MICROWAVE ASSISTED LEACHING APPROACHES TO RECOVER PLATINUM GROUP METALS FROM WASTE AND INTERMEDIATE STREAMS

Microwave (MW) assisted chloride leaching was studied to extract platinum group metals (PGMs) from waste and intermediate materials. Recently, we have shown that MW assisted leaching of spent ceramic car catalysts in 6 M HCl at 150 °C extracted PGMs without the need to add an oxidation agent at very fast leaching times (3-25 min). We present a similar approach to recover PGMs from three other materials: spent metallic foil car catalysts, capacitors from waste printed circuit board assemblies (PCBAs) and an industrial intermediate anode slime. These three materials contained elevated concentrations of metallic impurities, which dissolved during MW leaching in 6 M HCl at 150 °C. This caused consumption of the acid and a decrease in oxidation potential, which lowered the PGM leachability. Thus, for each material a two-step (MW) leaching process was developed. In the first leaching step, metal impurities were removed, and the reducing potential of the material was decreased. Whereas, in the second MW leaching step in 6 M HCl and 10 vol% H₂O₂ (30% (w/v)), the PGMs leached efficiently (>90% Pd, >97% Pt, >73% Rh). This approach increased the overall PGM extraction and their concentration in the final leachates, which is advantageous for downstream processing.