2,023,267 research outputs found
Comportamento dos íons pb(ii) e cd(ii) na Interface óxido - solução aquosa
Full text linkTCC (graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Físicas e Matemáticas. Curso de Química.Para um maior conhecimento referente ao movimento (transporte e mobilidade) de íons metálicos, na interface sólido-solução aquosa, é necessário avaliar o comportamento dos íons metálicos com relação a adsorção/dessorção dos mesmos em vários tipos de superfícies. A cinética e o equilíbrio na adsorção das espécies metálicas Pb(II) e Cd(II) em relação aos adsorventes argilominerais, como a hematita e a alumina dependem da presença de sítios do adsorvente que estejam disponíveis para ligação. No presente estudo é descrito o comportamento de Pb(II) e do Cd(II) em solução na presença de γ-alumina e α-hematita, utilizando-se diferentes técnicas analíticas que foram otimizadas. As determinações de Pb(II) utilizando um eletrodo íon seletivo, mostram: i) limite de detecção (2,44±0,50) x10-6 mol L-1 e, ii) limite de quantificação de (6,11±0,50) x 10-6 mol L-1. Os resultados da intracalibração entre os métodos espectrofluorimétrico e de eletrodo seletivo a íon , para determinar Pb(II) na presença de γ-alumina são satisfatórios. O tempo de equilíbrio para a adsorção do Cd(II) e Pb(II) em γ-alumina e α-hematita mostram que após um tempo de menos de uma hora é atingido o equilíbrio. Os parâmetros de Langmuir calculados para adsorção de Pb(II) em γ- alumina mostram uma capacidade de adsorção de 22 g Kg-1 de γ-alumina e uma constante de Langmuir de 2,36 x 106 mol L-1
HAXPES spectra of Pb
No full textThis dataset consists of HAXPES spectra at Pb measured at SPring-8 BL46XU, and is a part of HAXPES database (MDR HAXPES DB, https://doi.org/10.48505/nims.3056) as a collection of MD
SHRIMP ion probe zircon geochronology and Sr and Nd isotope geochemistry for southern Longwood Range and Bluff Peninsula intrusive rocks of Southland, New Zealand
No full textPermian–Jurassic ultramafic to felsic intrusive complexes at Bluff Peninsula and in the southern Longwood Range along the Southland coast represent a series of intraoceanic magmatic arcs with ages spanning a time interval of 110 m.y. New SHRIMP U-Pb zircon data for a quartz diorite from the Flat Hill complex, Bluff Peninsula, yield an age of 259 ± 4 Ma, consistent with other geochronological and paleontological evidence confirming a Late Permian age. The new data are consistent with an age of c. 260 Ma for the intrusive rocks of the Brook Street Terrane. SHRIMP U-Pb zircon ages for the southern Longwood Range confirm that intrusions become progressively younger from east to west across the complex. A gabbro at Oraka Point (eastern end of coastal section) has an age of 245 ± 4 Ma and shows virtually no evidence of zircon inheritance. The age is significantly different from that of the Brook Street Terrane intrusives. Zircon ages from the western parts of the section are younger and more varied (203–227 Ma), indicating more complex magmatic histories. A leucogabbro dike from Pahia Point gives the youngest emplacement age of 142 Ma, which is similar to published U-Pb zircon ages for the Anglem Complex and Paterson Group on Stewart Island
Synthesis, characterization and thermochemistry of synthetic Pb–As, Pb–Cu and Pb–Zn jarosites
Full text linkThe enthalpy of formation from the elements of well characterized Pb-As, Pb-Cu, and Pb-Zn synthetic jarosites, corresponding to chemical formulas (H3O)0.68±0.03Pb0.32±0.002Fe2.86±0.14(SO4)1.69±0.08(AsO4)0.31±0.02(OH)5.59±0.28(H2O)0.41±0.02, (H3O)0.67±0.03Pb0.33±0.02Fe2.71±0.14Cu0.25±0.01(SO4)2±0.00(OH)5.96±0.30(H2O)0.04±0.002 and (H3O)0.57±0.03Pb0.43±0.02Fe2.70±0.14Zn0.21±0.01(SO4)2±0.00(OH)5.95±0.30(H2O)0.05±0.002, was measured by high temperature oxide melt solution calorimetry and gave ΔH°f = -3691.2 ± 8.6 kJ/mol, ΔH°f = -3653.6 ± 8.2 kJ/mol, and ΔH°f = -3669.4 ± 8.4 kJ/mol, respectively. Using estimated entropies, the standard Gibbs free energy of formation from elements at 298 K ΔG°f of the three compounds were calculated to be -3164.8 ± 9.1 kJ/mol, -3131.4 ± 8.7 kJ/mol, and -3153.6 ± 8.9 kJ/mol, respectively. Based on these free energies, their logKsp values are -13.94 ± 1.89, -4.38 ± 1.81 and -3.75 ± 1.80, respectively. For this compounds, a log10{Pb2+} - pH diagram is presented. The diagram shows that the formation of Pb-As jarosite may decrease aqueous arsenic and lead concentrations to meet drinking water standards. The new thermodynamic data confirm that transformation of Pb-As jarosite to plumbojarosite is thermodynamically possible
Spatial and temporal variations in Pb concentrations and isotopic composition in road dust, farmland soil and vegetation in proximity to roads since cessation of use of leaded petrol in the UK
Full text linkResults are presented for a study of spatial distributions and temporal trends in concentrations of lead (Pb) from different sources in soil and vegetation of an arable farm in central Scotland in the decade since the use of leaded petrol was terminated. Isotopic analyses revealed that in all of the samples analysed, the Pb conformed to a binary mixture of petrol Pb and Pb from industrial or indigenous geological sources and that locally enhanced levels of petrol Pb were restricted to within 10 m of a motorway and 3 m of a minor road. Overall, the dominant source of Pb was historical emissions from nearby industrial areas. There was no discernible change in concentration or isotopic composition of Pb in surface soil or vegetation over the decade since the ban on the sale of leaded petrol. There was an order of magnitude decrease in Pb concentrations in road dust over the study period, but petrol Pb persisted at up to 43% of the total Pb concentration in 2010. Similar concentrations and spatial distributions of petrol Pb and non petrol Pb in vegetation in both 2001 and 2010, with enhanced concentrations near roads, suggested that redistribution of previously deposited material has operated continuously over that period, maintaining a transfer pathway of Pb into the biosphere. The results for vegetation and soil transects near minor roads provided evidence of a non petrol Pb source associated with roads/traffic, but surface soil samples from the vicinity of a motorway failed to show evidence of such a source
Toxicity of Pb and of Pb/Cd combination on the springtail Folsomia candida in natural soils: Reproduction, growth and bioaccumulation as indicators
Full text linkThe toxicity of Pb and Cd+Pb was assessed on the Collembola F. candida in two cultivated soils (SV and AU) with low organic matter (OM) content and circumneutral to basic pH, and an acid forested soil (EPC) with high OM content. Collembola reproduction and growth as well as metal content in Collembola body, in soil, exchangeable fraction and soil solutions, pH and DOC were investigated. Pb and Cd+Pb were the highest in exchangeable fraction and soil solution of the acidic soils. Soil solution pH decreased after metal spiking in every soil due to metal adsorption, which was similar for Cd and the highest in AU for Pb. With increasing Pb and Cd+Pb, the most important reproduction decrease was in EPC soil. The LOEC for reproduction after metal addition was 2400 (Pb) and 200/2400 (Cd/Pb), 1200 and 100/1200, 300 and 100/1200 μg g−1 for AU, SV and EPC, respectively. The highest and the lowest Pb toxicity was observed for EPC and AU bulk soil, respectively. The metal in Collembola increased with increasing soil concentration, except in AU, but the decreasing BFsolution with increasing concentrations indicates a limited metal transfer to Collembola or an increased metal removal. Loading high Pb concentrations decreases Cd absorption by the Collembola, but the reverse was not true. The highest Pb toxicity in EPC can be explained by pH and OM content. Because of metal complexation, OM might have a protective role but its ingestion by Collembola lead to higher toxicity. Metal bioavailability in Collembola differs from soil solution indicating that soil solution is not sufficient to evaluate toxicity in soil organisms. The toxicity as a whole decreased when metals were combined, except for Pb in AU, due to adsorption competition between Cd and Pb on clay particles and OM sites in AU and EPC soils, respectively
Sedimentology, sandstone provenance and palaeodrainage on the eastern Rockall Basin margin : evidence from the Pb isotopic composition of detrital K-feldspar
No full textThe Rockall Basin, west of Ireland, is a frontier area for hydrocarbon exploration but currently the age and location of sand fairways through the basin are poorly known. A recently developed provenance approach based on in-situ Pb isotopic analysis of single K-feldspar grains by laser ablation multi-collector inductively-coupled mass spectrometry (LA-MC-ICPMS) offers advantages over other provenance techniques, particularly when applied to regional palaeodrainage issues. K-feldspar is a relatively common, usually first-cycle framework mineral in sandstones and its origin is typically linked to that of the quartz grains in arkosic and sub-arkosic rocks. Consequently, in contrast to other techniques, the Pb-in-K-feldspar tool characterises a significant proportion of the framework grains. New Pb isotopic data from K-feldspars in putative Permo-Triassic and Middle Jurassic sandstones in Well 12/2-1z (the Dooish gas condensate discovery) on the eastern margin of the Irish Rockall Basin are reported. These data suggest that three isotopically distinct basement sources supplied the bulk of the K-feldspar in the reservoir sandstones and that the relative contribution of these sources varied through time. Archaean and early Proterozoic rocks (including elements of the Lewisian Complex and its offshore equivalents), to the immediate east, north-east and north of the eastern Rockall Margin, are the likely sources. More distal sourcelands to the north-west cannot be ruled out but there was no significant input from southern sources, such as the Irish Massif. These data, together with previously published regional Pb isotopic data, highlight the important role played by old, near and far-field Archaean – Proterozoic basement highs in contributing sediment to NE Atlantic margin basins. The Irish Massif appears to have acted as a significant, but inert, drainage divide from the Permo-Triassic to the Late Jurassic and hence younger, Avalonian and Variscan, sand sources appear to have been less important on the Irish Atlantic Margin.Science Foundation IrelandGriffiths Geoscience Awar
Production of neutral strange hadrons with high transverse momentum in Pb+Pb collisions at 158 A GeV
No full textThe motivation for studying ultrarelativistic heavy ion collisions is to search for signatures of a transition from hadronic matter to a partonic phase, the Quark-Gluon plasma. The bulk of the particles produced in these collisions possesses transverse momenta of pT = 2 GeV/c clearly indicates that the hydrodynamical picture is not valid in the higher range any more. Unfortunately, no calculations from coalescence models are available for the SPS energy range so far.In dieser Arbeit wird die Produktion seltsamer neutraler Teilchen mit hohen Transversalimpulsen in Pb+Pb Reaktionen bei 158A GeV untersucht. Diese Analyse basiert auf Daten, die mit dem Experiment NA49 am europäischen Teilchenlabor CERN aufgenommen wurden. Das Standardmodell der grundlegenden Teilchen und Kräfte stellt den heutigen Stand der Suche nach den Grundbausteinen der Natur dar. Neben den Leptonen sind darin Quarks als Elementarteilchen dargestellt. Ausser diesen Teilchen kennt das Standardmodell vier grundlegende Kräfte: Die starke, elektromagnetische und die schwache Wechselwirkung werden im Standardmodell durch Quanten-Feldtheorien beschrieben, d.h. sie wirken durch den Austausch von Vektorbosonen. Die vierte Kraft, die Gravitation, wirft noch Fragen auf. Im Gegensatz zu den Leptonen kommen Quarks in der Regel nicht einzeln vor, sondern nur in gebundenen Zuständen, den Hadronen. Das liegt an den Besonderheiten der Kraft, die zwischen den Quarks wirkt: der starken Wechselwirkung. Sie ist die einzige unter den vier Kräften, deren Stärke nicht mit dem Abstand abnimmt. Das liegt daran, dass ihre Austauschteilchen, die Gluonen, selber eine Ladung tragen und damit selbst der starken Wechselwirkung unterliegen. Dies führt zum Einschluss der Quarks in Hadronen, dem confinement. Die relativistische Schwerionenphysik befasst sich mit der Suche nach einem neuen Zustand hadronischer Materie, dem Quark-Gluon-Plasma. Man geht heute davon aus, dass dieser Zustand am Anfang unseres Universums bestand, bis etwa 10 exp (-5 ) s nach dem Urknall, als Dichte und Temperatur des Universums so groß waren, dass Hadronen keinen Bestand haben konnten und sich statt dessen Quarks und Gluonen frei bewegen konnten. Die Hadronen die sich nach der Abk¨uhlung dieses Zustandes bildeten, haben im Wesentlichen bis heute, 12 Milliarden Jahre nach dem Urknall Bestand. Nur im Inneren von Neutronensternen erwarten Physiker eine Dichte die so hoch ist, dass die Neutronen überlappen und ein Quark-Gluon-Plasma bilden. Eine Möglichkeit, diesen Zustand experimentell zu untersuchen, bieten Schwerionenkollisionen bei hoch-relativistischen Energien. Dazu werden z.B. im Beschleuniger SPS am CERN Bleikerne auf eine Energie von 158A GeV gebracht. Die von verschiedenen Experimenten dieses SPS-Schwerionenprogramms 2000 verkündete Entdeckung eines neuen Materiezustandes basierte auf einer Vielzahl von Messwerten, die ein Gesamtbild des Quark-Gluon-Plasma zeichneten. Später durchgeführte Experimente bei höheren Energien am RHIC-Beschleuniger brachten andere Observable ins Spiel, die dieses Bild ergänzen können. Die meisten in Schwerionenkollisionen produzierten Hadronen stammen aus Stößen mit geringem Impulsübertrag und weisen deshalb einen Transversalimpuls (senkrecht zur ursprünglichen Strahlrichtung) von pT < 1.5 GeV/c auf. Für den Bereich höherer Transversalimpulse kommen verschiedene Mechanismen zur Hadronisierung in Frage. Ein am RHIC beobachtetes Ansteigen der Verhältnisse von Baryonen zu Mesonen wird als Anzeichen für Hadronisierung durch Rekombination von Quarks erklärt. Das Experiment NA49 wurde dafür konzipiert, den hadronischen Endzustand von Schwerionenkollisionen zu untersuchen. Es hat eine große Akzeptanz, die es ermöglicht etwa 70% der tausenden von geladenen Teilchen, die in jeder Kollision entstehen, zu vermessen. Neutrale seltsame Teilchen, wie die in der vorliegenden Arbeit untersuchten K0 S und Lambda werden über ihren schwachen Zerfall in zwei geladene Teilchen identifiziert. Die V-Form der Tochterspuren gibt ihnen den Namen V 0-Teilchen. Die Analyse beruht auf der Rekonstruktion der invarianten Masse der V 0-Teilchen in einzelnen Bereichen des Phasenraums aus den Zerfallsprodukten. Die Reichweite in pT für diese Methode ist nur durch die statistische Häufigkeit, die mit pT stark abnimmt, beschränkt. Ein wichtiger Bestandteil dieser Analyse ist es, die Menge der V 0-Kandidaten durch geeignete Kriterien (“cuts”) so einzugrenzen, dass falsche Kombinationen unterdrückt werden. Gleichzeitig muss darauf geachtet werden, durch diese cuts das Signal so wenig wie möglich zu treffen. Der Anteil der Teilchen, die wegen der geometrischen Akzeptanz des Experiments oder durch Ineffizienzen in der Analyse nicht gemessen wurden, wird durch eine Simulation ermittelt. Daraus werden für jeden Bereich des Phasenraums Korrekturfaktoren ermittelt, um die gemessenen Rohwerte in korrigierte Spektren umzurechnen. Das aus diesen korrigierten Spektren berechnete Verhältnis K0 S/Lambda gleicht qualitativ den Messungen am RHIC und bestärkt die anderen Hinweise darauf, dass bei den höchsten am SPS verfügbaren Energien ein Quark-Gluon-Plasma erreicht wird
The graphical presentation of lead isotope data for environmental source apportionment
Full text linkLead isotope ratios are widely used to identify original sources of Pb in the environment. Such source apportionment depends on the ability to distinguish potential sources on the basis of their isotopic composition. However, almost all terrestrial Pb is co-linear in some of the plots i.e. <sup>206</sup>Pb/<sup>208</sup>Pb versus <sup>206</sup>Pb/<sup>207</sup>Pb and <sup>206</sup>Pb/<sup>204</sup>Pb versus <sup>206</sup>Pb/<sup>207</sup>Pb commonly presented in the literature. These diagrams are unable to distinguish more than two sources of environmental Pb. Linear trends in such plots are an inevitable consequence of the co-linearity of terrestrial leads and should not be taken necessarily to indicate simple binary mixing of sources. A more reliable test for multiple source mixing can be obtained from plots involving <sup>206</sup>Pb/<sup>204</sup>Pb, <sup>207</sup>Pb/<sup>204</sup>Pb and <sup>208</sup>Pb/<sup>204</sup>Pb and therefore requires measurements of the minor <sup>204</sup>Pb isotope
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