5:15 PM - 7:15 PM
[SMP29-P03] Formation of Fundamental Building Blocks Composed of Calcium Borate Minerals
Keywords:Hydrothermal experiment, dissolution-reprecipitation, gowerite, priceite, nobleite
The crystal structures of borate minerals contain three (Δ) and four-coordinated (◊) borate ions [BOx(OH)y; x + y = 3 or 4], which behave as the fundamental building blocks; FBBs (Burns et al. 1995). The FBBs composed of the combination of Δ and ◊ exhibit a considerably diversity and complexity. However, the detailed mechanisms underlying the polymerization of borate ions, was well as the specific conditions for the formation of each FBB and borate mineral remain unclear.
In this study, hydrothermal experiments were conducted to understand the detailed mechanisms using H3BO3, NaOH, and CaCl2 as start materials at temperatures ranging from 120℃ to 240℃ and reaction times ranging from 12 hours to 15 days. The formation conditions of FBBs in borate minerals were then investigated through analysis and evaluation of the resulting products and iterative feedback cycle.
Synchrotron powder XRD study revealed that three phases, gowerite CaB6O8 (OH)4･3H2O; FBB = <Δ2◊>-<2Δ◊>, Δ, priceite Ca2B5O7(OH)5･H2O; FBB = <Δ2◊>-<3◊>, and nobleite CaB6O9(OH)2･3H2O; FBB = [Φ]<Δ2◊>|<Δ2◊>|<Δ2◊> were formed in the experimental conditions. Gowerite was obtained at 120℃ and 150℃ for 12 h. Priceite was obtained by increasing the reaction time to 48 h at 150℃. Therefore, an increase of heating time was found to induce the transformation of gowerite into priceite through a dissolution-reprecipitation mechanism. Furthermore, priceite was obtained by increasing the heating temperature from 150℃ to 180-240℃ and decreasing the reaction time to 12 h, as well as by increasing the pH to approximately 14. In addition, nobleite and gowerite were obtained when the product heated at 150℃ for 12 h was naturally cooled and subsequently maintained at room temperature for 5 d. Moreover, nobleite was obtained a single phase when the product heated at 210℃ for 48 h was naturally cooled and then maintained at 35℃ for 15 d. Therefore, it was found that an increase of reaction time in solution induces the transformation of gowerite and priceite into nobleite through a dissolution-reprecipitation mechanism. Although the three phases possess different connection mode of FBB, a <Δ2◊> ring is common, which suggests that the connection mode of FBB is changed through the transformation, but a part of FBB (the <Δ2◊> ring) is inherited from the precursor (parent) phase during the dissolution-reprecipitation process. This study confirmed that the connection mode of FBB varies depending on the heating temperature and reaction time, and suggested that borate minerals have the potential to serve as an environmental indicator.
In this study, hydrothermal experiments were conducted to understand the detailed mechanisms using H3BO3, NaOH, and CaCl2 as start materials at temperatures ranging from 120℃ to 240℃ and reaction times ranging from 12 hours to 15 days. The formation conditions of FBBs in borate minerals were then investigated through analysis and evaluation of the resulting products and iterative feedback cycle.
Synchrotron powder XRD study revealed that three phases, gowerite CaB6O8 (OH)4･3H2O; FBB = <Δ2◊>-<2Δ◊>, Δ, priceite Ca2B5O7(OH)5･H2O; FBB = <Δ2◊>-<3◊>, and nobleite CaB6O9(OH)2･3H2O; FBB = [Φ]<Δ2◊>|<Δ2◊>|<Δ2◊> were formed in the experimental conditions. Gowerite was obtained at 120℃ and 150℃ for 12 h. Priceite was obtained by increasing the reaction time to 48 h at 150℃. Therefore, an increase of heating time was found to induce the transformation of gowerite into priceite through a dissolution-reprecipitation mechanism. Furthermore, priceite was obtained by increasing the heating temperature from 150℃ to 180-240℃ and decreasing the reaction time to 12 h, as well as by increasing the pH to approximately 14. In addition, nobleite and gowerite were obtained when the product heated at 150℃ for 12 h was naturally cooled and subsequently maintained at room temperature for 5 d. Moreover, nobleite was obtained a single phase when the product heated at 210℃ for 48 h was naturally cooled and then maintained at 35℃ for 15 d. Therefore, it was found that an increase of reaction time in solution induces the transformation of gowerite and priceite into nobleite through a dissolution-reprecipitation mechanism. Although the three phases possess different connection mode of FBB, a <Δ2◊> ring is common, which suggests that the connection mode of FBB is changed through the transformation, but a part of FBB (the <Δ2◊> ring) is inherited from the precursor (parent) phase during the dissolution-reprecipitation process. This study confirmed that the connection mode of FBB varies depending on the heating temperature and reaction time, and suggested that borate minerals have the potential to serve as an environmental indicator.