Mn Carbonate Research Articles

Evaluation of heavy metal contamination in sediments using the method of total digestion and determination of the binding forms-Tisa River Basin, Serbia

This paper describes an approach for the evaluation of metal contamination in sediment, using the determination of binding forms of elements (sequential extraction method), the total element content (digestion method), as well as a comparison of the obtained results with the legislative limits of the EU. Results indicate that silicates are significant substrates for Ni and Cr, whereas Zn, Cd, Pb, and Cu were not dominantly bound to silicates. Mg is present in the form of carbonates and silicates; Fe is in the form of oxides, and Mn is in the form of Mn carbonate and oxides. Zn, Cd, and Cu are dominantly extracted in the labile fractions and because of this they are likely to pose a direct and significant threat to the environment. The results of a comparison with the legislative limits of the EU indicated that in some of the sediments, elevated levels of Zn, Cd, and Cu exist. The contamination was caused by permanent pollution, originating mainly from industrial activities, municipal sewage discharge and agriculture. Results indicate to the significance of the employment both of methods, sequential extraction and total digestion, for metal investigation in sediment. With the aim of protecting the sediment quality of the Tisa River, of importance for Central Europe, the obtained results also indicate the necessity for systematic investigations in all countries through which this river flows.

Surface Microstructure Evolution during Phase Transformation on Mn, Al and Si Alloyed Ultra Low Carbon Steel

This paper investigates the surface texture evolution after a short phase transformation annealing in low vacuum on ultra low carbon steel sheets alloyed with high Mn and Al and the cold rolled steel sheets of industrial composition alloyed with silicon. The ultra low carbon steel sheets with high Mn and Al show surface monolayer which has a characteristic surface texture components <100>//ND texture and microstructure with special grain morphology. Contrastingly, the industrial composition alloyed with silicon does not show specific surface texture components inspired by surface energy anisotropy at the surface. The composition depth profiling investigations performed on the all steel sheet surface shows that oxidation characteristics of alloying elements at the metal vapour interface have played a decisive influence on surface texture evolution. Further, transformation annealing in higher vacuum reveals that surface texture can be obtained in an industrial composition alloyed with silicon.

Internal features, mineralogy and geochemistry of ferromanganese nodules from the Gulf of Cadiz: The role of the Mediterranean Outflow Water undercurrent

A large suite of Fe–Mn nodules (561 samples) were recovered during the Anastasya 20 01 cruise (TASYO project) along the continental margin of the Gulf of Cadiz (Eastern Central Atlantic), at the confluence of the Mediterranean Sea with the Atlantic Ocean, where extensive nodule fields were discovered. Based on wide previous studies that included swath bathymetry, multi-channel and very high-resolution seismic reflection, gravimetry, magnetism, heat flow probes and underwater photography surveys, nodules were collected at water depths ranging from 850 to 1000 m, associated with hydrocarbon-derived Mg-calcite, ankerite and dolomite chimneys and crusts. Forty-six selected samples among the various morphological types were used for the laboratory analysis of physical properties (morphology, color, surface texture, sphericity, weight and size), mineralogy (XRD, optical and electronic microscopy), geochemistry (XRF, AAS, ICP-MS, ICP-AES, EPMA, and GC-MS) and stable isotopes. The nodules show a wide range of sizes, densities, weights and morphologies. They are formed by multiple millimeter-thick layers of Fe and Mn oxyhydroxides surrounding the nucleus composed of Early–Middle Miocene plastic marl and sediment, which were derived from underlying units by fluid venting. Massive, laminated, detrital and mottled to dendritic textural features were developed by the Fe and Mn oxyhydroxide layers. The main components are Goethite, lepidocrocite, Mn oxides (7 Å manganates and 10 Å manganates), quartz, and phyllosilicates. Accessory minerals are calcite, dolomite, siderite, rhodochrosite, kutnahorite, pyrite, chalcopyrite, potassium feldspar, zircon, rutile, ilmenite and chlorite. Fe–Mn carbonates from the siderite–rhodochrosite continuous series are the principal constituent of the nuclei. Framboidal, filamentous and globular textures are observed in Fe–Mn oxides and pyrite, suggesting biogenic origin. The nodules show a high mean abundance of Fe (38.6%), moderate Mn (6.0%) and low contents of trace metals and REEs compared to the average content of deep-seabed polymetallic nodules from other oceanic areas. The Mn/Fe ratio ranges from 0.07 to 0.25. The studied nodules hold hydrocarbons ( n-alkanes) derived from marine bacterial activity in their oxide layers, with the presence of aromatic hydrocarbons as phenanthrene as well, characteristic of mature petroleum. The structure, mineralogy and chemical composition in the studied nodules are more similar to those of diagenetic–hydrogenetic continental margin nodules rather than deep-sea nodules. We suggest that the formation of this type of nodule could respond to a combined diagenetic–hydrogenetic growth process, where the fluid venting from deep-seated hydrocarbon reservoirs, the bio-mineralization processes and the bottom currents erosion and chemistry could have played an important role.

Manganese-Based Catalysts for the Catalytic Remediation of Phenolic Acids by Ozone

Manganese-based catalysts supported on Al2O3, TiO2, ZrO2 and CeO2 were tested for the catalytic ozonation of a simulated wastewater involving phenolic acids. Comparing the Mn-Ce catalysts preparation method, wetness impregnation and co-precipitation, the last one showed to be more active. Moreover, the increase of Mn/Ce molar proportion from 22/78 to 70/30 increased the ozonation efficiency. The catalysts stability in terms of Mn leaching, carbon adsorption and effluent biodegradability was evaluated. Mn-Ce-O (70/30) CP shows to be the most suitable catalyst to improve phenolic wastewaters catalytic remediation by ozone.

A Small-Scale Sulfate-Reducing Bioreactor for Manganese Removal from a Synthetic Mine Drainage

This research evaluated the efficiency of a mesocosm scale bioreactor to remove Mn from a synthetic mine drainage in the presence of selected organic and inorganic substrate combinations that could enhance sulfate reduction and induce Mn sulfide precipitation. The mine drainage tested was slightly acidic (pH 6.2) and had average Mn and SO4 concentrations of 90 and 1,500 mg/L, respectively. The substrates used were creek sediment amended with either wood mulch or a wood mulch and biosolid mixture. Greater than 90% of Mn and 70% of sulfate was removed over a 65-day test period. The results suggested multiple Mn removal mechanisms including sorption, complexation, and Mn sulfide, Mn oxide, and/or Mn carbonate precipitation.

Anthropogenic Heavy Metal Pollution in the Surficial Sediments of the Keratsini Harbor, Saronikos Gulf, Greece

The contents of ten elements [Cd, Pb, W, Zn, Mn, As, Se, Cr, Cu, and organic carbon (Corg)] have been determined in the surficial sediments of Keratsini harbor, Saronikos Gulf, Greece. The contamination of the sediments was assessed on the basis of geoaccumulation index and to corresponding sediment quality guidelines (SQGs) effects range low/effects range median. The results revealed highly elevated Cd, Pb, W, Zn, As, Se, Cr, Cu, and Corg values (Cd, 190–1,763 mg kg−1; Pb, 521–1,263 mg kg−1; W, 38–100 mg kg−1; Zn, 409–6,725 mg kg−1; Mn, 95–1,101 mg kg−1; As, not detectable–1,813 mg kg−1; Se, not detectable–58 mg kg−1; Cr, 264–860 mg kg−1; Cu, 195–518 mg kg−1; and Corg, 0.69–4.41%). The enrichment of metals in the sediments results from the contribution of the central Athens sewage outfall through which the waste of the Attica basin ends up in Keratsini harbor as well as from industrial and ship contaminants.

Hydrocarbon-derived ferromanganese nodules in carbonate-mud mounds from the Gulf of Cadiz: Mud-breccia sediments and clasts as nucleation sites

More than 500 Fe–Mn nodules were sampled during the Anastasya-01 cruise (TASYO project) along the continental margin of the Gulf of Cadiz (eastern Central Atlantic), at the confluence of the Mediterranean Sea with the Atlantic Ocean, where extensive nodule fields were discovered. Based on wide previous studies that included swath bathymetry, multi-channel and very high-resolution seismic reflection, gravimetry, magnetism and underwater photography surveys, nodules were collected at water depths ranging from 850 to 1000 m, associated with hydrocarbon-derived ankerite and dolomite chimneys and crusts. Thirty six selected samples among the various morphological types were used for the laboratory analysis of physical properties (morphology, colour, surface texture, sphericity, weight and size), mineralogy (XRD, optical and electronic microscopy) and geochemistry (XRF, AAS, ICP-MS, EPMA, GC-MS, S, C and O isotopes). Nodules show a wide range of sizes, densities, weights and morphologies. Nodules are formed of multiple millimetre-thick layers of Fe and Mn oxyhydroxides surrounding the nucleus composed of Early–Middle Miocene plastic marl. The textures developed by the Fe and Mn oxyhydroxides layers are massive, laminated, detrital and mottled to dendritic. Goethite, lepidocrocite, Mn-oxides (7 Å-manganates and 10 Å-manganates), quartz, and phyllosilicates are the main components. Accessory minerals are calcite, dolomite, siderite, rhodochrosite, kutnohorite, pyrite, chalcopyrite, potassium feldspar, zircon, rutile, ilmenite, and chlorite. Fe–Mn carbonates from the siderite–rhodochrosite continuous series are forming part of the marl nuclei. Framboidal, filamentous, and globular textures are observed in Fe–Mn oxides and pyrite suggesting biogenic origin. Nodules show a high mean abundance of Fe (38.6%) moderate Mn (6.0%), and low contents of trace metals and REEs compared to the average content of deep-seabed polymetallic nodules from other oceanic areas. The Mn/Fe ratio ranges from 0.07 to 0.25. The studied nodules hold in their oxide layers hydrocarbons (n-alkanes) derived from marine bacterial activity. Aromatic hydrocarbons in the form of phenanthrene, are also present which is characteristic of mature petroleum. The structure, mineralogy, and chemical composition in the studied nodules are similar to those of diagenetic–hydrogenetic continental margin nodules rather than deep-sea nodules. We suggest that the formation of this type of nodule occurred through a combined diagenetic–hydrogenetic growth process involving fluid venting from deep-seated hydrocarbon reservoirs, bio-mineralization processes, and bottom current erosion.

Electrochemical performance and local cationic distribution in layered LiNi 1/2Mn 1/2O 2 electrodes for lithium ion batteries

LiNi 1/2Mn 1/2O 2 electrodes with layered structure were synthesized by solid-state reaction between lithium hydroxide and mixed Ni,Mn oxides obtained from co-precipitated Ni,Mn carbonates and hydroxides and freeze-dried Ni,Mn citrates. The temperature of the solid-state reaction was varied between 800 and 950 °C. This method of synthesis allows obtaining oxides characterized with well-crystallized nanometric primary particles bounded in micrometric aggregates. The extent of particle agglomeration is lower for oxides obtained from freeze-dried Ni,Mn citrates. The local Mn 4+ surrounding in the transition metal layers was determined by X-band electron paramagnetic resonance (EPR) spectroscopy. It has been found that local cationic distribution is consistent with α,β-type cationic order with some extent of disordering that depends mainly on the precursors used. The electrochemical extraction and insertion of lithium was tested in lithium cells using Step Potential Electrochemical Spectroscopy. The electrochemical performance of LiNi 1/2Mn 1/2O 2 oxides depends on the precursors used, the synthesis temperature and the potential range. The best electrochemical response was established for LiNi 1/2Mn 1/2O 2 prepared from the carbonate precursor at 900 °C. The changes in local environment of Mn 4+ ions during electrochemical reaction in both limited and extended potential ranges were discussed on the basis of ex situ EPR experiments.

Dissolution, transport, and fate of lead on a shooting range in the Jefferson National Forest near Blacksburg, VA, USA

Samples taken from a shooting range near Blacksburg, VA, USA provide information about the reservoirs and pathways of lead at shooting ranges in an upland setting and humid environment. The metallic lead shot corrodes rapidly and develops a coating of hydrocerussite (Pb3(CO3)2(OH)2). Hydrocerussite dissolution releases soluble lead at concentrations ranging from 2 ppb to 2 ppm depending the soil pH values at this site. This soluble lead is captured by the Fe and Mn oxides and carbonates soil fractions. The highest concentration of extractable lead contained in the soil was directly correlated with the highest concentration of lead shot and bullets measured on the shotgun range surface. Eh-pH and hydrolysis diagrams provide a useful geochemical framework for understanding the corrosion process, recognizing the corrosion product(s), understanding their solubility, and identifying the geochemical barriers to lead migration that provides a basis for selecting best management practices for this and other shooting range.

Effect of the synthesis procedure on the local cationic distribution in layered LiNi 1/2Mn 1/2O 2

The effect of the synthesis procedure on the local cationic distribution in layered LiNi 1/2Mn 1/2O 2 oxides was examined. LiNi 1/2Mn 1/2O 2 oxides were synthesized by solid-state reaction between lithium hydroxide and mixed Ni,Mn oxides. Two types of mixed Ni,Mn oxides were used: an ilmenite-type oxide obtained from co-precipitated Ni,Mn carbonates and a spinel-type oxide obtained from freeze-dried Ni,Mn citrates. The interaction of NiMnO 3 ilmenite with LiOH starts at lower temperature as compared to that of Ni 1.5Mn 1.5O 4 spinel. A single LiNi 1/2Mn 1/2O 2 phase with layered crystal structure is formed between 800 and 950 °C. The extent of Li +,Ni 2+ disorder between the layers of LiNi 1/2Mn 1/2O 2 was determined by Rietveld refinement of the X-ray powder diffraction patterns. The local Mn 4+ arrangement in the layers was determined by X-band electron paramagnetic resonance spectroscopy (EPR). The EPR spectrum of LiNi 1/2Mn 1/2O 2 consists of a single Lorentzian line due to Mn 4+ ions only. The dependence of the EPR line width on the local Mn 4+ arrangement was used to determine the mean Ni-to-Mn ratio in the first coordination sphere of Mn 4+ for LiNi 1/2Mn 1/2O 2. It was found that the extent of Li/Ni mixing between the layers slightly decreased with the increase in the synthesis temperature. At a high synthesis temperature (950 °C) the Ni 2+ ions from lithium and the transition metal layers were ordered forming large Ni 2+–O–Ni 2+ magnetic clusters with a 180°-configuration. The extent of Li/Ni mixing remained insensitive towards the type of the precursor used. The cation distribution in the transition metal layer of LiNi 1/2Mn 1/2O 2 was consistent with α,β-type cationic order with some extent of disordering. Contrary to the Li/Ni mixing, the local Ni,Mn distribution in the transition metal layers was found to depend mainly on the precursor used. The low extent of disordering is observed for LiNi 1/2Mn 1/2O 2 obtained from Ni 1.5Mn 1.5O 4 spinel.

Adsorption of Neutral Red onto Mn-impregnated activated carbons prepared from Typha orientalis

Activated carbon was prepared from an inexpensive and renewable carbon source, Typha orientalis, by H 3PO 4 activation and then impregnated with different Mn salts and tested for its Neutral Red (NR) adsorption capacities. The amount of Mn impregnated in the activated carbon was influenced by the anion species. Impregnation with Mn decreased the surface area, changed the pore size and crystal structure, and introduced more acidic functional groups such as carboxyl, lactone and phenol groups. The optimum adsorption performance for all the activated carbons was obtained at pH 3.7, Mn–Carbon dose of 0.100 g/100 ml solution and contact time 4.5 h. The adsorption isotherms fit the Langmuir isotherm equation. The kinetic data followed the pseudo-second-order model. The thermodynamic parameters indicated that the processes were spontaneous and endothermic. According to these results, the prepared Mn modified activated carbons are promising adsorbents for the removal of Neutral Red from wastewater.

Rust formation and corrosion performance of Si- and Al-bearing ultrafine grained weathering steel

A high Si, Al type ultrafine-grained (UFG) weathering steel was produced by the multi-pass warm rolling method, and its corrosion resistance was estimated by a cyclic wet/dry corrosion test using chloride ions. The Si- and Al-bearing UFG steel exhibited excellent corrosion resistance in comparison with Si–Mn carbon steel (SM). EPMA and TEM analyses showed that Si and Al mainly exist in nano-scale iron complex oxides in the inner rust layer formed on the developed steel. The Al K X-ray spectrum of Al 2O 3 and metallic Al had different peak positions due to chemical shifts, and that of the test sample was the same as that of Al 2O 3 in the EPMA analysis. This result suggested that Al was present in the complex oxides as Al 3+. In the same way, Si was identified as an intermediate state such as Si 2+ in the complex oxides of the inner rust. EIS (electrochemical impedance spectroscopy) measurement of the corrosion test samples revealed that the rust resistance ( R rust) and corrosion reaction resistance ( R t) of the developed steel were much larger than those of SM. It was found that nano-scale complex iron oxides formed in the lower layer of iron rust in the developed steel, resulting in increased R rust and R t, and finally suppressing corrosion.

Pb–Zn mineralization in a Miocene regional extensional context: The case of the Sidi Driss and the Douahria ore deposits (Nefza mining district, northern Tunisia)

The Sidi Driss and Douahria sulfide ore deposits and showings are located in the Nefza mining district, northern Tunisia. The ores are hosted within Upper Miocene (Messinian) basins, within carbonate lenses composed of Fe–Mn-enriched dedolomite partially or totally replaced by early barite and celestite. The ore mainly consists of galena and spherulitic/colloform sphalerite (partially replaced by later Fe-sulfides). It is present as disseminated or banded ores and has been deposited within the host-rock through dissolution/replacement process or through void infilling. The remaining voids are filled by late calcite/barite locally associated with a late oxidation event. In situ ion microprobe sulfur isotope analyses show significant variability for sphalerite (from − 43.9 to 1.2‰), galena (from − 30.3 to − 2‰) and marcasite δ 34S (from − 35.9 to 25.8‰). These values are interpreted as the result of (i) the mixing of two sulfur end-members in the mineralizing fluids, corresponding to different reduction processes (bacterially-mediated sulfate reduction and thermochemical sulfate reduction, with early celestite and barite and/or contemporaneous Messinian seawater, together with Triassic sulfate, as sulfur sources, and (ii) Rayleigh fractionation process in a closed system. Several arguments (Fe–Mn enrichment in early diagenetic carbonates, involvement of Messinian seawater as a sulfur source, low temperature of deposition and soft-style sedimentary figures within sulfides) suggest that the Sidi Driss and Douahria Pb–Zn ore deposits are syn-diagenetic. Moreover, the properties of the ore deposits, with Fe–Mn carbonates having a wider distribution than that of the base metal sulfides, and the characteristics of the mineralization, in which diagenetic sulfates are a sulfur source and Cd enrichment in sphalerite, support the classification of the Sidi Driss and Douahria Pb–Zn deposits as SHMS-Sedex type. Late Miocene extension, comprising rifting dynamics and basalt emplacement, favored a thermally-driven fluid circulation origin for the Sidi Driss and Douahria deposits, enhancing inception of small-scale shallow convection cells. Such sulfide emplacement is significantly different from that of southernmost MVT ore deposits of Tunisia, which are associated with diapirs and are interpreted as the result of a Serravalian–Tortonian gravity-driven fluid circulation event related to late Alpine convergence.

Seasonal Influence of the Needle Rush Juncus roemarianus on Saltmarsh Pore Water Geochemistry

Previous studies have shown that saltmarsh macrophytes have a significant influence on sediment biogeochemistry, both through radial release of oxygen from roots and also via primary production and release of labile organic exudates from roots. To assess the seasonal influence of the needle rush, Juncus roemarianus, on saltmarsh sediment geochemistry, pore waters and sediments were collected from the upper 50 cm of two adjacent sites, one unvegetated and the other vegetated by Juncus roemarianus, in a Georgia saltmarsh during winter and summer. Pore waters collected at 1- to 2-cm intervals were analyzed for pH, alkalinity, dissolved phosphate, ammonium, Fe(II), Fe(III), Mn(II), sulfide, sulfate, and organic carbon. Sediments were collected at 5-cm intervals and analyzed for iron distribution in the solid phase using a two-step sequential extraction. The upper 50 cm of the sediment pore waters are mostly sulfidic during both winter and summer. The pore water and sediment geochemistry suggest organic matter degradation is coupled mostly to Fe(III) and sulfate reduction. In summer, there is greater accumulation of alkalinity, sulfide, ammonium, and phosphate in the pore waters and lower levels of ascorbate extractable Fe, which is presumed to be comprised primarily of readily reducible Fe(III) oxides, in the sediments, consistent with higher organic matter degradation rates in summer compared to winter. Lower pH, alkalinity, ammonium, and sulfide concentrations in sediments with Juncus, compared to nearby unvegetated sediments, is consistent with release of oxygen into the Juncus rhizosphere, especially during summer.

Petrography and geochemistry of intraclastic manganese–carbonates from the ∼2.2 Ga Nsuta deposit of Ghana: Significance for manganese sedimentation in the Palaeoproterozoic of West Africa

Intraclastic Mn carbonate rocks occur in the marginal areas of the manganese–carbonate orebody (manganesestone) of the Palaeoproterozoic Nsuta deposit in the Birimian of Ghana. Macroscopically the intraclastic rocks display graded bedding and are typified by a matrix-supported fabric with subangular to subrounded particles less than a millimetre to ∼1.5 × 0.5 cm. Both clasts and matrix consist mainly of varying proportions of microcrystalline and microconcretionary carbonates, quartz, muscovite and subordinate pyrite. Within individual intraclasts, carbonate minerals (including distinctly zoned microconcretions) are essentially Mg kutnahorite and Mg–Ca rhodochrosite, similar to the carbonate minerals in the manganesestone. Whole rock chemistry of the intraclastic carbonates shows significant variability in the amounts of SiO 2, Al 2O 3, MnO, MgO, CaO, Na 2O and, to a lesser extent, K 2O. Major element contents of the manganesestone similarly vary widely, except that these have, in particular, comparably higher MnO but less SiO 2 and Al 2O 3 than the intraclastic carbonates and host rock Mn phyllite. Rare earth element (REE) concentrations in the intraclastic carbonates are approximately an order of magnitude higher than in the manganesestone. Whereas both rocks exhibit positive Eu anomalies, only the manganesestone shows a discernibly negative Ce anomaly. Petrographic and geochemical features suggest that the intraclasts are fragments of reworked Mn carbonate sediments derived from intraformational erosion and subsequent (mass flow) deposition as carbonate “turbidite” mud. Processes such as submarine slumping, sliding and other sediment gravity flows may have likely interrupted Mn sedimentation and transported partially consolidated manganiferous sediments down slopes into the early Birimian ocean.

Organic-rich and manganese sedimentation during the Cenomanian–Turonian boundary event in the Outer Carpathian basins; a new record from the Skole Nappe, Poland

Upper Cenomanian–Lower Turonian strata in the Spława section of the Skole Nappe, Outer Carpathians, Poland, provide a detailed palaeoenvironmental record of the oceanic anoxic event (OAE-2) from a deep-water basin below the CCD at the northern margin of the Western Tethys. The OAE-2 succession consists of black, parallel-laminated radiolarian shales, enriched in organic matter of mainly marine origin (TOC up to 8%). Organic carbon isotope variations, together with microfossil datum events allowed to correlate the studied organic-rich facies with other black shale successions along the Outer Carpathians and other areas of the Western Tethys. The mean values of sedimentation rate (3.5–5.5 mm/kyr) and organic matter accumulation rate (0.5 g/m 2/year), calculated for the OAE-2 interval in the Outer Carpathian basins, are comparable to the values from other deep-water marginal basins in the Western Tethys. The average redox-sensitive trace metal contents and their enrichment factors, indicate water column anoxia in the Outer Carpathian basins, intensified during the interval of the largest shift in δ 13C values. The periods of bottom anoxia were interrupted by intervals of variable Eh conditions with sedimentation of hemipelagic green shales, including poor agglutinated foraminiferal assemblages. An increase in productivity of organic and siliceous plankton during the OAE-2 is documented, based on increased values of silica and barium enrichments. This closely corresponds to an interval of the largest positive stable carbon isotope excursion, related to the beginning of the largest sea level rise, linked with intensive coastal upwelling. Extremely low sedimentation rate or even hiatuses and the increase in deep-water circulation causing basin oxygenation resulted in precipitation of two ferromanganese layers. Their formation was related to changes in hydrodynamic conditions at the basin floor, expressed by precipitation of Fe–Mn carbonates. Some chemical indices seem to suggest that the primary metal enrichments could be related to hydrothermal activity. However, the concentrations of some elements show also on hydrogenic to diagenetic influences in these metalliferous sediments. The precipitation of these Fe–Mn sediments was probably synchronous with the manganese enrichment across the C–T transition recorded in other Western Tethyan basins and in the adjacent epicontinental seas.

Spatial variation of redox and trace metal geochemistry in a minerotrophic fen

Pore water and solid phase samples were collected from the upper 50 cm of a peat profile at four sites within a 10 m2 area in Kleinstuck Marsh, a minerotropic fen located in Kalamazoo, MI. Although the chosen sites are in close proximity to each other, they differ with respect to vegetation species and density. Pore water analyses for a suite of redox sensitive species (pH, alkalinity, dissolved Mn(II), Fe(II), Fe(III), sulfide, sulfate), together with Fe and Mn distributions inferred from operationally-defined sequential extractions, demonstrate that Fe(III) and Mn(IV) reduction occurs in the shallow peat at three of the four sites. At the fourth site, the only site containing the invasive purple loosestrife (Lythrum salicaria), accumulation of dissolved sulfide in the pore waters and increased levels of oxidizable phases in the shallow peat point to increased net sulfate reduction relative to the other three sites. Speciation calculations indicate that pore water concentrations of phosphate, especially below ∼10 cm depth, are largely controlled by the solubility of phases such as strengite or hydroxylapatite, and that at all but the loosestrife site, dissolved Ca and Mg are likely determined by carbonate solubility. Fe and Mn distribution among operationally defined solid phase fractions are consistent with reductive dissolution of FMO in the uppermost peat, leading to precipitation of Fe sulfides and Mn carbonates deeper in the peat profile. Zn, Co, Cr and Ni distributions are consistent with release from FMO to form sulfides or organic associations deeper in the peat. Pb and Cu may also be released by reductive dissolution of FMO, or more likely, shift from primary association with organic matter to increased association with sulfides under more sulfidic conditions. This study highlights the existence of extreme lateral variations in peat pore water and solid phase geochemical profiles, even over quite small areas.

Surface Texture Evolution during α-γ-α Transformation in Mn and Al Alloyed Ultra-Low Carbon Steel

This paper investigates the surface texture evolution during α−γ−α phase transformation. After austenite annealing of the cold rolled sheets a weak texture was formed at the surface of ultra low carbon steel alloyed with Mn and Al. This texture consists of <100>//ND and <110>//ND fiber orientations with an intensity of approximately 2 X random. This surface texture is confined to a mono-layer of surface grains which are in direct contact with the metal/vapour interface. In order to interpret this surface effect, two alternative mechanisms were considered: (i) one assumption attributes the occurrence of the specific surface texture to the minimization of the outer surface energy and (ii) according to an alternative hypothesis the release of elastic work parallel to ND in the surface area is responsible for the observed surface fibers. After analyzing the experimental data it is concluded that the evidence in support of hypothesis (i) is the more convincing in this experiment.

Chemical speciation of heavy metals in the Ase River sediment, Niger Delta, Nigeria

The speciation patterns of heavy metals were assessed with a view to providing information on the bioavailability of metals in the sediment matrix. The results indicate that cadmium is speciated into residual and readily exchangeable forms, while copper speciated into organic bound, residual and Fe–Mn oxide fractions: lead into Fe–Mn oxide, organic and residual fractions; chromium into Fe–Mn oxide, organic and residual fractions; nickel into residual and organic bound fraction; zinc into residual Fe–Mn oxide and carbonate fractions; iron and manganese into Fe–Mn oxide, residual and easily exchangeable fractions. The speciation pattern gave a general picture that the majority of the metals exist either in the organic, or Fe–Mn oxide and residual fractions except for cadmium. It implies that metals that are predominantly in the Fe–Mn oxide and organic fractions can only be remobilised under conditions that change the redox potential of the sediment. There are significant spatial and temporal variations in the speciation patterns of heavy metals in river sediment.

Mineralogical and geochemical constraints on environmental impacts from waste rock at Taojiang Mn-ore deposit, central Hunan, China

The mineralogy and geochemistry of the waste rocks distributed at Taojiang Mn-ore deposit, central Hunan province, China, were studied using X-ray powder diffraction (XRD), electron microprobe analysis (EMPA) fitted with energy dispersive spectrometer (EDS) and inductively coupled plasma mass spectrum (atomic emission spectra) ICP-MS (AES), with the aim of predicting the environmental impacts of weathering of the waste rocks. The mineralogical results from microscope observation and XRD and EMPA studies show that the waste rock is composed of black shale and minor Mn carbonates. The oxidation of sulfide minerals such as galena, pyrite and chalcopyrite is accompanied by decomposition of Mn carbonates and K-feldspar during exposure to atmospheric O2. The geochemical characteristics of major, rare earth elements (REE) and trace elements of the waste rocks also show that the waste rock can be divided into black shale and Mn carbonate, and both of them are currently under chemical weathering. The major alkalies and alkaline elements (Ca, Mg, Na, K, Rb, Sr and Cs) and major elements (Fe, S and P) and heavy metals (Sc, V, Cr, Th, U, Sn, Co, Ni, Cu, Zn, Pb, Mo, Cd, Sb, an Tl) are being released during weathering. The mobility of alkalis and alkaline elements Ca, Mg, Na, K, Rb, Sr and Cs is controlled by decomposition of Mn carbonates. The dispersion of Cr, Sc and Th (U) might be related to weathering of K-feldspar, and the release of the heavy metals Co, Ni, Cu, Zn, Pb, Mo, Cd Sb and Tl is dominated by the breaking of sulfide minerals. The REE of the waste rocks and surrounding soils and the spidery distribution patterns of heavy metals in the waste rocks, the surrounding soils and the surface waters show that weathering of the waste rocks and bedrock might be the sources of heavy metal contamination for the surrounding soils and surface water system for the mining area. This is predicted by the mass-balance calculation by using Zr as an immobile element. Therefore, it is urgently necessary take measures to treat the waste rocks distributed throughout the area for the local environmental protection.