Distributed-Rate Model Analysis of 1,2-Dichlorobenzene Batch Sorption and Desorption Rates for Five Natural Sorbents

Abstract

Rate-limited sorption and desorption strongly influence the fate, transport, and remediation of organic pollutants in subsurface environments. In this study, the rates of sorption and desorption were quantified for 1,2-dichlorobenzene to and from five natural sorbents using a batch methodology. Solute/sorbent contact times of 3, 7, 14, 49, and 99 d were studied for the desorption rate experiments. The sorption and desorption data were simulated with a distributed-rate model that used the Γ probability density function to generate the distribution of first-order rate coefficients. Ninety-five percent confidence intervals on the optimal model parameters were developed and translated into 95% confidence intervals on the various rate-coefficient distributions. Development of the confidence intervals on the rate coefficients facilitated a statistically rigorous evaluation of whether the rate of desorption was equal to the rate of sorption for the different sorbents. For three of the five sorbents studied, the rates of desorption were significantly slower than the rates of uptake for all solute/sorbent contact times studied. For the remaining two sorbents, the rates of desorption were significantly slower than the rates of uptake for solute/sorbent contact times greater than 2−3 d. For contact times greater than 2 d, a significant fraction of the 1,2-dichlorobenzene appeared to be resistant to desorption. However, the rate of desorption and the magnitude of the resistant fraction were independent of contact time for all but one sorbent. The rate observations for this study were consistent with an intraorganic matter diffusion mechanism.

Time-Dependency of Naphthalene Sorption in Soil: Simple Rate-, Diffusion-, and Isotherm-Parameter-Based Models

“…In the Forbes soil, this amount would presumably be smaller if the experiment were continued beyond 21 days due to nonattainment of apparent equilibrium. Very different initially adsorbed fractions (for sorption times Ͻ 1 h) were observed previously: Ball and Roberts (1991b) found ϳ4-25%, Weber and Huang (1996) found ϳ10-15%, and Deitsch et al (2000) found ϳ25-60%. Common to these observations is that the smaller the initial adsorbed amount, the longer the apparent equilibration time, in agreement with the observations in this study.…”

“…1d). Long and varying apparent equilibration times of sorption are a frequently observed phenomenon (e.g., Ball and Roberts, 1991b;Pignatello and Xing, 1996;Deitsch et al, 2000).…”

Long-term desorption behavior of uranium and neptunium in heterogeneous volcanic tuff materials /

“…The research of Deitsch, Smith et al (2000) focuses on the rate limited sorption/desorption of an organic pollutant 1,2-Dichlorobenzene from 5 different soils.…”

“…An intraparticle diffusion model with parameters determined from uptake experiments was able to account for the majority of sorption hysteresis (Miller and Pedit 1992). Cunningham and Deitsch et al (2005) quantify sorption and desorption time scales for an organic contaminant onto four natural sorbents from the previous study above (Deitsch, Smith et al 2000) using temporal moment analysis. The authors develop a probability distribution by integrating the mean and variance of sorption and desorption time scales obtained from batch experimental data.…”

Travel time moments for sorbing solutes in heterogeneous domains under nonuniform flow conditions

“…In the last few years new models have arisen. These models incorporate the possibility that sorption can be characterized by multiple rates at any single location, related to the presence of a nonuniform distribution of grain sizes [ Connaughton et al , 1993; Pedit and Miller , 1994; Culver et al , 1997; Cunningham and Roberts , 1998; Haggerty and Gorelick , 1998; Deitsch et al , 2000]. The most general model assumes a continuous distribution of mass transfer rates [ Haggerty and Gorelick , 1998] and was developed as an extension of various particular continuous and discrete models.…”