Mathematics
Scientific paper
Jul 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985gecoa..49.1593l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 49, Issue 7, pp.1593-1601
Mathematics
7
Scientific paper
The enthalpy, Gibbs free energy, and entropies of aqueous radium species and radium solids have been evaluated from empirical data, or estimated when necessary for 25°C and 1 bar. Estimates were based on such approaches as extrapolation of the thermodynamic properties of Ca, Sr, and Ba complexes and solids plotted against cationic radii and charge to radius functions, and the use of the Fuoss or electrostatic mathematical models of ion pair formation (Langmuir, 1979). Resultant log K (assoc) and H 0 (assoc) (kcal/mol) values are: for RaOH + 0.5 and 1.1; RaCl + -0.10 and 0.50; RaCO 0 3 2.5 and 1.07; and RaSO 0 4 2.75 and 1.3. Log Ksp and H 0 (dissoc) (kcal/mol) values for RaCO 3 (c) and RaSO 4 (c) are -8.3 and -2.8, and -10.26 and -9.4, respectively. Trace Ra solid solution in salts of Pb and of the lighter alkaline earths, has been appraised based on published distribution coefficient ( D ) data, where D ~- ( mM 2+ )( N RaX )/( mRa 2+ )( N MX ) ( m and N are the aqueous molality and mole fraction of Ra and cation M in salt X , respectively. The empirical solid solution data have been used to derive both enthalpies and Gibbs free energies of solid solution of trace Ra in sulfate and carbonate minerals up to 100°C. Results show that in every case D values decrease with increasing temperature. Among the sulfate and carbonate minerals, D values decrease for the following minerals in the order: anhydrite > celestite > anglesite > barite > aragonite > strontianite > witherite > cerussite.
Langmuir Donald
Riese Arthur C.
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