A probabilistic perspective on thermodynamic parameter uncertainties: Understanding aqueous speciation of mercury
Abstract
Speciation plays an important role in determining the fate and transport of metals in terrestrial surface and subsurface systems. Equilibrium speciation modeling in aqueous systems relies on thermodynamic constants (log K values) of complexes, which are subject to uncertainties. In this study, using Monte Carlo (MC) simulations with Latin hypercube sampling (LHS) we systematically analyze the propagation of thermodynamic constant uncertainty through speciation modeling of an inorganic mercury-sulfide-chloride-water system. We find that seemingly small variances of the input log K normal distributions can lead to output species concentrations spanning multiple orders of magnitude, with highly skewed probability distributions. When equilibrium with mineral metacinnabar (β-HgS(s)) is neglected, the relative uncertainty of each output species is strongly positively correlated with the skewness of its concentration probability distribution, i.e., the lowest uncertainty occurs when the species concentration probability distribution is the most negatively skewed as its concentration approaches the total element concentration limit. The highest uncertainty in the identity of dominant species is located around species equivalence points. For cases where the mineral equilibrium is included, we derive analytical probability density functions for the log concentrations of all major species in the system. The mineral log K uncertainty is found to be anmore »
- Authors:
-
[1];
[2];
[2];
[2];
[3]
- Univ. of Tennessee, Knoxville, TN (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Publication Date:
- Research Org.:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- OSTI Identifier:
- 1558553
- Alternate Identifier(s):
- OSTI ID: 1558177
- Grant/Contract Number:
- AC05-00OR22725; SC0016478
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Geochimica et Cosmochimica Acta
- Additional Journal Information:
- Journal Volume: 263; Journal Issue: C; Journal ID: ISSN 0016-7037
- Publisher:
- Elsevier; The Geochemical Society; The Meteoritical Society
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 58 GEOSCIENCES; 97 MATHEMATICS AND COMPUTING; Equilibrium speciation; Log K uncertainty; Mercury; Sulfide; Probability distribution; Metacinnabar
Citation Formats
Guo, Luanjing, Painter, Scott L., Brooks, Scott C., Parks, Jerry M., and Smith, Jeremy C. A probabilistic perspective on thermodynamic parameter uncertainties: Understanding aqueous speciation of mercury. United States: N. p., 2019.
Web. doi:10.1016/j.gca.2019.07.053.
Guo, Luanjing, Painter, Scott L., Brooks, Scott C., Parks, Jerry M., & Smith, Jeremy C. A probabilistic perspective on thermodynamic parameter uncertainties: Understanding aqueous speciation of mercury. United States. https://doi.org/10.1016/j.gca.2019.07.053
Guo, Luanjing, Painter, Scott L., Brooks, Scott C., Parks, Jerry M., and Smith, Jeremy C. Tue .
"A probabilistic perspective on thermodynamic parameter uncertainties: Understanding aqueous speciation of mercury". United States. https://doi.org/10.1016/j.gca.2019.07.053. https://www.osti.gov/servlets/purl/1558553.
@article{osti_1558553,
title = {A probabilistic perspective on thermodynamic parameter uncertainties: Understanding aqueous speciation of mercury},
author = {Guo, Luanjing and Painter, Scott L. and Brooks, Scott C. and Parks, Jerry M. and Smith, Jeremy C.},
abstractNote = {Speciation plays an important role in determining the fate and transport of metals in terrestrial surface and subsurface systems. Equilibrium speciation modeling in aqueous systems relies on thermodynamic constants (log K values) of complexes, which are subject to uncertainties. In this study, using Monte Carlo (MC) simulations with Latin hypercube sampling (LHS) we systematically analyze the propagation of thermodynamic constant uncertainty through speciation modeling of an inorganic mercury-sulfide-chloride-water system. We find that seemingly small variances of the input log K normal distributions can lead to output species concentrations spanning multiple orders of magnitude, with highly skewed probability distributions. When equilibrium with mineral metacinnabar (β-HgS(s)) is neglected, the relative uncertainty of each output species is strongly positively correlated with the skewness of its concentration probability distribution, i.e., the lowest uncertainty occurs when the species concentration probability distribution is the most negatively skewed as its concentration approaches the total element concentration limit. The highest uncertainty in the identity of dominant species is located around species equivalence points. For cases where the mineral equilibrium is included, we derive analytical probability density functions for the log concentrations of all major species in the system. The mineral log K uncertainty is found to be an important contributor to all output concentration uncertainties. The analysis of combined effects of both pH and total sulfide concentration on output concentration uncertainties shows that high concentration uncertainties occur under highly sulfidic alkaline conditions and low uncertainties at low pH and sulfide concentrations. Finally, an analysis as presented here can distinguish between conditions that require a full uncertainty analysis and those for which the classical deterministic speciation modeling suffices.},
doi = {10.1016/j.gca.2019.07.053},
journal = {Geochimica et Cosmochimica Acta},
number = C,
volume = 263,
place = {United States},
year = {Tue Aug 06 00:00:00 EDT 2019},
month = {Tue Aug 06 00:00:00 EDT 2019}
}
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Figures / Tables:
Table 1: Thermodynamic data including the mean (μ) and standard deviation (σ) values of Gaussian distributions for log K of Hg-containing species for the Hg(II)-S(-II)-Cl-H2O solution system at I = 0 and 25 °C.