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Arsenic removal has received much attention all over the world because of its toxicity and carcinogenicity. In the current research, the adsorption behavior of As(V) from aqueous solution onto Fe(III)-impregnated bentonite (Fe-Bent) was examined. Adsorption experiment results showed that the adsorption capacity of initial bentonite clay (Bent) was increased by Fe(III)-impregnation method. In Fe-Bent, the mononuclear Fe(III) cations, small oligomeric cluster and bulky FexOy particles were made such active sites identified by UV–Vis spectroscopy. X-ray diffraction results showed that Fe(III) species presented mainly in both crystalline and amorphous forms on the external surface of Fe-Bent. In an experimental study, the effect of different parameters such as contact times, arsenic concentrations, adsorbent dosages, pH and temperature conditions was investigated. Fe-Bent sample represented the maximum adsorption capacity of 10.06 mg L−1 to remove 5–20 mg L−1 of As(V) at pH = 6 and ambient temperature. In this experiment, the residual As(V) concentration decreased to less than 0.01 mg/L with the adsorption efficiency of 99% (i.e., below the limit of the WHO). The two- and three-parameter isotherm models revealed the best fit to the Freundlich, Sips, Toth, Temkin and Langmuir models, respectively. The isotherm models indicated the strong adsorption between arsenic and Fe-Bent. The adsorption kinetics was also considered by first-order, second-order and Elovich rate equations. It was noticed that the Fe-Bent adsorption followed the external surface reaction such as ligand exchange and surface complexation. The thermodynamics studies exposed that the process was spontaneous and endothermic for Fe-Bent.

Bentonite clays containing mostly montmorillonite as a nanostructure group of smectite have been used as industrial raw material in many applications. The presence of the other impurities in bentonite clays reduces the value of bentonite. Therefore, the bentonite purification is necessary. In this research, the purification and separation of montmorillonite from a low-grade natural bentonite were considered on the regular and comprehensive plan. For this purpose, a set of methods including dispersion, sodium-activation, sedimentation, sonication and centrifugation were used. In contrast to many methods, there were often complex, expensive and non-effective; this purification method was found to be effective for removing almost all quartz, carbonates and clinoptilolite as the major impurities. In this purification method, the montmorillonite content was increased from 15 to 84% with the separation yield of 80%. The influence of centrifugal force and the type of ultrasonication indicated the most critical parameters in the purification yield, the physical properties and the crystalline structure of the final products. The laser particle size distribution analysis, X-ray diffraction, semi-quantitative analysis and Fourier-transform infrared spectroscopy results showed the decrease of impure phase without any structural changes or damages in clay framework.