Reduction Of MnO2 Research Articles

The mechanism of foaming and thermal conductivity of glasses foamed with MnO2

We prepare foam glass from cathode ray tube (CRT) panels using MnO2 as foaming agent at different temperatures for various durations. The reduction of MnO2 to Mn2O3 leads to formation of O2 gas, and hence, causes initial foaming. The Mn2O3 particles dissolve into the glass melt and subsequently reduce, causing further formation of O2 gas and foaming of the glass melt. Increasing the treatment temperature and time enhances foam expansion, Mn2O3 dissolution, and lowers the closed porosity. Once the foam reaches a percolated stage, the foam continues to grow. This is caused by nucleation of new bubbles and subsequent growth. We discuss evolution of pore morphology in terms of pore number density, pore size and closed porosity. The thermal conductivity of the foam glasses is linearly dependent on density. The heat transfer mechanism is revealed by comparing the experimental data with structural data and analytical models. We show that the effect of pore size, presence of crystal inclusions and degree of closed porosity do not affect the overall thermal conductivity.

Effect of CaF2 Addition on the Silicothermic Reduction of MnO in Ferromanganese Slag

The effect of temperature and CaF2 (fluorspar) addition on the silicothermic reduction behavior of MnO in the CaO-40 pct MnO-SiO2 (C/S = 1.0) system, which is used to simulate high carbon ferromanganese (HCFeMn) slag, was investigated at 1773 K (1500 °C). The production of SiO2 was stoichiometrically balanced with the consumption of MnO in the slag phase in the CaF2-containing systems based on the reaction “[Si] + 2(MnO) = (SiO2) + 2[Mn],” whereas the SiO2 production was lower than the MnO consumption in the CaO-MnO-SiO2 ternary system, which may have originated from the production of SiO gas in the latter. From the temperature dependence of the mass transfer coefficient of SiO2, the activation energy of the silicothermic reduction process was determined to be about 217.9 kJ/mol, which was very close to the activation energy reported in the literature for mass transfer in the slag phase. The mass transfer coefficient of SiO2 exhibited a maximum value at 5 mass pct CaF2, which originated from an increase in the apparent viscosity of the slag due to the precipitation of solid cuspidine at CaF2 content greater than 5 pct. Consequently, the addition of fluxing additive CaF2 should be carefully determined, because an excess of CaF2 results in the formation of cuspidine during silicothermic reactions.

Reduction Kinetics of Polymeric (Soluble) Manganese (IV) Oxide (MnO2) by Ferrous Iron (Fe2+)

In numerous freshwater and marine environments, ferrous iron (Fe2+) can react with manganese oxides in a redox reaction. However, there are few quantitative data describing reaction rates. A “soluble” (colloidal and nanoparticulate) phase manganese dioxide (MnO2) was used to obtain kinetic data on MnO2 reduction by Fe2+ with a stopped flow UV–Vis method. Stopped flow experiments were carried out in unbuffered solutions between pH 4.9 and 5.36 and also at pH 7. The reaction was determined to be first order with respect to MnO2 and Fe2+ and second order overall. It is important to subtract absorbance of Fe(III) products from the UV–Vis data and to acquire data from the first milliseconds of the reaction. After subtracting Fe(III) product absorbance, the average second-order rate constant was determined to be 4338 ± 249 M−1 s−1 at 25 °C and pH 5. Reactions of 5 μM MnO2 with 50 and 100 μM Fe2+ were more than 50 % complete in 1.77 and 0.7 s, respectively. The reaction is an inner sphere electron transfer process as an outer sphere process is symmetry-forbidden. Studies show that Mn(III) intermediates are produced during the reaction. The fast kinetics makes this reaction significant to consider when modeling manganese oxide and reduced iron in environmental redox systems.

용융아연 도금욕에서 망간 산화물의 표면석출 거동

Advanced high strength steels undergo recrystallization annealing in reducing gas atmosphere before galvanizing to improve mechanical properties. The selective oxidations of elements such as Mn, Si, Cr and Al during annealing decrease wettability of liquid zinc, resulting in bare spots and other defects. In this work, Fe-3wt%Mn steel sheet was annealed at 780 o C for 1200 sec. in 5% H2-N2 atmosphere and then dipped into zinc bath held at 460 o C, which contained 0.2wt% dissolved Al. MnO crystallines in the average size of 200 nm were formed on the surface after annealing. It is estimated that MnO has been detached into bath with the formation and growth of inhibition layer with longer immersion time during galvanizing. No evidence of aluminothermic reduction of MnO has been found in this study.

Microscopic Study of Carbon Surfaces Interacting with High Carbon Ferromanganese Slag

The interaction of carbon materials with molten slags occurs in many pyro-metallurgical processes. In the production of high carbon ferromanganese in submerged arc furnace, the carbothermic reduction of MnO-containing silicate slags yields the metal product. In order to study the interaction of carbon with MnO-containing slags, sessile drop wettability technique is employed in this study to reduce MnO from a molten slag drop by carbon substrates. The interfacial area on the carbon substrate before and after reaction with slag is studied by scanning electron microscope. It is indicated that no Mn metal particles are found at the interface through the reduction of the MnO slag. Moreover, the reduction of MnO occurs through the contribution of Boudouard reaction and it causes carbon consumption in particular active sites at the interface, which generate carbon degradation and open pore growth at the interface. It is shown that the slag is fragmented to many micro-droplets at the reaction interface, potentially due to the effect on the interfacial energies of a provisional liquid Mn thin film. The rapid reduction of these slag micro-droplets affects the carbon surface with making deep micro-pores. A mechanism for the formation of slag micro-droplets is proposed, which is based on the formation of provisional micro thin films of liquid Mn at the interface.

Rationally designed hierarchical MnO2-shell/ZnO-nanowire/carbon-fabric for high-performance supercapacitor electrodes

High-performance supercapacitor electrodes with a novel hierarchical structure of MnO2/ZnO/carbon-fabric were rationally designed, and prepared by a simple three-step-solution method. The design comprises ZnO nanowires radially grown on each micron-size fiber of a carbon-fabric electrode, with a thin MnO2 shell on each ZnO nano-core. This multi-scale hierarchical structure yields: (a) high specific area of pseudo-capacitive MnO2 to maximize specific capacitance; (b) effective MnO2-electrolyte interface to facilitate fast charging/discharging; and (c) conductive MnO2–ZnO-electrode path to reduce energy loss. In addition, the overall capacitor performance is optimized by choosing proper thickness of MnO2 shell and aspect ratio of ZnO nano-core. The design was realized and validated with the development of a simple three-step-solution method: (a) radial deposition of nano-ZnO on carbon fabric; (b) coating ZnO by a thin layer of carbon; and (c) reduction of MnO4− and replacement of this carbon overlayer by MnO2. With this design and method, high specific capacitance of 886 F g−1 was found from electrodes with 5 nm MnO2 on ZnO having an average diameter of 50 nm and aspect ratio of 30. These samples showed specific energy of 16 Wh kg−1 and specific power of 27 kW kg−1 at current density of 20 mA cm−2, and good long-term cycling stability.

The distribution of dissolved manganese in the tropical–subtropical North Atlantic during US GEOTRACES 2010 and 2011 cruises

Dissolved manganese (Mn) concentration was determined in seawater samples collected along a section across the North Atlantic between 17°N and 40°N during US GEOTRACES North Atlantic 2010 and 2011 cruises (GT GA03). Dissolved Mn exhibits elevated concentrations in the surface, at the mid-ocean ridge and near oceanic boundaries, and low concentrations in the deep water of the gyre center. At both western and eastern boundaries, dissolved Mn concentration in the surface mixed layer (30–40m) and at depths below 200m decreases with increasing distance from shore, in contrast to the seaward increase of dissolved Mn concentration at depth between 80 and 120m. Simple model calculation suggests that in the North Atlantic gyre center, dissolved Mn concentration is controlled primarily by eolian Mn(II) deposition and in-situ photochemical reduction of MnO2 in the surface mixed layer (0–40m), and by the intensity of sunlight available for in-situ MnO2 photochemical reduction in the euphotic zone below the mixed layer (40–200m). At depth between 200 and 700m, dissolved Mn concentration is determined by regeneration, preformed Mn in the source water and lateral inputs from hydrothermal and sedimentary sources. Below 700m, dissolved Mn concentration is controlled predominantly by lateral inputs from hydrothermal and sedimentary sources. Accounting for the observed dissolved Mn concentration by lateral mixing at this depth range requires low rates of Mn(II) oxidation.

Nanostructured Two-Component Composite Approach for Better High-Rate Capability of Cathode Materials

Many efforts have been made to turn insulating compounds into attractive electrode materials, including nanosizing, carbon nanopainting and metal doping. A new approach to enhance high-rate capability of materials with poor electric conductivity is based on the development of two-component composites comprising of low-conductive and high-conductive electrode materials. Monoclinic Li3V2(PO4)3 is a promising cathode for high-power lithium-ion batteries because of its open three-dimensional framework allowing fast transport of lithium ions. Its theoretical capacity is 132 and 197 mAh×g-1 upon cycling to 4.3 and 4.8 V, respectively. Recently, the enhanced electrochemical performance of nanostructured LiVPO4F/Li3V2(PO4)3 composites has been reported [1]. The aim of the present work was to prepare (1-x)LiMPO4/xLi3V2(PO4)3 (M=Mn,Fe) nanocomposites with 0.05£x£0.50 by mechanochemically assisted solid state synthesis and to investigate their structural features and electrochemical performance. The composites were synthesized by the joint carbothermal reduction of MnO2 (Fe2O3) and V2O5 in the mixtures with Li2CO3 and (NH4)2HPO4 using AGO-2 planetary mill. Crystal structure was studied by X-ray and neutron powder diffraction (NPD) using Rietveld refinement. NPD spectra were obtained at IBR-2 reactor of JINR (Dubna). Particle size and morphology were studied by SEM and TEM. The local structure of the LiFePO4/Li3V2(PO4)3 composites was investigated by Mössbauer spectroscopy. The samples were cycled in Swagelok-type half-cells with Li anode, Whatman GF/C separator and LiPF6-based electrolyte in the 2.0-4.8 V (Mn) and 2.5-4.3(4.8) V (Fe) range at 0.1-10C cycling rates. Additionally, GITT method was applied for the evaluation of Li ionic diffusion coefficient in the composites upon cycling. Two phases were present on XRD and NPD patterns of all samples: orthorhombic LiMPO4 (space group Pnmb) and monoclinic Li3V2(PO4)3 (space group P21/n). The refined cell parameters of LiMPO4 and Li3V2(PO4)3 in the composites slightly deviate from those of pure components (Fig. 1). Mössbauer spectroscopy of the 0.75LiFePO4/0.25Li3V2(PO4)3 composite reveals the presence of tiny amounts of Fe3+ ions. According to SEM and TEM, the average particle size of the composite decreases as compared with pure components, indicating that Li3V2(PO4)3 and LiMPO4 phases hinder the crystal growth of each other. In the 2.5-4.8 V range, Li3V2(PO4)3 exhibits four redox plateaus corresponding to a sequence of phase transitions: Li3V2(PO4)3→Li2.5V2(PO4)3→Li2V2(PO4)3→ Li1V2(PO4)3→V2(PO4)3. On the dQ/dU=f(U) plots of the LiMPO4/Li3V2(PO4)3 composites, some additional peaks are also observed corresponding to two redox pairs: Mn3+/Mn4+ (at 4.4 V) and Fe3+/Fe2+ (at 3.45 V). Charge-discharge profiles of the composites and the variation of specific discharge capacity of the composites vs. cycling rate are shown in Fig. 2. When the voltage cut-off increases to 4.8 V for 0.75LiFePO4/0.25Li3V2(PO4)3, its capacity increases and discharge profile gets a sloping form. The enhancement of high-rate electrochemical performance of LiMPO4 in the composites is considered to be a result of reduction in particle size and the nucleation energy for the formation of the MPO4 phases. GITT measurements confirm the increase of D Li and the improvement of Li diffusion in the composites. Thus, the nanostructured two-component composite approach (combination of low- and high-conductive electrode materials) supported by mechanochemically assisted solid state synthesis is shown to be applicable and very promising. The increase in the number of voltage plateaus and the mean intercalation voltage should be advantageous for improvement of cell performance.[1] N.V. Kosova, E.T. Devyatkina, A.B. Slobodyuk, A.K. Gutakovskii // doi 10.1007/s10008-013-2213-1

No catalyst addition and highly efficient dissociation of H2O for the reduction of CO2 to formic acid with Mn.

The "greenhouse effect" caused by the increasing atmospheric CO2 level is becoming extremely serious, and thus, the reduction of CO2 emissions has become an extensive, urgent, and long-term task. The dissociation of water for CO2 reduction with solar energy is regarded as one of the most promising methods for the sustainable development of the environment and energy. However, a high solar-to-fuel efficiency keeps a great challenge. In this work, the first observation of a highly effective, highly selective, and robust system of dissociating water for the reduction of carbon dioxide (CO2) into formic acid with metallic manganese (Mn) is reported. A considerably high formic acid yield of more than 75% on a carbon basis from NaHCO3 was achieved with 98% selectivity in the presence of simple commercially available Mn powder without the addition of any catalyst, and the proposed process is exothermic. Thus, this study may provide a promising method for the highly efficient dissociation of water for CO2 reduction by combining solar-driven thermochemistry with the reduction of MnO into Mn.

ChemInform Abstract: A Rapid Microwave‐Assisted Solvothermal Approach to Lower‐Valent Transition Metal Oxides.

AbstractBinary oxides such as V4O9, Mn3O4 or MnO, CoO, and Cu2O are prepared within a short reaction time of 30 min by reduction of V2O5, MnO2, Co3O4, or CuO with tetraethylene glycol under microwave irradiation at <300 °C.

Influence of the TiO2 crystalline phase of MnOx/TiO2 catalysts for NO oxidation

Mn-based catalysts impregnated on TiO 2 with different crystalline phases (rutile (R), anatase (A), and P25 (P)) were studied for the oxidation of NO to NO 2 . 10%MnO x /TiO 2 (P) was the most active catalyst, giving 83% of NO conversion at 300 °C and a GHSV of 20000 h −1 . The catalyst activities were in the order MnO x /TiO 2 (P) > MnO x /TiO 2 (A) > MnO x /TiO 2 (R). The catalysts were characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, H 2 temperature-programmed reduction, and O 2 temperature-programmed desorption. Compared to anatase and rutile, P25 gave better dispersion of MnO x on the support surface, suppressed the agglomeration of catalyst particles, and also produced more Mn 2 O 3 , which was more active for the oxidation of NO. In addition, P25 enhanced the reduction of MnO x , especially for Mn 2 O 3 , and the formation of easily desorbed O 2 − generated from the Mn 3+ –O bond. Mn-based catalyst supported on P25 TiO 2 was more active for NO oxidation than those supported on anatase and rutile TiO 2 , achieving 83% of NO conversion at 300 °C and 20000 h −1 of GHSV.

Interfacial Reactions between Coke/HDPE Blends and High Carbon Ferromanganese Slag

The reduction of MnO in slag by blends of coke with high density polyethylene (HDPE) was investigated by the sessile drop method at 1500°C in this study. The results show improved wettability and extents of reduction are realised with the use of an HDPE/coke blend in this system by comparison to reduction by pure coke, whereby increasing HDPE content resulted in further improvement in extent of reduction and increased wettability. The extensive devolatilisation from HDPE samples is the primary cause for these improvements, whereby the gasified HDPE created both CH4 and H2 reducing gases. Additionally, increased sample porosity allowed for improved wetting, and thus improved reduction capabilities. The dynamic contact angle between the carbon substrate and the slag varied, with HDPE samples ranging between 140°–60°, whilst the coke samples ranged between 160°–120°. The addition of HDPE allowed for the near complete reduction of MnO and partial reduction of SiO2 from the slag with distinct metallic regions of Mn–Si formed in the sample; regions containing pure Si were also found.

Overcoming Permanganate Stalling during Electromigration

AbstractElectrokinetic experiments were undertaken to transport permanganate (MnO4−) through a low permeability porous media. The experiments employed a one-dimensional apparatus in which MnO4− was electromigrated through a central porous media core. Two outer porous media cores separated the electrode reservoirs from the inner permanganate source and permanganate target reservoirs. By utilizing a pH-isolation technique, whereby electrolysis reactions occurring at electrodes were isolated, uniform and repeatable MnO4− electromigration was achieved. This result was compared with non-pH-isolated experiments (normal mode), which resulted in a stalled MnO4− electromigration front. The research also investigated potential stalling mechanisms, including voltage gradient nonlinearity through the central porous media core and the reduction of MnO4− to Mn2+. It was observed that the voltage gradient decreased as a result of MnO4− stalling; however, it was not considered a stalling mechanism. Results from Mn2+ anal...

An EQCM investigation of capacitance of MnO2 in electrolytes containing multivalent cations

MnO2 is electrochemically deposited on Au coated quartz crystal to study the electrochemical capacitance properties and to monitor the mass variations that accompany reversible adsorption/desorption of Na+, Mg2+ and La3+ ions during discharge/charge cycling. There is an increase in the values of specific capacitance of MnO2 with increase in charge of the cation in the electrolyte. Also, there is an increase in mass during discharge due to adsorption of cations from the electrolyte resulting from reduction of MnO2. Mass decreases during charging process due to desorption of cations. The magnitude of mass variation is approximately proportional to the atomic weight of the cationic element.

Preparation and Characterization of MnxOy-Al2O3 Sorbents for H2S Removal from Biomass Gasification Gas

A series of MnxOy - Al2O3 materials have been prepared either by spray-drying (SD) of Al/Mn precursor solutions or by multiple wet-impregnations of two different Mn precursors on various alumina supports. The two Mn precursors used in the preparation were manganese nitrate (Mn(NO3)2.4H2O) and manganese acetate (Mn(CH3COO)2.4H2O). To study properties relevant for the sorption performance, the calcined materials were characterized using several methods. Textural properties (N2 sorption) of the Mn loaded samples show significant differences when compared to the parent supports. For the samples prepared by multiple wet-impregnations this is due to the relatively high Mn loading (up to 30wt. %) and the additional heat treatment. For the sample prepared by SD it is the presence of Mn species that modifies the textural properties and affects the way the final material is formed. X-ray diffraction measurements show that the ratio of Mn2O3/Mn3O4 depends on the Mn precursor used when the samples are prepared by the multiple wet-impregnation method. For the samples prepared by the SD method the use of a specific Mn precursor has no influence on the ratio of Mn2O3/Mn3O4 in the final material. UV-Raman spectra strongly indicate the presence of MnO2 on the surface of all MnxOy - Al2O3 sorbents. MnO2 was not detected by XRD. The presence of new MnxOy species was also detected by Raman spectroscopy and their existence is ascribed to a specific interaction between MnxOy and Al2O3. TPR data show there are three main reduction steps most likely due to the reduction of MnO2 to MnO through intermediate Mn2O3 and Mn3O4. The data, however, indicates that a new species is formed at high temperature (above approx. 550°C). It is proposed that the additional features observed in the TPR profiles might be due to the formation of the spinel structure MnAl2O4.

Structure-property relationships in manganese oxide - mesoporous silica nanoparticles used for T 1-weighted MRI and simultaneous anti-cancer drug delivery

The extremely low longitudinal relaxivity ( r 1) of manganese oxide has severely impeded their substitution for cytotoxic gadolinium-based contrast agents for safe clinical magnetic resonance imaging (MRI). Here, we report on a synthetic strategy of chemical oxidation/reduction reaction in-situ in mesopores, followed by hydrogen reduction, for the fabrication of non-toxic manganese oxide/MSNs-based MRI-T 1 contrast agents with highly comparable imaging performance to commercial Gd-based agents. This strategy involves a “soft-templating” process to prepare mesoporous silica nanoparticles, in-situ reduction of MnO 4 − by the “soft templates” in mesopores and heat treatment under reducing atmosphere, to disperse manganese oxide nanoparticles within mesopores. This special nanostructure combines the merits of nanopores for maximum manganese paramagnetic center accessibility for water molecules for enhanced MRI performance and encapsulation/sustained release/intracellular delivery of drugs. The synthesized manganese oxide/MSNs were successfully assessed as a high performance contrast agent for MRI-T 1 both in intro and in vivo, and meanwhile, was also demonstrated as an effective anti-cancer drug delivery (doxorubicin) vehicle, therefore, a family of manganese-based theranostics was successfully demonstrated based on the manganese oxide/MSNs composite.

Manganese sulfide formation via concomitant microbial manganese oxide and thiosulfate reduction

The dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1 produced γ-MnS (rambergite) nanoparticles during the concurrent reduction of MnO₂ and thiosulfate coupled to H₂ oxidation. To investigate effect of direct microbial reduction of MnO₂ on MnS formation, two MR-1 mutants defective in outer membrane c-type cytochromes (ΔmtrC/ΔomcA and ΔmtrC/ΔomcA/ΔmtrF) were also used and it was determined that direct reduction of MnO₂ was dominant relative to chemical reduction by biogenic sulfide generated from thiosulfate reduction. Although bicarbonate was excluded from the medium, incubations of strain MR-1 with lactate as the electron donor produced MnCO₃ (rhodochrosite) as well as MnS in nearly equivalent amounts as estimated by micro X-ray diffraction (micro-XRD) analysis. It was concluded that carbonate released from lactate metabolism promoted MnCO₃ formation and that Mn(II) mineralogy was strongly affected by carbonate ions even in the presence of abundant sulfide and weakly alkaline conditions expected to favour the precipitation of MnS. Formation of MnS, as determined by a combination of micro-XRD, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction analyses was consistent with equilibrium speciation modelling predictions. Biogenic manganese sulfide may be a manganese sink in the Mn biogeochemical cycle in select environments such as deep anoxic marine basins within the Baltic Sea.

Influence of MnO 2 on the sintering behavior and magnetic properties of NiFe 2O 4 ferrite ceramics

The samples with small amounts of MnO 2 (0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe 2O 3, NiO and MnO 2). Microstructural features, phase transformation, sintering behavior and magnetic properties of Mn-doped NiFe 2O 4 composite ceramics have been investigated by means of scanning electron microscopy (SEM), differential thermal analyzer, X-ray diffraction (XRD), thermal dilatometer and vibrating sample magnetometer (VSM) respectively. The XRD analysis and the result of differential thermal analysis indicate that the reduction of MnO 2 into Mn 2O 3 and the following reduction of Mn 2O 3 into MnO existed in sintering process. No new phases are detected in the ceramic matrix, the crystalline structure of the ceramic matrix is still NiFe 2O 4 spinel structure. Morphology and the detecting result of thermal dilatometer show that MnO 2 can promote the sintering process, the temperature for 1 wt% MnO 2-doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples. For 1 wt% MnO 2-doped samples, the value of the saturation magnetization ( M s) and coercivity ( H c) is 15.673 emu/g and 48.316 Oe respectively.

Kinetics of Microwave-Assisted Reduction of Manganese Oxide

The reduction rates of manganese oxide by carbon and SiC was examined by heating MnO2-carbon and MnO2-SiC mixtures in a 7-kW industrial microwave oven. The results show that the rate of the reduction increased with the amount of carbon in MnO2-carbon mixture and with SiC in MnO2-SiC mixture. The rate of the MnO2 reduction by carbon was proportional to the reaction time, and that by SiC was proportional to 2/3 power of the reaction time. The reduction was found to be controlled by chemical reaction. The reaction rate constant of the reduction of MnO2kC increased with increasing the amount of carbon in the mixtures but kSiC decreased with increasing the amount of SiC in the mixtures.

Pre-reduction of manganese ores for ferromanganese industry

Pre-reduction of manganese ores by solid carbon was investigated to try to increase the efficiency and cost effectiveness of the ferromanganese industry. The pre-reduction reactions of manganese ore containing 57·2%MnO2 has been conducted by solid carbon in a rotary kiln furnace at 800–1100°C. The reaction was stopped intentionally at the formation of MnO in order to investigate the pre-reduction behaviour of manganese ore and the factors affecting the process. The ore and reduced samples were characterised by X-ray diffraction, X-ray fluorescence, scanning electron microscopy and energy dispersive spectroscopy analysis. The isothermal pre-reduction behaviour was followed using a thermogravimeteric technique and a quadrupole mass spectrometer in order to determine the reduction kinetics and mechanisms of the process. Relatively, the rate of reduction of manganese ore increased with increasing reaction temperature. The highest reduction of MnO2 to MnO was achieved at 1000°C which was confirmed by bench scale rotary experiments where 45·3%MnO and 1·72%MnO2 were detected. Application of the optimum reduction condition on a semipilot scale resulted in 44·6%MnO and 2·55%MnO2. The pre-reduction reactions proceeded in stepwise manner. The calculated values of activation energy (129 kJ mol−1) revealed that a solid state diffusion mechanism plays a significant role in the carbothermic pre-reduction process of manganese ore.