Complexation studies of UO₂²⁺with humic acid at low metal ion concentrations by indirect speciation methods

Abstract

The complexation of uranium(VI) with humic acid was studied at pH 4 and 5 in 0.1 mol/l and 4.10 -3 mol/l NaClO 4 by indirect speciation methods, i.e., electrophoretic ion focusing (EIF) and anion exchange (AE). The concentration range investigated was from 10 -8 mol/l to 5 · 10 -6 mol/l for the uranyl ion and from 1 to 2.5 mg/l for the humic acid. The experimental data obtained by AE are well described by the complexation reaction involving the charge neutralization of the uranyl ion with two exchanging sites of humic acid. The complexation constant calculated by taking the loading capacity values into account is found to be log β = 6.08 ± 0.15. Concerning EIF, an interfering interaction between the humic acid and U(VI), occurring under the effect of the electric field, is evident and makes this separation technique not well suitable for the investigation of the U(VI):humic acid system.