Plutonium (IV) complexation with citric and alginic acids at low Pu_Tconcentrations

Abstract

Plutonium / Citric acid / Alginic acid / Complexation / BindingSummary. 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 β 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 1 : 2 and 1 : 3 Pu : alginic acid complexes using non-linear Schubert's analysis of ion-exchange data; average conditional stability constants (log β) of 13.479 ± 0.057 and 14.755 ± 0.305 at I = 0.1 M 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-assigned 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 mainly through carboxylic groups under the experimental conditions studied.

Influence of humic acid on plutonium sorption to gibbsite: Determination of Pu-humic acid complexation constants and ternary sorption studies

“…Similar discrete site approaches have been effectively used to quantify metal-HA binding [15][16][17]20]. These models at- tempt to reduce the complexity of HA into a simple binding model that can be easily incorporated into chemical speciation modeling program at the expense of neglecting specific metal-NOM interactions.…”

“…In this paper a slightly different discrete ligand model was utilized to describe proton-binding and actinide binding with HA. This technique is similar to that used by Westall et al [15] to study Co complexation by Leonardite HA as well as Pu complexation with a variety of ligands [16,17]. This approach assumes that the HA can be represented by a discrete number of monoprotic acid sites with a fixed pK spectrum (e.g., pK = 3, 5, 7, and 9 in this work).…”

In situ stabilization of chromium(VI) in polluted soils using organic ligands: The role of galacturonic, glucuronic and alginic acids

“…Note that the pK a values for the dissociation of carboxylic groups of galacturonic and glucuronic acids are less than 4 [45,46], indicating that both galacturonic acid and glucuronic acid are mostly deprotonated under the experimental conditions studied (e.g., pH > 4). Similarly, alginic acid is mainly composed of uronic acid COOH functional groups with a first pK a value of <3 [47,48]. Carboxylic groups are known to play a significant role in metal ion complexation and oxidation/reduction reactions [16,48].…”

“…Similarly, alginic acid is mainly composed of uronic acid COOH functional groups with a first pK a value of <3 [47,48]. Carboxylic groups are known to play a significant role in metal ion complexation and oxidation/reduction reactions [16,48]. However, the direct Cr(VI) reduction with organic ligands in solution is a slow process that may take weeks to months [11,17].…”

Actinide Sorption in Rainier Mesa Tunnel Waters from the Nevada Test Site

“…DOM in groundwater is composed of a wide variety of compounds including humic substances, hydrophilic acids, carbohydrates, carboxylic acids, amino acids and hydrocarbons (Thurman, 1986). It is known that organic-metal complexation can enhance the solubility of metal ions, therefore, increasing metal concentration in water (Marquardt and Kim, 1998, Alliot et al, 2005, Kantar and Honeyman, 2005.…”