Recycling Valuable Metals via Hydrometallurgical Routes

Abstract

The hydrometallurgical method is one of the key technologies in metal recycling, because it enables the fine separation between chemically-similar metals and a small-scale operation. In this paper, the recent results of our hydrometallurgical recycling studies are outlined. The topics include (i) noble extractants for precious metal separation, (ii) recovery of rare-earth elements from neodymium magnet scrap, (iii) nickel recovery from spent electroless nickel plating baths, and (iv) an energy-saving copper recycling process. In (i), new amide-type solvent extraction reagents have been developed for precious metals, one of which, thiodiglycolamide, rapidly and selectively extracts palladium from platinum and has a high durability against oxidation. In (ii), a process consisting of oxidative roasting – selective acid leaching followed by solvent extraction separation of dysprosium from neodymium has been proposed. In (iii), solvent extraction using a chelating reagent is used to extract nickel ions from spent electroless nickel plating baths, and the nickel ions are recovered as a nickel sulfate solution which can be reused in the plating process. In (iv), a copper recycling process utilizing monovalent copper in an ammoniacal alkaline solution is described, which would significantly reduce the energy requirement for copper electrowinning.