Radium Uptake by Recrystallized Gypsum: An Incorporation Study

Batch experiments of 226Ra uptake by recrystallized gypsum CaSO4.2H2O(s), monitored over 200 days, have shown that the published value for the distribution coefficient of 226Ra between gypsum and an aqueous phase, 0.03 (Gnanapragasam and Lewis, 1995), is an upper limit. This suggests that this value needs to be confirmed. A solid solution between gypsum and radium sulfate (Ca,Ra)SO4.2H2O(s) cannot be considered per se, which is not surprising considering gypsumʹs high solubility product (lg Ks = -4.58) and the ionic radius of VIIIRa (1.48 إ), when compared to that of VIIICa (1.12 إ).