Complexation of uranyl(VI) with polyoxometalates in aqueous solutions

Abstract

Solvent extraction techniques were applied to determine the stability constants of UO 2 2+ with the polyoxometalates: heteropoly molybdates, CrMo 6O 24H 6 3−, IMo 6O 24 5−, TeMo 6O 24 6−, and MnMo 9O 32 6−; isopoly anions, V 10O 28 6− and Mo 7O 24 6−. The stability constants, log β, of 1:1 complexes obtained for these above anions, are in the range of 2–4. The second complexation constant was obtained for TeMo 6O 24 6−. The log β 1 values decrease for most of the polyoxometalates in the sequence: log β 1(Th 4+)>log β 1(Eu 3+)>log β 1(UO 2 2+)≥log β 1 (Ca 2+). The relatively weak position of UO 2 2+ compared to Eu(III) complexation indicates that the steric effect of the uranyl oxygens is important.