Adsorption of silver(I) from aqueous solution by chelating resins with 3-aminopyridine and hydrophilic spacer arms: Equilibrium, kinetic, thermodynamic, and mechanism studies

The equilibrium, kinetics, thermodynamics, and mechanism of two novel chelating resins with 3-aminopyridine and hydrophilic spacer arms (denoted as PS-DEG-3-AP and PS-TEG-3-AP) for Ag(I) were investigated in detail. The Boyd, Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) models were applied to describe the adsorption of the resins for Ag(I). The saturated adsorption capacities of PS-DEG-3-AP and PS-TEG-3-AP for Ag(I) were (0.21 and 0.30) mmol.g(-1) at pH 4, respectively. The results showed that the adsorption processes were governed by film diffusion and followed the pseudo second-order model well. The Langmuir model was better than the Freundlich model to describe the isotherm process. The E values obtained from the D-R model indicated that the adsorption of Ag(I) ions onto the resins occurred by chemical ion exchange. The adsorption mechanism of the resins for Ag(I) was confirmed by X-ray photoelectron spectroscopy (XPS). The XPS results clarified that not only 3-aminopyridine but also S atoms existed in the spacer arm that could take part in the coordination with Ag(I). Five adsorption-desorption cycles were conducted for the reuse of the resins. The results indicated that these two resins were suitable for reuse without considerable change in adsorption capacity.