Reduction Of Manganese Oxides Research Articles

Preparation of ZrMn2 hydrogen storage alloy by electro-deoxidation in molten calcium chloride

ZrMn2 alloy was electro-synthesized directly from cathode pellets compacted with powdered mixture of MnO2 and ZrO2 in molten calcium chloride. Sintering temperature, cell voltage and electrolysis time were the dominant factors that affected the characteristics of the final product. The results confirmed the formation of pure ZrMn2 alloy through the electro-deoxidation of the mixed oxide pellets at 3.1 V for 12 h in 900 °C CaCl2 melt. The X-ray diffraction (XRD) and cyclic voltammetry analysis suggested that the electro-deoxidation proceeded from the reduction of manganese oxides to Mn, followed by ZrO2 or CaZrO3 reduction on the pre-formed Mn to ZrMn2 alloy. The cyclic voltammetry measurements using powder microelectrode showed that the prepared ZrMn2 alloy has a good electrochemical hydrogen storage property.

Predicted effect of ore composition on slag formation in manganese ore reduction

Previous work showed that manganese ore reduction rates are strongly influenced by the extent of slag phase formation. In this work, the effect of ore composition on slag formation during manganese oxide reduction was predicted using thermochemical calculations; FactSage 6·4 was used to calculate the equilibrium phase relations in the oxide system MnO–SiO2–CaO–MgO–Al2O3. Practically observed differences in ore composition, even within the same orebody, are predicted to cause significant differences in slag formation during reduction, with large differences in ore reducibility expected.

Numerical Modeling of Solar Thermochemical Reactor for Kinetic Analysis

A lab-scale thermochemical reactor is designed and fabricated for the solar-driven thermal reduction of non-volatile manganese oxide to produce hydrogen by water splitting thermo chemical cycles. A time dependent three dimensional numerical model is developed to investigate the performance of the reactor since the chemical kinetics strongly depends on irradiance, temperature and fluid flow distribution around the reactant. Radiation heat transfer is calculated by using surface-to-surface (S2S) radiation model. Thermo-fluid flow, absorption efficiency and the temperature distribution of the sample are predicted as a function of time and the model is validated by experimental measurements.

Removal of hydrogen sulfide using carbonated steel slag

High levels of hydrogen sulfide are sometimes observed in the pore water of eutrophic sediments. It is important to reduce the hydrogen sulfide concentration to maintain health ecosystems as well as aquaculture activities in enclosed water bodies. The purpose of this study is to reveal the removal mechanism of hydrogen sulfide using carbonated steel slag produced through carbonation processes to alleviate alkaline impacts. Batch adsorption experiments revealed that hydrogen sulfide was adsorbed onto carbonated steel slag based on a pseudo-first-order kinetic model; its adsorption maximum was 7.5mgg−1. The removal mechanisms of the hydrogen sulfide included (1) the formation of pyrite, and (2) oxidation to sulfur coupled with the reduction of manganese oxide on the carbonated steel slag.

Mind the gap: long range charge transfer across the periplasm of Shewanella oneidensis

Shewanella oneidensis a gram negative proteobacteria, is capable of the dissimilatory metal reduction (DMR) of insoluble iron and manganese oxides, through the deployment of multiple strategies, including using multiple multi‐heme c‐type cytochromes that electrochemically wire the cellular interior to the exterior. In order to harness the remarkably biological chemistry of Shewanella in bioenergy and microbial fuel cells, we examined the molecular details of long‐range electron transfer within and between Shewanella multi‐heme cytochromes that are implicated in the DMR pathway. To probe the model of Mtr cytochrome interactions, we have developed new analytical methods to quantify the directionality and stoichiometry of redox reactions in the Shewanella Mtr cytochromes. We have modified traditional PFE methods to probe the protein:protein interactions that may be at work in the Shewanella DMR pathway, revealing an unforeseen unidirectionality for electron transfer. These data, coupled to structural studies of MtrA using small angle x‐ray scattering (SAXS) and analytical ultracentrifugation (AUC), elucidate a model of long‐range electron transfer that occurs from the quinol pool of Shewanella to the cell surface, as mediated by a series of multi‐heme cytochromes c. For each multi‐heme cytochrome, the high number of redox cofactors and their similar reduction potentials, convolutes the routine assignment of specific macroscopic reduction potentials to individual hemes. Here, novel Mtr cytochrome mutants where predicted heme ligands have been mutated from His to Met/Ala mutagenically “map” the nature of each heme center. The electrochemical, spectroscopic and physiological impact of such mutations will be presented.

Effect of Silicon on the Desulfurization of Al-Killed Steels: Part I. Mathematical Model

Recent observations suggest that increased silicon levels improve ladle desulfurization of aluminum-killed steel. While the overall desulfurization reaction of Al-killed steels does not show a direct role of silicon in desulfurization, model calculations are presented which test the idea that silicon suppresses the reduction of silica which can consume aluminum at the slag/metal interface. Consumption of aluminum would increase the oxygen potential at the slag/metal interface and decrease the sulfur partition coefficient between slag and metal. The model considers the coupled reactions of the reduction of silica, iron oxide, and manganese oxide in the slag and desulfurization of the steel by aluminum. The results show that silicon can indeed suppress consumption of aluminum at the slag/metal interface by side reactions other than desulfurization, with silicon affecting both the kinetics and the equilibrium of desulfurization.

Migration of arsenic in multi-aquifer system of southern Bengal Basin: analysis via numerical modeling

A heterogeneous anisotropic steady-state groundwater flow model for the multi-aquifer system of a part of southern Bengal Basin shows that human intervention has changed the natural groundwater flow system. At present, the shallow groundwater flow is restricted within the aquifer, with very short travel time of tens of years and vertical path length. The deep aquifer is fed by surface water or rainwater from distant locations with travel time of thousands of years and has no hydraulic connection with the arsenic-rich shallow aquifer. Numerical simulations indicate that the future pumping of deep groundwater is not likely to drive in arsenic from the shallow aquifer. Therefore, new wells may be installed in the deep aquifer. High pumping of shallow unpolluted aquifer consisting of brown sand will drive in groundwater containing organic matter from the post-Last Glacial Maximum aquifer-aquitard system. The organic matter drives reduction of manganese oxides at strip interfaces between palaeo-channel and palaeo-interfluve. After the completion of manganese reduction, FeOOH reduction may take place in the marginal palaeo-interfluvial aquifer and release sorbed arsenic. Arsenic then moves into the interior of palaeo-interfluvial aquifer polluting its fresh groundwater. Arsenic migration rates ranges between 0.21 and 6.3 and 1.3 × 10−2 and 0.4 m/year in horizontal and vertical directions, respectively. Therefore, palaeo-interfluvial aquifer will remain arsenic-free for hundreds to thousands of years to supply safe drinking water.

On the in-situ aluminothermic reduction of manganese oxides in continuous galvanizing baths

The in-situ aluminothermic reduction of manganese oxide (MnO) by dissolved Al in the continuous galvanizing bath was investigated. Thick (approximately 410nm) MnO films were grown on a 5.1wt.% Mn steel by annealing at 770°C for 600s using a conventional −30°C dew point N2–5% H2 process atmosphere. The MnO films formed were then reacted with a 0.20wt.% dissolved Al bath at 460°C for reaction times ranging from 1.2s to 21.0s. Significant reductions of MnO film thickness were observed for all reaction times, with the reduction in MnO being a linear function of reaction time for the reaction times explored. It was determined that an Al2O3 reaction product was present at the coating-oxide interface with significant concentrations of Mn being detected in the metallic coating adjacent to the reaction front. It was also determined that the MnO layer was not altered chemically for any of the reaction times explored. From these results, it was concluded that the previously proposed in-situ aluminothermic reduction of MnO by the bath dissolved Al proceeds by a dissolution mechanism. It was further concluded that that the aluminothermic reduction of MnO in the continuous galvanizing bath has been validated.

Combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash

Hydrogen sulfide is highly toxic to benthic organisms and may cause blue tide with depletion of dissolved oxygen in water column due to its oxidation. The purpose of this study is to reveal the combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash that is a byproduct from coal electric power stations to apply the material as an adsorbent for hydrogen sulfide in natural fields. Sulfur species were identified in both liquid and solid phases to discuss removal mechanisms of the hydrogen sulfide with the granulated coal ash. Batch experiments revealed that hydrogen sulfide decreased significantly by addition of the granulated coal ash and simultaneously the sulfate ion concentration increased. X-ray absorption fine structure analyses showed hydrogen sulfide was adsorbed onto the granulated coal ash and successively oxidized by manganese oxide (III) contained in the material. The oxidation reaction of hydrogen sulfide was coupling with reduction of manganese oxide. On the other hand, iron containing in the granulated coal ash was not involved in hydrogen sulfide oxidation, because the major species of iron in the granulated coal ash was ferrous iron that is not easily reduced by hydrogen sulfide.

Roles of siderophore in manganese-oxide reduction by Shewanella oneidensisMR-1

Dissimilatory metal-reducing bacteria (DMRB), such as Shewanella oneidensis MR-1, are of great interest for their importance in the biogeochemical cycling of metals and utility in biotechnological processes, such as bioremediation and microbial fuel cells. To identify genes necessary for metal reduction, this study constructed a random transposon-insertion mutant library of MR-1 and screened it for isolating mutants that were deficient in metal reduction. Examination of approximately 5000 mutants on lactate minimal-medium plates containing MnO(2) resulted in the isolation of one mutant, strain N22-7, that showed a decreased MnO(2)-reduction activity. Determination of a transposon-insertion site in N22-7 followed by deletion and complementation experiments revealed that the disruption of SO3030, a siderophore biosynthesis gene, was responsible for the decreased MnO(2)-reduction activity. In ΔSO3030 cells, iron and cytochrome contents were decreased to approximately 50% of those in the wild-type cells, when they were incubated under MnO(2)-reduction conditions. In addition, the transcription of genes encoding outer-membrane cytochromes necessary for metal reduction was repressed in ΔSO3030 under MnO(2)-reduction conditions, while their transcription was upregulated after supplementation of culture media with ferrous iron. These results suggest that siderophore is important for S. oneidensis MR-1 to respire MnO(2), because iron availability influences the expression of cytochromes necessary for metal reduction.

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.

Complexation- and ligand-induced metal release from 316L particles: importance of particle size and crystallographic structure

Iron, chromium, nickel, and manganese released from gas-atomized AISI 316L stainless steel powders (sized <45 and <4μm) were investigated in artificial lysosomal fluid (ALF, pH 4.5) and in solutions of its individual inorganic and organic components to determine its most aggressive component, elucidate synergistic effects, and assess release mechanisms, in dependence of surface changes using atomic absorption spectroscopy, Raman, XPS, and voltammetry. Complexation is the main reason for metal release from 316L particles immersed in ALF. Iron was mainly released, while manganese was preferentially released as a consequence of the reduction of manganese oxide on the surface. These processes resulted in highly complexing media in a partial oxidation of trivalent chromium to hexavalent chromium on the surface. The extent of metal release was partially controlled by surface properties (e.g., availability of elements on the surface and structure of the outermost surface) and partially by the complexation capacity of the different metals with the complexing agents of the different media. In general, compared to the coarse powder (<45μm), the fine (<4μm) powder displayed significantly higher released amounts of metals per surface area, increased with increased solution complexation capacity, while less amounts of metals were released into non-complexing solutions. Due to the ferritic structure of lower solubility for nickel of the fine powder, more nickel was released into all solutions compared with the coarser powder.

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.

Environmental Factors Affecting Chromium-Manganese Oxidation-Reduction Reactions in Soil

Disposal of chromium (Cr) hexavalent form, Cr(VI), in soils as additions in organic fertilizers, liming materials or plant nutrient sources can be dangerous since Cr(VI) can be highly toxic to plants, animals, and humans. In order to explore soil conditions that lead to Cr(VI) generation, this study were performed using a Paleudult (Dystic Nitosol) from a region that has a high concentration of tannery operations in the Rio Grande do Sul State, southern Brazil. Three laboratory incubation experiments were carried out to examine the influences of soil moisture content and concentration of cobalt and organic matter additions on soil Cr(VI) formation and release and manganese (Mn) oxide reduction with a salt of chromium chloride (CrCl 3) and tannery sludge as inorganic and organic sources of Cr(III), respectively. The amount of Cr(III) oxidation depended on the concentration of easily reducible Mn oxides and the oxidation was more intense at the soil water contents in which Mn(III/IV) oxides were more stable. Soluble organic compounds in soil decreased Cr(VI) formation due to Cr(III) complexation. This mechanism also resulted in the decrease in the oxidation of Cr(III) due to the tannery sludge additions. Chromium(III) oxidation to Cr(VI) at the solid/solution interface involved the following mechanisms: the formation of a precursor complex on manganese (Mn) oxide surfaces, followed by electron transfer from Cr(III) to Mn(III or IV), the formation of a successor complex with Mn(II) and Cr(VI), and the breakdown of the successor complex and release of Mn(II) and Cr(VI) into the soil solution.

Carbothermal Solid State Reduction of Stable Metal Oxides

AbstractThe paper considers carbothermal solid state reduction of manganese, titanium and aluminium oxides in argon, helium and hydrogen. The difference in reduction in helium and argon was reflected by different diffusion coefficients of gaseous reactants and products, which are much higher in helium than in argon. When carbothermal reduction took place in hydrogen, it was involved in the reduction process by reducing oxides to suboxides and forming methane.Manganese and titanium oxides were reduced to carbide Mn7C3 and oxycarbide Ti(OxC1‐x) correspondingly, while products of alumina reduction included carbide Al4C3 and vapours of Al and Al2O, which were re‐oxidised to Al4O4C outside the reactor and deposited in the lower temperature zone. Gas atmosphere had a profound effect on the extent and rate of reduction. This effect was different in reduction of different oxides. Reduction of manganese oxides was the fastest in hydrogen, and faster in helium than in argon. Reduction of titania in argon and helium proceeded with about the same rate and was much faster in hydrogen than in the inert atmospheres. The rate and extent of alumina reduction in hydrogen and helium were higher than in argon, although no significant difference was observed in alumina reduction in hydrogen and helium. This reflects differences in reduction mechanisms, which are discussed in the paper.

ChemInform Abstract: XPS Study of the MnO2 Electrode in Borate Solution During the Discharge Process.

Abstract The thin hydrous manganese oxide electrodeposited on gold has been studied using X-ray Photoelectron Spectroscopy (XPS). The oxygen 1 s spectrum changes during the cathodic discharge process and can be deconvoluted into three components: MnO, MnOH or MnOH 2 and water adsorbed. The surface composition of the film, MnO x (OH) y (OH 2 ) z , has been described according to the O 1 s spectrum analysis. The x and y + z values were calculated from the I o / I m ratio peak intensities. The oxidation number of Mn has been calculated at different potentials during the manganese oxide reduction. These values indicate that MnO 2 is reduced to Mn(III) in borate solutions at pH 9.2

Structure and the Metal Support Interaction of the Au/Mn Oxide Catalysts

Gold catalysts with loading 1 and 10 wt % were prepared by deposition−precipitation method with urea over mesoporous manganese oxide, obtained through a surfactant-assisted procedure by using cetyltrimethylammonium bromide (CTAB), followed by treatment with sulphuric acid. For comparison, Au(10 wt %) was also deposited over commercial CeO2 and SiO2 supports. The materials were characterized by XRD and EXAFS at the Mn K and Au LIII edges and XPS. Moreover, the analyses were performed on the samples treated under 1%CO/He, at 250 °C for 90 min. The structural and surface results of the as prepared manganese oxide confirmed the formation of γ-MnO2 along with some amorphous Mn3O4 upon treatment of the precursor oxide with sulphuric acid. The CO treatment induces the formation of reduced phases, Mn3O4 (Hausmannite) and Mn2O3 (Bixbyite). Gold particles have a positive effect in promoting the reduction of manganese oxide and this effect is more pronounced in the Au(10 wt %) catalyst, which exhibits an enhanced CO oxidation activity with respect to both the Au(1 wt %) sample and the metal-free manganese oxide. The higher efficiency of Au(10 wt %) catalyst is attributed to a strong metal−support interaction between gold nanoparticles and support, as demonstrated by the presence of a component Au−O at 2.1 Å in the Fourier transform of the EXAFS signal of both the fresh and the CO-treated samples.

黄鉄鉱とのガルバニック反応によるコバルト・リッチ・クラストの浸出について

Cobalt-rich ferromanganese crusts (cobalt crust) contain strategic metals such as copper, nickel and cobalt. In order to recover cobalt, the reduction and dissolution of manganese oxide in crusts is required because cobalt is interlocked in manganese oxide. It is known that galvanic interactions between metal sulfide minerals and manganese nodule cause oxidation-reduction reactions on them. In this study, galvanic leaching of chemical analytical MnO2 and cobalt crust has been examined in the presence of pyrite.The measurement of rest potential indicated that MnO2 was nobler than pyrite. The dissolution of the MnO2 was accelerated in the presence of pyrite because MnO2 could act as cathode to be reduced in the galvanic couple MnO2/FeS2 .The dissolution of manganese and cobalt from the cobalt crust was enhanced in the presence of pyrite, and 84% of cobalt was extracted in three days while about 1% in the absence of pyrite in sulfuric acid solution of pH0.8. The leaching of the cobalt crust has been studied under various experimental parameters such as pH, amount of pyrite and particle size.

Carbothermal Solid State Reduction of Manganese Ores: 3. Phase Development

The paper considers phase development in the process of solid state carbothermal reduction of Wessels (South Africa) and Groote Eylandt (Australia) manganese ores in inert gases and hydrogen. Reduction starts with reduction of higher manganese oxides to MnO and iron oxides to metallic iron. When the graphite content in the graphite/ore mixture was in excess relative to the stoichiometric ratio, the final reduction product was (Fe, Mn) 7 C 3 carbide. In the process of reduction of Groote Eylandt ore, silica also was reduced. In the reduction of high silica-ore, manganese oxide was predominantly reduced from tephroite and rhodonite. Silicon in the alloy was present in the form of ferro-manganese-silicon carbide and silicide (Fe, Mn) 5 Si 3 .

Carbothermal Reduction of Manganese Oxide in Different Gas Atmospheres

Carbothermal reduction of manganese oxides was studied in hydrogen, helium, and argon at different temperatures and carbon-to-manganese oxide ratios. Isothermal and temperature programmed carbothermal reduction experiments were conducted in a fixed bed reactor in a vertical tube furnace, with on-line monitoring of gas composition by the CO-CO2 infrared sensor. The extent of reduction was calculated using the off-gas composition and LECO oxygen contents in the reduced samples. In all gas atmospheres, the reaction rate increased with temperature. The reduction rate of manganese oxide in hydrogen was higher than in helium, and in helium higher than in argon. This was attributed to the involvement of hydrogen in the reduction process and the difference in CO and CO2 diffusion coefficients in helium and argon.