Influence of Citric Acid and Glycine on the Adsorption of Mercury (II) by Kaolinite under Various pH Conditions

Abstract

Abstract--This investigation was carried out to study the effect of different concentrations of citric acid and glycine, which are common in freshwaters, on the kinetics of the adsorption of Hg by kaolinite under various pH conditions. The data indicate that Hg adsorption by kaolinite at different concentrations of citric acid and glycine obeyed multiple first order kinetics. In the absence of the organic acids, the rate constants of the initial fast process were 46 to 75 times faster than those of the slow adsorption process in the pH range of 4.00 to 8.00. Citric acid had a significant retarding effect on both the fast and slow adsorption process at pHs of 6.0 and 8.0. It had a significant promoting effect on the fast and slow adsorption process at pH 4.00. Glycine had a pronounced enhancing effect on the rate of Hg adsorption by kaolinite during the fast process. The rise in pH of the system further increased the effect of glycine on Hg adsorption. The magnitude of the retarding/promoting effect upon the rate of Hg adsorption was evidently dependent upon the pH, structure and functionality of organic acids, and molar ratio of the organic acid/Hg. The data obtained suggest that low-molecular-weight organic acids merit close attention in studying the kinetics and mechanisms of the binding of Hg by sediment particulates and the subsequent food chain contamination.

Kinetic analysis of the sorption of copper(II) ions on chitosan

“…26 However, it is often incorrect to apply simple kinetic models such as first-or second-order rate equations to a sorption system with solid surfaces that are rarely homogeneous and because the effects of transport phenomena and chemical reactions are often experimentally inseparable. 27 Singh et al 28 reported that the sorption of mercury(II) by kaolinite obeyed multiple first-order kinetics. Almost all the kinetic systems reported in the literature for metal ion sorption have only been subjected to pseudo-first-order model analysis.…”

A Nuclear Magnetic Resonance (NMR) and Fourier-Transform Infrared (FTIR) Study of Glycine Speciation on a Cd-Rich Montmorillonite

“…Organic and inorganic pollutants (e.g., large organic molecules such as atrazine and heavy metals such as Cd, Pb, and Hg) can easily exchange for innocuous elements, such as Ca or Na, from the interlayer of the expandable clay minerals. The intermolecular interactions of organic pollutants with clay-mineral surfaces are expected to be crucial in chemical/biological transformations, transportation, and retention of these contaminants (e.g., Inskeep and Baham, 1983;Siantar et al, 1994;Singh et al, 1996).…”

“…Glycine is an organic ligand commonly present in natural water systems and it may enhance the rate of heavy metal adsorption by kaolinite and montmorillonite (Singh et al, 1996). Barrie et al (1993) and Gyani (1994) studied the complexation of cadmium with glycine.…”

Effect of carboxylic and thiol ligands (oxalate, cysteine) on the kinetics of desorption of Hg(II) from kaolinite

“…It can also affect Hg transformation through other processes (e.g., Hg(II) binding to organic matter (see Benoit et al 2001and Haitzer et al 2002 and photoredox (see Mauclair et al 2008;Nriagu 1994;Zhang 2006;Zhang and Lindberg 1999;and references therein)). Numerous studies have been reported on adsorption of Hg(II) by various particles, e.g., clay minerals (Hamilton et al 1995;Sarkar et al 2000;Singh et al 1996), oxides (Bonnissel-Gissinger et al 1999;Gunneriuson and Sjoberg 1993;Gunneriuson et al 1995;Sarkar et al 1999;Thanabalasingam and Pickering 1985;Tiffreau et al 1995;Walcarius et al 1999;Weerasooriya et al 2006Weerasooriya et al , 2007, and soils (Schluter 2000;Schuster 1991;Yin et al 1996;Yin et al 1997a, b). Desorption of Hg(II) from particles has also received attention (Arias et al 2004;Yin et al 1997b), yet the literature in this regard has remained limited.…”

“…In natural waters as well soils, solid particles co-exist with natural organic matter (NOM) and both interact with Hg(II) species. A competition thus occurs between particles and NOM for binding Hg(II) (Arias et al 2004;Singh et al 1996). NOM can also bind to particles (Johnson et al 2004;Schuster 1991) and affect Hg(II) distribution between particles and solutions.…”