Affiliation:
1. Department of Nuclear Engineering, Kyoto University, Kyoto daigaku-Katsura C3, Nishikyo, Kyoto 615-8540, Japan
2. Research Reactor Institute, Kyoto University, Asashiro-nishi, Kumatori, Osaka 590-0494, Japan
Abstract
Abstract
A semi-empirical thermodynamic model was applied to estimate the
apparent formation constants of actinide ions, i.e., Th(IV),
Pu(IV) and Np(V), with humic substances (HSs), including
humic and fulvic acids, over a wide range of solution conditions,
i.e., pH, ionic strength, and HS and metal concentrations. The
hypothetical HSs consist of humic and fulvic acids with nine types of
simple organic ligands, which include aromatic and aliphatic carboxyl
groups and phenol groups, as binding sites. The abundance of each
binding site in the hypothetical HSs was determined via a fitting
analysis using an acid-dissociation dataset for several HSs. To
determine the apparent formation constant of a given metal ion with
HSs, 54 specific binding sites were considered, including nine
monodentate sites (1:1 metal/ligand complexes) and 45 bidentate
sites (1:2 metal/ligand complexes). The formation constant of each
monodentate binding was determined from the experimental data, while
those of the bidentate bindings were determined by considering two
monodentate bindings and the chelating effect, for which one of the
adjustable parameters was introduced in the model. Introduction of the
other parameter, which is related to the fraction of monodentate to
bidentate sites (i.e., the heterogeneity), afforded the parameter
values with good correlation with the apparent formation constant
data. The present model with adjusted parameter values well reproduced
the experimental apparent complex formation constants for actinide ion
interaction with HSs in a wide range of solution conditions except for
those obtained at trace concentrations.
Subject
Physical and Theoretical Chemistry
Cited by
7 articles.
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