Modeling of the complex formation of metal ions with humic acids

Abstract

Based on the conceptual model of cation-humic interactions considering the heterogeneous composition and polyelectrolyte nature of humic acids, the description of the interaction by the expression, logis the concentration of the cation bound to the humic acid, [M] is the concentration of the free cation with charge z, and [R] is the concentration of the free anionic sites of the humic acid, [R] = (C R − z[M · ·(zR)])α (C R is a total concentration of proton exchanging sites and α is a degree of dissociation). log K , m, a and b are the constant parameters depending on the cation and the humic acid. The expression is successfully applied to the experimental results on the complex formation (or protonation) of humate and polyacrylate (a homogeneous polymeric weak acid) with H + , NpO 2 + , Eu 3+ , Ca 2+ , Fe 2+ and Fe 3+ obtained under the condition where hydrolysis of cations and saturation of the reacting sites can be neglected.

Systematic change in relative stabilities of REE-humic complexes at various metal loading levels

“…This variation is consistent with previous studies on Eu-HA complexation Kubota et al, 2002 *Stookey (1970); ** Kim et al (1990). Purification procedure of Aldrich humic acid (AHA) was followed Kim et al (1990) Tochiyama et al, 2004). In the case of the multi-REE system, however, logβ M-HS of some LREEs (La, Pr, and Nd) increase with the REE loading level at the lower REE loading region (Fig.…”

“…Some experimental studies on Eu-HA interaction indicated that the apparent binding constant of Eu with HA depends on the Eu loading level to HA Kubota et al, 2002;Tochiyama et al, 2004). Hummel et al (2000) demonstrated that the experimental binding constants of Eu-HA complexes, which were reported by Caceci (1985) and Glaus et al (2000), decrease with an increase in the Eu loading level.…”

“…β M-HS of HSs complex is an apparent value, which depends on pH, ionic strength, and the metal loading level (i.e., [MA]/[A]) Kubota et al, 2002;Tochiyama et al, 2004;Yamamoto et al, 2005).…”

“…Humic substances (HSs) such as fulvic and humic acids (FA and HA) are typical organic matter, which interacts with metal ions in natural terrestrial water (Tipping, 2002). Although many previous studies have been conducted on the REE-HS interaction, most studies on the stability constants of REE-HS complexes were reported for a single REE, especially Eu (Torres and Choppin, 1984;Bidoglio et al, 1991;Moulin et al, 1992;Takahashi et al, 1994;Lead et al, 1998;Glaus et al, 2000;Dong et al, 2002;Kubota et al, 2002;Tochiyama et al, 2004). Reports for all (or several) REEs were much less than those for a single REE (Takahashi et al, 1997;Yamamoto et al, 2005;Sonke and Salters, 2006;Pourret et al, 2007a;Stern et al, 2007), and relative stabilities among REEs (i.e., REE pattern of the stability constants) are not consistent among these studies.…”

Determination of Apparent Formation Constants of Eu(III) with Humic Substances by Ion Selective Liquid Membrane Electrode

“…where m i , b, and logK i are the characteristic constant parameters of the humic substance [28]. At a given I, the [R -] is defined by the sum of two dissociated functional groups of the humic substance (R -) in meq/g, where j g of the humic substance is dissolved in V dm 3 of the solution,…”