CHEMICAL CONSEQUENCES OF NUCLEAR TRANSMUTATIONS IN MINERALS .2. BEHAVIOR OF U-234 AND U-238 DURING INCONGRUENT DISSOLUTION OF NATURAL PHOSPHATE AND SILICATE

The behavior of U-234 and U-238 during incongruent dissolution of minerals of pegmatite origin (orthite, monazite, xenotime) is studied. The relative content of U(IV) and U(VI) in the resulting extracts and the relative U-234/U-238 alpha-activity ratio in each of the oxidation states are determined. The difference in the behavior of U isotopes in phosphate and silicate minerals is found. The observed isotope effects are explained on the basis of a multiphase mineral structural model. The conclusion is made that fractionation of U isotopes in nature (Cherdyntsev-Chalov effect) includes a redistribution of U-234 between various components of the mineral system or rock as one of the steps.