Environmental context Toxicity and mobility of antimony and arsenic in aqueous systems are largely determined by their speciation and redox chemistry. In a highly contaminated freshwater system, one antimony species (dissolved SbV) dominated, while dissolved arsenic was more responsive to environmental conditions. Arsenic (as AsV) increased significantly during a drought period; this increase in As mobility presents a threat for first flush events and water contamination in a changing climate. Abstract Aqueous and solid-state antimony (Sb) and arsenic (As) speciation is assessed in an Australian freshwater system contaminated by mining of primary sulfide minerals. The study aims to understand metalloid transformation and mobilisation in the system, and coincides with a severe drought providing the opportunity to examine the influence of extreme low-flow conditions. X-ray absorption spectra identified only SbV in <2 mm sediments, despite boulder size stibnite evident in the creek. Roméite-group minerals were detected by X-ray diffraction in oxidation rims of creek-bed stibnite, which potentially limit the contribution of dissolved SbIII to the waterway. Arsenic in <2 mm sediments was dominated by AsV (17–91 %) and orpiment (16–93 %), while the co-occurrence of AsIII (11–36 %) with orpiment suggests that primary As minerals are an important ongoing source of AsIII to the system. Dissolved metalloids (<45 µm filtered) dominated total water column concentrations and comprised mainly pentavalent species. Arsenic(III) was however identified in most water samples (up to 6.6 µg L−1), while dissolved SbIII was only detected in one sample (3.4 µg L−1) collected during the drought period. Dissolved AsV increased significantly in samples collected in low-flow conditions, considered a result of reductive dissolution of sediment Fe-oxyhydroxide host phases, but a similar increase in dissolved Sb was not observed. This study highlights a greater risk from As in this system, and the likelihood of increased As mobility under the warmer and drier environmental conditions predicted with climate change, especially during first-flush events.
Reticulocyte counting was assessed on the Coulter STKS-2A automated blood cell counter. Using a two step procedure, blood samples were first incubated with the supravital stain new methylene blue. An acidic reagent was then added to clear the haemoglobin and any stained RNA was preserved within the cell. The cells were then analysed by measurement of volume, conductivity and light scatter (VCS). The results of 123 samples analysed on the STKS-2A were compared with those from a Toa Sysmex R-1000 reticulocyte counter. One hundred and seven samples gave no review flags and reticulocyte counts ranging from 0.5% to 22.8%, resulting in a correlation coefficient of 0.93 for the methods. Between run imprecision studies gave CVs ranging from 5.3% for a reticulocyte count of 8.7% to a CV of 16.3% for a 0.34% count. Stability studies showed insignificant changes over 72 h storage. These findings confirm that VCS technology can be adapted to provide precise and accurate routine reticulocyte analysis.
Carbon mineralization, the sequestration of carbon within minerals, presents one method through which we could control rising levels of anthropogenic carbon dioxide (CO2) emissions. The mineral wastes produced by some ultramafic-hosted mines have the ability to sequester atmospheric CO2 via passive carbonation reactions. Carbon accounting in mine tailings is typically performed using laboratory-based quantitative X-ray diffraction (XRD) or thermogravimetric methods, which are used to measure the abundances of carbonate-bearing minerals such as hydromagnesite [Mg5(CO3)4(OH)2⋅4H2O] and pyroaurite [Mg6Fe23+(CO3)(OH)16⋅4H2O]. The recent development of portable XRD instruments now allows for the characterization and quantification of minerals in the field. Here we assess the feasibility of using a portable XRD instrument for field-based carbon accounting in tailings from the Woodsreef Chrysotile Mine, New South Wales, Australia. Modal mineralogy was obtained by Rietveld refinements of data collected with an inXitu Terra portable XRD. The Partial Or No Known Crystal Structures (PONKCS) method was used to account for turbostratic stacking disorder in serpentine minerals, which are the dominant phases in tailings from Woodsreef. Weighed mixtures of synthetic tailings were made to evaluate the precision and accuracy of quantitative phase analysis using the portable instrument. An average absolute deviation (bias) of 8.2 wt% from the actual composition of the synthetic tailings was found using the portable instrument. This is comparable to the bias obtained using a laboratory-based diffractometer (9.6 wt% absolute) and to the results from previous quantitative XRD studies involving serpentine minerals. The methodology developed using the synthetic tailings was then applied to natural tailings samples from Woodsreef. Surface crusts forming on the tailings pile were found to contain hydromagnesite (~5.8 wt%) and pyroaurite (~2.1 wt%). Comparable results were obtained using the laboratory-based instrument and these results are expected to have similar biases to the analyses of the synthetic tailings. These findings demonstrate that portable XRD instruments may be used for field-based measurement of carbon sequestration in minerals in engineered and natural environments.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRapid method for determination of nitrate in plant and soil extractsRichie H. Lowe and J. L. HamiltonCite this: J. Agric. Food Chem. 1967, 15, 2, 359–361Publication Date (Print):March 1, 1967Publication History Published online1 May 2002Published inissue 1 March 1967https://pubs.acs.org/doi/10.1021/jf60150a002https://doi.org/10.1021/jf60150a002research-articleACS PublicationsRequest reuse permissionsArticle Views679Altmetric-Citations72LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
This study describes the capabilities and limitations of carrying out total scattering experiments on the Powder Diffraction (PD) beamline at the Australian Synchrotron, ANSTO. A maximum instrument momentum transfer of 19 Å −1 can be achieved if the data are collected at 21 keV. The results detail how the pair distribution function (PDF) is affected by Q max , absorption and counting time duration at the PD beamline, and refined structural parameters exemplify how the PDF is affected by these parameters. There are considerations when performing total scattering experiments at the PD beamline, including (1) samples need to be stable during data collection, (2) highly absorbing samples with a μ R > 1 always require dilution and (3) only correlation length differences >0.35 Å may be resolved. A case study comparing the PDF atom–atom correlation lengths with EXAFS-derived radial distances of Ni and Pt nanocrystals is also presented, which shows good agreement between the two techniques. The results here can be used as a guide for researchers considering total scattering experiments at the PD beamline or similarly setup beamlines.
Vanadium (V) is a redox-sensitive trace metal that typically exists in one of three oxidation states (+3, +4 and +5) in natural waters; a feature increasingly used in paleoredox studies of ancient marine sediments. However, our knowledge of V geochemistry in low-oxygen marine environments is still limited, especially regarding interactions of V with reduced iron minerals such as green rust. Carbonate green rusts (GRCO3) are mixed FeII/FeIII-phases found in some modern ferruginous settings, such as Lake Matano (Indonesia), and were likely abundant in ancient ferruginous marine systems where they may have played an essential role in authigenic V enrichments in sediments. Here, we present an abiotic pathway of V removal from seawater via reduction and adsorption onto amorphous GRCO3. Suspensions of the freshly precipitated GRCO3 (1 g L−1) were added to vanadate (1 mg VV L−1 initial concentration) in anoxic synthetic seawater solutions. Vanadium removal by GRCO3 was rapid and efficient, with 92–99% of V removed in under 20 seconds. Synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy showed that VV adsorbed by GRCO3 was partially reduced to a mixture of VV and VIV, with the average oxidation state of adsorbed V increasing (+4.3 to +4.7) with increasing solution pH (7.5 to 8.5). Extended X-ray absorption fine structure (EXAFS) modelling indicated that V may have formed a combination of monodentate and bidentate corner-sharing surface complexes with GRCO3. Upon subsequent exposure to aerated seawater, V-bearing GRCO3 oxidized to lepidocrocite [γ–FeO(OH)] within 24 hours, with concomitant reduction of all solid-phase VV to VIV. During oxidation, V was not released back into solution; rather, EXAFS modelling indicated that VIV was incorporated into the lepidocrocite structure as octahedral vanadyl (VO2+). Our work further constrains the aqueous geochemistry of V, which has implications for understanding V cycling and removal mechanisms in both modern and ancient marine systems.
Understanding the nature of the reactive sites of CO2 reduction catalysts is crucial to developing efficient and selective materials to help mitigate the greenhouse effect. In this research, materials based on cobalt phthalocyanine supported by carbon black and pyrolyzed at various temperatures under argon are fabricated and tested for CO2 electroreduction. The results show that the high reactivity of the catalysts for the electroreduction of CO2 to CO is maintained for materials prepared at temperatures up to 700 °C, with CO Faradaic efficiencies of >85% and CO current densities consistently at >40 mA cm–2 at −0.86 V vs RHE. The materials annealed up to 900 °C are also remarkably active, with CO Faradaic efficiencies of >40% and CO current densities of >12 mA cm–2. The combination of X-ray diffraction, infrared and Raman spectroscopies, and X-ray absorption analysis show that the annealed materials exhibit chemical structures drastically different from those of the original CoPC and unsupported pyrolyzed catalyst while highlighting the role of the carbon black support in the formation of active species. These results give crucial insight into the reactive structure of CoPC and open the way for the development of pyrolyzed Co-N4 macrocycles as a new class of materials efficient for the electroreduction of CO2.
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