溶融アルカリ金属塩化物を用いた白金族金属のリサイクル技術の開発

The platinum group metals (PGM: platinum, palladium, rhodium, ruthenium, iridium, and osmium) are widely used in electrical devices and in catalysts. It is important that sustainable methods of recycling PGMs in waste electrical devices and catalysts are developed because PGMs are expensive and new sources in the Earth's crust are limited. In this work, processes for recycling ruthenium, platinum, palladium, and rhodium based on chlorination in molten chloride flux are investigated. Scrap containing ruthenium was chlorinated using Cl2 at 873 K in molten LiCl-NaCl, then the ruthenium was reduced using flowing H2 in molten salt. As a result 99.96 mass% Ru powder was obtained. Platinum, palladium, or rhodium was chlorinated using Cl2 at 973 K in molten NaCl-CsCl. The chloride complex containing Pt, Pd, and Rh at the desired composition was then treated using one of two processes. In one, the complex was oxidized using Na2CO3 and then reduced on granular CaCO3 in flowing H2 at 1473 K. In the other, the complex in the solid state was directly reduced using flowing H2. Both processes gave PGM-alloy powder products with the desired compositions. The morphologies of the PGM powders could be controlled in recycling process.