Simultaneous Calculation of Chemical and Isotope Equilibria Using the GEOCHEQ_Isotope Software: Carbon Isotopesстатья
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Дата последнего поиска статьи во внешних источниках: 28 января 2019 г.
Аннотация:Abstract⎯The program package GEOCHEQ_Isotope was developed for the simultaneous calculation of
chemical and isotope equilibria in hydrothermal and hydrochemical systems by the method of Gibbs free
energy minimization. It utilizes the formalism of the β-factor and is a modification of the GEOCHEQ software,
which was designed to calculate chemical equilibria. An algorithm was proposed for the calculation of
the Gibbs free energy of formation of a rare isotopologue, G*(P, T), from the Gibbs free energy of formation
of the main isotopologue, the β-factor of this substance, and the mass ratio of the rare and main isotopes of
the element. The ideal mixing of isotopes was assumed. The temperature dependence of the β-factor was unified
as a polynomial in reciprocal absolute temperature. The implementation of the software and an appropriate
database was illustrated by the example of carbon isotopes. The available information on carbon isotope
equilibria involving geochemically important compounds was critically analyzed, and temperature
dependences of their β-factors were correspondingly optimized. The thermodynamic database was updated
by adding information on the temperature dependence of β-factors specified by eight polynomial coefficients
for each substance. The use of the GEOCHEQ_Isotope was exemplified calculating the equilibrium compositions
of phases and carbon isotope fractionations in carbonate hydrothermal systems with and without iron
at pH ranging from 4 to 11.