Modeling Short-Term Soil−Water Distribution of Aromatic Amines

Abstract

The applicability of a distributed parameter model for describing the distribution of aniline and α-naphthylamine between soil and aqueous phases at short contact times was assessed. Mass action equations considered in the distributed parameter model were (a) acid dissociation of the protonated organic amine (BH+); (b) sorption of the neutral species (B) to soil organic carbon through the partition coefficient K oc; and (c) ion exchange of the protonated organic amine and inorganic divalent cations (Ca2+ + Mg2+ = D2+). The last reaction was expressed mathematically as separated association reactions for each cation to unoccupied cation exchange sites, with constants K BH and K D. A Gaussian distribution on log K BH values with mode μ and standard deviation σ was employed. The overall model was expressed as a system of two nonlinear equations with two unknown values (BH+ and D2+). The model was evaluated with aniline and α-naphthylamine isotherms measured on three Indiana soils ranging in pH (4.5−7.0) and added calcium concentration (0.5−50 mM) after a 24 h contact period. The parameters K oc, μ, and σ for each amine were obtained by minimizing the sum of squared residuals between predicted and measured aqueous-phase organic amine concentrations (i.e., [B]aq + [BH+]aq) for all soil, pH, and CaCl2 conditions, simultaneously. Calculated isotherms were compared against those calculated with the general form of the speciation model in which a singular value of K BH was employed. The distributed parameter form of the model resulted in nonlinear calculated isotherms in general agreement with the curvature of α-naphthylamine measured isotherms. Skewed distributions on log K BH were evaluated also.

Sorption of Ionizable Organic Amines on Soil and Their Effects on Phenanthrene Sorption

“…When organic amines are cationic, the sorption is a combination of electrostatic attraction, polar interaction, and hydrophobic partition since the soil particles were negatively charged (ζ-potential = −21.24 at pH of 8). When they are in a neutral form, only hydrophobic partition together with polar interaction is the main mechanism, which is in agreement with previous observations (Fabrega et al 1998;Zhu et al 2003). Studies on other organic ionizable compounds also confirmed our results.…”

“…In addition, in the view of molecular structure, unlike n-hexylamine with a six-carbon linear alkyl chain, trimethylamine is only composed of three methyl groups and has no long hydrocarbon chain. Therefore, it cannot generate a new phase of hydrophobic organic environment for PHE sorption (Fabrega et al 1998). Figure 2c depicts the effect of 1-naphthylamine on the adsorption of PHE.…”

“…Ionic organic compounds (IOCs) differ from non-ionic chemicals and can exist either as nondissociated or dissociated forms in an aqueous phase, which is dependent on hydrochemical conditions, especially the pH of the solution. The dissociated forms, either as cations or as anions, may have other interactions with the sorbent except those above, and electrostatic repulsion (or attraction) may become the primary process for sorption (Fabrega et al 1998;Li et al 2001).…”

Effect of heavy metals and surfactants on the adsorption of phenolic compounds on sediment

“…The log (K F ) for 2, 4-DNP did not show a consistent trend, which the measured parameters decreased from 1.291 to 0.866 after pH value increased from 2.04 to 4.08, whereas parameters increased from 0.866 to 1.507 after pH value increased from 4.08 to 10.5. Phenolic compounds were kind of the ionizable organic compounds, which were highly influenced by solution pH, which determined the ionizable organic compounds exist in either ionic anion or neutral molecular forms (Fabrega et al 1998). Thus, varying pH had two competitive effects on the adsorption of phenolic compounds: (1) changing the adsorption of phenolic compounds by interaction between surface charged of sediment and substituent of phenolic compounds; (2) changing the existed form of phenolic compounds, which would lead to the changing of adsorption of phenolic compounds.…”

Sorption of Selected Aromatic Substances—Application of Kinetic Concepts and Quantum Mechanical Modeling

“…Authors supposed enhanced protonation at the sorption surface due to a possibly depressed dielectric constant of vicinal water near clay mineral surfaces and enhanced Brønsted acidity of solvated exchangeable cations. If ion exchange has to be expected (at low pH weak organic bases can be partly protonated) besides partitioning, an additional equilibrium ion exchange model should be included, or models such as the two-site model for reversible processes including ion exchange (e.g., developed by Fábrega et al (1998)) should be applied.…”