State of rare earth elements uranyl germanates in aqueous solutions

Uranyl germanates with formula M III (HGeUO 6 ) 3 ·8H 2 O (M III –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 M III (HGeUO 6 ) 3 ·8H 2 O destruct with GeO 2 , M III (OH) 3 and uranates formation. The compounds solubility changes from 10 −7 M to 10 −3 M in the investigated pH range. The M III (HGeUO 6 ) 3 ·8H 2 O 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 lg K S dependence as function of M III ionic radius has minimum at Gd(HGeUO 6 ) 3 ·8H 2 O (lg K S (La) = −51.40; lg K S (Gd) = −51.98; lg K S (Lu) = −51.28).