PCBS AND HYDROCARBONS IN SOIL MATRIX CONTROLLED BY SUPERCRITICAL-FLUID EXTRACTION (SFE) - PRELIMINARY STUDIES

Supercritical fluid ectraction (SFE) proven to be an attractive altern ative to solvent extraction of PCBs and petroleum hydrocarbons (PHCs) from contaminated soils. This paper discusses the effects of a number of parameters (pressure, temperature and modifier) on the SFE of PCBs and of the saturated (HCSs) and aromatic (PAHs) fractions which make u p a crude oil as determined by using CO2 as supercritical fluid. The e xperiments were carried out by spiking two different soils, composed b y clay and clay-sand, with Aroclor 1254 (PCBs = 0.38 mu g/g(soil)) and saturated (HCSs = 0.02 g/g(soil)) and aromatic (PAHs = 0.1 g/g(soil)) fractions from crude oil. CO2 modified by acetone yielded high recove ries of both PCBs (>95%) and polycyclic aromatic hydrocarbons (PAHs) ( 100%). Lower recoveries were observed for the aliphatic compounds due to the increase of the solvent polarity following on the addition of a cetone to the supercritical fluid. In particular this paper shows that the limiting factors of the extraction selectivity of compounds obser ved in a specific class of contaminants seems due to the Van der Waal sorptive forces, diffusivities through matrix and size esclusion. The choice of extraction conditions must lead to the optimization of extra ction efficiencies and selectivities for a standardized metodology of SFE of PCBs and hydrocarbon compounds from contaminated soils in order to determine a correct in situ or ex situ remediation strategy by phy sico-chemical and/or biological treatment.