Guaranteed reagent

All solutions were prepared using purified water from a Millipore system (Milli-Q water, MQW). To clean the low-density polyethylene (LDPE) bottles, surfactants (Extran MA01, Merck) and hydrochloric acid (HCl; Guaranteed Reagent, Wako Chemicals) were used. Ultrapure-grade aqueous ammonia, HCl (Tamapure AA-100, Tama Chemicals), and luminol sodium salt (Sigma-Aldrich) were purchased commercially. We dissolved 0.737 g of luminol sodium salts in 250 mL of MQW to prepare a 14.8 mM luminol solution. The solution containing luminol (0.74 mM), aqueous ammonia, HCl, and MQW was heated to 60 °C for over 15 h [37] (link) and left in the dark until the temperature reached room temperature. Standard stock solutions of Fe(II) (10 mM) were prepared by dissolving ferrous ammonium sulfate hexahydrate (Wako Chemicals) in a 0.1 M HCl solution before the research cruise and stored in a refrigerator until use. Standard working solutions (1 µM) were prepared by diluting the stock solutions with 0.1 M HCl before each use. All solutions were prepared in LDPE bottles (Nalge).

Guaranteed reagent 99.0+% and for residual solvents analysis (99.95+%) were purchased from Fujifilm Wako. For spectroscopy > 99.7% was obtained from Kanto Chemical Co., Inc. (Tokyo, Japan). For HPLC (≥ 99.7%) was from Sigma-Aldrich.

For the F standard solution, sodium fluoride (NaF, Wako Special Grade, Wako Pure Chemical Industries, Ltd.) was diluted by pure water. For F compounds, fluorite (CaF2, Wako Special Grade, Wako Pure Chemical Industries, Ltd.) was used. For synthesizing cuspidine (Ca4(Si2O7)(F,OH)2), SiO2 (Guaranteed Reagent, Wako Pure Chemical Industries, Ltd.) and CaF2 were mixed as molar equivalents and heated by an electric furnace in an argon (Ar) atmosphere with a closed crucible so as to avoid the volatilization of F. In order to synthesize fluoroapatite (Ca5(PO4)3F), 10CaO•3P2O5•H2O (Wako Pure Chemical Industries, Ltd.) and CaF2 reagents were treated under the same conditions of synthesizing cuspidine. The fluorite and the synthesized cuspidine and fluoroapatite were grounded and sieved under 75 μm in particle diameter; then, same particle size as much as possible to the artificial slag specimens shown in Table 1, expressed in terms of oxide, except for the fluorine concentration, were used in this study. The contents of the elements in slags, except F, were determined by XRF. The total fluorine concentration was determined by lanthanum/alizarin complexone spectrometry after the distillation of F from an alkaline-fused and acid-decomposed samples solution.