Adsorption of the hydrophobic organic pollutant hexachlorobenzene to phyllosilicate minerals

Environmental Science and Pollution Research International · 8 authors, 3 centres

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Experiments with native clays showed a broad range of HCB adsorption strengths (log Kd 0.9–3.3).

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Experiments with native clays showed a broad range of HCB adsorption strengths (log Kd 0.9–3.3). For cation-exchanged montmorillonite, most alkali and alkaline earth metal cations resulted in similar adsorption (log Kd 1.3–1.6), but Rb and Cs modifications led to highly increased adsorption (log Kd 2.5 and 3.8, respectively). Molecular calculations identified that for HCB adsorption, the ionic radius of cations is important, with Na+ and Ca2+ showing the strongest calculated adsorption energies. The study concludes that HCB adsorption strength is determined by the balance and interplay of the cation's ionic radius and hydration enthalpy. Limitations include that the gas-phase simulations did not account for solvent effects, which experiments in solution incorporate.

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ORIGINAL PAPER

PMC10039842

Adsorption of the hydrophobic organic pollutant hexachlorobenzene to phyllosilicate minerals

Environmental Science and Pollution Research International

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ABSTRACT

Abstract Hexachlorobenzene (HCB), a representative of hydrophobic organic chemicals (HOC), belongs to the group of persistent organic pollutants (POPs) that can have harmful effects on humans and other biota. Sorption processes in soils and sediments largely determine the fate of HCB and the risks arising from the compound in the environment. In this context, especially HOC–organic matter interactions are intensively studied, whereas knowledge of HOC adsorption to mineral phases (e.g., clay minerals) is comparatively limited. In this work, we performed batch adsorption experiments of HCB on a set of twelve phyllosilicate mineral sorbents that comprised several smectites, kaolinite, hectorite, chlorite, vermiculite, and illite. The effect of charge and size of exchangeable cations on HCB adsorption was studied using the source clay montmorillonite STx-1b after treatment with nine types of alkali (M + : Li, K, Na, Rb, Cs) and alkaline earth metal cations (M 2+ : Mg, Ca, Sr, Ba). Molecular modeling simulations based on density functional theory (DFT) calculations to reveal the effect of different cations on the adsorption energy in a selected HCB-clay mineral system accompanied this study. Results for HCB adsorption to minerals showed a large variation of solid–liquid adsorption constants K d over four orders of magnitude (log K d 0.9–3.3). Experiments with cation-modified montmorillonite resulted in increasing HCB adsorption with decreasing hydrated radii of exchangeable cations (log K d 1.3–3.8 for M + and 1.3–1.4 for M 2+ ). DFT calculations predicted (gas phase) adsorption energies (− 76 to − 24 kJ mol −1 for M + and − 96 to − 71 kJ mol −1 for M 2+ ) showing a good correlation with K d values for M 2+ -modified montmorillonite, whereas a discrepancy was observed for M + -modified montmorillonite. Supported by further calculations, this indicated that the solvent effect plays a relevant role in the adsorption process. Our results provide insight into the influence of minerals on HOC adsorption using HCB as an example and support the relevance of minerals for the environmental fate of HOCs such as for long-term source/sink phenomena in soils and sediments. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-022-24818-4. Keywords: Persistent organic pollutants (POP), Clay minerals, Montmorillonite, Molecular simulations, Halogenated aromatic hydrocarbons, Cations, Hydration enthalpy, Environmental fate

CITATION EXPORT

Leonard Böhm, Peter Grančič, Eva Scholtzová et al.. Adsorption of the hydrophobic organic pollutant hexachlorobenzene to phyllosilicate minerals. Environmental Science and Pollution Research International. (2022). https://doi.org/10.1007/s11356-022-24818-4

AUTHORS

8 · 3 CENTRES

Leonard Böhm, Peter Grančič, Eva Scholtzová, Benjamin Justus Heyde, Rolf-Alexander Düring, Jan Siemens, Martin H Gerzabek, Daniel Tunega

1Institute of Soil Science and Soil Conservation, Research Centre for BioSystems, Land Use and Nutrition (iFZ), Justus Liebig University Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany
2Institute for Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences Vienna, Peter-Jordan-Straße 82, 1190 Vienna, Austria
3Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská Cesta 9, 845 36 Bratislava 45, Slovakia