Preparation of chitosan resin by two-step crosslinking method and its adsorption for palladium in wastewater.

To preserve the activity of amine groups on chitosan, chitosan resin (CR) was synthesized using the reversed-phase suspension two-step crosslinking method for the adsorption of palladium from wastewater. The effects of varying the amounts of chitosan, liquid paraffin, ethyl acetate, formaldehyde solution, and epichlorohydrin on the adsorption capacity of CR were investigated using both single-factor experiments and response surface methodology. The preparation conditions for the chitosan resin were optimized, and its adsorption properties were systematically evaluated. The results indicated that CR exhibited a high saturated adsorption capacity for palladium, reaching 195.22 mg·g-1. The adsorption kinetics followed the pseudo-second-order model, while the adsorption isotherms were well described by the Sips model. Thermodynamic analysis demonstrated that the adsorption process was spontaneous and endothermic. Furthermore, CR maintained exceptional stability, with a palladium removal efficiency exceeding 99.8 % even after eight adsorption-desorption cycles. The primary adsorption mechanism is attributed to the interaction between palladium ions and the protonated amino groups of the chitosan resin.