Study on physicochemical states of uranium, thorium, and radium isotopes in some radio-active minerals by the leaching method

A series of leaching experiments with dilute HCl and BaCl2 aqueous solutions were carried out on radioactive minerals, uraninite and samarskite. The leachates were analyzed for uranium, thorium, and radium isotopes. The contribution of alpha-recoil ejection to the extraction of 223Ra from uraninite into 0.0008 M BaCl2 aqueous solution was small compared with that of chemical process. The amounts of uranium and thorium leached from a heated sample of uraninite were smaller than those from an unheated sample, while the amounts of actinium and radium were larger. The 234U/238U activity ratio in leachate from the heated sample was 0.99 +- 0.01, while that in leachate from the unheated sample was 1.23 +- 0.01. The observed isotopic fractionations of uranium, thorium, and radium were attributed to the difference in physicochemical state between the isotopes in the minerals. The difference is explained in terms of (1) damage due to alpha-recoil displacement, (2) annealing, and (3) the difference in oxidation states between 238U and 234U. (orig.)