Calculation of multicomponent ionic diffusion from zero to high concentration: I. The system Na-K-Ca-Mg-Cl-SO sub 4 -H sub 2 O at 25 degree C
Journal Article
·
· Geochimica et Cosmochimica Acta; (USA)
- Univ. of California, San Diego, La Jolla (USA)
A model is described for the calculation of diffusion coefficients and other vector transport processes for the six component seawater system Na-K-Ca-Mg-Cl-SO{sub 4}-H{sub 2}O at 25{degree}C, from low to high ionic strengths. The model is based upon an extension of the empirical equations of Miller (1967a) for the calculation of Onsager phenomenological coefficients and upon an accurate thermodynamic model utilizing the ion-interaction method of Pitzer (1979) and coworkers. The necessary parameters for the activity derivatives and the Onsager coefficients may be evaluated from binary and ternary data. Additional data are not required for applications in more complex systems. The model is also used to calculate diffusion coefficients at the composition of seawater. Our calculated values are supported by the measured conductivities, partial molal conductivities, and mutual diffusion coefficients of neutral components at seawater composition. The use of tracer diffusion coefficients is also discussed. The use of such coefficients in simplified forms of Fick's law is shown to be fundamentally inapplicable for electrolyte systems even at infinite dilution. When used in more comprehensive electrolyte diffusion models, isotope-isotope coupling effects complicate the use of tracer diffusion coefficients, especially at higher concentrations.
- OSTI ID:
- 5949827
- Journal Information:
- Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 55:1; ISSN GCACA; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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