Palladium(II) sorption of a diethylphosphate-modified thiacalix[6]arene immobilized on amberlite resin

Abstract

p-Diethylphosphonomethylthiacalix[6]arene (1) was impregnated on Amberlite XAD-7 resin (1-XAD), and the sorption kinetics of 1-XAD towards Pd(II) ions in HCl media were investigated. The maximum Pd(II) sorption capacity (SC) of 1-XAD was 18.7mgg−1 after a contact time of 24h in a 200mgL−1 Pd(II) solution. Batch sorption studies were then conducted to optimize a range of equilibration conditions, such as contact time, Pd(II) concentration, and temperature. The sorption process was then explained in the context of Freundlich and Langmuir isotherm models, thermodynamic parameters ∆G°, ∆H°, and ∆S°, and sorption kinetics were calculated to understand the nature of the sorption. Pd(II) sorption with 1-XAD was found to be spontaneous and endothermic nature. Pd(II) sorption kinetics follows a pseudo-second-order model. In addition, the SC of 1-XAD was investigated using the leach liquors of automotive catalysts containing Al, Ba, Ce, La, Pd, Pt, and Rh ions. The resin developed herein exhibited high selectivity towards Pd(II) ions, with a SC value of 4.12mgg−1 being obtained from leach liquors of automotive catalysts. Finally, Pd(II) desorption from Pd(II)-sorbed 1-XAD was achieved using a thiourea solution as the desorption reagent, and the resin was reused effectively over 5cycles. Pd(II) separation using the 1-XAD as a adsorbent is eco-friendly method as compared with conventional solvent extraction. The 1-XAD is highly useful for selective recovery of Pd(II) from leach liquors of automotive catalysts and secondary resources.