Modeling soil -water phase transfer processes of aromatic amines

Jose Rogelio Fabrega-Duque, Purdue University

Abstract

Abiotic loss of aromatic amines from the aqueous phase to soils occurs with an initial rapid loss due to reversible chemical processes, followed by a slow loss due to irreversible reactions. A distributed parameter model (DP model) was developed to account for the short term reversible interactions considered: (a) acid dissociation of the protonated organic base (BH +); (b) partitioning of the nonionic species of aniline (B aq) to soil organic carbon; and (c) ion-exchange on the soil between BH+ and inorganic divalent cations (D2+ = Ca 2+ + Mg2+). This model expresses ion-exchange as separated association reactions for each cation to unoccupied cation exchange sites, with constants KBH and KD. A Gaussian distribution on log KBH values was employed. Aniline and 1-aminonaphthalene 24hr-isotherms measured on three Indiana soils at different pH and added calcium concentration were employed to evaluate this model. Model predictions were compared against the general form of the speciation model in which a singular value of KBH was employed (TS Model). Besides capturing the magnitude and sorption trends observed, the DP model also captures the nonlinearity of 1-aminonaphthalene measured isotherms. A reaction of Baq with irreversible sites (Cir) on the soil was added to the TS model to describe the long-term irreversible reactions of aniline. A kinetic rate constant, kir, and the total concentration of irreversible sites, CT, were employed as adjustable model parameters. A good fit was obtained with a single value of kir for all soils, pH values, and soil-water ratios evaluated. Competition among aromatic amines for ion-exchange sites was modeled by adding a correlation coefficient (ρ) to the DP model. This coefficient relates ion-exchange association constants (KBH) among amines. This model was evaluated by employing 24hr-isotherms constructed at different aniline to 1-aminonaphthalene solute ratios (MR). Results indicate that: (i) competition has a greater effect at low pH values where ion-exchange is the predominant process, and (ii) an inverse correlation between KBH values for aniline and 1-aminonaphthalene exists when these compounds are competing for ion exchange sites.

Degree

Ph.D.

Advisors

Jafvert, Purdue University.

Subject Area

Environmental engineering|Soil sciences|Environmental science

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