【作者】 孙亚平；

【导师】 石辉；

【作者基本信息】 西安建筑科技大学 ， 环境科学， 2008， 硕士

【摘要】 土壤作为一种重要的环境介质,承担着90%以上的多环芳烃（PAHs）环境负荷,研究多环芳烃在土壤上的吸附行为对于认识其在土壤环境中的持留、分布、迁移转化、归宿及生物有效性等具有重要意义。本文采用批量平衡法研究了多环芳烃萘在填土耕层土、塿土粘化层土、塿土古土壤、黄壤土、紫色土和石灰土上的吸附行为,探讨了萘在不同土壤上吸附的动力学特征和热力学特征,分析了供试土壤理化性质与吸附参数之间的关系,以及萘在土壤上吸附的位置能量分布函数,为多环芳烃类物质在土壤中的环境化学行为和迁移转化规律提供理论依据。研究结果表明:（1）采用Elovich方程、双常数方程、抛物线扩散方程、Pseudo-first order模型和Pseudo-second order模型5种吸附动力学模型对土壤吸附萘的动力学特征进行研究,实验温度条件下,除壤土粘化层土（25℃）外,不同类型土壤吸附萘的最优动力学模型是Pseudo-second order模型。由此计算得到土壤对萘的吸附活化能,其中塿土古土壤和黄壤土的活化能E_a值十分接近,分别为27.50、27.21KJ·mol^-1;而紫色土的E_a值最大,为132.74KJ·mol^-1。（2）实验温度条件下,Henry模型、Freundlich模型和deBoer-Zwikker极化模型均能较好地拟合萘的吸附等温线。45℃下的吸附等温线明显地高于25℃的吸附等温线,表现出随温度升高吸附量增大的趋势;在25℃条件下,萘在土壤有机碳上的分配可能是吸附的主要机制。Freundlich模型的吸附容量参数K_F和deBoer-Zwikker模型的起始吸附势ε₀在两个温度下有极显著的差异;但Freundlich模型的n参数表征了土壤颗粒表面的性质,对温度变化不敏感。（3）土壤自水溶液中吸附萘的吉布斯自由能△G＜0,说明吸附是一个自发过程;并且吸附热△H＞0,为一吸热反应,整个吸附体系中熵增是吸附作用进行的主要驱动力。（4）随着平衡吸附量qe的增大,吸附位能E^*呈减小的趋势,并且初始阶段吸附能E^*下降明显,而后逐渐平缓。实验浓度范围内萘在供试土壤上吸附的位置位置能量分布曲线的形状和变化趋势一致,随着净吸附能E^*的增加,位置能量分布函数按指数函数衰减。（5）当温度由25℃增加到45℃时,塿土粘化层土、塿土古土壤对萘的吸附位置数或吸附容量都有增加,前者由32.98μg·g^-1增加为35.92μg·g^-1;而对其余土样而言随温度的上升吸附容量则呈下降趋势,t检验分析表明其在两个温度下无显著差异（p=0.727）。在25℃下,不同土壤对萘的吸附容量与其有机碳含量表现出较强的相关性（p=0.067）,而在45℃时两者之间的相关性变差（p=0.306）。更多还原

【Abstract】 Polycyclic aromatic hydrocarbons（PAHs）,which many countries view as the priority pollutants to deal with,are important organic contaminants with the nature of carcinogenic,harmonic and mutagenic.More than 90%of PAHs load in the environment was performed by soil medium and adsorption and desorption of polycyclic aromatic hydrocarbons（PAHs）by soils and sediments plays an important role in determining their transport and fate in the soil environment.The study will have a great significance for realizing the retention,distribution,fate and transportation,bioavailability of PAHs and exploring the rules of transportation and transformation of PAHs in soil environment.Adsorption of naphthalene by six different soils,including surface layer of lou soil,claying layer of lou soil,old soil layer of lou soil,yellow earth,purple soil,limestone soil,was examined using batch adsorption equilibrium methods.The adsorption kinetics and thermodynamics of naphthalene on different soils was studied,and the relationship between soil physicochemical properties and adsorption fitting parameters were analyzed.Further more,the site-energy distribution function for naphthalene adsorption in soils was obtained.The main findings are as follows:（1）All sets of experimental adsorption data were fitted using five different sorption kinetic models:the Elovich equation,the dual constant model,the parabolic diffusion model,the Pseudo-first order model,and the Pseudo-first order model.The kinetics of adsorption prcesses were best described by Pseudo-first order model for all the soils studied other than claying layer of lou soil（25℃）.The activation energy of adsorption was calculated using the rate constant k₂ of Pseudo-second order model, and it was found to be 27.50、27.21、132.74 KJ·mol^-1for the old soil layer oflou soil, yellow earth and purple soil,respectively.（2）Henry model,Freundlich model and deBoer-Zwikker model can better fit the adsorption isotherm of naphthalene by soils compared to Langmuir model and BET model.The adsorption isotherm by adsorption and relative balance concentration at 45℃were obviously higher than that at 25℃,these showed that adsorption capacity increased with the temperature increasing.At 25℃condition,naphthalene distribution between aqueous solution and soil organic carbon was the main adsorption mechanism,but the adsorption mechanism became more complicated as the temperature increasing.The adsorption capacity K_F of Freundlich model and the initial adsorption potential of deBoer-Zwikker model had obvious difference at two temperature degree,but the parameter n in Freundlich model was not sensitive to temperature change because it only characterizes the surface property of the soil particles.（3）The evaluated Gibbs free energy change and enthalpy change indicated the spontaneous and endothermic nature of naphthalene adsorption in soils,and the entropy gain in whole adsorption system is the main adsorption driving force.（4）The adsorption energy E^* decreased significantly in the initial stage with increasing the adsorption qe,and then decreased slowly.The site-energy distribution for naphthalene sorption on soils decreased exponentially with adsorption energy E^* increasing over the concentration range.（5）At the experimental concentration the adsorption energy E^* ranged from 4.15～12.25 KJ·mol^-1,8.19～17.95 KJ·mol^-1at 25℃and 45℃respectively.At 25℃condition,the area under the site energy distribution curve of naphthalene sorption on soils other than claying layer of lou soil and old soil layer of lou soil was larger than that at 45℃.The value of claying layer of lou soil was from 32.98μg·g^-1to 35.92μg·g^-1.The adsorption capacity of naphthalene in soils had no difference at two different temperatures（ρ=0.727）.The adsorption capacity of naphthalene in soils appeared to positively correlate with soil organic content at 25℃（ρ=0.067）,but as the temperature increasing this relationship was not obvious（ρ=0.306）.更多还原