Mn Carbonate Research Articles

An exploratory data analysis approach for assessing the sources and distribution of naturally occurring contaminants (F, Ba, Mn, As) in groundwater from southern Quebec (Canada)

The presence of naturally occurring contaminants in groundwater is a public health concern in rural areas of northeastern North America, where public and private wells are important sources of drinking water. In southern Quebec (Canada), inorganic groundwater chemistry data have been recently collected following standard procedures in several regional hydrogeological projects implemented by the government of Quebec. In this study, a groundwater chemistry database was compiled from 16 regional projects altogether covering an area of approximately 100,000 km2. The database includes information on water supply infrastructures, geological settings, hydrogeological conditions and inorganic water chemistry for 2369 water samples. Samples were mostly collected from private domestic wells, and to a lesser extent from municipal and observation wells. The data revealed that fluoride, barium, manganese and arsenic are the most common elements exceeding Canadian drinking water guidelines. Exploratory data analysis techniques were applied to selected subsets of data to gain insight into the sources and distribution of these hazardous groundwater contaminants. These exploratory methods include graphical data analysis (maps, Piper and empirical cumulative distribution function plots), multivariate compositional data analysis (clustering and correlation analysis) and geochemical modeling (saturation index calculations). The results suggest that fluoride, barium, manganese and arsenic are all derived from natural sources. Elevated fluoride concentrations are mainly associated with dilute Ca–Na–HCO3 bedrock groundwaters from granitic areas (Grenville Province), and more geochemically evolved Na–HCO3 to Na–HCO3–Cl bedrock groundwaters from shale areas (St. Lawrence Platform). High-F groundwaters are generally characterized by low Ca concentrations (<30 mg/L) and alkaline pH (pH > 8), suggesting that F is mainly controlled by fluorite (CaF2) precipitation and anion exchange with OH−. Barium is present at elevated concentrations in mineralized Ca–Na–HCO3, Na–HCO3 to Na–HCO3–Cl waters from bedrock aquifers of the St. Lawrence Lowlands. These groundwaters are mainly chemically evolved, strongly reducing waters occurring in confined aquifers and near major faults, which appear to correspond to discharge areas for deep regional flow. High Ba concentrations are generally associated with very low SO4 concentrations (< 5 mg/L) resulting from sulfate reduction, suggesting a solubility control of Ba through barite (BaSO4) precipitation. Most high manganese concentrations occur in less chemically evolved, near-neutral Ca–HCO3 groundwaters from both granular and bedrock aquifers, particularly those associated with metasedimentary and metavolcanic lithologies (Superior Province, St. Lawrence Platform and Appalachian Province). The results suggest that dissolved Mn concentrations are limited by the precipitation of Mn carbonates under alkaline conditions, but increase under reducing conditions owing to the dissolution of Fe–Mn oxyhydroxides. Elevated arsenic concentrations were mostly found in Ca-(Na–Mg)–HCO3 bedrock groundwaters of the Superior and Appalachian Provinces. As-rich groundwaters are associated with the presence of As-bearing sulfides in weakly metamorphosed sedimentary rocks (shale, slate, phyllite) and hydrothermally altered rocks. Most high As concentrations do not appear to be directly derived from sulfide oxidation, but rather from secondary sources, in particular through the reductive dissolution of As-rich Fe–Mn oxyhydroxides. This work shows that the combination of graphical, multivariate statistical and geochemical modeling techniques is a powerful approach to explore large hydrochemical datasets. It also reveals the benefits of using multivariate compositional data analysis instead of classical approaches based on raw data and log-ratios for groundwater chemistry data. Compositional data analysis techniques improved the detection of multivariate outliers, the cluster reliability in cluster analysis, and removed the spurious positive correlation between hydrochemical variables associated with total mineralization.

Trace Metal and Cd Isotope Systematics of the Basal Datangpo Formation, Yangtze Platform (South China) Indicate Restrained (Bio)Geochemical Metal Cycling in Cryogenian Seawater

The behaviour of bioavailable trace metals and their stable isotopes in the modern oceans is controlled by uptake into phototrophic organisms and adsorption on and incorporation into marine authigenic minerals. Among other bioessential metals, Cd and its stable isotopes have recently been used in carbonate lithologies as novel tracer for changes in the paleo primary productivity and (bio)geochemical cycling. However, many marine sediments that were deposited during geologically highly relevant episodes and which, thus, urgently require study for a better understanding of the paleo environment are rather composed of a mixture of organic matter (OM), and detrital and authigenic minerals. In this study, we present Cd concentrations and their isotopic compositions as well as trace metal concentrations from sequential leachates of OM-rich shales of the Cryogenian basal Datangpo Formation, Yangtze Platform (South China). Our study shows variable distribution of conservative and bioavailable trace metals as well as Cd isotope compositions between sequential leachates of carbonate, OM, sulphide, and silicate phases. We show that the Cd isotope compositions obtained from OM leachates can be used to calculate the ambient Cryogenian surface seawater of the restricted Nanhua Basin by applying mass balance calculations. By contrast, early diagenetic Mn carbonates and sulphides incorporated the residual Cd from dissolved organic matter that was in isotopic equilibrium with deep/pore waters of the Nanhua Basin. Our model suggests that the Cd isotopic composition of surface seawater at that time reached values of modern oxygenated surface oceans. However, the deep water Cd isotope composition was substantially heavier than that of modern fully oxygenated oceans and rather resembles deep waters with abundant sulphide precipitation typical for modern oxygen minimum zones. This argues for incomplete recycling of Cd and other bioavailable metals shortly after the Sturtian glaciation in the redox stratified Cryogenian Nanhua Basin. Our study highlights the importance of sequential leaching procedures when dealing with impure authigenic sediments such as OM-rich carbonates, mudstones, or shales to achieve reliable trace metal concentrations and Cd isotope compositions as proxies for (bio)geochemical metal cycling in past aquatic systems.

Rare earth element geochemistry of sediments from the southern Okinawa Trough since 3 ka: Implications for river-sea processes and sediment source

Abstract The sediment sources in the southern Okinawa trough (SOT) are still controversial and few studies have focused on the effects of transport processes on the elemental composition of initial terrigenous materials. Here we present rare earth element (REE) and trace element data on siliciclastic sediments from 14C age-dated Core S3, which was collected from the SOT, to provide reliable evidence for illustrating the modified effects of marine environments on terrigenous sediments deposited at different stages and exposing changes in sediment source over the past 3 ka. Compared with bulk sediments, the siliciclastic sediments in S3 have more variable REE fractionation parameters and lower middle REE (MREE) contents. Our REE data indicate that during river-sea processes, MREE-enriched fractions such as Fe–Mn oxides and carbonate were added to the original terrigenous sediments before deposition, weakening the degree of REE fractionation in the initial sediments; thus, care should be taken when using REE data from bulk samples to decipher source changes. The temporal changes in sediment source in S3 can be broadly identified based on the REE fractionation parameters of the residual fractions, and the results are largely consistent with the findings obtained by heavy mineral examinations. Units 1 and 3 are dominated by reworked shelf sediments of Changjiang origin,while the proportion of Taiwan-derived sediment is notably higher in Units 2 and 4. The sediment flux of Taiwan origin in the SOT was much smaller than previously thought. Huanghe-derived sediments and volcanic materials did not contribute significantly to the late Holocene sedimentation in the SOT. The large variations in sediment sources in S3 were possibly caused by changes in transport patterns driven by time-dependent changes in oceanic currents.

Microbially Mediated Ore-Forming Processes and Cell Mineralization.

Sedimentary black shale-hosted manganese carbonate and oxide ores were studied by high-resolution in situ detailed optical and cathodoluminescence microscopy, Raman spectroscopy, and FTIR spectroscopy to determine microbial contribution in metallogenesis. This study of the Urucum Mn deposit in Brazil is included as a case study for microbially mediated ore-forming processes. The results were compared and interpreted in a comparative way, and the data were elaborated by a complex, structural hierarchical method. The first syngenetic products of microbial enzymatic oxidation were ferrihydrite and lepidocrocite on the Fe side, and vernadite, todorokite, birnessite, and manganite on the Mn side, formed under obligatory oxic (Mn) and suboxic (Fe) conditions and close to neutral pH. Fe- and Mn-oxidizing bacteria played a basic role in metallogenesis based on microtextural features, bioindicator minerals, and embedded variable organic matter. Trace element content is determined by source of elements and microbial activity. The present Urucum (Brazil), Datangpo (China), and Úrkút (Hungary) deposits are the result of complex diagenetic processes, which include the decomposition and mineralization of cell and extracellular polymeric substance (EPS) of Fe and Mn bacteria and cyanobacteria. Heterotrophic cell colonies activated randomly in the microbialite sediment after burial in suboxic neutral/alkaline conditions, forming Mn carbonates and variable cation-bearing oxides side by side with lithification and stabilization of minerals. Deposits of variable geological ages and geographical occurrences show strong similarities and indicate two-step microbial metallogenesis: a primary chemolithoautotrophic, and a diagenetic heterotrophic microbial cycle, influenced strongly by mineralization of cells and EPSs. These processes perform a basic role in controlling major and trace element distribution in sedimentary environments on a global level and place biogeochemical constraints on the element content of natural waters, precipitation of minerals, and water contaminants.

Coupled anaerobic and aerobic microbial processes for Mn-carbonate precipitation: A realistic model of inorganic carbon pool formation

Abstract Mn carbonate is the main MnII mineral phase that precipitates in suboxic to anoxic environments. The coupled processes of MnIV oxide bioreduction and organic oxidation serve as dominant factors leading to Mn carbonate precipitation. This study examined the simultaneous respiration of oxygen and birnessite by a facultatively anaerobic bacterium, the Dietzia strain DQ12-45-1b (45-1b), and discussed the possible mechanism of rhodochrosite precipitation under general oxic environments. Compared to anaerobic experiments, the more rapid growth of 45-1b under aerobic conditions caused faster oxidation of acetate (1.0 × 103 μM h−1) and accumulation of HCO3− (5.5 × 102 μM h−1) within 72 h, which was coupled to a dramatic increase in pH from 7.0 to more than 9.2. By virtue of the higher biomass and bioactivity in the aerobic condition, the bioreduction of MnIV was accelerated and it caused a higher accumulating rate of soluble reduced Mn (4.0 μΜ h−1) than that in the anaerobic condition (2.0 μΜ h−1). Those rates indicated that an anaerobic-aerobic sub-interface was present in the aerobic system, in which anaerobic and aerobic respiration co-occurred to give rise to sufficient Mn(II) and alkalinity, thus, increased the supersaturation index (SI) for rhodochrosite. The mineral intermediates and products were identified by time-course XRD, SEM, and Raman spectra. Manganite (MnOOH) was found as the transient intermediate, which suggested the stepwise one-electron transfer mechanism of birnessite reduction. The dialysis tube, lysed cells, dead cells and two-compartment experiments suggested that the living 45-1b not only carried out a direct extracellular electron transfer for birnessite reduction but also provided necessary nucleation sites for rhodochrosite precipitation. Furthermore, both the isotope experiments and Raman analysis showed that the carbon source in rhodochrosite was mainly 13C isotope-labeled acetate, which corresponded well with the geological isotopic records. Finally, a conceptual model of Mn carbonate precipitation at oxic-suboxic/anoxic interfaces that could be possibly present in soil and sedimentary environments was proposed based on three prerequisites: (i) sufficient Mn(II) produced on an aerobic-anaerobic sub-interface, (ii) adequate alkalinity, and (iii) nucleation sites provided by cell surfaces. This model highlights the role of aerobic respiration in Mn(IV) reduction and Mn-carbonate formation, and may suggest a realistic way for inorganic carbon storage.

Effect of metal ion concentration in precursor solution on structure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2

LiNi0.6Mn0.2Co0.2O2 (622NCM) cathode materials are synthesized by a carbonate co-precipitation process. We decomposed Co and Mn carbonates to form porous CoMnO3 precursors, which were impregnated with Ni and Li salts to form final materials. To provide better hosts for the Ni and Li salts, we design the co-precipitation solutions with different total metal ion concentrations to achieve precursors with stable structures and appropriate porosity. We obtained 622NCM with hierarchical and porous properties, which shortened the lithium ion transmission distance and improved the electrolyte infiltration rate and rate capability. Furthermore, our 622NCM cathode materials showed no loss of thermodynamic or electrochemical stability during cycling. The most suitable concentration was determined to be 0.03 mol L−1 and the as-prepared 622NCM (0.03–622NCM) cathode material exhibited good cycle reversibility, a high capacity, and good rate capability, delivering a discharge capacity of 152 mA h g−1 at 0.2 C. A capacity of more than 100 mA h g−1 was achieved at a high rate of 5 C. This study provides guidance for preparing nickel-rich ternary cathode materials for high-performance lithium-ion batteries.

The metallogenic environment of the Dounan manganese deposit, Southeast Yunnan, China: evidence from geochemistry and Mössbauer spectroscopic

The Dounan manganese deposit is a typical large-scale marine sedimentary manganese deposit of the Middle Triassic in China. The metallogenic environment and change process directly dictate the migration, enrichment, and precipitation of Mn. To better understand its metallogenetic environment, a detailed study was undertaken involving field observation, mineralogical and geochemical and Mossbauer spectroscopic analyses. The major findings are as follows: (1) Lithofacies paleogeography, sedimentary structural characteristics, and geochemical indexes indicate that the deposits were formed in an epicontinental marine sedimentary basin environment of normal salinity; (2) there were three ore phases including Mn oxides, Mn carbonates, and mixed Mn ores. The ore minerals found were braunite, manganite, Ca-rhodochrosite, manganocalcite, and kutnahorite. Petrographic and mineralogical information indicates that the metallogenic environment was a weakly alkaline and weakly oxidized to weakly reduced environment, and the mineralization occurred near the redox interface; (3) the V/(V + Ni) ratios, δCe and Fe2+/Fe3+ found in profiles of Baigu and Gake ore sections show that the redox conditions of the ore-forming environment were continuously changing; and (4) three Fe species, α-Fe2O3, para-Fe3+, and para-Fe2+, were found in hematite and clay mineral samples using Mossbauer spectrum analysis. The presence and distribution of these Fe species indicate that the deposit was formed in a typical sedimentary environment during the mineralization process. In summary, our study showed that redox was a key factor controlling the mineralization of the Dounan manganese deposit. Our results have led us to the conclusion that transgression and regression caused fluctuations in sea level, which in turn caused the change of the redox environment. Mossbauer spectroscopy is an effective tool for studying the redox conditions of the paleoenvironment in which sedimentary manganese deposits were formed.

Aerobic iron and manganese cycling in a redox-stratified Mesoarchean epicontinental sea

Redox conditions in the marine realm prior to the Great Oxidation Event (GOE; ∼2.46–2.32 Ga ago), during which the atmospheric oxygen level rose dramatically for the first time, are still debated. Here, we present C, O, Fe, and Mo stable isotope systematics of Fe-, Mn-, and carbonate-rich shales, deposited at different water depths in association with iron formations (IFs) of the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. δ13C values between −22.3 and −13.5‰ VPDB, and δ18O values between −21.1 and −8.6‰ VPDB for Fe–Mn-rich carbonate minerals indicate their precipitation out of equilibrium with seawater. Instead, early diagenetic reduction of Fe–Mn-oxyhydroxide precursor minerals, along with microbially induced oxidation of organic matter (OM), formed these carbonates. δ56FeIRMM-014 values between −1.27 and 0.14‰ and δ98MoNIST3134+0.25 values between −0.46 and 0.56‰ co-vary with Mn concentrations and inferred water depth of deposition. This suggests that, despite the diagenetic origin of the Fe–Mn carbonates, the primary light Fe and Mo isotopic signature of Fe–Mn-oxyhydroxides that originally precipitated from seawater is still preserved. While isotopically light Mo implies that Mn(II) was oxidized to Mn(IV) due to the availability of free, photosynthetically produced O2, Mn enrichment suggests that the water column was redox stratified with a Mn-redoxcline situated at a depth below the storm wave base. A trend to highly negative δ56Fe values with increasing Mn/Fe ratios and decreasing depositional depth suggests progressive oxidation of Fe(II) as deep-waters upwelled across a redoxcline towards shallow, locally oxygenated waters where Mn(IV) oxyhydroxides precipitated. Combined δ56Fe and δ98Mo data indicate pervasive oxygenation of seawater with the O2 content in the photic zone likely reaching levels higher than the maximum value of 10 μM proposed for Archean oxygen oases. Since abiotic Mn(II) oxidation is kinetically very slow in marine environments, it is likely that Mn-oxidizing microorganisms catalyzed Mn-oxidation in the oxygenated Pongola surface waters during deposition of IFs. This implies that aerobic metabolism had evolved before the GOE in shallow, aquatic habitats, where it exerted a first-order control on the deposition of shallow-marine, Mn-rich iron formations.

Impact of the Major Baltic Inflow in 2014 on Manganese Cycling in the Gotland Deep (Baltic Sea)

The deep basins of the Baltic Sea, including the Gotland and Landsort Deeps, are well known for the exceptional occurrence of sedimentary Mn carbonate. Although the details of the mechanisms of Mn carbonate formation are still under debate, a close relationship with episodic major Baltic inflows (MBIs) is generally assumed, at least for the Gotland Basin. However, the few studies on Mn cycling during MBIs suffer from a limited temporal resolution. Here we report on Mn dynamics in the water column and sediments of the Gotland Deep following an MBI that entered the Baltic Sea in December 2014. Water column profiles of dissolved Mn were obtained at a monthly to bi-monthly resolution between February 2015 and March 2017 and revealed an impact of the MBI on the Gotland Deep bottom waters beginning in March 2015. Water column profiles and budget estimates provided evidence for remarkable losses of dissolved Mn associated with the enhanced deposition of Mn oxide particles, as documented in sediment trap samples and surface sediments. In July 2015, subsequent to the nearly full oxygenation of the water column, clear signals of the re-establishment of bottom water anoxia appeared, interrupted by a second inflow pulse around February 2016. However, dissolved Mn concentrations of up to 40 µM in the bottom waters in June 2016 again indicated a pronounced reduction of Mn oxide and the escape of dissolved Mn back into the open water column. The absence of substantial amounts of Mn carbonate in the surface sediments at the end of the observation period suggested that the duration of bottom water oxygenation plays an important role in the formation of this mineral. Data from both an instrumental time series and a dated sediment core from the Gotland Deep supported this conclusion. Enhanced Mn carbonate formation occurred especially between the 1960s and mid-1970s, when several MBIs caused a long-lasting oxygenation of the water column. By contrast, Mn carbonate layers were much less pronounced or even missing after single MBIs in 1993, 2003, and 2014, each of which provided a comparatively short-term supply of O2 to the deeper water column.

Authigenic rhodochrosite from a gas hydrate-bearing structure in Lake Baikal

Early diagenetic carbonates are rare in Lake Baikal. Siderite (Fe carbonate) concretions in the sediments were discovered only recently. Here, we discuss the first finding of rhodochrosite concretions (Mn carbonate) discovered in the near-bottom sediments of the gas hydrate-bearing seepage structure St. Petersburg-2 in the deep water environment of the Central Baikal Basin. The crystal lattice of rhodochrosite contains iron and calcium substituting to manganese. Based on pore water geochemistry and of δ13C values of rhodochrosite (− 23.3 and − 29.4‰), carbon dioxide (+ 3.8 to − 16.1‰) and methane (− 63.2 to − 67.8‰), we show that carbonate crystallization most likely occurred during microbial anaerobic oxidation of organic matter, and that part of the oxygen making up the rhodochrosite seems to be derived from the 18O-rich water released from dissociating gas hydrates.

Mechanisms of Late Pleistocene authigenic Fe–Mn-carbonate formation at the Laptev Sea continental slope (Siberian Arctic)

Study of the microstructure and isotopic composition of authigenic tubule-shaped carbonate concretions from sediment core PS51/154-11 on the western Laptev Sea continental slope (present water depth 270 m) has allowed for reconstruction of the conditions prevailing during their formation and identification of the mechanisms controlling their genesis. Concretions were collected from the basal sediment unit with an extrapolated age estimate of 16.3–17.6 cal.ka. Crystallization of carbonate tubules occurred at the beginning of the last deglaciation when the site was located in the proximity to the former coastline and the mouths of the Olenek and Anabar-Khatanga rivers in water depths of about 150–170 m. Microprobe analysis showed that the studied carbonate tubules consist of the minerals belonging to the siderite–rhodochrosite isomorphic series. The measured isotopic composition of δ13С and δ18O in the carbonates varies between − 21.0 and − 17.0‰ and between − 9.86 and 1.72‰ VPDB, respectively. The δ18O values in the authigenic carbonates give evidence for the gradual transition from a freshwater affected to modern-like marine sedimentation environment during carbonate crystallization. Water freshening is confirmed by the co-occurrence of authigenic Fe–Mn carbonates and Fe-phosphate vivianite that is a typical mineral of freshwater environments. The dominant source of dissolved inorganic carbon in the pore water was the isotopically light carbon derived from the diagenetic decomposition of organic matter. Two possible scenarios of authigenic carbonates formation are proposed: penetration of freshened ground waters and/or enhanced freshwater influence during short seasonal floods in combination with geochemical processes in a narrow marginal filter zone that was located extremely close to the Laptev Sea continental slope and the studied core site.

Manganese carbonates in the Upper Jurassic Georgiev Formation of the Western Siberian marine basin

Manganese (Mn) carbonate rocks are a common lithological constituent of the Upper Oxfordian to Lower Tithonian (Volgian) Georgiev Formation of the Western Siberian marine basin (WSMB). The Mn carbonates in the Georgiev Formation are present in the form of massive sediments, stromatolites, and oncolites, and are associated with glauconite and partly also phosphate-rich clay- and siltstones. Unlike most Mn carbonates, they are not directly associated with organic-rich sediments, but occur below an organic-rich succession (Bazhenov Formation). The Mn carbonate occurrences can be traced from the western central area of the WSMB to its center along a distance of at least 750km. The thickness of the Mn carbonates and their Mn contents becomes reduced in an eastward direction, related to increased detrital input. The geochemical and mineralogical heterogeneity within the Mn carbonates indicates that they were deposited stepwise in a diagenetic regime characterized by steep gradients in Mn, Ca, and Mg. A first step consisted in the replacement of initial sediments within the microbialites during an early diagenetic stage, followed by a second step where massive sediments were transformed into Mn carbonate. During both steps, the decomposition of organic matter was an important source of the newly formed carbonate. During a further step, voids were cemented by Mn carbonates, which are rich in pyrite. This last generation may only have formed once the organic-rich sediments of the overlying Bazhenov Formation were deposited. Accumulation of the Mn carbonates in the Upper Jurassic WSMB was controlled by the proximity of Mn-enriched parent rocks, likely in the Ural, which were subjected to intense geochemical weathering during the Late Jurassic.

Massive Mn carbonate formation in the Landsort Deep (Baltic Sea): Hydrographic conditions, temporal succession, and Mn budget calculations

The sediments of the Landsort Deep and Gotland Basin in the central Baltic Sea are strongly enriched in Mn carbonate. However, conceptual models attempting to explain the intense Mn carbonate precipitation in both basins are in part conflicting. In the Gotland Basin model, deposited Mn oxides are converted to Mn carbonate after the oxygenation of euxinic bottom waters enriched in dissolved Mn by major Baltic inflows (Huckriede and Meischner, 1996). By contrast, according to the Landsort Deep model, Mn carbonate precipitation occurs independent of oxygenation events below a euxinic water column (Lepland and Stevens, 1998; Lenz et al., 2015). In this study, we investigated Mn solid-phase signatures in recent/sub-recent well-dated sediments from the Landsort Deep and compared them to long-term observations to identify the hydrographic conditions favoring Mn carbonate formation. The comparisons of water column O2 and sulfide time series with sedimentary Mn carbonate enrichments identified long-lasting bottom water oxygenation as an important environmental factor in the enhancement of Mn carbonate precipitation (up to 32wt% Mn) in the Landsort Deep. Thus, by preventing the escape of dissolved Mn from still reducing sediments into the open water column, these conditions allow the accumulation of large amounts of Mn-oxide particles at the sediment/water interface, with their subsequent conversion to Mn carbonate. The euxinic conditions that have prevailed almost continuously in the Landsort Deep since roughly AD 2000 do not favor Mn enrichment (maximum 0.9wt% Mn), highlighting the importance of the recurring oxygenation of bottom water, most likely via medium-intensity inflows. The Mn abundances in seven sediment cores from water depths of 190–437m together with Mn balance calculations indicated that the Mn inventory in the water column in response to porewater Mn reflux and detrital Mn input is sufficient for Mn carbonate enrichment only in the deepest part of the basin.

Scalable and general synthesis of spinel manganese-based cathodes with hierarchical yolk–shell structure and superior lithium storage properties

Hierarchical yolk–shell structured cathodes with controllable composition are potentially attractive materials for the fabrication of lithium-ion batteries, but they are difficult to synthesize. In this work, we present a simple, scalable, and general morphology-inheritance strategy to synthesize spinel manganese cathodes with a hierarchical yolk–shell structure. Starting from uniform Mn carbonate spheres prepared by an ultrafast and scalable microwave-assisted method, we show that the subsequent sintering results in the formation of Mn2O3 precursors with a yolk–shell structure, which can be effectively transferred to spinel manganese cathodes via simple impregnation and solid-state reaction. Owing to the simple and scalable nature of the present strategy, materials prepared through this approach have great potential as cathodes of lithium-ion batteries, where they can lead to high specific capacity, outstanding cyclability, and superior rate capability. In particular, both LiMn2O4 and LiNi0.5Mn1.5O4 with hierarchical yolk–shell structure achieved nearly theoretical capacity, without any apparent decay after 100 cycles at 1 C. Moreover, 80% of the initial discharge capacities of both samples can be maintained for up to 500 cycles at a high rate of 10 C.

Fungal nanoscale metal carbonates and production of electrochemical materials.

Fungal biomineralization of carbonates results in metal removal from solution or immobilization within a solid matrix. Such a system provides a promising method for removal of toxic or valuable metals from solution, such as Co, Ni, and La, with some carbonates being of nanoscale dimensions. A fungal Mn carbonate biomineralization process can be applied for the synthesis of novel electrochemical materials.

Micronutrient supply through granular-coated single superphosphate under field conditions

ABSTRACTThe lack of efficient methods for soil-based micronutrient fertilization in field crops at sowing remains an important limiting factor for agricultural production in low fertility soils. Therefore, we evaluated the efficiency of single superphosphate (SSP) coated with either finely ground zinc (Zn) oxide or manganese (Mn) carbonate to supply Zn to corn (Zea mays L.), and Mn to soybean (Glycine max L.) and oat (Avena sativa L.) versus traditional sources (oxide and sulfate). One experiment for each micronutrient was performed under field conditions in two sequential growing cycles: rainy season (corn and soybean) and off-season (corn and oat). Treatments were combination of Zn or Mn fertilizers (oxide, sulfate, and SSP coated with Zn oxide or Mn carbonate) at rates of 1.25, 2.5, and 5.0 kg ha−1 of Zn or Mn, plus a control. Micronutrient fertilization showed, relative to the unfertilized control, significant increases in shoot biomass at flowering, crop yield (corn silage and soybean grain), and leaf concentration and shoot uptake of Zn and Mn during the rainy season. Residual effect of Zn on off-season corn crop represented a 43% increase in grain yield over the control. However, oat did not respond to residual Mn. The positive effects of Zn and Mn application on crop performance did not depend on fertilizer material, suggesting similar fertilizer-use efficiency. We concluded that banded application of SSP coated with either finely ground Zn oxide or Mn carbonate would be a viable option to supply these micronutrients at the time of sowing in micronutrient-deficient soils.

Ultrasonic and microwave effects on crystalline Mn(II) carbonate catalyzed biodiesel production using watermelon (Citrullus vulgaris) seed oil and alcohol (fibrous flesh) as exclusive green feedstock

ABSTRACTUltrasonic sonication and microwave irradiation exhibited pronounced effects on crystalline Mn(II) carbonate catalyzed biodiesel production using watermelon (Citrullus vulgaris) seed oil and alcohol (fibrous flesh) as exclusive green feedstock. Both ingredients, alcohol and oil, necessary for biodiesel production are extracted from watermelon fruit. Mn(II) carbonate and watermelon fruit, which are used for transesterification, are inexpensive, easily available and environmentally safe. The reactions occurred smoothly under conventional conditions and afforded good product yields. However, microwave assisted and ultrasonically assisted reactions exhibited highly significant reduction in reaction times with a trend: microwave assisted (35 min) << ultrasonically assisted (2.0 h) << conventional (8.0 h). The whole exercise is operationally simple, environmentally safe, energy saving, time saving and green, which fits well into the green chemical principles of Anastas and Warner.

Manganese carbonates as possible biogenic relics in Archean settings

AbstractCarbonate minerals such as dolomite, kutnahorite or rhodochrosite are frequently, but not exclusively generated by microbial processes. In recent anoxic sediments, Mn(II)carbonate minerals (e.g. rhodochrosite, kutnahorite) derive mainly from the reduction of Mn(IV) compounds by anaerobic respiration. The formation of huge manganese-rich (carbonate) deposits requires effective manganese redox cycling in an oxygenated atmosphere. However, putative anaerobic pathways such as microbial nitrate-dependent manganese oxidation, anoxygenic photosynthesis and oxidation in ultraviolet light may facilitate manganese cycling even in an early Archean environment, without the availability of oxygen. In addition, manganese carbonates precipitate by microbially induced processes without change of the oxidation state, e.g. by pH shift. Hence, there are several ways how these minerals could have been formed biogenically and deposited in Precambrian sediments. We will summarize microbially induced manganese carbonate deposition in the presence and absence of atmospheric oxygen and we will make some considerations about the biogenic deposition of manganese carbonates in early Archean settings.

Role of the Transition Metal Dissolution Species Formed at Li-Ion Positive Electrode Materials on the Battery Performance and Failure Modes

Detailed insight into the mechanism of interaction between electrolyte solvents and Li-ion high voltage electrodes as well as subsequent chemical cross talk is a fundamental requirement for development of improved electrical energy storage (EES) devices. At potentials > 4.2 V, surface reactivity of Li-ion positive electrode materials toward the electrolyte results in electrolyte oxidation accompanied by transition metal dissolution.[1-4] There is no doubt concerning the crucial role of the transition metal products formed in the gradual degradation of electrochemical performance in Li-ion batteries. Indeed, an impedance rise directly proportional to the concentration of the unknown MnII species in the SEI originating from LiMn2O4 was observed.[4] However, the mechanism of transition metal dissolution from Li[NixMnyCoz]O2positive electrode materials, their transport across the electrolyte, and the effect on function of the cell remain unclear. We have reported that contrary to the disproportionation mechanism proposed 30 years ago, transition metal dissolution occurs via the formation of Ni(II), Co (II/III) and Mn(II/III) coordination complexes at the Li[NixMnyCoz]O2 surface via oxidation of DEC and EC at potentials > 4.2 V. This result in the deposition of a mixture of M(II)(acac)2, M(II) oxalate, and M(II) carbonate at the anode electrode surface in the SEI.[1] In this work, using model systems, we have demonstrated that Li+ transport across the solid electrolyte interphases in Li-ion anodes is not only strongly dependent on the concentration but also on the nature of the transition metal species present in the SEI. While only a slight impedance rise is observed in the presence of Mn(II) carbonate and Mn(II) oxalate, the presence of Mn(II)(acac)2 and Mn(III)(acac)3 results in a drastic increase of resistance during cycling (Figure 1). This clearly highlights the peculiar interaction of β-diketone complexes with SEI components pinpointing these species as primary responsible for the observed impedance increase of the graphite anode. A detailed description of possible reaction mechanisms leading to the formation of metal complexes at the Li[NixMnyCoz]O2/organic carbonate electrolyte interfaces together with their effect on the the Li-ion transport across the SEI layer will be presented and discussed.

Fungal Biomineralization of Manganese as a Novel Source of Electrochemical Materials

Electrical energy storage systems such as rechargeable lithium-ion batteries (LiBs) and supercapacitors have shown great promise as sustainable energy storage systems [1-4]. However, LiBs have high specific energy density (energy stored per unit mass) and act as slow, steady suppliers for large energy demands. In contrast, supercapacitors possess high specific power (energy transferred per unit mass per unit time) and can charge and discharge quickly for low energy demands. In LiBs, graphite is the most common anode material, although high electrolyte sensitivity and low charge capacity can limit performance. Efforts have been made to improve LiB or supercapacitor performance using alternative electrode materials such as carbon nanotubes and manganese oxides (MnxOy) [3, 5-14]. Microorganisms play significant roles in metal and mineral biotransformations [15-22]. Fungi possess various biomineralization properties, as well as a filamentous mycelium, which may provide mechanical support for mineral deposition. Although some research has been carried out on the application of biological materials as carbon precursors [8, 9, 23], biomineralizing fungal systems have not been investigated. In this research, novel electrochemical materials have been synthesized using a fungal Mn biomineralization process based on urease-mediated Mn carbonate bioprecipitation [24]. The carbonized fungal biomass-mineral composite (MycMnOx/C) showed a high specific capacitance (>350 F g(-1)) in a supercapacitor and excellent cycling stability (>90% capacity was retained after 200 cycles) in LiBs. This is the first demonstration of the synthesis of electrode materials using a fungal biomineralization process, thus providing a novel strategy for the preparation of sustainable electrochemical materials.