The Effect of Soil Heterogeneity on the Sorption and Desorption of Organic Contaminants in Soil

• Main Authors: Yang-hsin Shih, 施養信
• Other Authors: Shian-chee Wu
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/15918779481927013583

博士 === 國立臺灣大學 === 環境工程學研究所 === 91 === Soil heterogeneity influences greatly the fate and the remediation efficiency of organic pollutants. Each component of the chemically heterogeneous soil exhibits a unique sorption behavior toward organic sorbates. For the macro-scale study, the sorption kinetics of some volatile organic compounds (VOCs) in disks made of pressed humic substance was investigated via a microbalance. The thin film/FTIR method was used to study the sorption kinetics by tracking the change of the absorbance intensity and tried to identify the possible sorption mechanisms in micro-scale. Three VOCs were used to study the interaction between humin and organic contaminants. Higher sorbing capacity of humin for more polar VOCs and the C13-NMR data of humin indicate that humin was more hydrophilic than Aldrich humic acid. The apparent diffusivity of acetone, toluene, and hexane in the disks ranged from 10-8 to 10-10 cm2/s. The sorbed toluene in humin does not seem persistent to desorption; however, acetone and hexane, a polar and a linear compound, respectively, show persistence against desorption. On the completion of the desorption experiments, there were approximately 35% and 20% sorbate residue for acetone and hexane, respectively. The sorption kinetics of toluene in dry and humid clay films was investigated by tracking the change of the IR absorbance. Under humid conditions, similar toluene sorbed intensities were found on Ca- and Cu- montmorillonites. However, higher intensities of sorbed toluene were found on Cu-form under dry conditions, which indicates stronger interactions occurring. On Ca- and Cu- montmorillonite, some portion of toluene is desorbed at an extremely slow rate under dry conditions. Either some original toluene peaks or some new peaks are persistent against desorption from montmorillonites, also suggesting the existence of irreversibly sorbed species. There may be some transformation of VOCs in clay systems. Molecular dynamic simulations were also used to study the sorption of organic contaminants in soil organic matter. The simulation results of the sorption kinetics and thermodynamics of toluene in humic acid are in good agreement with the experimental data. We believe that this technique will become a powerful tool not only to facilitate the solving of the problems of contaminated soil clean-up but also to be applied to a wider range of environmental problems. After studying soil heterogeneity, we found the intrinsic sorption is fast for VOCs into humin, humic acid and montmorillonite. So they do not contribute to the slow sorption/desorption in soil. The mass transfer of contaminants into soil plays the important role on the slow sorption/desorption in soil.