Amino-bearing calixcrown receptor grafted to micro-sized silica particles for highly selective enrichment of palladium in HNO3 media

Abstract

Palladium recovery in HNO3-containing radioactive waste is of great value due to its considerable amount and benign radioactivity level. In this study, a new calixcrown receptor decorated with amino ligands (soft N donors) was synthesized for the selective extraction of Pd(II) in HNO3 media. A high distribution ratio (D) of 278.6 was obtained within 10min in solvent extraction. Moreover, the calixcrown receptor was covalently grafted to micro-sized silica particles to obtain a novel solid phase extraction (SPE) material (labeled as ACGSi). Detailed batch and column experiments revealed that the ACGSi material had fast kinetics and favorable adsorption capacity towards Pd(II) in HNO3 solutions. Parameters influencing the adsorption ability such as contact time, acidity and initial metal concentration were fully evaluated. Kinetic equations (pseudo-first/second-order) and adsorption isotherm models (Langmuir and Freundlich models) were employed to fit the experimental data for inspecting the adsorption mechanism. On this basis, a facile chromatographic process was proposed for the selective enrichment and recovery of palladium in simulated high level liquid waste (HLLW). A recovery rate of 99.3% was obtained. The amino-decorated calixcrown extractant as well as the functionalized SPE material is believed to be promising to find applications in palladium separation from radioactive liquid wastes.