Adsorption of Mercury(II) by Kaolinite

Abstract

Adsorption of Hg(II) by kaolinite was investigated as a function of solution pH, ionic strength, and the competitive or complexation effects of ligands (Cl, SO4, PO4) and metals (Ni and Pb). Mercury(II) adsorption from a 0.6 μM Hg(II) solution was primarily influenced by pH. The Hg(II) adsorption edge was described by a pH50 (pH where 50% adsorption occurs) of 3.4 and a pHmax (pH where maximum adsorption occurs) of 4.4. At pH values above the pHmax, Hg(II) retention decreased with increasing pH. Chloride and Ni shifted pH50 from 3.4 to 7 and 4.1, respectively. Nickel and Pb reduced the amount of Hg(II) adsorbed throughout the pH range examined. Ionic strength and the presence of SO4 and PO4 had relatively little impact on the Hg(II) adsorption envelope. The adsorption of Hg(II) was predicted through the application of the triple layer model (TLM) by assuming that the kaolinite surface was composed of equal proportions of silanol and aluminol groups. The TLM model suggests that the silanol group was responsible for retaining the bulk of the adsorbed Hg(II), through the formation of the ≡SiO−‐HgOH+ outer‐sphere, and the ≡SiOHg OH−2 and ≡SiOHgCl0 or ≡SiOHgOHCl− (Cl system) inner‐sphere species. The ≡AlO−‐HgOH+ outer‐sphere complex accounted for a small percentage (<15–35%) of the adsorbed Hg(II). The TLM results suggested that Hg(II) adsorption by both ≡SiOH and ≡AlOH sites on kaolinite should be considered to predict adequately Hg(II) retention.

Chemical Speciation of Mercury in Soil and Sediment

“…Using Hg-cysteine ( − OOCHN 3 + CH 2 S) 2 Hg as a model, depending on pH and the point of zero charge of the mineral surface, the negatively charged carboxyl group, the positively charged amino group, or both groups may interact with the ≡XOH surface group. 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.…”

Influência das características físico-químicas dos solos no ciclo hidrobiogeoquímico do mercúrio na região do Rio Aracá - AM

“…15,23 Há estudos que mostram que a adsorção do mercúrio pela kaolinita é influenciada pelo pH, força iônica e presença dos grupos silanol e aluminol em sua estrutura. 24 Sendo este último o menos impactante na retenção do mercúrio. 24 Em relação à forte interação observada entre matéria orgânica e mercúrio, esta tem sido atribuída à ligação de mercúrio com grupos funcionais contendo enxofre presentes na matéria orgânica.…”

“…24 Sendo este último o menos impactante na retenção do mercúrio. 24 Em relação à forte interação observada entre matéria orgânica e mercúrio, esta tem sido atribuída à ligação de mercúrio com grupos funcionais contendo enxofre presentes na matéria orgânica. 25 Em solos ácidos, vários autores têm descrito correlações entre mercúrio e matéria orgânica, nos quais a matéria orgânica, principalmente na forma de substâncias húmicas, compreende a principal classe de compostos que atua nos processos de complexação, redução e transporte de mercúrio para o ambiente.…”

Development of an Enhanced Hydro-geochemical Model to Address Mercury-speciation Fate and Transport in Aquatic Environments

“…The modeling of adsorption of Hg(II) by kaolinite was conducted, using the surface complexation and the intrinsic equilibrium constants (log K int ) of Hg(II) adsorption onto quartz and gibbsite (see Tables 13 and 14). Sarkar et al (2000)'s modeling and experimental results were comparable. This supports the Zachara et al (1988)'s conclusion on the ideal structure of kaolinite.…”

“…The surface complexation and the intrinsic equilibrium constants (log K int ) for quartz (≡Sio) and gibbsite (≡Aloh) used in this study are shown in Tables 13 and 14 respectively. Sarkar et al (2000) study are shown in Table 15 (Riese, 1982). The modeling of adsorption of Hg(II) by kaolinite was conducted, using the surface complexation and the intrinsic equilibrium constants (log K int ) of Hg(II) adsorption onto quartz and gibbsite (see Tables 13 and 14).…”