Fire and brimstone : the roasting of a Merensky PGM concentrate

Show simple item record Rambiyana, R.I. Den Hoed, P. Garbers-Craig, Andrie Mariana 2015-08-28T07:15:57Z 2015-08-28T07:15:57Z 2015-06
dc.description This paper was first presented at the, Platinum Conference 2014, 20–24 October 2014, Sun City South Africa. en_ZA
dc.description.abstract Four 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.librarian am2015 en_ZA
dc.description.sponsorship The National Research Foundation of South Africa (Grant number TP1208219517). en_ZA
dc.description.uri en_ZA
dc.identifier.citation Rambiyana, 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.issn 0038-223X (print)
dc.identifier.issn 2225-6253 (online)
dc.language.iso en en_ZA
dc.publisher Southern African Institute of Mining and Metallurgy en_ZA
dc.rights © The Southern African Institute of Mining and Metallurgy, 2015 en_ZA
dc.subject Roasting en_ZA
dc.subject Concentrate en_ZA
dc.subject Pyrrhotite en_ZA
dc.subject Pentlandite en_ZA
dc.subject Chalcopyrite en_ZA
dc.subject Smelting en_ZA
dc.subject Matte en_ZA
dc.subject Base metal en_ZA
dc.subject Platinum group metals (PGMs) en_ZA
dc.title Fire and brimstone : the roasting of a Merensky PGM concentrate en_ZA
dc.type Article en_ZA

Files in this item

This item appears in the following Collection(s)

Show simple item record