1,721,022 research outputs found
An innovative method for highly-efficient fabrication of carbon fiber precursors via acrylonitrile emulsion copolymerization coupled to a chemical oscillator
No full textA new synthetic protocol to produce the carbon fiber precursor polyacrylonitrile (PAN) and its block copolymers with polyethylene glycol (PEG) is proposed here. The constant flux of radical species produced at low concentrations during the oscillating Belousov-Zhabotinsky (BZ) reaction was properly exploited to initiate the radical polymerization reaction. Compared with conventional methods, this oscillating initiation decreases the probability of chain termination, thus favouring the production of high molecular weight polymers, and it does not require an inert atmosphere and elevated temperatures to be produced. The solubility of the polymeric chains during the polymerization reaction was improved by adding the anionic micelle-forming surfactant sodium dodecyl sulphate (SDS). Following the initiation step, short oligomer chains are able to overcome the micellar interface, thereby reaching a favourable environment for the increase of the polymeric chains, thus strongly contributing to the increase of the molecular weight of the fibers' precursors. The synthesis was conducted by adding the monomer acrylonitrile (AN) to the unperturbed and PEG-perturbed BZ system after the onset of the oscillations, in the absence and presence of increasing amounts of the SDS surfactant. The potentiometric technique was utilized to detect the dynamics of the oscillatory reaction. Preliminarily, the response of the BZ system to the monomer addition was investigated. Additional information was provided from the study of the effect of the SDS and PEG concentration on the dynamics of the BZ reaction during AN polymerization, thus obtaining a deepening in the understanding of the BZ mechanism. The characterization of the obtained polymers and copolymers, by melting point measurements, molecular weight determinations, Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) analyses, and thermal treatments, indicated that the proposed synthetic method produces carbon fiber precursors with high molecular weight and good thermal stability. The addition of the surfactant was revealed as a good method to improve and/or finely tune the precursor molecular weight. The proposed synthetic protocol represents a valuable alternative to conventional methods to produce highperformant precursors of carbon fibers
Maturation stages of glauconites: A combined electron microprobe, Raman, and thermogravimetric study
Full text linkGlauconite mineral is one of the most sensitive indicators of low sedimentation rate in the marine environment.
The time of residence of glauconites at the sea bottom before burial is reflected by their so-called maturity that is
differentiated based on their K2O content.
The present work aims to investigate the evolution of glauconites during the transition toward the highly
evolved level. Complementary electron microprobe, Raman, and Thermogravimetric analysis were performed on
glauconitic grains from the Belluno basin (N Italy) with different K2O content in order to verify whether the level
of glauconites evolution affects the results of these surveys
Synthetic and natural chromium-bearing spinels: An optical spectroscopy study
No full textFour samples of synthetic chromium-bearing spinels of (Mg, Fe2+)(Cr, Fe3+)2O4composition and four samples of natural spinels of predominantly (Mg, Fe2+)(Al, Cr)2O4composition were studied at ambient conditions by means of optical absorption spectroscopy. Synthetic end-member MgCr2O4spinel was also studied at pressures up to ca. 10 GPa. In both synthetic and natural samples, chromium is present predominantly as octahedral Cr3+seen in the spectra as two broad intense absorption bands in the visible range caused by the electronic spin-allowed4A2g→4T2gand4A2g→4T1gtransitions (U- and Y-band, respectively). A distinct doublet structure of the Y-band in both synthetic and natural spinels is related to trigonal distortion of the octahedral site in the spinel structure. A small, if any, splitting of the U-band can only be resolved at curve-fitting analysis. In all synthetic high-chromium spinels, a couple of relatively narrow and weak bands of the spin-allowed transitions4A2g→2Egand4A2g→2T1gof Cr3+, intensified by exchange-coupled interaction between Cr3+and Fe3+at neighboring octahedral sites of the structure, appear at ~14,400 and ~15,100 cm-1. A vague broad band in the range from ca. 15,000 to 12,000 cm-1in synthetic spinels is tentatively attributed toIVCr2++VICr3+→IVCr3++VICr2+intervalence charge-transfer transition. Iron, mainly as octahedral Fe3+, causes intense high-energy absorption edge in near UV-range (ligand-metal charge-transfer O2-→ Fe3+, Fe2+transitions). As tetrahedral Fe2+, it appears as a strong infrared absorption band at around 4,850 cm-1caused by electronic spin-allowed5E →5T2transitions ofIVFe2+. From the composition shift of the U-band in natural and synthetic MgCr2O4spinels, the coefficient of local structural relaxation around Cr3+in spinel MgAl2O4-MgCr2O4system was evaluated as ~0.56(4), one of the lowest among (Al, Cr)O6polyhedra known so far. The octahedral modulus of Cr3+in MgCr2O4, derived from pressure-induced shift of the U-band of Cr3+, is ~313 (50) GPa, which is nearly the same as in natural low-chromium Mg, Al-spinel reported by Langer et al. (1997). Calculated from the results of the curve-fitting analysis, the Racah parameter B of Cr3+in natural and synthetic MgCr2O4spinels indicates that Cr-O-bonding in octahedral sites of MgCr2O4has more covalent character than in the diluted natural samples. Within the uncertainty of determination in synthetic MgAl2O4spinel, B does not much depend on pressure. © 2014 Springer-Verlag Berlin Heidelberg
Detrital Cr-spinel in the Sambron-Kamenica Zone (Slovakia): evidences for an ocean spreading zone in the Northern Vardar suture?
No full textThe Sambron–Kamenica Zone is situated on the northern margin of the Levocske vrchy mountains and Sarisska vrchovina Highland, where the Central Carpathian Paleogene joins the Pieniny Klippen Belt. Sandstone outcrops in this area. From Cretaceous to Late Oligocene in age, these sediments suggest transport directions from Sand SE. The heavy mineral assemblages of this sandstone include Cr-spinel grains, mainly displaying types II and III alpine-peridotite affinities, and are representative of Ocean Island Basalt volcanism. A sample from Upper Eocene sediments at Vitaz shows a clear change in Cr-spinel composition, which turns out to have types I and II peridotite affinities, and to derive from arc and Middle Ocean Ridge Basalt volcanism, with sediment transport directions from SW and WSW. These data indicate major variations in the Upper Eocene tectonic setting, giving constraints to paleogeographic reconstruction of the Slovak Central Carpathians
The clays involved in the 1963 Vajont landslide: Genesis and geomechanical implications
Full text linkThe catastrophic Vajont landslide that occurred on 9 October 1963 caused about 2000 deaths when 270–300 Mm3 of rock and debris slid from the northern slope of Mt. Toc into the newly created artificial reservoir, displacing some huge water waves that flooded the nearby villages. The 1963 slide was an en-block remobilisation of a prehistoric rockslide lying on the southern reservoir bank. Basal sliding took place within a complex lithostratigraphic sequence of cherty–marly limestones and clay interbeds belonging to the Fonzaso Formation of Upper Jurassic age. In this work, we investigate the geological origin and provenance of the Vajont clays according to the results of mineralogical and geochemical analyses performed on several clay samples which were collected from the landslide failure surface and the same limestone sequence in the surrounding area. The sampled clayey materials contained variable amounts of clay minerals (36–96%), calcite (4–64%) and quartz (0–6%). The dominant clay minerals were illite/smectite (I/S) mixed layers with a high illite content (85–50%), which was consistent with the high percentage of K2O (1.17–5.77%). The Vajont clays included in the Fonzaso Fm. can be referred to as K-bentonites and can be interpreted as distinct deposits of volcanoclastic materials (tephra), representing the sedimentary inputs of volcanic ashes that interrupted the “normal” calcareous sedimentation during the late Oxfordian–upper Tithonian (158–145 Ma). The soft clay interbeds played a different mechanical role in the occurrence of the prehistoric rockslide and the 1963 en-block remobilisation. When referring to the ancient slope failures, distinct clay-rich layers that were concentrated within some specific lithostratigraphic intervals of the Jurassic cherty limestone sequence caused a localised decrease in the available shear strength, allowing for relative shear displacements along the dip-slope bedding planes. This caused additional shear/tensile fracturing of limestone beds and the formation of a stepped basal failure surface. During the 1963 remobilisation, the clay layers contributed to the average shear strength decrease of the debris material forming the basal shear zone of the slide, but the main triggering factor was the increase in pore pressures caused by the reservoir-induced groundwater inflow
The Österplana Fossil Meteorites and... What Else? Terrestrial Cr-Spinels and Zircons in the Ordovician Limestones of the Thorsberg Quarry (Sweden)
No full textIn the Ordovician limestone of the Thorsberg quarry (South Sweden), about 130 meteorites have been found. Among the extraterrestrial material, several terrestrial Cr-spinels and zircons have been found too. In particular, in the interval 416–447 cm above the Arkeologen bed, terrestrial Cr-spinels, compositionally different from previous studied Cr-spinels of the same sequence, are present. Previous studies on zircon provided depositional ages that range from 464.22 ± 0.37 Ma to 465.01 ± 0.26 Ma. The trace element content of zircons suggests different possible source rocks. In fact, zircons from the oldest ash layer resemble those from dolerite, while those in the youngest layers are similar to zircons commonly found in granitoids, with more than 65% wt. SiO2 . The chemistry of Cr-spinels suggests a strong alteration, so that it is difficult to assign them to a specific area, however they recall the chemistry of altered spinels from ophiolitic occurrences (among other possibilities). The geological setting of the Laurentia and Baltica areas, including the description of basalts to rhyolite association and the presence of ophiolitic slices, makes us confident about the derivation of these zircons and Cr-spinels from those areas
Environmental concerns and future perspectives related to the legacy of metal(loid) contamination in the vicinity of a dismissed Pb-Zn mining area (Raibl, NE Italy)
No full textThe occurrence of relevant amounts of potential toxic elements (PTEs) in the environment as a legacy of past extraction and metallurgical activities at decommissioned mining areas represents a worldwide concern, potentially posing a threat to ecosystems and human health. This aspect is strongly dependent on the mobility and bioavailability of PTEs once released in the environment (Favas et al., 2011). However, in addition to being sources of contamination, mine waste such as tailings ponds can potentially be a resource since they may still host notable amounts of various elements of economic interest such as those included in European Union’s list of Critical Raw Materials (CRMs) (Rosario-Beltré et al., 2023).
This study is focused on the assessment of metal(loid) distribution and environmental impact related to past extraction activities on the soils at the Pb-Zn Raibl mining district (NE Italy), which ended in 1991. Concentrations of several PTEs (As, Cd, Fe, Pb, Tl, Zn) and CRMs (As, Ge, Mn, Sb) were determined on sub-surface samples of various solid matrices (soils, waste rocks, tailings) collected throughout the mining district. A single-step extraction with 0.5 M HCl solution was used to evaluate the labile fraction of PTEs, potentially more mobile and bioavailable in the environment.
As expected, mine waste heaps, consisting of waste rocks and flotation tailings stored in tailings impoundments and scattered within the mining district, showed high concentrations of metal(loid)s (≤ 100 mg/kg for Sb, Cd and Ge; > 500 mg/kg for Tl and Mn; > 1,000 mg/kg for As; > 1 wt% for Zn; > 10 wt% for Fe and Zn). Notably low concentrations were found in samples collected upstream the former mine, which are considered representative of the natural background of the study area. Overall, the leachable metal(loid)s concentrations are well correlated with the total content, with the highest PTEs (i.e. Zn, Pb, Fe, Cd) values generally observed in unprocessed waste rock samples. The only exception is represented by Tl which showed the highest labile concentration in tailings (up to 255 mg/kg), confirming their potential impact on local water resources (Barago et al., 2023). However, the highest percentages of the metal(loid)s leachable fraction were generally found for soils with a greater organic matter (OM) content, due to the lower pH and the potential formation of soluble organometallic complexes during soil ageing. Considering that remediation of the en-tire area is not feasible due to the extension of the contamination, this potential in-creased in the mobility of PTEs as soil ages should be considered when evaluating appropriate management strategies aimed at limiting PTEs dispersion and impact on local ecosystems. These strategies may also include the reprocessing of mine wastes accumulated in tailings ponds, which could both reduce the risk to water resources and human health and to recover critical or strategic elements such as As or Ge. Fur-ther research is still ongoing with the aim of broadening knowledge on the residual content in CRMs and PTEs buried in tailings ponds and providing data to assess the feasibility of this approach.
REFERENCES
Barago, N., Pavoni, E., Floreani, F., Crosera, M., Adami, G., Lenaz, D., and Covelli, S., 2023. Hydrogeo-chemistry of thallium and other potentially toxic elements in neutral mine drainage at the decom-missioned Pb-Zn Raibl mine (Eastern Alps, Italy). Journal of Geochemical Exploration, 245, 107129.
Favas, P.J.C., Pratas, J., Gomes, M.E.P., and Cala, V., 2011. Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: environmental implications. Journal of Geo-chemical Exploration, 111, 160-171.
Rosario-Beltré, A.J., Sánchez-España, J., Rodríguez-Gómez, V., Fernández-Naranjo, F.J., Bellido-Martín, E., Adánez-Sanjuán, P., and Arranz-González J.C., 2023. Critical raw materials recovery potential from Spanish mine wastes: a national-scale preliminary assessment. Journal of Cleaner Production, 407, 137163
Effects of groundwater and tailings interaction on the mobility of Thallium and other potentially toxic elements in a decommissioned Pb-Zn mining site (Raibl mine, north-eastern Italian Alps)
No full textMining activity at the Raibl district (northeastern Italian Alps) date back to 1320, reaching the peak production in the 20th century. Nearly 350,000 tons of lead-zinc (Pb- Zn) ore, primarily sphalerite (ZnS) and galena (PbS), were annually extracted during the last years of operation until the mine closure in 1991. The ore deposit also includes iron (Fe) sulfides (pyrite and marcasite), baryte, and secondary minerals such as Fe oxy-hydroxides, smithsonite, hydrozincite, and cerussite, with dolomite and calcite as gangue minerals.
Between 1976 and 1991, nearly 4 million tons of mine tailings, byproducts of the milling and flotation processes employed to extract the elements of economic interest, were accumulated in tailings ponds located nearby the Rio del Lago stream, the main watercourse in the area. These tailings are highly enriched in Zn, Pb, and Fe, as well as PTEs, including Thallium (Tl), and represent a secondary source of Tl and other PTEs in surface and groundwater, especially under conditions of heavy rainfall and high river flow (Barago et al., 2023). Moreover, the carbonate host rocks provide a buffering effect, leading to neutral mine drainage (NMD), despite ongoing sulphide oxidation.
Currently, the site is undergoing remediation, as concentrations of PTEs in surface and groundwater often exceed national regulatory limits. Specifically, Tl concentrations persist at levels one order of magnitude above the threshold limit (>2 μg L−1) downstream the mining district.
This study aims at assessing the interactions between groundwater and tailings accumulated in the impoundments which promotes the release of Tl and other PTEs in the dissolved phase. Boreholes were recently drilled in the tailings ponds, followed by on-site analyses using portable X-ray fluorescence spectroscopy (pXRF), a key geochemical technique for multi-elemental screening in contaminated sites (Barago et al., 2022). Subsequent sub-sampling of representative tailings levels allowed for a detailed characterisation of the material in the laboratory through inductively coupled plasma atomic emission and mass spectrometry (ICP-AES, ICP-MS). As expected, results con-firmed elevated concentrations of Zn (1.21 – 7.99 wt%), Pb (0.29 – 1.76 wt%), Fe (2.15 –14.2 wt%), As (505 – 2964 μg g-1), and Tl (65.8 – 677 μg g-1).
Based on this characterisation, tailings samples with high Tl concentrations (rang-ing from 185 and 677 μg g-1) were selected for further extraction and leaching tests to evaluate the geochemical behaviour of Tl and other PTEs as well as the processes con-trolling their release in solution. Gaining insights into these mechanisms is crucial for assessing the environmental impact of Tl contamination and developing effective strategies to mitigate its mobility, contributing to the protection of surrounding eco-systems and water resources.
ACKNOWLEDGEMENTS
The authors want to thank Claudio Ellero for his help during field and laboratory activities.
REFERENCES
Barago, N., Pavoni, E., Floreani, F., Crosera, M., Adami, G., Lenaz, D., Larese Filon, F., and Covelli, S., 2022. Portable X-ray Fluorescence (pXRF) as a Tool for Environmental Characterisation and Man-agement of Mining Wastes: Benefits and Limits. Applied Sciences, v.12, 12189.
Barago, N., Pavoni, E., Floreani, F., Crosera, M., Adami, G., Lenaz, D., and Covelli, S., 2023. Hydrogeo-chemistry of thallium and other potentially toxic elements in neutral mine drainage at the decom-missioned Pb-Zn Raibl mine (Eastern Alps, Italy). Journal of Geochemical Exploration, v.245, 107129
- …
