Chitosan-grafted polymerized Fe-pillared bentonite: Efficient removal of Cd and As from wastewater

The rapid development of mineral resources exploitation and industries has brought a large amount of wastewater containing cadmium (Cd) and arsenic (As) to the environment. Among these, the mining industry has become a major challenge in wastewater treatment due to the coexistence of both pollutants at high concentrations. Developing a sustainable and low-cost adsorbent capable of simultaneously adsorbing both anionic and cationic pollutants is a key breakthrough direction for solving this practical problem. In this study, chitosan-grafted Fe-pillared bentonite (CS@Fe@Bt) was synthesized using natural bentonite, aiming to provide an efficient material for treating Cd and As co-contaminated wastewater (especially mining industry wastewater). Results suggested that the specific surface area (SSA) and total pore volume of Fe-pillared bentonite increased by 1.85 and 1.32 times, respectively, compared with the raw bentonite. Pillaring the bentonite also significantly enhanced its chitosan loading capacity, improving both the structural stability and adsorption performance of CS@Fe@Bt. Kinetic and isothermal adsorption experiments revealed that CS@Fe@Bt possessed a multilayer heterogeneous surface, with Cd and As adsorption following the Pseudo-second-order kinetic model. CS@Fe@Bt showed strong adsorption capacity for both Cd(II) and As(III) when the initial pH_i of the solution ranged from 6 to 8. The maximum adsorption capacities (Q_m) for Cd(II) and As(III) were 80.79 mg g^-1 and 34.90 mg g^-1, respectively, surpassing most comparable adsorbents. The primary adsorption mechanisms of CS@Fe@Bt in Cd(II) and As(III) co-polluted water included oxidation (57.81 % of As(III) was converted to low-toxicity As(V)), electrostatic interactions, and the formation of B-type ternary surface complexes (CS@Fe@Bt-As-Cd). Additional mechanisms included ion exchange, pore adsorption. These findings highlight the potential of CS@Fe@Bt as an effective adsorbent for Cd(II) and As(III) adsorption, providing technical support for addressing practical wastewater treatment challenges.