Physical chemistry of uranophosphates and uranoarsenates of lanthanides

Results of experimental investigation of heterogeneous equilibria LnCl3 (solution in H2O) - HP(As)UO6·4H2O (crystal) and HCl (solution in H2O) - Ln[P(As)UO6]3·nH2O (crystal), where Ln=La, Gd, Lu, are presented. Standard Gibbs formation functions are calculated taking obtained for Ln[P(As)UO6]3·nH2O results as a basis. Isobaric heat capacity in 80-300 K temperature interval are measured for La(PUO6)3·14H2O and La(AsUO6)3·15H2O using the methods of calorimetry. For these compounds at 298.15 K formation enthalpies are determined and absolute entropy, entropy and formation Gibbs functions are calculated. Comparison of results obtained on the basis of data on heterogeneous equilibria with ones on direct calorimetric measurements are done