Geochemistry of Fe-Mn crusts at seamounts in the Northwest Pacific

Hydrogenetic ferromanganese crusts were dredged from four seamounts in the western Pacific, OSM7, OSM2, Lomilik, and Lemkein, aligned in a NW-SE direction parallel to Pacific Plate movement. The crusts consist of four well-defined layers with distinct textural and geochemical properties. The topmost layer 1 is relatively enriched in Mn, Co, Ni, and Mo compared to the underlying layer 2, which is relatively enriched in Al, Ti, K, and Rb and Cu, Zn, and excess Ba. Textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux. Such conditions are met in the equatorial Pacific (i.e., between the Intertropical Convergence Zone (ITCZ) and equatorial high-productivity zone). Layer 2 likely formed when each seamount was beneath the equatorial Pacific along its back track path. On the other hand, layer 1 probably started to grow after seamounts moved northwest from the ITCZ. This interpretation is consistent with the thickness of layer 1 across the four crusts, which increases to the northwest. Ages of the layer 1-layer 2 boundary in each crust, a potential proxy for northern margin of the ITCZ, also increase to the northwest at 17, 11, 8, and 5 Ma for OSM7, OSM2, Lomilik, and Lemkein, respectively. Assuming Pacific Plate motion of 0.3°/Myr, the seamounts were located at 12°N, 11°N, 9°N, and 8°N at the time of boundary formation. This result suggests that the north edge of the ITCZ has shifted south since the middle Miocene in the western Pacific, which agrees with information from the eastern Pacific.

Woodleigh, Southern Carnarvon Basin, Western Australia: history of discovery, Late Devonian age, and geophysical and morphometric evidence for a 120 km-diameter impact structure

The discovery of the Woodleigh impact structure, first identified by R. P. lasky, bears a number of parallels with that of the Chlcxulub impact structure of K-T boundary age, underpinning complications inherent in the study of buried impact structures by geophysical techniques and drilling. Questions raised in connection with the diameter of the Woodleigh impact structure reflect uncertainties in criteria used to define original crater sizes in eroded and buried impact structures as well as limits on the geological controls at Woodleigh. The truncation of the regional Ajona - Wandagee gravity ridges by the outer aureole of the Woodleigh structure, a superposed arcuate magnetic anomaly along the eastern part of the structure, seismic-reflection data indicating a central > 37 km-diameter dome, correlation of fault patterns between Woodleigh and less-deeply eroded impact structures (Ries crater, Chesapeake Bay), and morphometric estimates all indicate a final diameter of 120 km. At Woodleigh, pre-hydrothermal shock-induced melting and diaplectic transformations are heavily masked by pervasive alteration of the shocked gneisses to montmorillonite-dominated clays, accounting for the high MgO and low K2O of cryptocrystalline components. The possible contamination of sub-crater levels of the Woodlelgh impact structure by meteoritic components, suggested by high Ni, Co, Cr, Ni/ Co and Ni/Cr ratios, requires further siderophile element analyses of vein materials. Although stratigraphic age constraints on the impact event are broad (post-Middle Devonian to pre-Early Jurassic) high-temperature (200-250 degrees C) pervasive hydrothermal activity dated by K-Ar isotopes of illite - smectite indicates an age of 359 +/- 4 Ma. To date neither Late Devonian crater fill, nor impact ejecta fallout units have been identified, although metallic meteoritic ablation spherules of a similar age have been found in the Conning Basin.

Microchemistry and microstructures of hydrothermally altered shock-metamorphosed basement gneiss, Woodleigh impact structure, Southern Carnarvon Basin, Western Australia

Hydrothermally altered shock-metamorphosed gneisses consisting of relic igneous biotite-K-feldspor-Na-rich alkali feldspar - plagioclase - quartz assemblages ( accessory garnet, corundum, titanite, monazite, zircon), and showing extensive replacement by montmorillonite, illite, sericite, and to a lesser extent chlorite, calcite, epidote, zoisite and pyrite, occur in the basement core uplift of the Woodleigh impact structure, Western Australia. The rocks display extensive hydrothermal clay alteration, complicating identification of pre-hydrothermal and pre-impact textures and compositions. Analysis of quartz-hosted planar deformation features (PDFs) indicates a majority of indexed sets parallel to omega{10 (1) over bar3}, a lesser abundance of sets parallel to pi{10 (1) over bar2}, and some sets parallel to the basal plane (0001) and r,z {10 (1) over bar1}, consistent with pressures about or over 20 GPa. Feldspar-hosted FDFs form reticulate vein networks displaying checkerboard-like to irregular and serrated patterns attributable to preferential replacement of shock-damaged PDFs and/or perthitic twin lamella by clay minerals. The gneisses are pervaded by clay-dominated intergranular and intragranular veins of cryptocrystalline material that display marked departures from bulk-rock chemistry and from mineral compositions. XRD analysis identifies the cryptocrystalline components as illite - montmorillonite, illite and chlorite, while laser Raman analysis identifies high-fluorescence sub-micrometre clay assemblage, feldspar, quartz and minor mica. SEM/EDS-probe and laser-ICPMS analysis indicate low-K high-Mg clay mineral compositions consistent with montmorillonite. Quartz PDF-hosted cryptocrystalline laminae display distinct enrichments in Al, Mg, Ca and K. Altered intergranular veins and feldspar-hosted cryptocrystalline components show consistent enrichment in the relatively refractory elements (Al, Cc, Mg, Fe) and depletion in relatively volatile elements (Si, K, Na). The clay alteration retards determination whether clay-dominated vein networks represent altered shock-induced pseudotachylite veins, diaplectic zones and/or shock-damaged twin lamella, and/or result from purely mineralogical and chemical differentiation affected by hydrothermal fluids, Overall enrichment of the shocked gneiss and of the cryptocrystalline components in Mg and trace ferromagnesian elements (Ni, Cc, Cr) may be attributed alternatively to introduction of siderophile element-rich fluid from the projectile, or/and contamination of hydrothermal fluids by MgO from dolomites surrounding the basement uplift. High Ni/Co and Ni/Cr and anomalous DGE (platinum group elements) may support the former model.

The geochemistry of radioactive waste disposal

The present study attempted to identify the significant parameters which affect radionuclide migration from a low level radioactive waste disposal site located in a clay deposit. From initial sorption studies on smectite minerals, increased Kd with decreasing initial cation concentration was observed, and three sorption mechanisms were identified. The observation of anion dependent sorption was related to the existence of a mechanism in which an anion-cation pair are bound to the clay surface through the anion. The influence of competing cations, typical of inorganic groundwater constituents, depended on: (1) Ni/Co:Mn+(Mn+ = competing cation) ratio, (2) nature of M^n+, (3) total solution ionic strength. The presence of organic material in groundwater is well documented, but its effect on cation sorption has not been established. An initial qualitative investigation involving addition of simple organic ligands to Ni(Co)-hectorite samples demonstrated the formation of metal complexes in the clay interlayers, although some modified behaviour was observed. Further quantitative examination involving likely groundwater organic constituents and more comprehensive physical investigation confirmed this behaviour and enabled separation of the organic compounds used into two classes, according to their effect on cation sorption; (i) acids, (ii) amine compounds. X-ray photoelectron spectroscopy, scanning electron microscopy and Mossbauer spectroscopy were used to investigate the nature of transition metal ions sorbed onto montmorillonite and hectorite. Evidence strongly favoured the sorption of the hexaaquo cation, although a series of sorption sites of slightly different chemical characteristics were responsible for broadened peak widths observed in XPS and Mossbauer investigations. The surface sensitivity of XPS enabled recognition of the two surface sorption sites proposed in earlier sorption studies. Although thermal treatment of Fe^3+/Fe^2+-hectorite samples left iron atoms bonded to the silicate sheet structure, Mossbauer evidence indicated the presence of both ferric and ferrous iron in all samples.

The relationship of mineralization to petrology at Parys Mountain, Anglesey

The Lower Palaeozoic succession at Parys Mountain overlies a Precambrian basement (the Iona Series). This succession consists of Ordovician slates, overlain by, and in part interbedded with, Ordovician dacitic and rhyolitic volcanics, which in turn are unconformably overlain by Silurian slates. Both basement and Palaeozoic rocks have been deformed during Caledonian and Variscan orogenies. The resultant structure of Parys Mountain is interpreted as an east-north-easterly trending, single syncline overturned to the north. Many primary extrusive characters are retained by the volcanic rocks, despite the high degree of deformation. The lithologies and textures allow subdivision and interpretation of these rocks as dacite, lithic tuff, siliceous sinter, rhyolitic tuff, rhyolitic ignimbrite, rhyolitic tuff-lava, and rhyolitic lava. The results of 61 bulk chemical analyses are interpreted to show that the volcanism was of the orogenic calc-alkaline type from a continental margin/island arc environment. The magmas probably result from either partial melting of the crustal part of the oceanic lithosphere on a Benioff zone, or partial melting of the mantle, above a Benioff zone, under high load pressures and high water pressures. The mineral deposits are largely confined within the volcanic succession though some occur in the Ordovician and Silurian slates near to their contacts with the volcanics. The majority of the deposits form conformable lenses and tabular bodies, with subordinate deposits as veins and stockworks. The ore mineral assemblages are of chalcopyrite, galena, sphalerite, and pyrite. The general paragenetic sequence (73 sections) is pyrite--chalcopyrite--galena-sphalerite. The main mineralization episode is interpreted to be syngenetic, genetically related to the volcanism. The veins and stockworks probably result from Caledonian and Variscan remobilization of the primary mineralization. Trace element analyses (Cu, Zn, Pb, Ni, Co, Cd, Cr, Hg, Ba, Sr), on 350 specimens, detected anomalous concentrations of these elements around the mineralized zones, though some occur where no mineralization was found. The analyses also indicate a close relationship between the mineralization and the volcanic horizons, especially the siliceous sinter.

Trace element contents in bottom sediments from the North Indian Ocean

Contents and distributions of Cu, Ni, Co, V, Cr, Zn, Pb, Mo, W, and Zr in near-coast and pelagic sediments of the Northern Indian Ocean are under consideration in the paper. Chemical analyses showed enrichment of pelagic clayey radiolarian oozes by Mn, Cu, Ni, Co, Pb, W, and Mo. According to enrichment factors these elements have the following order: Mo> Mn> Cu> Ni> Co> Pb> W. Enrichment of pelagic sediments from the Indian Ocean is mainly determined by the mechanism of the sedimentation process. Enrichment factors of Cu, Ni, Co, W, Mo, and Mn in pelagic sediments of the North Indian Ocean are intermediate between ones in pelagic sediments of the Pacific and Atlantic Oceans.

Description, geochemistry and growth rate of buried nodules from the Central Indian Basin

Buried nodules from siliceous sediments in the central Indian Basin are morphologically variable and mineralogically consist of d-MnO2 and incipient todorokite. Compositionally they are weakly diagenetic. The sediment coarse fractions (>63 µm) at different depths show variable abundances of micronodules, volcanic glass shards and biodebris. Dissolution of biodebris increases and abundance of micronodules decreases with increasing depth. Enrichment in Mn, Fe, Cu, Ni, Co, together with a decrease in organic carbon in the sediment column, may result from diagenetic metal remobilization. Diagenetically remobilized trace metals might have been utilized for the growth of micronodules over the buried nodules.

(Table 2, page 156), The comparison of heavy elements in manganese nodules

The comparison of Mn/Fe, Co/Ni, Co/Fe, Ni/Mn, and Cu/Fe ratios is presented and it is noticed that Co/Ni and Ni/Mn ratios of nodules fairly coincide with those of coexisting sediments. This agreement suggests that Mn, Ni, and Co are accumulated in both nodules and sediments at about the same rates. According to the calculation of Somayajulu et al. similar consideration is also applicable to Cu. Results are, however, implying that Cu co-precipitates with Fe, rather than Mn.

Geochemistry of the Japan Trench sediments at DSDP Legs 56-57 Holes

The main objective of this investigation was to study distribution of main chemical constituents and several minor elements in sediment sections drilled during DSDP Legs 56 and 57 in the Japan Trench, in order to infer geochemical features of different lithologic types of sediments, and to find out how the geochemistry is associated with major lithologic constituents, such as terrigenous detrital matter, clay, volcanic ash, and biogenic particles. The geochemical data may help to indicate the nature of the sediments and to interpret sedimentation processes. The analyzed samples seem to be representative of most lithologic units, sub-units, and sediment types drilled at all sites on both legs, except for some shallow-water deposits at Sites 438 and 439. We analyzed bulk-sediment composition by X-ray fluorescence (Kuzmina and Turanskaya) and routine wet-chemical methods (Mikhailov); amorphous SiO2, extracted in a boiling sodium carbonate solution (Analythical Laboratory, P. P. Shirshov Institute of Oceanology); Cr, Zn, Cu, Ni, Co, and Al by atomic absorption (Gordeev); and Sn, Pb, Zn, Cu, Ni, Co, Cr, V, B, and Ag by quantitative spectrographic analyses in both bulk samples and granulometric fractions (Mikhailov). In addition, Fe, Ti, Mn, and CaCO3 have been determined in selected samples by routine wet-chemical methods (Analytical Laboratory, P. P. Shirshov Institute of Oceanology). Murdmaa was responsible for interpretation of the results.

Catalizzatori polifunzionali per la sintesi di Metil Isobutil Chetone

In this work, we have examined the activity and selectivity of new catalysts for the single-stage production of methyl isobutyl ketone (MIBK, 4- methyl-2-pentanone) from acetone (both in liquid and gas phase), using a fixed bed reactor operated in the temperature range between 373 and 473 K. The main reaction pathways for the synthesis of MIBK from acetone are given in Fig.1. The first step is the self condensation of acetone to diacetone alcohol (DAA, 4-hydroxy-4-methyl-2-pentanone); the second step is the dehydration of DAA to mesityl oxide (MO, 4-methyl-3-penten-2-one); the final step is the selective hydrogenation of the carbon–carbon double bond of MO to form MIBK. The most commonly observed side reactions are over-condensations and unselective hydrogenations (also shown in Fig.1). Two types of catalysts were studied: i)Pd supported on MgO-SiO2 mixed oxides with ratio of Mg to Si, synthetized using Ohnishi’s method and ii)Pd supported on alumina doped with 5% or 10% of MgO. The different Mg-Si and Mg-Al catalysts were characterized by different techniques (XRD, BET, SEM, NH3-TPD and CO2-TPD) and tested under different conditions in the condensation of acetone to diacetone alcohol and its dehydration to mesityl oxide to enhance the activity. Palladium was chosen as metal component, and its hydrogenation activity was studied. A low hydrogenation activity negatively affects the acetone conversion and promotes the production of mesityl oxide. Hydrogenation conditions being too severe may favor the unwanted hydrogenation of acetone to 2-propanol and of MIBK to methyl isobutyl carbinol (MIBC, 4-methyl-2-pentanol) but this effect is less detrimental to the MIBK selectivity than an unsufficient hydrogenation activity.

Degradação do PMMA através da reação despolimerização uitlizando catalisadores de óxidos mistos

In this work, mixed oxides were synthesized by two methods: polymeric precursor and gel-combustion. The oxides, Niquelate of Lanthanum, Cobaltate of Lanthanum and Cuprate of Lanthanum were synthesized by the polymeric precursor method, and treated at 300 º C for 2 hours, calcined at 800 º C for 6h in air atmosphere. In gel-combustion method were produced and oxides using urea and citric acid as fuel, forming for each fuel the following oxides Ferrate of Lanthanum, Cobaltato of Lanthanum and Ferrato of Cobalt and Lanthanum, which were submitted to the combustion process assisted by microwave power maximum of 10min. The samples were characterized by: thermogravimetric analysis, X-ray diffraction; fisisorção of N2 (BET method) and scanning electron microscopy. The reactions catalytic of depolymerization of poly (methyl methacrylate), were performed in a reactor of silica, with catalytic and heating system equipped with a data acquisition system and the gas chromatograph. For the catalysts synthesized using the polymeric precursor method, the cuprate of lanthanum was best for the depolymerization of the recycled polymer, obtaining 100% conversion in less time 554 (min), and the pure polymer, was the Niquelate of Lanthanum, with 100% conversion in less time 314 (min). By gel-combustion method using urea as fuel which was the best result obtained Ferrate of Lanthanum for the pure polymer with 100% conversion in less time 657 (min), and the recycled polymer was Cobaltate of Lanthanum with 100 % conversion in less time 779 (min). And using citric acid to obtain the best result for the pure polymer, was Ferrate of Lanthanum with 100% conversion in less time 821 (min and) for the recycled polymer, was Ferrate of Lanthanum with 98.28% conversion in less time 635 (min)

Preparação de óxidos mistos de níquel e zinco nanoparticulados a partir de combustíveis alternativos

The field of "Materials Chemistry" has been developing in recent years and there has been a great increase of interest in the synthesis and chemical and physical properties of new inorganic solids. New routes of synthesis and synthesis modified has been developed with the aim not only to optimize the processes in laboratory scale, but also on an industrial scale, and make them acceptable by current environmental legislation. The phenomenology of current solid state chemistry properties coupled with the high temperature superconductivity, ferromagnetism, porosity molecular and colors are evidence affected by the synthesis method, which in turn can influence the technological application of these materials. From this understanding, mixed oxides of nickel and zinc nanoparticulate were synthesized by microwave-assisted combustion route using three specific types of organic fuels employing the weight ratios 1:1/2 and 1:1 of cation metallic/fuel, in order to investigate the influence of such proportions to obtain the solids. The new fuels were chosen to replace, for example, urea or glycine that are the fuels most commonly preferred in this kind of synthesis. The powders without heat treatment were studied by Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and then calcined at 900°C. After heat treatment, the samples were characterized by analysis of X Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The modified synthesis route porposed was effective for obtaining powders. Both the alternative fuels chosen as the different weight ratios employed, influenced in the morphology and obtaining oxides

Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt–Ni–Co Alloy Nanocatalysts

Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction “one-step” conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a “two-step” route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this, scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.

Catalytic asymmetric transfer hydrogenation of ketones: recent advances

In this review, we consider the main processes for the asymmetric transfer hydrogenation of ketones from 2008 up today. The most effective organometallic compounds (derived from Ru, Rh, Ir, Fe, Os, Ni, Co, and Re) and chiral ligands (derived from amino alcohols, diamines, sulfur- and phosphorus-containing compounds, as well as heterocyclic systems) will be shown paying special attention to functionalized substrates, tandem reactions, processes under non-conventional conditions, supported catalysts, dynamic kinetic resolutions, the use of water as a green solvent, theoretical and experimental studies on reaction mechanisms, enzymatic processes, and finally applications to the total synthesis of biologically active organic molecules.

Mixed valency in the high-temperature phases of transition metal molybdates,AMoO4 (A=Fe, Co, Ni)

Transition metal molybdates of the formulaAMoO4 whereA=Fe, Co or Ni exhibit a first-order phase transition between 670K–970K. An investigation of the lowtemperature (lt) and high-temperature (ht) phases by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, magnetic susceptibility and other physical methods shows that the phase transition is associated with a valence change of the typeA 2++Mo6+αA 3++Mo5+ in the cases of iron and cobalt molybdates.