| dc.description.abstract | The effects of soil structure and chemical properties on the adsorption/desorption of volatile organic compounds were evaluated. The migration and the fates of nonionic organic compounds in soils are found to be highly depended on their vapor-phase sorptive behavior. However, it is difficult to explicit the mechanism of adsorption/desorption due to the complexity of environmental medium.
Vapor-phase adsorption/desorption isotherms of water, benzene, hexane, and cyclohexane on dry soil with different soil organic matters, such as Ca-montmorillonite, Ti-montmorillonite, Shamon Mountain Soil and Florida Peat, were gravimetrically measured under 15°C, 20°C and 25°C. The surface area, pore structure, and adsorption/desorption characteristic were analyzed to show the soil structure and chemical properties effect on the adsorption/desorption of VOCs.
After exchanged with metal cations, the porous structure of the soil mineral fraction was significanting changed. The results demonstrate that Ti-montmorillnite possess higher surface area, extensive pore size distribution, and better pore connection. Both the surface area and the pore structure of soil were characterized based on the classical and fractal analyses of the nitrogen adsorption isotherms. The surface fractal dimension D was calculated from their nitrogen isotherms using the fractal version of FHH (Frenkel-Halsay-Hill) equation. The results revealed that a smaller metal cation on the clay may slightly increase D values as a result of the increase in the BET surface area and the decrease in the pore size.
The adsorption capacity of Florida Peat is greater than that of the Shamon Mountain Soil for the sorption of water and benzene, owing to the Florida Peat contains aromatic groups. Conversely, the mineral fraction was significant for aliphatic compounds, and the soil organic matter was quite significant for aromatic compounds. The steric structure of molecular effect on VOCs adsorption for soil, following the order：the plane form-benzene＞the chain form-hexane＞the chair form-cyclohexane.
The experimental data were examined by the four sorption kinetic model：the pseudo-first order equation, the pseudo-second order equation, the intraparticle diffusion model and the Elovich rate equation. According to the sum of the errors squared (SSE), it showed that the intraparticle diffusion model fitted the data well, and the Elovich rate equation fitted the Florida Peat data well at relatively high pressure. | en_US |