Remediation of flare pit soil using supercritical fluid extraction (SFE)

Supercritical fluid extraction (SFE) proved to be a promising new technology for remediation of flare pit soils. Two flare pit soils (one sand and one loam) were collected from sites in Alberta and investigated. Extraction experiments were conducted at conditions of temperature and pressure ranging from 40°C to 80°C and 11.0 MPa to 24.1 MPa, respectively, in an attempt to identify optimum extraction conditions. SFE was found to be solvent density dependent. Of the various extraction conditions investigated, a pressure of 24.1 MPa and a temperature of 40°C (highest supercritical fluid density) yielded the highest extraction efficiency for both the soils. These conditions led to 89% extraction efficiency for total petroleum hydrocarbons (C10 to C50) for the sand and 80% extraction efficiency 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.