Abstract: Fission noble metals contained in an insoluble residue and/or a high-level radioactive liquid waste generated in the step of reprocessing spent nuclear fuels are dissolved in nitric acid to prepare a palladium-containing nitric acid solution, which is then brought into liquid-liquid contact with an extracting solvent containing a dialkyl sulfide in which each alkyl group has 4 to 10 carbon atoms as an extractant to extract the palladium component into the extracting solvent. The palladium-containing extracting solvent is brought into liquid-liquid contact with an aqueous thio compound solution or aqueous ammonia solution to strip the palladium component into the aqueous solution. A borohydride compound in added to the palladium-containing aqueous solution to precipitate palladium from this solution by reduction, and metallic palladium is recovered by separating the precipitate from the aqueous solution.

Abstract: A process for recovering valuable metals from a waste catalyst based on an alumina carrier includes (a) roasting the waste catalyst at a temperature range of 400.degree. to 1,000.degree. C. to obtain a roasted product; (b) preparing a reduction dissolution by dissolving the roasted product with sulfuric acid in the presence of a metal as a dissolution catalyst; (c) separating a large part of the aluminum from the reduction dissolution solution and recovering aluminum as ammonium aluminum sulfate from the solution, optionally after subjecting the reduction dissolution solution to a treatment of removing iron; (d) extracting molybdenum as a molybdate by solvent extraction from the solution after separating and recovering aluminum from the solution; (e) extracting vanadium as a vanadate by solvent extraction from the solution obtained as a residue after extracting molybdenum; and (f) recovering nickel and cobalt each as a hydroxide from the extraction residue after recovering vanadium.

Abstract: A process for dissolving used catalyst includes the steps of roasting, after subjecting to an optional deoiling treatment, the used catalyst at a temperature lower than 1,000.degree. C. but not lower than the temperature at which any of the residual components in the used catalyst undergoes ignition and combustion where the residual components are selected from the group consisting of oils, sulfur components, and carbon components; and dissolving the roasted product using sulfuric acid after adding a metal to the roasted product as a catalyst for accelerating dissolution. The process provides a simple and efficient method for completely dissolving a used catalyst having a carrier containing alumina as the principal component.