Post-regrind selective depression of pyrite in pyritic copper–gold flotation using aeration and diethylenetriamine Eric A. Agorhom a,b,⇑ , W. Skinner b , M. Zanin b a Department of Mineral Engineering, University of Mines and Technology, P.O. Box 237, Tarkwa, Ghana b Ian Wark Research Institute, University of South Australia, Mawson Lakes Campus, Adelaide, SA 5095, Australia article info Article history: Received 7 July 2014 Accepted 27 November 2014 Keywords: Pyrite depression Oxygen demand Flotation Surface analysis Gold abstract The present study investigates the effect of aeration and diethylenetriamine (DETA) on the selective depression of pyrite in a porphyry copper–gold ore, after regrinding (at grind sizes, d 80 = 38 and 8 lm) with respect to Au recovery and grade using oxygen demand tests, flotation, QEMSCAN, X-ray spectros- copy (XPS) and EDTA extraction analysis. It was found that pyrite depression increases after aeration and with decreasing grind size. This was observed to be due to the markedly higher oxygen consumption rate of pyrite at the 8 lm (kla = 0.10 min 1 ) than at the 38 lm grind size (kla = 0.02 min 1 ). The addition of DETA improved pyrite depression (9% with aeration only versus 39% with aeration + DETA) at the 38 lm grind size. Gold and copper flotation recovery followed pyrite recovery for the two grind sizes using XD5002 in the presence of air and DETA. The surface analysis (XPS and EDTA extraction) revealed that the significant pyrite depression at the 8 lm grind size was due to increased amount of surface iron oxides, oxy-hydroxides (FeAO/OH), sulphate species and increased liberation of mineral phases (QEMSCAN analysis), whilst the poorer pyrite depres- sion at the 38 lm grind size was due to insufficient liberation of mineral phases and the persistence of activating Cu on the pyrite surface. The addition of DETA increased pyrite depression at the coarser grind size due to a significant reduction in Cu(I)S and increased Cu(II)AO species, correlating with the flotation results of pyrite under this test condition. Two-stage copper and pyrite flotation, followed by Au cleaning after regrinding to 38 lm grind size, under high pH or aerated condition is proposed as the recommended route to optimise Au flotation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Gold and chalcopyrite are the main valuable mineral phases in most porphyry copper–gold ores with pyrite and silicates as the major gangue and host minerals for gold (Agorhom et al., 2012; 2013). Pyrite does not only host gold but also, it is intimately asso- ciated with chalcopyrite in most cases (Agorhom et al., 2012; 2013). The significant association of gold with pyrite rather than chalcopyrite creates flotation selectivity problems and conse- quently reduces the final concentrate grade. Effective selectivity between chalcopyrite and pyrite can also be problematic in flotation due to ‘‘inadvertent’’ activation of pyrite by dissolved copper ions from copper sulphides through superficial oxidation, and/or their association with pyrite as fine complex intergrowths. It has been proposed and confirmed that activation of pyrite occurs by adsorption of Cu(II), which is subsequently reduced to Cu(I) through sulphide oxidation to form a Cu(I)S-like species on the pyrite surface (Voigt et al., 1994; von Oertzen et al., 2007). This process is enhanced by galvanic effects, when chalcopyrite (or galena, chalcocite, bornite, etc.) comes into contact with a more cathodic sulphide mineral like pyrite. This ‘inadver- tent’ pyrite activation and flotation adversely affects concentrate grades. As a consequence, most flotation circuits processing complex sulphide ores, containing pyrite, use regrinding (to liberate pyrite, gold and chalcopyrite) and depression strategies such as aeration, cyanide, sulphite, high pH (pH > 10), etc., to minimise pyrite flota- tion during cleaner stages. Though pyrite may be sufficiently liber- ated from gold and chalcopyrite after regrinding, maximum depression is not often achieved at the cleaner stage (Hu et al., 2009). The general mechanism governing depression of pyrite using sulphite and aeration involves the formation of hydrophilic metal sulphite species, decomposition of xanthate, oxygen consumption (Misra et al., 1985; Yamamoto, 1980; Miller 1970) http://dx.doi.org/10.1016/j.mineng.2014.11.019 0892-6875/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Ian Wark Research Institute, University of South Australia, Mawson Lakes Campus, Adelaide, SA 5095, Australia. E-mail address: Aminartey.Agorhom@mymail.unisa.edu.au (E.A. Agorhom). Minerals Engineering 72 (2015) 36–46 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng