A Distributed Reactivity Model for Sorption by Soils and Sediments. 11. Slow Concentration-Dependent Sorption Rates

Abstract

Long-term temporal phase distribution relationships (PDRs) were measured for sorption of a hydrophobic organic contaminant probe by seven EPA reference soils and sediments and six shale and kerogen samples. The times required for attainment of apparent sorption equilibrium by the phenanthrene probe were found to be highly dependent upon the aqueous phase-solute concentration, C(t), for a given sorbent, and the type of soil organic matter (SOM) associated with a particular sorbent. Organic-carbonnormalized single-point temporal distribution ratios corresponding to low residual solution phase concentrations were found to approach their respective apparent equilibrium values after times ranging from several days to 90 days for the EPA soils and sediments and from 90 days to g 368 days for the shales and kerogens. Conversely, at residual solution phase concentrations 2 orders of magnitude larger, apparent equilibrium conditions were attained within a few hours for the EPA soils and sediments and within a year for the shale and kerogen samples. The observed dependencies of sorption rate on C(t) and on the type of SOM appear to result from differences in solute diffusion behavior within chemically reduced and structurally condensed SOM domains and that in highly amorphous SOM domains. In the former case the very slow and concentration-dependent non-Fickian behavior observed is likely attributable to the slow and energetically driven reconfiguration of local condensed SOM structures to accommodate solute migration into the matrixes. The results of the study extend the applicability of the Dual Reactive Domain Model introduced earlier in this series of papers to the interpretation and description of sorption rate behavior.

Remediation of persistent organic pollutants (POPs) in two different soils

“…Sorption/desorption of organic contaminants in soil is a biphasic process with a fast initial loss followed by a slow and gradual approach to apparent equilibrium (Cousins et al, 1998;Huang & Weber, 1998). Sustained sorption over a long period of time (aging) is an important variable that needs greater consideration in order to understand its impact on bioavailability and biodegradability of contaminants.…”

Sorption interaction of phenanthrene with soil and sediment of different particle sizes and in various CaCl2 solutions

“…Once the sorbate molecules penetrate one domain and begin to access another new domain, the sharpened rate of change of the sorption parameters occurs [14,16]. From Fig.…”

Immobilization of pentachlorophenol in soil using carbonaceous material amendments

“…Johnson et al (2001) found that rates and extents of desorption of HOCs are strong functions of the type of natural organic matter that soil contains. Pignatello and Xing (1996), and Huang and Weber (1998) hypothesized that rigid parts of the organic matter matrix could be responsible for slow desorption of HOCs. Cornelissen et al (2005) suggested that the ''rigid'' or ''glassy'' parts of SOM is in fact the same as the carbonaceous geosorbents (CG), such as black carbon, char, and kerogen, and thus that sorption to CG probably causes slow desorption.…”