State of rare earth elements uranyl germanates in aqueous solutions

Uranyl germanates with formula MIII(HGeUO6)3·8H2O (MIII–La–Lu, Y) were investigated in aqueous solutions in the pH range of 0–14. The compounds preserve own structure at pH 3.0–12.0. Out of this interval MIII(HGeUO6)3·8H2O destruct with GeO2, MIII(OH)3 and uranates formation. The compounds solubility changes from 10−7M to 10−3M in the investigated pH range. The MIII(HGeUO6)3·8H2O solubility products(K S ), standard formation Gibbs function and solubility curves were calculated, speciation diagrams of U(VI), Ge(IV) and M(III) in saturated solutions and solids were plotted. The lgK S dependence as function of MIII ionic radius has minimum at Gd(HGeUO6)3·8H2O (lgK S (La) = −51.40; lgK S (Gd) = −51.98; lgK S (Lu) = −51.28).