Preparation, Characterization and Fluoride Adsorption Characteristics of Iron-Oxide-Modified Vermiculite

Abstract

Iron-oxide-modified vermiculite (Verm-Fe x , x =5, 10, 20) was prepared by a co-precipitation procedure. The surface properties and fluoride adsorption of pure vermiculite (Verm) and Verm-Fe x were investigated. Compared to Verm, the d (002) spacing of Verm in Verm-Fe x increases slightly, and the pore volumes, different surface areas and surface fractal dimension of Verm-Fe x increase with increasing the Fe contents. The increased magnitude of the micropore volume and external surface area of Verm-Fe x is more significant. The isoelectric point (IEP) of the samples increases in the order of Verm 5 10 20 , and the ζ potential at pH 5.0 of the four samples is -16.4, -6.1, 10.5, and 28.4 mV, respectively. One-site Langmuir model was used to describe the fluoride adsorption by the samples ( R 2 =0.973~0.995), and the determination coefficient ( R 2 ) for Verm is the highest. The R 2 fitted from two-site model for Verm-Fe x ( x =5, 10, 20) is higher than that from one-site model, indicating that the adsorption data of Verm-Fe x can be fitted by two-site model well. The R 2 fitted from Freundlich model of the samples is lying in the range of 0.835~0.937 and follows the sequence of Verm 5 10 20 . This indicates that Verm-Fe x possesses the heterogeneous surfaces with different reactive sites. When pH=5.0, the adsorption capacities ( q max ) of Verm, Verm-Fe 5 , Verm-Fe 10 and Verm-Fe 20 are 3.18, 6.76, 9.27 and 12.43 mg·g -1 , respectively. Compared to Verm, Verm-Fe x with a high Fe content has a higher adsorption capacity for fluoride in solutions.