SUPERCRITICAL-FLUID EXTRACTION OF CONTAMINATED SOIL

The objective of this preliminary investigation is to determine the ab ility of supercritical carbon dioxide (SC-CO2) to remove contaminant o rganic compounds from soil. The focus is to obtain experimental data o n the extraction of organic hazardous waste from soils by SC-CO2. The aim of this study is to evaluate this information for its applicabilit y to the design of a supercritical fluid extraction (SFE) process for environmental remediation and waste management. An experimental contin uous-flow extraction apparatus that can be operated up to 340 atm has been constructed at Vanderbilt University. With this apparatus the eff ects of pressure, temperature, flow rate, and soil properties on the e quilibrium thermodynamics and mass-transfer coefficient of the SFE pro cess can be studied. For the purposes of this paper, it is assumed tha t the supercritical solvent flows through a fixed bed extracting organ ic contaminants from spherical soil particles. To verify the apparatus and our experimental technique, preliminary studies on the equilibriu m solubility of naphthalene were conducted. The extraction cell was pa cked with a single section of one layer of pure cylindrical naphthalen e pellets. The results show that naphthalene solubility in supercritic al CO2 experimentally determined at constant temperature (55 degrees C ) agree over the entire pressure range studied (125-270 atm) with resu lts published by other investigators. Experiments were also conducted with naphthalene and 1,2,4 trimethylbenzene in soil formed into spheri cal shape. Preliminary results of this investigation has demonstrated that effective extraction (98%) of naphthalene from soil by supercriti cal CO2 can be achieved in our apparatus.