Geochemical behaviour of platinum-group elements (PGE) in particulate emissions by automobile exhaust catalysts: experimental results and environmental investigations

The increasing use of automobile catalysts leads to the emission of the platinum-group elements (PGE) platinum, rhodium and palladium into the environment. Experiments were conducted in order to assess the possibility of their mobility caused by species transformation. Soil material was contacted with a ground catalyst and, after varying parameters such as pH, chloride or sulfur concentration, the solubility of platinum and rhodium was measured. Laboratory results were compared with those from different environmental materials (soil, run-off sediments, surface waters, tunnel dust). Analytical techniques were GFAAS (after preconcentration by nickel sulfide fire assay), XRF, ICP-MS, AV, XPS and SIMS. Experimental results show that small, although significant, amounts of platinum and rhodium are adsorbed in soil or soluble in surface waters. Environmental materials exhibit a relatively constant Pt/Rh ratio of 5, which points to a common source, the automobile catalysts. A direct determination of PGE species by surface analysis is still not possible, due to low surface concentrations. As most of the PGE seem to behave in an inert manner and are immobile they do not constitute a hazard to health.