Abstract
Ex-situ thermal desorption treatment (ESTD) of petroleum contaminated soil (PCS) was developed to investigate the desorption behavior of five carbon number-based fractions of extractable petroleum hydrocarbons (EPHs) and the morphology changes of soils. The experimental kinetics, isotherm models and thermodynamic parameters were analyzed to provide mechanism insight. Results suggest that most of the diesel range organics (DRO, C10-C28) was removed at low temperatures (100–350 °C), while high temperature (350–550 °C) thermal desorption (HTTD) was effective in removing EPHs due to the high removal efficiency of oil range organics (ORO, C28-C40). Under HTTD treatment, the re-adsorption of low molecular weight hydrocarbons was observed. The particle size of sandy soil barely changed during desorption process, while a significant agglomeration was found in red clayey at high temperatures. The desorption kinetics can be well fitted by the exponential decay model, and the desorption equilibrium agrees with the Langmuir isotherm model. The removal process of EPHs was controlled by multiple diffusion mechanisms. ΔH° values of GS and RS were 65.73 kJ/mol and 76.29 kJ/mol, respectively. DRO was mainly controlled by physical adsorption, while to a great extent ORO release was controlled by chemical adsorption. Finally, removal mechanisms and matrix control mechanisms during ESTD treatment were proposed.
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