Search

The present research explores the potential of manganese oxide waste ore in energy storage applications, focusing on supercapacitors. The investigation assesses the electrochemical capabilities of natural manganese oxides obtained from the Drama region, which has been the main mining center of Greece for manganese ore, especially that of battery-grade quality. Samples were collected from abandoned mining sites in the Kato Nevrokopi area, Drama. The structure and composition of the manganese minerals were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical tests involved the preparation of electrodes using natural nsutite and heat-treated nsutite (hausmannite). Then, the designed electrodes were subjected to cyclic voltammetry tests and charge–discharge measurements. The hausmannite electrode exhibited a higher specific capacitance of 667 F/g at a current density of 0.2 A/g, and the electrode material retained 98.3% of its initial capacitance after 1000 cycles. This study provides new perspectives on simple and efficient methods for transforming natural nsutite material from mining waste to hausmannite with greater structural homogeneity and better electrochemical behavior. [ABSTRACT FROM AUTHOR]

A new X-ray fluorescence technique is proposed as an alternative to the labor-consuming volumetric method for the estimation of manganese valence state in ferromanganese nodules. The approach is based on the measurement of the relative intensities of some X-ray fluorescence spectrum characteristic spectral lines and satellites (MnKβ5 and MnKβ′) preconditioned by electron transfer from the valence shell. Calibration curves were created using manganese oxide samples (MnO, Mn2O3, MnO2) and 12 certified reference materials of ferromanganese nodules, cobalt-bearing ferromanganese crusts, and manganese ores with certified (or determined by approved methods) total and tetravalent manganese content. The presence of high iron content was taken into account. A set of oceanic ferromanganese nodules samples collected in the Magellan Seamounts (Pacific Ocean) were analyzed. Differences between the results of the X-ray fluorescence method and volumetric techniques for tetravalent manganese content were 4.9 rel.%, which is comparable with the accuracy of the volumetric technique (3.6 rel.%). [ABSTRACT FROM AUTHOR]

The low-cost Fe(II) reductants used in the leaching of pyrolusite usually cause high concentrations of iron ions in the leaching solution, which are difficult to treat and recover. Herein, a green cyclic leaching process for pyrolusite with recycling and reusing of Fe(II) reductants was developed. Sodium sulfide was introduced to reduce and precipitate iron ions in the leaching solution. Ep-H diagrams show that Fe3+ can be reduced to Fe2+ by S2− and form a precipitate with the high efficiency of 93.09%. Since the main component of the precipitate was ferrous disulfide with reducibility, it was used as a reducing agent for low-grade manganese oxide ores. A total of 97.96% of the manganese was highly reductively leached by the obtained precipitate of 0.28 g·g−1 ore. Furthermore, the leaching efficiency was almost unchanged after five iterations of cyclic experiments. The cyclic leaching process enables the efficient leaching of manganese and the recycling of iron, which provides a green and economic method for the efficient utilization of low-grade pyrolusite resources. [ABSTRACT FROM AUTHOR]

The effect of raw materials on the temperature development and prereduction behavior of Comilog and Nchwaning manganese ores (3.33–4.00 mm or 11.20–15.00 mm) were investigated in a CO-CO2 atmosphere. Experiments were conducted at a heating rate of 6 °C/min from room temperature to 1000 °C where the ore was mixed with inert material (quartz) in various ratios. A similar heating program gave dissimilar temperature development for Comilog and Nchwaning ores due to differences in oxygen levels and reduction rates. The temperature development, and thus reduction rate, decreased with the increasing amount of inert material in the mix for Comilog ore in size 3.33–4.00 mm. The peak reaction rates observed during reduction were 2.4 wt%/min, 1.0 wt%/min, and 0.8 wt%/min for an ore:quartz weight ratio of 1:0, 1:1, and 1:3, respectively. For Comilog ore in size 11.20–15.00 mm, and Nchwaning ore in both sizes, the temperature development and reduction rates were slightly or insignificantly affected. It was suggested that the effect was low for reactions under a diffusion-controlled kinetic regime. [ABSTRACT FROM AUTHOR]

The removal of high concentration flue gas sulfur dioxide (SO2) using manganese carbonate ore desulfurization (MCO-FGD) is a promising route that combines economic benefits and pollution control. However, the problems of intermediate oxidation and by-product control have plagued the industrial application of the MCO-FGD technique for a long time. Based on the fact that there is symbiosis of manganese and iron in natural manganese ore, in this study, small amounts of Fe(III) and MnO2 were introduced into the MCO-FGD reaction system to enhance the oxidation of SO2 to SO4− and suppress the manganous dithionate (MnS2O6) by-product generation. The results suggested that the addition of Fe(III) led to the generation of potent oxidant Mn(III) in the reaction system, which accelerated the generation of SO3−• radicals and, thus, enhanced the oxidation of SO2. Under the optimum reaction conditions, the 2.0% of inlet SO2 could be removed to 62 ppm, obtaining 90.1% manganese leaching efficiency, and the concentration of MnS2O6 in the desulfurized liquid was kept below 2.5 g/L after a six-stage desulfurization. The results are of great importance for the sustainable development of the manganese metallurgical industry, which provides theoretical and technical support for the recycling of sulfur and manganese. The influences of different operational conditions on SO2 removal, the catalytic mechanism, and manganese leaching were studied to provide theoretical and technical support for resourceful MCO-FGD technology. [ABSTRACT FROM AUTHOR]

In the big data era, mineral explorations need to accommodate for the growth in spatial dimensions and data dimensions, as well as the data volume and the correlation between data. Aiming to overcome the problems of limited and scattered data sources, chaotic data types, questionable data quality, asymmetric data information, and small sample sizes in current mineral prospecting data, this paper improved traditional 3D prediction methods based on the characteristics and actual needs of relevant mineral prospecting data. First, for the regions with incomplete data, a new 3D prediction method based on transfer learning was proposed. Meanwhile, random noise was adopted to compensate for the limited sample size in mineral prediction. By taking the Huayuan Mn deposit in Hunan Province as the study area, 22 proposed ore-controlling variables were divided into six groups for comparative tests under different combinations, and each group was further divided into the 3D CNN prediction method and the transfer learning prediction method. After the similarities between the regional metallogenic backgrounds were proven, the convolution kernel of the Minle area was transferred to that of the Huayuan area with poor data. Then, both were used to train a 3D prediction model to realize the training and transfer of the spatial correlation between the spatial distribution of ore-controlling factors and the manganese ore. The results indicated that the accuracy of the transfer learning model in test 6 could reach 100%, with good stability of the transfer learning prediction model and a high convergence speed. By comparing the 3D-predicted targets before and after the transfer learning of tests 5 and 6, it was found that the 3D CNN model of test 5 still performed well, but the transfer learning model of test 6 was superior. In verifications based on superposition with the basin model and the growth fault model, the prediction results were consistent with the geological characteristics of the research area. To sum up, the 3D CNN prediction method has advantages in mineral prediction when big data are available, and transfer learning based on the 3D CNN algorithm helps to realize 3D deep mineral prospect prediction in the case of incomplete data. [ABSTRACT FROM AUTHOR]

Biochar (BC) is considered to be a great potential adsorbent to remove various contaminants, but the sorption capacity for chromium (Cr) is predominantly limited for the net negative charge. In this study, BC from rice husk was impregnated with Mn(NO3)2 solution to synthesize MnOx-modified BC (MnOBCs) for enhancing Cr(VI) removal in an aqueous solution. MnOBCs were characterized, and MnOx (manganese ore) was found to be the dominant crystal in MnOBCs. Batch sorption and kinetic experiments combined with spectral analysis were carried out to elucidate the sorption capacity and mechanisms of Cr(VI) sorption onto BC and MnOBCs. Results showed that the sorption kinetic process fitted to the Elovich model, and the modification enhanced the sorption capacity of Cr(VI) on BC. Compared to ion strength, pH is the main control factor for Cr(VI) fixed on BC and MnOBCs, and the sorption amount decreased with the pH value increasing. Moreover, X-ray photoelectron spectroscopy results showed that the proportion of Mn(II) decreased from 33.59% to 8.33%, and that of Mn(VI) increased from 30.58% to 52.72% after Cr(VI) sorption on MnOBCs. Meanwhile, the reduction reaction of Cr(VI) occurred during the sorption process on the BC and MnOBCs surface, and the reduction reaction was more obvious on the MnOBCs surface. MnOx loaded in BC can enhance the electrostatic attraction and redox capacity, which can improve the removal of Cr(VI) in an aqueous solution. This study provides information on the sorption and redox of Cr(VI) on BC, and allows us to better understand the mechanism of Cr(VI) removal in solutions by MnOBCs. [ABSTRACT FROM AUTHOR]

Considering the electromagnetic protection needs of important ground buildings, exploring the electromagnetic wave (EMW) absorption performance of manganese ore powder (MOP) building materials is an effective way to overcome its low added value and difficulty in popularizing. Here, choosing filling ratios commonly used in building materials such as autoclaved bricks, MOP/paraffin samples with 20%, 40%, and 60% mass fraction of MOP were prepared, and electromagnetic properties were analyzed at 2–18 GHz using the coaxial method. The results show that 60 wt% sample has the best absorption performance, with a minimum reflection loss (RLmin) value of −22.06 dB at 15.04 GHz, and the effective absorption bandwidth (EAB, RL < −10 dB) reaches 4.16 GHz at a 7.65 mm absorber thickness, covering most of the Ku-band region. The excellent microwave absorption performance of MOP is due to its multi-oxide forming multi-interface structure and rough surface, which can not only form abundant dipole and interfacial polarization under the action of EMW, but also reflect and scatter the incident EMW, prolong the transmission path, and enhanced the absorption of microwaves. This study demonstrates that MOP building materials can have excellent microwave absorption properties, thus becoming a new way to address harmful manganese residue; for example, autoclaved bricks, which can not only improve the added value of manganese residue building materials but also can be consumed on a large scale. It provides a new idea to solve the harm of manganese residue. [ABSTRACT FROM AUTHOR]

The synergetic utilization of ferruginous gibbsite ores (Al-Fe ores) and ferruginous manganese ores (Mn-Fe ores) by the carbothermic co-reduction roasting–magnetic separation process was proposed as an innovative and green process for the separation and recovery of the valuable metal elements of Mn, Fe and Al from these ores. In this paper, a ferromanganese crude alloy with 72.47% Fe and 10.19% Mn and a high recovery of 85.89% Fe was prepared, which produces an acceptable feed to produce manganese steels with an electric arc furnace. The synergistic co-reduction of the two kinds of complex and refractory minerals was favored to separate Fe, Mn and Al from these ores. The influence of the operating variables on the recovery and separation of valuable metals from Mn-Fe ores and Al-Fe ores is initially studied. Then, the stepwise reduction behaviors of a composite oxide Mn1-xFexO (0 ≤ x ≤ 1) and hercynite (Mn1−yFeyAl2O4, 0 ≤ y ≤ 1) were investigated to clarify that Mn-Fe ores have a positive impact on the reduction of fayalite and hercynite in Al-Fe ores. This study reported a simple green route, the carbothermic co-reduction–magnetic separation process, to economically and effectively treat Al-Fe ores and Mn-Fe ores. [ABSTRACT FROM AUTHOR]

Because of the nano-scale tunnel constructed by the active Mn-O octahedron in cryptomelane, cryptomelane-type manganese oxides have high activity in the oxidation of several volatile organic compounds (VOCs). Natural cryptomelane, in the form of supergene oxide manganese ore, carpets much of South China. In the lower part of the Datangpo Formation of Nanhua System on the southeastern Yangtze Platform, cryptomelane is one of the major manganese oxides in black shale of the Xiangtan manganese deposit in this deposit. Formaldehyde is a dominant indoor pollutant among volatile organic compounds (VOCs), and applications of synthetic cryptomelane have been reported to eliminate it. To study the removal capacity of naturally outcropping cryptomelane, representative samples of manganese oxide (the primary mineral component of cryptomelane) from the Xiangtan Mn deposit were analyzed in this study. The chemical composition, crystal structure and micromorphology of the manganese oxide minerals were explored using ICP-AES, XRD, EPMA, SEM and HR-TEM techniques. Fine-grained and poorly crystalline, these minerals consist primarily of cryptomelane, along with minor amounts of pyrolusite, hollandite, lithiophorite, limonite and quartz. Natural cryptomelane is a monoclinic crystal, and its cell parameters are refined. The results of catalytic tests revealed that natural cryptomelane has obvious catalytic activity in the oxidation of formaldehyde in a static environment under room temperature. This study may provide a natural mineral material as an inexpensive and efficient catalyst for the purification of formaldehyde in industrial or indoor air treatment. [ABSTRACT FROM AUTHOR]

The stream sediments that have been impacted by manganese (Mn) containing wastewater for decades contain not only abundant microorganisms but also organic/inorganic substances. To achieve effective treatment of manganese (Mn)-containing effluent and recovery of Mn from water/sediments, the Mn(II) sorption behaviors and mechanism on sediments of a stream in Mn mining areas were studied. In addition, the study analyzed the effects of various factors (initial concentration, solution pH, sediment dose, contact time, and coexisting cations) on the Mn sorption efficiency of Daxin sediments, and explored the contribution of microbial activity in the sediment sorption of Mn(II). The results showed that the sorption process of Mn(II) on the sediments was consistent with the Elovich and Freundlich models, and the removal of heavy metals was maximum at 40 °C (62.47–98.93%), pH = 8 (77.51%), initial concentration of 1 mmol·L−1 (95.37%) and sediment dosing of 12 g·L−1 (98.93%). The addition of 50 mM NaN3 inhibited the microbial activity in the Daxin sediment, reducing the sorption and removal rates of Mn(II) by 0.605 mg·g−1 and 8.92%, respectively. After sorption, the proportion of the Fe–Mn oxidation(iron–manganese) state in Daxin sediments decreased from 54% to 43%, while the proportion of the exchangeable state increased by 10.80%. Microorganisms in the sediment had a positive effect on inhibiting heavy metal migration and reducing the bioavailability of contaminants in the soil. Through this study, we hope to further understand the sorption and desorption mechanism of manganese by stream sediments in manganese ore areas, so as to provide a guide on the management and recovery of Mn from stream sediments in manganese mining areas. [ABSTRACT FROM AUTHOR]

Manganese dioxide is typically reduced to a bivalent state before being extracted; here, sulfur is considered an efficient reductant and sulfur–based reduction has been industrialized in China. In this study, the reaction mechanism between MnO2 and gaseous sulfur was investigated. Thermodynamically, the reduction of MnO2 by gaseous sulfur is feasible. The predominant phase diagram as functions of temperature and input S2(g) fraction in the S2–MnO2 system was calculated. Experimental validation showed that MnO2 was reduced stepwise to low-valence manganese oxides and manganese sulfate. The phase composition of the roasted products was complex, and MnS was inevitably formed. The valence state as well as microstructure of manganese dioxide during reduction roasting were also investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). The reaction process could be described by an unreacted nuclear model. Manganese was extracted by sulfuric acid solution after reduction by sulfur waste. In sulfuric acid, 95.2 wt% Mn extraction was achieved, using a roasting temperature of 450 °C, roasting time of 30 min, and S2/MnO2 molar ratio of 0.40. With the same conditions, low Fe extraction was achieved. On the other hand, in deionized water, 24.3 wt% Mn extraction was achieved, confirming the formation of MnSO4. [ABSTRACT FROM AUTHOR]

This paper presents research on Fe and Mn removal from groundwater. In treatment systems of aeration followed by rapid filtration (no chemical dosage), manganese removal is possible due to the manganese dioxide catalyst present on the grains of filtration material. The goal of the presented research was to find a correlation between the catalyst layer’s composition as well as its internal porosity and the effectiveness and stability of manganese removal in the filtration process. In order to establish the influence of catalyst characteristics on manganese removal effectiveness, the filtration experiment was conducted using filtration materials with catalytic contact layers of different origin. Oxide coated auto-activated silica sand and Gabon manganese ore were tested. Inactive silica sand was used as reference. The results of filtration experiments were combined with analyses of chemical composition, internal porosity, and crystalline parameters of catalyst contact layers of grains. For the determination catalyst contact layer parameters, the following methods were used: Raman spectroscopy, X-ray powder diffractometry (XRD), Scanning Electron Microscope – Energy dispersive spectroscopy (SEM-EDAX), nitrogen adsorption. Pilot scale research on the filtration process demonstrated that auto-activated filtration material was characterized by the highest efficiency of manganese removal and stability of effects during the whole research. The effectiveness of Gabon manganese ore dropped from 90% and stabilized on the level of ca. 60% within 15 days of the experiment. [ABSTRACT FROM AUTHOR]

The reductive leaching of manganese from a low-grade manganese oxide ore was investigated by using pretreated sawdust as the reductant in a sulfuric acid medium. The effects of stirring speed, liquid/solid ratio, sawdust/ore mass ratio, sulfuric acid concentration, reaction temperature and time on the manganese extraction were examined. It was found that the leaching efficiency is strongly dependent on temperature and acid concentration. The leaching efficiency of manganese reached 94.1% under the optimal conditions: stirring speed of 300 rpm, liquid/solid ratio of 8:1, mass ratio of sawdust to ore 0.25, sulfuric acid concentration of 1 mol/L and a temperature of 363 K for 180 min. The kinetic analysis was carried out based on the shrinking core model, which indicated that the reductive leaching process was controlled by the chemical reaction. The reaction orders with respect to the sulfuric acid concentration and mass ratio of sawdust are 1.66 and 0.57, respectively. The apparent activation energy for the leaching process has been calculated using the Arrhenius expression and was found to be 51.7 kJ/mol. [ABSTRACT FROM AUTHOR]

The extraction of manganese from a semi-oxidized manganese ore was investigated with sucrose as the reducing agent in dilute sulfuric acid medium. The kinetics of leaching manganese from the complex ore containing MnCO3 and MnO3 was also investigated. The effects of sucrose and sulfuric acid concentrations, leaching temperature and reaction time on the totalMn (TMn), MnO3 and MnCO3 leaching were investigated. Results showed that MnCO3 could more easily react with hydrogen ions than MnO3 in ores, and MnO3 decomposition could be advantageous for MnCO3 leaching. The leaching efficiencies of 91.8% for total Mn, 91.4% for MnO3 and 96.9% for MnCO3 were obtained under the following optimized conditions: 0.035 mol/L sucrose concentration, 5 mol/L sulfuric acid concentration, 60 min of reaction time and 363.2 K of leaching temperature. In addition, it was found that the leaching process of semi-oxidized manganese ore follows the shrinking core model and the leaching rate was controlled by chemical reaction and diffusion. The apparent activation energy of the total manganese, MnO3, and MnCO3 leaching were 40.83, 40.59, and 53.33 kJ.mol-1, respectively. [ABSTRACT FROM AUTHOR]

With the depletion of rich manganese ore resources, plentiful manganese ore powders with various Mn/Fe mass ratios are produced. The physicochemical aspects of oxidative consolidation behavior of manganese ores with various Mn/Fe mass ratios were investigated in this work to determine whether manganese ore powders with high iron content (Fe-Mn ore) can be prepared as high-quality pellets. Physicochemical properties of the pellets were investigated, including cold compression strength (CCS), phase transformation, microstructural evolution, Vickers hardness (HV), porosity, and lattice parameter. CCS testing indicated that the strength of roasted Fe-Mn ore pellets was observably lower than that of pure hematite or manganese ore pellets. Phase and morphology results showed that in Fe-Mn ore pellets, an Mn ferrite phase was generated between hematite and pyrolusite particles. However, newborn Mn ferrites and hematite had an obvious crystal boundary in the crystallographic particles. Moreover, poorly crystallized Mn ferrite particles were evident, along with Mn and Fe element concentration gradients, due to the inadequate diffusion of metal ions. This resulted in poor mechanical properties of the Fe-Mn ore pellets. A temperature over 1275 °C and a roasting time of 15 min is required for the oxidative consolidation of Fe-Mn ores. In such optimized cases, Mn, Fe, O, and Al elements were uniformly distributed in the well-crystallized Mn ferrite grains, which provided favorable mineralogy for the consolidation of Fe-Mn ore powders. [ABSTRACT FROM AUTHOR]

The research aims to reveal the structure, phase, and elemental content of manganese ores from deposits—Bogach (Karaganda region, Kazakhstan) and Zhaksy (Akmola region, Kazakhstan). The samples were studied with scanning electron microscopy with energy dispersive analysis (SEM-EDA), X-ray diffractometry (XRD), Infra-red spectroscopy (IRS). During the research, structural peculiarities, elemental and phase content of the samples have been revealed. The mineral matter of the Bogach deposit ore mainly consists of hollandite, cryptomelane, braunite, calcite, bixbyite, quartz. The Zhaksy deposit ore includes quartz, hollandite, bixbyite, pyrolusite. Bogach ore includes (wt.%) C(10.68), O(32.00), Mn(43.26), Ca(6.36), Si(3.51), Na(0.52), Al(1.13), Mg(0.69), K(1.85). The elemental content of Mn in Zhaksy ore is two times lower. Zhaksy ore includes (wt.%) C(23.77), O(32.1), Mn(21.81), Si(10.52), Al(5.13), K(1.21), Fe(5.47). The obtained data of the conducted spectral analysis indicate that both samples represent a polymineral heterogeneous structure. Conducted research allows to conclude, that by phase-elemental content the Bogach ore can be used for obtaining trimanganese tetraoxide pigment similar to manganese ores from West Sumatera deposit (Indonesia) by top-down method using grinding with a milling tool and high-temperature sintering. [ABSTRACT FROM AUTHOR]

The break-up of the supercontinent Rodinia in the late Neoproterozoic led to the formation of the Nanhua rift basin within the South China Block. The Datangpo-type manganese deposit, which developed in the Nanhua rift basin, is one of the most important types of manganese deposits in South China. Although it is widely accepted that deep sedimentary structures significantly affect the manganese ore system, the relationship between the manganese deposits in South China and the Nanhua rifting process is still unclear. The origin of the manganese ore layer remains controversial. In this paper, we integrated the audio-frequency magnetotelluric (AMT) data, gravity data, and comprehensive geological and borehole data analysis to characterize the structure of the Datangpo-type manganese deposit in Songtao, Guizhou Province. The resistivity and density models produced an inclined layered structure, which correlated well with the coeval sediment strata of the Nanhua rift basin. A high-resistivity cap was observed from the surface to a depth of 800 m, corresponding to the Cambrian Loushanguan ( ϵ 3 − 4 ls ) and Palang dolomite formation ( ϵ 2 p ), which has helped the storage of the manganese ore. The most significant low-resistivity anomaly (25–40 Ω·m) resides at a depth of 1400 m in the Nantuo (Nh3n) gravel sandstone and Datangpo (Nh2d) silty and carbonaceous shale, corresponding to the ore-forming layer. This distinct low-resistivity layer was possibly produced by aqueous fluids and pyrite in the syn-sedimentary fault and alteration zone. The accumulations of sulfide minerals in the rock samples suggest a possible anoxic-euxinic deposition environment during the manganese mineralization and precipitation. The fault revealed in the resistivity models is perhaps a previous fault zone produced by extension in the Nanhua rifting process, which provided migration and upwelling channels for ore-forming minerals. Based on our resistivity models, density models, and geological survey, the manganese ore-forming model was derived, which can help to provide geophysical evidence for the origin of the Datangpo-type manganese deposit. [ABSTRACT FROM AUTHOR]

The Guangxi Zhuang Autonomous Region is an important manganese ore district in Southwest China, with manganese ore resource reserves accounting for 23% of the total manganese ore resource reserves in China. The Xialei manganese deposit (Daxin County, Guangxi) is the first super-large manganese deposit discovered in China. The Mn oxide in the supergene oxidation zone of the Xialei deposit was characterized using scanning electron microscopy (SEM), energy spectrometer (EDS), transmission electron microscopy (TEM, HRTEM), and X-ray diffraction analysis (XRD). The Mn oxides have a gray-black/steel-gray color, a semi-metallic-earthy luster, and appear as oolitic, pisolitic, banded, massive, and cellular textures. Scanning electron microscopy images show that the manganese oxide minerals are present as fine-spherical particles with an earthy surface. TEM and HRTEM indicate the presence of oriented bundled and staggered nanorods, and nanopores between the crystals. The Mn oxide ore can be classified into two textural types: (1) oolitic and pisolitic (often with annuli) Mn oxide, and (2) massive Mn oxide. Pyrolusite, cryptomelane, and hollandite are the main Mn oxide minerals. The potassium contents of cryptomelane and pyrolusite are discussed. The unit cell parameters of pyrolusite are refined. [ABSTRACT FROM AUTHOR]

Manganese ore reduction is quite complex at intermediate reaction temperatures of 1100–1400 °C due to the formation of liquid oxide and/or alloy phases in varying phase proportions and distributions. Evidence in the literature shows that MnO reduction rates are higher for manganese ores of higher iron mineral content. This is due to a lowering of the manganese activity in the presence of iron and carbon in the alloy. Consequently, the minimum required temperature for carbothermic reduction of MnO is lowered. The simplification of the complex ore reduction system is achieved by reacting pure MnO with carbon instead of using gangue-containing ore. The effect of variation in the %C in the alloy product has not been well quantified in previous works. Here the complete alloy phase analyses are used to clarify the role of metallic iron added to MnO-Fe-C compressed pellets reacted at 1100 and 1200 °C. The phase chemistry analyses show that the alloy compositions follow a polynomial curve in %Mn vs. %C plots, with alloy phase compositions formed internal to the MnO particles containing lower %Mn (<50%) and lower %C (<6%) vs. alloy phase compositions formed external to the MnO particles at 60–71% Mn and 6–10% C. Most of the Mn-Fe-C alloy areas internal to the MnO particles are liquid at 1200 °C. Thermodynamic analysis shows that the low-temperature reduction (1200 °C) of MnO in the presence of metallic iron is possibly due to lowered Mn activity in the product alloy Mn-Fe-C alloy and reduction via CO. [ABSTRACT FROM AUTHOR]

Prereduction of Nchwaning manganese ore was investigated by isothermal reduction between 600 and 800 °C to optimize the conditions for industrial pretreatment of manganese ores. Experiments were conducted in CO/CO2 gas mixtures with and without hydrogen at two different oxygen partial pressures. Ore in the size fraction 9.52–15 mm was reduced in a thermogravimetric furnace, and the O/Mn ratio from the chemical analysis was used to determine the extent of prereduction. The samples were investigated by X-ray diffraction to investigate the evolution of phases under the course of reduction. The X-ray diffraction revealed that bixbyite and braunite (I and II) were reduced to manganosite with no or limited formation of hausmannite. Reduction of iron oxides subsided with wüstite, which is stabilized by manganese in the monoxide phase, and hydrogen was seen to improve the reduction of iron oxides. Modeling revealed that the reduction rate increased 2.8-fold upon increasing the CO content from 30% to 70% in a CO/CO2 gas mixture. The addition of hydrogen improved the reduction rate with factors of 1.3 and 2.6 for the low and the high oxygen partial pressures, respectively. Hence, the optimal conditions for pretreatment can be achieved by keeping the oxygen partial pressure as low as possible while adding hydrogen to the reducing gas and ensuring a high reduction temperature. Successful pretreatment limits the extent of the Boudouard reaction in the submerged arc furnace, reducing the amount of CO produced and, thus, reducing the CO available for pretreatment. Hydrogen is a useful addition to the pretreatment unit since it lowers the oxygen partial pressure and improves the kinetics of prereduction. [ABSTRACT FROM AUTHOR]

The ferromanganese (FeMn) alloy is produced through the smelting-reduction of manganese ores in submerged arc furnaces. This process generates large amounts of furnace dust that is environmentally problematic for storage. Due to its fineness and high volatile content, this furnace dust cannot be recirculated through the process, either. Conventional MnO2 production requires the pre-reduction of low-grade ores at around 900 °C to convert the manganese oxides present in the ore into their respective acid-soluble forms; however, the furnace dust is a partly reduced by-product. In this study, a hydrometallurgical route is proposed to valorize the waste dust for the production of battery-grade MnO2. By using dextrin, a cheap organic reductant, the direct and complete dissolution of the manganese in the furnace dust is possible without any need for high-temperature pre-reduction. The leachate is then purified through pH adjustment followed by direct electrowinning for electrolytic manganese dioxide (EMD) production. An overall manganese recovery rate of >90% is achieved. [ABSTRACT FROM AUTHOR]

Manganese and Fe have similar geochemical properties in the supergene environment. Separation of Mn and Fe is an important process for the formation of high-grade sedimentary manganese deposits. Large-scale manganese carbonate deposits (total reserves of approximately 700 Mt) were formed during the interglacial of the Sturtian and Marinoan in South China. The orebodies are hosted in the black rock series at the basal Datangpo Formation of the Cryogenian period. The Fe contents in ores range from 1.15 to 7.18 wt.%, with an average of 2.80 wt.%, and the average Mn/Fe ratio is 8.9, indicating a complete separation of Mn and Fe during the formation of manganese ores. Here, we present element data of manganese carbonates and sulfur isotopes of pyrite from the Dawu deposit, Guizhou, China, aiming to investigate the separation mechanism of Mn and Fe and the ore genesis. The Fe in ores mainly occurs as carbonate (FeCO3) and pyrite (FeS2). The Mn, Ca, Mg and Fe exist in the form of isomorphic substitutions in manganese carbonate. The contents of FeCO3 in manganese carbonates are similar in different deposits, with averages of 2.6–2.8 wt.%. The whole-rock Fe and S contents have an obvious positive correlation (R = 0.69), indicating that the difference of whole-rock Fe content mainly comes from the pyrite content. The δ34SV-CDT of pyrite varies from 40.0 to 48.3‰, indicating that the pyrite formed in a restricted basin where sulfate supply was insufficient and the sulfate concentrations were extremely low. Additionally, the whole-rock Fe content is negatively correlated with the δ34S values of the whole-rock and pyrite, with correlation coefficients of −0.78 and −0.83, respectively. Two stages of separations of Mn and Fe might have occurred during the mineralization processes. The reduced seawater became oxidized gradually after the Sturtian glaciation, and Fe2+ was oxidized and precipitated before Mn2+, which resulted in the first-stage separation of Mn and Fe. The residual Mn-rich and Fe-poor seawater flowed into the restricted rift basin. Mn and Fe were then precipitated in sediments as oxyhydroxide as the seawater was oxidized. At the early stage of diagenesis, organic matter was oxidized, and manganese oxyhydroxide was reduced, forming the manganese carbonate. H2S was insufficient in the restricted basin due to the extremely low sulfate concentration. The Fe2+ was re-released due to the lack of H2S, resulting in the second-stage separation of Mn and Fe. Finally, the manganese carbonate deposit with low Fe and very high δ34S was formed in the restricted basin after the Sturtian glaciation. [ABSTRACT FROM AUTHOR]

Magnetic separation is often considered pertinent for manganese ore beneficiation when the ore is abundant with siliceous rich gangue mineral phases. However, the process is deemed to be inapposite for the ferruginous type of ore, and remains a grey area of research. In the present investigation, two different types of manganese ore were studied in detail to understand the influence of mineralogy on their magnetic separation performance. Detailed experiments were performed by varying the critical variables of the dry magnetic separator, and the separation features were studied. The ore samples were thoroughly characterized by various techniques, including an automated advanced mineralogical tool. The mineralogical results revealed that primary manganese bearing minerals in both the ores are rich in cryptomelene, pyrolusite, psilomelane, and bixybyite. Similarly, the major gangue minerals were alumina-bearing minerals and iron-bearing phases (hematite and goethite). The optimum grade that could be obtained from single-stage dry magnetic separation was 35.52% Mn, and with a Mn:Fe ratio of 1.77, and 44% Mn recovery in the case of sample 1; whereas, a 33.75% Mn grade, with a Mn:Fe ratio of 1.66 at Mn recovery of 44% was reported for Sample 2. It was observed that both samples had a similar input chemistry (~28% Mn, ~1 Mn: Fe ratio) however, they had distinctive mineralogical assemblages. Furthermore, it was observed that the liberation of manganese mineral was in a course size range, i.e., 300 to 450 µm, while the association of iron and manganese bearing phases was lower in sample 1 when compared to sample 2. [ABSTRACT FROM AUTHOR]

For groundwater treatment, the technologies involving oxidation on MnOx filter bed are beneficial, common, and effectively used. The presence of MnOx is the mutual feature of filter media, both MnOx-coated mineral materials like quartz sand and gravel, chalcedonite, diatomite, glauconite, zeolite, or anthracite along with consisting of MnOx manganese ores. This review is based on the analysis of research and review papers, commercial data sheets, and standards. The paper aimed to provide new suggestions and useful information for further investigation of MnOx filter media for groundwater treatment. The presented compilations are based on the characteristics of coatings, methods, and conditions of its obtaining and type of filter media. The relationship between the properties of MnOx amendments and the obtained purification effects as well as the commonly used commercial products, their features, and applications have been discussed. The paper concludes by mentioning about improving catalytic/adsorption properties of non-reactive siliceous media opposed to ion-exchange minerals and about possible significance of birnessite type manganese oxide for water treatment. Research needs related to the assessment of the use MnOx filter media to heavy metals removal from groundwater in field operations and to standardize methodology of testing MnOx filter media for water treatment were identified. [ABSTRACT FROM AUTHOR]

The reduction and liquidus behaviour of manganese slag with different basicities were studied in non-isothermal experiments in the temperature range of 1400–1500 °C. Certain amounts of quartz were added to Assmang ore (South Africa), and lime was added to Comilog ore (Gabon), to adjust the charge basicity to 0.5, 0.8 and 1.2. The extent of manganese ore reduction as a function temperature were determined by thermo-gravimetric (TG) balance. Morphology of ores and its change in the course of reduction was examined by scanning electron microscopy (SEM). The results show that the reduction rate of Assmang slag decreases with decreasing basicity, as the liquidus temperature of slag decreases. When spherical MnO phase is present, the activity of MnO is high, and the reduction rate is rapid. Comilog slags show a much higher reduction rate than Assmang slags. The activation energies of MnO reduction between 1400 to 1500 °C are estimated in this study and found to be 230 kJ/mol for Assmang charges and 470 kJ/mol for Comilog charges. The dissolution behaviours of Assmang and Comilog slags were also studied by FactSage simulation and verified by experiments. [ABSTRACT FROM AUTHOR]

Manganese ores, especially the oxyhydroxides in their different forms, are the dominant Mn-bearing minerals that occur in marine and terrestrial environments, where they are typically found as poorly crystalline and intermixed phases. Mn oxyhydroxides have a huge range of industrial applications and are able to exert a strong control on the mobility of trace metals. This paper reports the results of a detailed study on the Mn oxyhydroxides occurring in the manganiferous deposit outcropping in the Messinian sediments from Serra D'Aiello (Southern Italy). Nine Mn samples were characterized in detail using X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), thermogravimetry (TG), transmission electron microscopy combined with energy dispersive spectrometry (TEM/EDS), and X-ray fluorescence (XRF). The results indicated that the Mn deposit included the oxyhydroxide mineral species birnessite, todorokite, and rancièite. The size, morphology, and chemical composition of Mn oxyhydroxide samples were investigated in order to define their impact on the environment and human health. Todorokite displayed asbestiform shapes and could disperse fibers of breathable size in the air. Furthermore, since in-depth characterization of minerals within Mn deposits may be the first step toward understanding the genetic processes of manganese deposits, hypotheses about the genesis of the Mn oxyhydroxide deposits were discussed. [ABSTRACT FROM AUTHOR]

High-phosphorus manganese ores provide an important source of manganese, which is regarded as an irreplaceable material in the steel industry. The ammonia-ammonium carbonate leaching method was proposed for the removal of phosphorus and extracting manganese from high-phosphorus manganese ore, both effectively and environmentally. To explore the dissolution behavior of phosphorus and manganese in the ammonia-ammonium carbonate solution, the effect of the ammonia-to-ammonium carbonate concentration ratio, the leaching temperature, and the liquid-to-solid ratio on manganese extraction and dephosphorization rate were investigated. In addition, the composition of precipitated manganiferous sample, which was obtained from high-phosphorus manganese ores by ammonia-ammonium carbonate leaching process, was also studied. The results indicated that more than 99.2% phosphorus was removed and more than 83.5% of manganese was extracted by ammonia-ammonium carbonate leaching under the following conditions: ammonia to ammonium carbonate concentrations: 14:2 mol/L; liquid/solid ratio: 5:1 mL/g; leaching temperature: 25 °C; The precipitated manganiferous sample has little impurities, Mn% is 44.12%, P% is 0.02%, P/Mn = 0.00045. [ABSTRACT FROM AUTHOR]

Metallurgical processing of low-grade manganese ore with high iron content is gaining increasing attention due to the gradual depletion of high-grade Mn ores, amid the difficulties in its efficient extraction for both Mn and Fe values in an environmentally-friendly manner. Attempting to tackle the difficulties, this paper describes an innovative process for selectively chlorinating and reducing the high-Fe manganese ore in a simultaneous manner, aiming to produce water-soluble MnCl2 and metallic Fe. After pre-mixing with carbonaceous reductant, CaCl2 and MgCl2 as the chlorinating agent, the Mn ore was heated at 1000 °C. As much as 89.4% Mn can be chlorinated in its water-soluble form, with dissolution of only 3.0% Fe. The presence of CaCl2 during carbothermic reduction resulted in significant promotion in both the Fe reduction rate and formation of large metallic Fe particles due to the segregation effect, facilitating subsequent separation. Selective Mn chlorination by MgCl2 took place with or without the involvement of SiO2, forming MgSiO4 or MgO, respectively. [ABSTRACT FROM AUTHOR]

The Postmasburg Manganese Field (PMF), Northern Cape Province, South Africa, once represented one of the largest sources of manganese ore worldwide. Two belts of manganese ore deposits have been distinguished in the PMF, namely the Western Belt of ferruginous manganese ores and the Eastern Belt of siliceous manganese ores. Prevailing models of ore formation in these two belts invoke karstification of manganese-rich dolomites and residual accumulation of manganese wad which later underwent diagenetic and low-grade metamorphic processes. For the most part, the role of hydrothermal processes and metasomatic alteration towards ore formation has not been adequately discussed. Here we report an abundance of common and some rare Al-, Na-, K- and Ba-bearing minerals, particularly aegirine, albite, microcline, banalsite, sérandite-pectolite, paragonite and natrolite in Mn ores of the PMF, indicative of hydrothermal influence. Enrichments in Na, K and/or Ba in the ores are generally on a percentage level for most samples analysed through bulk-rock techniques. The presence of As-rich tokyoite also suggests the presence of As and V in the hydrothermal fluid. The fluid was likely oxidized and alkaline in nature, akin to a mature basinal brine. Various replacement textures, particularly of Na- and K- rich minerals by Ba-bearing phases, suggest sequential deposition of gangue as well as ore-minerals from the hydrothermal fluid, with Ba phases being deposited at a later stage. The stratigraphic variability of the studied ores and their deviation from the strict classification of ferruginous and siliceous ores in the literature, suggests that a re-evaluation of genetic models is warranted. New Ar-Ar ages for K-feldspars suggest a late Neoproterozoic timing for hydrothermal activity. This corroborates previous geochronological evidence for regional hydrothermal activity that affected Mn ores at the PMF but also, possibly, the high-grade Mn ores of the Kalahari Manganese Field to the north. A revised, all-encompassing model for the development of the manganese deposits of the PMF is then proposed, whereby the source of metals is attributed to underlying carbonate rocks beyond the Reivilo Formation of the Campbellrand Subgroup. The main process by which metals are primarily accumulated is attributed to karstification of the dolomitic substrate. The overlying Asbestos Hills Subgroup banded iron formation (BIF) is suggested as a potential source of alkali metals, which also provides a mechanism for leaching of these BIFs to form high-grade residual iron ore deposits. [ABSTRACT FROM AUTHOR]