Disolucion de manganeso en ambiente reductivo

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Hydrometallurgy 90 (2008) 207 – 212 www.elsevier.com/locate/hydromet

Reductive dissolution of manganese ore in sulfuric acid in the presence of iron metal
Mohammad Sh. Bafghi, Alireza Zakeri ⁎, Zahra Ghasemi, Mandana Adeli
Department of Metallurgical and Materials Engineering, Iran University of Science & Technology, Tehran, Iran Received 16 May2007; received in revised form 6 July 2007; accepted 12 July 2007 Available online 18 July 2007

Abstract The dissolution of a manganese dioxide ore in dilute sulfuric acid facilitated by Fe metal in the form of powdered sponge iron was investigated. Effects of such parameters as molar ratios of sponge iron and sulfuric acid to manganese dioxide, temperature, particle size of sponge iron as wellas ore particle size on the dissolution efficiency were studied. The results showed that manganese could be rapidly leached out to a complete degree even at room temperature. Based on both theoretical and experimental facts, it was concluded that the usage of metallic iron for the reductive leaching of manganese dioxide was superior to that of ferrous ion as far as dissolution rate and efficiencywere concerned. © 2007 Elsevier B.V. All rights reserved.
Keywords: Reductive leaching; Manganese dioxide; Pyrolusite; Sulfuric acid; Sponge iron

1. Introduction Although the conventional treatment of reduction roasting has been widely applied for processing manganese ores, alternative hydrometallurgical techniques have drawn much attention in recent years. Electrochemical and kinetic aspectsof reductive dissolution of MnO2 in acidic media have been discussed lately (Senanayake 2003; Xueyi et al., 2003). Extensive research works have been performed on the dissolution of MnO2 in dilute sulfuric or hydrochloric acids in the presence of a variety of reducing agents. Some of the reductants which have been employed are sulfur dioxide (Senanayake, 2004; Nayak et al., 2003; Asai and Konishi,1986; Grimanelis et al., 1992; Dixit and Raisoni, 1987; Miller and Wan, 1983),
⁎ Corresponding author. Tel.: +9821 7391 2824; fax: +9821 7724 0480. E-mail address: zakeria@iust.ac.ir (A. Zakeri). 0304-386X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2007.07.003

aqueous ferrous sulfate or ferrous chloride solutions (Koch, 1957; Tekin and Bayramoglu,1993; Das et al., 1982), iron sulfides (Kanungo, 1999a,b; Nayak et al., 1999; Vracar and Cerovic, 1984), nitrous acid (Dresler, 1984), organic acids such as EDTA and oxalic acid (Pankratova et al., 2001; Sahoo et al., 2001), hydrogen peroxide (Jiang et al., 2004), methanol (Momade and Momade, 1999) and even some types of carbohydrates like glucose (Trifoni et al., 2001). Among all these reducingagents examined so far, ferrous ion seems to be one of the most satisfactory reductants due to its good reactivity, availability and relatively lower cost. Koch (1957) studied the kinetics of the reaction between manganese dioxide and ferrous ion in acid solutions using the potential of ferrous-ferric couple as a measure of the extent of reaction. It was suggested that the reaction occurred mostreadily at certain active sites on the manganese dioxide surface and that surface

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M.Sh. Bafghi et al. / Hydrometallurgy 90 (2008) 207–212

Table 1 Feasible half-reactions in the present study with the relevant standard reduction potentials Equation (1) (2) (3) (4) Half-reaction 2H+(aq) + 2e− = H2(g) Fe2+(aq) + 2e− = Fe(s) MnO2(s) + 4H+(aq) + 2e– = Mn2+(aq) + 2H2O(l) 2Fe3+(aq) + 2e– =2Fe2+(aq) E° (V) 0 −0.44 1.23 0.77

diffusion of ferrous ion was the rate-determining step. On the other hand, Tekin and Bayramoglu (1993) concluded that under the conditions of intensive agitation, the reaction is chemical-controlled with the apparent activation energy of 28 kJ/mole. Dissolution of manganese dioxide in the presence of iron sulfides has been the subject of some recent studies....