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 separati on of the platinum group elements Ru, Pd, Ir, Pt and the siderophile m etals Re, Ag, Zn and Cd from geological samples following a NiS fire a ssay digestion procedure. Both methods are simple and permit the isola tion of these elements in sufficient purity for quantitative analysis by isotope dilution-inductively coupled plasma mass spectrometry (ID-I CPMS) at yields of 75-95%. The high affinity of the considered element s to anion exchange resins allows the use of small (1.25 mi) columns e ven for the processing of 5-10 g sized silicate rock samples. Followin g fire assay digestion and dissolution of the NiS buttons in aqua regi a, 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 a nd 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 stabilizat ion of strongly retained Ir(IV). Following this, the ion-exchange tech niques 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 appl ied to separation of Ru, Pd, Re, Ir and Pt from the geological referen ce material SU-la prior to concentration measurements by ID-ICPMS. Our analytical results are in good agreement with previously published da ta for this sample and display an external reproducibility (based upon repeat dissolutions) of approximately 2-10% for the elements consider ed in this study. (C) 1997 Elsevier Science B.V.