The activity-composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions: I. vapor-liquid water equilibration of single salt solutions from 50 to 100[degrees]C

Journal Article · Tue Jun 01 04:00:00 EDT 1993 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(93)90391-9· OSTI ID:6265655

Horita, J; Wesolowski, D J; Cole, D R ^[1]

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1. Oak Ridge National Laboratory, TN (United States)

The differences between oxygen and hydrogen isotope activity and composition ratios of water in single salt solutions (NaCl, KCl, MgCl[sub 2], CaCl[sub 2], Na[sub 2]SO[sub 4], and MgSO[sub 4]) were determined by means of a vapor-liquid water equilibration method over the temperature range of 50 to 100[degrees]C. A parallel equilibration technique of pure water and salt solutions with the same isotopic composition at the same experimental conditions enabled the precise determination of the isotope salt effects. Hydrogen isotope activity ratios of all of the salt solutions studied were appreciably higher than composition ratios. That is, D/H ratio of water vapor in isotope equilibrium with a solution increases as salt is added to the solution. Magnitudes of the hydrogen isotope effects are in the order CaCl[sub 2] [ge] MgCl[sub 2] > MgSO[sub 4] > KCl [approximately] NaCl > Na[sub 2]SO[sub 4] at the same molality. Except for KCl solutions at 50[degrees]C, oxygen isotope activity ratios in the solutions were lower than, or very close to, the composition ratios. The isotope effects observed are all linear with the molalities of the salt solutions, and either decrease with temperature or are almost constant over the temperature range. Salt solutions of divalent cations (Ca and Mg) exhibited oxygen isotope effects much larger than those of monovalent cations (Na and K). Magnitudes of the oxygen isotope effects in NaCl solutions, and of the hydrogen isotope effects in Na[sub 2]SO[sub 4] and MgSO[sub 4] solutions, may increase from 50 to 100[degrees]C. Our results agree with most of those from the literature near room temperature, but are at notable variance with those by Truesdell (1974) around 100[degrees]C. The results in this study and the literature data near room temperature were satisfactorily fitted to simple equations as a function of concentration of the salt solutions and temperature.

• OSTI ID: 6265655
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 57:12; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ACTIVITY LEVELS
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
AQUEOUS SOLUTIONS
CALCIUM CHLORIDES
CALCIUM COMPOUNDS
CALCIUM HALIDES
CHEMICAL ANALYSIS
CHLORIDES
CHLORINE COMPOUNDS
DISPERSIONS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPE RATIO
ISOTOPES
MAGNESIUM CHLORIDES
MAGNESIUM COMPOUNDS
MAGNESIUM SULFATES
MIXTURES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
POTASSIUM CHLORIDES
POTASSIUM COMPOUNDS
QUANTITATIVE CHEMICAL ANALYSIS
SODIUM CHLORIDES
SODIUM COMPOUNDS
SODIUM SULFATES
SOLUTIONS
SULFATES
SULFUR COMPOUNDS
TEMPERATURE DEPENDENCE