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This study investigated the geochemical controls on selenium mobility by two forms of birnessite mineral, focusing on the influence of pH, concentration, and the presence of cations. The research aimed to understand the dominant reaction mechanism (redox vs. sorption) under environmentally relevant selenium concentrations. Experiments were conducted to study the interaction of selenium with the birnessite minerals under varying conditions. The results demonstrated a significant shift in the dominant reaction mechanism from slow redox reactions observed at artificially elevated selenium concentrations to fast sorption processes at environmentally relevant concentrations, with second order rates increasing from 7.63 x 10-7 to 0.0224 L mol-1 h-1, respectively. This finding highlights the crucial role of selenium concentration in determining its interaction with birnessite minerals and emphasizes the importance of conducting research under realistic conditions to accurately predict selenium mobility and develop effective remediation strategies.

This study examined effective removal methods for high amounts of manganese (Mn) and zinc (Zn) in acid mine drainage (AMD) by addition of different neutralizing agents (NaOH and NaClO) and synthesized birnessite (δ-MnO2) using two-type AMD samples which Mn and Zn concentrations were 778 and 410 mg L−1 for A mine and 18.0 and 5.51 mg L−1 for B mines, respectively. The precipitation mechanism of these metal ions was investigated by geochemical modeling (PHREEQC) and X-ray absorption near edge structure (XANES) analysis. Mn concentrations were below the effluent standard (10 mg L−1) at pH 9–10 with the NaOH neutralization, whereas it was accomplished at lower pH (6–7) condition with the NaClO addition; it could act as an oxidizing agent, resulting that most of Mn precipitated as δ-MnO2. Zn concentrations decreased below the effluent standard (2 mg L−1) at pH 8–9 using both neutralizing agents. XANES analysis results indicated Zn was removed by the surface complexation formation on manganite and δ-MnO2 surface. More effective removal of Mn and Zn from AMD was found around pH 6 when a sufficient amount of δ-MnO2 was added to both AMD before the NaOH neutralization; a geochemical model coupling charge distribution multisite ion complexation revealed the triple-corner-sharing on δ-MnO2 was the most reasonable mechanism. Our result suggests that the presence of sufficient δ-MnO2 was the most effective for high Mn and Zn contents AMD treatment; however, ferrous ion (Fe2+) can inhibit the adsorption reaction and decompose δ-MnO2. Thus, pre-precipitation of Fe2+ is required to enhance the effect of δ-MnO2 on Mn and Zn removals from AMD.

Abstract Manganese(III/IV) oxide is a promising pseudocapacitive material for supercapacitor electrodes due to favorable attributes such as its chemical resilience, high earth abundance and low specific cost. Herein, the morphological, compositional and electrochemical characteristics of co‐precipitated manganese(III/IV) oxide products, each described by the general formula NaxKyMnOz, are investigated to establish how these properties are influenced by synthesis conditions. NaxKyMnOz growths in low‐temperature (

Mn(II)-oxidizing organisms promote the biomineralization of manganese oxides with specific textures, under ambient conditions. Controlling the phases formed and their texture on a larger scale may offer environmentally relevant routes to manganese oxide synthesis, with potential technological applications, for example, for energy storage. In the present study, we sought to use biofilms to promote the formation of electroactive minerals and to control the texture of these biominerals down to the electrode scale (i.e., cm scale). We used the bacterium Pseudomonas putida strain MnB1 which can produce manganese oxide in a biofilm. We characterized the biofilm–mineral assembly using a combination of electron microscopy, synchrotron-based X-ray absorption spectroscopy, X-ray diffraction, thermogravimetric analysis and electron paramagnetic resonance spectroscopy. Under optimized conditions of biofilm growth on the surface of current collectors, mineralogical characterizations revealed the formation of several minerals including a slightly crystalline MnOx birnessite. Electrochemical measurements in a half-cell against Li(0) revealed the electrochemical signature of the Mn4+/Mn3+ redox couple indicating the electroactivity of the biomineralized biofilm without any post-synthesis chemical, physical or thermal treatment. These results provide a better understanding of the properties of biomineralized biofilms and their possible use in designing new routes for one-pot electrode synthesis.

Abstract Mn-based rechargeable aqueous zinc-ion batteries (ZIBs) are highly promising because of their high operating voltages, attractive energy densities, and eco-friendliness. However, the electrochemical performances of Mn-based cathodes usually suffer from their serious structure transformation upon charge/discharge cycling. Herein, we report a layered sodium-ion/crystal water co-intercalated Birnessite cathode with the formula of Na0.55Mn2O4·0.57H2O (NMOH) for high-performance aqueous ZIBs. A displacement/intercalation electrochemical mechanism was confirmed in the Mn-based cathode for the first time. Na+ and crystal water enlarge the interlayer distance to enhance the insertion of Zn2+, and some sodium ions are replaced with Zn2+ in the first cycle to further stabilize the layered structure for subsequent reversible Zn2+/H+ insertion/extraction, resulting in exceptional specific capacities and satisfactory structural stabilities. Additionally, a pseudo-capacitance derived from the surface-adsorbed Na+ also contributes to the electrochemical performances. The NMOH cathode not only delivers high reversible capacities of 389.8 and 87.1 mA h g−1 at current densities of 200 and 1500 mA g−1, respectively, but also maintains a good long-cycling performance of 201.6 mA h g−1 at a high current density of 500 mA g−1 after 400 cycles, which makes the NMOH cathode competitive for practical applications.

Abstract The aim of this work was to study the effect of the microwave radiation on the thermal and spectroscopic features, as well as about arrangement (order-disorder) and morphological properties, of the layered manganese oxide with birnessite-type structure. The route employed to obtain Na-birnessite matrix was redox precipitation. The products were characterized by X-ray diffraction, thermal analysis (TG-DTG-DSC), infrared (FTIR) and Raman spectroscopy, scanning electron microscopy (SEM) and nitrogen adsorption-desorption technique. The results showed that microwave radiation influenced in a short time (5 min) the octahedral ordering of birnessite, as well as in increasing the crystallite size. Thermal analysis showed that the thermal behavior of the lamellar matrix was different from that of birnessite under microwave radiation. After microwave-assisted hydrothermal treatment, FTIR and Raman spectroscopy investigations were used to differentiate ordered and disordered birnessites. Otherwise, there were no changes in SEM morphology of the lamellar-type phases, but the particle size changed.

Birnessite nanoflowers composed of layers have been proven to be the strongest adsorbent and oxidant in the surface environment. However, the current synthesis methods of birnessite nanoflowers are suffering from long reaction time and high reaction temperature. Based on these, this paper explores a new method for the rapid and controlled synthesis of layered manganese oxides. The method relies on the molar ratios of KMnO4 and H2O2 redox reacting species to drive the production of birnessite nanoflowers under acidic conditions. The molar ratios of KMnO4 and H2O2 are the key to the crystal structure of the as-prepared. It was found that when the molar ratios of KMnO4 and H2O2 is from 1:1.25 to 1:1.90, the sample is birnessite nanoflowers, and when the ratio is increased to 1:2.0, the sample is a mixture of birnessite nanoflowers and feitknechtite nanoplates. Among the as-prepared samples, BF-1.85 (molar ratios of KMnO4 and H2O2 is 1:1.85) shows the highest capacity for Pb2+ adsorption (2,955 mmol/kg) and greatest degradation efficiency of phenol and TOC. The method proposed herein is economical and controllable, and it yields products with high efficiency for the elimination of inorganic and organic pollutants.

Manganese oxide is perspective material for selective removal of strontium ions from multicomponent solu-tions. Birnessite-type manganese oxide with the hexagonal disordered structure has been synthesized in the form of round microparticles. The synthesized samples have been tested for the removal of strontium ions from mono - and multicomponent solutions. It was found that birnessite can effectively remove strontium ions from mono-component solutions. The presence of alkaline metal ions (up to ~ 0.3 M) in the multicomponent solutions has no significant effect on adsorption; however, calcium ions (Ca/Sr ~ 30/1) lead to the considerable decrease in ad-sorption. The rather high adsorption parameters received in the experimental work allow to consider the synthe-sized birnessite as a sorbent with high selectivity towards strontium ions.

Fermentation and dissimilatory manganese (Mn) reduction are inter-related metabolic processes that microbes can perform in anoxic environments. Fermentation is less energetically favorable and is often not considered to compete for organic carbon with dissimilatory metal reduction. Therefore, the aim of our study was to investigate the outcome of the competition for lactate between fermentation and Mn oxide (birnessite) reduction in a mixed microbial community. A birnessite reducing enrichment culture was obtained from activated sludge with lactate and birnessite as the substrates. This enrichment was further used to test how various birnessite activities (0, 10, 20, and 40 mM) affected the rates of fermentation and metal reduction, as well as community composition. Increased birnessite activity led to a decrease of lactate consumption rate. Acetate and propionate were the main products. With increasing birnessite activity, the propionate/acetate ratio decreased from 1.4 to 0.47. Significant CO2 production was detected only in the absence of birnessite. In its presence, CO2 concentrations remained close to the background since most of the CO2 produced in these experiments was recovered as MnCO3. The Mn reduction efficiency (Mn(II) produced divided by birnessite added) was the highest at 10 mM birnessite added, where about 50% of added birnessite was reduced to Mn(II), whereas at 20 and 40 mM approximately 21 and 16% was reduced. The decreased birnessite reduction efficiency at higher birnessite activities points to inhibition by terminal electron acceptors and/or its toxicity which was also indicated by retarded lactate oxidation and decreased concentrations of microbial metabolites. Birnessite activity strongly affected microbial community structure. Firmicutes and Bacteroidetes were the most abundant phyla at 0 mM of birnessite. Their abundance was inversely correlated with birnessite concentration. The relative sequence abundance of Proteobacteria correlated with birnessite concentrations. Most of the enriched populations were involved in lactate/acetate or amino acid fermentation and the only previously known metal reducing genus detected was related to Shewanella sp. The sequencing data confirmed that lactate consumption coupled to metal reduction was only one of the processes occurring and did not outcompete fermentation processes.

The heterogeneous oxidation of Cr(III) to Cr(VI), a toxic inorganic anion, by a synthetic birnessite (δ-MnO2) was investigated in batch reactions using a combination of analytical techniques including UV–Vis spectrophotometry, microwave plasma–atomic emission spectrometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), to evaluate both the solution speciation of Cr(III)/Cr(VI) and the surface of the reacted δ-MnO2. The formation of dissolved Mn(II) was determined during the batch reactions to evaluate the extent and stoichiometry of the Cr(III) oxidation reaction. A stoichiometric 3:2 Mn(II):Cr(VI) molar relationship was observed in the reaction products. The reductive dissolution of the δ-MnO2 by Cr(III) resulted in a surface alteration from the conversion of Mn(IV) oxide to reduced Mn(II) and Mn(III) hydroxides. The results of this investigation show that naturally occurring Cr(III) will readily oxidize to Cr(VI) when it comes in contact with MnO2, forming a highly mobile and toxic groundwater contaminant.

The determination of reaction pathways and identification of products of pollutants degradation is central to photocatalytic environmental remediation. This work focuses on the photocatalytic degradation of the herbicide Imazapyr (2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl) pyridine-3-carboxylic acid) under UV-Vis and visible-only irradiation of aqueous suspensions of CaxMnOy-TiO2, and on the identification of the corresponding degradation pathways and reaction intermediates. CaxMnOy-TiO2 was formed by mixing CaxMnOy and TiO2 by mechanical grinding followed by annealing at 500 °C. A complete structural characterization of CaxMnOy-TiO2 was carried out. The photocatalytic activity of the hetero-nanostructures was determined using phenol and Imazapyr herbicide as model pollutants in a stirred tank reactor under UV-Vis and visible-only irradiation. Using equivalent loadings, CaxMnOy-TiO2 showed a higher rate (10.6 μM·h−1) as compared to unmodified TiO2 (7.4 μM·h−1) for Imazapyr degradation under UV-Vis irradiation. The mineralization rate was 4.07 µM·h−1 for CaxMnOy-TiO2 and 1.21 μM·h−1 for TiO2. In the CaxMnOy-TiO2 system, the concentration of intermediate products reached a maximum at 180 min of irradiation that then decreased to a half in 120 min. For unmodified TiO2, the intermediates continuously increased with irradiation time with no decrease observed in their concentration. The enhanced efficiency of the CaxMnOy-TiO2 for the complete degradation of the Imazapyr and intermediates is attributed to an increased adsorption of polar species on the surface of CaxMnOy. Based on LC-MS, photocatalytic degradation pathways for Imazapyr under UV-Vis irradiation have been proposed. Some photocatalytic degradation was obtained under visible-only irradiation for CaxMnOy-TiO2. Hydroxyl radicals were found to be main reactive oxygen species responsible for the photocatalytic degradation through radical scavenger investigations.

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.

The focus of this paper is centered on the thermal reduction of KMnO4 at controlled temperatures of 400 and 800 °C. The materials under study were characterized by atomic absorption spectroscopy, thermogravimetric analysis, average oxidation state of manganese, nitrogen adsorption−desorption, and impedance spectroscopy. The structural formulas, found as a result of these analyses, were K 0.29 + ( M n 0.84 4 + M n 0.16 3 + ) O 2.07 · 0.61 H 2 O and K 0.48 + ( M n 0.64 4 + M n 0.36 3 + ) O 2.06 · 0.50 H 2 O . The N2 adsorption−desorption isotherms show the microporous and mesoporous nature of the structure. Structural analysis showed that synthesis temperature affects the crystal size and symmetry, varying their electrical properties. Impedance spectroscopy (IS) was used to measure the electrical properties of these materials. The measurements attained, as a result of IS, show that these materials have both electronic and ionic conductivity. The conductivity values obtained at 10 Hz were 4.1250 × 10−6 and 1.6870 × 10−4 Ω−1cm−1 for Mn4 at 298 and 423 K respectively. For Mn8, the conductivity values at this frequency were 3.7074 × 10−7 (298) and 3.9866 × 10−5 Ω−1cm−1 (423 K). The electrical behavior was associated with electron hopping at high frequencies, and protonic conduction and ionic movement of the K+ species, in the interlayer region at low frequencies.

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.

Óxido hidróxido de manganês (γ - MnOOH) do tipo da manganita foi sintetizado por uma rota simples, em que a chave precursora K-birnessita foi preparada pelo método sol-gel. O tratamento hidrotermal da estrutura lamelar do tipo da birnessita favorece a obtenção de estruturas em túnel, sendo que o tamanho destes túneis depende das condições empregadas na síntese (pH, temperatura e tempo). A comprovação da formação de manganita sob as condições de síntese empregadas foi verificada pelas técnicas de difração de raios X, microscopia eletrônica de varredura, análises termogravimétrica e térmica diferencial e espectroscopia de infravermelho.Manganese oxyhydroxide (g - MnOOH) of the manganite type has been synthesized by a simple route with K-birnessite prepared by the sol-gel method. The hydrothermal treatment of the lamellar birnessite type structure facilitates the formation of tunnel structures where the size of the tunnels depends on the synthesis conditions (pH, temperature and time). The evidence of manganite formation under the synthesis conditions were made by X-ray diffraction, scanning electron microscopy, thermogravimetry, differential thermal analysis and infrared spectroscopy.

By means of X-rays diphractometric analyses on powders, we evidence an association of minerals in “Peştera cu Lilieci din satul Peştera”, made up of hydroxylapatite(carbonate-hydroxylapatite), brushite, taranakite, calcite, quartz, illite and birnessite

Birnessites containing Na+ or K+ in the interlayer have been prepared following a sol-gel method, with an initial glucose/cation ratio of 1 or 1.5. The solids have been submitted to ion exchange with Li+, Mg2+, and Cu2+, and all the materials have been characterised by several physicochemical techniques (elemental chemical analysis, X-ray diffraction, FT-IR spectroscopy, thermal analysis and specific surface area assessment). Total cation exchange was not achieved in any case, although sodium is better exchanged than potassium. Exchange is larger for Li+, lower for Cu2+ and even lower for Mg2+. Ionic exchange is topotactic, and the layered structure is maintained in all cases, with an interlayer spacing close to 7 Å. The samples are stable up to 600 °C; above this temperature cryptomelane (a 2x2 tunnel structure) is formed in most of the samples containing potassium, while LiMn2O4 spinel is formed is Li was present in the birnessite.Se han preparado birnesitas con Na+ o K+ en la interlámina mediante un método sol-gel, con una relación inicial glucosa/catión de 1 y 1.5. Estas muestras se han sometido a cambio iónico con los cationes Li+, Mg2+ y Cu2, caracterizando las muestras intercambiadas por diversas técnicas (análisis químico elemental, difracción de rayos X, espectroscopía FT-IR, análisis térmico y determinación de superficie específica). En ningún caso se alcanza un cambio iónico completo de los iones sodio o potasio iniciales, aunque el sodio se intercambia en mayor medida que el potasio. El intercambio es más efectivo al incorporar el Li+, menor en el caso del Cu2+ y menos eficiente, todavía, al incorporar Mg2+. El cambio iónico se produce topotácticamente, manteniéndose en todos los casos la estructura laminar con una distancia interlaminar de, aproximadamente, 7 Å. Las muestras son estables hasta 600 ºC; a partir de esta temperatura se produce la transformación a estructura túnel 2x2 (criptomelano) en el caso de la birnesita de K y a la espinela de Li-Mn (LiMn2O4) en el caso de tener Li en la interlámina.

Synthesis and physicochemical characterization (elemental chemical analysis, powder X-ray diffraction, FT-IR spectroscopy, thermal analysis and specific surface area determination) of Na, K and Li birnessites are described. The ionic exchange abilities of these materials have been studied, and the exchanged samples have been characterized following the same experimental techniques. An almost complete ionic exchange has been observed for Li, while exchange for Cu and Mg is rather low, probably because of ionic radii differences.Se describe la preparación y caracterización fisicoquímica por diversas técnicas (análisis químico elemental, difracción de rayos X, espectroscopía FT-IR, análisis térmico y determinación de superficie específica) de birnesitas de Na, K y Li preparadas por diversos métodos. Asimismo, se han estudiado sus propiedades de cambio iónico, caracterizando las muestras intercambiadas por las mismas técnicas. Se ha encontrado que el intercambio es prácticamente total en el caso del Li, mientras que en el caso de Cu y Mg el porcentaje intercambiado es relativamente bajo.

Resumo O presente trabalho descreve um estudo comparativo das propriedades química e mineralógica de birnessita natural (BIR-AZ) proveniente da mina do Azul (Província Mineral de Carajás, Brasil) e seu análogo sintético obtido pelo método sol-gel (K-OL-SG). As caracterizações foram realizadas por difração de raios X, espectroscopia FT-Raman, análise térmica (TG-DTA), microscopia eletrônica de varredura e análise química. Os resultados confirmam a presença das fases lamelares com sistema monoclínico, grupo espacial C2/m e com os seguintes parâmetros de cela unitária: BIR-AZ, a = 5,148 Å; b=2,843 Å, c=7,175 Å e β = 100,75º; K-OL-SG, a = 5,150 Å; b = 2,846 Å, c = 7,214 Å e β = 101,29º. Birnessita possui estabilidade térmica próxima a 600 ºC, enquanto seu análogo sintético acima de 900 ºC. Bandas obtidas por espectroscopia Raman foram observadas a 635, 570 e 410 cm-1 e atribuídas às deformações Mn-O e K-O na estrutura lamelar. O estudo da morfologia dos produtos revela que birnessita se apresenta como folhas tabulares de 1 a 5 µm, enquanto que o composto sintético possui morfologia em glóbulos (< 1 μm) dispostos aleatoriamente.