Mn Enrichment Research Articles

Apportionment of some chemical elements in soils around the coal mining area in northern Bangladesh and associated health risk assessment

In this work, fifteen chemical elements viz., Pb, Cd, Cr, As, Ag, Mn, Fe, Co, Ni, Cu, Zn, Na, K, Ca, and Mg were estimated in the coal mine-impacted soil samples sourced from Barapukuria coal mine area of Bangladesh using atomic absorption spectrometer and flame photometer for assessing their contamination levels with an implication to human health and environment. The level of considered elements was found to be lower compared to their corresponding world normal limit, except for Zn. Physicochemical properties of soils such as pH, oxidation-reduction potential, and electrical conductivity, as measured using a multiparameter meter in aqueous solution, indicated the acidic nature of soils with the presence of considerable oxidizing and ionic substances. Principal component, cluster, and correlation analyses ascertained the probabilistic anthropogenic sources of elemental contaminations and significant inter-parameter associations. These analyses suggest that Zn, Cu, Ni, Co, Cd, Mn, and As in soil originated from anthropogenic activities, particularly from the adjacent coal mining operations, indicating a common source of origin. Enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), ecological risk factor (Er), potential ecological risk index (RI), and human health risk assessment of chemical elements were employed for evaluating the impact of potentially hazardous elements in soils on surrounding environment and local residents. EF values suggest a significant enrichment of Ag, As, Zn, Cd, Pb, Co, Ni, Mn, and Cu in soils having anthropogenic origin while K, Cr, Ca, Na, and Mg originated from geogenic sources. The Igeo and CF data indicate a considerable accumulation of Cd, As, Ag, and Zn in the soil. A moderate risk potential was manifested by the Er and RI indices posing a threat to the soil environment. The non-carcinogenic threat was observed mostly among the children cohort due to the preponderance of these elemental concentrations.

The Chemostratigraphy of the Murray Formation and Role of Diagenesis at Vera Rubin Ridge in Gale Crater, Mars, as Observed by the ChemCam Instrument

AbstractGeochemical results are presented from Curiosity's exploration of Vera Rubin ridge (VRR), in addition to the full chemostratigraphy of the predominantly lacustrine mudstone Murray formation up to and including VRR. VRR is a prominent ridge flanking Aeolis Mons (informally Mt. Sharp), the central mound in Gale crater, Mars, and was a key area of interest for the Mars Science Laboratory mission. ChemCam data show that VRR is overall geochemically similar to lower‐lying members of the Murray formation, even though the top of VRR shows a strong hematite spectral signature as observed from orbit. Although overall geochemically similar, VRR is characterized by a prominent decrease in Li abundance and Chemical Index of Alteration across the ridge. This decrease follows the morphology of the ridge rather than elevation and is inferred to reflect a nondepositionally controlled decrease in clay mineral abundance in VRR rocks. Additionally, a notable enrichment in Mn above baseline levels is observed on VRR. While not supporting a single model, the results suggest that VRR rocks were likely affected by multiple episodes of postdepositional groundwater interactions that made them more erosionally resistant than surrounding Murray rocks, thus resulting in the modern‐day ridge after subsequent erosion.

Depositional environment and metal distribution in mangrove sediments within middle region of tropical estuaries, Karnataka, west coast of India

Two mangrove sediment cores representing middle region of the Panchagangavali Estuary (one each at Chakra Estuary and Halady Estuary) were analysed for sedimentological and geochemical parameters. The data revealed prevalence of uniform violent hydrodynamic energy condition in the Chakra Estuary (core G3), whereas, varying and relatively calm hydrodynamic energy conditions in the Halady Estuary (core G4). All the studied metals (Al, Fe, Mn, Ni, Zn, Cu and Cr) were of mainly lithogenic origin in both the estuaries, except Co which may be derived from a different source. The Enrichment Factor (EF) indicated deficiency to minimal enrichment of Fe, Mn, Ni, Zn, Cu and Co whereas, Cr showed a moderate enrichment in sediments. However, metals Fe, Ni, Zn, Cr and Cu were relatively enriched in the top section 3 of Halady Estuary indicating their enhanced release in recent years possibly due to increased human activities and high rain fall in the catchment area.

Manganese-rich deposits in the Mesoproterozoic Gaoyuzhuang Formation (ca. 1.58 Ga), North China Platform: Genesis and paleoenvironmental implications

The redox state of the surface ocean–atmosphere system has long been considered to have been remarkably stable during the mid-Proterozoic (ca. 1800–800 Ma); however, there is a growing body of evidence that supports dynamic redox fluctuations during this time. Sedimentary Mn enrichment in the ca. 1.58 Ga Gaoyuzhuang Formation (North China) may represent an important archive of mid-Proterozoic paleoenvironmental conditions. We present a sedimentological and geochemical study of the Mn-rich carbonate succession in the Gaoyuzhuang Formation in order to further elucidate the genesis and paleoredox implications of this Mn-rich deposit. We suggest that the Mn-rich interval was deposited in deep subtidal environments close to storm wave-base. Manganese occurs either as millimeter-sized Mn-oxide (pyrolusite) nodules or as Mn-rich dolomite, which features moderately positive I/(Ca+Mg) values (0.5–1.7 μmol/mol) and Ce anomalies (1.1–1.2). In contrast, the underlying and overlying carbonates that lack Mn-oxides were deposited in a shallow subtidal environment above fair-weather wave-base. They have relatively low I/(Ca+Mg) values (<0.5 μmol/mol) and negligible Ce anomalies (average Ce/Ce* = 1.05 ± 0.05). Thus, we suggest that during the deposition of the highly Mn-enriched strata shallow seawaters were sufficiently oxygenated to drive active redox cycling of Mn, and that this interval was bracketed by less-oxygenated shallow marine conditions. Given the widespread distribution of the Mn-rich deposits across the North China platform, we argue that the Mn-rich deposits may have recorded a basin-scale, pulsed oxygenation. The association of this interval with enigmatic macrofossils in the overlying strata of the upper Gaoyuzhuang Formation warrants further investigation of the potential link between pulsed episodes of oxygenation and evolutionary advances in the early Mesoproterozoic.

Enrichment and Occurrence of Mn in 5-2 Coal from Qinglongsi Coal Mine, Northern Ordos Basin, China.

High concentrations of Mn were observed in 5–2 coal (Jurassic age) from Qinglongsi coal mine in the Northern Ordos Basin. To study the occurrence characteristics and sedimentary environment of the 5–2 coal (3.9 m), 22 samples were collected from a mining face. The test result indicates that the 5–2 coal is in low-ash, high-volatile, very low-sulfur, and bituminous rank, with high inertinite content. The minerals in Jurassic 5–2 coal are composed primarily of kaolinite, siderite, calcite, quartz, pyrite, K-feldspar, and fluorapatite. The Mn element is enriched in the upper part of the 5–2 coal seam with an average of 1243.01 μg/g, which is about 17.5 times higher than the average of world hard coal. The concentration level of Mn has a positive correlation with that of Fe2O3 and carbonate minerals. A weak reduction environment of the coal-accumulating swamp may induce the enrichment of Mn, which is mainly carried by siderite in the 5–2 coal.

Arctic Continental Margin Sediments as Possible Fe and Mn Sources to Seawater as Sea Ice Retreats: Insights From the Eurasian Margin

AbstractContinental margins are hot spots for iron (Fe) and manganese (Mn) cycling. In the Arctic Ocean, these depositional systems are experiencing rapid changes that could significantly impact biogeochemical cycling. In this study, we investigate whether continental margin sediments north of Svalbard represent a source or sink of Fe and Mn to the water column and how climate change might alter these biogeochemical cycles. Our results highlight that sediments on the Yermak Plateau and Sofia Basin exhibit accumulations of Fe and Mn phases compared to average shale. Conversely, sediments from the Barents Sea slope exhibit lower enrichments of Fe and Mn compared to average shale, with the exception of enriched, near‐surface sediment layers. Pore waters from these slope sites provide evidence for Fe and Mn reduction and diffusion of Fe and Mn into near surface sediments, which are susceptible to physical or biogeochemical remobilization. These regional patterns are best explained by the spatial distribution of sea ice coverage and labile organic carbon fluxes to the seafloor. As sea ice continues to retreat and the Yermak Plateau becomes seasonally ice‐free, productivity is expected to increase, which would increase the flux of carbon to the sediments, thereby increasing oxidant demand, and the reduction of Fe and Mn mineral phases. Our results suggest that as sea ice continues to retreat, the Yermak Plateau and other Arctic continental margins could become sources of Fe and Mn to Arctic bottom waters.

Insights into the regulation of FeNa catalysts modified by Mn promoter and their tuning effect on the hydrogenation of CO2 to light olefins

This study unravels the effect of Mn promoter on the surface enrichment and competition of promoters and the evolutions of the chemical and structural of Fe species during the reaction, and illustrates the regulation of FeMn and FexCy for CO2 conversion and hydrogenation of intermediates. With the contents of Mn promoter increasing from 0.5% to 10.0%, the selectivity of light olefins decreasing from 38.73% to 30.58% and the ratio of olefin to paraffin decreases from 4.97 to 3.56. The surface ratio of Mn/Fe and Na/Fe is much higher than the impregnation ratio, which confirms the surface enrichment of Mn and Na promoters. It turns out that the iron oxides are transformed into iron carbides in the bulks and oligomeric FexOy on the surface after reaction. The enrichment of Mn promoters leads to more surface Fe species near the Mn promoters for the strong adsorption of CO2 and decreases the surface actual density of FexCy sites for the hydrogenation of CO to hydrocarbons, which consequently decreases the conversion of CO2 and the FTY value. The increasing content of Mn promoters from 0.5% to 3.0% also increases the adsorption ability of H2 on the surface of iron carbides, which is possibly associated with the hydrogenation of intermediates and leading to decreasing of the ratio of olefins to paraffins ranging from C2-C4.

Hydrothermal cerium oxide in manganese-oxide-cemented breccia, Quadrilátero Ferrífero of Minas Gerais, Brazil

Cerium (Ce) oxide has been found in Mn-oxide-cemented breccia in the Quadrilátero Ferrífero of Minas Gerais, and identified as cerianite-(Ce) on the basis of backscattered-electron imaging and energy-dispersive spectrometry. The Ce oxide compound occurs as nano- to microscale crystals that are dispersed within, or locally concentrated along, colloform bands of cryptomelane, and in open spaces. The breccia shows a prominent positive anomaly of Ce and has enrichment of Mn, Cd and Hg. The occurrence of abundant cryptomelane, a mineral typically formed under near-surface conditions, and its colloform bands that cement angular fragments of vein quartz suggest that Ce oxide directly precipitated as colloidal particles by supersaturation under low-temperature hydrothermal conditions that followed seismic rupturing. This scenario is remarkable because little is known about natural Ce oxide of hydrothermal origin.

Kimberlite Metasomatism of the Lithosphere and the Evolution of Olivine in Carbonate-rich Melts — Evidence from the Kimberley Kimberlites (South Africa)

AbstractOlivine is the most abundant phase in kimberlites and is stable throughout most of the crystallization sequence, thus providing an extensive record of kimberlite petrogenesis. To better constrain the composition, evolution, and source of kimberlites we present a detailed petrographic and geochemical study of olivine from multiple dyke, sill, and root zone kimberlites in the Kimberley cluster (South Africa). Olivine grains in these kimberlites are zoned, with a central core, a rim overgrowth, and occasionally an external rind. Additional ‘internal’ and ‘transitional’ zones may occur between the core and rim, and some samples of root zone kimberlites contain a late generation of high-Mg olivine in cross-cutting veins. Olivine records widespread pre-ascent (proto-)kimberlite metasomatism in the mantle including the following features: (1) relatively Fe-rich (Mg# &amp;lt;89) olivine cores interpreted to derive from the disaggregation of kimberlite-related megacrysts (20 % of cores); (2) Mg–Ca-rich olivine cores (Mg# &amp;gt;89; &amp;gt;0·05 wt% CaO) suggested to be sourced from neoblasts in sheared peridotites (25 % of cores); (3) transitional zones between cores and rims probably formed by partial re-equilibration of xenocrysts (now cores) with a previous pulse of kimberlite melt (i.e. compositionally heterogeneous xenocrysts); (4) olivine from the Wesselton water tunnel sills, internal zones (I), and low-Mg# rims, which crystallized from a kimberlite melt that underwent olivine fractionation and stalled within the shallow lithospheric mantle. Magmatic crystallization begins with internal olivine zones (II), which are common but not ubiquitous in the Kimberley olivine. These zones are euhedral, contain rare inclusions of chromite, and have a higher Mg# (90·0 ± 0·5), NiO, and Cr2O3 contents, but are depleted in CaO compared with the rims. Internal olivine zones (II) are interpreted to crystallize from a primitive kimberlite melt during its ascent and transport of olivine toward the surface. Their compositions suggest assimilation of peridotitic material (particularly orthopyroxene) and potentially sulfides prior to or during crystallization. Comparison of internal zones (II) with liquidus olivine from other mantle-derived carbonate-bearing magmas (i.e. orangeites, ultramafic lamprophyres, melilitites) shows that low (100×) Mn/Fe (∼1·2), very low Ca/Fe (∼0·6), and moderate Ni/Mg ratios (∼1·1) appear to be the hallmarks of olivine in melts derived from carbonate-bearing garnet-peridotite sources. Olivine rims display features indicative of magmatic crystallization, which are typical of olivine rims in kimberlites worldwide; that is, primary inclusions of chromite, Mg-ilmenite and rutile, homogeneous Mg# (88·8 ± 0·3), decreasing Ni and Cr, and increasing Ca and Mn. Rinds and high-Mg olivine are characterized by extreme Mg–Ca–Mn enrichment and Ni depletion, and textural relationships indicate that these zones represent replacement of pre-existing olivine, with some new crystallization of rinds. These zones probably precipitated from evolved, oxidized, and relatively low-temperature kimberlite fluids after crustal emplacement. In summary, this study demonstrates the utility of combined petrography and olivine geochemistry to trace the evolution of kimberlite magmatic systems from early metasomatism of the lithospheric mantle by (proto-)kimberlite melts, to crystallization at different depths en route to surface, and finally late-stage deuteric or hydrothermal fluid alteration after crustal emplacement.

Ecological assesment of Akkuyu nuclear power plant site marine sediments in terms of radionuclide and metal accumulation

Trace element availability and radioactivity concentrations of marine sediments of AKKUYU Nuclear Power Plant site were determined. The measured Cd, Cr, Cu, Mn, Ni, Pb and Zn concentrations were 3.4 ± 0.020, 22 ± 0.94, 17 ± 0.66, 226 ± 11.9, 58.9 ± 10.3, 8.3 ± 0.45 and 39.9 ± 1.65 ppm, respectively. Cd, Mn and Ni enrichment were observed. The calculated mean 226Ra, 232Th, 40 K and 137Cs concentrations were 24.7 ± 1.64, 19.4 ± 1.31, 416 ± 25.8 and 3.2 ± 0.53 Bq kg−1, respectively. Findings were comparable with reported literature for Turkey, Mediterranean Basin and other countries from the world. The presented data would enable to determine the possible future effects of the Nuclear Power Plant to the marine environment. Radionuclide and trace metal concentrations of marine sediments were presented in log scale.

Effects of cementite size and chemistry on the kinetics of austenite formation during heating of a high-formability steel

To understand how austenite forms in high-formability steels during the heating step of intercritical annealing, calculations based on atomic diffusion and local equilibrium assumption were used to simulate the transformation kinetics. It appears that chromium must be considered in the calculations to allow for a good fit with the austenite formation kinetics obtained by dilatometry. Indeed, Cr has a strong delaying effect on this kinetics, even though it is a minor element in the steel chemistry. The parametric study reveals that cementite initial radius is the most influential parameter on transformation kinetics. Mn and Cr enrichments also prove to be important parameters to consider.

A comparative study on hydrochemical evolution and quality of groundwater in coastal areas of Thailand and Bangladesh

In recent years, Thailand and Bangladesh have been drawing more attention due to groundwater pollution, but there is rarely a comparative study on hydrochemical evolution and quality assessment of groundwater in the areas In this paper, end-member mixing and Gibbs model are used to study the evolution of groundwater hydrochemistry based on the 74 water samples. Due to the seawater intrusion, the evolution path of groundwater in Bangkok Bay is Ca/Mg-HCO3 → Na (Ca/Mg)-HCO3 and Na (Ca/Mg)-Cl → Na-Cl, which led to increased Na+, K+, and HCO3– concentrations in groundwater and enrichment of fluorine in groundwater caused fluorine pollution. In contrast, although the evolution path of groundwater in southern Bangladesh shows a similar pattern as Ca/Mg-HCO3 → Na (Ca/Mg)-HCO3 and Ca/Mg-Cl → Na-Cl, the principal influence factors are residential, agricultural and industrial pollutants. The scope of seawater intrusion is only limited to estuary areas of the southern estuary, whereas most groundwater is received recharge of polluted surface water, which resulted in the enrichment of Fe and Mn. In addition, compared with shallow groundwater, deep groundwater is updated slowly and evolved to higher degree, and is in the Na (Ca/Mg)-HCO3 and Ca/Mg-Cl stage. For improving groundwater conditions in southern Bangladesh, enhancing the supply capacity of surface potable water and significantly reducing groundwater exploitation are priority. Strictly controlling the generation, storage and treatment of domestic waste, industrial and agricultural pollutants are also important. In Bangkok Bay, reducing the groundwater exploitation and dispersing the exploitation area is required.

Assessment, Distribution and Regional Geochemical Baseline of Heavy Metals in Soils of Densely Populated Area: A Case Study.

To understand the content, pollution, distribution and source and to establish a geochemical baseline of heavy metal elements in soil under the influence of high-density population, the concentrations of heavy metal elements Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Hg, Pb and Fe were determined in 23 soil samples in Suzhou University, and geo-accumulation index, enrichment factor, principal component analysis, spatial analysis and regression analysis were completed. The results showed the following: The elements Cu and As were slightly polluted, while the other heavy metal elements were not. The elements Cd, Cu, Ni and As in soils were mainly caused by agricultural activities of chemical fertilizer, whereas the elements Zn and Hg were impacted by the chemicals and batteries. The heavy metal elements in the north were lower than in the south of the campus, as a whole. The enrichment of elements Cu, As and Cd was caused by the east–west river on the campus, and the enrichment of the elements Mn, Ni and Zn was induced by the reservoir. Biochemical experiments and vehicle parking influenced the spatial enrichment of Cr, Co and Pb, while domestic waste led to the spatial differentiation of Hg concentrations. The regression curve between heavy metal elements and Fe was established, and the background values of the heavy metals Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Hg and Pb are 50.90, 489.37, 11.76, 37.74, 55.70, 58.22, 20.07, 0.09, 0.08 and 24.13 mg/kg, respectively.

Evaluating a primary carbonate pathway for manganese enrichments in reducing environments

Most manganese (Mn) enrichments in the sedimentary rock record are hosted in carbonate minerals, which are assumed to have formed by diagenetic reduction of precursor Mn-oxides, and are considered diagnostic of strongly oxidizing conditions. Here we explore an alternative model where Mn-carbonates form in redox-stratified water columns linked to calcium carbonate dissolution. In ferruginous Brownie Lake in Minnesota, USA, we document Mn-carbonates as an HCl-extractable phase present in sediment traps and in reducing portions of the water column. Mn-carbonate becomes supersaturated in the Brownie Lake chemocline where dissolved oxygen concentrations fall below 5 μM, and Mn-oxide reduction increases the dissolved Mn concentration. Supersaturation is enhanced when calcite originating from surface waters dissolves in more acidic waters at the chemocline. In the same zone, sulfate reduction and microaerobic methane oxidation add dissolved inorganic carbon (DIC) with negative δ13C. These observations demonstrate that sedimentary Mn enrichments may 1) develop from primary carbonate phases, and 2) can occur in environments with dissolved oxygen concentrations <5 μM. Primary Mn-carbonates are likely to originate in environments with high concentrations of dissolved Mn (>200 μM), and where Mn and Fe are partitioned by S cycling, photoferrotrophy, or microaerophilic Fe-oxidation. A shallow lysocline enhances Mn-carbonate production by providing additional DIC and nucleation sites for crystal growth. This carbonate model for Mn-enrichments is expected to be viable in both euxinic and ferruginous environments, and provides a more nuanced view of the relationships between Mn and carbon cycling, with applications throughout the rock record.

Ni and Mn enrichment effects on reformed austenite: thermodynamical and low cycle fatigue stability of 13%Cr–4%Ni and 13%Cr–6%Ni stainless steels

By comparing the behavior of 13%Cr–4Ni and 13%Cr–6Ni alloys, this paper investigated the effect of Ni and Mn enrichment on the amount, mechanical stability, and microstructure of reformed austenite. 4%Ni and 6%Ni–1.5%Mn weld multilayer deposits were made and heat treated to stabilize various amounts of austenite content at room temperature. The maximum austenite content has been obtained at the same temperature (630 °C for 1 h) for both alloys, but 3.6 times more austenite content was formed in the 6%Ni steel. For both alloys similar austenite contents were obtained by post-weld heat treating at different temperatures and were compared experimentally. Results showed that with the addition of Ni and Mn, thinner and lower Ni content austenite was formed. Moreover, austenite generated at lower temperature was mechanically more stable under low cycle fatigue loading. Its rate of transformation has been reduced by a factor of 2.3, resulting in the stabilization of twice more austenite after 20 cycles at 2% strain considering the results of the present study, it is concluded that Ni and Mn contents do significantly affect the mechanical stability of reformed austenite; furthermore austenite lamellae morphology and thickness also seem to play a significant role in stabilizing this phase.

Assessment of Cu, Zn, Mn, and Fe enrichment in Mt. Kenya soils: evidence for atmospheric deposition and contamination.

Mountains are the preferred sites for studying long-range atmospheric transportation and deposition of heavy metals, due to their isolation and steep temperature decrease that favors cold trapping and condensation of particulate forms of heavy metals. Any enrichment of heavy metals in mountains is presumed to primarily occur through atmospheric deposition. In this particular study, we assessed the status of 27 subsurface soils collected along two elevation gradients of Mt. Kenya using enrichment factors (EFs) as the ecological risk assessments. The collected soils were analyzed for total organic carbon, zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu). The mean concentration of Mn, Fe, Zn, and Cu was 0.376mg/kg, 47.6mg/kg, 12.3mg/kg, and 4.88mg/kg in Chogoria and 0.560mg/kg, 113mg/kg, 12.7mg/kg, and 2.70mg/kg in Naro Moru respectively. These concentrations were below the US-EPA maximum permissible levels for soils, implying that the levels recorded had low toxicity. Meanwhile, the mean enrichment factors for Mn, Cu, and Zn were 0.447, 131, and 78.8 in Chogoria and 0.463, 38.9, and 53.0 in Naro Moru respectively. This implied that Zn and Cu in Chogoria sites were extremely enriched, while in Naro Moru, enrichment levels ranged from significant to extreme. However, Mn was found to have minimal enrichment in all the sites. Lower montane forest and bamboo zone recorded relatively high enrichment due to distance from source of pollution. Ericaceous zone also had high mean enrichment due to influence of wind which favors higher deposition at mid-elevations.

Geochemistry of magnetite from the giant Paleoproterozoic Dahongshan Fe-Cu deposit, SW China: Constraints on nature of ore-forming fluids and depositional setting

The Dahongshan Fe-Cu ore deposit, hosted in the Paleoproterozoic meta-volcanic and meta-sedimentary sequences, is a giant deposit in the Fe-Cu metallogenic province of southwestern China. Two ore types have been identified: (1) massive and disseminated Fe ores hosted dominantly in meta-volcanic rocks and (2) disseminated and banded Fe-Cu ores in meta-sedimentary rocks. Magnetite presents in all orebodies, and is dominant in the Fe ores. Chemistry of magnetite suggest that the fluids for iron mineralization in the Fe and Fe-Cu orebodies are likely chemically similar and cogenetic. Minor sulfides (e.g., molybdenite) occur at the end of iron mineralization stage, indicating the gradually decrease in oxygen fugacity for the mineralizing fluids with magnetite precipitation. Along with evolution, mineralizing fluids generate magnetite with depletions in Cr, Ni, Ga and V, but enrichments in Mn, Sn and Co, which are primarily reflective of the temperature decrease of fluids.We have discovered some magnetite grains that are extremely rich in V (~10000 ppm), but low in Ti and Cr. Geochemical patterns suggest that they were formed by fluids similar to those of ordinary ores. Available knowledge about the unique high-V magnetite indicates highly-reduced marine environments for its generation. Ore bulk REE patterns showing remarkable positive Eu anomalies and absence of obvious Ce anomalies suggest a BIF-like marine environment, consistent with the morphology of both Fe and Fe-Cu orebodies. Our results provide independent evidence for submarine environment in the formation of the giant Precambrian stratiform Fe(-Cu) ore deposit.

Surface Water Sediments Characterization Using Metallic Trace Elements (MTEs): Case of the Artisanal Gold Mining Sites of Kokumbo (C&amp;#244;te d’Ivoire)

The main purpose of this study is to characterize the surface sediments of the Kokumbo artisanal gold mining sites in Metallic trace Elements (MTEs). A total of 12 samples of surface water sediments were collected for this study. The samples were analyzed using the Atomic Absorption Spectrophotometer (AAS). The mean concentrations of Mn (611.37 mg/kg) and Zn (955.86 mg/kg) in the sediments were very high compared to the standard in unpolluted sediments. The enrichment factor (EF) shows that there is an enrichment of Mn at some sites (EF (Mn) > 2). The presence of As, Mn, and Zn is also highlighted by the geo-accumulation index (I-geo) which shows slight pollution in Mn (0 3). This study shows that the presence of Zn in the sediments is linked to artisanal gold mining activities. Indeed, Zn is much used for gold recovery. The statistical analysis (PCA) shows, on the one hand, natural mineralization of the sediments and addition of metals linked to anthropic activities corresponding to the erosion of mining discharges. The surface sediments of the Kokumbo mining sites show pollution in As, Mn, and Zn.

Employing Geochemical Analysis to Reveal Pedogenic Processes in Wisconsin Bisequal Soils Having Spodic and Alfic Sequa

Bisequal soils in northern Wisconsin were described and characterized with the intent to determine if a near total elemental analysis protocol may estimate the effect of selected soil pedogenic pathways on soil morphology. The protocol reveals that gross elemental soil profile distributions do provide evidence that certain pedogenic processes are operating within a group of soils. Concentration differences between instrumental neutron activation analysis and an aqua regia digestion protocol infer that alkali metals, alkaline earth metals, transition metals and the rare earth elements are only incompletely weathered from primary minerals. Transition metals, alkali metals, alkaline earths, metalloids, and the rare earth elements all show inter-horizon mobility. Lessivage and the mobility of elements presumably adsorbed on soluble or suspended organic materials are the dominant soil processes influencing the soil profile redistribution of elements and the majority of these elements are shown to correlate with the soil profile distribution of Fe. Base cycling by the forest vegetation was shown to support A horizon enrichment of Ca, Sr, Ba, P, S, Mn, Zn, Sn and Pb. For clinical practice, elemental analysis may reveal important soil profile elemental differences when applied to variation of one soil forming factors, such as a chronosequence or toposequence within a landscape or soil association. Advantages and limitations of the protocol in identifying pedogenic pathways are discussed.

Modeling of the austenite decomposition kinetics in a low-alloyed steel enriched in carbon and nitrogen

A model predicting the effect of carbon (0.1–0.7%mC) and nitrogen (0.3–0.4%mN) enrichment of a low-alloyed steel (23MnCrMo5) on its austenite decomposition kinetics during cooling is introduced here. Its practical purpose concerns the simulation of microstructure evolutions after surface treatments of carburizing, nitriding or carbonitriding. Effects of nitrogen in solid solution in austenite are considered for the first time. Regarding the carbon, previous approaches from literature which estimate IT C curves displacements along time and temperature axes are adapted. Phase transformation kinetics are predicted from phenomenological rules (JMAK, Koistinen–Marburger). However, the number of empirical model parameters is reduced to a minimum thanks to thermodynamic calculations. JMAK kinetic parameters have to be established in one single reference steel composition. The model gathers, in one comprehensive framework, several phenomena which are generally considered separately, such as, e.g., the austenite stabilization after the proeutectoid ferrite transformation (by carbon enrichment) or after the bainite transformation. The kinetics simulations and the predicted final microstructures are critically compared to a large set of experiments carried out on dilatometry samples with different homogeneous C/N composition and samples with composition gradients. After carbonitriding, microstructure and hardness profiles differ strongly from the classical case of carburizing. This highlights the consequences of the previously reported, unexpected acceleration of the austenite decomposition when it has been enriched in nitrogen.