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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.

Biogenic Mn oxides (BMOs) have become captivating with regard to elemental sequestration, especially at circumneutral pH conditions. The interaction of BMOs with oxyanions, such as vanadate (V), molybdate (VI), and tungstate (VI), remains uncertain. This study examined the sequestration of V(V), Mo(VI), and W(VI) (up to ~1 mM) by BMOs formed by the Mn(II)-oxidizing fungus, Acremonium strictum KR21-2. When A. strictum KR21-2 was incubated in liquid cultures containing either Mo(VI) or W(VI) with soluble Mn2+, the oxyanions were sequestered in parallel with enzymatic Mn(II) oxidation with the maximum capacities of 8.8 mol% and 28.8 mol% (relative to solid Mn), respectively. More than 200 μM V(V) showed an inhibitory effect on growth and Mn(II) oxidizing ability. Sequestration experiments using preformed primary BMOs that maintained the enzymatic Mn(II) oxidizing activity, with and without exogenous Mn2+, demonstrated the ongoing BMO deposition in the presence of absorbent oxyanions provided a higher sequestration capacity than the preformed BMOs. X-ray diffraction displayed a larger decline of the peak arising from (001) basal reflection of turbostratic birnessite with increasing sequestration capacity. The results presented herein increase our understanding of the role of ongoing BMO formation in sequestration processes for oxyanion species at circumneutral pH conditions.

A cost-effective, iron- and manganese-oxide-supported clinoptilolite-based rock was prepared. Based on its nanoporous structure, it worked as a nanoreactor, thereby providing enhanced functionalities. The mono- and bimetallic Fe- and Mn-oxide-supported clinoptilolite was thoroughly characterized with thermoanalytical FT-IR, XRD, SEM, and XPS spectroscopy. All the spectral procedures that were used confirmed the occurrence of a new MnO2 phase (predominantly birnessite), including mostly amorphous iron oxi(hydr)oxide (FeO(OH)) species on the surface of the above-synthesized adsorbents. The synthesized products validated a considerably higher adsorption capacity toward Pb(II) pollutants compared to the natural clinoptilolite. The following order of a(max) toward Pb(II) was found: MnOx-zeolite (202.1 mg/g) &gt, FeO(OH)-MnOx-zeolite (101.3 mg/g) &gt, FeO(OH)-zeolite (80 mg/g) &gt, natural zeolite (54.9 mg/g). The adsorption equilibrium data were analyzed by the two-parameter empirical isotherm models Langmuir, Freundlich, and BET as well as the three-parameter Redlich–Peterson isotherm.

As one of the most appealing options for large-scale energy storage systems, the commercialization of aqueous zinc-ion batteries (AZIBs) has received considerable attention due to their cost effectiveness and inherent safety. A potential cathode material for the commercialization of AZIBs is the manganese-based cathode, but it suffers from poor cycle stability, owing to the Jahn–Teller effect, which leads to the dissolution of Mn in the electrolyte, as well as low electron/ion conductivity. In order to solve these problems, various strategies have been adopted to improve the stability of manganese-based cathode materials. Among those, the doping strategy has become popular, where the dopant is inserted into the intrinsic crystal structures of electrode materials, which would stabilize them and tune the electronic state of the redox center to realize high ion/electron transport. Herein, we summarize the ion doping strategy from the following aspects: (1) synthesis strategy of doped manganese-based oxides; (2) valence-dependent dopant ions in manganese-based oxides; (3) optimization mechanism of ion doping in zinc-manganese battery. Lastly, an in-depth understanding and future perspectives of ion doping strategy in electrode materials are provided for the commercialization of manganese-based zinc-ion batteries.

Iron and manganese are ubiquitous in the natural environment. FeII-FeIII layered double hydroxide, commonly called green rust (GR), and MnIII-MnIV birnessite (Bir) are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles. Moreover, ferromanganese solid compounds are potentially interesting materials for water treatment. Here, a {Fe(OH)2, FeIIaq} mixture was oxidized by Bir in sulphated aqueous media in the presence or absence of dissolved O2. In oxic conditions for an initial FeII/OH&minus, ratio of 0.6, a single GR phase was obtained in a first step, the oxidation kinetics being faster than without Bir. In a second step, GR was oxidised into various final products, mainly in a spinel structure. A partial substitution of Fe by Mn species was suspected in both GR and the spinel. In anoxic condition, GR was also observed but other by-products were concomitantly formed. All the oxidation products were characterized by XRD, XPS, and M&ouml, ssbauer spectroscopy. Hence, oxidation of FeII species by Bir can be considered as a new chemical pathway for producing ferromanganese spinels. Furthermore, these results suggest that Bir may participate in the formation of GR minerals.

Different types of ferromanganese coatings were collected from the Chinese mainland to study their mineralogical characteristics and semiconducting properties. Measurements, including by optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, micro-Raman spectrometer and transmission electron microscope, were employed to study their morphology, mineral assemblage, element abundance and distribution patterns. Soil Fe coatings are mainly composed of Al-rich hematite and clays. Soil Fe/Mn coatings can be divided into an outer belt rich in birnessite and an inner belt rich in hematite, goethite, ilmenite and magnetite. Goethite is the only component of rock Fe coatings. Rock Fe/Mn coatings mainly consist of birnessite and hematite, and alternating Fe/Mn-rich layers and Fe/Mn-poor layers can be observed. Powders were scraped off from the topmost part of ferromanganese coatings to conduct laboratory photochemical experiments. The photocurrent&ndash, time behavior indicates that natural coating electrodes exhibit an immediate increase in photocurrent intensity when exposed to light irradiation. Natural coatings can photo-catalytically degrade 14.3&ndash, 58.4% of methyl orange in 10 h. Under light irradiation, the photocurrent enhancement and organic degradation efficiency of the rock Fe/Mn coating, which has a close intergrowth structure of Fe and Mn components, is most significant. This phenomenon is attributed to the formation of semiconductor heterojunctions, which can promote the separation of electrons and holes. Terrestrial ferromanganese coatings are common in natural settings and rich in semiconducting Fe/Mn oxide minerals. Under solar light irradiation, these coatings can catalyze important photochemical processes and will thus have an impact on the surrounding environment.

A series of layered birnessite (AMn4O8) catalysts containing different alkali cations (A = H+, Li+, Na+, K+, Rb+, or Cs+) was synthesized. The materials were thoroughly characterized using X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, Raman spectroscopy, specific surface area analysis, work function, thermogravimetry/differential scanning calorimetry, and transmission electron microscopy. The catalytic activity in soot combustion in different reaction modes was investigated (tight contact, loose contact, loose contact with NO addition). The activity in the oxidation of light hydrocarbons was evaluated by tests with methane and propane. The obtained results revealed that alkali-promoted manganese oxides are highly catalytically active in oxidative reactions. In soot combustion, the reaction temperature window was shifted by 195 &deg, C, 205 &deg, C, and 90 &deg, C in tight, loose + NO, and loose contact conditions against uncatalyzed oxidation, respectively. The catalysts were similarly active in hydrocarbon combustion, achieving a 40% methane conversion at 600 &deg, C and a total propane conversion at ~450 &deg, C. It was illustrated that the difference in activity between tight and loose contacts can be successfully bridged in the presence of NO due to its facile transformation into NO2 over birnessite. The particular activity of birnessite with H+ cations paves the road for the further development of the active phase, aiming at alternative catalytic systems for efficient soot, light hydrocarbons, and volatile organic compounds removal in the conditions present in combustion engine exhaust gases.

Sodium and magnesium batteries with intercalation electrodes are currently alternatives of great interest to lithium in stationary applications, such as distribution networks or renewable energies. Hydrated laminar oxides such as birnessites are an attractive cathode material for these batteries. Sodium and potassium birnessite samples have been synthesized by thermal and hydrothermal oxidation methods. Hybrid electrochemical cells have been built using potassium birnessite in aqueous sodium electrolyte, when starting in discharge and with a capacity slightly higher than 70 mA h g&minus, 1. Hydrothermal synthesis generally shows slightly poorer electrochemical behavior than their thermal counterparts in both sodium and potassium batteries. The study on hybrid electrolytes has resulted in the successful galvanostatic cycling of both sodium birnessite and potassium birnessite in aqueous magnesium electrolyte, with maximum capacities of 85 and 50 mA h g&minus, 1, respectively.

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 ranci&egrave, ite. 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.

Manganese (Mn) is a major element in various aqueous and soil environments that is sometimes highly concentrated in mine water and other mineral processing wastewater. In this study, we investigated Mn removal from alkaline mine water (pH > 9) with an Mn-coated silica sand packed into a pilot-scale column reactor and examined the specific reaction mechanism using X-ray absorption near-edge structure (XANES) analysis and geochemical kinetic modeling. The kinetic effect of dissolved Mn(II) removal by birnessite (δ-Mn(IV)O2) at pH 6 and 8 was evaluated at different Mn(II)/Mn(IV) molar ratios of 0.1–10. Our results confirmed the positive effect of the presence of δ-MnO2 on the short-term removal (60 min) of dissolved Mn. XANES analysis results revealed that δ-MnO2 was more abundant than Mn(III)OOH in the reactor, which may have accumulated during a long-term reaction (4 months) after the reactor was turned on. A gradual decrease in dissolved Mn(II) concentration with depth was observed in the reactor, and comparison with the kinetic modeling result confirmed that δ-MnO2 interaction was the dominant Mn removal mechanism. Our results show that δ-MnO2 contents could play a significant role in controlling Mn removability from mine water in the reactor.

Plant nutrients such as potassium (K) may be limited in soil systems and additions (i.e., fertilizer) are commonly required. Glaucony is a widely distributed and abundant marine-derived clay mineral present in soils worldwide which may serve as a source of potassium. The South Island of New Zealand contains numerous deposits of glaucony-rich rocks and related soils providing an opportunity to explore how glaucony might be a beneficial source of potassium. Here, the geochemistry of glaucony and its suitability as a mineral source of soil K from four deposits in New Zealand was examined using spatially resolved chemical analyses and dissolution experiments. Geochemical and morphological analyses revealed that glaucony from all deposits were K-enriched and were of the evolved (6%&ndash, 8% K2O) to highly evolved type (&gt, 8% K2O). Glaucony derived from growth inside pellets contain elevated K and Fe concentrations compared to bioclast-hosted glaucony. Solubility analysis showed that K was released from glaucony at rates higher than any other metal present in the mineral. Additionally, decreasing the pH and introducing an oxidizing agent (i.e., birnessite which is ubiquitous in soil environments) appeared to accelerate K release. Trace metals including Cr, Zn, Cu, and Ni were present in the solid phase analysis, however, further investigation with a focus on Cr revealed that these elements were released into solution at low concentrations and may present a source of soil micronutrients. These results suggest that glaucony may offer a source of slow releasing K into soils, and so could be used as a locally sourced environmentally sustainable K resource for agriculture, whether in New Zealand or worldwide

Biogenic manganese oxides (BMOs) formed in a culture of the Mn(II)-oxidizing fungus Acremonium strictum strain KR21-2 are known to retain enzymatic Mn(II) oxidation activity. Consequently, these are increasingly attracting attention as a substrate for eliminating toxic elements from contaminated wastewaters. In this study, we examined the Ba2+ sequestration potential of enzymatically active BMOs with and without exogenous Mn2+. The BMOs readily oxidized exogenous Mn2+ to produce another BMO phase, and subsequently sequestered Ba2+ at a pH of 7.0, with irreversible Ba2+ sequestration as the dominant pathway. Extended X-ray absorption fine structure spectroscopy and X-ray diffraction analyses demonstrated alteration from turbostratic to tightly stacked birnessite through possible Ba2+ incorporation into the interlayer. The irreversible sequestration of Sr2+, Ca2+, and Mg2+ was insignificant, and the turbostratic birnessite structure was preserved. Results from competitive sequestration experiments revealed that the BMOs favored Ba2+ over Sr2+, Ca2+, and Mg2+. These results explain the preferential accumulation of Ba2+ in natural Mn oxide phases produced by microbes under circumneutral environmental conditions. These findings highlight the potential for applying enzymatically active BMOs for eliminating Ba2+ from contaminated wastewaters.

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.

The article is devoted to the evolution of structural, morphological, and sorption characteristics of layered manganese oxide (birnessite) under various conditions close to the real operating regime of the sorbents for radioactive waste processing. To identify the phase composition in the birnessites, we implemented XRD analysis, while SEM and temperature-programmed reduction (TPR) were used to study morphological and redox features of the materials, respectively. Structural changes after various kinds of treatment of birnessites were tracked using low temperature nitrogen sorption. Sorption characteristics were assessed under static and in dynamic conditions on the efficiency of Sr2+ removal from simulated seawater. TPR combined with kinetic analysis revealed the decrease of particle sizes in the birnessites after repeated use in sorption-regeneration cycle and reduction with hydrazine. Despite the fact that the porous structure of the materials remains preserved, the surface morphology of birnessite changes drastically depending on the reducing agent. Hydrazine treatment increases the sorption performance of the birnessite followed by degradation of mechanical properties, thus, preventing such sorbent from repeated use. Kinetic analysis of TPR allows quantifying differences in morphology and porous structure of manganese oxide materials. The specific surface area, amorphous surface structure, and accessibility of Mn+3 sites are the most important factors for birnessite sorption performance.

In this study, porous manganese oxide (MnOx) thin films were synthesized via electrostatic spray deposition (ESD) and evaluated as pseudocapacitive electrode materials in neutral aqueous media. Very interestingly, the gravimetric specific capacitance of the ESD-based electrodes underwent a marked enhancement upon electrochemical cycling, from 72 F∙g−1 to 225 F∙g−1, with a concomitant improvement in kinetics and conductivity. The change in capacitance and resistivity is attributed to a partial electrochemical phase transformation from the spinel-type hausmannite Mn3O4 to the conducting layered birnessite MnO2. Furthermore, the films were able to retain 88.4% of the maximal capacitance after 1000 cycles. Upon verifying the viability of the manganese oxide films for pseudocapacitive applications, the thin films were integrated onto carbon micro-pillars created via carbon microelectromechanical systems (C-MEMS) for examining their application as potential microelectrode candidates. In a symmetric two-electrode cell setup, the MnOx/C-MEMS microelectrodes were able to deliver specific capacitances as high as 0.055 F∙cm−2 and stack capacitances as high as 7.4 F·cm−3, with maximal stack energy and power densities of 0.51 mWh·cm−3 and 28.3 mW·cm−3, respectively. The excellent areal capacitance of the MnOx-MEs is attributed to the pseudocapacitive MnOx as well as the three-dimensional architectural framework provided by the carbon micro-pillars.

Manganese oxides are widespread in soils and natural waters, and their capacity to adsorb different trace metals such as Co, Ni, or Zn is well known. In this study, we aimed to compare the extent of trace metal coprecipitation in different Mn oxides formed during Mn(II) oxidation in highly concentrated, metal-rich mine waters. For this purpose, mine water samples collected from the deepest part of several acidic pit lakes in Spain (pH 2.7&ndash, 4.2), with very high concentration of manganese (358&ndash, 892 mg/L Mn) and trace metals (e.g., 795&ndash, 10,394 &micro, g/L Ni, 678&ndash, 11,081 &micro, g/L Co, 259&ndash, 624 mg/L Zn), were neutralized to pH 8.0 in the laboratory and later used for Mn(II) oxidation experiments. These waters were subsequently allowed to oxidize at room temperature and pH = 8.5&ndash, 9.0 over several weeks until Mn(II) was totally oxidized and a dense layer of manganese precipitates had been formed. These solids were characterized by different techniques for investigating the mineral phases formed and the amount of coprecipitated trace metals. All Mn oxides were fine-grained and poorly crystalline. Evidence from X-Ray Diffraction (XRD) and Scanning Electron Microscopy coupled to Energy Dispersive X-Ray Spectroscopy (SEM&ndash, EDX) suggests the formation of different manganese oxides with varying oxidation state ranging from Mn(III) (e.g., manganite) and Mn(III/IV) (e.g., birnessite, todorokite) to Mn(IV) (e.g., asbolane). Whole-precipitate analyses by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), and/or Atomic Absorption Spectrometry (AAS), provided important concentrations of trace metals in birnessite (e.g., up to 1424 ppm Co, 814 ppm Ni, and 2713 ppm Zn), while Co and Ni concentrations at weight percent units were detected in asbolane by SEM-EDX. This trace metal retention capacity is lower than that observed in natural Mn oxides (e.g., birnessite) formed in the water column in a circum-neutral pit lake (pH 7.0&ndash, 8.0), or in desautelsite obtained in previous neutralization experiments (pH 9.0&ndash, 10.0). However, given the very high amount of Mn sorbent material formed in the solutions (2.8&ndash, 4.6 g/L Mn oxide), the formation of these Mn(III/IV) oxides invariably led to the virtually total removal of Co, Ni, and Zn from the aqueous phase. We evaluate these data in the context of mine water pollution treatment and recovery of critical metals.

This work reports on the synthesis of layered manganese oxides (&delta, MnO2) and their possible application as cathode intercalation materials in Al-ion and Zn-ion batteries. By using a one-pot microwave-assisted synthesis route in 1.6 M KOH (MnVII:MnII = 0.33), a pure layered &delta, MnO2 birnessite phase without any hausmannite traces was obtained after only a 14 h reaction time period at 110 &deg, C. Attempts to enhance crystallinity level of as-prepared birnessite through increasing of reaction time up to 96 h in 1.6 M KOH failed and led to decreases in crystallinity and the emergence of an additional hausmannite phase. The influence of MnII:OH&minus, ratio (1:2 to 1:10) on phase crystallinity and hausmannite phase formation for 96 h reaction time was investigated as well. By increasing alkalinity of the reaction mixture up to 2.5 M KOH, a slight increase in crystallinity of birnessite phase was achieved, but hausmannite formation couldn&rsquo, t be inhibited as hoped. The as-prepared layered &delta, MnO2 powder material was spray-coated on a carbon paper and tested in laboratory cells with Al or Zn as active materials. The Al-ion tests were carried out in EMIMCl/AlCl3 while the Zn-Ion experiments were performed in water containing choline acetate (ChAcO) or a ZnSO4 solution. Best performance in terms of capacity was yielded in the Zn-ion cell (200 mWh g&minus, 1 for 20 cycles) compared to about 3 mAh g&minus, 1 for the Al-ion cell. The poor activity of the latter system was attributed to low dissociation rate of tetrachloroaluminate ions (AlCl4&minus, ) in the EMIMCl/AlCl3 mixture into positive Al complexes which are needed for charge compensation of the oxide-based cathode during the discharge step.