Development and application of new ion-exchange techniques for the separation of the platinum group and other siderophile elements from geological samples

Two new anion-exchange techniques have been developed for the separation of the platinum group elements Ru, Pd, Ir, Pt and the siderophile metals Re, Ag, Zn and Cd from geological samples following a NiS fire assay digestion procedure. Both methods are simple and permit the isolation of these elements in sufficient purity for quantitative analysis by isotope dilution-inductively coupled plasma mass spectrometry (ID-ICPMS) at yields of 75-95%. The high affinity of the considered elements to anion exchange resins allows the use of small (1.25 mi) columns even for the processing of 5-10 g sized silicate rock samples. Following fire assay digestion and dissolution of the NiS buttons in aqua regia, the samples are loaded onto the resin bed as solutions in 1 M HCl. After elution of the bulk sample matrix with dilute HCl and HNO3, Zn and Cd are stripped from the column using 0.8 M HNO3. Small amounts of bromine water are added to the dilute mineral acids for the stabilization of strongly retained Ir(IV). Following this, the ion-exchange techniques permit the sequential elution of Ag, Re and the PGE using 11 M HCl, 8 M HNO3 and 13.5 M HNO3. The ion-exchange methods have been applied to separation of Ru, Pd, Re, Ir and Pt from the geological reference material SU-la prior to concentration measurements by ID-ICPMS. Our analytical results are in good agreement with previously published data for this sample and display an external reproducibility (based upon repeat dissolutions) of approximately 2-10% for the elements considered in this study. (C) 1997 Elsevier Science B.V.