The environmental fate of emerging contaminants, such as pesticides and pharmaceuticals, is influenced by the sorption of these chemicals to solid phases such as sediments and soils. Cationic amine moieties are important substructures of many pesticides and pharmaceuticals. As such, recent advances in predictive models for aromatic cationic amine sorption have furthered our ability to anticipate the fate of these contaminants. Efforts to date have focused on structures with amine moieties outside the aromatic ring (non-heterocyclic amines) but have not included heterocyclic amines, such as pyridines, in predictive model development. The goal of this study is to determine quantitative and qualitative differences in the nature and extent of heterocyclic and non-heterocyclic amine sorption to aluminosilicate clays. To accomplish this, we used pulse input chromatography to obtain isotherms for pyridine and methylpyridine sorption to a range of aluminosilicates. We found that pyridines sorbed to a higher extent (~2.5 times greater) onto Na-montmorillonite than Ca-montmorillonite. In contrast, sorption of non-heterocyclic amines (such as benzylamines) was about 5.5 times greater onto Na-montmorillonite than Ca-montmorillonite. It is likely that the positive charge delocalization over the aromatic ring in pyridines allowed for stronger electrostatic interactions with negatively charged surface sites. Pyridines also showed a greater (3-4.5 times) sorption to Na-montmorillonite than Na-illite as compared to benzylamines, for which the extent of sorption was only 1.7 times greater. The greater density of delocalized charge sites on montmorillonite (as compared with illite) may have allowed for more favorable interactions with the delocalized positive charge on pyridines. Further, methyl substitution on the pyridine aromatic ring had a minor impact on the extent of sorption to montmorillonite and illite at low surface coverage, contrasting studies on methyl substituted non-heterocyclic amines, such as methylanilines. Finally, non-linear S-shaped isotherms noted for methylpyridine sorption to Na-montmorillonite indicated that potential secondary interactions may also influence sorption. Future work aims to expand the study to include more clay types, exchangeable inorganic cations, and heterocyclic amines.

Sorption of pyridine cations to aluminosilicate clays: Influence of solid phase composition and structure

255th National Meeting (2018)

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