Converter processing of platinum group metals

ABSTRACT

The history and variety of commercial Platinum Group Metal (PGM) matte converting processes are explored. Aspects unique to pneumatic converting of high iron, lower grade mattes (typically up to 30% NiCuCo), often containing chrome (0.5–2% Cr₂O₃), to PGM-enriched (1500–25000 g/t PGM) converter mattes, to endpoints specific to promote downstream refining to final metal are described. The range of converter vessels, involving batch, to staged, to continuous converting processes are presented, along with some of the operating requirements and challenges.

KEYWORDS:

• Platinum group metal (PGM)
• nickel-copper-cobalt (NiCuCo) matte
• converting
• Peirce-Smith converter (PSC)
• top submerged lance (TSL) bath converter
• Anglo Converting Process (ACP)
• top blown rotary converter (TBRC)

Acknowledgements

Permission by Anglo American Platinum Ltd. to publish and assistance with manuscript collation by Lettie Chomane and Luke Ngubane are gratefully acknowledged, as are contributions from Steve Burks, Dan Legrand, Louis Mabiza, Robert Matusewicz, Loucas Pouroulis, Greg Roset and Nico Steenekamp.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 Sulphur-deficient, or metallized matte is generally accepted to refer to matte with sulphur content below that stoichiometrically required to combine, in sequence of sulphur allocation, all copper, cobalt, nickel and iron, except for any iron associated with oxygen as magnetite, typically as the sulphides Cu₂S, Co₉S₈, Ni₃S₂ and FeS, respectively (Bustos, Ip et al. 1988 ; Donald et al. 2005). While the specific sequence of metallisation is argued to be more complex and composition dependent (Tsymbulov and Yertseva 2006), at Ni/Cu ratios of 1.6 typical of PGM converting, the rate of metallisation by iron is predicted to exceed nickel, so the sequence above remains directionally consistent.

2 ‘The mush consists of magnetite and silica double saturated slag. Solid nickel ferrite, NiO.Fe₂O₃, a very stable compound also forms as a distinct solid’ (Warner and Díaz 2003).