Removal kinetics of petroleum hydrocarbons from low-permeable soil by sand mixing and thermal enhancement of soil vapor extraction.

Thermally enhanced remediation of n-alkanes-contaminated silty soil mixed with coarse quartz sands was demonstrated in a laboratory cylindrical tank with diameter of 40 cm and depth of 30 cm. The removal kinetics of semi-volatile n-alkanes (C10, C11, C13-16) under three pulsed heating operations of soil vapor extraction (SVE) was investigated. CMG-STARS software was adopted to simulate the dynamics of heat transfer within the soil column. The results indicated the dramatic increase of air permeability of soil and acceleration of heat transfer after introduction of sand, with the result of achieving rapid soil remediation. Gas-phase transfer of n-alkanes mainly occurred when average soil temperature was ≥100 °C. At the end of remediation with soil subjected to heating for 30.8 h (total running time), the average soil concentration of total n-alkanes was reduced from initial 3106.5 to 202.4 mg/kg, corresponding to 93.4% of mass removal. The residual n-alkanes of C10, C11, C13 and C14 in all collected soil samples were declined to levels of lower than 10 mg/kg. Most of the soil concentration-gradient curves for n-alkanes tested almost coincided with their isothermal contours, indicating the key impact of thermal drive force on contaminant transfer.