Platinum Group Metals (PGMs) are valuable materials for various industries. Their accurate analysis for major metal content and impurities is of great importance in the production of the metals and in the recycling process. The preferred method is acid digestion followed by ICP-MS or ICP-OES analysis.

However, the digestion of PGMs is challenging as it requires high temperatures, typically 280°C, reaction times of an hour or more and highly "aggressive" acids such as aqua regia and perchloric acid. While many microwave digestion oven systems cannot operate under these conditions, it is shown how the concept of a Pressurised Digestion Cavity (PDC) provides such extreme reaction conditions required for complete dissolution of the most resistant precious metals.

Platinum, palladium and rhodium powders have been selected to demonstrate the digestion of pure PGMs. A palladium catalyst and a Si-Mg-Fe ore were also digested. The latter is an internal laboratory standard and contains known traces of PGMs as a reference for evaluating the results.

Platinum and palladium can be digested with aqua regia, whereas rhodium requires the addition of perchloric acid to hydrochloric acid for complete digestion. The importance of stirring during the reaction was also investigated. For the zeolite-based palladium catalyst, the reagent mixture was optimised for complete digestion of the silicate support. However, for catalysts only the PGM content counts, so leaching is usually sufficient.

Peter Kettisch