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Sorption/desorption reversibility of polycyclic aromatic hydrocarbons (PAHs) in soils and carbonaceous materials

Abstract

Understanding sorption/desorption is an important prerequisite for the prediction of fate and transport of pollutants in the environment. During the last two decades, numerous studies have reported hysteresis phenomenon for the interaction of hydrophobic organic contaminants (HOCs) with natural organic matter (NOM). It manifests as nonsingular sorption/desorption isotherms or different rates for sorption and desorption, where during desorption a higher affinity of a compound on a given sorbent and a longer time scale for release than for sorption is observed. Other studies showed that some of the reported sorption/desorption hysteresis phenomena are due to experimental artifacts, mainly resulting from non-attainment of sorption equilibrium before desorption experiments, which result in 'pseudo-hysteresis'. Except for the hypothesis of sorbent reconfiguration, clear experimental evidence for the physical or chemical mechanisms proposed to lead to hysteresis is still lacking. In this study, sorption/desorption equilibrium and kinetics of phenanthrene sorption/desorption from two soils and three carbonaceous samples were investigated using both batch and column techniques. The main objective of this work was to monitor hysteresis phenomenon by carefully recovering the solute mass in the system and to compare sorption/desorption equilibria and kinetics thermodynamically. Nonsingular isotherms and higher desorption enthalpies as well as increased activation energies with  More>>
Authors:
Publication Date:
Jul 01, 2008
Product Type:
Thesis/Dissertation
Report Number:
ETDE-DE-1968
Resource Relation:
Other Information: TH: Diss. (Dr.rer.nat.)
Subject:
54 ENVIRONMENTAL SCIENCES; ACTIVATION ENERGY; ADSORPTION; ADSORPTION ISOTHERMS; AGING; CARBONACEOUS MATERIALS; DESORPTION; ENTHALPY; HYSTERESIS; LEACHING; PHENANTHRENE; POLLUTANTS; POLYCYCLIC AROMATIC HYDROCARBONS; SOILS; TEMPERATURE DEPENDENCE; VAPOR CONDENSATION
OSTI ID:
21157673
Research Organizations:
Tuebingen Univ. (Germany). Geowissenschaftliche Fakultaet
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
TRN: DE09G4139
Availability:
Commercial reproduction prohibited; OSTI as DE21157673
Submitting Site:
DE
Size:
121 pages
Announcement Date:
May 18, 2009

Citation Formats

Wang, Guohui. Sorption/desorption reversibility of polycyclic aromatic hydrocarbons (PAHs) in soils and carbonaceous materials. Germany: N. p., 2008. Web.
Wang, Guohui. Sorption/desorption reversibility of polycyclic aromatic hydrocarbons (PAHs) in soils and carbonaceous materials. Germany.
Wang, Guohui. 2008. "Sorption/desorption reversibility of polycyclic aromatic hydrocarbons (PAHs) in soils and carbonaceous materials." Germany.
@misc{etde_21157673,
title = {Sorption/desorption reversibility of polycyclic aromatic hydrocarbons (PAHs) in soils and carbonaceous materials}
author = {Wang, Guohui}
abstractNote = {Understanding sorption/desorption is an important prerequisite for the prediction of fate and transport of pollutants in the environment. During the last two decades, numerous studies have reported hysteresis phenomenon for the interaction of hydrophobic organic contaminants (HOCs) with natural organic matter (NOM). It manifests as nonsingular sorption/desorption isotherms or different rates for sorption and desorption, where during desorption a higher affinity of a compound on a given sorbent and a longer time scale for release than for sorption is observed. Other studies showed that some of the reported sorption/desorption hysteresis phenomena are due to experimental artifacts, mainly resulting from non-attainment of sorption equilibrium before desorption experiments, which result in 'pseudo-hysteresis'. Except for the hypothesis of sorbent reconfiguration, clear experimental evidence for the physical or chemical mechanisms proposed to lead to hysteresis is still lacking. In this study, sorption/desorption equilibrium and kinetics of phenanthrene sorption/desorption from two soils and three carbonaceous samples were investigated using both batch and column techniques. The main objective of this work was to monitor hysteresis phenomenon by carefully recovering the solute mass in the system and to compare sorption/desorption equilibria and kinetics thermodynamically. Nonsingular isotherms and higher desorption enthalpies as well as increased activation energies with proceeding desorption are expected if significant hysteresis exists. Sorption-desorption cycles were carried out to compare equilibrium isotherms and associated sorption/desorption enthalpies (AeH, isosteric heats). Instead of the traditional decant-and-refill batch method, the experiments were conducted using a newly designed batch protocol, which enables the determination of sorption/desorption isotherms at different temperatures using a closed batch system. This method additionally allows the determination of the sorption/desorption enthalpies which gives insight into the sorbent-sorbate interactions. In order to attain sorption/desorption equilibrium, all the samples were pulverized to shorten the laboratory experimental time. The sorbate losses were carefully monitored and considered in the isotherm calculation. Additionally, release of native phenanthrene was also investigated at different temperatures and compared with the freshly spiked samples to investigate the aging effect. The batch results show that for all individual temperature steps sorption and desorption isotherms coincide. Furthermore, the solubility-normalized sorption/desorption isotherms at different temperatures collapse to unique overall isotherms. Leaching of native phenanthrene occurred at much lower concentrations but was well predicted by extrapolation of the spiked equilibrium sorption isotherms. The absolute values of sorption/desorption isosteric heats ({delta}H) determined are in a range of 19 - 35 kJ mol{sup -1}, which is higher than the heat of aqueous solution of subcooled phenanthrene but much less than the heat of condensation of solid phenanthrene from water. No significant difference of the enthalpies between sorption and desorption was observed. Furthermore, the desorption enthalpy of the native phenanthrene was not significantly higher than expected from the sorption experiments with spiked samples. Sorption and desorption kinetics were monitored in on-line column experiments with stepwise increases of temperature. An intraparticle diffusion model was used to simulate the desorption profile in order to get the apparent diffusion coefficients of phenanthrene from the carbonaceous materials. Desorption activation energies were calculated by Arrhenius relationship based on the high-resolution measurement of concentration increases at each temperature step. The activation energies determined range from 58 - 71 kJ mol{sup -1}. No significant trend of increasing desorption activation energies along with the increased degree of desorption was observed although desorption was almost completed, i.e., only 0.2% (lignite) and 6% (high-volatile bituminous coal) of the initially sorbed mass were present after the last temperature step. Both batch and column results imply that no significant hysteresis occurred for the sorption/desorption of phenanthrene with the samples investigated in this study. (orig.)}
place = {Germany}
year = {2008}
month = {Jul}
}