Adsorption of Pb2+ by inorganic liquid-treated sepiolite: Adsorption process optimization and mechanism analysis via response surface methodology

This study proposes a simple modification method of sepiolite based on inorganic liquid (which contains hydrochloric acid, sodium chloride and sodium hexametaphosphate), and the modified sepiolite (as@sep) is used to remove Pb2+ in aqueous solution. More importantly, this study optimized the modification conditions of sepiolite by the response surface method (RSM), and the results showed that the optimized as@sep had significantly higher adsorption capacity for Pb2+ than that before modification (the adsorption capacity before and after modification were 19.04 and 31.81 mg g-1, respectively). A series of characterizations combined with adsorption kinetics and thermodynamics analysis revealed the adsorption mechanism of as@sep for Pb2+. The analysis results show that the adsorption of as@sep to Pb2+ is mainly carried out by ion exchange, surface hydroxyl complexation, pore filling and electrostatic attraction, and this adsorption reaction is a spontaneous exothermic process in low temperature. The above positive results indicate the superiority of the facile modification strategy of sepiolite proposed in this study.