Estonian phosphorite ore contains trace amounts of rare earth elements (REEs), many other d-metals, and some radioactive elements. Rare earth elements, Mo, V, etc. might be economically exploitable, while some radioactive and toxic elements should be removed before any other downstream processing for environmental and nutritional safety reasons. All untreated hazardous elements remain in landfilled waste in much higher concentration than they occur naturally. To resolve this problem U, Th, and Tl were removed from phosphorite ore at first using liquid extraction. In the next step, REE were isolated from raffinate. Nitrated Aliquat 336 (A336[NO3]) and Bis(2-ethylhexyl) Phosphate (D2EHPA) were used in liquid extraction for comparison. An improved method for exclusive separation of radioactive elements and REEs from phosphorite ore in 2-steps has been developed, exploiting liquid extraction at different pH values.
Bauxite and bauxite residue, a by-product of alumina production, were studied using a combination of microanalytical techniques — electron microprobe wavelength dispersive spectrometry, laser ablation inductively coupled plasma mass spectrometry and μ-Raman spectroscopy. The aim of the work was to reveal the modes of occurrence of scandium (Sc). The motivation behind this effort was to provide mineralogical insight for the support of ongoing development of Sc extraction technologies from bauxite residue. In the analyzed bauxites and residue, Sc is mainly hosted in hematite, where Sc3+ probably substitutes Fe3+. The average concentration of Sc in the hematite matrix of bauxite is about 200 mg/kg, while in the bulk sample it ranges from 42 to 53 mg/kg Sc. In bauxite residue, the average concentration of Sc in hematite matrix is about 170 mg/kg, and in the bulk sample it is 98 mg/kg. In bauxite residue, goethite was also identified to host Sc with a concentration of about two times more than in hematite — 330 mg/kg. In bauxite residue, hematite, goethite and zircon host respectively 55 ± 20%, 25 ± 20% and 10 ± 5% of the total Sc. The effect of the Bayer process to the modes of occurrences of Sc is minor. The secondary bauxite residue minerals formed during bauxite processing do not capture any or capture very low amounts of Sc. New evidences of Sc leaching behavior from bauxite residue show that Sc is first released from goethite, then from hematite and the unrecovered proportion of Sc is likely associated with zircon.
Nanowire poly(vinylidene fluoride) (PVDF) polymer membranes activated with Ag and Zn nanoclusters were prepared using the electrospinning method. The structure of membranes was varied by using different polymer concentrations in N,N-dimethylacetamide, electric field strength, and concentration of AgNO3 and ZnCl2 in an electrospinning solution. Materials synthesised were analysed by nitrogen sorption and mercury intrusion porosimetry, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, thermogravimetry, inductively coupled plasma mass spectroscopy, particle filtration efficiency, and pressure drop methods. The concentration of Ag and Zn nanoclusters in PVDF membranes was established and the influence on nanofibers activity has been discussed. The hydrophobicity of membranes was tested using the wetting (contact) angle measurement method. The human influenza A virus (IAV) A/WSN/1933 (H1N1) strain was used to evaluate the virucidal activity of filtration materials. The virucidal activity increased with Ag nanoclusters concentration in fibres. The most hydrophilic nanofibers with Zn nanoclusters showed very high and practically concentration independent virucidal activity that was two orders of magnitude higher compared to materials activated with Ag nanoclusters.
The Zaonega Formation in northwest Russia (~2.0 billion years old) is amongst the most complete successions that record the middle of the Palaeoproterozoic era. As such, geochemical data from the formation have played a central role in framing the debate over redox dynamics in the aftermath of the Great Oxidation Event (GOE). However, uncertainty over local redox conditions and the degree of hydrographic restriction in the formation has led to contradictory interpretations regarding global oxygen (O2) fugacity. Here, we provide new iron (Fe) isotope data together with major and trace element concentrations to constrain the local physiochemical conditions. The Zaonega Formation sediments show authigenic Fe accumulation (Fe/Al ≫ 1 wt.%/wt.%) and δ56Fe ranging from −0.58‰ to +0.60‰. Many of the data fall on a negative Fe/Al versus δ56Fe trend, diagnostic of a benthic Fe shuttle, which implies that Zaonega Formation rocks formed in a redox-stratified and semi-restricted basin. However, basin restriction did not coincide with diminished trace metal enrichment, likely due to episodes of deep-water exchange with metal-rich oxygenated seawater, as evidenced by simultaneous authigenic Fe(III) precipitation. If so, the Onega Basin maintained a connection that allowed its sediments to record signals of global ocean chemistry despite significant basinal effects.
With an increasing energy demand, there is a need for renewable energy conversion devices. Among the possible options are low temperature polymer electrolyte fuel cells, in which electrocatalysts play vital roles, especially on the cathode, where the oxygen reduction reaction (ORR) occurs. The most efficient electrocatalysts for the ORR are based on noble metals, mainly platinum, which however have various disadvantages including their high price and scarcity. As a replacement, different transition metal-nitrogen-carbon (M−N−C) catalyst materials have shown great promise. 1,2 Herein, a composite of nanocarbons, namely carbide-derived carbon/carbon nanotube (CDC/CNT), is employed as a support to produce the M−N−C type of catalysts. This composite offers a novel catalyst structure in which both micro- and mesopores are present that can be beneficial for the anion exchange membrane fuel cell (AEMFC) application. The doping was done via pyrolysis at 800 °C in the presence of a cobalt salt and a nitrogen precursor (either dicyandiamide, urea or melamine). 3 The catalysts were characterized using different physico-chemical methods ( e.g. SEM, TEM, XPS, XRD, Raman spectroscopy, and N 2 adsorption), which proved the success of doping as well as the feasible micro- and mesoporous structure with defects present. Both the RDE and RRDE methods were employed for the electrochemical testing and in alkaline medium all three catalyst materials exhibited similar and good electrocatalytic activity for the ORR. The half-wave potential for ORR of Co-N-CDC/CNT catalysts was close to that of a Pt/C catalyst (Figure 1, left). The possible application of the Co-N-CDC/CNT material was tested out by employing it as a cathode catalyst in AEMFC. The Co-N-CDC/CNT catalyst together with a novel HMT-PMBI 4 membrane exhibited excellent performance with peak power density of 577 mW cm –2 , which was significantly higher than that obtained with a Pt/C cathode (Figure 1, right). This shows that the Co-N-CDC/CNT materials are promising cathode catalysts for the AEMFC application. 3 References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, J. Mater. Chem. A , 6 , 776-804 (2018). G. Wu, A. Santandreu, W. Kellogg, S. Gupta, O. Ogoke, H. Zhang, H. L. Wang, and L. Dai, Nano Energy, 29 , 83−110 (2016). J. Lilloja, E. Kibena-Põldsepp, A. Sarapuu, M. Kodali, Y. Chen, T. Asset, M. Käärik, M. Merisalu, P. Paiste, J. Aruväli, A. Treshchalov, M. Rähn, J. Leis, V. Sammelselg, S. Holdcroft, P. Atanassov, and K. Tammeveski, ACS Appl. Energy Mater ., 2020, (DOI: 10.1021/acsaem.0c00381) A. G. Wright, J. T. Fan, B. Britton, T. Weissbach, H. F. Lee, E. A. Kitching, T. J. Peckham, and S. Holdcroft, Energy Environ. Sci. , 9 , 2130-2142 (2016). Figure 1
Preparation of electrocatalysts often relies on the use of multiple starting materials – inorganic salts or organometallic precursors, nanostructured carbon supports, organic additives, dopants and carbonization under modifying atmospheres (e.g. NH 3 or H 2 ) – with the examples of electrocatalysts arising from a single precursor being much less common. Herein, we have surveyed a series of heterobivalent scaffolds to identify an iron/benzimidazole-based metal– organic framework as a uniform starting material. By merging the catechol and imidazole units together, we get direct entry into a highly efficient bifunctional oxygen electrocatalyst, which alleviates the need for additional dopants and modifying conditions (ORR: E on = 1.01 V, E 1/2 = 0.87 V vs. RHE in 0.1 M KOH; OER: 1.60 V @10 mA cm –2 in 0.1 M KOH; ∆ E = 0.73 V). We demonstrate that by fine-tuning the chemical nature of an organic linker, one is able modulate the electrochemical properties of a single precursor-derived electrocatalyst material.
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