title: Modeling competitive cation exchange of aromatic amines in water-saturated soils.
abstract: Competitive association to several components of soil through ion exchange processes influences the fate of organic cations in the environment. To examine these processes, the distributions of aniline and 1-aminonaphthalene between aqueous 5 mM CaCl2 solutions and three different Indiana soils were evaluated. Solute ratios (Sr) of aniline to 1-aminonaphthalene of 0.4-4.7 were employed, and the soil solutions ranged in pH from 2.7 to 7.5, with all measurements made 24 h after the introduction of the chemicals to the soils. Two previously proposed equilibrium models--the two-site (TS) and distributed parameter (DP) models--were modified to predict competition. These models assume instantaneous equilibrium of the following reversible processes: (i) acid dissociation of the protonated organic base (BHaq+) in the aqueous phase; (ii) ion exchange on the soil between the protonated organic base and inorganic divalent cations (Daq2+ = Caaq2+ + Mgaq2+); and (iii) partitioning of the nonionic species of aniline (Baq) to soil organic carbon. The TS model is a general mass action model that does not take into consideration cation exchange site heterogeneity, whereas the DP model considers association constants to these sites to be distributed in a log-normal fashion. To describe competition for cation exchange sites within the DP model, it was necessary to add a correlation coefficient (rho) that relates the ion-exchange association constant (KBH) probability density distribution functions of the two compounds. The value of rho is characteristic of each soil. Results indicate that competition has a greater effect at low pH values, where ion exchange is the predominant process. For all cases, these models capture the general trends in the soil-water distribution data of both amines. The DP model also captures the nonlinearity of the 1-aminonaphthalene isotherms at low pH while at the same time capturing the nearly linear isotherms of aniline as a competing organic base.
authors.affiliation: School of Civil Engineering and Department of Agronomy, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Fábrega
authors.forename: C T
authors.initials: CT
authors.lastname: Jafvert
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: L S
authors.initials: LS
authors.lastname: Lee
mesh_terms: D015057:1-Naphthylamine / Q000737:chemistry; D000588:Amines / Q000737:chemistry*; D000814:Aniline Compounds / Q000737:chemistry; D002273:Carcinogens / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D008962:Models, Theoretical; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D000588:Amines; D000814:Aniline Compounds; D002273:Carcinogens; D002412:Cations; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D015057:1-Naphthylamine; C023650:aniline