Elastic strain energy and the distribution coefficient of radium in solid solutions with calcium salts

Distribution coefficients for radium in heterogeneous equilibrium with gypsum and calcite were determined with solid solutions containing Ra in the mole fraction range 10(-10) to 10(-7) at 25 +/- 3 degrees C. The correlation approach of Langmuir and Riese for predicting empirical distribution coefficients is improved when a term for the elastic strain energy is included for the case in which the Ca atom is replaced by the larger Ra atom. A method is described in which distribution coefficients can be estimated and applied in geochemical equilibrium models to account for Ra incorporation into sulfates, carbonates, and halides when radium-containing wastes are chemically treated. It is suggested that the method may have application to radium-containing minerals, in general.