The effect of sulfide concentrate mineralogy and texture on Reactive Oxygen Species (ROS) generation Gavin C. Jones a , Megan Becker b , Robert P. van Hille a , Susan T.L. Harrison a,⇑ a Centre for Bioprocess Engineering Research, Department of Chemical Engineering, University of Cape Town, Private Bag, Rondebosch 7701, South Africa b Centre for Minerals Research, Department of Chemical Engineering, University of Cape Town, Private Bag, Rondebosch 7701, South Africa article info Article history: Received 14 August 2012 Accepted 29 November 2012 Available online xxxx abstract The generation of Reactive Oxygen Species (ROS), H 2 O 2 and Å OH, has been observed from sulfide mineral containing particles in acidic solutions. The implications of this phenomenon, as a potential microbial stress-causing effect, have been studied previously with respect to thermophilic bioleaching performance in the presence of finely milled pyrite and chalcopyrite concentrates. In this study, the effect of sulfide mineralogy on ROS generation in the absence of microbes under physicochemical conditions typical for the bioleach environment was investigated. The mineralogical and elemental composition of eleven different samples containing sulfide mineral was obtained. These Au, Cu and other base metal-containing sulfide mineral concentrates as well as a milled whole ore of low Cu grade were tested for ROS genera- tion. The whole ore sample and two refractory Au concentrates containing approximately 50% pyrite, generated significantly less ROS compared to the base metal-containing concentrates when compared on a constant surface area loading basis. Sulfide mineral-related variables were correlated with ROS gen- eration. A significant difference was observed between FeS 2 and CuFeS 2 grades separately, whereas a combined measure of both minerals present in samples showed a consistently strong correlation to ROS generation. The Cu grade, total Cu-containing sulfides and the chalcopyrite content of Cu-containing samples correlated well with ROS generation. However, a common deterministic variable with a strong association to increased ROS generation was not found. A sub-set of samples were subjected to QEM- SCAN Ò for textural analysis. Results suggested that a decrease in sulfide mineral liberation, caused by gangue silicate mineral occlusion to solution, resulted in decreased reactivity as shown in one of the Au-containing samples. Well-liberated chalcopyrite and pyrite phases corresponded to increased reactiv- ity of samples. Pyrite, which was present in all of the reactive samples, was shown to be associated with other sulfide minerals, implicating its importance in galvanic interactions. Micro-analysis of chalcopyrite and pyrite phases from highly reactive samples showed an abundance of particles with extensive crack- ing and the possible presence of secondary transformation phases (szomolnokite). These results suggest that sulfide mineralogy, liberation and extent of physical processing affect sulfide mineral concentrate reactivity in acidic solutions. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Sulfide mineral particles are generally appreciated to be reac- tive. This ‘‘sulfide reactivity’’ includes a number of complex physi- cochemical processes that occur either at the surface or inside the bulk of sulfide mineral-containing particles or both, reducing sta- bility under certain conditions and leading to transformation and oxidation. The detrimental effects of this reactivity have been stud- ied mostly in the context of uncontrolled exposure to biological systems, both human (Schoonen et al., 2006) and environmental (Salmon and Malmström, 2006; Moncur et al., 2009), upon mining activities. More recent developments have looked at harnessing sulfide mineral reactivity for application in advance oxidation pro- cesses, to treat recalcitrant organic pollutants (Che and Lee, 2011; Che et al., 2011; Hara, 2011; Wang et al., 2012). Enhanced sulfide mineral reactivity is often promoted in hydrometallurgical pro- cesses where the extraction of the contained metal value is desired. In sulfide mineral biohydrometallurgy for the extraction of base and precious metals from sulfide mineral concentrates using Fe- and S-oxidising microorganisms (i.e. bioleaching/biooxidation), there is a need to understand sulfide mineral reactivity and its po- tential effects on the microbial catalysts used in the process. The bulk mineralogies of sulfide mineral concentrates used in two different tank bioprocessing technologies are shown in Table 1 (Rawlings et al., 2003). The sulfide mineral pyrite, is common to both processes. For the commercial BIOX Ò process it is intention- ally recovered from the run of mine ore into the concentrate due 0883-2927/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeochem.2012.11.015 ⇑ Corresponding author. E-mail address: Sue.Harrison@uct.ac.za (S.T.L. Harrison). Applied Geochemistry xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem Please cite this article in press as: Jones, G.C., et al. The effect of sulfide concentrate mineralogy and texture on Reactive Oxygen Species (ROS) generation. Appl. Geochem. (2013), http://dx.doi.org/10.1016/j.apgeochem.2012.11.015