Restoring the floatability of oxidised sulfides using sulfidisation A.J.H. Newell a, ⁎ , W.M. Skinner b , D.J. Bradshaw a a Mineral Processing Research Unit, Department of Chemical Engineering, University of Cape Town, Private Bag, Rondebosch, 7701, South Africa b Ian Wark Research Institute, The ARC Special Research Centre for Particle and Material, Interfaces, University of South Australia, Mawson Lakes Campus, South Australia, 5095, Australia Received 9 May 2006; received in revised form 15 August 2006; accepted 15 August 2006 Available online 4 October 2006 Abstract While sulfide minerals generally are easy to recover by flotation, surface oxidation can have a significant impact on both the recovery and selectivity. The extent of this impact depended upon the mineral type for oxidised Nkomati sulfides (chalcopyrite b pentlandite ∼ pyrrhotite). The floatability of these oxidised sulfides has been shown to be restored by sulfidisation with varying degrees of success (chalcopyrite b pyrrhotite b pentlandite). Electrophoretic measurements showed that the oxidised sulfides strongly adsorbed hydrosulfide ions during sulfidisation which corresponded with the onset of strong floatability. XPS analyses showed that the surface of the oxidised chalcopyrite was readily converted to a chalcocite-like stoichiometry through an electrochemical mechanism coupled with the oxidation of copper and iron. The sulfidisation of oxidised pyrrhotite proceeded through both an anionic exchange mechanism and a direct precipitation reaction to form a pyrrhotite-like surface, which was subsequently converted electrochemically to a pyrite-like composition via iron and copper oxidation. Under more intense sulfidisation, the precipitation reaction was more dominant and a more pyrrhotite-like surface was evident. For the sulfidisation of oxidised pentlandite, although small quantities of a millerite-like and a pyrite-like surface may have formed, significant flotation in the presence of other oxidised sulfides appears to have been achieved through either adsorbed ferric hydroxides that became sulfidised or precipitated iron sulfides generated from the oxidised pyrrhotite. A feature common to all the sulfidised surfaces was the presence of reasonable quantities of either polysulfides or elemental sulfur, which may well contribute to any subsequent flotation. © 2006 Elsevier B.V. All rights reserved. Keywords: Oxidised sulfides; Sulfidisation; X-ray photoelectron spectroscopy; Chalcopyrite; Pentlandite; Pyrrhotite; Flotation; Electrophoresis 1. Introduction Good flotation is generally achieved with most sulfide minerals. For example, in Merensky type ores, where the sulfide minerals are predominantly pyrrhotite, pentlandite and chalcopyrite and the flotation recovery of all the sulfides are targeted, the order of floatability is chalcopyrite b pentlandite b pyrrhotite (Bradshaw et al., 1999). However, sulfide mineral floatability becomes increasingly poorer as the sulfide surfaces become more oxidised and hydrophilic. Sulfidisation offers considerable opportunities for the remediation of oxidised sulfides, based on the effec- tiveness of sulfidisation in the treatment of base-metal “oxide” ores (Shungu et al., 1988; John et al., 1991; Mwema and Mpoyo, 2001). Additionally reports of applications from industry that use sulfidisation to recover oxidised sulfides include the treatment of: oxidised nickel sulfides at the Trojan mine (Barker Int. J. Miner. Process. 84 (2007) 108 – 117 www.elsevier.com/locate/ijminpro ⁎ Corresponding author. Tel.: +27 21 650 5520; fax: +27 21 650 5501. E-mail address: andrew@chemeng.uct.ac.za (A.J.H. Newell). 0301-7516/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.minpro.2006.08.002