Metalurgia

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Minerals Engineering 21 (2008) 23–30 This article is also available online at: www.elsevier.com/locate/mineng

Leaching of a zinc concentrate in H2SO4 solutions containing H2O2 and complexing agents
Teresa Pecina *, Telhma Franco, Pedro Castillo, Erasmo Orrantia
´ ´ CIMAV, S.C. (Centro de Investigacion en Materiales Avanzados), Quımica deMateriales, Miguel de Cervantes 120, Complejo Industrial Chihuahua, C.P. 31109, Chihuahua, Chihuahua, Mexico Received 22 May 2007; accepted 5 July 2007 Available online 4 September 2007

Abstract The extraction of zinc from a sphalerite concentrate by means of hydrogen peroxide as an oxidant in sulfuric acid solutions was examined. The oxidative leaching study focused on two topics: zinc dissolutionkinetics, and finding complex agents that increase zinc recovery in an oxidative aqueous medium. In the first stage, a study was performed to assess the influence of various parameters such as acid and peroxide concentrations, particle size, reaction time, and temperature on zinc dissolution kinetics. It was found that oxidative leaching of sphalerite follows the shrinking core model and, in spite of thelayer of elemental sulfur surrounding the particles, the dissolution is controlled by a reaction control step with an activation energy of 50 kJ/mol. The addition of phosphonic acid, phosphoric acid, oxalic acid, and citric acid enhanced the leaching of the sphalerite. The use of complexing agents is a viable option for zinc dissolution. Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Sulfideores; Leaching; Reaction kinetics

1. Introduction Sulfides (sphalerite, marmatite) are primary sources of zinc. Due to the low solubility of zinc sulfides in acid media, zinc is concentrated using froth flotation methods. Afterwards, the concentrate is roasted to obtain zinc oxide. Finally, the zinc is recovered through electrowinning or carbothermic processes. During calcination, SO2 is releasedcausing pollution. Another commercial route for zinc leaching is a costly autoclavable method. Due to these problems, the necessity of direct routes of sphalerite leaching under atmospheric pressure in industry is evident. One route is the oxidizing leaching process. Oxidative leaching research has evaluated many oxidizing agents such as acids, alkalis, ferric salts, oxygen, ammonium salts,manganese dioxide, and bacteria (Crundwell, 1987; Balaz and Ebert, 1991; Dutrizac, 1991; Jin and War´ ren, 1993; Limpo and Gomez, 1997; Pandey, 1998; Babu
*

et al., 2002; Da Silva, 2004). Hydrogen peroxide has been successfully used as an oxidizing agent for the leaching of bulk zinc concentrates in hydrochloric solutions (Vazarlis, 1987), mechanically activated sphalerite (Balaz and Ebert, 1991),and chalcopyrite systems (Antonijevic et al., 2004). The oxidation reaction of sphalerite in an acid solution (pH 6 2) is an electrochemical process which entails the dissolution of the mineral (Eq. (1)). This process releases metal ions and forms elemental sulfur (Abramov and Avdohin, 1997). ZnS ) Zn2þ þ S þ 2eÀ ; E ¼ 0:265 þ 0:0295 log½Zn2þ Š ð1Þ

The anodic process is supported by thecathodic reduction of hydrogen peroxide (Eq. (2)). H2 O2 þ 2Hþ þ 2eÀ ( 2H2 O; ) E ¼ 1:77 V; ð2Þ

where E° is the standard potential of the electrode in the given reaction with the overall mechanism being: ZnS þ H2 O2 þ 2Hþ ) Zn2þ þ S þ 2H2 O ð3Þ

Corresponding author. Tel.: +52 614 439 1100; fax: +52 614 439 1130. E-mail address: teresa.pecina@cimav.edu.mx (T. Pecina).

0892-6875/$ - see frontmatter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2007.07.006

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T. Pecina et al. / Minerals Engineering 21 (2008) 23–30

In spite of the applicability of oxidative leaching methods, most mineral sulfide processes conducted in aqueous environments have problems due to metal ion interference, precipitation of insoluble precipitates, formation of solid product layers,...