Reactive Iron Mineral Coatings in Redox Transition Zones and Their Impact on Natural Attenuation

Reactive Fe mineral coatings play an important role in contaminant attenuation in redox transition zones at sites with subsurface contamination. An anaerobic 60 foot core was collected from the Chambers Works Site in Deepwater, NJ. Working in a glovebox, two-inch subsamples were used to evaluate redox transition zones using bulk composition, redox potential, pH, VOCs in the headspace, as well as abundant bacteria. A number of redox transition zones were identified and further studied with a suite of complementary analyses to characterize the surface chemistry. Analyses have included sequential extraction (phases and speciation), x-ray diffraction (mineralogy), x-ray fluorescence (composition), fieldemission scanning electron microscopy (surface morphology down to the nm scale) with energy dispersive analysis (surface composition), and bench-scale experiments. Results reveal a clear trend in reactive iron (II)/(III) mineral coatings throughout transition zones. Reactive iron mineral coatings reveal iron (II) minerals pyrite, mackinawite, pyrrhotite, and siderite in a transition zone running through an aquitard. Ferrihydrite, goethite, and lepidocrocite were dominant iron (III) minerals in a transition zone that was observed in an aquifer, while pyrite, greigite and gypsum were the most abundant mineral coating in an upper aquitard transition zone. Overall, the most significant reactive mineral coatings were observed in redox transition zones located in aquitards where there is Fe2+/Fe3+ cycling. Ongoing studies are focused on abiotic degradation pathways for halogenated solvents present in the system

Surface complexation of Pb(II) on amorphous iron oxide and manganese oxide: Spectroscopic and time studies.

Abstract Hydrous Fe and Mn oxides (HFO and HMO) are important sinks for heavy metals and Pb(II) is one of the more prevalent metal contaminants in the environment. In this work, Pb(II) sorption to HFO (Fe 2 O 3 ·nH 2 O, n = 1-3) and HMO (MnO 2 ) surfaces has been studied with EXAFS: mononuclear bidentate surface complexes were observed on FeO 6 (MnO 6 ) octahedra with Pb-O distance of 2.25-2.35 Å and Pb-Fe(Mn) distances of 3.29-3.36 (3.65-3.76) Å. These surface complexes were invariant of pH 5 and 6, ionic strength 2.8 × 10 −3 to 1.5 × 10 −2 , loading 2.03 × 10 −4 to 9.1 × 10 −3 mol Pb/g, and reaction time up to 21 months. EXAFS data at the Fe K-edge revealed that freshly precipitated HFO exhibits shortrange order; the sorbed Pb(II) ions do not substitute for Fe but may inhibit crystallization of HFO. Pb(II) sorbed to HFO through a rapid initial uptake (∼77%) followed by a slow intraparticle diffusion step (∼23%) resulting in a surface diffusivity of 2.5 × 10 −15 cm 2 /s. Results from this study suggest that mechanistic investigations provide a solid basis for successful adsorption modeling and that inclusion of intraparticle surface diffusion may lead to improved geochemical transport depiction

A theoretical study of the structural phases of Group 5B - 6B metals and their transport properties

In order to predict the stable and metastable phases of the bcc metals in the block of the Periodic Table defined by groups 5B to 6B and periods 4 to 6, as well as the structure dependence of their transport properties, we have performed full potential computations of the total energies per unit cell as a function of the c/a ratio at constant experimental volume. In all cases, a metastable body centered tetragonal (bct) phase was predicted from the calculations. The total energy differences between the calculated stable and metastable phases ranged from 0.09 eV/cell (vanadium) to 0.39 eV/cell (tungsten). The trends in resistivity as a function of structure and atomic number are discussed in terms of a model of electron transport in metals. Theoretical calculations of the electrical resistivity and other transport properties show that bct phases derived from group 5B elements are more conductive than the corresponding bcc phases, while bct phases formed from group 6B elements are less conductive than the corresponding bcc phases. Special attention is paid to the phases of tantalum where we show that the frequently observed beta phase is not a simple tetragonal distortion of bcc tantalum

Investigation of the structure of beta-Tantalum

The local structure of beta-tantalum was investigated by comparing experimental extended x-ray absorption fine structure (EXAFS) measurements with calculated spectra of proposed models. Four possible structure candidates were examined: a beta-Uranium based structure, a distorted A15 structure, a bcc-Ta based superlattice structure with N interstitials and a simple hcp structure. The local structural measurements were found to be consistent with the beta-Uranium based model containing 30 atoms per unit cell and having the space group P42/mnm. The thermal effect analysis on x-ray diffraction and EXAFS spectra, which reveals that beta-Ta is highly disordered, agrees with the low symmetry and anisotropic system of the beta-U model.Comment: 26 pages, two tables, 8 figures, submitted to Journal of Applied physic

The structure and stability of beta-Ta thin films

Ta films with tetragonal crystalline structure (beta-phase), deposited by magnetron sputtering on different substrates (steel, silicon and silicon dioxide), have been studied. In all cases, very highly preferred (001) orientation was observed in x-ray diffraction (XRD) measurements. All diffraction data revealed two weak reflections corresponding to d-spacing of 0.5272 and 0.1777 nm. The presence of the two peaks, attributed to (001) and (003) reflections, indicates that beta-Ta films exhibit a high preference for the space group of P-421m over P42/mnm, previously proposed for beta-Ta. Differences in relative intensities of (00l) reflections, calculated for single crystal beta-Ta sigma-type Frank-Kasper structure and those measured in the films, are attributed to defects in the films. Molecular dynamics simulations performed on tantalum clusters with six different initial configurations using the embedded-atom-method (EAM) potential revealed the stability of beta-Ta, which might explain its growth on many substrates under various deposition conditions.Comment: 27 pages, 6 figures,1 tabl

The class IA phosphatidylinositol 3-kinase p110-β subunit is a positive regulator of autophagy

p110-β associates with the Vps34–Vps15–Beclin 1–Atg14L complex and facilitates generation of PtdIns(3)P to promote autophagy

Antiplatelet therapy with aspirin, clopidogrel, and dipyridamole versus clopidogrel alone or aspirin and dipyridamole in patients with acute cerebral ischaemia (TARDIS): a randomised, open-label, phase 3 superiority trial

Background: Intensive antiplatelet therapy with three agents might be more effective than guideline treatment for preventing recurrent events in patients with acute cerebral ischaemia. We aimed to compare the safety and efficacy of intensive antiplatelet therapy (combined aspirin, clopidogrel, and dipyridamole) with that of guideline-based antiplatelet therapy. Methods: We did an international, prospective, randomised, open-label, blinded-endpoint trial in adult participants with ischaemic stroke or transient ischaemic attack (TIA) within 48 h of onset. Participants were assigned in a 1:1 ratio using computer randomisation to receive loading doses and then 30 days of intensive antiplatelet therapy (combined aspirin 75 mg, clopidogrel 75 mg, and dipyridamole 200 mg twice daily) or guideline-based therapy (comprising either clopidogrel alone or combined aspirin and dipyridamole). Randomisation was stratified by country and index event, and minimised with prognostic baseline factors, medication use, time to randomisation, stroke-related factors, and thrombolysis. The ordinal primary outcome was the combined incidence and severity of any recurrent stroke (ischaemic or haemorrhagic; assessed using the modified Rankin Scale) or TIA within 90 days, as assessed by central telephone follow-up with masking to treatment assignment, and analysed by intention to treat. This trial is registered with the ISRCTN registry, number ISRCTN47823388. Findings: 3096 participants (1556 in the intensive antiplatelet therapy group, 1540 in the guideline antiplatelet therapy group) were recruited from 106 hospitals in four countries between April 7, 2009, and March 18, 2016. The trial was stopped early on the recommendation of the data monitoring committee. The incidence and severity of recurrent stroke or TIA did not differ between intensive and guideline therapy (93 [6%] participants vs 105 [7%]; adjusted common odds ratio [cOR] 0·90, 95% CI 0·67–1·20, p=0·47). By contrast, intensive antiplatelet therapy was associated with more, and more severe, bleeding (adjusted cOR 2·54, 95% CI 2·05–3·16, p<0·0001). Interpretation: Among patients with recent cerebral ischaemia, intensive antiplatelet therapy did not reduce the incidence and severity of recurrent stroke or TIA, but did significantly increase the risk of major bleeding. Triple antiplatelet therapy should not be used in routine clinical practice