No abstract

Synthetic multielement solutions of the platinum group metals (PGE: Ru; Rh; Pd; Ir; Pt) and gold, with analysis by ICP-AES and ICP-MS, have been used to study the behaviour of the precious metals on Dowex 1-X8 resin. Simple solutions of precious-metal chlorocomplexes showed near-complete adsorption ( > 99%) of most elements, and only minor breakthrough of Ru and Ru ( ≈ 5%). Solutions pre-treated with acid mixtures typically used to decompose geological samples, demonstrated that perchloric acid adversely affects the adsorption of the PGEs on the resin. Solutions treated with HF-HNO 3 -HCl maintained good retention of Ir, Pt, Au ( > 99%), Pd ( > 94%) and Ru ( > 90%), but displayed significant loss (up to 40%) of Rh. A two-step procedure was necessary to elute the precious metals from the resin: 0.3 mol l 21 thiourea prepared in 0.1 mol 21 HCl removed Ru, Pd, Pt, Au, and some Rh: 12 mol l 21 HCl eluted remaining Rh and all Ir. Recoveries ranged from 50 to 100%. At low levels, the determination of PGE and Au in the thiourea fraction by ICP-MS was compromised by high levels of total dissolved solids (TDS), which necessitated dilution of the eluate prior to analysis. The TDS was reduced by decomposing thiourea with HNO 3 and removing SO 4 22 by precipitation of BaSO 4 , but this led to lower and more erratic results, and increased contamination. An assessment of the optimised procedure employing geological reference materials PTM-1, PTC-1 and SARM7, indicated that acceptable results should be attainable for ICP-MS determination of most elements in geological samples containing high concentrations ( > 1 mg g 21 ) of the PGE, for which decomposition of thiourea is unneccessary. The addition of a decomposition step led to low recovery of all elements except Ir, which was present entirely in the HCl eluate. The method is viable for the determination of Ir in a range of geological materials, but modifications will be required if it is to be extended to the other precious metals.

No abstract

The platinum group elements (PGEs) Pt, Pd, Ru, Rh, Os, and Ir are found in nature heterogeneously distributed at ultratrace levels. They are, however, of major economic importance, being used as catalysts in the petroleum and chemical industries, as a raw material in the manufacture of electronic components and jewellery, and as a form of investment. Levels of a few þgþg-1 may be economic to recover, and consequently determinations of sub-ngþg-1 levels are required for geological studies. Recent developments in analytical instrumentation, such as graphite furnace-atomic absorption spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and ICP-mass spectroscopy (ICP-MS), have encouraged a reassessment of methods for PGE determination. To analyze at the ultratrace levels present in natural materials, however, usually requires a preconcentration and/or separation step before final analysis. Traditionally, fire assay has been used to concentrate PGEs in ores, collecting the noble metals in a lead, copper, or nickel sulphide button. This technique requires specialized equipment, large amounts of analytical reagents, and special procedures to avoid loss of volatile Os and Ru compounds. Additionally, analytical results are highly dependent on the assay conditions. Tellurium collection has also been used to separate and collect the PGEs, although this procedure is lengthy and isotope dilution is necessary to correct for incomplete co-precipitation. An alternative to Te collection is ion-exchange chromatography. The PGEs readily form anionic chloro-complexes enabling two approaches to ion exchange: (1) an anionic resin can be used and PGE species trapped on the resin, to be subsequently eluted and analyzed; or (2) a cationic resin can be used to remove the matrix elements, thereby allowing the analysis of concentrated solutions of PGEs. This paper will present results from our research programme which aims to develop simplified procedures for the determination of the PGEs. A two-step dissolution will be discussed which combines a quick acid attack in sealed microwave vessels, followed by lithium borate fusion of the refractory minerals. Results for two types of ion-exchange resins will be presented (anionic resin, Dowex 1-X8, and cationic resin, Dowex 50W-X8), based on data obtained by ICP-AES and ICP-MS. Procedures will be evaluated using a range of PGE certified reference materials from South Africa (SARM-7) and Canada (PTA-1, PTC-1, PTM-1, and SU-1a).

No abstract

No abstract

No abstract

No abstract