A facile chemical modification of polystyrene copolymer to its amine functional derivative: Exploration of Pd separation from PUREX originated simulated raffinate under acidic conditions

Abstract

Pd separation from a synthetic acidic formulation mimicking the high active radioactive waste composition that could originate from nuclear fission of U (or Pu) has been studied by using a styrene based polymer-chemically functionalized with amine moiety. For this purpose, a straightforward synthetic protocol was adopted to introduce an amine moiety into a polystyrene copolymer by reacting chloromethylated resin with the ‘amine donor’ precursor, diethyelenetriamine. The emergence of the NH signature in the adsorbent by the disappearing CCl functional group of the resin precursor, as observed by FTIR, and the signature of N 1 s of the adsorbent, observed based on XPS studies, revealed the formation of the adsorbent, in addition to the thermogravimetric studies that corroborate a characteristic thermal degradation pattern typical of a polystyrene network. To qualify the adsorbent for Pd removal from nuclear waste, preliminary Pd adsorption studies from an acidic medium were performed by batch mode and fixed-bed adsorption using an extraction chromatography column. The studies revealed that Pd uptake increases with acidity, reaching a maximum of 5 M. A faster separation of Pd with a maximum adsorption capacity of approximately 710 mg/g and a breakthrough adsorption capacity of approximately 42 mg/g were achievable. An ion-exchange interaction between Pd and the amine ligand was attributed based on the XPS study, and the variation of NH vibrational stretching frequency with the increase in Pd concentration further corroborates the interaction between Pd and the amine moiety of the adsorbent. Fitting of the experimental data with different reaction kinetics and adsorption isotherm models suggests a pseudo-second-order type interaction between Pd and the amine ligands in the polystyrene matrix, wherein the interaction is mostly governed by a mono layered interaction of the Langmuir type. The recovery of adsorbed Pd from the resin was investigated using thiourea as a complexing agent. The Pd uptake was examined from acidic solutions in presence of a large excess of metal ions present in radioactive waste that corresponded to the compositions of PUREX raffinate.