Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6 ·2H2O(cr)]

Xiong, Yongliang; Kirkes, Leslie Dawn; Knox, Jandi; Marrs, Cassandra; Burton, Heather Lynn

doi:10.1016/j.chemgeo.2018.02.008

Title: Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg₃B₇O₁₃Cl(cr)] and aksaite [MgB₆O₇(OH)₆ ·2H₂O(cr)]

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Abstract

In this work, solubility measurements regarding boracite [Mg₃B₇O₁₃Cl(cr)] and aksaite [MgB₆O₇(OH)₆·2H₂O(cr)] from the direction of supersaturation were conducted at 22.5 ± 0.5 °C. The equilibrium constant (log₁₀K⁰) for boracite in terms of the following reaction, Mg₃B₇O₁₃Cl(cr) + 15H₂O(l) ⇌ 3Mg²⁺ + 7B(OH)₄^– + Cl^– + 2H⁺ is determined as -29.49 ± 0.39 (2σ) in this study. The equilibrium constant for aksaite according to the following reaction, MgB₆O₇(OH)₆•2H₂O(cr) + 9H₂O(l) ⇌ Mg²⁺ + 6B(OH)₄^– + 4H⁺ is determined as -44.41 ± 0.41 (2σ) in this work. This work recommends a set of thermodynamic properties for aksaite at 25 °C and 1 bar as follows: ΔH$$0\atop{f}$$ =-6063.70 ± 4.85 kJ·mol^-1, ΔG =-5492.55 ± 2.32 kJ·mol^-1, and S⁰ = 344.62 ± 1.85 J·mol^-1·K^-1. Among them, ΔG$$0\atop{f}$$ is derived from the equilibrium constant for aksaite determined by this study; ΔH$$0\atop{f}$$ is from the literature, determined by calorimetry; and S⁰ is computed in the present work from ΔG$$0\atop{f}$$ and ΔH$$0\atop{f}$$. This investigation also recommends a set of thermodynamic properties for boracite at 25 °C and 1 bar as follows: ΔH$$0\atop{f}$$ =-6575.02 ± 2.25 kJ·mol^-1, ΔG$$0\atop{f}$$ =-6178.35 ± 2.25 kJ·mol^-1, and S⁰ = 253.6 ± 0.5 J·mol^-1·K^-1. Among them, ΔG$$0\atop{f}$$ is derived from the equilibrium constant for boracite determined by this study; S⁰ is from the literature, determined by calorimetry; and ΔH$$0\atop{f}$$ is computed in this work from ΔG$$0\atop{f}$$ and S⁰. The thermodynamic properties determined in this study can find applications in many fields. For instance, in the field of material science, boracite has many useful properties including ferroelectric and ferroelastic properties. The equilibrium constant of boracite determined in this work will provide guidance for economic synthesis of boracite in an aqueous medium. Similarly, in the field of nuclear waste management, iodide boracite [Mg₃B₇O₁₃I(cr)] is proposed as a waste form for radioactive ¹²⁹I. Therefore, the solubility constant for chloride boracite [Mg₃B₇O₁₃Cl(cr)] will provide the guidance for the performance of iodide boracite in geological repositories. Boracite/aksaite themselves in geological repositories in salt formations may be solubility-controlling phase(s) for borate. Finally, solubility constants of boracite and aksaite will enable researchers to predict borate concentrations in equilibrium with boracite/aksaite in salt formations.

Authors:

^[1]; Kirkes, Leslie Dawn ^[1]; Knox, Jandi ^[1]; Marrs, Cassandra ^[1]; Burton, Heather Lynn ^[1]

Sandia National Laboratories (SNL), Carlsbad, NM (United States). Carlsbad Programs Group

Publication Date:: 2018-02-03

Research Org.:: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:: USDOE Office of Environmental Management (EM); USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:: 1429647

Alternate Identifier(s):: OSTI ID: 1872485

Report Number(s):: SAND-2017-10729J
Journal ID: ISSN 0009-2541; 657530; TRN: US1802613

Grant/Contract Number:: AC04-94AL85000; NA0003525; NA-0003525; SAND2017-10729

Resource Type:: Accepted Manuscript

Journal Name:: Chemical Geology

Additional Journal Information:: Journal Volume: 483; Journal Issue: C; Journal ID: ISSN 0009-2541

Publisher:: Elsevier

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 58 GEOSCIENCES; Borate deposits; Salt formations; Salt lakes; Borax; Sodium tetraborate; Pitzer model

Citation Formats


                    Xiong, Yongliang, Kirkes, Leslie Dawn, Knox, Jandi, Marrs, Cassandra, and Burton, Heather Lynn. Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6 ·2H2O(cr)].  United States: N. p., 2018. 
Web.  doi:10.1016/j.chemgeo.2018.02.008.

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                    Xiong, Yongliang, Kirkes, Leslie Dawn, Knox, Jandi, Marrs, Cassandra, & Burton, Heather Lynn. Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6 ·2H2O(cr)].  United States.  https://doi.org/10.1016/j.chemgeo.2018.02.008

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                    Xiong, Yongliang, Kirkes, Leslie Dawn, Knox, Jandi, Marrs, Cassandra, and Burton, Heather Lynn. Sat .  
"Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6 ·2H2O(cr)]".  United States.  https://doi.org/10.1016/j.chemgeo.2018.02.008.  https://www.osti.gov/servlets/purl/1429647.

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@article{osti_1429647,

  title        = {Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6 ·2H2O(cr)]},

  author       = {Xiong, Yongliang and Kirkes, Leslie Dawn and Knox, Jandi and Marrs, Cassandra and Burton, Heather Lynn},

  abstractNote = {In this work, solubility measurements regarding boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6·2H2O(cr)] from the direction of supersaturation were conducted at 22.5 ± 0.5 °C. The equilibrium constant (log10K0) for boracite in terms of the following reaction, Mg3B7O13Cl(cr) + 15H2O(l) ⇌ 3Mg2+ + 7B(OH)4– + Cl– + 2H+ is determined as -29.49 ± 0.39 (2σ) in this study. The equilibrium constant for aksaite according to the following reaction, MgB6O7(OH)6•2H2O(cr) + 9H2O(l) ⇌ Mg2+ + 6B(OH)4– + 4H+ is determined as -44.41 ± 0.41 (2σ) in this work. This work recommends a set of thermodynamic properties for aksaite at 25 °C and 1 bar as follows: ΔH$0\atop{f}$ =-6063.70 ± 4.85 kJ·mol-1, ΔG =-5492.55 ± 2.32 kJ·mol-1, and S0 = 344.62 ± 1.85 J·mol-1·K-1. Among them, ΔG$0\atop{f}$ is derived from the equilibrium constant for aksaite determined by this study; ΔH$0\atop{f}$ is from the literature, determined by calorimetry; and S0 is computed in the present work from ΔG$0\atop{f}$ and ΔH$0\atop{f}$. This investigation also recommends a set of thermodynamic properties for boracite at 25 °C and 1 bar as follows: ΔH$0\atop{f}$ =-6575.02 ± 2.25 kJ·mol-1, ΔG$0\atop{f}$ =-6178.35 ± 2.25 kJ·mol-1, and S0 = 253.6 ± 0.5 J·mol-1·K-1. Among them, ΔG$0\atop{f}$ is derived from the equilibrium constant for boracite determined by this study; S0 is from the literature, determined by calorimetry; and ΔH$0\atop{f}$ is computed in this work from ΔG$0\atop{f}$ and S0. The thermodynamic properties determined in this study can find applications in many fields. For instance, in the field of material science, boracite has many useful properties including ferroelectric and ferroelastic properties. The equilibrium constant of boracite determined in this work will provide guidance for economic synthesis of boracite in an aqueous medium. Similarly, in the field of nuclear waste management, iodide boracite [Mg3B7O13I(cr)] is proposed as a waste form for radioactive 129I. Therefore, the solubility constant for chloride boracite [Mg3B7O13Cl(cr)] will provide the guidance for the performance of iodide boracite in geological repositories. Boracite/aksaite themselves in geological repositories in salt formations may be solubility-controlling phase(s) for borate. Finally, solubility constants of boracite and aksaite will enable researchers to predict borate concentrations in equilibrium with boracite/aksaite in salt formations.},

  doi          = {10.1016/j.chemgeo.2018.02.008},

  journal      = {Chemical Geology},

  number       = C,

  volume       = 483,

  place        = {United States},

  year         = {2018},

  month        = {2}

}

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Title: Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6 ·2H2O(cr)]

Abstract

Citation Formats

Title: Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg₃B₇O₁₃Cl(cr)] and aksaite [MgB₆O₇(OH)₆ ·2H₂O(cr)]