Abstract

The clay soil has specific properties that cause difficulty in the contaminated site assessment and the remediation process. The difficulty in extraction of HOC (hydrophobic organic compounds) from clay material was reported. Therefore, the SFE (supercritical fluid extraction) has a potential to substitute classical methods. The efficiency of using SFE (ISCO 200 model) for clay soil (illite) was investigated. SFE tests were performed on various compositions of clayey soils. Phenanthrene was used to examine the extraction efficiency of PAHs from clayey soil. Phenanthrene concentration in soil specimen was determined by UV. Carbon dioxide was chosen as the supercritical fluid and 5% (mol) methanol was used as a modifier. The highest recovery (72%) from clay was obtained at a pressure of 55 kPa (8000 psi) and temperature of 150$\sp\circ$C with modifier when dynamic time of 30 min was applied. The impact of pressure (5000 to 8000 psi), temperature (50 to 150$\sp\circ$C) and time (static and dynamic) were discussed. The extraction efficiency of phenanthrene from soil was modeled. The model accounts for effective diffusion of the phenanthrene in the solid pores, axial dispersion in the fluid phase and external mass transfer to the fluid phase from the particle surface. This model, involving partial differential equations, was solved using the finite difference. The model showed the relationship between diffusivity, mass transfer coefficient and properties of porous media (clay texture). Solubility of phenanthrene in carbon dioxide was calculated. The porous media analysis was reported by an electron microscopy and an image analysis. The developed model can be applied for more precise analysis necessary for contaminated site assessment as well as for evaluation of the remediation technology efficiency.