Supercritical Fluid Extraction of a Light PAH Contaminated Sand

This work was aimed at evaluating the feasibility of a remediation treatment performed by means of a supercritical carbon dioxide extraction on a sandy soil recently contaminated by light polycyclic aromatic hydrocarbons. The soil utilized in this study was artificially contaminated by naphthalene and anthracene. The artificial contamination process was intended to simulate a recent accidental spillage of hydrocarbon fuels. Several extractions, aimed at singling out the operating parameters (pressure, temperature, supercritical fluid mass flow rate) that are able to obtain the residual required concentration (50 mg/kg dry soil) in the shortest time, were carried out on a on-purpose made system. The best extraction conditions were 120 bar and 40◦C for a naphthalene contaminated soil and 200 bar and 80–100◦C for an anthracene contaminated soil. The results obtained in the experimental tests made it possible to build an analytical model able to correlate, for the given soil, the extraction length to the operating parameters such as supercritical fluid density, temperature and mass flow rate. In order to evaluate the economic feasibility of the process, a unit treatment cost was evaluated for the case of an extraction carried out in a 10 m3 reactor in the presence of the best extraction conditions that were previously determined. The extraction unit cost was therefore equal to 35 000–65 000 /t for a soil with a starting contaminant concentration equal to 1000 mg/kg of dry soil.