沉积物颗粒表面分形特征的研究

Study on the particle surface fractal characteristics of sediments

通过一阶分子连接性指数1 χ与分子表面积TSA之间的相关性计算出吸附分子的尺度 ,采用分形吸附等温线法计算出妫河沉积物的Ds为 2 3 79,官厅沉积物的Ds 为 2 83 6.基于沉积物对N2 的吸附 脱附等温线数据 ,采用FHH (Frenkel Halsey Hill)方程计算出两种沉积物的表面分形维数Ds,发现官厅沉积物与妫河沉积物的Ds 相差不大 ;温度影响Ds 主要是由于升温改变了沉积物的组成与结构 .在本实验中采用热力学模型 (thermodynamicmodel)计算出的Ds 值大都超过 3 .此外 ,沉积物的Ds 与其比表面积、矿物含量、CEC、有机质的相关性差 .以萘、菲、芘作为码尺计算出的Ds 并不完全是表面空间填充能力的客观表现 。

The surface fractal dimensions (D_s) of two natural sediments were determined by using different models. Fractal Freundlich isotherm equation was used to fit the adsorption data of three polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, phenanthrene and pyrene. Based on the relations of the molecular cross-section areas (a_0), the first molecular connective indexes (~1χ) and the molecular surface areas (TSA) of the three PAHs, the D_s values of 2.836 and 2.379 were obtained for the two sediments from Guanting reservoir and Guihe river, respectively.Based on the nitrogen adsorption-desorption data, the D_s values of the same sediments were also calculated by using FHH and thermodynamic models separately. The results showed that the D_s values of these two sediments had little differences when FHH model was applied. The D_s variation of the Guanting reservoir sediments at different temperature could be explained by their composition and structure changes with temperature. And most of D_s values are greater than 3 in this thermodynamic model. Furthermore surface fractal dimension D_s of sediments had weak correlation with the specific surface area (SSA), ion exchange capacity (CEC) and the amount of organic component in particles. It was postulated that the surface fractal dimension D_s of particles calculated by using the three PAHs was an important integrated feature parameter related to the surface adsorption process, rather than a parameter of fully characterizing the space occupation capacity of particle irregular surface.