Fire and brimstone : the roasting of a Merensky PGM concentrate

dc.contributor.authorRambiyana, R.I.
dc.contributor.authorDen Hoed, P.
dc.contributor.authorGarbers-Craig, Andrie Mariana
dc.date.accessioned2015-08-28T07:15:57Z
dc.date.available2015-08-28T07:15:57Z
dc.date.issued2015-06
dc.descriptionThis paper was first presented at the, Platinum Conference 2014, 20–24 October 2014, Sun City South Africa.en_ZA
dc.description.abstractFour sulphide minerals – pyrite (FeS2), pyrrhotite (Fe1–xS), pentlandite ([Ni,Fe]9S8), and chalcopyrite (CuFeS2) – contain the base metals and most of the iron in concentrates of platinum group metals (PGMs). In the pyrometallurgical processing of PGM concentrates these sulphides form a matte during smelting, and iron and sulphur are removed from the matte during the converting process. This paper discusses the roasting of Merensky concentrate in air before smelting, with the purpose of reducing the matte load to the converter. Roasting tests were conducted in a bench-scale rotary kiln at temperatures from 350°C to 700°C. The concentrate tested contained 17.4% sulphur and consisted of 23% pyrrhotite, 16% pentlandite, 11% chalcopyrite, and 2% pyrite. The particles were fine (d50 = 22 μm), and all the sulphide particles were liberated. Roasting in air at 550°C and 650°C for 20 minutes removed respectively 60% and 70% of the sulphur. The iron in the sulphides was oxidized to Fe3O4 (magnetite) at temperatures below 500⁰C and to Fe2O3 (haematite) at temperatures above 550⁰C. At 700⁰C the bed sintered and copper oxides formed. At temperatures below 450°C oxidation was incomplete: pyrrhotite remained and only 30% of the sulphur was removed. Smelting tests were conducted to assess matte fall and the deportment of copper and nickel to matte. It was evident that roasting resulted in lower matte falls (a drop of approximately 60%) compared with matte falls from unroasted concentrate. The iron and sulphur levels in the matte were reduced to below 3.5% and 22% respectively. This paper also briefly describes the mechanisms by which pyrrhotite, chalcopyrite, and pentlandite are oxidized during roasting. For chalcopyrite, the mechanism proceeds through an intermediate solid solution phase, which extends from Cu1.02Fe1.04S2 to Cu2.04Fe0.72S2 to a copper-rich solid solution of bornite (Cu4Fe1.4S4–Cu2S). The oxidation of pentlandite proceeds through a monosulphide solid solution (Ni0.39Fe0.53S–Ni0.74Fe0.15S) to a solid solution of heazlewoodite ([Ni,Fe]3±xS2). These mechanisms are explored in relation to chemical thermodynamics and microstructures.en_ZA
dc.description.librarianam2015en_ZA
dc.description.sponsorshipThe National Research Foundation of South Africa (Grant number TP1208219517).en_ZA
dc.description.urihttp://www.saimm.co.za/journal-papersen_ZA
dc.identifier.citationRambiyana, RI, Den Hoed, P & Garbers-Craig, AM 2015, 'Fire and brimstone : the roasting of a Merensky PGM concentrate', Journal of The Southern African Institute of Mining and Metallurgy, vol. 115, pp. 507-514.en_ZA
dc.identifier.issn0038-223X (print)
dc.identifier.issn2225-6253 (online)
dc.identifier.urihttp://hdl.handle.net/2263/49629
dc.language.isoenen_ZA
dc.publisherSouthern African Institute of Mining and Metallurgyen_ZA
dc.rights© The Southern African Institute of Mining and Metallurgy, 2015en_ZA
dc.subjectRoastingen_ZA
dc.subjectConcentrateen_ZA
dc.subjectPyrrhotiteen_ZA
dc.subjectPentlanditeen_ZA
dc.subjectChalcopyriteen_ZA
dc.subjectSmeltingen_ZA
dc.subjectMatteen_ZA
dc.subjectBase metalen_ZA
dc.subjectPlatinum group metals (PGMs)en_ZA
dc.subject.otherEngineering, built environment and information technology articles SDG-09
dc.subject.otherSDG-09: Industry, innovation and infrastructure
dc.subject.otherEngineering, built environment and information technology articles SDG-12
dc.subject.otherSDG-12: Responsible consumption and production
dc.subject.otherEngineering, built environment and information technology articles SDG-13
dc.subject.otherSDG-13: Climate action
dc.titleFire and brimstone : the roasting of a Merensky PGM concentrateen_ZA
dc.typeArticleen_ZA

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