Experimental determination of the activity-composition relations and phase equilibria of H2O-CO2-NaCl fluids at 500°C, 500 bars

L. M. Anovitz; T. C. Labotka; J. G. Blencoe; J. Horita

doi:10.1016/j.gca.2003.12.012

Experimental determination of the activity-composition relations and phase equilibria of H₂O-CO₂-NaCl fluids at 500°C, 500 bars

L. M. Anovitz, T. C. Labotka, J. G. Blencoe, J. Horita

Geochemistry & Interfacial Science

Research output: Contribution to journal › Article › peer-review

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Abstract

An understanding of the activity-composition (a-X) relations and phase equilibria of halite-bearing, mixed-species supercritical fluids is critically important in many geological and industrial applications. We have performed experiments on H₂O-CO₂-NaCl fluids at 500°C, 500 bar, to obtain accurate and precise data on their a-X relations and phase equilibria. Two kinds of experiments were performed. First, H₂O-CO₂-NaCl samples were reacted at fixed activities of H₂O = 0.078, 0.350, 0.425, 0.448, 0.553, 0.560, 0.606, 0.678, 0.798, 0.841, and 0.935 to define the tie lines of known H₂O activity in the halite-vapor and vapor-brine fields. Results indicate that fluids with all but the last of these H₂O activities lie in the vapor-halite two-phase region and that a fluid with a _H2O = 0.841 has a composition close to the three-phase (vapor + brine + halite) field. A second set of experiments was performed to determine the solubility of NaCl in parts of the system in equilibrium with halite. Data from these experiments suggest that the vapor corner of the three-phase field lies at H₂O contents above X_H2O = 0.58 and X_NaCl = 0.06, and below X_H2O = 0.75 and X_NaCl = 0.06, which is a significantly more H₂O-rich composition than indicated by existing thermodynamic models.

Original language	English
Pages (from-to)	3557-3567
Number of pages	11
Journal	Geochimica et Cosmochimica Acta
Volume	68
Issue number	17
DOIs	https://doi.org/10.1016/j.gca.2003.12.012
State	Published - Sep 1 2004

Funding

We thank Leonya Aranovich, John Ferry, and an anonymous reviewer for their comments and insightful critiques of an earlier version of this paper. Funding for the research was primarily provided by the National Science Foundation under grant number EAR-0106990. Additional funding for the research was provided by (1) the Division of Engineering and Geosciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by UT-Battelle Corporation, and by (2) the U. S. Department of Energy, Environmental Management Science Program (TTP OR17-SP22), under contract number DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by UT-Battelle Corporation.

Funders	Funder number
Division of Engineering and Geosciences
Office of Basic Energy Sciences
U. S. Department of Energy, Environmental Management Science Program	TTP OR17-SP22
UT-Battelle Corporation
National Science Foundation	EAR-0106990
U.S. Department of Energy	DE-AC05-96OR22464
Oak Ridge National Laboratory

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title = "Experimental determination of the activity-composition relations and phase equilibria of H2O-CO2-NaCl fluids at 500°C, 500 bars",

abstract = "An understanding of the activity-composition (a-X) relations and phase equilibria of halite-bearing, mixed-species supercritical fluids is critically important in many geological and industrial applications. We have performed experiments on H2O-CO2-NaCl fluids at 500°C, 500 bar, to obtain accurate and precise data on their a-X relations and phase equilibria. Two kinds of experiments were performed. First, H2O-CO2-NaCl samples were reacted at fixed activities of H2O = 0.078, 0.350, 0.425, 0.448, 0.553, 0.560, 0.606, 0.678, 0.798, 0.841, and 0.935 to define the tie lines of known H2O activity in the halite-vapor and vapor-brine fields. Results indicate that fluids with all but the last of these H2O activities lie in the vapor-halite two-phase region and that a fluid with a H2O = 0.841 has a composition close to the three-phase (vapor + brine + halite) field. A second set of experiments was performed to determine the solubility of NaCl in parts of the system in equilibrium with halite. Data from these experiments suggest that the vapor corner of the three-phase field lies at H2O contents above XH2O = 0.58 and XNaCl = 0.06, and below XH2O = 0.75 and XNaCl = 0.06, which is a significantly more H2O-rich composition than indicated by existing thermodynamic models.",

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Experimental determination of the activity-composition relations and phase equilibria of H₂O-CO₂-NaCl fluids at 500°C, 500 bars

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