Development of methods for separation and determination of platinum, palladium and rhodium, utilizing solid phase extraction, ICP-OES and ICP-MS

Summary

The platinum group elements (PGMs) Pt, Pd and Rh are used extensively in different industrial and technological applications. Particularly important is their use in autocatalysts in order to reduce emissions of harmful pollutants from car exhaust. Increased use of the PGMs has resulted in high interest of their recovery from spent autocatalysts in addition to determination of low concentrations of the PGMs in different sample matrices. In this study, separation of the PGMs (and selected base metals) in HCl solutions have been studied using solid phase extraction. Strong anion exchange (SAX) and strong cation exchange (SCX) resins was tested due to the PGMs forming (mostly) anionic chlorocomplexes in HCl solution, while the base metals are present as cations. Cyano (CN) and dioctyl sulphide (DOS) modified reverse phase was tested due to the PGMs having a large affinity towards N and S. The differences in adsorption due to HCl concentration and storage time of the solutions was investigated on SAX and SCX and optimum results were found using fresh solutions with 0.15 M HCl, in which Pt and Pd were quantitatively adsorbed on SAX and the base metals quantitatively adsorbed on SCX. Pd was found to be selectively retained on CN and DOS modified resin. Recovery of the analytes was tested using several elution solutions. Thiourea was found to be needed in order to recover Pt from SAX and Pd from DOS modified resins. 3 M HCl could be used for recovery of Pd from SAX, recovery of base metals from SCX and recovery of Pd from CN. None of the tested resins adsorbed Rh to any large degree. A separation scheme was proposed using SCX and SAX and a good, although not quantitative, separation was obtained. Additionally, high pressure liquid chromatography (HPLC) was tested using a SAX column and the ICP-MS as a detector, with a mobile phase containing a maximum of 2 M HCl. High background of Pt and Pd was found in the HPLC method, presumably due to previous contamination of the column. Rh was the only PGM showing peaks not present in the blank. Analyses of the samples were performed using inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). Both were found to be good techniques for determining low concentrations of PGMs in HCl solutions with detection limits ~ 0.1 – 0.9 ng mL-1 for ICP-MS and ~ 10 - 15 ng mL-1 for ICP-OES. Determination of the selected base metals on the ICP-MS was problematic and this instrument was therefore only used for analysis of the PGMs.