THE DETERMINATION OF PLATINUM-GROUP ELEMENTS (PGE) BY NICKEL SULFIDE FIRE-ASSAY - COEXISTING PGE-PHASES IN THE NICKEL SULFIDE BUTTON

The chemical composition of phases in buttons obtained by nickel sulfi de fire-assay during the determination of platinum-group elements (PGE ) has been investigated by electron microprobe analysis. Different PGE -containing phases, due to varying flux constituents and species of ad ded PGE, have been detected. By using sodium tetraborate as flux const ituent and adding PGE as chlorides, in a cryptocrystalline Ni3S2 matri x with low PGE (mainly Rh and Ru) contents, Rh- and Ru-bearing nickel sulfides ((Ni7.68-7.80Ru0.84-0.90Rh0.35-0.43)(9)S-8) and Ir alloys r,P t,Os)(0.56-0.62)(Ru,Rh)(0.25-0.28)Ni-0.12-0.19) are found. Treatment w ith lithium tetraborate leads to a Ni3S2 matrix exhibiting slightly hi gher Rh and Ru contents, with inclusions of nickel-rhodium sulfides (N i8Rh4S9) and platinum-nickel alloys (Pt0.45Ni0.36-0.39Ru0.11-0.14Rh0.0 5). Finely dispersed metallic colloidals from an automobile catalyst, with platinum and rhodium as main components, have given only platinum -nickel alloys (Pt1-xNix). Considerable losses of PGE during analytica l steps following the fire assay are expected when their contents in s ulfidic phases, which are more likely to be dissolved, are high.