Minerals Mn Research Articles

Paleoproterozoic manganese oxide precipitation in oxic seawater surface and reductive enrichment in anoxic seafloor

Accelerated precipitation of Mn-rich rocks in the early Paleoproterozoic ocean is considered to reflect the irreversible rise of oxygen in the atmosphere during the Great Oxidation Event (GOE), 2.501–2.220 billion years ago. But the precipitation conditions, pathways, mechanisms, and linkages to ocean redox, broadly remain unresolved. The Lagoa do Riacho Mn deposit in Borborema Province, northeastern Brazil, Ceará state, consists mainly of manganese-rich and manganese-poor silicates deposited during the GOE epoch. Negative Ce anomalies in the manganese-poor silicates point to the scavenging of Ce3+ onto Mn-oxyhydroxide reactive surfaces in the oxygenated surface waters. In contrast, samples with positive Ce anomalies, predominantly associated with the manganese-rich silicates, indicate a reductive dissolution of Mn-oxyhydroxides across a redoxcline, enriching the anoxic bottom water with Ce and Mn2+. A paleoredox reconstruction based on couple Mn, Mo, and U systematics supports the existence of the proposed Mn-oxide redox shuttle that enriched the anoxic sediment pile with Mn precipitated from the oxygenated shallow surface waters. This study uncovers a unique pathway in Paleoproterozoic Mn mineralization involving the transfer of Mn oxides from an oxygenated upper ocean reservoir to a predominantly deep anoxic silicate reservoir that was subsequently metamorphosed. The proposed Mn oxide sink switch mechanism is different from the commonly reported reductive transfer of Mn to a diagenetic carbonate sink during the Paleoproterozoic.

Iron and manganese shuttle has no effect on sedimentary thallium and vanadium isotope signatures in Black Sea sediments

Thallium and V isotopes in organic-rich sediments have recently been explored for reconstructing marine oxygenation by tracking the burial of Mn oxides either locally or globally. The ‘Fe and Mn shuttle’ is a well known mechanism that can transport elements associated with Fe and Mn oxide phases formed under mildly oxidizing shallow water environments both laterally and vertically to euxinic (sulfidic water column) deep waters. The Fe and Mn shuttle has been demonstrated to strongly affect Fe and Mo isotope compositions of sediments accumulating beneath anoxic and euxinic settings. Similar to Mo, Tl and V are also enriched in oceanic ferromanganese crust and nodules, which impart the largest isotopic offsets from modern seawater for Tl and V. Thus, the mechanism of an Fe and Mn shuttle has the potential to, but currently unconstrained, affect Tl and V isotopic compositions (ε205Tl and δ51V) in organic-rich sediments in the modern and ancient records.We have used Black Sea sediments that are known to preserve enrichment and sedimentary isotope signatures for an Fe shuttle. This is due to an Fe transport from the more oxic margin to the deep euxinic basin and corresponding enrichment in the underlying sediments. These samples were used to test for a potential Fe and Mn shuttle effect on ε205Tl and δ51V in sediments deposited under oxic, suboxic, and euxinic water columns. Authigenic ε205Tl from all three depositional settings is indistinguishable (–2.7 ± 0.3, –2.4 ± 0.5, and –2.4 ± 0.3), which is within error of the Black Sea surface seawater (–2.2 ± 0.3). In contrast, oxic and suboxic sediment have similar δ51V values (–1.06 ± 0.33‰ and –1.04 ± 0.30‰), which are significantly more negative than euxinic sediments (–0.57 ± 0.06‰).All the sediments deposited under oxic, suboxic, and euxinic water columns in the Black Sea capture ε205Tl of the surface seawater because there is almost no permanent burial of Mn oxides in this basin. This finding is consistent with the indistinguishable ε205Tl between the surface seawater and the riverine input. Sedimentary δ51V appears to be controlled predominantly by the redox state of the depositional environments with little effect from an Fe or Mn shuttle. The lack of Fe and Mn shuttle effect on ε205Tl and δ51V in the Black Sea is likely due to the shallow (∼100 m) chemocline in the strongly, 2000-m deep redox-stratified water column of this basin and very slow deep-water renewal rate. Iron and Mn in oxides are not delivered to the sediments, instead, they are dissolved and captured in the water column as iron sulfide and reduced Mn mineral phases. Our results suggest that Fe and Mn shuttle transport mechanisms may not strongly affect Tl and V isotopes, at least in extreme cases of water column redox stratification. Further work is required to constrain the isotopic signals using other modern and, by inference, diverse ancient settings for additional shuttling mechanisms.

Mineralogical Characterization of Manganese Oxide Minerals of the Devonian Xialei Manganese Deposit

The Guangxi Zhuang Autonomous Region is an important manganese ore district in Southwest China, with manganese ore resource reserves accounting for 23% of the total manganese ore resource reserves in China. The Xialei manganese deposit (Daxin County, Guangxi) is the first super-large manganese deposit discovered in China. The Mn oxide in the supergene oxidation zone of the Xialei deposit was characterized using scanning electron microscopy (SEM), energy spectrometer (EDS), transmission electron microscopy (TEM, HRTEM), and X-ray diffraction analysis (XRD). The Mn oxides have a gray-black/steel-gray color, a semi-metallic-earthy luster, and appear as oolitic, pisolitic, banded, massive, and cellular textures. Scanning electron microscopy images show that the manganese oxide minerals are present as fine-spherical particles with an earthy surface. TEM and HRTEM indicate the presence of oriented bundled and staggered nanorods, and nanopores between the crystals. The Mn oxide ore can be classified into two textural types: (1) oolitic and pisolitic (often with annuli) Mn oxide, and (2) massive Mn oxide. Pyrolusite, cryptomelane, and hollandite are the main Mn oxide minerals. The potassium contents of cryptomelane and pyrolusite are discussed. The unit cell parameters of pyrolusite are refined.

Environmental Aspects of Historical Ferromanganese Tailings in the Šibenik Bay, Croatia

The former manganese ferroalloy plant and the remaining tailings are affecting the quality of the environment in Šibenik Bay, Croatia, even though industrial activities ceased more than 25 years ago. This study has revealed that the main manganese mineral phases present in the recently collected tailings, as well as in the dust collected on the roof of the plant during the production period, are bustamite and Mn-oxides. The same type of Mn mineral phases was also found in recently collected sediments from Šibenik Bay. Detailed chemical and phase analyses (XRD, BCR sequential analysis, aqua regia and lithium borate fusion) of the dust sample revealed high manganese values (24.1%), while granulometric analysis showed that 50% of the particles are smaller than PM2.5. The influence of the tailings is visible in the sediment, but the concentrations of the potentially toxic elements determined by the sequential BCR analysis are within the legal limits. Some higher values (20.3 g/kg Mn, 595 mg/kg Pb and 494 mg/kg Zn) are detected in the tailings, which are still exposed to weathering and as such should be additionally monitored. On the other hand, this material contains a considerable number of elements that could be considered lucrative (∑ REE up to 700 mg/kg, Mn up to 23 g/kg, Fe up to 37 g/kg and Al up to 25 g/kg), opening the possibility of reuse and recovery.

Insights Into Manganese Solubilizing Bacillus spp. for Improving Plant Growth and Manganese Uptake in Maize.

Manganese (Mn) is an essential micronutrient for plant growth that is involved in the structure of photosynthetic proteins and enzymes. Mn deficiency is widespread mainly in dry, calcareous, and sandy soil, which leads to a significant decrease in crop yield. Mn-reducing bacteria promote the solubilization of Mn minerals, thus increasing Mn availability in soil. The present study aimed to assess the Mn solubilizing ability and plant growth-promoting potential of Bacillus spp. strains for maize plants with insoluble Mn compounds. Several Mn-solubilizing bacterial (MSB) strains were isolated from the maize rhizosphere using nutrient agar media amended with 50 mM MnO2. These strains were screened based on qualitative and quantitative solubilization of Mn, phosphorus, potassium, and zinc and production of ammonia. The majority of MSB strains were positive for catalase, protease, amylase, and oxidase activity, while more than 60% of tested strains were positive for lipase activity, and the production of indole-3-acetic acid and siderophores. Forty-five percent of the tested strains also showed solubilization of potassium. All the MSB strains were evaluated for their ability to promote plant growth and Mn uptake in the presence of MnO2 under axenic sand culture conditions. The results revealed that inoculation with MSB strains under sand culture significantly improved the growth of maize seedlings except for strains ASH7, ASH10, and ASH12. Comparatively, strains ASH6, ASH11, ASH19, ASH20, and ASH22 demonstrated a better increase in plant growth, fresh and dry biomass, and Mn uptake in roots and shoots than the other strains tested. All of these strains were identified as Bacillus spp. through 16S rRNA partial gene sequencing. Maize inoculation with these selected identified MSB strains also resulted in an increase in maize growth and nutrient uptake in maize roots and shoots under soil culture conditions in the presence of native soil Mn. The current study highlights the importance of MSB strain inoculation which could be a potential bioinoculants to promote plant growth under Mn deficiency.

Insights into hydrothermal controls and processes leading to the formation of the Late Ediacaran Gaoyan stratiform manganese-carbonate deposit, Southwest China

The stratiform Mn-carbonate ore from the Gaoyan deposit occurs within terrigenous-sedimentary rocks of the upper part of the Ediacaran Doushantuo Formation and is characterized by rhodochrosite spherulites. Here we examine the effect of depositional environment and hydrothermal contribution based on new petrographical, mineralogical and geochemical data to shed light on major controls on formation of sedimentary Mn mineralization. The significant geochemical characteristics such as high Mn/Fe ratios (average 32.07), high Ba content (average 1940.9 ppm), positive Eu anomalies (average 1.38) and low REE contents (average 51 ppm) reveal a hydrothermal source. Meanwhile, 87Sr/86Sr ratios of Mn ores are substantially higher than those of carbonate wall rocks and contemporaneous seawater, indicating mixing of radiogenic Sr from the Mn-rich hydrothermal extraction from underlying sediments. This explanation is supported by a positive linear correlation between 87Sr/86Sr ratios and Eu anomalies. The slightly positive Ce anomaly of most Mn carbonate ore samples is mirrored in the negative Ce anomaly of black shale, while different Ce anomalies provide evidence that Mn redox cycling took place across a sub-oxic to anoxic/euxinic water interface. The euxinic conditions, as evidenced by the co-occurrence of fine-grained disseminated pyrite to framboidal aggregates (average diameters <5 μm) with rhodochrosite, can account for the high Mn/Fe ratios via ongoing Fe-sulfide precipitation. Calcite introduction to metal-rich hydrothermal waters with a lower pH relative to surface waters, together with Mn-oxide reduction and sulfate reduction, triggers substantial increases in rhodochrosite saturation and precipitation near the water–sediment interface. Subsequently, increasing Ca2+ in early diagenesis resulted in the precipitation of kutnohorite rims. Altogether, we develop a hydrothermal sedimentary model of the Gaoyan Mn mineralization with rhodochrosite spherulites as the hydrothermal sedimentary mineral phases, and kutnohorite forming during early diagenesis. Slightly light carbon isotope compositions (∼–6.1‰) of the manganese carbonate ores than those of normal dolostones (∼–4.8‰) suggest a limited carbon source from oxidation of organic material by methanogenesis processes during burial diagenesis. This model supports the model for direct Mn-carbonate precipitation from redox-stratified water columns and means that sedimentary Mn mineralization may be mainly controlled by hydrothermal contribution, rather than seawater redox conditions. This means exploration strategies that focus on oxic zone alone as an indication of prospectivity may be ineffective.

Geochemistry and Diagenetic Evidence of Middle-Late Permian Deposits, Northern Iran

This study provides a evaluation of the initial carbonate mineralogy, and diagenetic condition of the Ruteh Formation, a middle-late Permian carbonate sequence, in the Emarat section in Central Alborz, northern Iran. 200 samples were examined for petrographical contents and thirty-four samples were collected for geochemical analysis. The high Sr and Na contents, Sr/Na>1, and the presence of dolomites and dissolution fractures are indicative aragonite early mineralogy. The diagenetic process in the Ruteh Fm. are an indication of the marine, meteoric and burial diagenetic environments. The original carbonate texture in the Ruteh Fm. are Severely affected by diagenetic process. The data obtained from the values of the Major (Ca and Mg), minor (Sr, Na, Fe, and Mn), oxygen and carbone isotopes show the initial aragonite composition of the Ruteh Fm. deposited in a subtropical shallow water. An open diagenetic system was indicated by changes in the values of Sr / Ca and δ18O vs. Mn. The shallow burial diagenetic temperature of the Ruteh carbonate was approximate 28.6°C with the maximum diagenetic temperature of 53.4°C.

Mineralogy and petrogenesis of fracture coatings in Athabasca Group sandstones from the McArthur River uranium deposit

ABSTRACT The McArthur River unconformity-related uranium deposit, located in the Athabasca Basin of Saskatchewan, Canada, is structurally hosted near the unconformity between Archean to Paleoproterozoic metasedimentary basement and the Proterozoic Athabasca Group sandstones. In this study, the mineralogy and geochemistry of fracture materials within the entire ca. 550 m thickness of the Athabasca Group sandstones and the metasedimentary (host) rocks from the McArthur River area were used to determine the paragenetic sequence and origin of minerals in and near the fractures. Our work sought to determine if the host minerals record elements associated with the uranium deposit at depth and if they could be used to guide exploration (vectoring). Fracture orientations indicate that most are moderately dipping (&amp;lt;50°) and provided permeable pathways for fluid movement within the basin, from below, and through the overlying sedimentary rocks. Many of the fractures and adjacent wall rocks record evidence of multiple distinct fluid events. Seven types of fracture fillings were identified from drill core intersecting the Athabasca Basin and present distinct colors, mineralogy, and chemical features. Brown (Type 1) and pink (Type 7) fractures host paragenetically late botryoidal goethite, Mn oxide minerals, and poorly crystallized kaolinite that formed from relatively recent low-temperature meteoric fluids, as indicated by poor crystallinity and low δ2H values of –198 to –115‰. These minerals variably replaced higher temperature minerals that are rarely preserved on the fractures or in wall rock near the fractures. Hydrothermal alteration associated with the mineralizing system at ca. 200 °C is recorded in assemblages of dickite, well-crystallized kaolinite, and spherulitic dravite in some white and yellow (Type 2) and white (Type 3) fractures, as reflected by the crystal habits and variable δ2H values of –85 to –44‰. Fibrous goethite in white and yellow (Type 2) and black and orange (Type 5) fractures and microfibrous Mn oxy-hydroxide minerals in black (Type 4) fractures also crystallized from hydrothermal fluids, but at temperatures less than 200 °C. White and yellow fractures (Type 2) containing fibrous goethite reflect fracture networks indicative of hydrothermal fluids associated with the mineralizing system during primary dispersion of pathfinder elements and therefore extend the deposit footprint. Brown (Type 1) and pink (Type 7) fractures have low δ2H values in botryoidal goethite and poorly crystallized kaolinite and are indicative of the movement of meteoric waters. Secondary dispersion of elements from the deposit to the surface on some fractures is evidence that fractures are pathways for element migration from the deposit to the surface, over distances exceeding ∼500 m.

Re-evaluation of the mechanical properties and creep resistance of commercial magnesium die-casting alloy AE44

This paper presents a re-evaluation of the room temperature mechanical properties and high temperature creep resistance of magnesium die-casting alloy AE44 (Mg-4Al-4RE) in light of the influence of minor Mn addition. It is shown that the Mn-containing AE44 exhibits distinct age hardening response upon direct ageing (T5) due to the precipitation of nanoscale Al-Mn particles, as reported previously in a similar alloy. The T5 ageing leads to a significant improvement in strength with similar ductility. Consequently, the T5-aged AE44 has a remarkably better strength-ductility combination than most Mg die-casting alloys and even the Al die-casting alloy A380. Minor Mn addition is also shown to be critical for the creep resistance of AE44 whereas the influence of the RE constituent is not as significant as previously thought, which reaffirms that precipitation hardening of the α-Mg matrix is more important than grain boundary reinforcement by intermetallic phases for the creep resistance of die-cast Mg alloys. The findings in this work could provide new application perspectives for AE44, particularly in the automotive industry.

Dynamic biogeochemical cycling and mineralization of manganese of hydrothermal origin after the Marinoan glaciation

The aftermath of the Marinoan glaciation is an important period in the evolutionary history of Earth. Here we report on the dynamically biogeochemical cycling and organic mineralization processes of Mn in the Doushantuo Formation, Yangtze Block, South China, which was sourced hydrothermally during this time. This process occurred in an extensional tectonic setting as the water depth became shallower. Mn(+2) ascended with deep reducing hydrothermal fluids and accumulated in the form of Mn(+4) near the redox interface of locally oxidized water, which may be associated with metabolism by autotrophic microorganisms. Mn(+4) was reduced to Mn(+2), with organic matter acting as an electron donor during its degradation, which may be mediated by heterotrophic microorganisms. Mn(+2) in the water combined with CO32− generated by the oxidation and degradation of organic matter to form rhodochrosite. Algae and bacteria provided nucleation sites for the crystallization of rhodochrosite. Finally, spherical and ellipsoidal rhodochrosite with a biological structure and negative carbon isotope values (average δ13CPDB = −7.04‰) under the influence of Mn bacteria was formed. The input of hydrothermal material, mineralization involving the participation of organic matter, and mixed enrichment during syngenesis and syngenetic–early diagenetic stage were unique factors in the formation of Mn deposits in the Doushantuo Formation along the northern margin of the Yangtze Block. This represents the first report of Mn mineralization in carbonate form in the Ediacaran globally (Doushantuo Formation), and provides new insights into the biogeochemical cycling of Mn in the Ediacaran.

DIRECT Re-Os DATING OF MANGANESE CARBONATE ORES AND IMPLICATIONS FOR THE FORMATION OF THE ORTOKARNASH MANGANESE DEPOSIT, NORTHWEST CHINA

Abstract Sedimentary manganese carbonate deposits, the major economic source of Mn globally, are the product of complex interactions that occur in the marine environment, including both biological Mn(II) oxidation and Mn(IV) reduction. Precise and accurate age constraints for Mn carbonate deposits have been difficult to obtain, hindering the understanding of possible correlations between Mn metallogenic and paleoenvironmental processes at regional to global scale. The involvement of organic matter during Mn carbonate mineralization, however, allows for the Re-Os system, an ideal geochronological tool for determining the depositional or alteration ages of organic-rich rocks, to be applied. Here we present the first Re-Os systematics of Mn carbonate ores from the giant Ortokarnash Mn deposit in the West Kunlun orogenic belt, Xinjiang, China. The use of the Re-Os geochronometer, along with petrographic, whole-rock total organic carbon, and major element analyses, allows for the depositional age and mineralizing processes to be directly constrained. The Mn carbonate ores with relatively homogeneous initial 187Os/188Os values yield a robust mineralization age of 320.3 ± 6.6 Ma (Model 1; Isoplot regression) or 321.8 ± 14.5 Ma (Monte Carlo simulation). This age correlates well with U-Pb ages of the youngest detrital zircon group from the footwall volcanic breccia-bearing limestone and a newly obtained Re-Os age from the hanging-wall marlstones. Enrichment of hydrogenous Re and Os in the Ortokarnash Mn carbonate ores is likely related to the variable redox environments during Mn carbonate mineralization, where Re tends to be preserved in the organic matter that persists following the diagenetic reduction of the Mn(IV) oxyhydroxides in suboxic or anoxic sediment pore water. Conversely, Os was likely absorbed by Mn(IV) oxyhydroxides in oxic seawater during Mn(II) oxidation. Elevated Osinitial(i) for the Mn carbonate ores relative to that of the coeval global seawater value suggests that an increased riverine flux may have been a contributing factor leading to Mn mineralization.

Bioleaching of Transition Metals From Limonitic Laterite Deposits and Reassessment of the Multiple Roles of Sulfur-Oxidizing Acidophiles in the Process.

Using acidophilic bacteria to catalyze the reductive dissolution of oxidized minerals is an innovative process that facilitates the extraction of valuable base metals (principally cobalt and nickel) from limonites, which are otherwise often regarded as waste products of laterite mining. The most appropriate conditions required to optimize reductive mineral dissolution are unresolved, and the current work has reassessed the roles of Acidithiobacillus spp. in this process and identified novel facets. Aerobic bio-oxidation of zero-valent sulfur (ZVS) can generate sufficient acidity to counterbalance that consumed by the dissolution of oxidized iron and manganese minerals but precludes the development of low redox potentials that accelerate the reductive process, and although anaerobic oxidation of sulfur by iron-reducing species can achieve this, less acid is generated. Limited reduction of soluble iron (III) occurs in pure cultures of Acidithiobacillus spp. (Acidithiobacillus thiooxidans and Acidithiobacillus caldus) that do not grow by iron respiration. This phenomenon (“latent iron reduction”) was observed in aerated cultures and bioreactors and was independent of electron donor used (ZVS or hydrogen). Sufficient ferrous iron was generated in the presence of sterilized hydrophilic sulfur (bio-ZVS) to promote the effective reductive dissolution of Mn (IV) minerals in limonite and the solubilization of cobalt in the absence of viable acidophiles.

Application of the C-N fractal model, factor analysis and geochemical mineralization probability index (GMPI) for delineating geochemical anomalies related to a Mn-Fe deposit and associated Cu mineralization in west-central Sinai, Egypt

The west-central Sinai area includes one of the most productive manganese deposits in Egypt (Um Bogma Mn-Fe ore). The explored area is covered by a Carboniferous and Cambro-Ordovician sedimentary succession overlying Precambrian basement rocks. The purpose of this study is to delineate geochemical anomalies of ore and related elements and track their dispersion trains, which may lead to the discovery of unknown ore deposits. For this purpose, 143 stream sediment samples were analysed and the data were interpreted using the concentration–number (C-N) fractal model, factor analysis and the geochemical mineralization probability index (GMPI). Geochemical thresholds obtained from the C-N fractal model, factor scores and GMPI were used for constructing geochemical anomaly maps and delineating probable anomalous sites. The spatial distribution of Mn, Cu, Co, Pb and Zn anomalies was correlated to Mn and Cu mineralization sites whereas those of Fe and Cr were consistent with mafic rock distributions. Factor analysis revealed significant element associations for mineralization (Cu, Co, Mn, Zn, Pb), country rock composition (Fe, Cr) and element mobility (Cd, Zn). The spatial distribution of ore elements (Mn, Cu) delineated by the factor score and GMPI distribution maps was confirmed and more accurately interpreted using geochemical anomaly maps constructed based on the fractal-derived thresholds. Based on the current study, recent Cu and Mn mineralization sites may be suggested. Cobalt, Zn, Pb and Cd are suggested as efficient pathfinder elements for marine Mn deposits. A dispersion sequence of Cd&gt;Mn&gt;Co&gt;Pb&gt;Zn&gt;Cu&gt;Cr&gt;Fe was proposed based on the threshold distribution patterns of these elements. Supplementary material: Tables S1–S3 and Figures S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.5463511

Field to laboratory comparison of metal accumulation on aged microplastics in coastal waters

The ubiquity of microplastics in the environment has attracted much attention on their risks. Though newly produced plastics were considered inert to aqueous metals, a few studies suggest aged microplastics can accumulate metals. Still, knowledge gap exists on the comparability of metal accumulation in field condition and that acquired in controlled laboratory settings. Accordingly, we comparatively assessed the field accumulation and laboratory adsorption of metals on aged microplastics in coastal waters. Microplastics of different polymeric types were aged for 8 weeks at three coastal sites with different contamination levels. Microplastics accumulated metals to substantial concentrations during ageing (median concentrations, μg g−1: Fe = 950, Mn = 94, Zn = 19, Cu = 2.8, Ni = 1.7, Pb = 1.6, and Cd = 0.005). Adsorption capacity of (aged) microplastics was evaluated in laboratory using a stable isotope tracer method. At environmentally realistic concentrations (μg L−1, 114Cd = 1.7, 65Cu = 4.4, 62Ni = 5.4, 206Pb = 0.5, and 68Zn = 13), the median concentrations of newly adsorbed isotopes on the aged microplastics were 0.01, 1.4, 0.07, 0.56, and 1.1 μg g−1, respectively, one to two orders of magnitude higher than those adsorbed on pristine microplastics. However, the composition pattern of metals accumulated on aged microplastics differed from the composition of metals newly adsorbed in laboratory: the prior one reflected the contamination status of ageing sites and varied by polymeric types; whereas the laboratory newly adsorbed metals on aged microplastics were uniformly correlated to particulate Fe and Mn concentrations, suggesting Fe and Mn mineral coatings mediated the ensuing metal adsorption. Such discrepancy unveiled the complexity of metal accumulation behavior in the real environment and highlighted that cares should be taken when translating laboratory findings to risk assessment of metal contaminated microplastics in the real environment.

Spectral and chemical studies of iron and manganese oxyhydroxides in laterite developed on ultramafic rocks

AbstractIron (Fe) oxyhydroxides (goethite and hematite) and manganese (Mn)‐oxyhydroxides (lithiophorite, asbolane, lithiophorite‐asbolane intermediate) are typically fine‐grained and poorly crystalline in nature, and as such are difficult to identify by conventional X‐ray powder diffraction. This study employs Raman spectroscopy and electron probe microanalysis (EPMA) to characterize Fe‐ and Mn‐oxyhydroxides found in the Berong Ni–Co laterite deposit at Palawan Island, Philippines. Accurate identification of these minerals is important because these phases contain high Ni and Co contents. Goethite and hematite occur in a wide range of textures, which are related to their compositional variations with respect to Ni, Al, Mn, Cr, and Si. The change in the intensity of the Raman peaks can be linked to the variable concentrations of Ni, Al, Mn, Cr, and Si in goethite. These chemical variations affect the textural transformation of goethite from amorphous to cryptocrystalline. Lithiophorite, asbolane and their intermediates were properly distinguished using Raman spectroscopy. EPMA data shows that these Mn minerals contain appreciable concentrations of Ni, Co, Al, and Fe. The band shift from lithiophorite to asbolane end terms in the 486–593 cm−1 domain indicates the substitution of Al in lithiophorite by Ni, Co, and Fe.

Geochemical and mineralogical correlations between the bog iron ores and roasted iron ores of the Podravina region, Croatia

Throughout the Podravina region, NE Croatia, over one hundred locations with signs of iron production, dating to the late Antique period and the Middle Ages, have been discovered in the last 30 years. Recently, signs of various bog iron ore types and formations were discovered throughout the area. This study investigates the mineralogical and geochemical characteristics of local bog iron and roasted iron ores. Furthermore, statistical clustering of different geochemical components in the ores is presented, while the abundance and distribution of macro-, micro- and rare earth elements (REE) and how they correlate within the bog iron ores and roasted iron ores is considered. A total of 15 samples acquired from geological investigations and 13 samples found during archaeological excavations were analysed using geochemical and mineralogical methods. In bog iron ores, X-ray diffraction (XRD) confirmed goethite and quartz as the primary mineral phases, while roasted iron ores contained several Fe minerals and had variable quartz and clay mineral contents. Chemical analyses confirmed high Fe contents in both bog iron ores (up to 70.89 mass. %) and roasted iron ores (up to 84.97 mass. %), with a distinct differentiation of Fe and Si between the different bog iron ore types. Scanning electron microscopy with attached EDS detector (SEM-EDS) showed features of laminar Fe and Mn mineralization, confirming the theory that bog iron ore forms as seasonal precipitation from groundwater. Using the hierarchical clustering analysis, a geochemical correlation of the iron component in bog iron ores and roasted iron ores was compared to other major oxides, micro- and REEs. It was established that the iron component has very little influence on REE and microelements behaviour. Therefore, microelements and REEs were used as a tracer for establishing a geographical connection between the bog iron ores and roasted iron ores in the Podravina region.

Hydrogen peroxide decomposition into oxygen in different soils: Kinetic analysis, mechanism and implication in catalyzed hydrogen peroxide propagations

Rapid hydrogen peroxide (H2O2) decomposition in soils is one of the most important barriers standing in front of catalyzed H2O2 propagations (CHP) for soil and groundwater remediation, and the rates depend greatly on soil components. However, there are lack of indicators to quantitatively evaluate the processes in various soils. Different from previous studies focusing on H2O2 decomposition, O2 production kinetics are more valuable due to the direct relationship with H2O2 utilization. In this contribution, O2 production during H2O2 decomposition in the soil slurry was in situ detected using a fiber-optic oxygen transmitter. A kinetic model of O2 production was developed, which can be fitted well by the measured data of 18 soil samples. A kinetic constant on O2 production (kO2) ranging from 0.001 min−1 to 0.057 min−1 was obtained from the model, which represents the diverse catalytic activity of the soils. The constant kO2 is correlated with the contents of manganese, iron as well as inorganic carbon in the soils, and Mn mineral is the dominant factor. Three types of soils were selected to investigate the effect of acid-washing and stabilizer phosphate addition on phenol oxidation in CHP. Acid-washing can greatly suppress O2 production, while phosphate addition is not desirable for the highly active soils. Phenol slightly inhibits O2 production in the soils with higher kO2 values, which are inverse with those of phenol degradation. Acid-washing can remove Mn minerals but retain most of Fe components, and accordingly increase phenol degradation. Both hydroxyl radicals and superoxide radicals contribute to phenol degradation, and the latter ones display a more significant role. This work increases the understanding of the mechanism of H2O2 decomposition in the soils and provides a parameter (kO2) to guide CHP technologies in soil remediation.

Self-corrosion, electrochemical and discharge behavior of commercial purity Al anode via Mn modification in Al-air battery

The self-corrosion, electrochemical and discharge behavior of commercial purity Al anode via Mn modification in Al–air battery was studied by the hydrogen evolution, weight loss, electrical conductivity, electrochemical and discharge tests. Results show that the synergetic effects of the dissolved Mn and Mn-modifying Al3Fe intermetallic decrease the weight loss and inhibit the hydrogen evolution of commercial purity Al in NaOH solution when minor Mn is introduced. However, more Mn addition leads to the formation of Al6Mn intermetallic, which has little effect on the weight loss, but accelerates the hydrogen evolution. Mn introduction plays a positive role in activating Al anodes, resulting in a decrease in the anodic polarization and an increase in the discharge voltage. Among all the commercial purity Al–xMn anodes, 0.1 wt% Mn addition exhibits the best discharge efficiency for Al–air battery.

Oxidative dissolution of TcO2 by Mn(III) minerals under anaerobic conditions: Implications on technetium-99 remediation

Manganese oxides are prolific minerals with strong oxidizing properties causing them to strongly influence the stability of any redox sensitive metal and metalloid reduced species in the environment. Their potential to oxidize reduced species is disproportionate to their concentration due to regeneration of Mn(III) mineral formed by abiotic processes or by microorganisms even under suboxic conditions. Tc-99 is produced during uranium fission in nuclear power generation and it is a risk driving environmental contaminant because it is found as highly soluble Tc(VII)O4− under oxidizing conditions. Current remediation efforts have focused on the immobilization of highly soluble Tc(VII) to sparingly soluble Tc(IV) under anoxic conditions. This publication investigates for the first time the impact of Mn(III) minerals on the oxidative dissolution of TcO2 under anaerobic conditions. α-Mn(III)2O3 and γ-Mn(III)OOH were used in batch experiments in contact with TcO2 under anaerobic conditions at different pH values and solid:liquid ratios and in the presence of cations common in groundwater. Both minerals incurred significant oxidation of TcO2 and consequently, release of pertechnetate in the aqueous phase at pH 6.5, and negligible oxidation of TcO2 at pH 8.0. For both minerals, increasing the solid:liquid ratio increased the extent of TcO2 oxidation. γ-Mn(III)OOH was insensitive to the presence of Ca2+ and Mn2+ ions, whereas α-Mn(III)2O3 sorbed Ca2+, which substantially reduced the mineral's oxidative capacity. These experimental findings demonstrate the liability of manganese minerals in oxidizing Tc(IV) insoluble phases to highly soluble Tc(VII) even in the absence of oxygen and highlights the need to be taken into account when it comes to remediation efforts for the abatement of Tc-99 in the environment.

Control of basement on Paleozoic mineralizations in the Wuyi metallogenic belt

The Wuyi metallogenic belt can be divided into the South and the North Wuyi metallogenic belt by the ENE-trending Nanping–Ninghua–Ganzhou Tectonic Belt. In the Wuyi metallogenic belt, Paleozoic mineralization, which has caused typical deposits such as the Yongping, Fenglin, and Yushui Cu deposits and the Makeng Fe deposit, exhibits notable variations. However, systematic research on the controlling factors of these mineralization episodes is lacking. In order to understand the Paleozoic minerlization in the Wuyi metallogenic belt, we study the genesis of typical deposits in Wuyi metallogenic belt. The phenomenon of “basal ore control” was observed as different basement units control different ore types in the Wuyi metallogenic belt. We believed that Paleozoic mineralization in the Wuyi metallogenic belt includes siliceous–carbonate Jingshe, Lindi, and Chuanshan Formations, which are related to the Fe–Mn deposits such as the Makeng Fe deposit, Dapai Fe–Pb–Zn deposit, and Luoyang Fe deposit in the Southwest Fujian Province, carbonate formations of the Hutian Group related to Cu deposits such as the Yushui Cu deposit in the North Guangdong Province of the southern Wuyi region, and the Carboniferous Outangdi Formation related to the Yongping and Fenglin Cu deposits in the Northeast Jiangxi Province of the northern Wuyi region. Based on a systematic analysis on typical metallogenic deposits and basement characteristics in the Wuyi metallogenic belt, we proposed that the Paleozoic mineralization is not only controlled by Paleozoic strata and Mesozoic magmatism, but also by the basement. The basement controls Paleozoic Cu mineralizations in the southern and northern Wuyi regions. However, Fe–Mn mineralization is mostly related to Late Paleozoic sedimentation. The superposition and transformation of Mesozoic magmatism to the basement and Paleozoic strata is an indispensable factor in the Cu and Fe–Mn mineralizations in the Wuyi metallogenic belt.