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

Abstract

Sorption and desorption of Hg(II) on clay minerals can impact the biogeochemical cycle and bio-uptake of Hg in the environment. We studied the kinetics of the desorption of Hg(II) from kaolinite as affected by oxalate and cysteine, representing the ligands with carboxylic and thiol groups of different affinities for Hg(II). The effects of pH (3, 5, and 7), ligand concentration (0.25 and 1.0 mM), and temperature (15°C, 25°C, and 35°C) on the Hg(II) desorption were investigated through desorption kinetics. Our study showed that the Hg(II) desorption was pH dependent. In the absence of any organic ligand, >90% of the previously adsorbed Hg(II) desorbed at pH 3 within 2 h, compared to <10% at pH 7. Similar results were observed in the presence of oxalate, showing that it hardly affected the Hg(II) desorption. Cysteine inhibited the Hg(II) desorption significantly at all the pH tested, especially in the first 80 min with the desorption less than 20%, but the inhibition of the desorption appeared to be less prominent afterwards. The effect of the ligand concentration on the Hg(II) desorption was small, especially in the presence of oxalate. The effect of temperature on the Hg(II) desorption was nearly insignificant. The effect of the organic acids on the Hg(II) sorption and desorption is explained by the formation of the ternary surface complexes involving the mineral, ligand, and Hg(II). The competition for Hg(II) between the cysteine molecules adsorbed on the particle surfaces and in the solution phase probably can also affect the Hg(II) desorption.

Chemical Speciation of Mercury in Soil and Sediment

“…There are numerous studies on the interaction between Hg and oxidized mineral surfaces such as illite (Hamilton et al, 1995), kaolinite (Sarkar et al, 2000), and goethite (Barrow and Cox, 1992), but only a few on the interaction with MeHg (Gunneriusson et al, 1995;Desauziers et al, 1997). In the few studies in which NOM- (Yin et al, 1996) or thiol- (Senevirathna et al, 2011) containing molecules have been included, the conclusion has been that Hg(II) does not adsorb directly to ≡XOH surface groups. There is so far only one study in which Hg, thiols, and mineral surfaces have been considered in a mixed system, highlighting the importance of ternary surface complexes for the regulation of adsorption and desorption of Hg-thiols onto surfaces of kaolinite (Senevirathna et al, 2011).…”

“…In the few studies in which NOM- (Yin et al, 1996) or thiol- (Senevirathna et al, 2011) containing molecules have been included, the conclusion has been that Hg(II) does not adsorb directly to ≡XOH surface groups. There is so far only one study in which Hg, thiols, and mineral surfaces have been considered in a mixed system, highlighting the importance of ternary surface complexes for the regulation of adsorption and desorption of Hg-thiols onto surfaces of kaolinite (Senevirathna et al, 2011). Desorption of Hg(SR-DOM) 2 and MeHgSR-DOM complexes is likely responsible for the observed concurrent release of Hg and MeHg together with Fe and Mn from lake sediments into the bottom water (Regnell et al, 2001).…”

Fabrication of hyperbranched polyamine functionalized graphene for high-efficiency removal of Pb(II) and methylene blue

“…Among these methods, adsorption is regarded as the most effective and widely used approach due to its relatively low cost, simple operation, and availability for many pollutants [6]. Therefore, various adsorbents, such as activated carbon [7], zeolite [8], clay [9] and polymeric adsorbents [10], have been produced to meet different needs. However, these traditional adsorbents are typically limited by low adsorption capacities or recycling problems.…”

X-ray fluorescence mapping of mercury on suspended mineral particles and diatoms in a contaminated freshwater system

“…Similarly in the contaminated East Fork Poplar Creek (EFPC) at the US Department of Energy's (DOE) Y-12 National Security Complex (NSC) in Oak Ridge, Tennessee, about 75-95 % of the Hg is associated with suspended particles (Brooks and Southworth, 2011) (Supplement Fig S1), although the range of particlebound Hg varies with season, flow conditions, and the distance from the contamination source. In freshwater lakes and stream systems, studies have also shown that Hg mainly associates with particulate natural organic matter (NOM) and iron and aluminum oxyhydroxides (Adams et al, 2009;Quemerais et al, 1998), resulting in elevated Hg concentrations on these particles since Hg sorption on phyllosilicate minerals is relatively low (Hintelmann and Harris, 2004;Senevirathna et al, 2011). The association of Hg with riverine particles is usually attributed to passive adsorption, and both abiotic and biological processes are important for this process (Mason et al, 1996;Pickhardt and Fisher, 2007).…”