Japan) were used as CO₂ sources to optimize the CaCO₃ production system.Figure 2

Representative X-ray diffraction (XRD) pattern of the employed calcium silicate.

PS300 was generously provided by Tomita Pharmaceutical Co., Ltd. (Tokushima, Japan). CaSiO₃ was purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). IBU was generously provided by Kaken Pharmaceutical Co., Ltd. (Tokyo, Japan). Zirconia beads of 0.3 mm in diameter were purchased from Nikkato Co., Ltd. (Osaka, Japan). Ethanol, 1 mol/L sodium hydroxide solution, calcium chloride, phosphoric acid, acetonitrile, and distilled water were purchased from Kanto Chemical Co., Inc. (Tokyo, Japan). All received chemicals and solvents were of analytical reagent grade.