The rapid determination of the platinum group elements and gold with nickel sulphide fire assay and neutron activation analysis (NAA)

Abstract

Nickel sulphide fire assay is now a routine method of preseparating the platinum group elements (PGEs) and gold before their determination using AAS, ICP, NAA, or ICP-MS. In general there has been more effort devoted to the analytical techniques than to the preconcentration step. However, the main problems of analysis occur in the fusion and dissolution of the nickel sulphide button. The authors have been working on improving the fusion step, with the result that for most applications the technique can be straightforward and entirely free from reagent blank problems. The major problem remaining has been the recovery of the elements, which is reproducible (81-83% PGE, 76% Au) but the losses are significant. The problem of losses may be avoided entirely if the nickel sulphide bead is analyzed directly. In the past the background effects have given very poor sensitivities when the bead was analyzed by NAA, but the improvements made by the authors to the fusion process have resulted in a sensitive technique for direct analysis of the bead. We have developed a rapid and sensitive method which is sufficiently simple that large numbers of samples may be processed routinely, providing an inexpensive and reliable technique for determination of the PGEs. The validity of the method has been demonstrated using certified reference materials.