skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Experimental determination of solubilities of magnesium borates: Solubility constants of boracite [Mg 3B 7O 13Cl(cr)] and aksaite [MgB 6O 7(OH) 6 ·2H 2O(cr)]

Abstract

In this work, solubility measurements regarding boracite [Mg 3B 7O 13Cl(cr)] and aksaite [MgB 6O 7(OH) 6·2H 2O(cr)] from the direction of supersaturation were conducted at 22.5 ± 0.5 °C. The equilibrium constant (log 10K 0) for boracite in terms of the following reaction, Mg 3B 7O 13Cl(cr) + 15H 2O(l) ⇌ 3Mg 2+ + 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, MgB 6O 7(OH) 6•2H 2O(cr) + 9H 2O(l) ⇌ Mg 2+ + 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 S 0 = 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 S 0 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 S 0 = 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; S 0 is from the literature, determined by calorimetry; and ΔH$$0\atop{f}$$ is computed in this work from ΔG$$0\atop{f}$$ and S 0. 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 [Mg 3B 7O 13I(cr)] is proposed as a waste form for radioactive 129I. Therefore, the solubility constant for chloride boracite [Mg 3B 7O 13Cl(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:
ORCiD logo [1];  [1];  [1];  [1];  [1]
  1. Sandia National Laboratories (SNL), Carlsbad, NM (United States). Carlsbad Programs Group
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Environmental Management (EM)
OSTI Identifier:
1429647
Report Number(s):
SAND-2017-10729J
Journal ID: ISSN 0009-2541; 657530
Grant/Contract Number:  
AC04-94AL85000; NA0003525
Resource Type:
Journal Article: 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.
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. doi:10.1016/j.chemgeo.2018.02.008.
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. doi:10.1016/j.chemgeo.2018.02.008.
@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 = {Sat Feb 03 00:00:00 EST 2018},
month = {Sat Feb 03 00:00:00 EST 2018}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on February 3, 2019
Publisher's Version of Record

Save / Share: