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Platinum Palladium [pdf]

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Platinum Palladium [pdf]

Bioleaching of platinum group metals (PGM) from spent automotive catalyst (SAC) was studied using two mesophiles, Pseudomonas fluorescens and Bacillus megaterium. Leaching studies under different conditions were carried out to investigate the formation of biocyanide and its role in PGM solubilisation. Both P. fluorescens and B. megaterium produce cyanide as a secondary metabolite that forms water-soluble complexes with PGM. The factors that affect bioleaching, namely initial pH of culture, free cyanide ion concentration, and pulp density were examined. Two leaching strategies - two-step bioleaching and spent medium leaching were examined. P. fluorescens showed higher extraction compared to B. megaterium. Using spent medium leaching for pretreated SAC at 0.5% (w/v) pulp density and initial, pH 10, P. fluorescens yielded the highest extraction of platinum (58%), palladium (65%) and rhodium (97%) on day 1. This study demonstrates the bioleaching potential of cyanogenic bacteria for the extraction of PGM from SAC.

Naturally occurring platinum and platinum-rich alloys have been known for a long time. The Spaniards named the metal "platina," or little silver, when they first encountered it in Colombia. They regarded platinum as an unwanted impurity in the silver they were mining.

In order to reduce the emission of harmful by-products from the combustion of petrol in engines, automotive catalysts have been increasingly implemented during the last decades [1]. Although modern catalysts are effective in reducing CO, NOx and residual hydrocarbons, they release platinum group elements (PGEs) during operation (e.g., [2, 3]). As a consequence of aerosol deposition, concentrations of platinum, palladium and rhodium in roadside soils increased over the years [4]. Studies have revealed that catalyst-borne PGEs can be taken up by plants and other species (e.g., [1, 5]). The toxicological potential of traffic-related PGEs is still not completely understood, making it necessary to study their effect on various species in exposure studies, as well as to improve analytical methods for reliable environmental monitoring of those elements.

So far, the DPE-approach achieved good results in extracting cationic metals from environmental aqueous samples [25], as well as in extracting cationic rare earth elements from saline waters [26]. Here, we have deployed the DPE-approach for the first time to the isolation of anionic platinum and palladium chloro-complexes from chemically digested road dust samples. This new approach was validated by successful analysis of reference material BCR CRM 723 (road dust) and used for analysis of road dust samples collected in downtown Vienna (Austria).

In order to reduce the nitrogen oxide, hydrocarbon, and carbon monoxide emissions (they are considered as harmful gases) produced by different vehicle engines, it has been a must for all vehicles produced since 1993 to be fitted with catalytic converters. A catalytic converter contains precious metals (as active components) such as palladium, platinum, and rhodium (referred to as PGMs) in order to convert harmful gases emitted from vehicle engines to relatively harmless ones by both the reduction of nitrogen oxides (NOx) into nitrogen N2 and the oxidation of hydrocarbons and CO to CO2 [1]. 59ce067264


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