title: Polyfunctional ionogenic compound sorption: challenges and new approaches to advance predictive models.
abstract: Polyfunctional ionogenic compounds are unique in that they sorb to environmental solids at multiple receptor sites via multiple interaction mechanisms. However, existing sorption models fail to accommodate: (i) sorption via a single mechanism (e.g., cation exchange) at one sorbent receptor site type (e.g., exchange site) distributed across multiple soil components (e.g., organic matter and aluminosilicates); and (ii) sorption at a specific sorbent receptor site (e.g., exchange site) involving distinct sorbate structural moieties (e.g., -NH(3)(+) and -COOH) and distinct interaction mechanisms (e.g., cation exchange and cation bridging). In response, this study offers a mechanism-based framework for conceptualizing the equilibrium solid-water sorption coefficient, K(d), with particular emphasis on the mechanisms of cation exchange and surface complexation/cation bridging. The unique mapping of sorbate structural moieties, sorbent receptor sites, and sorption mechanisms is used to advance mechanism-specific probe compounds for cation exchange and surface complexation/cation bridging for quantifying the relevant site abundance and baseline sorption free energy. Existing literature studies point to the feasibility of developing mechanism-specific structural corrections to "adjust" mechanism-specific probe sorption measures to estimate the magnitude of sorption for any polyfunctional ionogenic compound of interest. Advancement of our conceptual framework to a quantitative K(d) model requires more extensive evaluation of ionogenic compound sorption under consistent experimental conditions.
authors.affiliation: Civil and Environmental Engineering Department, University of Connecticut, Storrs, Connecticut 06269-2037, United States. mackaya@engr.uconn.edu
authors.forename: Allison A
authors.initials: AA
authors.lastname: MacKay
authors.forename: Dharni
authors.initials: D
authors.lastname: Vasudevan
mesh_terms: D000327:Adsorption; D007477:Ions / Q000737:chemistry* / Q000302:isolation & purification; D008956:Models, Chemical; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D007477:Ions; D012987:Soil; D012989:Soil Pollutants