Separation/purification method for noble metal fission product

Palladium containing-nitric acid solution generated in a reprocessing step for spent nuclear fuels is put to liquid-to-liquid contact with an extracting solvent containing alkyl disulfide having an alkyl group of 4 to 10 carbon atoms as an extracting agent, to extract a palladium ingredient into the solvent. The palladium extracting solvent is back extracted by an aqueous solution of thio compound or an aqueous ammonium solution, and a boron hydride compound is added to the aqueous palladium-containing solution to precipitate palladium by reduction. The precipitates are applied with an appropriate solid-liquid separation to obtain metal palladium. Palladium having high purity can efficiently be recovered selectively by such a solvent extracting method. (T.M.)