高岭石、针铁矿及其二元体对胡敏酸的吸附特性

研究了高岭石、针铁矿及其混合物(KGM)和复合物(KGC)的表面性质及吸附胡敏酸的特性.结果表明,4种物质的比表面积(SSA)表现为针铁矿KGCKGM高岭石,KGM的SSA接近两种纯物质的平均值,而KGC的SSA明显升高.高岭石、针铁矿、KGM和KGC的等电点(IEP)分别为3.2、7.9、6.1和6.7;初始p H=5.0时,其表面Zeta电位分别为-13.9、38.2、14.3和19.7 m V.4种样品对胡敏酸的动力学吸附过程适合用准二级动力学模型描述,表明化学吸附是主要作用机制.一、二位Langmuir模型可较好地拟合等温吸附数据(R~2为0.962~0.993),其中二位Langmuir模型对KGM和KGC吸附数据的拟合度R~2分别为0.989和0.993;Freundlich模型对等温吸附数据的拟合度较低,但两种二元体的拟合度高于两种纯物质.初始p H=5.0时,高岭石、针铁矿、KGM和KGC对胡敏酸的吸附容量(q_(max))分别为6.02、61.83、35.13和42.10 mg·g~(-1);两种二元体的q_(max)都高于两种纯物质q_(max)的平均值,其中KGC的q_(max)明显升高.热力学参数表明,4种样品对胡敏酸的吸附均属于吸热反应,其中高岭石的吸附为非自发过程,其余样品的吸附为自发过程.

Adsorption Characteristics for Humic Acid by Binary Systems Containing Kaolinite and Goethite

In this study, the binary systems of kaolinite-goethite mixture (KGM) and kaolinite-goethite complex (KGC) were prepared by different methods, and the surface properties and humic acid adsorption of the samples were investigated. Results showed that the specific surface area (SSA) of the samples followed the order of goethite> KGC> KGM> kaolinite, and the SSAs increased significantly for KGC while slightly for KGM when compared to the average value of kaolinite and goethite. The isoelectric point (IEP) of kaolinite, goethite, KGM and KGC appeared around 3.2, 7.9, 6.1 and 6.7, and the Zeta potential at pH 5.0 was -13.9, 38.2, 14.3 and 19.7 mV, respectively. The adsorption kinetic data for humic acid were well fitted using the pseudo-second-order kinetic models, suggesting that chemisorption was important in the adsorption process. Both one-site and two-site Langmuir models were suitable to describe the isotherm adsorption data (R² 0.962-0.993), and the correlation coefficients of two-site model for the binary systems were relatively higher (R2>0.989). The R2 values of Freundlich model fiting the adsorption data were low for the four samples, especially for the two pure samples. This indicated that the adsorption with various sites and mono-layer model was important in adsorbing humic acid onto the binary systems. At the initial pH of 5.0, the adsorption capacity (q_max) of kaolinite, goethite, KGM and KGC was 6.02, 61.83, 35.13 and 42.10 mg·g^-1, respectively. The q_max values of KGC and KGM increased to different extents when compared to the average of kaolinite and goethite. Thermodynamic parameters indicated that the adsorption of humic acid were endothermic for the four samples and non-spontaneous for kaolinite while spontaneous for the other samples.