Speaker
Description
Platinum group metals (PGMs) are listed among critical raw materials essential for economic development, everyday life, and industrial applications as defined by the European Commission [1]. Spent nuclear fuel represents a promising secondary resource, as PGMs are present in higher concentrations than in primary ores [2]. Their recovery could also contribute to reducing the overall cost of spent nuclear fuel reprocessing.
This study therefore investigates the possibility of separating PGMs from nitric acid media by liquid-liquid extraction, applicable in spent nuclear fuel reprocessing. The aqueous phase contained nitric acid (3 mol/L) and nitrates of rhodium, ruthenium, and palladium at concentrations representative of those expected in spent nuclear fuel raffinate. Initial experiments were focused on the extraction of PGMs into pure solvents (kerosene, benzene, chloroform, n-octanol, bromobenzene, and selected ionic liquids) to provide a baseline for subsequent experiments. The effect of solvent pre-saturation with the aqueous phase on PGMs extraction was also evaluated. The essential part of the study was focused on PGMs extraction using primarily extractant N′-benzoyl-N,N-diethyl-thiourea, with particular emphasis on the effect of various parameters e.g. extractant concentration, nitric acid concentration, nitrite presence, and mutual-phase contact time. In these experiments, ruthenium showed partial extraction, while rhodium was not extracted. Palladium was quantitatively extracted even at low extractant concentrations. Additionally, palladium extraction increased with decreasing nitric acid concentration. No positive effect of nitrite presence on PGMs extraction was observed.