A new preconcentration technique for the determination of PGMs and gold by fire assay and ICP-OES

A Masasire,P Dzomba,F Rwere,M Mupa

doi:10.17159/2411-9717/1638/2022

Abstract

Accurate determination of platinum group metals (PGMs) and gold (Au) has always proven to be a difficult task, due to their low concentrations in platiniferous ores. The most common preconcentration technique used in analysis of these metals is fire assay with a flux containing nickel or lead. This technique can be improved by using co-collectors. Here we hypothesise that Fe, Co, and Cu can be used as co-collectors to enhance separation and preconcentration of PMGs and gold by fire assay. To test this hypothesis, geological exploration samples from Siyanda Union Mine (Northam, South Africa) were analysed by an inductively coupled plasma-optical emission spectrometer (ICP-OES) for PGMs (Pt, Pd, and Rh) and Au. A control sample (certified reference material AMIS 0426) was also analysed by the same technique. The PGM and Au recoveries from the control sample ranged from 83% to 105% for all three co-collectors, with relative standard deviations less than 10% for the control sample and 7% for the geological samples. The PGM and Au recoveries by Fe and Co co-collectors were modestly higher than that of the Cu-collector. These results indicate that Fe and Co are better co-collectors than Cu, presumably due to the loss of analyte when using Cu. Taken together, Fe and Co co-collectors can be viable alternatives for analysis of PGMs and gold using the fire assay method.

Highlights

South Africa is a prominent global supplier of platinum group metals (PGMs)
The recoveries obtained from the Cu co-collector were 92.2% for Pt, 88.1% for Pd, 83.1% for Rh, and 88.1% for Au. These results demonstrate that Fe and Co co-collectors can be used for the determination of PGMs and Au
The nickel sulphide fire assay method offers the advantage of accommodating a large sample mass, and all of the PGMs can be concentrated by this procedure

Summary

Introduction

South Africa is a prominent global supplier of platinum group metals (PGMs). The main reserves of PGMs are the Bushveld Complex (Tanner et al, 2019), where platiniferous ores are obtained from the Merensky Reef (Creech et al, 2014). The PGMs are found in low concentrations, typically less than 10 g/t (Serbin, Bazel, and Ru, 2017). The low PGM grade of these ores contributes to their high market value. The analysis of the platiniferous ores and flotation concentrate samples is challenging because of the low PGM concentrations and their heterogeneous distribution in the matrix. Their determination is usually preceded by isolation from the gangue material and preconcentration (Berezhnaya and Dubinin, 2016; Bayrak et al, 2017). In South African mining and metallurgical testing laboratories this is accomplished mainly by fire assay using nickel sulphide or lead collection followed by spectrometric determination (Vanhaecke et al, 2010)

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