A comparative study about adsorption of natural palygorskite for methylene blue

Various methods including acid treatment, heat treatment and surface modification have been used to improve the adsorption properties of natural palygorskite. However, the comparative study about the effect of source of palygorskite on the adsorption properties remains a gap to be filled. Here we first studied the structure and chemical composition of three palygorskite samples from Jiangsu, Anhui and Gansu Provinces of China using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and X-ray Fluorescence Spectrometry (XRF). Subsequently, the adsorption properties of the palygorskites for methylene blue (MB) were evaluated and compared. The palygorskite from Jiangsu (JSHS) is Mg-poor and has an analogous dioctahedral structure. The palygorskite from Anhui (AHGS) is Mg-rich, and has an intermediate structure of dioctahedron and trioctahedron. The palygorskite from Gansu (GSHN) also has an intermediate structure of dioctahedron and trioctahedron, but is associated with muscovite, clinochlore, dolomite and feldspar. The maximum adsorption capacity of the palygorskites from JSHS, GSHN, AHGS for MB at 303 K is 158.03, 98.34, 77.92 mg/g, respectively. It was found that a lower Mg content and the dioctahedral structure of palygorskite are favorable to its adsorption for MB. More negative value of Gibbs free energy (Delta G(0)) for JSHS further illustrates that JSHS has higher efficiency in removing the MB molecules than the others. The adsorption mechanism studies suggest that the zeolitic H2O plays a fundamental role in the interaction between MB and palygorskite. (C) 2014 Elsevier B.V. All rights reserved.