【作者】 周蔚凤；

【导师】 张建英；

【作者基本信息】 浙江大学 ， 环境科学， 2011， 硕士

【摘要】 本文综述了中国土壤多氯联苯(Polychlorinated Biphenyls, PCBs)污染现状和分布规律,选取中国西部黄土、中国东部青紫泥和水稻土三种理化性质不同的土壤作为地质吸附剂(geosorbents)开展吸附机理研究,从吸附动力学和热力学的角度,比较三种不同类型的土壤对PCBs的吸附特征和吸附机理,探讨其结构特征与其对PCBs吸附能力之间的关系,得到以下研究结论。(1)青紫泥和水稻土对PCBs吸附量大,可作为PCBs良好地质吸附剂,而黄土对PCBs的吸附量较小。通过土壤静态序批吸附实验,在常温24 h条件下,黄土、青紫泥和水稻土对Aroclor1260中10种PCBs的吸附基本达到表观平衡状态。本文研究的三种土壤对PCBs的吸附能力顺序为：青紫泥>水稻土>黄土,与三种土壤有机质含量多少相一致。青紫泥、水稻土和黄土对PCBs的吸附量分别为1.46×10-1-9.08μg/g,1.37×10-1-7.89μg/g和6.29×10-3-4.424×10-1μg/g,青紫泥和水稻土的吸附能力分别是黄土的17.64-24.00倍和15.24-21.76倍。青紫泥和水稻土是PCBs良好的地质吸附剂；而黄土吸附能力小,可作为PCBs污染区土壤(青紫泥和水稻土)的覆盖材料。(2)PCBs在三种土壤中的吸附均符合准二级反应动力学模型,膜扩散和颗粒内扩散是其吸附过程中的控速步骤。通过动力学实验和模型拟合,比较三种动力学方程(准一级反应动力学方程、准二级反应动力学方程和Elovich方程)对土壤吸附Aroclor1260中10种目标PCBs数据的拟合结果发现,准二级反应动力学方程拟合时的相关系数最高,R2≥0.953；且由该方程计算出来的平衡吸附量qe,cal与实验值qe,exp相吻合,认为PCBs在黄土、青紫泥和水稻土中的吸附动力学均符合准二级反应动力学模型。黄土、青紫泥和水稻土对PCBs的吸附均表现出“两阶段”特性,初始的快吸附和随后的慢吸附阶段,这主要是由吸附位点的数量及吸附位点的强弱决定的。颗粒内扩散和膜扩散是土壤吸附PCBs过程中的控速步骤,共同决定了三种土壤地质吸附剂对PCBs的吸附速率。(3)在实验条件下,黄土对PCBs的吸附呈线性,青紫泥和水稻土则呈现非线性,温度对三种土壤吸附量存正负影响。应用线性等温方程、Langmuir等温方程和Freundlich等温方程对吸附数据拟合的结果表明,当Aroclor1260的浓度为0.10-0.80 mg/L时,黄土对其中10种目标PCBs的吸附不能用Langmiur方程和Freundlich方程描述,但符合线性吸附等温方程(R2>0.96)；而青紫泥和水稻土对PCBs的吸附则表现出明显的非线性吸附特征,且对于每一种目标多氯联苯而言,其在水稻土中吸附的非线性更大,这两种土壤对PCBs的吸附数据用Freundlich模型拟合程度最好(R2≥0.92),这可能和土壤中两相态(无定形态相和浓缩态相)有机质的相对含量相关。同时,通过对△G0、△H0和△S0等热力学参数的比较分析发现,PCBs在三种土壤中的吸附均为自发过程(△G0<0),室温条件下(22℃),PCBs在三种土壤中吸附的驱动力大小为：青紫泥>水稻土>黄土。在所研究的温度范围(22-46℃)内,随着温度的升高,青紫泥和水稻土对PCBs的吸附量略有下降,而黄土对PCBs的吸附量反而增大,常温条件下黄土作为PCBs土壤(青紫泥和水稻土)覆盖层的效果最好。热力学参数△H0进一步证明,黄土吸附PCBs是一个吸热过程(△H0>0),而青紫泥和水稻土吸附PCBs则是放热过程(△H0<0)。黄土吸附PCBs过程中将增加系统的无序性(△S0>0),但青紫泥和水稻土吸附PCBs过程中固液界面的混乱度降低(△S0＜0),与熵变相关的作用力控制了它们对PCBs的吸附,其中疏水效应(hydrophobic effect)是青紫泥和水稻土吸附PCBs的主要驱动力。更多还原

【Abstract】 According to Polychlorinated Biphenyls (PCBs) pollution and distribution characteristics in Chinese soils, this research selected three different soils—loess, blue purple clay and paddy soil—as the geosorbents to carry out sorption research, compared the sorption characteristics and sorption mechanisms of PCBs in the three soils from the view of sorption kinetics and thermodynamics, and explored the relationships between the structural characteristics of soils and their sorption capacities. The results of research are listed as follows.(1) Blue purple clay and paddy soil exhibiting powerful PCBs sorption capabilities are good geosorbents for PCBs, while loess has low PCBs sorption capacities.The batch experiments showed that the apparent equilibriums of 10 PCBs in the three soils were reached at 24 h, and the sequence of equilibrium sorption capacities of three soils for every PCB congener was:blue purple clay>paddy soil>loess, which was consistent with the contents of organic matter of the soils selected. The sorption amounts of blue purple clay, paddy soil and loess for PCBs were 1.5×10-1-9.1μg/g,1.4×10-1-7.9μg/g and 6.3×10-3-4.2×10-1μg/g, respectively, and the sorption capabilities of blue purple clay and paddy soil were found to be 17.64-24.00 times and 15.24-21.76 times that of loess. Blue purple clay and paddy soil are good geosorbents for PCBs; while loess with low sorption capabilities for PCBs can be recommended as covering material for soils (blue purple clay and paddy soil) polluted by PCBs.(2) PCBs sorption in three soils fit the pseudo-second-order equation well, and the intraparticle diffusion and film diffusion were the sorption controlling steps.Three sorption kinetic equations (pseudo-first-order equation, pseudo-second-order equation and Elovich equation) were applied to simulate the sorption kinetic data, and the pseudo-second-order model could describe PCBs sorption in the three soils well with R2>0.953 and a good agreement between the experimental qe,exp values and the calculated qe,cal values. Two stages were found in all sorption process, the initial stage of rapid sorption and the following stage of slow sorption, which were determined by the numbers and capabilities of sorption sites. The film diffusion and intraparticle diffusion were the sorption controlling steps, together determining the sorption rapid of PCBs in all three soils.(3) PCBs sorption in loess fit a linear model, while PCBs sorption in blue purple clay and paddy soil indicated nonlinear sorption characteristics under laboratory condition.Three sorption isotherm equations were applied to simulate the experimental data, and the result showed that, when the concentrations of Aroclor1260 were 0.1-0.8 mg/L, the sorption behaviors of 10 PCBs in loess fit a linear model with R2>0.96; however, the nonlinear sorption isotherms of PCBs in blue purple clay and paddy soil were observed (n>1) and the Freundlich model could describe the sorption behaviors of PCBs in three soils well (R2>0.92). That could be explained by the relative content of two-phase (amorsphous phase and condensed phase) organic matter.According to the thermodynamic parameters calculated, the results showed that PCBs sorption in the three soils was a spontaneous sorption process (ΔG0>0), and the sequence of driving force for PCBs sorption in the three soils at room temperature (22℃) was:blue purple clay>paddy soil>loess. The sorption amounts of PCBs in blue purple clay and paddy soil decreased slightly with temperature raised from 22 to 46℃, while the sorption amounts of PCBs in loess increased in the same range of temperature. Therefore, loess as the covering material could be reached the best effect in room temperature (22℃). The calculated values ofΔS0 andΔH0 were positive in loess suggesting that the process was endothermic and the sorption of PCBs increased the disorder in the system; whereas for blue purple clay and paddy soil, both were negative indicating that the process was exothermic and the sorption of PCBs decreased the randomness at the solid-solution interface. The interaction force related with entropy change affected the sorption of PCBs in blue purple clay and paddy soil and hydrophobic effect was the main sorption driving force for PCBs sorption in these two soils.更多还原