Solution Equilibria for Uranium Ore Processing: The BaSO _{4}H _{2}SO _{4}H _{2}O System and the RaSO _{4}H _{2}SO _{4}H _{2}O System
Abstract
A radiotracer determination of the solubility of BaSO _{4} in H _{2}SO _{4}H _{2}O mixtures was undertaken at temperatures of 25°C and 60°C. These were subsequently modelled using the Pitzer model for the activity coefficients, and estimates were made for Ba ^{2+}SO _{4}^{2} and Ba ^{2+}HSO _{4 } interaction parameters. The final model yields an excellent description of the solubility of BaSO _{4} in H _{2}SO _{4}H _{2}O mixtures up to 6 mol/kg and at both 25°C and 60°C. The logarithm of the thermodynamic solubility product constant (log K_{sp}) for barite obtained by regression analysis was 10.02 ± 0.02 at 25°C and 9.68 ± 0.01 at 60°C. The values of the ion association constant derived from these data are 2.49 ± 0.03 at 25°C and 2.55 ± 0.1 at 60°C. The enthalpy of dissolution for BaSO _{4} was estimated to be 17.6 ± 0.2 kJ mol ^{1}. Literature solubility data for the RaSO _{4}H _{2}SO _{4}H _{2}O system have also been interpreted, using the Pitzer model for the necessary activity coefficients. The logarithm of the thermodynamic solubility product constant (log K_{sp}) for radium sulfate obtained was 10.21 ± 0.06 at 25°C, while the value of the ion association constant derived is 2.76 ± 0.05 at 25°C. The high negative value of the Pitzer parameter β ^{2} obtained by regression analysis of these data suggests that the explicit recognition of a RaSO _{4}(aq) ion association species is to be preferred in this case.
 Publication:

Geochimica et Cosmochimica Acta
 Pub Date:
 January 1998
 DOI:
 10.1016/S00167037(97)003207
 Bibcode:
 1998GeCoA..62...15P