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We investigated the electrocatalytic properties of Ir/β‐MnO2, with 4.2–5.6 atomic % (at %) iridium. The Ir/β‐MnO2 was synthesized by heating Ir/R‐MnO2—formed via a surfactant‐assisted (SA) method using KMnO4, IrCl3.H2O, and sodium dodecyl sulfate (SDS)—to 400 °C. The Ir/β‐MnO2 (SA) was nano‐sized based on scanning and transmission electron microscopy (SEM and TEM). Using linear sweep voltammetry (LSV), 5.6 at % Ir/β‐MnO2 (SA) exhibited an overpotential (η) ${\eta){\rm \ }}$ of 327±5 mV for the oxygen evolution reaction (OER), at 10 mAcm-2 ${\hskip0.17em{{\rm c}{\rm m}}^{-2}}$ in 0.5 M H2SO4 electrolyte. At 10 mA cm-2 ${{{\rm c}{\rm m}}^{-2}}$ the Ir/β‐MnO2 (SA) catalyzed the OER for 72 h at an η ${\eta }$ of 534 mV. During this time there was a 12 % loss in Mn and 8 % loss in Ir from the structure. An IrO2 catalyst exhibited an initial η of 420±7 for the OER, but after 20 h of operation at 10 mA cm-2 ${{{\rm c}{\rm m}}^{-2}}$ there was a steep rise in potential (>550 mV) and 12 % loss in Ir. The enhanced activity and stability of Ir/β‐MnO2 (SA) is attributed to the incorporation of Ir into the MnO2 lattice during synthesis and the formation of nano‐sized particles using the SA method. [ABSTRACT FROM AUTHOR]

Pyrolusite comprises the foremost manganese oxides and is a major source of manganese production. An innovative hydrogen-based mineral phase transformation technology to pyrolusite was proposed, where a 96.44% distribution rate of divalent manganese (Mn2+) was observed at an optimal roasting temperature of 650°C, a roasting time of 25 min, and an H2 concentration of 20vol%; under these conditions. The manganese predominantly existed in the form of manganosite. This study investigated the generation mechanism of manganosite based on the reduction kinetics, phase transformation, and structural evolution of pyrolusite and revealed that high temperature improved the distribution rate, and the optimal kinetic model for the reaction was the random nucleation and growth model (reaction order, n = 3/2) with an activation energy (Ea) of 24.119 kJ·mol−1. Throughout the mineral phase transformation, manganese oxide from the outer layer of particles moves inward to the core. In addition, pyrolusite follows the reduction sequence of MnO2 → Mn2O3 → Mn3O4 → MnO, and the reduction of manganese oxides in each valence state simultaneously proceeds. These findings provide significant insight into the efficient and clean utilization of pyrolusite. [ABSTRACT FROM AUTHOR]

Copyright of Hydrometallurgy of China is the property of Hydrometallurgy of China Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Manganese dioxide in pyrolusite was directly reduced to manganese sulfate by high-temperature roasting with ammonium sulfite as reducing agent, so as to achieve efficient extraction of pyrolusite. The effects of mass ratio of ammonium sulfite to pyrolusite, roasting temperature and time, leaching temperature and time on the extraction rate of manganese were investigated, and the optimum process conditions were determined. The results show that the optimal conditions are the mass ratio of ammonium sulfite to pyrolusite of 0.75:1, roasting temperature of 500 °C, roasting time of 1.5 h, leaching temperature of 25 °C, leaching time of 30 min. Under the conditions, the leaching rate of manganese and iron is about 93% and about 9.5%, respectively. The extraction effect of manganese is good. [ABSTRACT FROM AUTHOR]

In view of the complex structure, difficult flotation and difficult leaching of low-grade mixed tungsten and molybdenum ore of a domestic company, the synergistic leaching of molybdenum and tungsten from molybdenum tungsten ore by hydrochloric acid pretreatment--pyrolusite + sulf uric acid was studied. The effects of various factors on the leaching rate of tungsten and molybdenum were investigated. The results show that under the conditions of hydrochloric acid concentration of 1.5 mol/L, liquid volume to solid mass ratio of 6.5/1 and atmospheric pressure, the tungsten and molybdenum ores are pretreated with hydrochloric acid. Under the optimal conditions of filter slag of 20 g, particle size of 200 mesh, pyrolusite dosage of 4 g, sulfuric acid of 8 mol/L, liquid volume to solid mass ratio of 5/1, temperature of 90 °C and leaching time of 3 h, the leaching rates of molybdenum and tungsten are 83% and 73%, respectively. [ABSTRACT FROM AUTHOR]

With the growth of the new energy industry, the requirements for manganese have increased significantly. In this paper, the method of manganese extraction from pyrolusite using ammonium sulfate roasting and water leaching was presented. At the optimal process parameters: mass ratio of (NH4)2SO4 to pyrolusite of 2:1, the roasting temperature of 420°,C and duration of 120 min, the leaching efficiency of Mn and Fe was 94.55% and 54.38%, respectively. The mechanism analysis shows that MnO2 and Fe2O3 in pyrolusite were converted to (NH4)2Mn2(SO4)3, (NH4)3Fe(SO4)3, and NH4Fe(SO4)2 by roasting with ammonium sulfate. Iron was removed from the leaching solution with the addition of ammonia. Afterward, manganese carbonate products were prepared from iron‐free manganese sulfate solution by adding ammonium carbonate at a stirring duration of 60 min, a reaction temperature of 40°C, a pH of 7, and a molar ratio of ammonium carbonate to the manganese of 1.1:1, the precipitation efficiency of manganese could reach 99.8%, and the obtained manganese carbonate products were compliant with the industry standards. The ammonia released during the roasting process could be absorbed to regenerate (NH4)2SO4 and the final filtrate after evaporation and crystallization could be used to recycle (NH4)2SO4, both of which were used again into roasting process to reduce the consumption of raw material. In this process, the roasting temperature was only 420°C, which was significantly lower than the pyrometallurgical process suggested in earlier studies. [ABSTRACT FROM AUTHOR]

Fabrication of polysaccharide-supported metal oxide composites is effective in eliminating aqueous contaminants including dyes. Herein, a starch-fabricated pyrolusite (SFP) composite was successfully synthesized by copolymerization-induced grafting of starch with pyrolusite and was tested to remove malachite green (MG) dye from water. Here, sodium dodecyl sulfate (SDS) was used for cross-linker with pyrolusite, and ammonium persulfate (APS) was instrumental for grafting initiator with starch and pyrolusite. The synthesized SFP was obtained as a dark brown powder and was analyzed by powder XRD, SEM, BET surface area, pHzpc, HRTEM, and FTIR. An excellent maximum adsorption capacity was found (170 mg.g−1) at neutral pH. The adsorption kinetics could be best described by pseudo-second-order and multi-step intra-particle-diffusion model Langmuir isotherm best describes (R2 = 0.999) the adsorption pathway, suggesting a monolayer process. The negative thermodynamic parameters suggest a spontaneous (∆G value – 18.893 kJ/mol to – 26.635 kJ/mol), endothermic, and feasible process. A high degree of regeneration, (87%), and cyclic reusability is advantageous. A comparison with contemporary adsorbents affirms the efficacy of the material. [ABSTRACT FROM AUTHOR]

The mechanism involved in the phase transformation process of pyrolusite (MnO2) during roasting in a reducing atmosphere was systematically elucidated in this study, with the aim of effectively using low-grade complex manganese ore resources. According to single-factor experiment results, the roasted product with a divalent manganese (Mn2+) distribution rate of 95.30% was obtained at a roasting time of 25 min, a roasting temperature of 700°C, a CO concentration of 20at%, and a total gas volume of 500 mL·min−1, in which the manganese was mainly in the form of manganosite (MnO). Scanning electron microscopy and Brunauer–Emmett–Teller theory demonstrated the microstructural evolution of the roasted product and the gradual reduction in the pyrolusite ore from the surface to the core. Thermodynamic calculations, X-ray photoelectron spectroscopy, and X-ray diffractometry analyses determined that the phase transformation of pyrolusite followed the order of MnO2→Mn2O3→Mn3O4→MnO phase by phase, and the reduction of manganese oxides in each valence state proceeded simultaneously. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South-Central Minzu University (Natural Science Edition) is the property of Journal of South-Central Minzu University (Natural Science Edition) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the shortage of high-quality raw materials and increasingly strict environmental regulations, the recovery of metals from copper slag and pyrolusite has become a research hotspot. A novel method for simultaneously extracting Mn and Fe from pyrolusite and copper slag has been proposed. Under the optimal conditions (Copper slag / Pyrolusite = 2, H2SO4 = 2 M, liquid—solid ratio = 10, T = 90 ℃, holding time = 60 min), the leaching efficiencies of Mn and Fe can reach 98.28% and 99.04%, respectively. In addition, the treated residue containing 60.04 wt% SiO2 can be used as a raw building material. Through chemical kinetics and mineralogical transformation analyses, Fe2SiO4 in copper slag decomposes to release Fe2+, which can reduce and leach Mn from pyrolusite. The unreacted shrinkage nuclear reaction model under the control of the surface chemical reaction is the most suitable model to describe the process, and when the apparent activation energy is 35.50 kJ/mol, the apparent rate equation is: 1 - 1 - × 1 / 3 = 979.65 CS / Pyrolusite 2.6072 H 4 SO 4 1.3143 L / S 0.5649 e xp - 35.50 / RT [ABSTRACT FROM AUTHOR]

In this paper, manganese is used as a medium to connect pyrolusite with lithium-ion batteries, which not only meets the needs of comprehensive utilization of global strategic mineral resources, but also maximizes the performance of lithium-ion batteries under the goal of global carbon neutralization and carbon peak. Firstly, the optimum experimental conditions for sulfuric acid roasting of pyrolusite were investigated by single factor experiment and orthogonal experiment: the roasting temperature was 650 °C, the roasting time was 4 h, the acid-to-ore ratio was 2:1, and the water-to-ore ratio was 0.6:1. The roasting temperature plays a major role. Then, LMF x P-C (x = 0, 1/4, 1/8, 1/12, 1/24) cathode materials were prepared by adding different mass Fe elements with manganese element purified from pyrolusite as manganese source. Its electrochemical analysis was carried out: the capacity retention rate of LMF 1/4 P–C cathode material is 92.54% after 500 cycles. After a total of 150 times of rate tests at different rates, the discharge specific capacity of LMF 1/4 P–C can still reach 148.5 mAh g−1. At the same time, the EIS results show that the values of R e and R ct of LMF 1/4 P–C cathode material are the smallest compared with other materials. Finally, the LMF x P-C cathode material was analyzed by first-principles, and the optimal Fe doping amount was theoretically predicted. The crystal structure, bonding and density of states of the LMF x P-C cathode material were calculated and discussed. The results show that when the Fe doping amount is 1/4, the LMF x P-C system has the highest conductivity and the best electrochemical performance. The calculation results are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Manganese oxides have influential sorptive properties to efficiently sequester metals, such as uranium. Sorption can become complicated by metal chelating siderophores, which create a ternary system that is capable of multiple feasible mechanisms. This study analyzes the sorption behavior of desferrioxamine B (DFOB) and desferrioxamine D (DFOD) onto pyrolusite, β-MnO2, in the presence of U(VI) at pHs 6 and 8. The electrostatic adsorption performance is shown to have a 23% difference between the DFOB and DFOD surface sorption at pH 6. Inner-sphere coordination was identified through hydrolysis products of succinate and acetate. Together, these behaviors indicate a ternary complex system where both metals and ligands interact with the surface. Therefore, uranium in the environment can be attenuated by the conditions of a complex configuration involving multiple species and functional groups. This mechanism needs to be considered for any future modeling or strategies involving radionuclide remediation. [ABSTRACT FROM AUTHOR]

Manganese compounds have a toxic effect on the human body. Therefore, its content in drinking water should not exceed 0.05–0.1 mg/L, according to the hygienic standards of most countries. The concentration of manganese ions in some underground waters is 0.5–2 mg/L and can reach 6–10 mg/L in some cases. A method for the purification of drinking water from manganese by catalytic oxidation on modified pyrolusite is developed in this study. For this, the particles of crushed natural mineral pyrolusite are coated with a layer of inorganic and organic polymers (polysilicic acid and polymethyl methacrylate), which makes it possible to obtain dispersed particles with high structural stability in an aqueous medium. The filtering characteristics of modified pyrolusite with respect to soluble manganese compounds that are contained in aqueous solutions are evaluated. It is established the protective coating increases the structural stability of crushed pyrolusite and makes it possible to increase the specific volume of water purified from Mn2+ to maximum permissible concentration levels without reducing the pressure loss on the filter and to increase the value of the sorption capacity of the filter material with respect to Mn2+. The filtering material made of modified pyrolusite allows one to additionally purify tap water from colored organic substances present in it (estimated by the optical density of water), simultaneously with manganese. [ABSTRACT FROM AUTHOR]

To solve the problem of environmental pollution, Distiller's dried grains (DDGS), a biomass, is used as a clean reducing agent for the leaching process of pyrolusite. Experimental results have shown that the leaching rate of manganese can reach 92.1% with the optimized conditions including a sulfuric acid concentration of 3.5 mol/L, a DDGS to pyrolusite ratio of 0.4, a liquid–solid ratio of 3 mL/g, a temperature of 363K, a time of 3 h, and a rotation speed of 400 rpm. This article explored the mechanism of the entire leaching process: the crude fiber in DDGS is hydrolyzed into reducing sugars, and the MnO2 in pyrolusite undergoes an oxidation–reduction reaction to generate Mn2+ and studied the kinetics of the leaching process following the unreacted shrinkage nuclear reaction model controlled by the surface chemical reaction (1-(1-X)1/3 = kt). The equation of leaching kinetics is 1−1−X13=3738.06·[H2SO4]0.57·[LS]0.78·[DDGSpyrolusite]0.25·[rpm]0.09·exp(−48.448/(RT)) This work provides a green and effective leaching process for the leaching of pyrolusite.

A very low concentration of manganese (Mn) in water is a critical issue for municipal and industrial water supply systems. Mn removal technology is based on the use of manganese oxides (MnOx), especially manganese dioxide (MnO2) polymorphs, under different conditions of pH and ionic strength (water salinity). The statistical significance of the impact of polymorph type (akhtenskite ε-MnO2, birnessite δ-MnO2, cryptomelane α-MnO2 and pyrolusite β-MnO2), pH (2–9) and ionic strength (1–50 mmol/L) of solution on the adsorption level of Mn was investigated. The analysis of variance and the non-parametric Kruskal–Wallis H test were applied. Before and after Mn adsorption, the tested polymorphs were characterized using X-ray diffraction, scanning electron microscope techniques and gas porosimetry analysis. Here we demonstrated the significant differences in adsorption level between MnO2 polymorphs' type and pH; however, the statistical analysis proves that the type of MnO2 has a four times stronger influence. There was no statistical significance for the ionic strength parameter. We showed that the high adsorption of Mn on the poorly crystalline polymorphs leads to the blockage of micropores in akhtenskite and, contrary, causes the development of the surface structure of birnessite. At the same time, no changes in the surfaces of cryptomelane and pyrolusite, the highly crystalline polymorphs, were found due to the very small loading by the adsorbate. [ABSTRACT FROM AUTHOR]

• A method of ball-milled Fe doping to strengthen the SO 2 -resistant and As 2 O 3 (g) removal performance of PY has been invented. • Adsorption of As 2 O 3 (g) by PY was improved by doping Fe into PY through ball milling. • The As 2 O 3 (g) adsorption capacity of 10Fe/PY is 20.90 mg/g at SO 2 concentration of 7.5 v/v%, which is 1.4 times that of PY. Arsenic pollution in the atmosphere caused by smelting flue gas is a huge environmental challenge, and the removal of gaseous arsenic (As 2 O 3 (g)) from smelting flue gas is a matter of urgency. Adsorption has been shown to be an effective method for the removal of As 2 O 3 (g) from high temperature smelting flue gas. However, due to the high concentration of SO 2 in smelting flue gas, the capture of As 2 O 3 (g) by adsorbents is inhibited. In previous studies, the mechanism by which SO 2 affects the adsorption of As 2 O 3 (g) by pyrolusite (PY) has been clearly elucidated. Therefore, this study proposes a method to improve PY's resistance to SO 2 and its As 2 O 3 (g) removal efficiency through Fe modification. Under optimal preparation conditions, the 10Fe/PY adsorbent exhibited an adsorption capacity for As 2 O 3 (g) that was nearly uninhibited by SO 2. The 10Fe/PY achieving an adsorption capacity of 20.90 mg/g under 7.5 v/v% SO 2 , which is 1.4 times that of PY. The doped Fe increased the active sites on the 10Fe/PY surface for As 2 O 3 (g) adsorption, while preferentially reacting with SO 2 to form Fe 2 (SO 4) 3 , thereby reducing the competition between SO 2 and As 2 O 3 (g) for the active sites on the adsorbent. The findings provide a theoretical basis for the adsorption and removal of As 2 O 3 (g) from high-SO 2 smelting flue gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adsorption and oxidation capabilities of pyrolusite is synchronously intensified. • A substantial efficiency increment of 30.6 % is obtained after HNO 3 -etching. • Stability, sulfur/water resistance and regenerated performance are enhanced. • Performance enhancement mechanism is speculated systematically. Using natural low-grade pyrolusite as a novel Hg0 absorbent has economic and environmental benefits, but faces the challenge of restricted adsorption and oxidation capacity. Herein, a HNO 3 -etching strategy is employed to modify the physicochemical property. Characterizations and relevant theoretical calculations reveal the etching's role: (i) dissolving impurities and adjusting pore structure, which magnify pre-adsorption capacity of reactants and facilitate mutual mass transfer; (ii) creating more oxygen vacancies and promoting electron transfer, which favor the adsorption-dissociation of O 2 and the migration of more O-containing species; (iii) increasing reaction rate and lowering energy barrier. The 12-hour experimental results show that the removal efficiency of Hg0 can reach 92.8 % through etching, and the increment of 30.6 % reflects the huge promotion of etching on mercury removal. Moreover, the etching also improves the stability, sulfur/water resistance and regeneration performance. Furthermore, the desorption temperature of HgO diminishes after etching, as the etching enhances the activity of O ads and O lat. By contrasting the preferential and co-adsorption pathways on pristine/defective surfaces, alterations in adsorption mechanism are revealed, further elucidating the effects of increased defects on the enhanced Hg0 oxidation activity. This work offers a practical strategy to synchronously achieve structural optimization and defect construction of pyrolusite, thereby enhancing its removal performance, which holds potential implications for industrial applications in mitigating mercury emissions. [ABSTRACT FROM AUTHOR]

• Battery-grade MnSO 4 obtained from low - grade pyrolusite via high efficiency and cost-effective innovative scheme. • The preparation of battery-grade MnSO 4 by self-oxidation in-situ removal technology was successfully realized. • Pyrolusite self-oxidative in-situ removal of K, Na and Fe require no additional oxidant. • The dissolved impurity ions were all removed in situ according to the ascending order of the precipitation pH of them. As an essential crucial intermediate in the green new energy, achieving sufficient global supply of battery-grade manganese sulfate holds significant strategic importance. However, high efficiency and cost-effective preparation of battery-grade manganese sulfate and efficiently removing impurity ions pose highly challenging. Herein, an innovative self-oxidation in-situ removal scheme successfully prepared battery-grade MnSO 4 from low-grade pyrolusite. Specifically, during the purification of qualified MnSO 4 , abundant Fe3+ was generated in situ through the self-oxidation of pyrolusite without the need for additional oxidants. This significantly facilitated the formation of jarosite (XFe 3 [SO 4 (OH) 3 ] 2 , X=K/Na), greatly enhancing the removal efficiency of K, Na, and Fe (99.69 %, 99.82 % and 99.99 %), and promoted the removal of subsequent impurity ions. Subsequently, the dissolved impurity ions were successively removed in-situ using industrial reagents, achieving technical indices (Cu 99.93 %, Co 99.73 %, Cd 93.26 %, Zn 99.50 %, Ni 98.42 %, Al 99.71 %, Si 98.67 %, Ca 99.82 %, Mg 97.90 %, and F 99.78 %) that are far superior to those of battery-grade MnSO 4.This fruitful innovative scheme has promising commercia prospects and is conducive to the efficient and low-cost comprehensive utilization of global pyrolusite resource. [ABSTRACT FROM AUTHOR]

Pyrolusite modified carbon was prepared from walnut shell for enhancing removal of Cu(II) from aqueous solution. 1% pyrolusite addition was proved to be efficient and economic on adsorption capacity improvement of the produced carbon. Cu(II) removal rate on the modified walnut shell-based carbon was ca. 20% higher than the unmodified one, while the adsorption capacity for the modified carbon was high up to 34.4 mg/g. Within weakly acidic pH range (pH = 5 ~ 6), it was suitable for Cu(II) adsorption with larger than 97% removal rate on the produced carbon. SEM and BET analysis showed that pyrolusite played an important role on pore formation of the produced carbon. The specific surface area, mesopore and micropore volume of the modified carbon were 27.2%, 39.5%, 17.5%, respectively, higher than those of the unmodified one. After modification, oxygen-containing functional groups, especially phenol and carbonyl groups, were remarkably increased on the produced carbon, which were helpful for Cu(II)'s adsorption. FTIR showed that a large amount of organic carbon was decomposed into inorganic carbon skeleton during the carbonisation process, thus forming a large number of pores, and was conducive to adsorbing copper ions. This work is expected to be helpful for an effective agricultural residue management and innovative modification of walnut shell-based adsorbent as low-cost precursors for heavy metal treatment. [ABSTRACT FROM AUTHOR]

The data in this work provides the effect of aging temperature on manganese oxide allotropes prepared by hydrothermal method in the presence of boron dopant. The synthesized samples were labeled as B/Mn x O y -100, B/Mn x O y -150, and B/Mn x O y -180 corresponding to the hydrothermal temperature at 100, 150, and 180 °C, respectively. X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS) methods were conducted to clarify the crystalline structure, as well as the amount of potassium, manganese, and boron elements in the three synthesized samples. Major cryptomelane crystal was achieved at 100 °C of aging temperature for B/Mn x O y -100 sample. Pyrolusite which was detected as impurity phase over B/Mn x O y -150 powder was characterized as main crystalline phase for B/Mn x O y -180 sample. ICP-MS analysis proved an absence of potassium element only for the B/Mn x O y -180 sample being in comprised of a push of potassium cations out the tunnel system of cryptomelane structure. Furthermore, scanning electron microscope (SEM) images evidenced noticeably morphological change from cryptomelane nanorods (for B/Mn x O y -100) to pyrolusite slabs (for B/Mn x O y -180) while increasing the aging hydrothermal condition from 100 to 180 °C. Size distribution diagrams were defined with the assistance of ImageJ and were plotted in Origin software. The diameter of nanorods were 14.8 ± 0.3 nm for B/Mn x O y -100 and 17.2 ± 0.4 nm for B/Mn x O y -150 while that was 100.3 ± 2.5 nm for B/Mn x O y -180 sample indicating an aggregation of nanorods into slabs at 180 °C of aging temperature. Formaldehyde conversion data were collected and computed with a gas chromatograph flame ionization detector (GC-FID) instrument. The B/Mn x O y -180 material deteriorated into formaldehyde degradation at 80 °C of oxidation reaction temperature suggesting an inactivated pyrolusite phase for catalytic oxidation. The formaldehyde removal efficiency over the B/Mn x O y -100 material reached 28.4 ± 1.2 % and 36.9 ± 0.9 % at 80 and 100 °C, respectively offering an active cryptomelane-phase of B/Mn x O y -100 for formaldehyde abatement at low reaction temperature. Altogether, the current data provided valuable insights into the influence of aging temperature on the crystalline of manganese oxide-based materials and a feasibly catalytic performance of B/Mn x O y -100 cryptomelane in formaldehyde elimination., (© 2024 The Author(s).)

There is a substantial production increase especially in the iron-steel industry, which is the main consumption area of manganese ores, besides battery and chemical industries. However, it is seen that high-grade raw material resources are decreasing with the increasing demand in the world. For this reason, presenting low-grade ores to the industry as raw materials is of importance today. In this study, in order to evaluate the low-grade manganese reserves in Turkey, classification and enrichment experiments with a roll-type dry magnetic separator were carried out on manganese ore from İzmir-Karaburun region. First, after grinding (size reduction) and classification processes, the ore was divided into three different size fractions as -1150+850, -850+425 and -425+150μm then the effect of size on magnetic separation performance was investigated. As a result of magnetic separation tests, a concentrate with 69.39% recovery and 39.42% Mn grade was obtained from the coarse size fraction feed having 17,21% Mn. In the mid-size fraction, a concentrate with a recovery of 78.25% and 31.30% Mn grade was obtained from the feed containing 15.15% Mn, while obtaining a magnetic product with a recovery of 86.97% and 28.56% Mn grade from the fine size fraction feed containing 16.85% Mn. When the results obtained were examined, it was determined that the concentrate obtained in the coarse-grained fraction with a grade of 39.42% Mn was determined to be a salable product for the iron-steel industry, while additional concentration studies were required for other size ranges.

The basis of the traditional technology of hydrometallurgical processing of manganese ore is the process of ore roasting. The results obtained in this article make it possible to exclude the roasting process and directly leach the crushed ore under the action of an electric current. The process of electrochemical leaching includes two simultaneous operations: reduction of hard-soluble higher manganese oxides (pyrolusite - MnO2, vernadite - MnO2- nH2O) in an acid medium and transition of reduced manganese into an aqueous solution. The main part of the reduction process of higher manganese oxides proceeds in the Fe2+ ↔ Fe3+ catalytic system, the remaining part proceeds at the cathode under stirring. The degree of influence of iron (III) ions was determined. During studies on the transfer of manganese into solution from manganese ore by electrochemical leaching, the influence of L:S: ratio, sulfuric acid concentration, and cathodic current density on the degree of manganese extraction were studied. As a result of electrochemical leaching studies in the presence of the catalyst system, Fe2+ ↔ Fe3+ under optimal electrolysis parameters the degree of manganese extraction was 99%. [ABSTRACT FROM AUTHOR]

Purpose. This paper aims to understand the genesis and nature of the manganese ore deposits associated with the Ras Samra Member of the Um Bogma Formation in the southwest of Sinai. Methods. Mineralogical and geochemical studies of 50 selected samples of manganese ores and host shale have been conducted. These samples have been taken from different sites representing the Ras Samra Member. Findings. The dominant manganese minerals are pyrolusite and hausmannite. In most samples, helvite and hematite are noted in association with pyrolusite. In the investigated manganese ores, wide ranges of MnO (17.70-81.90 wt. %) and Fe2O3 (1.16-65.49 wt. %) concentrations are observed. Based on their Mn/Fe ratio, they can be classified into high-Mn ore content (76.94-6.46%), medium-Mn ore content (4.87-2.58%), and low-Mn ore content (1.51-0.30%). Originality. The compositions of major and trace elements in Ras Samra manganese ores, together with their textures and mineralogical compositions, suggest an epigenetic hydrothermal contribution for high-Mn ores, as well as syngenetic sedimentary precipitation for medium- Mn and low-Mn ores. The epigenetic nature of the high-Mn samples may be related to a younger phase of hydrothermal activity associated with Tertiary basalt flows. Ore-bearing hypogene solutions, which penetrate the bedding planes, have impregnated and cemented non-diagenetic terrigenous sandstones and shale. Practical implications. In contrast to low-Mn ores, high-Mn and medium-Mn ores of Um Bogma are preferable for obtaining a significant economic effect in the production of ferromanganese alloys. However, low-Mn ores need to be processed appropriately to achieve the desired quality in order to meet the present level of manganese demand in Egypt. [ABSTRACT FROM AUTHOR]

Titanium dioxide industry produces a large amount of titanium white waste acid every year. In this work, to make full use of and recover valuable components in titanium white waste acid, a processing for recovery of Ti from titanium white waste acid with N1923 extraction and leaching of low‐grade pyrolusite using raffinate was proposed. After a two‐stage countercurrent extraction, 99.93% Ti was extracted, while 6.51% Fe,.11% Mg,.06% Mn, and.08% Al were co‐extracted under N1923 concentration of 25% and phase ratio (O/A) of 2/1. The scrubbing efficiency of iron reached 98.53%, while the loss efficiency of titanium was only.94% with 1.5 mol/L sulfuric acid solution under the phase ratio of 1/1. Then, the Ti‐loaded organic phase could be effectively stripped by.8 mol/L ammonia water; the single‐stage stripping efficiency of titanium was 99.23%. Subsequently, the raffinate could be used for the extraction of manganese from low‐grade pyrolusite. The leaching efficiency of manganese was 99.39% at the S/L ratio of 48.00 g/L, leaching temperature of 50°C, and leaching time of 40 min. In addition, thermodynamic calculations revealed that the titanium extraction process by N1923 from titanium white waste acid was an exothermic reaction. The proposed approach is suitable for co‐recovery of titanium from titanium white waste acid and manganese from low‐grade pyrolusite. [ABSTRACT FROM AUTHOR]

Manganese sulfate is widely used in electrolytic manganese production, catalysts, batteries, and other fields. However, the preparation of manganese sulfate from conventional roasting process of pyrolusite with additive of pyrite has disadvantages including long roasting time and low efficiency. Thus, microwave heating is used as an alternative for the preparation of manganese sulfate instead of traditional heating to destroy the dense structure of minerals and to further improve the heating efficiency which is dominating by dielectric properties of the material. Therefore, to evaluate the mechanism of preparation of manganese sulfate with microwave heating, experiments were carried out to explore the dielectric and thermochemical properties of pyrolusite-pyrite mixture at high temperature. The dielectric properties of pyrolusite-pyrite mixtures with different ratios were measured at high temperature using the resonant cavity perturbation technique, which has been widely used to study the dielectric properties of different metallurgical materials. It was found that with the increase of temperature, the microwave absorption properties of pure pyrolusite decreased from 28.173 F/M to 25.931 F/M. The wave-absorbing property of the soft pyrite/pyrite mixture increased to 41.218 F/M, indicating that pyrite can obviously improve the wave-absorbing property of the mixture. In addition, the characteristics of pyrolysis and reduction were studied systematically, and the pyrolysis and reduction process was divided into four stages according to the difference of temperature: 30 ℃-200 ℃, 200 ℃-400 ℃, 400 ℃-600 ℃, 600 ℃-900 ℃, corresponding to the separation of adsorbed water and bound water, MnO2 decomposition, desulfurization redox reaction of FeS2 and desulfurization redox reaction of Fe(1-x) S, respectively. This work highlights the possibility of reducing manganese ore by microwave heating with an additive of pyrite and finds that pyrite can modify the microwave absorption properties of pyrolusite.

The unique characteristics of sulfurous river sediment located in Ungaran, Indonesia, are a reservoir of novel fungi with manganese bioleaching properties. Fungi are known to produce metabolic organic acids that have a potential for the industrial application of leaching metal from the ores. This application has high advantages, including low cost, low energy, and creates minimal environmental damage. Therefore, this research was performed to analyze the manganese bioleaching activities of two fungal isolates (KA2B2 and KB4B) from Indonesian sulfurous river sediment on pyrolusite and determine their phenotypic characters. These activities were investigated in terms of changes in fungal biomass, soluble manganese concentration, pH reduction, and organic acid production during 16 days of leaching. Soluble manganese concentrations were measured by atomic absorption spectrometry (AAS), whereas organic acid concentrations were analyzed by high-performance liquid chromatography (HPLC). According to bioleaching investigations, KA2B2 strain was more efficient than KB4B1 strain in extracting manganese from 0.02 g/cm3 pyrolusite. It also produced higher levels of organic acids, such as oxalic acid and citric acid, than KB4B1 strain, proving that strain of KA2B2 could be used to extract manganese from pyrolusite. Based on the phenotypic characters, both strains were identified as genus Penicillium.

The two most common polymorphs of MnO2, ramsdellite and pyrolusite, are often found in natural association. Our starting sample is from the Mistake mine (Arizona) containing macroscopic crystals of both ramsdellite (a = 4.5131(6), b = 9.2689(13), c = 2.8610(4) Å, V = 119.69(3) Å3; S.G. Pbmn) and pyrolusite (a = 4.4030(2), c = 2.87392(16) Å, V = 55.715(5) Å3; S.G. P42/mnm), along with a smaller amount of “groutellite”. A mixed powder was used to study the ramsdellite→pyrolusite transformation by in situ high-temperature X-ray powder diffraction. Our results reveal that this transformation is not a direct transition, but it occurs in two steps, as a function of temperature; ramsdellite transforms into an amorphous phase, which then recrystallizes into pyrolusite. Amorphization of ramsdellite and crystallization of pyrolusite kinetics were studied by the universal equation for solid–solid reactions. The two activation energies are comparable, but the pre-exponential factor of the ramsdellite amorphization is two orders of magnitude larger than pyrolusite crystallization’s. As a consequence, ramsdellite→pyrolusite transformation implies the formation of an amorphous transition, due to a mismatch between the conversion rates, that reaches its maximum at around 630 K and then decreases at higher T, when pyrolusite crystallization is strongly promoted. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering & Architectural Faculty of Eskisehir Osmangazi University / Eskişehir Osmangazi Üniversitesi Mühendislik ve Mimarlık Fakültesi Dergisi is the property of Eskisehir Osmangazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Removal of gaseous arsenic from copper smelting flue gas by solid-phase adsorption effectively reduces the emission of arsenic-containing pollutants into the atmosphere. Nevertheless, the high concentration of SO 2 in the flue gas unavoidably impacts the effectiveness of the adsorbent in capturing gaseous arsenic. Currently, there is no research focusing on the adsorption capacity of pyrolusite (PY) for As 2 O 3 (g), including the influence of SO 2. This study examines the capacities of PY to capture As 2 O 3 (g) with and without SO 2 under different conditions and delves into the mechanism by which SO 2 affects the capture of As 2 O 3 (g) by PY. Compared to the states without SO 2 , the As 2 O 3 (g) capture by PY in an atmosphere containing SO 2 (2.5 v/v% SO 2) decreased to 89.1 % at 400 °C. SO 2 can diminish the As 2 O 3 (g) capture capacity of PY by competing for active sites, generating sulfate (MnSO 4), inhibiting arsenic oxidation, and obstructing the pores of the adsorbent. In addition, SO 2 enhances PY's As 2 O 3 (g) capture capacity by creating (As 2 O 2)SO 4 and forming new active centers. Moreover, the phase transition of PY guided by the high concentration of SO 2 during As 2 O 3 (g) capture also favors arsenic capture. This research confirms that PY has substantial potential for effectively removing As 2 O 3 (g) from high-SO 2 flue gas. [Display omitted] [ABSTRACT FROM AUTHOR]

Biohydrometallurgy is an increasingly popular ore extraction technology and is especially applicable for low-grade ores. In particular, Acidithiobacillus ferrooxidans (A. ferrooxidans) is by far the most widely used bioleaching microorganism for leaching ores, including for sulfide ores and manganese dioxide ores. At present, many works are focused on the vital facilitating role of A. ferrooxidans in the cycles of sulfur and iron for sulfide ores bioleaching. However, research on the effect of A. ferrooxidans on manganese dioxide ores leaching is limited. The effects of A. ferrooxidans on the electrochemistry behavior of pyrolusite in simulated solutions (9K basic medium, A. ferrooxidans, Fe(Ⅲ), A. ferrooxidans+Fe(Ⅲ)) were investigated using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. Mott-Schottky curves were utilized to determine the passive film formed on the surface of pyrolusite ore in the presence or absence of bacteria bath solutions. The results show that A. ferrooxidans promotes the redox of MnO2/Mn2+ and triggers the reaction of MnO2/Mn(OH)2. A. ferrooxidans accelerates electron exchange between pyrolusite and solution; in the A. ferrooxidans-simulated solution, the charge-transfer reaction resistance of manganese dioxide is 34% lower than that of the control (9K) and 11% lower than that of the Fe(Ⅲ) solution. Germs cause polarization of pyrolusite, leading to an increase in oxidative activity of manganese dioxide. Bacteria facilitate the transformation of MnO2 to MnO·OH and is beneficial to its diffusion. The indirect action mechanism is adopted to explain the interaction between A. ferrooxidans and pyrolusite. The passive films formed in simulated solutions exhibit p-n-p-n type semiconductor properties at the polarization potential of 0.2 V when pH is 2.0, and the depletion layer of pyrolusite appears between 0.2 and 0.4 V. Introducing A.ferrooxidans to the Fe(Ⅲ)-free solution decreases the donor density and the acceptor density because bacteria contain a variety of groups involved in electron transfer, which accept free electrons or fill holes, prompting the exchange of species between manganese oxide and solution. Admixing A. ferrooxidans to Fe(Ⅲ)-containing solution increases carrier density, reducing the corrosion resistance of membrane. The corrosion rate of pyrolusite increases with the addition of A. ferrooxidans.

The hydrothermal treatment of neutral and acidified KMnO4 solutions at concentration of 0.037–0.093 mol/L and temperature of 120, 170, and 220°С for 24 h leads to selective synthesis of three different manganese dioxide modifications: α-MnO2, δ-MnO2, and β-MnO2. The temperature of hydrothermal treatment and medium acidity has been shown to affect considerably the phase composition of KMnO4 reduction products and reaction yield. The obtained samples of MnO2 have been characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and diffuse reflectance spectroscopy. [ABSTRACT FROM AUTHOR]

Cold, binder-free tableting experiments under controlled pressure (0-450 MPa), water addition (0-10 wt.%) and pH (4, 11) were performed on powder of pyrolusite ore concentrates, refined hausmannite, bentonite, kaolinite, as well as blends of those materials. It has been shown that increased pressure was beneficial for agglomeration of oxide materials, but pressure > 250 MPa triggered an elastic recovery in the clay minerals. Water addition up to 4 wt.% improved tabletability, increasing diametral resistance and reducing elastic recovery and fines generation. Amounts above 6 wt.% decreased diametral resistance. The presence of layered-structure minerals (such as montmorillonite, kaolinite, lithiophorite) appeared to be key to determine the agglomeration potential of a sample. This study also showed that tableting provides good performances for recycling industrial manganese oxide fines by obtaining industrial-grade resistance for tablets made with an 80/20 pyrolusite concentrate/hausmannite blends and 4 wt.% H 2 O. Unlabelled Image • Tableting presents an alternative recycling process for Mn processing fines. • Mn refining and laterite ore fines can be recycled at 20/80 wt.% with 4 wt.% H 2 O. • Soft, plastic material with high specific surface area is key for good tableting. • Lithiophorite acts as natural binder in tableting due to its layered structure. • Prediction of fines tableting behavior requires a deep understanding of materials. [ABSTRACT FROM AUTHOR]

The final disposal of tailings in the form of paste is a technological alternative. The objective of the present study is to obtain knowledge and compare different operational conditions that are favorable to the production of paste with the fine tailings generated after final desliming stage, obtained from the processing of metallic and non-metallic ores. The sample tailings, despite having a specific weight and similar granulometry, presented different behaviors related to the formation of paste. The minerals calcite and dolomite were predominant in the phosphate tailings while in the manganese tailings, there were pyrolusite and kaolinite. The used column thickener with the best operational conditions found to obtain a maximum concentration of solids after 3 hours of continuous thickening: 55% (manganese tailing) and 70% (phosphate tailing), with values of yield stress around 100 Pa and 300 Pa respectively. This indicates that the pumping conditions are not the same. According to the slump and flume tests, it was possible to preliminary estimate the reduction of the disposal area and the recovery of process water considering the case of a final disposal paste. [ABSTRACT FROM AUTHOR]

Activated carbons were prepared from sewage sludge by chemical activation with pyrolusite (PAC) to develop an efficient adsorbent for phosphate removal from aqueous solution. One percent (wt.) pyrolusite addition was proved to have an important effect on pore formation of the produced carbon. PAC showed 17.06% larger Brunauer–Emmett–Teller (BET) surface area than the sewage sludge-based activated carbon without modification (SAC). The adsorption results showed that the phosphate removal by PAC was 13% higher than SAC's. The adsorption experiments also showed that PAC had very good performance with high phosphate removal rate (ca. 90%) in a wide pH range (pH = 4–8), and could be stable after 30 min reaction. Adsorption isotherm and kinetics studies demonstrated that phosphate adsorption onto the modified adsorbent was well fitted by the Langmuir isotherm and could be described by the pseudo-second-order kinetic model. The modified sewage sludge-based activated carbons were effective and alternative adsorbents for the removal of phosphorus from aqueous solution due to their considerable adsorptive capacities and the low-cost renewable sources.

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Copyright of Hydrometallurgy of China is the property of Hydrometallurgy of China Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microwave heating is a developing noncontact heating method in dewatering technology. It has been proved to be effective to dewater high moisture content in mineral substance via the application of the dielectric loss of materials. In this study, the effects of microwave power levels (250–550 W) and different sample masses (20–40 g) on microwave drying behavior of pyrolusite have been investigated. For the purpose of the mechanism and morphological changes to the pyrolusite in the process of drying, thermogravimetric analysis, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) were used, respectively. The experiment results demonstrated that an increase in the microwave power as well as sample mass was found to increase the drying rate during pyrolusite drying processes, with there are four main mass loss stages from 20 to 900 °C. The SEM-EDS analysis results show that morphological changes with the presence of more pores and appearance in spiral cross-linking way reduced the particle size and the shrinkage of the faces and edges, in which it can been concluded that the microwave drying is an effective method to produce the high-grade pyrolusite. By analysis, the increased pore structure and shrinkage phenomena can be observed, which increase the specific surface area of manganese ore effectively and may benefit the subsequent reduction process of high valence manganese, after the process of microwave heating. [ABSTRACT FROM AUTHOR]

Copyright of Mining & Metallurgy (10057854) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The preparation of nanostructured MnO 2 from low-grade pyrolusite using a H 2 SO 4 roasting-water leaching process without any reducing agent is studied in this paper. In the second step of our study, we synthesize different morphologies of MnO 2 created by hydrothermal reactions by controlling the ferric ion concentration in the reaction system; this process does not require any surfactant, template or additional materials. X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical composition analysis are used to investigate the components and morphological structure of the roasting clinker by adjusting the roasting temperature. We discuss the effect of the ferric ion concentration in the filtrate on the phase structure, microstructure, specific surface area and electrochemical performance of the MnO 2. The results indicate that the ferric ion concentration has a significant influence on the morphology and internal structure of the MnO 2 products, which subsequently changes the specific surface area and electrochemical properties of the material. In the different nanostructured MnO 2 products, hollow γ-MnO 2 microspheres composed of small nanorods obtained from the MnSO 4 solution of 500 °C exhibit the highest specific surface area (63.9 m2 g−1). The studied sample presents excellent electrochemical behavior for supercapacitor applications. The proposed approach is simple, economical and reasonable, and therefore provides new ideas for the sustainable development of low-grade pyrolusite. [ABSTRACT FROM AUTHOR]