Study of the digestion of chromite during nickel sulphide fire assay for the platinum group elements and gold

This paper describes an improved fusion procedure for the fire assay of the Pt group elements and Au in chromite. The effectiveness of the modified fusion procedure compared with the traditional method is demonstrated with optical microscopy, X-ray diffraction, electron probe microanalysis and neutron activation analysis. All these techniques confirm that the dissolution of chromite is improved. In particular, the work shows that chromite must be completely dissolved for quantitative recovery of the Pt group elements, as there is no change in the crystal structure of the undissolved chromite grain during dissolution to release the elements. The quality of data generated with the proposed modified method is demonstrated with in-house reference material.