|dc.description.abstract||The objective of this research is to evaluate the effect of soil structure on the adsorption/desorption of volatile organic compounds (VOCs). The migration and the fate of nonionic organic pollutants in soils are highly depended on their vapor-phase sorptive behavior. However, it is difficult to explicit the mechanism of adsorption/desorption due to complexity of environmental medium. In order to show the effects of soil structure on adsorption/desorption of VOCs, two kinds of montmorillnite with different exchange cation, calcium and titanium were individually used to examine the isotherms for the vapor uptake of benzene and n-hexane under 288K and 298 K.
After exchanged with metal cation, the porous structure of the mineral samples was changed. These changes were explored by quantifying the BET surface area, total pore volume, micropore volume, pore size distribution, surface fractal dimension (calculated from N2 adsorption/desorption isotherms), c-spacing (by XRD) and surface image (by SEM) of mineral phase. The results demonstrate that Ti-montmorillnite has higher surface area, extensive pore size distribution, and better pore connection.
The influences of temperature and soil properties were also investigated. A gravimetric adsorption apparatus was developed and used to generate adsorption/desorption isotherms of benzene and hexane on two dry soil samples at 288 and 298 K. Isosteric heats of adsorption were calculated and heat curves were established. Equilibrium isotherms were all Type II, characterizing vapor condensation to form multilayers. The sorption capacity of soils is positively correlated with specific surface area, pore size distribution and pore connection. Nevertheless, Ti-montmorillnite didn’t reveal hysteresis loop, which might be attributed to better pore size distribution and pore connection. Isosteric heats of adsorption on Ca-montmorillnite were influenced by the reaction between adsorbent and adsorbate as well as among adsorbate molecules.
The results of this study are to further understanding of soil properties, as a basis for desorption predictions. Findings, apply not only to environment applications but also to theoretical development.||en_US|