Adsorption properties and mechanism of purified palygorskite on methylene blue

The palygorskite clay minerals from Gansu Province in China were purified by suspension precipitation method using sodium hexametaphosphate solution as dispersion reagent. The content of quartz and dolomite associated minerals in palygorskite clay minerals reduced effectively after purification, as confirmed by X-ray diffraction (XRD), infrared spectra (IR), scanning electron microscope (SEM), and energy-dispersive spectroscopy (EDS) analyses. The purified palygorskite exhibits excellent adsorption capacity for methylene blue (MB) in water, with the maximum adsorption capacity of 219.69mgg(-1). The adsorption kinetic studies revealed that adsorption kinetic of palygorskite on MB followed pseudo-second-order model. The adsorption mechanism of palygorskite for MB was discussed in detail via zeta potential analysis, N-2 adsorption desorption curve and BET analysis, and infrared absorption spectrum analysis. The results demonstrated that the adsorption mechanism may be attributed to electrostatic interaction between MB and the negative charge on the palygorskite surface. Meanwhile, the bond M-OH in palygorskite structure can combine with N, S element in MB to form intermolecular hydrogen bonds.