Iridium recovery from compact metal scrap

Abstract

At present, recovery of iridium from solid secondary raw materials is feasible only by hydrometallurgical processes. For this purpose iridium must be finely divided, which can be achieved by alloying with base metals followed by selective dissolution. Alloy formation of iridium with copper or aluminium has been investigated. Melting of alloys M-5-10wt.%Ir ( M ≡ Cu or Al) in a vacuum induction furnace did not generate any problems. From these alloys, high recoveries of finely divided iridium powder (diameter 2–50 μm) are obtained after treatment with acids or bases. The powders still containing 2–4% copper or aluminium take up considerable amounts of oxygen by chemisorption. Apart from this, in aluminiumcontaining powders, oxygen is present as Al 2O 3. All iridium powders obtained from Al-Ir alloys are thermally unstable and deflagrate during heating in various atmospheres. The tendency for deflagration is attributed to the presence of reactive hydrogen and oxygen in the iridium powder. Methods to eliminate deflagration are described. Iridium powders produced can be treated by conventional processes to obtain pure iridium.