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Title: Conversion and optimization of the parameters from an extended form of the ion-interaction model for Ca(NO3)2(aq) and NaNO3(aq) to those of the standard Pitzer model, and an assessment of the accuracy of the parameter temperature representations

Abstract

The electrolytes Ca(NO{sub 3}){sub 2}(aq) and NaNO{sub 3}(aq) are both extremely soluble but differ in several important respects. Ca(NO{sub 3}){sub 2}(aq) has complex behavior at low ionic strengths and forms several thermodynamically stable and metastable solid phases, whereas NaNO{sub 3}(aq) forms only an anhydrous solid phase. The thermodynamic properties of both have previously been modeled using extended Pitzer ion-interaction models that include higher-order virial terms, in addition to those of the standard Pitzer model. The parameters of the original Pitzer model, however, are often needed for thermodynamic modeling calculations. In this paper we convert the parameters of the extended ion-interaction models for Ca(NO{sub 3}){sub 2}(aq) and NaNO{sub 3}(aq) to the standard Pitzer model using an extension of the methodology previously described by Rard and Wijesinghe [J. Chem. Thermodynamics 35 (2003) 439.473]. In this variant, the exponential coefficient {alpha}{sub 1}{sup P} of Pitzer's model is also optimized to yield the most accurate overall representation of the osmotic coefficients {phi} over the ionic strength and temperature ranges of interest. The optimal values of {alpha}{sub 1}{sup P} = 0.87 kg{sup 1/2} {center_dot} mol{sup -1/2} for Ca(NO{sub 3}){sub 2}(aq) and {alpha}{sub 1}{sup P} = 1.43 kg{sup 1/2} {center_dot} mol{sup -1/2} for NaNO{sub 3}(aq) aremore » smaller than the value {alpha}{sub 1}{sup P} = 2.00 kg{sup 1/2} {center_dot} mol{sup -1/2} normally used for electrolytes of these valence types. In both cases, the accuracy of the osmotic coefficients predicted by the standard Pitzer model was nearly equal to that of the extended Pitzer model up to the solubility limit for T = (298.15 to 423.15) K. This result is consistent with the findings of Rard, Wijesinghe, and Wolery [J. Chem. Eng. Data 49 (2004) 1127-1140] who obtained a substantial improvement in model accuracy for Mg(NO{sub 3}){sub 2}(aq) at T = 298.15 K by optimizing this parameter. The use of a temperature dependent {alpha}{sub 1}{sup P}that is optimal at each temperature did not yield a significant improvement in accuracy over using a constant optimal value. We also investigated the impact of choosing different temperature functions to develop temperature correlations for the Pitzer parameters. Higher-order temperature functions were needed for evaluations with solubility limited maximum ionic strength compared to evaluations performed at constant maximum ionic strength over the temperature range, especially for Ca(NO{sub 3}){sub 2}(aq) because of its more complex thermodynamic behavior. Accurate temperature correlations are presented for both Ca(NO{sub 3}){sub 2}(aq) and NaNO{sub 3}(aq).« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
15020076
Report Number(s):
UCRL-JRNL-208876
Journal ID: ISSN 0021-9614; JCTDAF; TRN: US200519%%160
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Thermodynamics
Additional Journal Information:
Journal Volume: 37; Journal Issue: 11; Journal ID: ISSN 0021-9614
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 58 GEOSCIENCES; ACCURACY; ELECTROLYTES; OPTIMIZATION; SIMULATION; SOLUBILITY; THERMODYNAMIC PROPERTIES; THERMODYNAMICS; VALENCE

Citation Formats

Wijesinghe, A M, and Rard, J A. Conversion and optimization of the parameters from an extended form of the ion-interaction model for Ca(NO3)2(aq) and NaNO3(aq) to those of the standard Pitzer model, and an assessment of the accuracy of the parameter temperature representations. United States: N. p., 2004. Web.
Wijesinghe, A M, & Rard, J A. Conversion and optimization of the parameters from an extended form of the ion-interaction model for Ca(NO3)2(aq) and NaNO3(aq) to those of the standard Pitzer model, and an assessment of the accuracy of the parameter temperature representations. United States.
Wijesinghe, A M, and Rard, J A. 2004. "Conversion and optimization of the parameters from an extended form of the ion-interaction model for Ca(NO3)2(aq) and NaNO3(aq) to those of the standard Pitzer model, and an assessment of the accuracy of the parameter temperature representations". United States. https://www.osti.gov/servlets/purl/15020076.
@article{osti_15020076,
title = {Conversion and optimization of the parameters from an extended form of the ion-interaction model for Ca(NO3)2(aq) and NaNO3(aq) to those of the standard Pitzer model, and an assessment of the accuracy of the parameter temperature representations},
author = {Wijesinghe, A M and Rard, J A},
abstractNote = {The electrolytes Ca(NO{sub 3}){sub 2}(aq) and NaNO{sub 3}(aq) are both extremely soluble but differ in several important respects. Ca(NO{sub 3}){sub 2}(aq) has complex behavior at low ionic strengths and forms several thermodynamically stable and metastable solid phases, whereas NaNO{sub 3}(aq) forms only an anhydrous solid phase. The thermodynamic properties of both have previously been modeled using extended Pitzer ion-interaction models that include higher-order virial terms, in addition to those of the standard Pitzer model. The parameters of the original Pitzer model, however, are often needed for thermodynamic modeling calculations. In this paper we convert the parameters of the extended ion-interaction models for Ca(NO{sub 3}){sub 2}(aq) and NaNO{sub 3}(aq) to the standard Pitzer model using an extension of the methodology previously described by Rard and Wijesinghe [J. Chem. Thermodynamics 35 (2003) 439.473]. In this variant, the exponential coefficient {alpha}{sub 1}{sup P} of Pitzer's model is also optimized to yield the most accurate overall representation of the osmotic coefficients {phi} over the ionic strength and temperature ranges of interest. The optimal values of {alpha}{sub 1}{sup P} = 0.87 kg{sup 1/2} {center_dot} mol{sup -1/2} for Ca(NO{sub 3}){sub 2}(aq) and {alpha}{sub 1}{sup P} = 1.43 kg{sup 1/2} {center_dot} mol{sup -1/2} for NaNO{sub 3}(aq) are smaller than the value {alpha}{sub 1}{sup P} = 2.00 kg{sup 1/2} {center_dot} mol{sup -1/2} normally used for electrolytes of these valence types. In both cases, the accuracy of the osmotic coefficients predicted by the standard Pitzer model was nearly equal to that of the extended Pitzer model up to the solubility limit for T = (298.15 to 423.15) K. This result is consistent with the findings of Rard, Wijesinghe, and Wolery [J. Chem. Eng. Data 49 (2004) 1127-1140] who obtained a substantial improvement in model accuracy for Mg(NO{sub 3}){sub 2}(aq) at T = 298.15 K by optimizing this parameter. The use of a temperature dependent {alpha}{sub 1}{sup P}that is optimal at each temperature did not yield a significant improvement in accuracy over using a constant optimal value. We also investigated the impact of choosing different temperature functions to develop temperature correlations for the Pitzer parameters. Higher-order temperature functions were needed for evaluations with solubility limited maximum ionic strength compared to evaluations performed at constant maximum ionic strength over the temperature range, especially for Ca(NO{sub 3}){sub 2}(aq) because of its more complex thermodynamic behavior. Accurate temperature correlations are presented for both Ca(NO{sub 3}){sub 2}(aq) and NaNO{sub 3}(aq).},
doi = {},
url = {https://www.osti.gov/biblio/15020076}, journal = {Journal of Chemical Thermodynamics},
issn = {0021-9614},
number = 11,
volume = 37,
place = {United States},
year = {Tue Dec 21 00:00:00 EST 2004},
month = {Tue Dec 21 00:00:00 EST 2004}
}