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Title: Enthalpies of formation of polyhalite: A mineral relevant to salt repository

Journal Article · · Journal of Chemical Thermodynamics
 [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Polyhalite is an important coexisting mineral with halite in salt repositories for nuclear waste disposal, such as Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico. The thermal stability of this mineral is a key knowledge in evaluating the integrity of a salt repository in the long term, as water may release due to thermal decomposition of polyhalite. Previous studies on structural evolution of polyhalite at elevated temperatures laid the basis for detailed calorimetric measurements. Using high-temperature oxide-melt drop-solution calorimetry at 975 K with sodium molybdate as the solvent, we have determined the standard enthalpies of formation from constituent sulfates (ΔH°f,sul), oxides (ΔH°f,ox) and elements (ΔH°f,ele) of a polyhalite sample with the composition of K2Ca2Mg(SO4)4·1.95H2O from the Salado formation at the WIPP site. The obtained results are: ΔH°f,sul = -152.5 ± 5.3 kJ/mol, ΔH°f,ox = -1926.1 ± 10.5 kJ/mol, and ΔH°f,ele = -6301.2 ± 9.9 kJ/mol. Furthermore, based on the estimated formation entropies of polyhalite, its standard Gibbs free energy of formation has been derived to be in the range of -5715.3 ± 9.9 kJ/mol to -5739.3 ± 9.9 kJ/mol. In conclusion, these determined thermodynamic properties provide fundamental parameters for modeling the stability behavior of polyhalite in salt repositories.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Laboratory Directed Research and Development (LDRD) Program
Grant/Contract Number:
AC52-06NA25396; 237546
OSTI ID:
1364549
Alternate ID(s):
OSTI ID: 1550156
Report Number(s):
LA-UR-17-20042
Journal Information:
Journal of Chemical Thermodynamics, Vol. 114; ISSN 0021-9614
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 17 works
Citation information provided by
Web of Science

References (18)

The Dehydration of Polyhalite journal June 1963
First-principles study of anhydrite, polyhalite and carnallite journal February 2014
Separations and Transmutation Criteria to Improve Utilization of a Geologic Repository journal April 2006
Charge-Coupled Substituted Garnets (Y 3– x Ca 0.5 x M 0.5 x )Fe 5 O 12 (M = Ce, Th): Structure and Stability as Crystalline Nuclear Waste Forms journal March 2015
The Thermal Decomposition of Polyhalite K2SO4 · MgSO4 · 2 CaSO4 · 2 H2O journal January 1996
Thermal behavior of polyhalite: a high-temperature synchrotron XRD study journal September 2016
Hydrous Mineral Dehydration Around Heat-Generating Nuclear Waste in Bedded Salt Formations journal May 2015
The prediction of mineral solubilities in natural waters: the NaKMgCaClSO4H2O system from zero to high concentration at 25° C journal July 1980
The prediction of mineral solubilities in natural waters: The Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O system to high ionic strengths at 25°C journal April 1984
Enthalpy of formation of natural polyhalite journal July 2016
Polyhalite Application to Sorghum-Sudangrass and Leaching in soil Columns journal January 1991
Energetics of metastudtite and implications for nuclear waste alteration journal November 2014
Crystal Structure and Thermodynamic Stability of Ba/Ti‐Substituted Pollucites for Radioactive Cs/Ba Immobilization journal April 2015
Progress and new directions in high temperature calorimetry revisited journal April 1997
On the thermochemistry of the solid solution between jarosite and its chromate analog journal November 2003
Thermodynamics of formation of coffinite, USiO 4 journal May 2015
Thermochemistry of some pyroxenes and related compounds journal October 1976
Standard Absolute Entropy, , Values from Volume or Density. 1. Inorganic Materials journal December 2003

Cited By (2)

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