Plutonium (IV) complexation with citric and alginic acids at low Pu(T) concentrations

Kantar C. , HONEYMAN B.

RADIOCHIMICA ACTA, vol.93, no.12, pp.757-766, 2005 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 93 Issue: 12
  • Publication Date: 2005
  • Doi Number: 10.1524/ract.2005.93.12.757
  • Title of Journal : RADIOCHIMICA ACTA
  • Page Numbers: pp.757-766


The conditional stability constants for trace-level concentrations of Pu(IV) complexing with citric and alginic acids were determined at pH 4 and an ionic strength of 0.1 M NaCl using an ion-exchange technique. The results of these experiments were analyzed with: 1) the graphical Schubert's approach, 2) a non-linear simulation of 'Schubert'-type data, and 3) an affinity distribution approach to describe the alginic acid. Analysis of the results of ion-exchange data for Pu(IV)-citric acid systems using Schubert's method indicates the formation of a 1 : 1 Pu-citrate complex with a stability constant (log beta(1, 1)) of 16.536 +/- 0.015 at I = 0. 1 M. Alginic acid exhibits a strong affinity for plutonium and, unlike citric acid, the experimental results were interpreted as a mixture of I : 2 and I : 3 Pit : alginic acid complexes using non-linear Schubert's analysis of ion-exchange data; average conditional stability constants (logo) of 13.479 +/- 0.057 and 14.755 +/- 0.305 at I=0.1M NaCl, respectively, were determined. The results from the ion-exchange experiments were also modeled based on a non-electrostatic, discrete ligand approach in which alginic acid is conceptualized as being composed of a suite of monoprotic acids, HL(i), of arbitrarily-as signed pK(a(i)) values (e.g., 2, 4, 6 and 8). The experimental ion-exchange data were best described by postulating complexation reactions between Pu(IV) and the model ligands L(2) (pK(a)=4) and L(3) (pK(a)=6), forming the species Pu(L(2))(2) (2+) and Pu(L(3))(3)(+), indicating that the Pu(IV) binding by alginic acid occurs