Reductive acid leaching of manganese dioxide with glucose: Identification of oxidation derivatives of glucose

The oxidation of glucose during the reductive leaching of pure MnO2 and manganese ore in sulphuric, acid at 90 degrees C MnO2 was investigated. The aim was to identify the derivatives and the chemical pathway of glucose oxidation. Organic derivatives were monitored by HPLC using an Aminex HPX-78H column and UV detection. Chromatographic patterns of leaching solutions showed that major compound formed was formic acid. Minor quantities of glycolic, glycerie and traces of gluconic acids were identified. Results suggest that during the leaching reaction, the carbon chain of glucose is shortened by detachment of one carbon atom as formic acid. (c) 2006 Elsevier B.V. All rights reserved

Preparation and characterisation of chemical manganese dioxide: Effect of the operating conditions

In this study MnO2 preparation by chemical methods is investigated for possible applications in dry cell batteries of chemical manganese dioxide (CMD) instead of electrolytic manganese dioxide (EMD). Three preparation procedures were tested: precipitation-oxidation by air plus acid activation (two-step-air), precipitation-oxidation by H2O2 plus acid activation (two-step-H2O2), precipitation-oxidation by KClO3 (singlestep-ClO3). Replicated factorial designs and related statistical analysis of experimental data by analysis of variance were performed in order both to obtain a preliminary optimization of the operating conditions and to take into account the intrinsic sample heterogeneity associated to each specific procedure. Comparisons among three different preparations denoted that in the investigated conditions two-step preparations give larger yields of activated solid in comparison with single-step preparation. Preliminary optimized conditions denoted final solid yields (80-86%) for both two-step procedures. The effect of operating conditions on the chemical, structural and electrochemical properties of CMDs produced in preliminary optimised conditions was investigated and compared with those of a commercial EMD sample by acid and acid-reducing leaching for Mn speciation in solid phase, potentiometric titrations, X-ray and IR spectra and cyclic voltammetry. These characterisation tests denoted the significant effect of acid activation in both preparation procedures to obtain CMD samples with high % of Mn(IV)oxides. Potentiometric titrations of solid samples obtained by first and second steps denoted that both procedures gives two CMD samples with the same acid-base properties, which in comparison with commercial EMD present a residual dissociation in the basic pH range (similar structure and proton insertion properties for CMDs and EMD, but different structural defects). X-ray and IR spectra of solid samples by first and second steps denoted highly disordered systems and the presence of Mn2O3 in first step products and of gamma-MnO2 in second step product. Voltammetric cycles denoted that CMD samples obtained after acid digestion present similar peaks than commercial EMD but with higher current intensity. (c) 2007 Elsevier B.V. All rights reserved

Leaching of low-grade manganese ores by using nitric acid and glucose: Optimization of the operating conditions

Manganese extraction from low-grade ores was investigated by using glucose as a reducing agent in dilute nitric acid medium. Ore characterisation by X-ray and SEM denoted that manganese is present as a mixed oxide Mn7O 13 (6MnO2·MnO) surrounding and joining together aluminosilicate fragments. The effects of temperature, particle size, glucose and nitric acid concentrations were investigated and compared with previous results using H2SO4. The operating conditions of leaching were optimised to obtain maximum manganese extraction and purity by performing sequential factorial designs and evaluating the statistical significance of the different factors by analysis of variance (ANOVA). The optimised conditions are 90°C, stoichiometric nitric acid, -20% below stoichiometric glucose and 295-417 μm size fraction. The stoichiometric reagent concentrations were evaluated according to the following reaction assuming all manganese in the ore as Mn(IV): C6H12O6+12MnO2+24H +=6CO2+12Mn2++18H2O Optimised leaching conditions with HNO3 give up to 99% manganese extraction, <0.05% iron dissolution and reduced reagent consumption compared to previous tests using H2SO4. © 2004 Elsevier B.V. All rights reserved

Automobile shredded residue valorisation by hydrometallurgical metal recovery

The aim of this work was developing a hydrometallurgical process to recover metals from automobile shredded residue (or car fluff). Automobile shredded residue (ASR) was characterised by particle size distribution, total metal content and metal speciation in order to guide the choice of target metals and the operating conditions of leaching. Characterisation results showed that Fe is the most abundant metal in the waste, while Zn was the second abundant metal in the fraction with diameter lower than 500 mu m. Sequential extractions denoted that Zn was easily extractable by weak acid attack, while Fe and Al required a strong acid attack to be removed. In order to recover zinc from <500 mu m fraction leaching tests were operated using acetic acid, sulphuric acid and sodium hydroxide at different concentrations. Sulphuric acid determined the highest zinc extraction yield, while acetic acid determined the highest zinc extractive selectivity. Sodium hydroxide promoted an intermediate situation between sulphuric and acetic acid. Zn recovery by electro winning using acetic leach liquor determined 95% of Zn electro deposition yield in 1 h, while using sulphuric leach liquor 40% yield in 1 h and 50% yield in 2 h were obtained. Simulation results showed that the sulphuric leaching process was more attractive than acetic leaching process. (C) 2010 Elsevier B.V. All rights reserved

Recovery of manganese from zinc alkaline batteries by reductive acid leaching using carbohydrates as reductant

Acid leaching of manganese from the powders of exhausted zinc alkaline batteries has been studied using carbohydrates as reducing agents. A mono-saccharide (glucose) and a di-saccharide (lactose) have been tested, the second as a template of industrial wastes. Manganese leaching was complete in the presence of both carbohydrates, along with zinc. Data from the factorial test with lactose have been analysed with ANOVA. The most significant effects for manganese extraction were sulphuric acid concentration, temperature, and lactose concentration. (C) 2009 Elsevier B.V. All rights reserved