ASSESSMENT OF DOWEX 1-X8-BASED ANION-EXCHANGE PROCEDURES FOR THE SEPARATION AND DETERMINATION OF RUTHENIUM, RHODIUM, PALLADIUM, IRIDIUM, PLATINUM AND GOLD IN GEOLOGICAL SAMPLES BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

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 breakthrou gh of Ru and Ru (approximate to 5%). Solutions pre-treated with acid m ixtures typically used to decompose geological samples, demonstrated t hat perchloric acid adversely affects the adsorption of the PGEs on th e resin, Solutions treated with HF-HNO3-HCl maintained good retention of Ir, Pt, Au (>99%), Pd (>94%) and Ru (>90%), but displayed significa nt loss (up to 40%) of Rh. A two-step procedure was necessary to elute the precious metals from the resin: 0.3 mol l(-1) thiourea prepared i n 0.1 mol(-1) HCl removed Ru, Pd, Pt, Au, and some Rh: 12 mol l(-1) HC l eluted remaining Rh and all Ir. Recoveries ranged from 50 to 100%. A t low levels, the determination of PGE and Au in the thiourea fraction by ICP-MS was compromised by high levels of total dissolved solids (T DS), which necessitated dilution of the eluate prior to analysis. The TDS was reduced by decomposing thiourea with HNO3 and removing SO42- b y precipitation of BaSO4, but this led to lower and more erratic resul ts, and increased contamination. An assessment of the optimised proced ure employing geological reference materials PTM-1, PTC-1 and SARM7, i ndicated that acceptable results should be attainable for ICP-MS deter mination of most elements in geological samples containing high concen trations (>1 mu g g(-1)) of the PGE, for which decomposition of thiour ea is unneccessary. The addition of a decomposition step led to low re covery of all elements except Ir, which was present entirely in the HC l eluate, The method is viable for the determination of Ir in a range of geological materials, but modifications will be required if it is t o be extended to the other precious metals.