菲和萘在黄土上的吸附等温线和吸附热力学

Sorption isotherms and sorption thermo- dynamics of phenanthrene and naphthalene on loess soil

研究了菲和萘在黄土上的吸附行为 ,比较分析了 Linear方程、Freundlich方程和 L angmuir方程描述吸附等温线的准确性。结果表明 ,菲和萘在黄土上的吸附等温线呈非线性 ,Freundlich方程最符合其吸附行为。菲和萘在天然黄土上的吸附量随温度升高而降低。其吸附是一个放热过程 ,吸附热分别为 0 .0 1774k J·mol- 1和 -0 .0 612 5 k J· mol- 1 ;吸附的标准自由能改变量分别为 -9.93 9k J· mol- 1和 -7.3 3 3 k J· mol- 1。标准自由能的变小是菲和萘在黄土上吸附的推动力。经过阳离子表面活性剂改性后的黄土对菲和萘的吸附能力 ,随加入的表面活性剂占原土阳离子交换容量 ( CEC)的百分数增大明显增强 。

This paper aims to introduce the author's research on the sorption isotherms and sorption thermodynamics on the natural and HDTMA bromide modified loess soils. As is known, loess soil topographically covers the vast land in China's northwest, where oil fields are widely exploited in the recent two decades. As a result, the soil has been severely contaminated and water resources have been seriously spoiled due to spillage of crude oil and leakage from storage tanks and pipelines. Loess soils with a low organic carbon has, scientifically speaking, little absorbing capabilities for organic contaminants in the northwest China soil environment, and therefore they have very limited function to diminish the potential contamination resulted by organic pollutant leaching through the unsaturated zone to the groundwater level. On the other hand, as a class of petroleum compounds, attributed to the CERLA Priority List of Hazardous Substances, polycyclic aromatic hydrocarbons (PAHs) present a group of compounds with two or more fused aromatic rings that are mutagenic, carcinogenic and teratogenic. In this paper, we have chosen phenanthrene and naphthalene as the indicators of PAHs to study the sorption isotherms and sorption thermodynamics on the natural and HDTMA bromide modified loess soils. Since it is found that fused ring polycyclic aromatic hydrocarbons, naphthalene and phenanthrene, including their substituted derivatives, exist in the crude oil and refined oil products, they usually serve as the typical model substrates for studies on fate, transport and metabolism of carcinogenic PAHs. Careful studies of Linear, Freundlich and Langmuir equations on accuratity, indicate that Freundlich was the most appropriate type for the two compounds. The absorbed amount of phenanthrene and naphthalene in the cationic surfactant-modified loess soils proves higher than those on the natural loess soils, and the amount of PAHs removed from solution is significantly dependent on the concentration of HDTMA in the loess soil. In addition, since absorption is the exothermic process, whose sorption thermodynamics is -9.939 kJ·mol^(-1) and -7.333 kJ·mol^(-1), respectively, the free energy changes of phenanthrene and naphthalene sorption on natural loess soils works out at about (-9.939) kJ·mol^(-1) and -7.333 kJ·mol^(-1) respectively, so the sorption would take place on the loess soils due to the decrease of the free energy. Thus, the above research can be taken as a contribution to founding a theoretical basis of studying contamination control and remediation.