Study in reduction-roast leaching manganese from low-grade manganese dioxide ores using cornstalk as reductant

Abstract

In this study cornstalk was used as reductant for reduction roasting of low-grade manganese dioxide ores, and sulfuric acid was used as leaching solvent for the roasted ore. The effects of weight ratio of ore to cornstalk, roasting temperature, roasting time, ore particle size, leaching temperature, stirring speed and sulfuric acid concentration on the leaching recovery were discussed. The leaching recovery of manganese reached 90.2% under the optimal condition which was determined as manganese dioxide ore to cornstalk weight ratio of 10:3, roasting temperature of 500 °C for 80 min, leaching stirring speed of 400 r/min, sulfuric acid concentration of 3 mol/L, leaching temperature of 50 °C for 40 min.

Introduction

Manganese plays an important role in many fields, such as steel production, preparation of dietary additives, fertilizers, cells and fine chemicals (Sahoo et al., 2001, Hazek et al., 2006). Hence, many efforts have applied to develop a economical and efficient process to recover manganese from low-grade manganese dioxide ores. Because manganese dioxide is stable in acid or alkaline oxidizing conditions, the leaching of manganese must be carried out under reducing condition (Abbruzzese et al., 1990, Das et al., 1982). Coal is used as reductant in traditional technology in order to convert manganese dioxide to manganese oxide which can be leached by sulfuric acid (Sahoo and Rao, 1989). But this kind of method produces a great deal of smoke-dust, oxysulfide, nitrogen oxides, and so on, which pollute environment greatly. In addition, this method requires over 800 °C as reaction temperature, which is so high that most of reactors can not bear (Abbruzzese, 1990, Jiang et al., 2004, Ismail et al., 2004). There are also some new reduction methods reported, such as sucrose reduction leaching (Beolchini et al., 2001), H₂O₂ reduction leaching in HCl (Hazek et al., 2006), molasses reduction leaching (Su et al., 2008), glucose reduction leaching in acidic medium (Trifoni et al., 2001, Vegliò et al., 2001, Pagnanelli et al., 2004, Furlani et al., 2006). Recently, our research group found that low-grade manganese dioxide ores can be reduced fully by biomass cornstalk roasting at temperature of only 500 °C. Using sulfuric acid as the leaching agent, the manganese can be leached from the roasted product. Though the crude cornstalk is lighter than coal, it can be pulverized and compressed to the same volume with coal while their weights are identical. Hence, it is feasible to substitute cornstalk for coal with the roasters and storage facilities used in conventional industrialization production.

As we know, biomass cornstalk resource is abundant renewable resource. In 2007, the global total output of cornstalk was about 1.8 billion ton, which equalled to 900 million ton standard coal. It is expected that the global total output of cornstalk reaches 2.6 billion ton in 2010 which equals to 1.3 billion ton standard coal (Zhang and Zhou, 2007). Making use of cornstalk to reduce manganese dioxide ores can not only widen the channels of energy to lower the cost, but also comply with the requirement of green economy.

In this paper, using the low-grade manganese dioxide ore from Guangxi (China) and cornstalk from Beijing (China) as raw material, the effects of roasting and leaching condition on the leaching recovery were investigated. Manganese recovery of 90.2% was obtained under the experimental condition: manganese dioxide ore to cornstalk weight ratio of 10:3, ore size of 150 μm, roasting temperature of 500 °C, roasting time of 80 min, leaching stirring speed of 400 rpm, sulfuric acid concentration of 3 mol/L, leaching time of 40 min at 50 °C. For proving this technology can be applied widely due to the nature of cornstalk, not due to the particularity of Guangxi manganese ore, experimental conditions applicability of cornstalk as reductant to other types of low-grade manganese dioxide ores were also tried.