Mn Oxyhydroxides Research Articles

АНОМАЛИИ РЕДКИХ ЭЛЕМЕНТОВ В МАРГАНЦЕВЫХ МИКРОКОНКРЕЦИЯХ ИЗ ЭТМОДИСКУСОВЫХ ИЛОВ БРАЗИЛЬСКОЙ КОТЛОВИНЫ АТЛАНТИЧЕСКОГО ОКЕАНА

The composition of manganese micronodules from miopelagic clays and Ethmodiscus oozes of the central part of the Brazil Basin (station 1537, R/V Akademik Sergei Vavilov) is considered. Micronodules were recovered from >50 μm fraction of sediments from the depth intervals of 300 to 305, 405 to 410 and 442 to 452 cm below seafloor. The composition of micronodules was determined in separate size fractions of 50–100, 100–250 and 250–500 μm after dissolution in 0.5N NH2OH × HCl + 25% CH3COOH. The contents of Co, Ni, Cu, Ce, Pb, W, Th, and Bi in micronodules of miopеlagic clays were found to be higher than in micronodules from Ethmodiscus oozes. In the latter, the positive anomalies of Li, As, Mo, Cd, Tl, and U were revealed. The REE composition of micronodules in miopelagic clays is similar to the composition of hydrogenous crusts with a maximum in middle REE and a positive cerium anomaly. Micronodules of Ethmodiscus oozes have a positive Ce anomaly 2.8–3.8 and a deficiency of light lanthanides, similar to the composition of dissolved REEs in pore and bottom ocean waters. High accumulation of redox-sensitive elements in micronodules (As, Mo, V, and Cd) indicates an anaerobic stage in the post-sedimentary period in Ethmodiscus ooze caused by high biological productivity of waters. The formation of micronodules began during the period when the reducing conditions changed to oxidizing ones. Elements with low mobility (As, Mo, V, and Cd) accumulated in sediments and pore water during the anaerobic stage were then sorbed on Mn oxyhydroxides during the oxidation stage.

Bioleaching of dewatered electroplating sludge for the extraction of base metals using an adapted microbial consortium: Process optimization and kinetics

The main objective of this study was to optimize bioleaching process parameters for high co-extraction of base metals (Cu, Ni, Zn, and Cr) from hazardous electroplating sludge using an adapted microbial consortium and to explore the relevant bioleaching mechanisms. Microbial cultivation and sludge bioleaching were separated. The effect of the relevant process parameters (i.e., bulk pH, pulp density, and Fe2+ concentration) on the extraction of four selected metals through bioleaching by an adapted microbial consortium was investigated in a 1 L stirred tank reactor. Results indicated that maximum metal solubilization (>95.6% for each of Cu, Zn, and Ni, and 90.3% of Cr) was achieved at a bulk pH of 2.0, Fe2+ of 9.0 g/L, and pulp density of 15% (w/v). Bioleaching kinetics of the selected metals was described by a modified shrinking core model. This indicated that the interfacial transfer and diffusion across the solid film layer was the rate controlling step and controlled the dissolution kinetics. Data from bioleaching and chemical leaching systems showed that bioleaching had some advantages over simple chemical leaching. The mechanisms of improved Cu, Ni, Zn, and Cr extraction by bioleaching were demonstrated. Bioleaching improved metal release, especially from the residual fraction, as indicated by Community Bureau of Reference (BCR) three-stage sequential extraction analysis. Most of the Cu, Ni, and Zn extraction was attributed to H+ attack, as these metals were primarily distributed in the water/acid soluble and exchangeable fractions, along with Fe and Mn oxyhydroxides (>72.3%). For the extraction of Cr, besides H+, microorganisms and Fe3+ were also responsible. They improved Cr extraction, especially from the residual fraction. These findings indicate that bioleaching with an adapted microbial consortium appears promising for recycling and reutilizing valuable heavy metals from hazardous electroplating waste.

Geochemical Behavior of REE in Stream Water and Sediments in the Gold-Bearing Lom Basin, Cameroon: Implications for Provenance and Depositional Environment

Stream water and associated bottom sediments were sampled within the Lom Basin, and their rare earth element (REE) concentrations have been used to decipher their provenance and environment of deposition. Stream waters in the lower Lom Basin have variable Post Archean Australian Shale-normalized REE concentrations (0.24–4978 ng/l), positive Ce anomalies (Ce/Ce* ranges from 1.08 to 8.03), a general positive Eu anomaly (Eu/Eu* varies from 0.9 to 15.2, average = 4.9) and are slightly enriched in the light rare earth elements (LREE/HREE varies from 1.7 to 10.3). Similarly, the sediments are slightly depleted in heavy rare earth elements (HREE), have a predominant negative Ce anomaly, but show a ubiquitous positive Eu anomaly. The dissolved REE content is controlled by the near-neutral pH of the stream water and adsorption onto Fe and Mn oxyhydroxides. The variable LREE/HREE ratios and Eu anomalies observed in the sediments indicate that these sediments are sourced mainly from felsic rocks with little mafic input. Moreover, Ce anomalies and redox-sensitive trace elemental ratios of Ni/Co, V/(V + Ni), V/Cr, Cu/Zn and V/Ni revealed the sediments were deposited under oxic to reducing conditions. Variations in the concentration of REE in the stream water and sediment indicate that Fe and Mn oxyhydroxides are important sinks for the HREE. The newly generated data will guide future studies and environmental policy makers.

Assessment of metal contamination in a tropical estuary, West Coast of India

In this study, we report an assessment of metal (Fe, Mn, Zn, Cr, Cu and Pb) contamination in surface sediments of a tropical estuary from Goa-the West coast of India. Surface sediment samples were collected along the 35 km stretch of the Zuari estuary on monthly basis for a period of 1 year and samples were analyzed for texture, organic carbon (OC) and metals. Seasonal variation of metals did not show any significant variation, except for Zn and Pb in the present study. Spatial variation of metals was influenced by sediment texture, OC and land runoff. The contamination factor and Geo-accumulation index (I Geo) revealed moderate contamination of Pb and Cr. Factor analyses suggest role of Fe–Mn oxy-hydroxide, OC and textural variables in abundance of trace metals in the sediments. Further, an attempt was made to understand the impact of mining on the Zuari estuary by comparing the present data (during mining ban period) with earlier published reports (during extensive mining period). It revealed influence of mining on the concentrations of Fe and Mn in surface sediments, but had no impact on the concentration of Cu, Cr, Zn and Pb in the Zuari estuary.

Phenazine-1-Carboxylic Acid-Producing Bacteria Enhance the Reactivity of Iron Minerals in Dryland and Irrigated Wheat Rhizospheres.

Phenazine-1-carboxylic acid (PCA) is a broad-spectrum antibiotic produced by rhizobacteria in the dryland wheat fields of the Columbia Plateau. PCA and other phenazines reductively dissolve Fe and Mn oxyhydroxides in bacterial culture systems, but the impact of PCA upon Fe and Mn cycling in the rhizosphere is unknown. Here, concentrations of dithionite-extractable and poorly crystalline Fe were approximately 10% and 30-40% higher, respectively, in dryland and irrigated rhizospheres inoculated with the PCA-producing (PCA+) strain Pseudomonas synxantha 2-79 than in rhizospheres inoculated with a PCA-deficient mutant. However, rhizosphere concentrations of Fe(II) and Mn did not differ significantly, indicating that PCA-mediated redox transformations of Fe and Mn were transient or were masked by competing processes. Total Fe and Mn uptake into wheat biomass also did not differ significantly, but the PCA+ strain significantly altered Fe translocation into shoots. X-ray absorption near edge spectroscopy revealed an abundance of Fe-bearing oxyhydroxides and phyllosilicates in all rhizospheres. These results indicate that the PCA+ strain enhanced the reactivity and mobility of Fe derived from soil minerals without producing parallel changes in plant Fe uptake. This is the first report that directly links significant alterations of Fe-bearing minerals in the rhizosphere to a single bacterial trait.

Testing Geochemical Predictions of Trace Element Toxicity and Bioavailability at a Rehabilitated Mine Site

The speciation, toxicity and bioavailability of trace elements in mine drainage environments can be readily predicted using geochemical modelling, and this is frequently the basis for assessing the likely impacts of mine effluents and efficacy of rehabilitation plans. However, such predictions are rarely validated against observed trace element characteristics after mine rehabilitation is complete. In this study of a former Pb–Zn mine in New Zealand, PHREEQC was used to predict dissolved trace element and sediment-bound speciation for the rehabilitated mine site, and the results were compared to the observed water and sediment quality. For Fe, Mn, Al, Cu, Pb, Zn, Cd, Ni, As, and Sb, it was predicted that only Zn2+ and Cd2+ concentrations would exceed recommended guideline values for ecosystem health. PHREEQC indicated that the pH would have to be raised to > 9.5 to reduce these toxicants to a level fit for ecosystem health. Modelling of potential mineral formation indicated that the waters were saturated with respect to a variety of Fe-, Mn- and Al (oxy)hydroxides at and immediately downstream of the mine site, but were not saturated with respect to any trace element-bearing minerals, or sulfide or carbonate phases. This was consistent with X-ray diffraction and scanning electron microscopy (SEM) observations of the sediment. Sequential extraction of the sediment showed strong associations of Zn, Cu, Pb, As and Sb with iron (oxy)hydroxides. Modelling trace element adsorption onto only hydrous ferric oxide surfaces accurately predicted the adsorption of Zn, Cd, Cu, and Ni, but predictions of Pb and As adsorption were less reliable. Additionally, a strong association between Zn and Mn oxyhydroxide was observed in SEM analysis.

Postglacial sedimentation in the White Sea (northwestern Russia) reconstructed by integrated microfossil and geochemical data

AbstractThe White Sea being connected with the Arctic Ocean via the Barents Sea has an influence on its water temperature/salinity structures and biological processes and thus has an indirect impact on the Eurasian climate system. In this work, we have managed to find a correspondence between the climate fluctuation in the Holocene and changes in the geochemical and microfossil properties in the sediment core of the White Sea. For the first time, the element speciation in the sediment core covering about 10,000 cal yr BP period was investigated. The cooling periods (the early Holocene and the Subboreal stage) were characterized by a trend of increase in Si, Al, and Ti contents and Ti/Al ratios, which reflect lithogenous contribution, and decrease in geochemically labile forms of trace elements. A significant increase in the content of organic-bound trace elements and biogenic components (Сorg, BSi, and chlorin) was observed during periods of Holocene climatic optimums. The evident relationship between the metal speciation and indicators of the sedimentation paleoenvironment is observed at the stage of the active phase of early diagenesis after the slowing down of the biogeochemical processes. Down-core decrease in the Mn oxyhydroxide content exhibited a weakening of diagenesis processes at the ~130–150 cm depth.

Precession-driven monsoonal activity controlled the development of the early Albian Paquier oceanic anoxic event (OAE1b): Evidence from the Vocontian Basin, SE France

In the Vocontian Basin in southeastern France, the Aptian-Albian boundary is marked by the occurrence of four laminated black shales (Jacob, Kilian, Paquier, Leenhardt) corresponding to Oceanic Anoxic Event 1b (OAE1b). Equivalents of one or more of these intervals are also known from different regions in the Tethys, Atlantic, and Pacific, and correspond in time to major climatic and evolutionary perturbations. Here, we performed an integrated multi-proxy high-resolution study on the section at l'Arboudeysse in the northwestern part of the Vocontian Basin including mineralogical (whole rock and clay minerals) and geochemical (carbon and oxygen isotopes, organic matter, major and trace elements, mercury contents) analyses. The aim of this study is to reconstruct the level of productivity and related state of oxygenation, in addition to the weathering coditions on the adjacent continent during the Paquier event, Modest enrichments in redox-sensitive trace elements (RSTE; Mo, As, V, U, Ni) associated with moderate total organic carbon contents (between 0.57 and 5.52 wt %) indicate the development of suboxic/anoxic conditions during deposition of the Paquier level. The strong enrichment of Mo (10–229) relative to other RSTE (<5) may be explained by the importance of a particulate Fe–Mn oxyhydroxide shuttle. The high phosphorus (P) contents are related to the presence of fish remains. The weathering and detrital indices estimated from clay and whole-rock mineralogy suggests temporal fluctuations in weathering conditions and detrital input, likely resulting from variable humid conditions. These variations display a cyclic pattern linked to Milankovitch precession cycles varying from humid, high weathering conditions, causing oxygen-depletion in the bottom water to dryer, low weathering conditions associated with less oxygen depleted bottom waters. This oscillation was probably controlled by changes in evaporation/precipitation patterns related to variably intense monsoonal activity. A lack of significant mercury enrichments is not supportive of a direct link between volcanic activity and environmental change during the Paquier event.

Fractionation of Zn isotopes in terrestrial ferromanganese crusts and implications for tracing isotopically-heterogeneous metal sources

Zinc liberated from geological sources during surface weathering is the main source of Zn to the surface environment, and is ultimately sequestered by sinks such as Mn oxides and oxyhydroxides. This behaviour has been applied to geochemical mineral exploration studies and terrestrial ferromanganese crusts have been shown to have anomalously-high Zn/Mn ratios around known Zn-Pb ore deposits. This poses the question: if Zn isotopic compositions of these Fe-Mn crusts can also discriminate the underlying anomalous metal sources from the surrounding non-mineralized lithologies. Isotopic fractionation during fractionation onto Mn oxides in well-studied marine Fe-Mn crusts has shown that isotopically-heavy Zn is preferentially-adsorbed in that environment, which has a comparatively isotopically-homogeneous Zn reservoir. However, isotopic fractionation behaviour in terrestrial Fe-Mn crusts that may have more heterogeneous Zn sources is unknown. Here, we present the first Zn and Pb isotope study of terrestrial Fe-Mn crusts to test if Zn isotopic compositions can be used to delineate isotopically-different lithological metal sources.Our data from Fe-Mn crusts that formed overlying isotopically-variable lithologies; hydrothermal polymetallic (Zn-Pb) deposits, and non-mineralized Archean rocks show that, while adsorption of Zn onto Mn oxyhydroxides in terrestrial Fe-Mn crusts generally favours isotopically-heavy Zn, the magnitudes of isotopic fractionation varies in Fe-Mn crusts overlying mineralized and non-mineralized areas. Fractionation factors (Δ66/64Zncrust – source up to 0.54‰) in crusts overlying non-mineralized lithological sources with a δ66Zn value of 0.30‰ are comparable with the predicted equilibrium fractionation onto birnessite. Conversely, magnitudes of Δ66/64Zncrust – source up to 0.37‰ in crusts overlying isotopically-light Zn-Pb mineralization, that has a mean δ66Zn value of -0.15‰, are much lighter than non-mineralized counterparts with similar Zn/Mn ratios. This difference may be explained by changes in hydrogeochemical complexation of Zn, with localized chloro-complexes that carry isotopically-light Zn from the isotopically-light mineralization.These findings demonstrate that different lithological Zn sources that are isotopically-variable give rise to isotopic heterogeneity in the surface Zn reservoir. This can be reflected by differing fractionation patterns following adsorption onto Mn oxyhydroxides in terrestrial Fe-Mn crusts that overly different Zn sources. Furthermore, Pb isotope compositions of the Fe-Mn crusts also closely reflect that of the underlying geology. This highlights that the use of Zn isotopes may be a valuable means of vectoring towards anomalous metal sources such as ore deposits.

Are Clay Minerals the Primary Control on the Oceanic Rare Earth Element Budget?

The rare earth elements (REEs) are an important tool for understanding biogeochemical cycling and sedimentary processes in the global ocean. However, ambiguities in the marine REE budgets, including questions around the dominant source of REEs to the ocean, hinder the application of this tool. A bottom-up model for REE release into the ocean has recently been proposed, driven by early diagenetic processes such as sediment dissolution, with potentially significant implications for the interpretation of marine REE and Nd isotope paleo-records. Here, our goal is to identify the phase or phases that interact with the pore fluids to drive such a benthic flux. We use new pore water REE, microbeam imaging and mineralogical data in combination with published pore water REE data to evaluate potential sedimentary REE host phases. Mineralogical and direct imaging observations suggest that authigenic Fe or Mn oxyhydroxides, which are widely considered a dominant REE host phase, are not sufficiently abundant sediment components to account for the high Nd concentrations recovered in reductive leaches, and are unlikely to be the primary source of pore water REEs. Pore water REE signatures similar to river sourced clays indicate a detrital clay dissolution source, while the spread in heavy to light REE enrichment in pore fluids and bottom waters relative to this clay source is best explained by fractionation during authigenic clay uptake of REEs. We therefore conclude that clay mineral dissolution and authigenesis are likely the primary influences on the REE cycling near the seafloor. We propose that the balance between dissolution and authigenesis controls the concentration, ratio of heavy and light REE abundances, and the isotopic composition of the pore waters. We discuss the implications of this hypothesis on an oceanic REE budget controlled by a benthic flux from a sedimentary REE source, and the use of authigenic neodymium isotopes as a paleoproxy for shifts in ocean circulation.

REE concentration processes in ion adsorption deposits: Evidence from the Ambohimirahavavy alkaline complex in Madagascar

Ion adsorption deposits, in which the rare earth elements (REE) occur adsorbed onto clay mineral surfaces, currently provide the world’s dominant supply of heavy REE (Gd-Lu). Concentration of REE within ion adsorption deposits has been proposed to be a dominantly supergene process, where easily degradable REE-minerals (e.g. REE-fluorcarbonates) break down and release REE that are then adsorbed onto clay mineral surfaces in the weathered material. Here we present data from the Cenozoic Ambohimirahavavy alkaline complex in Madagascar, with the aim of further constraining controls on the formation and HREE enrichment processes in ion adsorption deposits.The laterite weathering profiles described here are developed on alkaline igneous rocks, including both SiO2-undersaturated and oversaturated lithologies. The latter group includes REE mineralised peralkaline granitic pegmatites and granitic dykelets. The weathering mineralogy includes gibbsite, clay minerals and minor Fe and Mn oxyhydroxides. X-ray diffraction and infrared spectroscopy show that the clay fraction in all sites is dominated by kaolinite and halloysite (7 Å and 10 Å). Extraction with ammonium sulfate (0.5 M (NH4)2SO4, pH = 4; removes weakly adsorbed metals retained on the solid surface and dissolves carbonates) indicates that, in the different profiles and along the same profile, the leachable REE content is heterogeneous, ranging from 5 to 2300 mg/kg total REE, with 1 to 32% heavy REE. Leaching with magnesium chloride (0.5 M MgCl2, pH = 6; removes only weakly adsorbed REE) releases similar total REE concentrations, suggesting that most of the leachable REE are adsorbed onto mineral surfaces. In most of the laterite profiles, the amount of leachable REE continuously increases with depth up to the saprock. Recovery rates depend on the REE atomic number, generally decreasing from La to Lu except for Ce which is invariably low.In the Ambohimirahavavy complex, the nature of the protolith is the main factor controlling the amount of easily leachable REE in the laterite weathering profile. Hydrology and topography are secondary factors. The most favourable protoliths include SiO2-undersaturated volcanic lithologies and altered mudstone with granitic dykelets. The main primary REE minerals include agpaitic minerals (eudialyte) and allanite-(Ce). Locally in granitic pegmatite dykes, autometasomatism by late magmatic fluids inhibits formation of ion adsorption ore by transforming easily weathered agpaitic minerals into unweatherable zircon.

Mn(II) oxidation catalyzed by nanohematite surfaces and manganite/hausmannite core-shell nanowire formation by self-catalytic reaction

Abstract The present study investigated the solid products of heterogeneous catalytic oxidation of aqueous Mn(II) by O2 in the presence of hematite nanoparticles (NPs) using transmission electron microscopy (TEM), scanning TEM (STEM), and electron energy-loss spectroscopy (EELS). The oxidation experiments were conducted at room temperature (22 ± 2 °C) in solutions containing 10−3 M Mn(II) at pH 7.5 in the dark. During 48 h of reaction, a single-phase manganite (a Mn oxyhydroxide) nanowire was formed by way of metastable groutite and feitknechtite nanowires, both of which are polymorphs of manganite. Between 48 and 168 h, the manganite further altered to core-shell structured nanowires with hausmannite (a mixed valent Mn oxide) forming a very thin (2 nm) outer-shell on the manganite wire core. The formation of Mn-oxyhydroxide nanowires was catalyzed by the hematite NPs surface through electrochemical pathways. This is described via the electron transfer across a redox couple from adsorbed Mn(II) to another site with adsorbed O2 via the band structure of the semiconducting hematite. On the other hand, the Ostwald step rule was operative in the sequential crystallization from metastable groutite and feitknechtite to stable manganite, which could have resulted from the differences in the surface free energies, sizes, and morphologies of product polymorphs at the nanoscale. The final product (at least in the time range of our experiments) exhibited manganite/hausmannite core-shell structures. This product is most likely to be formed by the reactions catalyzed by the manganite nanowires themselves. Microscopic investigation of interfacial changes in structure and chemistry at the nanoscale is key, and it can be essential to understand the kinetic and thermodynamic phenomena related to the redox chemistry and phase stability of nanoparticles in complex, heterogeneous systems such as natural environments.

Assessing rare-earth elements and anthropogenic gadolinium in water samples from an urban artificial lake and its tributaries in the Brazilian Federal District

This work highlights the rare earth elements (REE) dynamic in water samples from Paranoá Lake and its tributaries in the Brazilian Federal District. Variation of anthropogenic Gd in Paranoá Lake after a 4 years laps time, characterization of regional REE background levels and possible contaminations in the tributaries were studied. REE were assessed by thulium (Tm)-spiked solid-phase extraction followed by ICP-MS. Method validation was performed using synthetic samples and the SLRS-6 reference material. The method was efficient to remove the interfering Ba (>99.99%) with REE recoveries (SLRS-6) varying from 81 ± 6 (Tb) to 105 ± 4% (Dy). In the Paranoá Lake, water samples were enriched for high and middle REE (PrSN/YbSN varied from 0.15 to 0.39, DySN/PrSN ranged from 1.10 to 2.25, DySN/YbSN varied from 0.27 to 0.45) while the tributaries at Southern part of lake presented an enrichment of lower REE (PrSN/YbSN 1.24 and 2.30; DySN/PrSN 0.80 and 0.49). Gd anomalies were observed in the Paranoá Lake samples, with high levels of anthropogenic Gd (Gdanth) nearby two wastewater treatment plants (33.6 and 22.1 ng L−1). No significant increase in total anthropogenic Gd stock was observed compared to 2013 data. Positive Ce anomaly observed in the dissolved phase may be associated to mineral colloids (Fe or Mn oxy-hydroxides) or agricultural supplies, while positive La anomaly registered in waters requires further studies.

Accumulation of heavy metals in sediments of Amur Bay (Sea of Japan) under the infl uence of biochemical factors

The average content of the elements Fe, Mn, Zn, Pb, Cu, Cr, V, Co, Cd, Ni, As, and Mo in the subcolloidal fraction of bottom sediments in the northern and central parts of the Amur Bay (in Russia) was determined. An increase of 5–17% in the content of the metals Pb, Co, Ni, Zn, Cr, V, and As in bottom sediments affected directly by the Razdolnaya River was determined and was found to be associated with sorption on Fe and Mn oxyhydroxides. An increase of 21–55% in the content of the metals Cu and Mo and of the metalloid As compared to their average content in the bottom sediments of the bay was found to be associated with the accumulation by humic substances.

Investigation of legacy industrial mercury in floodplain soils: South River, Virginia, USA

Mercury (Hg) was used during 1929–1950 as a catalyst to produce rayon acetate at the former DuPont plant in Waynesboro, Virginia, and released into the South River. Though the use of Hg ceased in the 1970s, the affected ecosystem is still a matter of concern. Here, high total mercury (THg) and total organomercury, stated as methylmercury (MeHg) are reported in historically contaminated floodplain soils and shallow groundwater from five locations sited 5.6 km downstream from the plant of one river edge site. In soils, THg ranged from 0.1 to 1201.5 mg/kg exceeding the health-based screening Hg levels for residential and industrial soils while MeHg varied between 0.1 and 54 µg/kg. Concentrations decreased sharply with depth indicating the stratification of legacy industrial Hg-rich soils underlain by the pre-industrial soils with minor Hg. Strong linear correlation between THg and MeHg was observed. Highest soil MeHg was associated with total carbon, poorly crystalline and amorphous Fe and/or Mn oxyhydroxides. Sequential extraction analyses indicated that Hg was present mostly in relatively recalcitrant forms, as determined with procedures that targeted β-HgS, HgS, HgSe, HgAu, thiol-bound Hg, Hg0, and some organo-complexed Hg, Hg2Cl2 phases. High Cu (≤ 404.3 mg/kg), Zn (≤ 151.3 mg/kg), Cr (≤ 123.9 mg/kg) were also identified. In shallow groundwater, THg ranged from 28 to 538 ng/L and MeHg varied between 1.2 and 137 ng/L. During the intermittent precipitation, the highest MeHg was linked to the highest Fe2+, Mn, SO42−, total alkalinity, and conductivity, which could be due to either the potential leaching and dissolution of soil minerals and/or the saturation of the vadose zone. A sharp increase in the soil moisture at the top 40–70 cm of the Hg-rich soils after rainfall and overbank flooding was followed by redox gradients from oxidizing (≈ + 600 mV) to reducing (≈ − 300 mV) and a reverse response in a transmissive gravel zone at the base of the bank (≈ − 400 to + 200 mV) with a defined lag with depth. These dynamic seasonal fluctuations at the South River might be crucial for solubilization of Hg, Fe, and Mn redox-sensitive minerals triggering the anoxic response for new MeHg production.

Accumulation of Heavy Metals by Amur Bay Sediments (the Sea of Japan) under the Effect of Biochemical Factors

The average concentrations of elements Fe, Mn, Zn, Pb, Cu, Cr, V, Co, Cd, Ni, As, and Mo in the subcolloidal fraction of bottom sediments were determined in the northern and central parts of the Amur Bay. The concentrations of metals Pb, Co, Ni, Zn, Cr, V, and As in bottom sediments subject to direct influence of the Razdol’naya River were shown to increase by 5–17% because of their sorption on Fe and Mn oxy hydroxides. The concentrations of some elements (As, Cu, and Mo) in the bottom sediments of the bay were found to be 21–55% above their average concentrations because of their accumulation by humic substances.

Dynamics of the Organic Matter Content of Bottom Sediments along the Razdolnaya River–Amur Bay Boundary (Sea of Japan)

The contents of Corg, humiс acids (HA), and fulvic acids (FA) in soil and riverine and marine bottom sediments have been investigated along a transect between the Razdolnaya River and Amur Bay. The revealed higher Corg content of soil compared to that of riverine and marine sediments is associated with peatlands. The increased HA content of sediments compared to the FA content, corresponding to the initial period of water mixing, is explained by flocculation. The identified riverine sediments with increased FA, Fe, and Mn contents indicate active processes of flocculation and the formation of Fe and Mn oxyhydroxides. Soil shows significantly larger amounts of humified organic matter than marine sediments. Marine sediments contain mostly biochemically unrecycled organic matter.

Ni–Co–Mn Oxyhydroxide Nanosheets with a Semiconductor-Like Electronic Structure

Abstract In this study, the yield of nanosheets fabricated through the exfoliation of Li(Ni0.33Co0.33Mn0.34)O2 in aqueous solution was enhanced by performing an additional chemical oxidation step. The lateral dimensions and thickness of the obtained nanosheets were estimated via atomic force microscopy, and their chemical composition was determined using thermogravimetry, chemical composition analysis, and X-ray absorption near edge structure measurements, while their local crystal structure was examined using Raman spectroscopy and X-ray absorption fine structure techniques. In addition, the electrode properties of the restacked nanosheets in aqueous KOH solution were compared with those of the layer-structured bulk material.

GROUNDWATER CHARACTERIZATION IN SOUTHWESTERN ROMANIA USING FUZZY HIERARCHICAL CROSS CLUSTERING

A simultaneous hierarchical classification of groundwater in the Banat Plain-southwestern Romania and associated characteristics such as As(III), As(V), total As, trace metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn), pH and redox potential using Fuzzy Hierarchical Cross Clustering Algorithm was carried out. In samples containing more than 10 g/L total As (13.9 77.3 g/L), the As(V) species represented 57 20% and 73 18% in the others. Arsenic speciation pattern was in agreement with basic pH (8.31 8.49) and oxidizing conditions (369.0 409.1 mV) in aquifer. The contents of metals were below the threshold values excepting Mn. The Fuzzy Hierarchical Cross Clustering Algorithm emphasized pH and redox potential as main parameters responsible for water samples grouping. Part of water samples containing > 10 g/L As have as associated parameters the content of Pb, Cr, Zn and Fe, and pH plays a key role in natural occurrence of these elements by desorption from Fe minerals/oxyhydroxides. The other water samples with > 10 g/L As were grouped based on redox potential, As (III), As (V), total As, Cd, Ni, Cu, Al and Mn concentrations. The source of these elements was attributed to desorption processes from Al minerals/oxyhydroxides and Mn oxyhydroxides governed by the redox potential. The Fuzzy Hierarchical Cross Clustering emphasized the importance of trace metals quantification for classification of groundwater with naturally enriched As content.

Factors controlling arsenic and selected potentially toxic elements in stream sediment–soil and groundwater–surface water systems of a hydrologically modified semi-closed basin (Uluova) in Elazığ Province, Eastern Turkey

The Uluova basin aquifer system (UBAS), comprised of fractured/karstic rock and multilayer basin-fill aquifers, provides water for both domestic and agricultural needs in the Elazığ province (Eastern Turkey). Although, the UBAS has been subject of large-scale hydrological modifications and controversial water management practices since late 1950s, thus far no studies have examined basinwide implications of such human perturbations in an integrated manner. In this study, GIS, geostatistics, R-mode factor analysis (R-mFA) and geochemical modeling techniques were employed to unravel the factors controlling the distribution and sources of arsenic (As) and selected potentially toxic elements (PTEs) in the stream sediment-soil and groundwater-surface water systems of the UBAS. As revealed by the results from R-mFA, three geogenic factors (F1: Clay minerals and Fe–Mn oxyhydroxides, F2: Weathering of parent materials, and F3: Sulfide oxidation in mineralized zones) govern the geochemical dynamics of the PTEs in the stream sediment/soil media. In stream sediment and soil samples, especially Ni, Cr, and Co presented significant enrichment relative to upper continental crust average composition, whereas As contents were relatively low, varying from 0.3 to 13 mg kg−1. Factors extracted from the combined water dataset (F1: Groundwater salinization and arsenic mobilization, F2: Clay minerals and Fe–Mn oxyhydroxides, F3: pH and redox conditions, and F4: Aquifer oxygenation and nitrate contamination) accounted for 72.59% of the total variance. Water-rock interaction (e.g. sulfide oxidation, carbonate dissolution, silicate hydrolysis, adsorption-desorption, ion exchange, and evaporite dissolution), dilution/mixing with fresh/saline water components, evapoconcentration, and human induced perturbations causing internal salinization and oxygenation of the UBAS were the key mechanisms controlling the chemistry of waters and mobilization of As. In the UBAS, majority of As-rich water samples are confined to central-northern half of the basin and typically display high levels of dissolved O2, inorganic oxyanions (HCO3−, SO42− and of Si, B, Mo, Sb and V) and alkaline pH. Oxidation of sulfides (e.g. pyrite and arsenopyrite) found within the highly fractured Elazığ magmatics in the upland areas at north and subsequent competitive adsorption-desorption processes occurring under alkaline, oxidizing and high ionic strength aquifer conditions along the downgradient groundwater flow path play a pivotal role in the As-enrichment in the UBAS. As concentrations ranged between 0.02 and 367.2 μg L−1 in groundwater, 0.13–4842 μg L−1 in spring water, and 0.04–31.1 μg L−1 in the stream water samples, of which 20.83% exceeded the WHO provisional guideline value. In the water samples, As occurs mainly as As(V) species (HAsO42− and H2AsO4−), indicated by the Eh-pH diagram and speciation calculations. The results of this study have shown that As enrichment in the UBAS can be attributed to both geogenic processes and anthropogenic activities that have modified the basin hydrology/hydrochemistry.