Phenanthrene sorption and desorption equilibria were measured for 10 natural sorbents having significantly different geological ages and organic matter compositions. Three geologically young peats, one humic acid, three geologically old shales, and samples of kerogen isolated from each of the shales were examined. Elemental analyses and solid-state 13C-NMR spectra reveal that the oxygen/carbon (O/C) atomic ratios of the soil organic matter (SOM) as sociated with the samples decrease with increased age and, thus, apparently with diagenetic alteration. The sorption affinities of these materials for phenanthrene as well as their respective isotherm nonlinearities and hysteretic behaviors were found to correlate inversely with the O/C atomic ratio; samples containing more physically condensed and chemically reduced SOM matrices exhibited greater solute affinity, more nonlinear sorption equilibria, and more pronounced hysteresis. Observed relationships between the chemical and structural characteristics of ass...

A Distributed Reactivity Model for Sorption by Soils and Sediments. 10. Relationships between Desorption, Hysteresis, and the Chemical Characteristics of Organic Domains.

Analysis of a humic acid by differential scanning calorimetry has revealed the existence of a glass transition point. Glass transition temperatures, Tg, of water-wet and desiccator-dry specimens we...

A distributed reactivity model for sorption by soils and sediments. 8. Sorbent organic domains : Discovery of a humic acid glass transition and an argument for a polymer-based model

Sorption isotherms of 13 apolar liquids and solids and polar solidssix in unprecedented detailare used to evaluate a polymer-based model for natural organic matter. While all isotherms are nonlinear, the “running” Freundlich exponent n varies markedly with concentration. The isotherms show linear-scale inflection consistent with the presence of flexible (deformable) porosity as predicted by the glassy polymer-based Extended Dual-Mode Model (EDMM). The EDMM assumes dissolution and hole-filling domains in the organic solid, with provision for sorbate-caused plasticization of the solid and “melting” of the holes. Features of the EDMM are illustrated for chlorinated benzenes in poly(vinyl chloride). The solutes fall into categories of “hard” (aliphatics and 2,4-dichlorophenol) and “soft” (chlorinated benzenes, 2-chloronitrobenzene) according to their ability to plasticize organic matter. Comparison of domain coefficients at infinite dilution reveals that organic solutes have a modestly greater affinity for ho...

Detailed Sorption Isotherms of Polar and Apolar Compounds in a High-Organic Soil

A new method was presented to estimate the strength distribution of hydrogen bonds in coal. The hydrogen bonds include the coal intramolecule hydrogen bonds and coal−water hydrogen bonds formed by hydroxyls in coal. The method analyzes the FTIR spectrum ranging from 2400 to 3700 cm-1 obtained using the in-situ diffuse reflectance IR Fourier transform (DRIFT) technique with neat, undiluted, coal samples. The FTIR spectra during the heat-up of eight coals (seven Argonne premium coals and an Australian brown coal), an ion-exchange resin, and a lignin were measured every 20 °C from room temperature to 300 °C. Each spectrum was divided into six hydrogen-bonded absorption bands by a curve-resolving method, then the amount of hydroxyls contributing to each hydrogen bond was estimated by Beer's law by using different absorptivity for each band. The strength of each hydrogen bond was estimated using a relation presented by Drago et al. that is known as one of the “linear enthalpy−spectroscopic shift relations”. Us...

Estimation of Hydrogen Bond Distribution in Coal through the Analysis of OH Stretching Bands in Diffuse Reflectance Infrared Spectrum Measured by in-Situ Technique

Sorption controls the physical and biological availability of chemicals in soil. Most organic molecules undergo primarily weak physisorption interactions and the driving force for sorption is the hydrophobic effect. Sorption and desorption rates, therefore, are governed mainly by molecular diffusion through the fixed interstitial pores of particle aggregates and through the three-dimensional pseudophase of soil organic matter. Retardation in the fixed pore system is due to tortuosity, chromatographic adsorption to pore walls, and, in the smallest pores, steric hindrance. Soil organic matter, which has the strongest affinity for most organic compounds, may exist in rubbery and glassy phases and retards sorption and desorption by its viscosity and by the presence of internal nanopores, which detain molecules and may sterically inhibit their migration. Soot carbon and/or ancient organic matter may be present in some soils but their roles are yet unclear. Desorption rates are correlated with the size and shape of the diffusant. Hysteresis is commonly observed but a satisfactory explanation for it has yet to emerge. Mathematical models based on bond energetics, driving force theory, diffusion, and stochastic analysis are discussed. These models have been used to describe batch experiments and have been coupled to advection-dispersion transport equations for use in flowing water systems. Diffusion models are the most realistic but also the most difficult to apply because diffusion is highly dependent on the geometry and composition of the sorbent. Soil heterogeneity impedes the mechanistic interpretation of rates. Particles span an extremely wide range of sizes. The appropriate diffusion length scale is of ten uncertain. The diffusion coefficient is expected to be concentration dependent in any diffusing medium in which sorption is nonlinear. Furthermore, the diffusant may alter the structure of soil organic matter. Bioavailability can be rate limited by desorption. Cells are believed to access only dissolved molecules, but organisms may affect sorption kinetics indirectly by steepening the concentration gradient or by altering soil properties through bioactivity. Coupled sorption-biodegradation models are necessary whenever nonequilibrium conditions prevail during exposure. Models coupling Monod or first-order biodegradation kinetics with “two-site,” driving-force, or diffusion models have been employed. Some have been used in conjunction with the advection-dispersion transport model.

The Measurement and Interpretation of Sorption and Desorption Rates for Organic Compounds in Soil Media

Determination de la temperature de transition vitreuse d'echantillons de charbon de differentes teneurs en carbone, par calorimetrie differentielle a balayage. Les echantillons sont utilises tels quels ou extraits a la pyridine

Lucy M. Lucht

Papers

Macromolecular structure of coals. 9. Molecular structure and glass transition temperature