Oxygen and Hydrogen Isotope Partitioning Between Water Liquid and Vapor at Elevated Temperatures.

摘要

Oxygen and hydrogen isotope fractionation factors ((alpha)(sub (ell)-v)(sup O) and (alpha)(sub (ell)-v)(sup D)) between liquid water and water vapor have been calculated from vapor pressure ratio measurements and equations of state over the temperature range of 0 to 370C. These data are compared to the liquid-vapor fractionation factors determined by direct mass spectral measurements. The values for (alpha)(sub (ell)-v)(sup D) derived from the vapor pressure ratios are in close agreement with the experimental mass spectral measurements from 0 to 300C when fugacity coefficient and molar volume corrections are used. Deviations from the direct measurements above 0 to 300C are due to inadequacies in either (1) the magnitude of the molar volume correction for D2O near the critical point, (2) the assumption of ideal mixing of the isotopic gases and liquids, and/or (3) the selection of 1.91 as the disproportionation factor for the formation of HDO. On the other hand, the (alpha)(sub (ell)-v)(sup O) values derived form vapor pressure data (no fugacity or molar volume corrections) agree closely with low-temperature direct measurement data, pass through some of Bottinga's (1968) high temperature results, and extrapolate smoothly to (alpha)(sub (ell)-v)(sup O) = 0 at the critical temperature as is required by thermodynamics. This behavior coupled with the fact that Bottinga's (1968) oxygen isotope results exhibit a large scatter, indicated that liquid-vapor oxygen isotope fractionation factors based on vapor pressure measurements should be applied to high-temperature geothermal systems rather than the direct mass spectral data. 15 refs., 2 figs., 1 tab.