Mn Deposits Research Articles

Application of Machine Learning Algorithms to Classification of Pb–Zn Deposit Types Using LA–ICP–MS Data of Sphalerite

Pb–Zn deposits supply a significant proportion of critical metals, such as In, Ga, Ge, and Co. Due to the growing demand for critical metals, it is urgent to clarify the different types of Pb–Zn deposits to improve exploration. The trace element concentrations of sphalerite can be used to classify the types of Pb–Zn deposits. However, it is difficult to assess the multivariable system through simple data analysis directly. Here, we collected more than 2200 analyses with 14 elements (Mn, Fe, Co, Ni, Cu, Ga, Ge, Ag, Cd, In, Sn, Sb, Pb, and Bi) from 65 deposits, including 48 analyses from carbonate replacement (CR), 684 analyses from distal magmatic-hydrothermal (DMH), 197 analyses from epithermal, 456 analyses from Mississippi Valley-type (MVT), 199 analyses from sedimentary exhalative (SEDEX), 377 analyses from skarn, and 322 analyses from volcanogenic massive sulfide (VMS) types of Pb–Zn deposits. The critical metals in different types of deposits are summarized. Machine learning algorithms, namely, decision tree (DT), K-nearest neighbors (KNN), naive Bayes (NB), random forest (RF), and support vector machine (SVM), are applied to process and explore the classification. Learning curves show that the DT and RF classifiers are the most suitable for classification. Testing of the DT and RF classifier yielded accuracies of 91.2% and 95.4%, respectively. In the DT classifier, the feature importances of trace elements suggest that Ni (0.22), Mn (0.17), Cd (0.13), Co (0.11), and Fe (0.09) are significant for classification. Furthermore, the visual DT graph shows that the Mn contents of sphalerite allow the division of the seven classes into three groups: (1) depleted in Mn, including MVT and CR types; (2) enriched in Mn, including epithermal, skarn, SEDEX, and VMS deposits; and (3) DMH deposits, which have variable Mn contents. Data mining also reveals that VMS and skarn deposits have distinct Co and Ni contents and that SEDEX and DMH deposits have different Ni and Ge contents. The optimal DT and RF classifiers are deployed at Streamlit cloud workspace. Researchers can select DT or RF classifier and input trace element data of sphalerite to classify the Pb–Zn deposit type.

Microbially-mediated Mn redox cycling and Mn carbonate precipitation in the Marinoan glacial aftermath, South China

Carbonate-type Mn deposits developed at the top of the Ediacaran Doushantuo Formation (Marinoan glacial aftermath) along the northern margin of the Yangtze Block, South China, provide an exceptional opportunity to study Mn redox cycling in deep time, which remains a controversial topic of Mn biogeochemistry. To address this issue, here we conduct integrated petrological and geochemical work. Results show that Mn oxidizing microorganisms may fix CO2 into organic matter by oxidizing Mn(II). This process provides energy for metabolism of the microorganisms under obligatory oxidation conditions in natural geological environments. At the same time, Mn(II) is oxidized to unstable todorokite, with accompanying Co and Ce oxidation and enrichment. Under suboxic conditions, heterotrophic Mn-reducing bacteria use organic matter as an electron donor and Mn bio-oxide as a terminal electron acceptor to generate Mn(II) and 12C-rich dissolved inorganic carbon (DIC; carbonate and/or bicarbonate). Furthermore, microorganisms and macroalgae also provide nucleation sites for the precipitation of Mn carbonate minerals with structures consistent with microbially precipitated carbonates. Spherical and ellipsoidal Ca-rich rhodochrosite was formed in the syngenetic stage and cemented by Mg-rich kutnohorite in the early diagenetic stage. Microorganisms thus play an important role in Mn redox cycling and precipitation of Mn carbonate minerals, in a possibly universal phenomenon in geological evolution. The bloom of microorganisms and associated formation of mineral deposits may be a general phenomenon in the aftermath of a glaciation.

Field Observations and Geophysical Research Applied to the Detection of Manganese (Mn) Deposits in the Eastern Part of Oban Massif, South-Eastern Nigeria: An Integrated Approach

The growing need for an industrialized world, especially in Africa, cannot be feasible without adequate mineral resources. Thus, the search for more mineral deposits will continue to be necessary. An integrated approach involving geological mapping and a high-resolution geophysical (aeromagnetic) investigation was conducted to assess the manganese mineralization in parts of the Oban Massif, southeast Nigeria. The aeromagnetic data were processed using regional-residual anomaly separation techniques, first vertical derivative (1VD), analytical signals, source parameters imaging (SPI), and Euler deconvolution to better understand magnetic source distributions and their depths of occurrence. The geological investigation revealed a dominant variety of metamorphic rock types, including migmatitic (banded) gneisses hornblende granite gneisses, amphibolites, charnockites, and some quartzite ridges. Also present are some indications of pockets of dolerites. The study area also observed epithermal Mn+Fe+Qtz vein type mineralization associated with hydrothermal alteration zones whose orientation coincides with dominant structural orientation from aeromagnetic interpretation. Analysis of aeromagnetic data shows that the study area is dominated by ENE, NNE, and E-W structural directions (near-surface basement structures), with the ENE trends related to mineralization in the area. The manganese mineralization within Oban Massif is structurally controlled. The depths of the magnetic anomalies in the study area were estimated using SPI and Euler decomposition algorithms. SPI delineated the shallow, intermediate, and deep magnetic anomalies at 84–142 m, 152–200 m, and 215–656 m, respectively. Euler decomposition, however, revealed that shallow, intermediate, and deep depths occurrence of the magnetic anomalies are at 200–377 m, 393–472 m, and 499–793 m, respectively.

Mesoproterozoic surface oxygenation accompanied major sedimentary manganese deposition at 1.4 and 1.1Ga.

Manganese (Mn) oxidation in marine environments requires oxygen (O2 ) or other reactive oxygen species in the water column, and widespread Mn oxide deposition in ancient sedimentary rocks has long been used as a proxy for oxidation. The oxygenation of Earth's atmosphere and oceans across the Archean-Proterozoic boundary are associated with massive Mn deposits, whereas the interval from 1.8-1.0Ga is generally believed to be a time of low atmospheric oxygen with an apparent hiatus in sedimentary Mn deposition. Here, we report geochemical and mineralogical analyses from 1.1Ga manganiferous marine-shelf siltstones from the Bangemall Supergroup, Western Australia, which underlie recently discovered economically significant manganese deposits. Layers bearing Mn carbonate microspheres, comparable with major global Mn deposits, reveal that intense periods of sedimentary Mn deposition occurred in the late Mesoproterozoic. Iron geochemical data suggest anoxic-ferruginous seafloor conditions at the onset of Mn deposition, followed by oxic conditions in the water column as Mn deposition persisted and eventually ceased. These data imply there was spatially widespread surface oxygenation ~1.1Ga with sufficiently oxic conditions in shelf environments to oxidize marine Mn(II). Comparable large stratiform Mn carbonate deposits also occur in ~1.4Ga marine siltstones hosted in underlying sedimentary units. These deposits are greater or at least commensurate in scale (tonnage) to those that followed the major oxygenation transitions from the Neoproterozoic. Such a period of sedimentary manganogenesis is inconsistent with a model of persistently low O2 throughout the entirety of the Mesoproterozoic and provides robust evidence for dynamic redox changes in the mid to late Mesoproterozoic.

Chloramine Prevents Manganese Accumulation in Drinking Water Pipes Compared to Free Chlorine by Simultaneously Inhibiting Abiotic and Biotic Mn(II) Oxidation

The oxidation of residual Mn(II) in finished water can lead to MnOx deposit formation in drinking water pipes. Previous work has illustrated that microbes readily cause Mn deposit build-up in nondisinfected pipes. Here, we investigated how disinfectant type and dose affected Mn(II) oxidation and MnOx accumulation through long-term pipe experiments using water produced by a full-scale water treatment plant. The results showed that Mn(II) oxidation initiated quickly in the new pipes chlorinated with 1.0 mg/L free chlorine. After 130 days of MnOx accumulation, 100 μg/L Mn(II) in water could drop to 1.0 μg/L within 1.5 h, resulting from autocatalytic Mn(II) oxidation and Mn(II) adsorption by MnOx deposits accumulated on pipe walls. In contrast to chlorination, chloramination (1.0 mg/L Cl2) caused almost no MnOx accumulation during the entire study period. The underlying mechanism was probably that monochloramine inhibited microbial Mn(II) oxidation without causing significant abiotic Mn(II) oxidation like free chlorine. A low free chlorine dose (0.3 mg/L) also reduced Mn deposit formation by mass but to a lesser extent than chloramination. After disinfection (chlorination or chloramination) was discontinued for days, biotic Mn(II) oxidation occurred, and this process was inhibited again once disinfection was resumed. In addition, Fe(III) of 200 μg/L enhanced the stability of MnOx accumulated on pipe surfaces, while humic acid induced MnOx deposit resuspension. Overall, this study highlighted the regulating role of disinfectants in MnOx formation and provided insights into developing appropriate disinfection strategies for Mn deposit control.

The recycling of pure metallic indium from waste LCD screens by a combined hydro-electrometallurgical method

The Liquid Crystal Display (LCD) panels were removed and crushed to be leached. Sulphuric acid of 0.25 M H2SO4 was found best for relatively fast reactions and selectivity, recovering >99% of the indium from the indium‑tin oxide (ITO) layers, while >95% of the tin content was left in the solid residue. As potential impurities, Sn, Fe, Mn, Ni, Zn, Bi, Pb, Al and Cu were analysed in the solutions and in the final product. Synthetic solutions of larger volumes corresponding to the obtained leachate were used for developing the purification and metal recovery steps. Metallic indium was extracted selectively from the solution by cementation on Al plates. The purity of the primary indium deposit was controlled by increasing the temperature to 50–60 °C and keeping the pH in the 0.25–0.5 range, while the aluminium consumption was close to the stoichiometric value. The cemented sponge was vacuum-melted to produce an indium anode block of >99.9% purity for electrorefining. According to the galvanostatic and potentiodynamic results, the optimal electrolyte conditions were found as 50 g/dm3 In, 1 M free Cl− ions, pH 1. The cathodic deposition of Zn, Mn, and Fe was negligible; however, the prior removal of Cu and Sn from the solution is required for producing high-purity indium. Generally, increasing the cathodic current density in the range of 150–600 A/m2 enhanced the purity of the cathodes, while a maximum pH 2 value should be assured. Chloride ion concentration strongly influences the deposit morphology.

Influence of Bi Content on the Temperature of the Formation of the Hard Magnetic MnBi Phase: Simultaneous Irreversible Drop of Resistance

Pulsed laser-deposited (PLD) MnBi films were fabricated by alternating deposition of Mn and Bi layers. In order to obtain the ferromagnetic MnBi phase, heat treatments were performed on the samples. Simultaneously, the resistance of the samples was monitored as a function of the temperature. Thus, on increasing the temperature, a steep decrease in the resistance of the films was observed, simultaneous to the onset of the formation of the MnBi phase. At room-temperature, these annealed samples showed a ferromagnetic behavior, as well as the presence of the characteristic LT-MnBi phase diffraction peaks in the X-ray diffraction patterns. The temperature of the generation of the MnBi phase depended on the relative concentration of Mn and Bi in the different samples: on increasing the Bi atomic concentration, the temperature of the generation of the MnBi phase decreased.

Lithium Occurrence in Italy—An Overview

Italy has no record of Li production, even though it is well known for its outstanding Li mineral specimens from the Elba Island pegmatites. Because of the current geopolitical situation, the opportunity for a systematic appraisal of resources is evident. Most European Li production comes from deposits associated with Late Paleozoic magmatic rocks. In Italy, such rocks occur extensively in Sardinia and Calabria, but their potential for Li is unknown, and deserves a more systematic exploration. Also of potential interest are the Permo–Triassic spodumene pegmatites in the Austroalpine units of the Central Alps. The Tertiary pegmatites (Elba Island and Central Alps) contain Li minerals, but do not appear large enough to warrant bulk mining. However, we notice that Tertiary–Quaternary magmatic rocks of the Tuscan and Roman magmatic provinces have systematically higher Li contents than those recorded in normal arc igneous rocks worldwide. Specifically, Tuscan granites contain up to 350 μg/g Li, mostly hosted by biotite (up to 4000 μg/g Li); the Capo Bianco aplite (Elba Island) contains up to 1000 μg/g. There are other small Li occurrences associated with Mn deposits and metabauxites, and there is a hypothetical potential for sediment-hosted deposits in the post-orogenic Lower Permian Alpine basins. However, the most promising potential seems to be associated with subsurface fluids. High-enthalpy fluids in geothermal fields may contain up to 480 mg/L Li. Lower-temperature thermal waters may also contain significant Li (>10 mg/L). Moreover, a visionary, but not impossible, perspective may consider a deep injection of water to interact with, and extract Li from, magmatic rocks.

Copper activated near-full two-electron Mn4+/Mn2+ redox for mild aqueous Zn/MnO2 battery

Compared with traditional one-electron Mn4+/Mn3+ redox couple (308 mAh g−1), two-electron Mn4+/Mn2+ redox mechanism doubles the theoretical capacity (616 mAh g−1) of Zn/MnO2 batteries. However, in most cases, activating the Mn4+/Mn2+ redox couple requires a low pH value, which often leads to corrosion issues. Herein, a binder-free Cu-doped ε-MnO2 (CMO) was synthesized through a facile electrodeposition method and the two-electron Mn4+/Mn2+ redox is achieved in near-neutral ZnSO4 electrolyte with a working potential window of 0.8–1.9 V. Detailed characterizations demonstrate that the synergistic effect between Cu and Mn can boost the further reduction of Mn4+ and Mn3+ to dissoluble Mn2+ below 1.1 V. Compared with the capacity of ε-MnO2 (MO, 282.4 mAh g−1), which mainly involves Mn4+/Mn3+ redox couple, the CMO cathode demonstrates an improved specific capacity of 397.4 mAh g−1 at 0.2 A g−1. Besides, the fast reaction kinetics of H+ insertion, Mn dissolution, and Mn deposition reactions endow CMO with excellent rate performance, achieving a high specific capacity of 298.9 mAh g−1 at 5 A g−1.

Low Level of Dietary Organic Trace Minerals Improved Egg Quality and Modulated the Status of Eggshell Gland and Intestinal Microflora of Laying Hens During the Late Production Stage.

This study aimed to investigate the effects of dietary organic trace minerals on egg quality and intestinal microflora of laying hens during the late production stage. In total, 1,080 Jinghong-1 laying hens aged 57 weeks were randomly assigned to five treatment groups: CON, basal diet containing about 6, 29, 49, and 308 mg·kg−1 of Cu, Mn, Zn, and Fe; IT100, basal diet supplemented with 10, 80, 80, and 60 mg·kg−1 of Cu, Mn, Zn, and Fe (each as inorganic sulfates), respectively; OT20, basal diet supplemented with 2, 16, 16, and 12 mg·kg−1 of Cu, Mn, Zn, and Fe (each as organic trace minerals chelated with lysine and methionine in the ratio of 2:1 amino acid: organic trace minerals), respectively; OT30, basal diet supplemented with 3, 24, 24, and 18 mg·kg−1 of organic Cu, Mn, Zn, and Fe, respectively; and OT50, basal diet supplemented with 5, 40, 40, and 30 mg·kg−1 of organic Cu, Mn, Zn, and Fe, respectively. Overall, OT20, OT30, and OT50 had equal or higher potential to promote Cu, Mn, Zn, and Fe deposition in egg yolks compared with IT100. In addition, OT50 enhanced the eggshell breaking strength and the antioxidant status of the eggshell gland. Cecal microbiota, including Barnesiellaceae and Clostridia, were significantly decreased in IT100- and OT50-treated hens compared with the CON group. Clostridia UCG-014 was negatively correlated with eggshell weight and OCX-32. In conclusion, reduced supplementation of organic trace minerals can improve the eggshell quality and trace mineral deposition, possibly by modulating genes involved in the eggshell formation in the eggshell gland and by controling of the potentially harmful bacteria Barnesiellaceae and Clostridiales in the cecum. Inorganic trace minerals may be effectively replaced by low level of complex organic trace minerals in laying hens during the late production stage.

Rare earth elements and origin of Fe[sbnd]Mn ores from the Lower Carboniferous Um Bogma Formation, Southwest Sinai, Egypt: A mixed source of metals and multiple formation processes

The economic FeMn ores of the Lower Carboniferous Um Bogma Formation, Southwest Sinai are an important mineral resource, and are also of interest because of their significant enrichment in Cu and U compared to other Phanerozoic Mn deposits. However, their origin remains controversial. Genetic theories range from sedimentary, to hydrothermal, to karst and to laterization origins. This study integrates geological, sedimentological, mineralogical, and geochemical data, particularly rare earth elements, to elucidate the origin of these deposits. Field relations showed the occurrence of FeMn deposits as lenses of Mn-rich material surrounded by Fe-rich clastic deposits, which then are overlain by dolostones, which, in the subsurface, are known to also contain MnFe lenses. The occurrence of the largest of these deposits at a major transgressive surface is consistent with syndepositional Mn mineralization, but not of ironstones. Geochemical proxies, based on modern hydrothermal, diagenetic and hydrogeneous Mn deposits, are mixed: some suggest a hydrogenous and some a hydrothermal source of Fe and Mn. The sweater (hydrogenous) source of Mn and Fe is indicated by the plotting of these ores in the hydrogenous field of the SiAl discrimination plot, by high ΣREE (42–327 ppm), low La/Ce ratios (0.261.5), relatively high Y/Ho ratios for Mn but not for Fe (averages of 35 and 28), and positive YSN anomalies (1–1.8). The ores plot in the sweater fields of the (La/Sm)SN-(La/Yb)SN and (Sm/Yb)SN-Y/Ho diagrams, which also supports this interpretation. However, the hydrothermal input to the source of these ores cannot be ignored and is indicated by high Ba, Cu, Zn, and by high LREE/HREE ratio as well as the plotting of the FeMn samples in the hydrothermal field of the Fe-Mn-(Ni + Co + Cu)*10, (Co + Ni)-(As+Cu + Mo + Pb + V + Zn), (Co + Ni + Cu)-Co/Zn, CeSN/CeSN*-YSN/HoSN and CeSN/CeSN*-NdSN diagrams. In addition, lower Er/Nd ratios than that of seawater and similarity of REE parameters such as ΣREY, Nd and CeSN/CeSN* between the diagenetic FeMn nodules and the FeMn ores of Um Bogma Formation suggest a post-depositional overprint on the REEs geochemistry of these ores. We propose, as most consistent with the evidence from tectonic subsidence history, sequence stratigraphy, and our geochemical-mineralogical data combined with that of others, an initial synsedimentary deposition of Mn, derived from a distally-located back-arc spreading center where modified seawater at relatively low temperature was the hydrothermal fluid released into the surrounding seawater. This plume of Mn-rich water, which can be far-travelled, deposited Mn on the unconformity surface during a rapid transgression. This accumulation of Mn was subsequently modified and significantly upgraded during karstification of the host dolostones soon after deposition of the dolostones. It is likely that the Fe was introduced at this stage via low-oxygen ground water flow along with As and possibly Ba. Finally, much later, there was a flow of warm, saline oxidizing water through the dolomitic aquifer that precipitated Cu, U and Zn in the weathered material accumulated in the karst cavities.

Source Characteristics of the Carboniferous Ortokarnash Manganese Deposit in the Western Kunlun Mountains

The specific source of ancient sedimentary manganese (Mn) deposits is commonly complex. Here we use systematic major and trace element data with strontium (Sr) and neodymium (Nd) isotopic analyses of the Ortokarnash Mn(II) carbonate ores and associated carbonate rocks from the Upper Carboniferous Kalaatehe Formation (ca. 320 Ma) in order to constrain the Mn source. This formation consists of three members: the first member is a volcanic breccia limestone, the second member is a sandy limestone, and the third member is a black marlstone with the Mn(II) carbonate interlayers. Petrographic observations in combination with low Al2O3 (<3.0 wt%) and Hf (<0.40 ppm) contents and the lack of correlations between the Al2O3 and 87Sr/86Sr ratios as well as εNd(t) values demonstrate a negligible influence of terrigenous detrital contamination on both Sr and Nd isotopic compositions of the Mn(II) carbonate ores. The Sr isotopes of Mn(II) carbonate ores are most likely affected by post-depositional alteration, while Nd isotopes remain unaltered. The initial 87Sr/86Sr ratios in the associated carbonate rocks are likely the result of a mixture of the chemical components (i.e., seawater) and the Al-rich components (e.g., volcanoclastic material), while the detrital effects on Nd isotopes are negligible. In addition, both Sr and Nd isotopes in these non-mineralized wall rocks remained unchanged during post-depositional processes. The relatively low Th/Sc ratios and positive εNd(t) values suggest that the aluminosilicate fraction in the calcarenite and sandy limestone was mainly derived from the weathering of a depleted mafic source, representing the riverine input into the seawater. Given that the Mn(II) carbonate ores are characterized by negative εNd(t) values, these suggest that seafloor-vented hydrothermal fluids derived from interaction with the underlying old continental crust mainly contribute to the source of the Mn(II) carbonates.

Benthic megafauna habitats, community structure and environmental drivers at Rio Grande Rise (SW Atlantic)

The Rio Grande Rise (RGR) is a large and geomorphologically complex feature located in the Southwest Atlantic, with great commercial and scientific interest due to its potential for mining rare earth elements that are critical for low-carbon technologies. Brazilian interest in this area led to the submission of a petition to the UN Commission on the Limits of the Continental Shelf in 2018 to include RGR on the limits of its continental shelf beyond 200 nautical miles. However, mining activities are potentially harmful to deep-sea ecosystems and will likely cause some extent of biodiversity loss. Thus, baseline and continuous environmental studies in the RGR are important to address potential conflicts between mineral extraction and the conservation of deep-sea biodiversity. The RGR is characterized by a series of summit plateaus of ∼600 m deep divided NE-SW by a rift valley, up to 2000 m deep. In 2018, the plateaus and rift of a small area in RGR (30°35′S – 31°03′S, 35°36′W – 36°16′W) were explored through 13 dives of the robotic underwater vehicle (RUV) HyBIS. Videos were analyzed for the description of structuring factors (topography and habitat types) and to record benthic megafauna occurrences. Video transects revealed highly heterogeneous and rapidly changing habitats. Eleven habitats, five in the rift and six in the plateaus are proposed based on geomorphology, slope, and substrate textures. We recorded 17,008 megabenthic organisms classified in 83 morphotypes and six different phyla, from which Porifera (42.7%) and Cnidaria (41.5%) were the most representative. Samples were characterized by a high dominance and the dissimilarities result chiefly from differences in abundance scores. PERMANOVA tests indicated that Habitat and Region variables were the most important to explain structure within the community data, followed by depth and slope. The rift floor exhibited a low abundance of megabenthic epifauna, except in a sinkhole in the northern part of the rift. The lower and upper rift wall were characterized by different communities delimited by the transition between the Antarctic Intermediate Water and the Upper Circumpolar Deep Water. The habitats formed by Fe–Mn deposits were dominated by distinct communities, which were rarely observed elsewhere. Additionally, we found variations in community structure at regional scales (20–30 km), with distinct communities on each side of the rift and at the southwest of the study area. Our results contribute toward understanding the diversity, biogeography, and environmental drivers of the RGR. Fauna distribution is patchy, linked to habitats with potential mining resources, and dominated by Vulnerable Marine Ecosystems (VMEs) indicator taxa. Extensive community analysis should occur at a given site prior to consideration for the exploitation of natural resources.

Effect of manganese incorporation on the excitonic recombination dynamics in monolayer MoS2

Using x-ray photoelectron spectroscopy, atomic force microscopy, and Raman spectroscopy techniques, we investigate the incorporation of manganese (Mn) in monolayer (1L)-MoS2 grown on sapphire substrates by microcavity based chemical vapor deposition method. These layers are coated with different amounts of Mn by pulsed laser deposition technique. The study reveals two contrasting Mn-incorporation regimes. Below a threshold deposition amount, thin Mn-coating with large area coverage is found on MoS2 layers where substitution of Mo ions by Mn is detected through XPS. Dewetting takes place when Mn deposition crosses the critical mark, resulting in the formation of Mn-droplets on MoS2 layers. In this regime, substitutional incorporation of Mn is suppressed, while the Raman study suggests an enhancement of disorder in the lattice with the Mn deposition time. This knowledge can help us in tackling the challenge of doping of 2D transition metal dichalcogenides in general. From the temperature dependent photoluminescence study, it has been found that, even though Mn deposition enhances the density of non-radiative recombination channels for the excitons, the thermal barrier height for such recombinations to take place also rises. The study attributes these non-radiative transitions to Mo-related defects (Mo-vacancies and/or distorted Mo–S bonds), which are believed to be generated in large numbers during Mn-droplet formation stage.

Carbon Metabolism of a Soilborne Mn(II)-Oxidizing Escherichia coli Isolate Implicated as a Pronounced Modulator of Bacterial Mn Oxidation.

Mn(II)-oxidizing microorganisms are generally considered the primary driving forces in the biological formation of Mn oxides. However, the mechanistic elucidation of the actuation and regulation of Mn oxidation in soilborne bacteria remains elusive. Here, we performed joint multiple gene-knockout analyses and comparative morphological and physiological determinations to characterize the influence of carbon metabolism on the Mn oxide deposit amount (MnODA) and the Mn oxide formation of a soilborne bacterium, Escherichia coli MB266. Different carbon source substances exhibited significantly varied effects on the MnODA of MB266. A total of 16 carbon metabolism-related genes with significant variant expression levels under Mn supplementation conditions were knocked out in the MB266 genome accordingly, but only little effect on the MnODA of each mutant strain was accounted for. However, a simultaneous four-gene-knockout mutant (namely, MB801) showed an overall remarkable MnODA reduction and an initially delayed Mn oxide formation compared with the wild-type MB266. The assays using scanning/transmission electron microscopy verified that MB801 exhibited not only a delayed Mn-oxide aggregate processing, but also relatively smaller microspherical agglomerations, and presented flocculent deposit Mn oxides compared with normal fibrous and crystalline Mn oxides formed by MB266. Moreover, the Mn oxide aggregate formation was highly related to the intracellular ROS level. Thus, this study demonstrates that carbon metabolism acts as a pronounced modulator of MnODA in MB266, which will provide new insights into the occurrence of Mn oxidation and Mn oxide formation by soilborne bacteria in habitats where Mn(II) naturally occurs.

Metal enrichment and toxicity assessment through total and speciation of metals in lower and middle regions of tropical (Mandovi) Estuary, western coast of India.

The study aimed to understand the metal enrichment and toxicity in lower and middle regions of a tropical Mandovi Estuary, revealed metals dilution by coarser intertidal mudflat sediments in the lower estuary (downstream of the fishing jetty-core S). A relatively calm depositional environment prevailed at the middle estuary (core M) and also at the upstream of the jetty of the lower estuary (core L) facilitating deposition and enrichment of Mn and Zn in cores M and Mn, Cu and Co in core L. The distribution of trace metals in sediments was regulated by grain size, total organic carbon and Fe-Mn oxides. The potential contamination index indicated a moderate degree of metal contamination in sediments while the anthropogenic factor showed the signatures of human-induced activities in the enrichment of metals. The sequential extraction of metals showed bioavailability of Mn, Cu, Zn and Co. Fe-Mn oxide and organic/sulphide were key phases for the retention of bioavailable metals. The elevated level of these metals suggested possible toxicity to benthic biota, particularly from Mn (cores L and M) and Co (core L) according to the screening quick reference table.

Manganese Oxide Minerals from the Xiangtan Manganese Deposit in South China and Their Application in Formaldehyde Removal

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

Initial Formation and Accumulation of Manganese Deposits in Drinking Water Pipes: Investigating the Role of Microbial-Mediated Processes

Microbial Mn(II) oxidation occurs in areas with insufficient disinfectants in drinking water distribution systems. However, the overall processes of microbial-mediated Mn deposit formation are unclear. This research investigated the initial Mn(II) oxidation, deposit accumulation, and biofilm development in pipe loops fed with nondisinfected finished water for 300 days. The results show that it took 20 days for microbial Mn(II) oxidation and deposition to be initiated visibly in new pipes continuously receiving 100 μg/L Mn(II). Once started, the deposit accumulation accelerated. A pseudo-first-order kinetic model could simulate the disappearance of Mn(II) in well-mixed pipe loop water. The observed rate constant reached 2.81 h-1 [corresponding to a Mn(II) half-life of 0.25 h] after 136 days of operation. Without oxygen, Mn(II) in the water also decreased rapidly to 1.0 μg/L through adsorption to deposits, indicating that after the initial microbial formation of MnOx, subsequent MnOx accumulation was attributable to a combination of microbial and physicochemical processes. Compared to the no-Mn condition, Mn(II) input resulted in 1 order of magnitude increase in biofilm formation. This study sheds light on the increasingly rapid processes of Mn accumulation on the inner surfaces of water pipes resulting from the biological activity of Mn(II)-oxidizing biofilms and the build-up of MnOx with strong adsorption capacity.

Investigation on the fracture behaviour of wire arc additive manufactured rotor steel weldments after heat treatment

This paper discusses the additive welding of Cr-Mo steel weldment carried out with Cold Metal Transfer Technology (CMT). The mechanical characterization including fracture behaviour and metallography of the Wire Arc Additive Manufacture (WAAM) weldments in the As Welded (AW) and Post Weld Heat Treated (PWHT) conditions were investigated. The longitudinal and transverse orientations parallel to building and deposition directions respectively were found to influence the fracture behavior of weldments. The specimens of longitudinal direction showed lower toughness and tensile strength when compared to the specimens of transverse direction both in the case of AW and PWHT weldments. Orientation was also observed to influence the elastic–plastic fracture toughness (J integral) values both in the as welded and heat-treated specimens. Fracture topographical analysis of specimens carried out by Scanning Electron Microscope (SEM) in association with Energy Dispersive Spectroscopy (EDS) showed the presence of soft ductile features and Mn deposition respectively in the specimens of transverse direction and justified the findings.

Mineral paragenesis in Paleozoic manganese ore deposits: Depositional versus post-depositional formation processes

Unlike modern Mn(IV)-dominated manganese nodules, ancient manganese deposits primarily contain Mn(II) (manganous) mineral phases. The general assumption is that these manganous minerals formed post-depositionally from a Mn(IV) precursor phase during diagenesis and metamorphism. However, recent studies have shown that aqueous Mn(II) may combine with either CO32–(aq) or H4SiO4(aq) to nucleate and precipitate as primary manganous phases within anoxic waters. These findings thus make it difficult to assess what comprised the primary mineral assemblage of ancient Mn deposits, which in turn, has implications for understanding the redox fabric of the past marine water column. Here, we investigate the paragenesis and oxidation state of various Mn minerals (oxides, carbonates, and silicates) from the late Devonian Xialei and middle to late Permian Zunyi manganese deposits in South China. Through characterization of the micro-scale distribution, composition, and speciation of different Mn-bearing mineral phases, we provide evidence to support an oxidative mechanism during Mn cycling at the time of deposition. We document the presence of a residual oxide phase (hausmannite; Mn3O4) that represents a primary to early formed Mn(III)-bearing oxide preserved in Mn(II)-carbonate nodules. Additionally, we observe spherulitic textures comprised of mixed-valence Mn(II,III,IV)-silicates enclosed in diagenetic Mn(II)-carbonate laminations. Our results allow for the construction of a paragenetic model for these deposits beginning with the reduction of a primary Mn(IV) phase and the subsequent precipitation of intermediate Mn(III)-oxide or -silicate mineral phases. Following continued exposure to reducing conditions during early diagenesis, Mn(III)-oxides were then replaced by Mn(II)-carbonates. Similarly, Mn(III)-silicates were transformed into various Mn(II)-silicates during late-stage diagenesis and metamorphism. This model suggests that the accumulation of various divalent Mn mineral phases in ancient sediments may, therefore, be indicative of deposition under a water column with a sufficient oxidizing potential to induce Mn(II) oxidation.