Soils contaminated by polycyclic aromatic hydrocarbons (PAHs) were sampled from a typical coking plant in southeast Beijing

China

and tested by thermal desorption under the controlled condition of 50—450℃ heating temperature and 30 min constant residual time using an indirect rotary heating laboratory equipment. After each thermal desorption program

decontamination level

residual contamination of 16 EPA priority PAHs and changes in soil characteristics

i.e. total organic carbon (TOC)

dissolved organic carbon (DOC)

surface area (SA) and soil particle size distribution

were investigated for low PAHs concentration soil (S1) and high PAHs concentration soil (S2)

respectively. The results showed that with increasing heating temperature

the decontamination level of LPAHs (low molecular weight PAHs

sum of Nap to Pyr)

HPAHs (high molecular weight PAHs

sum of BaA to BgP) and total PAHs increased significantly (p<0.01)

which was governed successively by heating temperature

PAHs molecular weight and contaminant concentration due to the F values based on a multivariate analysis. The decontamination level began to increase significantly around the melting point and for the isothermal desorption the significant difference of decontamination level between LPAHs and HPAHs existed only below 300℃ for S1 and 400℃ for S2. It was revealed that the thermal desorption process were evidently associated with the form of PAHs in soils and the bioavailable PAHs were almost removed at 200—300℃. The decontamination level reached 91.3% and 98.4% at 450℃ heating temperature where the eight target residual PAHs concentration ranged from 0.07 mg·kg-1 to 0.71 mg·kg-1 for S1 and from 0.26 mg·kg-1 to 40.20 mg·kg-1 for S2

whereas several PAHs species still exceeded the corresponding screening levels for soil environmental risk assessment of residential land in Beijing. After thermal desorption at 450℃

it was also found that TOC decreased by 51.4% (p<0.05) for S1 and by 23.1% (p<0.05) for S2

simultaneously with an inverse change trend in DOC between S1 and S2. Moreover

surface areas of S1 and S2 after heating were smaller than that before heating

which coincided with the slight increase in soil particle size and agglomeration existing at an electron scanning program.