Platinum Group Metal Recovery from Spent CatalyticConverters Using XRFMetals - March 20, 2014
Author : Stephen Dietz
There are precious metals in those catalytic converters.
A catalytic converter is a device used to convert toxic vehicle emissions to less harmfulsubstances by way of catalyzed, or accelerated, chemical reactions. Most present-day vehiclesthat run on gasoline, including automobiles, trucks, buses, trains, motorcycles, and planes, haveexhaust systems employing a catalytic converter.
The catalyst component of a catalytic converter is usually platinum (Pt), along with palladium(Pd), and rhodium (Rh). All three of these platinum group metals, or PGMs, are extremely rarebut have a broad range of applications in addition to catalytic converters. Platinum, for example,is used in laboratory and dental equipment, electrical contacts and electrodes, and jewelry,while palladium plays a key role in fuel cell technology. With numerous applications and limitedsupply, these valuable metals are an attractive target for recovery and reuse from spentcatalytic converters. In 2010, the total value of Pt, Pd, and Rh reclaimed from the recycling ofspent catalytic converters was $3 billion.
Determining the recovery value of the PGMs in a catalytic converter begins with knowing thecomposition and ratios of the metals used. Automotive catalyst material is made either of aceramic substrate, mostly cordierite coated with a precious metal containing a wash coat, or of ametallic substrate with an aluminum oxide wash coat also containing precious metals. Theaverage concentration and the ratio of Pt and Rh were more or less constant 20 years ago, so asimple weighting was sufficient to arrive at a good estimation of the precious metal content.However, the price of these three elements has fluctuated strongly over the last 20 years,depending on the supply, demand, and speculation. These variations, as well as the tightening
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of emission legislation, have had a direct correlation on the composition of the catalysts, whichthemselves have had a strong influence on demand.
Currently, the composition, which depends on the engine displacement and the type of fuelused, varies dramatically. The formulation can consist of only Pt, or various ratios of Pt-Pd-Rh,Pt-Rh, and Pd-Rh. Most of todays recycled catalytic converters come from cars manufactured,on average, 10 to 15 years ago. The recoverable amounts of Pt, Pd, and Rh in each can rangefrom 1-2 grams for a small car to 12-15 grams for a big truck in the US.
The corresponding value in recoverable PGMs ranges from $25 to a few hundred dollars pervehicle. Moreover, the trade of ground-up material sold as catalysts can be very dangerousbecause of possible alterations, which can mean inclusion of lead or spent nickel-cadmiumbatteries.
To avoid considerable financial losses, companies need to quickly and accurately determine thecontents of Pt, Pd, and Rh in spent catalytic converters at the collectors site or in the refineries.But there is no technique for analyzing non-homogeneous materials like catalytic convertersdirectly without sample preparation. Therefore, the collected catalysts with ceramic substrateundergo a de-canning operation, which is the extraction of the honeycomb-structured ceramicmaterial from the steel case. All of the ceramic is then sorted crushed, milled, and mostlyblended with other catalysts. In contrast, converters with a metallic substrate are first shreddedor milled, and then the metallic parts are separated using magnets and winnowing from thewash coat powder containing precious metals. Because of this enrichment, the PGM content ofthese wash coat samples is usually much higher than that for milled ceramics. In both cases,the materials are pulverized to a maximum 250m and loaded into sample cups or sample bagsfor analysis, and then analyzed using x-ray fluorescence (XRF) technology.
A recent study evaluated x-ray fluorescence (XRF) analysis as compared to lab assays forachieving this objective. To see the results, including the correlation curves, repeatability data,methodology, and comments, read Automotive Catalytic Converters application summary.
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