Adsorptive removal of arsenic(V) from aqueous phase by feldspars: Kinetics, mechanism, and thermodynamic aspects of adsorption

The present study investigated the adsorption of arsenic(V) (As(V)) on feldspar mineral samples collected from Finland and Italy. A ground sample with quartz composition was also utilized to study the effect of aluminum content of the minerals on As(V) adsorption. The mineral samples were characterized by X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and Fourier transform infrared spectroscopy (FTIR) analyses. Batch experiments were performed to examine the influence of various operational parameters such as contact time, initial As(V) concentration, temperature, solution pH and the presence of competing anions on the adsorption of As(V) by feldspars. The point of zero charge (pHpzc) for the feldspars was determined, and the optimal pH range for adsorption was below this point. The feldspar sample with a higher aluminum content showed a higher adsorption capacity. Electrostatic forces between the terminal aluminol groups of the samples and predominant form of arsenate in acidic medium were found to be the main cause of the adsorption reaction. The As(V) adsorption onto feldspars was observed to follow pseudo-second-order kinetics and the thermodynamic data confirmed the endothermic and favorable nature of the adsorption.