Evaporation phenomena during thermal decontamination of soils
Effects of thermal treatment conditions on removal of a low volatility aromatic contaminant from soil are quantified. Shallow beds (10 mg) of a clay soil pretreated with 8 ± 0.4 wt % pyrene were heated in a thermogravimetric analysis at 5, 25, or 50 °C/min or isothermally. Effects of temperature, time, initial soil mass, initial contaminant mass, heating rate, and flow rate of carrier gas (helium at standard conditions) were studied, as were weight loss of uncontaminated soil and evaporation rates of pure pyrene. Extensive pyrene removal from foil (85−90%) was found between 200 (at 5 °C/min) and 300 °C (at 50 °C/min). Soil decontamination was modeled as pyrene transport without chemical reaction, i.e., (1) evaporation from a liquid sheath encasing each soil particle; (2) diffusion through the soil pile; and (3) diffusion to the ambient through a concentration boundary layer between the soil pile and the top of the thermobalance crucible. Evaporation is important in removing most, i.e., 70% or more, of the...