Remediation of flare pit soils using supercritical fluid extraction

Abstract

Supercritical fluid extraction (SFE) is a promising remediation technology for contaminated soils. This work investigates the use of SFE to remove petroleum hydrocarbons (PHCs) from flare pit soils. Extractions were performed on two flare pit soils at pressures ranging from 11.0 to 24.1 MPa and at temperatures ranging from 40 to 80 °C in an attempt to identify the best extraction conditions and to understand the effects of pressure, temperature, supercritical fluid flow rate, soil type, and extraction time on the extraction efficiency. For the conditions studied, the efficiency of the SFE process appeared to be solvent-density dependent. Conditions of 24.1 MPa and 40 °C (highest supercritical fluid density) yielded the highest extraction efficiency for both soils (89% for the sand and 80% for the loam). An increase in temperature at a fixed pressure led to a decrease in the extraction efficiency while an increase in pressure at a fixed temperature led to an increase in the extraction efficiency. The treated soils appeared to be drier, grainy, and lighter coloured than the soil prior to extraction.Key words: supercritical fluid extraction (SFE), supercritical carbon dioxide, flare pit soils, contaminated soil, soil remediation, biorecalcitrant petroleum hydrocarbons.