Precipitation Of Mn Research Articles

High-Selective Separation Recovery of Ni, Co, and Mn from the Spent LIBs Via Acid Dissolution and Multistage Oxidation Precipitation.

For recovering Ni, Co, and Mn from lithium-ion batteries, traditional chemical precipitation methods demonstrate low selectivity and significantly contribute to environmental pollution. This study proposes a separation recovery technique for transition metals, specifically Ni, Co, and Mn, from spent LIBs, involving "acid dissolution" and "multistage oxidation precipitation". More than 98 % of transition metals can be extracted from spent LIBs using a low acid concentration (0.5 M) without reducing agents. The feasibility of separating different metals via multistage oxidation precipitation, based on their different electrode potentials for oxidizing Me2+ (Me=Mn/Co/Ni), was confirmed. The combination of oxidizing agent S2O8 2- and the precipitant OH- was universally applied to the fractional precipitation of Mn, Co, and Ni respectively. About 99 % of Mn, 97.06 % Co, and 96.62 % Ni could be precipitated sequentially by changing the concentrations of S2O8 2- and the pH value of solution. XRD, XPS, XRF, ICP-MS and other methods were employed to elucidate the mechanism behind the multistage oxidation precipitation of target metal compounds, exploiting the differential electrode potentials for oxidizing Me2+ ions. This technique surpasses traditional solvent extraction in cost-effectiveness and selectivity, showing promise for large-scale industrial applications in recovering Mn, Co, and Ni.

Effects of extrusion temperature on the microstructure and mechanical properties of low-alloyed Mg-Bi-Ca-Mn alloy

A new rare earth-free low-alloyed Mg-0.5Bi-0.8Ca-0.8Mn (wt.%) alloy was prepared at three extrusion temperatures (225, 250 and 275 °C). The effects of low-temperature extrusion on the microstructure and mechanical properties of the alloy were studied. Experimental results show that the dynamic recrystallization (DRX) grains are significantly refined by low-temperature extrusion, and the dynamic recrystallization process is further delayed by the Mn precipitate phase, resulting in a bimodal structure composed of ultrafine DRXed grains and coarse undynamic recrystallized (unDRXed) regions. At an extrusion temperature of 225 °C, the grain size was significantly refined, with an average DRXed grain size of 0.84 μm and a tensile yield strength of 418 MPa. Compared with other extruded magnesium alloys, the ultra-fine DRXed grains, strong basal fiber texture, high Schmid Factors of pyramidal <c + a> slip in the unDRXed regions, and along with a certain amount of second phase (Mg2Ca) distributed along the grain boundaries and nano-Mn particles uniformly distributed in the matrix, are the main reasons for the strength enhancement of low-temperature extruded magnesium alloys. The orientation of the DRXed grains in the alloy after extrusion at 250 °C is more random, which improves ductility. In addition, when the extrusion temperature reaches 275 °C, the alloy shows a fully recrystallized structure and exhibits rare earth (RE)-texture, obtaining high ductility but decreasing strength. This study provides a new idea for the development of high-strength Mg-Bi-based magnesium alloys by adjusting the extrusion temperature and alloying elements. This new high-strength and low-alloyed Mg-Bi-based alloy will help to enrich the series of high-performance, rare-earth free, low-cost extruded Mg alloy with certain application prospects.

Suspended particulate matter in the Gulf of Oman: Spatial variations in concentration, bulk composition, and particulate metals controlled by physical and biogeochemical processes

The present work aims to assess the biogeochemical and physical sources of variation in the spatial distribution of suspended particulate matter (SPM), its major biotic and abiotic components, particulate metals, and the Redfield (N:P) stoichiometry of particles in a poorly understood basin of the Gulf of Oman. Particulate samples were collected in February 2022 from the Gulf of Oman aboard the R/V Persian Gulf Explorer, revealing surface SPM concentrations ranging from 140 to 1145 μg/l. The elemental composition of crustal-type elements in the surface offshore region confirmed the input of lithogenic components by aeolian dust from the surrounding deserts. The highest mid-depth SPM levels, with remarkable contribution from CaCO3, were observed at the western shelf edge at 100–300 m depth, supported by the Persian Gulf outflow. Conversely, mid-depth maxima with elevated concentrations of terrigenous elements were observed in the eastern edge, emanating from sediment resuspension and lateral transport under eddy-topography interaction. Organic matter is the most important phase, followed by biogenic silica from the basin-wide winter bloom of diatoms. While signs of CaCO3 dissolution are evident at depths >500 m, the oxidative precipitation of Mn (II) in the upper boundary of the oxygen minimum zone leads to the appearance of perceptible maxima in the vertical profile of particulate MnO2. Seasonal variations in the organic N:P ratio, from summer to winter, at the western station were linked to shifts in phytoplankton assemblage structure, transitioning from cyanobacteria dominance in summer to chain-forming diatoms in winter. The particulate pool of biologically important trace metals was dominated by a non-crustal fraction with enrichment factor followed a descending order: Cd > Mo > Pb > Zn > Ni in surface offshore samples. Metal/P ratios comparison with some previous data from the open ocean SPM and lab cultures of phytoplankton reveals that the Zn/P ratio is significantly exceeded in cultured communities, whereas the Cd/P ratio reflected the consistent demand in the Gulf of Oman compared to reported lab culture requirements.

Ageing Characteristics of Stir Cast AZ 61 Alloy with Minor Additions

Background: Knowing that magnesium (Mg) alloys and its composites bear the potential of being used simultaneously for light structural as well as biomedical applications, it appears prudent to look for developing a novel Mg alloy; the concurrent demand is to monitor recent trend in development of functional Mg-alloy and its composite materials through extensive patent search. Review of recent patents in the related field makes it relevant to investigate this aspect. Objective: The authors aim to study the evolution of structure and properties in stir cast of AZ- 61 alloy with minor additions of scandium, calcium and manganese. This paper reports the results of this investigation. Methods: The castings are prepared by stirring the molten alloy at 600 rpm for 10 minutes, followed by pouring into a preheated metal mould. The solidified alloys are homogenized at 550°C for 12 hours. The homogenized alloys are then subjected to solutionising treatment at 500°C for 5 hours; subsequently, the alloys are quenched in iced water. The quenched alloys are subjected to ageing treatment at different temperatures between 100°C to 400°C at an interval of 100°C. Similar experiments are conducted with its statically cast counterparts. The structure and properties of all the samples have been characterized by optical and scanning electron microscopy, and XRD analysis; DSC heating run is conducted to study the kinetics of phase transformation. Mechanical behaviour of castings is studied with the aid of tensile testing and fractography. Moreover, tribological behaviour of alloys is assessed by wear testing with the help of pin on disc method. Results: The results show that the stir cast alloy produces a homogeneous structure with significant improvement in properties. The precipitates of Mg17Al12, Al Mn, Mg Zn2, Al2 Ca and Mg2 Ca are formed due to the ageing of both stir cast and statically cast alloy. It is found that the diffusion of Al in magnesium controls the precipitation process. The tribological properties are found to be satisfactory for the stir cast alloy. Conclusion: The modified AZ61 alloy with minor additives, achieves excellent structural homogeneity and mechanical properties after stir casting followed by quench ageing.

Evaluation of the Potential of Boiler Ash from Palm Oil Mill as an Alternative Material for the Improvement of Acid Coal Main Drainage

The study aimed to evaluate the potential of boiler ash from palm oil mills to improve the quality of acid mine drainage (AMD). The experiment was conducted using boiler ash with five doses of 0, 3, 6, 9, 12, and 15 mg. Quicklime was used as a comparison material with doses of 0, 0.02, 0.03, 0.05, 0.1, and 0.3 mg. Boiler ash and quicklime were added to each 500 mL AMD. The parameters of the AMD quality measured were pH, dissolved iron (Fe) and manganese (Mn), and the precipitates of Fe and Mn. The results showed that the addition of boiler ash and quicklime into AMD increased the pH and decreased the concentration of dissolved Fe and Mn and increased the precipitate of Fe and Mn. The pH value of AMD increased with increasing doses of boiler ash and quicklime. An increase in the pH value was followed by a decrease in the dissolved Fe and Mn and anincrease in the Fe and Mn precipitate. The highest pH values, Fe and Mn precipitates, and the lowest dissolved Fe and Mn were obtained by the treatment of 15 mg/L boiler ash and 0.3 mg/L quicklime. The boiler ash showed promising potential as an alternative neutralizing reagent to improve AMD even though the amount of boiler ash needed to repair AMD was more than quicklime.

A method for studying the influence of Mn oxyhydroxides on the trace element content of aquatic bryophytes

The main objective of this study was to develop and test a method of separating externally deposited Mn oxyhydroxides and co-precipitated elements from samples of aquatic moss (the moss Fontinalis antipyretica). The method, which uses 0.1 M hydroxylamine to dissolve the oxyhydroxides, was tested with samples collected in rivers with slightly acidic, well‑oxygenated waters, where high rates of Mn precipitation occur. The method was effective (it extracted up to 84 % of the Mn) and selective (Fe oxyhydroxides were not extracted). The elements Ba, Cd, Zn and Ni were associated with the Mn oxyhydroxides, while Al, As, Cr, Cu, Fe, Hg and Pb were not. Deposition of Mn therefore increased the concentration of some elements in the moss samples. However, as Mn precipitation depends on Eh and pH, which are independent of the concentrations of the elements in water, the relationship between water and moss element concentrations is not clear (i.e. the data are noisy). This is a problem in biomonitoring studies, which assume a close relationship between element concentrations in moss and water. The value of the proposed extraction method is that it can be used to correct the effect of Mn deposition. We present an example of this correction applied to the Cd concentrations in the test data. We found that the noise introduced by the Mn, including age-related effects (observed by comparing concentrations in 0–2.5 and 2.2–5.0 cm sections from the shoot apex), can be reduced. Additionally, the correction revealed recent increases in Cd concentrations in one site that were not observed in the uncorrected data. Another finding of interest was the low content of total Mn and different extractability (of most elements) observed in moss samples collected in alkaline waters. Finally, we discuss how future studies designed for different environmental scenarios can benefit from application of the proposed method.

A New Negative Carbon Isotope Interval Caused by Manganese Redox Cycling After the Shuram Excursion

AbstractSeveral negative C isotope excursions (CIEs) occurred at the end of the Neoproterozoic era which have been generally attributed to the oxidation of organic carbon using sulfate as the terminal electron acceptor and the subsequent release of 13C‐depleted dissolved inorganic C (DIC). Based on new analyses from the Doushantuo Formation in South China, we observe a negative C isotope excursion right after the well‐known Shuram excursion. This excursion is equivalent to the ∼550 Ma negative CIE which is globally expressed within several continental margins. However, the origins of this CIE in the termination of Ediacaran remain unresolved. Here, we hypothesize that this post‐Shuram negative CIE was caused by a localized manganese cycling that began with the oxidation of hydrothermal Mn(II) in a water column to insoluble Mn(IV)‐oxide, followed by accumulation of Mn(IV)‐oxide to the seafloor and its subsequent dissolution via Mn(IV) reduction leading to the release of dissolved Mn(II) and 13C‐depleted DIC into ambient seawaters. This ultimately led to the precipitation of particulate Mn(II)‐carbonate characterized by low δ13Ccarb values ranging from −11.1‰ to −2.8‰. The presence of microbial fabrics in association with the Mn(II)‐carbonate further suggests that Mn(II)‐carbonate precipitation took place at the seafloor in shallow sun‐lit waters rather than in the deeper sediment pile, which archived ambient seawater C isotopic signal. Although most Ediacaran negative CIEs were generally attributed to sulfate reduction, our findings suggest that at a local level, Mn cycling can also lead to negative CIE in the Neoproterozoic, and potentially at other times in Earth's history.

Transformation sequence of Mg-Si precipitates towards a precipitation of Mn and Cr containing phase governed by the high strain-rate collision during magnetic pulse welding of Al-Mg-Si alloy

This paper investigates the transformation of Mg-Si precipitates formed at an interface of an Al-Mg-Si alloy joint, welded by the high strain-rate collision during magnetic pulse impact welding. The Transmission Electron Microscopy (TEM) and Energy dispersive X-Ray (EDX) analysis of the precipitates reveal a nucleation of circular shape AlFeMnSiCr precipitate (size of ∼100 nm) from the dissolution of the native β″ (needle-shaped) precipitate. The AlFeMnSiCr phase can also reach a size up to several microns and grows into diverse shapes (rod-shaped, polygonal-shaped, ovoid-shaped). Based on the microstructural characterizations and on observations available in the literature including relevant data of Lodgaard and Ryum, the transformation sequence due to the high-speed collision can be described as follows: β″-Mg-Si (needle-shaped) → β’-Mg2Si (rod-shaped) ‘u-phase’ → Al(MnCrFe)Si (round-shaped) → Al(MnCrFe)Si +(+: Cr; Cu and/or Ni, rod-shaped, polygonal-shaped, ovoid-shaped). The comparison of samples welded at three different impact conditions (low impact intensity, intermediate impact intensity, high impact intensity) shows that the area fraction of the precipitates decreases with the increase of the impact intensity. The identification of the crystal structure of these different precipitates, from the nucleation to the final complete formation of the precipitation, can further enrich the transformation sequence in this paper. The role of the high strain kinematics on the deformation of the Al lattice and on the diffusion rate of alloying elements is also a perspective that can further explain this new observation of precipitation during magnetic pulse welding.

Efficient separation of Li and Mn from spent LiMn2O4 cathode materials by NH4HSO4 reduction roasting-selective ammonia leaching

With the imminent peak in the retirement of rechargeable lithium-ion batteries worldwide, the development of efficient methods for recycling valuable elements from LIBs has attracted considerable attention. In this work, a novel method of NH4HSO4 reduction roasting-selective ammonia leaching was proposed to thoroughly separate Li and Mn from the spent LiMn2O4 cathode materials. Using the TG-DSC-FTIR, XRD, SEM-EDS and ICP methods, the detailed mechanism of reduction roasting process was revealed, showing that the Mn4+ and Mn3+ in the spinel structure of LiMn2O4 were reduced by the NH4+ from the molten ammonium salt, and transformed into water-soluble MnSO4 and Li2Mn2(SO4)3. According to the water-leaching performance of the roasting products, the sulfation conversion rate of Mn reaches 98.1 %, while Li is almost completely transformed under the optimal roasting conditions (475 ℃, 60 min). Using the NH3·H2O-air leaching-system, complete separation of Li and Mn can be achieved. It was shown that the introduction of air into the ammonia solution at a rate of 0.2 L/min under the optimal leaching condition leads to Mn precipitation in the form of nanoscale Mn3O4 particles with a precipitation rate of over 99.99 %, while Li still remains completely leached. Based on the in situ detection of the oxidation reduction potential and pH during the selective leaching, the key mechanism of efficient Mn precipitation was revealed. that is, the increasing potential accelerates the oxidation of Mn(OH)2, and the rapid consumption of Mn(OH)2 promotes the hydrolysis of Mn2+, thereby achieving a significant improvement in the separation efficiency of Li and Mn.

Competitive Mn(II) removal occurs in Lysinibacillus sp. MHQ-1 through microbially-induced carbonate precipitation (MICP) and indirect Mn(II) oxidation

Biological Mn(II) removal usually involves adsorption and precipitation of Mn(II) in the form of various minerals. Manganese oxides (MnOx) formation through the activity of Mn(II) oxidation bacteria (MnOB) contributes to the majority of Mn(II) removal. However, whether other bacterial-mediated pathway could couple or competitive with Mn(II) oxidation during Mn(II) removal is scarcely reported. In this study, we reported a competitive Mn(II) removal occurred in nutrient-rich condition during the indirect Mn(II) oxidation of Lysinibacillus sp. MHQ-1, i.e., microbially-induced carbonate precipitation (MICP). In the presence of 1 mM Mn(II), 39.4% of free Mn(II) converted to MnCO3(s) quickly within 100 h, and then 11.6% of initial Mn(II) slowly oxidized to MnOx within 442 h. The urease activity assay and the genome sequencing confirmed the existence of urease and the absence of Mn(II)-oxidizing enzymes in the genome of strain MHQ-1. The urease catalyzed the formation of carbonate ion that reacts with Mn(II) and the formed ammonia raises the pH to initiate indirect Mn(II) oxidation. Genome survey suggests the urease widely exists in various Mn(II)-oxidizing bacteria (MnOB), emphasizing the importance to reconsider the composition, stability and environmental effects of biological Mn(II) removal products in nutrient-rich environment.

Mechanistic understanding of the localized corrosion behavior of laser powder bed fused 316L stainless steel in pressurized water reactor primary water

The laser powder bed fused (LPBFed) stainless steels showed anomalous and localized corrosion behavior in the nuclear reactor high-temperature water compared to their wrought counterparts, which affects their performance during plant operation. In this study, advanced microstructural characterization was performed on LPBFed 316 L sample along with wrought 316 L sample after corrosion tests to understand the underlying mechanisms. The results showed that an inhomogeneous/discontinuous inner oxide layer formed on LPBFed 316 L, in contrast to the continuous inner oxide layer on the wrought 316 L specimen. This discontinuous inner oxide layer was identified to consist of Cr-enriched nano-sized spinel oxide and the barrier layer features a Ni-enriched hexagonal close-packed Laves phase. Localized/preferential oxidation was found to occur along the cellular walls which were tangled with high density dislocations and decorated with Mn and Si-enriched nano-sized precipitates, and the nano-precipitates were observed in the core of dispersed Cr-enriched inner oxide crystals.

A combined simulation and experimental study of the equilibrium shapes of η′ and α precipitates in Mn-containing 7xxx Al-alloys

The addition of Mn to 7xxx series Al-alloys helps improve tensile properties owed to the presence of α precipitates (Al(Mn,Fe)Si, simple cubic, 50–200 nm, non-shearable) in addition to the η′ precipitates (Mg2Zn5−xAl2+x, hexagonal, 4–6 nm, shearable) commonly observed in the 7xxx series Al-alloys. The coexistence of multiple α and η′ variants, 24 for α and 4 for η′, coupled with their small size-scale, makes the experimental determination by x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) challenging. This work formulates a phase-field model to predict precipitate shapes in three-dimension (3D) using experimental characterization as inputs to create virtual precipitate cross-sections for use in morphological comparison with experimental 2D (S)TEM images. Based on the atomic structures and orientation relationships observed in the experiments, the lattice site correspondences between the matrix and the two precipitate phases are derived, which are required for the prediction of shapes of coherent precipitates. Systematic phase-field simulations are then carried out to document the 3D shapes for all possible variants, as well as the corresponding 2D cross-sectional shapes when observed parallel to low-index matrix planes. These 2D cross-sectional shapes are compared with high-angle annular dark-field STEM (HAADF-STEM) images, which demonstrates that the identification of Mn precipitate type is possible by such comparisons. This helps unravel some of the complications encountered when characterizing precipitate microstructures in Mn containing Al-alloys by STEM. Finally, the equilibrium shapes as a function of precipitate size and the effect of interfacial energy anisotropy are investigated.

Cobalt and Manganese Extraction from Ocean Nodules by Co-Processing with Steel Metallurgical Slag

Polymetallic nodules, also called manganese nodules (due to their high content of this element), contain various valuable metals such as Cu, Ni and Co. These seabed minerals are a good alternative source of Co and Mn due to the decrease in the grade of mineral deposits on the earth’s surface. For the treatment of manganese nodules, acid-reducing leaching is apparently the most attractive, due to its low cost compared to other processes, short operational times, and it is more friendly to the environment. In this investigation, the extraction of Mn and Co from manganese nodules from two different locations was studied in acid media and by reusing a steel slag obtained from a steel smelting process. An ANOVA analysis was performed to determine the most appropriate Manganese Nodule/Fe(res) ratio and time to dissolve Co and Mn from the nodules. Effect of temperature on the process was evaluated, and then a residue analysis was carried out. Finally, it was discovered that the best results were obtained when working at 60 °C in a time of 15 min, obtaining extractions of approximately 98% Mn and 55% Co. Additionally, the formation of polluting elements was not observed, nor the precipitation of Mn and Co species in the studied residues.

Effect of small vanadium addition on the microstructure, transformation temperatures, and corrosion behavior of a Cu72Al17Mn11 shape memory alloy

In the present work, effects of 0.1 at.% and 0.2 at.% vanadium content on the microstructure, transformation characteristics and corrosion behavior of the Cu72Al17Mn11 shape memory alloy (SMA) have been investigated by means of OM, SEM, XRD, DSC measurements and corrosion test. The alloys were produced in an induction furnace under air atmosphere. The results indicate that microstructure at room temperature consisted of a mixture of β3(L21) parent phase with 0.06–0.08 at% of vanadium into solid solution, small amounts of a cubic bcc δ(V,Mn) precipitate, β1′(18R) and γ1′(2H) martensites. The small addition of vanadium contributes to the induction of martensite γ1′ and broads the hysteresis of the alloys. Thermal analysis evidences the shift of Af, Ms to higher temperatures, showing multi-stage phase transformations of the reaction β1′→γ1′→β3, which results in increased values of ΔHM→A, ΔSM→A, ΔGe. The addition of V also interfered in the corrosion resistance of the alloy. Electrochemical measurements were carried out to evaluate the corrosion resistance alloys. With the results obtained, an increase in corrosion resistance was observed with the increase in the vanadium content in the alloy. The results of this work provide an important systematic analysis for the development and application of corrosion resistant CuAlMn SMA.

Siderophore-Mediated Mobilization of Manganese Limits Iron Solubility in Mixed Mineral Systems.

Recent laboratory and field studies show the need to consider the formation of aqueous Mn(III)-siderophore complexes in manganese (Mn) and iron (Fe) geochemical cycling, a shift from the historical view that aqueous Mn(III) species are unstable and thus unimportant. In this study, we quantified Mn and Fe mobilization by desferrioxamine B (DFOB), a terrestrial bacterial siderophore, in single (Mn or Fe) and mixed (Mn and Fe) mineral systems. We selected manganite (γ-MnOOH), δ-MnO2, lepidocrocite (γ-FeOOH), and 2-line ferrihydrite (Fe2O3·0.5H2O) as relevant mineral phases. We found that DFOB mobilized Mn(III) as Mn(III)-DFOB complexes to varying extents from both Mn(III,IV) oxyhydroxides but reduction of Mn(IV) to Mn(III) was required for the mobilization of Mn(III) from δ-MnO2. The initial rates of Mn(III)-DFOB mobilization from manganite and δ-MnO2 were not affected by the presence of lepidocrocite but decreased by a factor of 5 and 10 for manganite and δ-MnO2, respectively, in the presence of 2-line ferrihydrite. Additionally, the decomposition of Mn(III)-DFOB complexes through Mn-for-Fe ligand exchange and/or ligand oxidation led to Mn(II) mobilization and Mn(III) precipitation in the mixed-mineral systems (∼10% (mol Mn/mol Fe)). As a result, the concentration of Fe(III) mobilized as Fe(III)-DFOB decreased by up to 50% and 80% in the presence of manganite and δ-MnO2, respectively, compared to the single mineral systems. Our results demonstrate that siderophores, through their complexation of Mn(III), reduction of Mn(III,IV), and mobilization of Mn(II), can redistribute Mn to other soil minerals and limit the bioavailability of Fe in natural systems.

Recovery of pure MnSO4 by crystallization after separation of Fe(III) and Zn(II) from the reductive leaching solution of manganese dust containing Mn3O4

Manganese dust generated during the production of ferroalloys contains iron and zinc oxides together with other minor oxides. Pure manganese compounds can be recovered from the leaching solution of the manganese dust by removing the impure ions. In this work, sulfuric acid and ferrous sulfate were employed as leaching and reducing agents for the manganese oxides in the dust. First, the leaching conditions for complete dissolution of the manganese oxides were investigated by varying the concentration of sulfuric acid and ferrous sulfate, and pulp density. Second, after oxidizing Fe(II) to Fe(III) by hydrogen peroxide, Fe(III) was removed from the solution by three stages of counter current extraction with D2EHPA. Third, Zn(II) was removed by two stages of cross current extraction with Cyanex 272. Stripping conditions for Fe(III) and Zn(II) were determined from the respective loaded organics. Fourth, Mn(OH)2 was precipitated from the raffinate by adjusting the pH of the solution to 10 with NaOH solution. The MnSO4 crystals with 99.5% purity were recovered by crystallization from the sulfuric acid solutions after the precipitates of Mn(OH)2 were dissolved. A comparison of the cost of the chemicals used to recover MnO2 and MnSO4 indicated that the current process was much more economical.

Episodic ventilation of euxinic bottom waters triggers the formation of black shale-hosted Mn carbonate deposits

Many manganese (Mn) carbonate deposits over geologic history are often closely associated with black shales. However, the mechanism(s) by which the Mn entered the sediments remains controversial because on one hand oxygenated waters are required for primary Mn(IV) oxide formation but on the other hand black shales generally form under reducing conditions. China hosts some of the world’s largest black shale-hosted Mn deposits, for example, the Carboniferous Ortokarnash and Malkantu Mn deposits in the Malkansu region, offering a good opportunity to revisit the genesis of black shale-hosted Mn carbonate deposits. Here, we present the first coupled, systematic paleoredox and hydrographic reconstruction of those deposits with the aim of elucidating the redox-state of the depositional basin at the time of their initial deposition. The Mn ore beds in this region are hosted within laminated, organic-rich mudstones (i.e., black shales) reflective of a relatively deep-water depositional environment. The Mn ores are comprised of the Mn(II) carbonate minerals (rhodochrosite and Ca-rhodochrosite), with minor alabandite, pyrite, and monazite. Multiple independent lines of evidence, including positive shale-normalized Ce anomalies (average 3.0), negative δ13CVPDB values (average −11.55 ‰), and negative δ98MoNIST+0.25 values (average −1.07 ‰), indicate that the Mn(II) carbonate ores were formed during diagenesis via the coupled oxidation of organic matter and reduction of Mn(IV) oxides originally deposited from an oxygenated water column. However, in apparent contradiction, highly reactive iron to total iron (FeHR/FeT; average 0.66) and pyrite iron to highly reactive iron (FePy/FeHR; average 0.71) ratios, combined with a high abundance of small framboidal pyrites (mean diameter ∼5 μm) with narrow size ranges (standard deviations <2 μm), suggest that the associated black shales were deposited in euxinic (H2S-bearing) bottom waters. Euxinia resulted from sluggish water mass circulation, with sedimentary Mo/TOC ratios indicating a relatively strong hydrologic restriction. During this stage, dissolved Mn(II) would have accumulated in euxinic waters but not become permanently fixed into sediments, as indicated by higher degrees of enrichment for Mo over U and lower Mo isotope values than coeval seawater recorded in the black shales. These reveal an active Mn(IV) oxide shuttle across a redox-stratified water column. Combined, the Mn ore intervals document sharp benthic oxygenation of euxinic bottom waters, a process that might be induced by the periodic incursions of oxic seawater associated with eustatic sea level rises. This model is supported by the Mo isotopic characteristics of the Mn carbonate ores, which indicate original Mn oxide precipitation from an overlying water with Mo isotopic composition close to coeval open seawater (minimum δ98MoNIST+0.25 of 1.9 ‰). In contrast to the generalized “bathtub ring” model envisaging that the black shale-hosted Mn deposits were formed at shallow basin margins, our results highlight that they were more likely formed by in-situ ventilation of anoxic (especially euxinic) deep waters of basin center settings. In this regard, we suggest that the ventilation model better explains the close association of Mn carbonate ores with black shales, and has profound implications for understanding the paleoredox framework of otherwise Mn-rich black shale successions.

Catalytic performances and leaching behavior of typical natural iron minerals as electro-Fenton catalysts for mineralization of imidacloprid

Catalytic performances and leaching behavior of 9 natural iron minerals as heterogeneous electro-Fenton catalysts for the treatment of imidacloprid wastewater were studied. The results showed that magnesioferrite exhibited the best catalytic ability among these minerals with UV absorbance at 270 nm (UV270) removal of 83.59% and COD removal of 49.11% within 4 h using graphite cathode and Ti/(RuO2)0.88-(IrO2)0.12 anode at initial pH 3 with a catalyst dose of 5 g/L, a current density of 40 mA/cm2 and an electrode spacing of 2 cm. The instantaneous current efficiency (ICE) at 4 h and energy consumption (EC) reached 2.30% and 2.20 kWh/gCOD respectively. It was found that the components contained in natural iron minerals, such as Al, alkali metal (K) and alkaline earth metals (Mg, Ca, Ba), would dissolve into the electrolyte solution, raising the final pH to 6.5–8.5 and ultimately reducing the reaction efficiency. Except magnetite and magnesioferrite, other minerals, such as ilmenite and V-Ti magnetite, were likely to cause secondary pollution. The subsequent adjustment to alkaline state for chemical precipitation of leached Mn was needed. Pyrite showed relatively high leachability in hazardous elements (especially Pb), which should be carefully evaluated before its actual application in electro-Fenton process.

Facile synthesis and characterization of β-cobalt hydroxide/hydrohausmannite/ramsdellitee/spertiniite and tenorite/cobalt manganese oxide/manganese oxide as novel nanocomposites for efficient photocatalytic degradation of methylene blue dye

In this paper, our research team has synthesized new nanocomposites by simple precipitation/ignition method and using low-cost chemicals. Hence, β-cobalt hydroxide/hydrohausmannite/ramsdellitee/spertiniite and tenorite/cobalt manganese oxide/manganese oxide new nanocomposites were synthesized by precipitation of Mn(II)/Co(II)/Cu(II) solution using sodium hydroxide and ignition of precipitate at 700 °C for 3 hrs, respectively. The synthesized nanocomposites were characterized using different instruments such as energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), nitrogen gas sorption analyzer, and UV–vis spectrophotometer. Energy dispersive X-ray analysis revealed that the nanocomposite formed as a result of precipitation consists of copper, cobalt, manganese, and oxygen where the weight percentages are equal to 31.73, 27.01, 17.26, and 24 %, respectively. Also, the nanocomposite formed as a result of ignition consists of copper, cobalt, manganese, and oxygen where the weight percentages are equal to 31.26, 23.87, 14.56, and 30.31 %, respectively. Transmission electron microscope revealed that the nanocomposites formed as a result of precipitation and ignition consist of polyhedral and spherical shapes with an average diameter of 34.50 and 28.56 nm, respectively. The synthesized nanocomposites were used as new photocatalysts for the efficient degradation of methylene blue dye. 0.05 g of the synthesized nanocomposites degrade 100 % of 50 mL of 15 mg/L of methylene blue dye solution within 25 min in the presence of H2O2 under UV light.

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.