外源有机质对土壤中菲热脱附的影响及机制

The effect and mechanism of exogenous organic matters on thermal desorption of phenanthrene in contaminated soil

热脱附是治理多环芳烃污染场地土壤的有效途径.污染场地土壤中可能存在多种复杂的外源性有机质,其在热脱附过程中的变化及对污染物去除效率的影响尚不清楚.本文以菲(Phe)为多环芳烃的代表,猪粪、秸秆、聚丙烯(PP)分别作为动物性、植物性和人工合成外源有机质的代表添加至污染土壤中,利用管式炉模拟了200~400℃下的热脱附过程.结果显示,在相同条件下,含PP的土壤中Phe热脱附效率最高,含猪粪的土壤热脱附效率最低,但其去除率随温度变化的敏感度最高.固-气吸附平衡实验证明,3种土壤中Phe的热脱附去除率高低与3种外源有机质对Phe的吸附能力强弱相符.元素分析、傅里叶红外、三维荧光及扫描电镜表征证明,不同外源有机质在高温下发生的差异性变化也影响了土壤中Phe的热脱附规律.200~400℃热处理下PP发生了物理形态改变,造成土壤比表面积显著减小、平均孔径显著增大,有利于Phe从固相到气相的传质.两种天然有机质则在高温下发生了脂肪性减小、芳香性增大的化学改变,其中猪粪的化学结构随温度升高变化最显著,因此含猪粪土壤中Phe的去除率随温度变化的敏感性最高.本研究首次证明了场地土壤中潜在的外源有机质对热脱附修复效率的重要影响,为场地土壤热脱附修复工艺的精准优化提供了理论参考.

Thermal desorption has been identified as a viable method for remediating site soils contaminated with polycyclic aromatic hydrocarbons(PAHs).Complex exogenous organic matter may be present in contaminated sites,the transformation of which occurs during the thermal desorption process,and its impact on pollutant removal efficiency remains poorly understood.In this study,phenanthrene(Phe)was employed as a model compound for PAHs,while pig manure,straw,and polypropylene(PP)were introduced into the contaminated soil as representatives of animal,vegetable,and synthetic exogenous organic matter,respectively.The thermal desorption process was simulated using a tube furnace operating at temperatures ranging from 200 to 400℃.The results showed that under the same conditions,the soil containing PP exhibited the highest efficiency in the thermal desorption of Phe,whereas the soil containing pig manure demonstrated the lowest efficiency in Phe desorption,although its removal ratio was most susceptible to variations in temperature.Solid-gas adsorption equilibrium experiments demonstrated that the thermal desorption removal of Phe from the three soils depended on the adsorption capacity of the three exogenous organic matter samples for Phe.Elemental analyses,Fourier transform infrared spectroscopy,three-dimensional fluorescence spectroscopy,and scanning electron microscopy revealed that different changes in the physical and chemical structure of exogenous organic matter at elevated temperatures result in distinct thermal desorption patterns of contaminants in various soils.The physical morphology of PP changed under heat treatment at 200~400℃,resulting in a significant decrease in the specific surface area of the soil and a significant increase in the average pore size,which favored the mass transfer of Phe from the solid phase to the gas phase.Conversely,the other two natural organic matter components experienced chemical transformations at elevated temperatures,characterized by a decrease in aliphaticity and an increase in aromaticity.Among these constituents,pig manure exhibited the most pronounced modification in chemical composition as temperature increased,leading to a heightened susceptibility of Phe removal from soils containing pig manure to temperature variations.This study has illustrated the significant impact of potential exogenous organic matter in site soils on the efficacy of thermal desorption remediation,offering a theoretical framework for the precise optimization of the thermal desorption remediation process for site soils.