A distributed reactivity model for sorption by soils and sediments. 1. Conceptual basis and equilibrium assessments

Abstract

Contaminant sorption by soils and sediments is characterized as a multiple reaction phenomenon. The approach is predicated on the observation that most natural soils and sediments are intrinsically heterogeneous even at the microscopic scale; that is, variable in composition and structure at both interparticle and intraparticle scales. Heterogeneity is demonstrated for a number of soils which, on the basis of conventional macroscopic properties, would be considered "homogeneous". That such heterogeneities are reflected in sorption reactions which differ between soils and between different fractions of soil is also demonstrated. A composite model, the distributed reactivity model (DRM), is introduced to characterize intrinsic heterogeneities in the properties and behaviors of soils and sediments and to capture the resulting nonlinearities of sorption isotherms. Finally, the significance of particlescale heterogeneity and distributed reactivity is illustrated by using measured parameters and DRM calculations to characterize differences in the relative sorption behavior of soils comprising different mass fractions of differently reactive components.

Phenanthrene Sorption to Soil Humic Acid and Different Humin Fractions

“…In the current study, the KOC (Ce ) 0.05 mg/L) of lipid was 3.7 times that of BHA, demonstrating the greater heterogeneous properties of humin. Weber et al (1) suggested that N value could be taken as an index of site energy distribution. Smaller N values represent more heterogeneous sorption sites in nature.…”

“…Weber et al (1) introduced the concept of multiple discrete reactive mineral and SOM domains to explain the nonlinear behavior of HOC sorption. Soils and sediments can be treated as heterogeneous combinations of active organic and inorganic components.…”

Effects of time, soil organic matter, and iron oxides on the relative retention and redistribution of lead, cadmium, and copper on soils

“…However, Cd(II) sorption on these soils was better fitted to the Freundlich adsorption isotherm (r 2 ≥0.75) than to the Langmuir, indicating probably multi-layer adsorptions on heterogeneous sites (Diagboya et al 2014b). In addition, comparing the Q o or q e (similar) to r 2 (≥0.75) values for Pb(II) and Cu(II) sorption on LF and JB soils (Table 3) suggests that these data may be described simultaneously by the Langmuir and Freundlich isotherms, suggesting that the final isotherms were combinations of several Langmuir-type isotherm (Weber et al 1992). (Fig.…”

Aging effects on sorption–desorption behaviors of PAHs in different natural organic matters

“…Weber et al introduced a composite model, the distributed reactivity model for sorption by soils and sediments to characterize intrinsic heterogeneities in the properties and behaviors of soils and sediments [16]. A similar model was applied by Schlebaum in a study with humic acid (HA) [17].…”