Reductive leaching of manganese from low grade Sinai ore in HCl using H2O2 as reductant

doi:10.1016/j.hydromet.2006.05.006

Hydrometallurgy

Volume 84, Issues 3–4, November 2006, Pages 187-191

https://doi.org/10.1016/j.hydromet.2006.05.006 Get rights and content

Abstract

Manganese leaching from a low-grade ore (8.52% Mn) from Sinai was investigated by using hydrochloric acid in the presence and absence of hydrogen peroxide as a reducing agent. Sample characterization by XRD showed the presence of a variety of manganese minerals mainly cryptomelane, chalcophanite, pyrolusite, and crednerite. The presence of iron minerals like goethite, hematite, and minor quantities of pyrite were also observed, as well as gibbsite and dolomite. Although pyrite can act as a reductant for the tetravalent manganese minerals, it was necessary to use H₂O₂ as an additional reductant to realize over 97% Mn leaching. Both Zn and Cu that are present in the manganese minerals chalcophanite and crednerite respectively, were simultaneously leached.

The relevant leaching factors were optimized as 2 M HCl and 0.4 M H₂O₂ for 1 h when using a solid–liquid ratio of 1/12 at 60–95 °C. Under these conditions, the leaching efficiencies were > 97% Mn, 98% Zn together with about 81% Al and complete leaching of Cu; whilst iron dissolution did not exceed 14%.

Introduction

Manganese is a strategic element that has several industrial applications such as steel production, carbon–zinc batteries production, fertilizers, as well as colorants for bricks, dyes and medicines (Sahoo et al., 2001). The world annual consumption of manganese is above 1,300,000 annual tons and it is destined to increase. Low grade ores are gaining increasing attention due to developments in exploitation technologies.

Various hydrometallurgical methods have been suggested in the literature for treatment of low grade manganese ores. Such ores can be treated either by reduction roasting followed by acid leaching (Sahoo and Srinivasa, 1989) or directly by reductive acid leaching using different reducing agents. To realize the latter, several procedures have been suggested; namely mixed methanol–sulphuric solution (Momade and Momade, 1999), coke (Panda and Gupta, 1988), non aqueous dimethyl sulfoxide (Raisoni and Dixit, 1988), sulphuric and oxalic acid mixtures (Sahoo and Srinivasa, 1989), iron(Π) sulphate (Das et al., 1982), aqueous sulphur dioxide (Abbruzzese, 1990, Abbruzzese et al., 1990, Naik et al., 2000, Vegliò and Toro, 1994), sulphuric acid and hydrogen peroxide (Tao Jiang et al., 2003, Tao Jiang et al., 2004), hydrochloric acid and nickel matte (Chen et al., 1992), hydrochloric acid and pyrite (Kanungo, 1999a, Kanungo, 1999b). Recently, Jana et al. (1995) have reported the dissolution of MnO₂ in an aqueous alcoholic-HCl acid mixture. These authors have pointed out that the chloride ion at high concentrations was responsible for the reduction of higher valence state oxides. On the other hand leaching processes in basic media involve the use of ammonium sulphite as reductant (Das et al., 1986), in addition to several patented leaching processes (Cardwell and Kane, 1976, Kane and Card well, 1974, Van Peteghem, 1977).

The high grade Paleozoic manganese deposit of south west Sinai has essentially been exploited. Nevertheless, extensive tonnages of low grade ore material still exist and require developed technologies for their economic processing. A proper mineralogical sample of this low grade ore was therefore collected from Abu Zeneima locality (11.00% MnO) and was subjected to processing via reduction leaching. For this study, a mixture of hydrochloric acid and hydrogen peroxide was used for the first time. The redox chemistry of the latter in aqueous solution shows that it is a strong oxidizing agent in either acid or basic solution as shown from the following equations (Cotton and Wilkinson, 1988).H₂O₂ + 2H⁺ + 2 ē → 2H₂O E₀ = 1.77 VO₂ + 2H⁺ + 2 ē → H₂O₂ E₀ = 0.68 VHO₂⁻ + H₂O + 2 ē → 3OH⁻ E₀ = 0.87 V

However, H₂O₂ behaves as a reducing agent only towards very strong oxidizing agents such as MnO₄⁻ and MnO₂ and chloride ion is not a reductant in dilute acid solutions. Accordingly, the chemical dissolution of MnO₂ in acidic solution can be described by the following equationMnO₂ + 4H⁺ + 2 ē → Mn^+ 2 + 2H₂O

This study examines the different relevant factors affecting the leaching of manganese and other impurities from the ore. These factors involved the concentration of both acid and H₂O₂, the leaching temperature and time, as well as the pulp density and the grain size of the ore.

Section snippets

Ore material

To define the mineralogical composition of the working ore material, the bulk and sieved samples were subjected to X-ray diffraction analysis. For this purpose, a Philips X-ray diffractometer, model PW 223/20 was used where the copper tube was operated at 40 kV and 20 mA. The obtained diffractogram was properly interpreted using standard diffraction mineral patterns. The obtained results revealed the presence of several manganese minerals such as cryptomelane, chalcophanite, pyrolusite and

Effect of HCl concentration

A series of leaching experiments was carried out at different HCl concentration (1.25 to 3.25 M). The other leaching conditions were fixed at 0.4 M H₂O₂, a solid/liquid ratio of 1:12 at 95 °C for 2 h and an ore grain size of − 200 mesh (− 74 μm). From the obtained leaching efficiencies as shown in Fig. 1, it is clear that as the HCl concentration increases, the dissolution efficiencies of all the studied metal values increase. Thus, at 2 M acid concentration, the economic metal values of Mn, Cu

Effect of temperature

In order to reduce the heat energy and in turn the leaching costs, three further leaching experiments were carried out at room temperature, 60 °C and 85 °C under the same leaching conditions previously used at 95 °C. Fig. 4 indicates that temperature plays an important role, especially in case of Al and Cu leaching. Accordingly, the extraction of aluminium decreased to only 16.9% while that of copper decreased to about 55% at room temperature. This compared to about 84% Mn and 91% Zn extraction.

Conclusions

A reductive leaching process for Sinai low grade manganese ore material has been successfully demonstrated for the first time using an optimum mixture of hydrochloric acid and hydrogen peroxide as reductant. In the proposed leach system, relatively little iron was leached from the goethite matrix but other associated metal values were leached; namely Al present in gibbsite as well as the Cu and Zn values replacing some Mn in its minerals. The studied leaching factors were optimized as 2 M HCl

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Reductive leaching of manganese from low grade Sinai ore in HCl using H2O2 as reductant

Abstract

Introduction

Section snippets

Ore material

Effect of HCl concentration

Effect of temperature

Conclusions

Hydrometallurgy

Miner. Eng.

Hydrometallurgy

Hydrometallurgy

Hydrometallurgy

Hydrometallurgy

Hydrometallurgy

Hydrometallurgy

Hydromettalurgy

Hydrometallurgy

Hydrometallurgy

Reductive leaching of manganese from low grade Sinai ore in HCl using H₂O₂ as reductant