Importance of roasted sulphide concentrates characterization in the hydrometallurgical extraction of zinc Julio Ce ´zar Balarini * , Ludmila de Oliveira Polli, Ta ˆnia Lu ´ cia Santos Miranda, Roberto Machado Zica de Castro, Adriane Salum Departamento de Engenharia Quı ´mica, Escola de Engenharia da Universidade Federal de Minas Gerais, Rua: Espı ´rito Santo, 35 – 6° andar – CEP: 30.160-030 – Belo Horizonte, MG, Brazil Received 5 July 2007; accepted 5 October 2007 Abstract The production of electrolytic zinc from sulphide ores consists mainly of four stages: roasting, acid leaching, purification and elec- trolysis. The roasting step plays an important role in zinc extraction due to the transformation from sulphide to oxide structure which provides more reactivity in presence of acid solutions. Incomplete particle roasting and presence of highly stable zinc ferrite (ZnFe 2 O 4 ) formed in the pyrometallurgical step are the two major obstacles in the hydrometallurgical extraction of zinc. The objective of this study is to detect problems observed in an industrial electrolytic zinc circuit. For this purpose, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF) and scanning electron microscopy (SEM/EDS) techniques were used to characterize sulphide and roasted concen- trate samples. Microscopic investigations of cross-sectional particles revealed incomplete roasting in some particle sizes and the presence of ferrite clusters inside the roasted ores. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Sulphide ores; Roasting; Particle morphology; Ore mineralogy; Industrial minerals 1. Introduction Sphalerite present in sulphide ores is the main mineral source for the zinc production (Peng et al., 2005). It is widely distributed in the nature and it is present in a variety of sulphide deposits. It is commonly associated with galena (PbS), pyrite (FeS 2 ) and/or pyrrhotite (Fe 1x S (hexagonal), Fe 7 S 8 (monoclinic)) and it may be accompanied by one or more copper or copper–iron sulphides (chalcopyrite (CuFeS 2 ) or others) (Lusk and Calder, 2004). Currently, more than 80% of the world’s zinc metal output is pro- duced from zinc sulphide concentrates using the roast– leach–electrowinning process (Corriou et al., 1988; Elgersma et al., 1993; Chen and Dutrizac, 2004; Harmer et al., 2007). In the roasting step, the sulphur in the iron- bearing sphalerite ((Zn,Fe)S) is converted to sulphur diox- ide and subsequently to sulphuric acid in a recovery unity. ZnS is converted to ZnO, but a significant fraction reacts with the iron impurities to form ZnFe 2 O 4 (Chen and Dutri- zac, 2004; Xia and Pickles, 1999; Graydon and Kirk, 1988). According to Dimitrov et al. (2000), at temperatures exceeding 850 °C and under the industrial conditions of roasting (900–1000 °C and fluid bed), ZnO, Fe 2 O 3 and ZnFe 2 O 4 are the stable phases. Despite the production of SO 2 as a pollutant and the problems related to iron release, the roasting is still an important and very used step in the electrolytic zinc circuit (Corriou et al., 1988; Elgersma et al., 1993; Chen and Dutrizac, 2004; Harmer et al., 2007). C ¸ opur et al. (2003) summarized a set of main reactions taking place in the process of roasting of a typical zinc sul- phide concentrate at 800 °C (Eqs. (1)–(15)) 0892-6875/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2007.10.002 * Corresponding author. E-mail addresses: julio@deq.ufmg.br (J.C. Balarini), salum@deq. ufmg.br (A. Salum). This article is also available online at: www.elsevier.com/locate/mineng Available online at www.sciencedirect.com Minerals Engineering 21 (2008) 100–110