载气流量及升温速率对污染土壤中多氯联苯热脱附的影响

摘要

利用小型管式炉进行了载气流量和升温速率对多氯联苯污染土壤的热脱附过程影响的实验研究。结果表明流量的增大对多氯联苯含量和毒性当量的去除效率影响不大，载气流量小于400 ml·min-1时，气相中的脱附量明显增大，载气流量大于400 ml·min-1则脱附量变化较小，而多氯联苯的毒性当量则随着载气流量增大呈线性增加趋势。实验结果还表明污染土壤中多氯联苯变化速率与升温速率呈明显的正线性相关，随着升温速率增加，污染土壤中多氯联苯去除效率总体呈上升趋势，毒性当量去除效率降低。总体结果分析可以看到升温速率越大，总体效果也越好。污染土壤经热脱附处理后气固相的二英毒性当量则有不同程度提升，尤其气相内检测到了大量多氯二苯并呋喃生成。%A real soil contaminated by high concentration polychlorinated biphenyl (PCBs) was heated in a tube furnace at various carrier gas flow rate and at various heating rate to investigate their effect on thermal desorption of PCBs in contaminated soil. With the rising of carrier gas flow rate, a slight increase of PCBs removal efficiency (from 93.5%to 95.1%) and toxic equivalency quantity (TEQ) in soil were observed. With increase of the flow rate desorption amount of PCBs was obvious large when it was lower than 400 ml·min-1, then a little chang at>400 ml·min-1, while TEQ of PCBs showed a trend of linear increase with the rising of flow rate. The TEQ of polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/Fs) in treated soil decreased, while in carrier gas a large increase of TEQ of PCDD/Fs especially PCDFs was observed.The removal rate of PCBs in soil showed a significant positive linear relationship with the heating rate. With the rising of heating rate, the removal efficiency of PCBs in soil increased, and the TEQ of PCBs had a little change. The desorption amount of PCBs decreased. The TEQ removal efficiency of PCDD/Fs increased. After thermal desoption there was significant formation of PCDD/Fs while there was TEQ high increase of PCDD/Fs. Generally, the effect of flow rate on the removal efficiency of PCBs in soil was less but on the desorption amount of PCBs was significant. Higher heating rate can make a better removal efficiency of PCBs and lower formation of PCDD/Fs.