环境因子对胡敏酸吸附3,3',4,4'-四氯联苯的影响

Effect of Environmental Factors on 3,3',4,4'-Tetrachlorobiphenyl Adsorption onto Humic Acid

3,3',4,4'-四氯联苯(PCB77)是毒性最强的PCBs同系物之一。采用振荡平衡法研究pH、离子强度以及温度等环境因子对胡敏酸(HA)吸附PCB77的影响。采用linear模型、Freundlich模型以及Langmuir模型拟合吸附等温线,结果表明,低pH时,HA分子发生团聚,形成大量"微孔"和"中孔"结构,吸附位点增多,吸附能力增强,随着pH的升高,HA溶解性增强,疏水性降低,吸附PCB77的能力降低,Langmuir模型拟合最优;随着离子强度的增大,Ca^(2+)所带正电荷中和HA表面负电荷并与PCB77形成竞争吸附,吸附PCB77的能力降低,Freundlich模型拟合最优;随着温度的升高,外部热量弥补了系统熵和焓的负变化,PCB77溶解度增大,HA吸附PCB77的能力降低,Freundlich模型拟合最优。实验结果表明,低pH、低离子强度、低温条件下,利于HA对PCB77的吸附。研究环境因子对HA吸附PCB77的影响,以期阐明环境因子与PCB77环境行为的动态关系,为原位修复PCBs污染土壤提供理论依据。

3,3＇,4,4＇-tetrachlorobiphenyl（PCB77） is one of the most toxic congeners of PCBs. The effect of some environmental factors such as p H, ionic strength and temperature on PCB77 adsorption on humic（HA） acid was studied by adsorption experiment with different models to fit the sorption isotherms. The experimental study showed that at low p H, the structure of HA molecule changed and amount of micropore and mesopore structures formed resulting in sorption capacity enhancement, while at high pH the sorption amount decreased due to the enhanced solubility of HA and decreased hydro-phobicity, the process of which was better described by the Langmuir adsorption model; and with the increase of ionic strength, calcium ion neutralized the negative charges on HA surface and formed competitive adsorption against PCB77 causing the sorption amount to decrease, meanwhile the sorption process at different ionic strength was accurately described by the Freundlich adsorption model. Furthermore, external heat could compensate for the negative change of system entropy and enthalpy as the temperature rose, which led to enhanced solubility of PCB77 and decreased sorption capacity, and the fitting results could be better illustrated by the Freundlich model. In summary, low p H, low ionic strength and low temperature were beneficial to PCB77 adsorbed on HA, and the results of the study could make clear the dynamic relationship between environmental factors and environmental behavior of PCB77, which would be useful in on-site remediation of PCBs-contaminated soil.