Abstract: 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.

Key words: thermal desorption, PAHs, soil, decontamination level, residual contamination, soil characteristics

摘要： 采用滚筒式间接加热设备，在50～450℃加热温度和30 min停留时间实验条件下，测试了焦化厂污染场地低含量（S1）和高含量（S2）PAHs污染土壤中16种PAHs的热脱附效率和残留量的变化，并初步分析了热脱附处理对土壤有机碳（TOC）、可溶性有机碳（DOC）、比表面积（SA）和粒径分布的影响，结果表明：加热温度、污染物含量和污染物分子量对PAHs的脱附效率均存在极显著影响（p<0.01），其中加热温度影响程度最大。S1和S2土壤中各类PAHs在加热温度达到其熔点附近开始有效脱附，LPAHs（低分子量PAHs）与HPAHs（高分子量PAHs）之间的热脱附效率仅在不超过300℃（S1土壤）和400℃（S2土壤）加热条件下存在明显差别。土壤中各类PAHs的脱附与其有效态密切相关，S1和S2土壤中有效态PAHs分别在200～250℃和250～300℃加热条件下几乎全部脱附。450℃加热温度条件下，S1和S2土壤中∑PAHs（总PAHs）脱附效率能够达到91.3%和98.4%，其中8种目标PAHs的含量范围分别为0.07～0.71 mg·kg^-1和0.26～40.20 mg·kg^-1，土壤中部分PAHs仍超过相应的北京市《场地土壤环境风险评价筛选值》住宅用地筛选值；450℃加热温度下，S1和S2土壤中TOC含量分别下降51.4%（p<0.05）和23.1%（p<0.05），S1和S2土壤中DOC变化趋势相反，SA的下降、较粗颗粒比例略有增加和电镜扫描中土壤颗粒团聚现象相吻合。

关键词: 热脱附, 多环芳烃, 土壤, 脱附效率, 残留量, 土壤性质