Magnetic fraction of the atmospheric dust in Kraków – physicochemical characteristics and possible environmental impact
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Abstract. It is well established that airborne, magnetic nano- and microparticles accumulate in human organs (e.g. brain) thereby increasing the risk of various diseases (e.g. cancer, neurodegenerative diseases). Therefore, precise characterization of the material, including its origins, is a key factor in preventing further, uncontrolled emission and circulation. The magnetic fraction of atmospheric dust was collected in Kraków using a static sampler and analysed using several methods (scanning electron microscopy with energy-dispersive spectrometry, transmission electron microscopy with energy-dispersive spectrometry, X-ray diffraction, Mössbauer spectroscopy, and vibrating sample magnetometry (VSM) measurements). The magnetic fraction contains magnetite, hematite and α-Fe, as well as quartz, feldspar and pyroxene often attached to the magnetic particles. The magnetic particles vary in size, from over 20 µm to nanoparticles below 100 nm, as well as in morphology (irregular or spherical). Their chemical composition is dominated by Fe, often with Mn, Zn, Cr, Cu, Si, Al, S, Ca and other elements. Mössbauer spectroscopy corroborates the composition of the material, giving further indications of particles smaller than 100 nm present in the atmospheric dust. VSM measurements confirm that the strength of the magnetic signal can be treated as a measure of the anthropogenic impact on the suspended particulate matter, once again highlighting the presence of nanoparticles.Keywords:
Fraction (chemistry)
Artificial meteor ablation was performed on natural minerals composed predominately of magnetite and hematite by using an arc-heated plasma stream of air. Analysis indicates that most of the ablated debris was composed of two or more minerals. Wustite, a metastable mineral, was found to occur as a common product. The ‘magnetite’ sample, which was 80% magnetite, 14% hematite, 4% apatite, and 2% quartz, yielded ablated products consisting of more than 12 different minerals. Magnetite occurred in 91% of the specimens examined, hematite in 16%, and wustite in 39%. The ‘hematite’ sample, which was 96% hematite and 3% quartz, yielded ablated products consisting of more than 13 different minerals. Hematite occurred in 47% of the specimens examined, magnetite in 60%, and wustite in 28%. The more volatile elements (Si, P, and Cl) were depleted by about 50%. Also the relative abundance of Fe increased as a result of both volatile depletion (loss of Si, P, Cl, and Ca) and reduction in its oxidation state. Hematite was converted to magnetite in the ablation zone along the front face of the sample. Also quartz and apatite minerals reacted with the iron oxide melt to form an Fe-rich glass consisting of varying amounts of Si, P, Cl, and Ca, depending on the accessory minerals available at the time of melting. These glass phases occurred as unusual myrmekiticlike intergrowths, which are unique textural indicators of the environment through which the material has survived. The chemistry and mineralogy of these phases remain the only trace of the original minerals. This study has shown that artificially created ablation products from iron oxides exibit unique properties that can be used for identification. These properties are morphologic characteristics, textural parameters, and the existence of metastable minerals and depend on the composition of the original material and the environmental conditions of formation.
Wüstite
Banded iron formation
Mineral redox buffer
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The article presents in detail the geochemical and mineralogical characteristics of magnetic particles formed during energetic combustion of hard coal and lignite. The aim of the research was to assess their suitability as a source of possible raw materials necessary for the development of new technologies. Both hard coal and lignite fly ash, as well as the magnetic fractions separated from them, have been tested using various analytical methods. The chemical composition, phase composition, the size, and morphology of magnetically susceptible particles were determined. The main phases identified in the magnetic fraction are magnetite, hematite, and multicomponent phases, often trapped in aluminosilicate or calcium-aluminosilicate basic glass. In order to compare the chemical composition of the magnetic fractions and raw ashes, EF was calculated - the enrichment factor of the component in the magnetic fraction in relation to ash. Among the elements that have been enriched, apart from Fe, the following should be mentioned: Mg, Mn, Co, Nd, Cu, Ni, and Au. Only the concentrations of Cu and Ni in the magnetic fraction of lignite are much higher than the Clarke value (average concentration in ash), therefore the recovery of these raw materials can only be profitable from this ash. Research confirmed that when choosing the waste for the separation of metal concentrates, the content of the raw material in the ash is not always the most important, but also the form of its occurrence.
Fraction (chemistry)
Magnetic separation
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The characterization of magnetic minerals in rocks often uses methods that measure induced magnetization. When rocks, sediments or soils contain two magnetic phases, in which one has a high saturation magnetization (MS), for example magnetite, and the other a low MS, for example hematite, the induced magnetization will be dominated by the stronger phase. An earlier study by Frank and Nowaczyk has shown that even when magnetite makes up <10 wt per cent of the ferromagnetic content, it will mask hematite. This makes identification of phases with low MS difficult to identify. We conduct a systematic study of synthetic mixtures of single domain magnetite and hematite with a broad spectrum of particle size, using hysteresis properties, acquisition of isothermal remanent magnetization (IRM) and first-order reversal curve distributions (FORC). Hysteresis parameters and FORC distributions do not vary significantly from the pure magnetite sample for hematite concentrations ≤90 wt per cent. IRM is not saturated for hematite concentration of 30 wt per cent or higher. Principle component analysis (PCA) of the processed FORCs, detects the presence of hematite for concentrations 70 wt per cent at the very least. Our results illustrate the difficulty in identifying hematite when it is found together with magnetite. IRM acquisition is the most sensitive method for identifying hematite when it occurs together with magnetite.
Saturation (graph theory)
Hysteresis
Single domain
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Mullite
Magnetic separation
Ferrimagnetism
Maghemite
Magnetic mineralogy
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The transformation of magnetite to hematite is described and analyzed in three natural samples of banded iron formation, from Quadrilátero Ferrífero, Brazil. In each sample, a particular microstructure related to the transformation process is described. In the first, magnetite crystals are large and euhedral, and they display the beginning of the transformation into hematite. In the second sample, a relict crystal of magnetite was found and the fabric of the transformed hematite was evaluated. In the last sample, the foliation was the main observed structure and the correlations of magnetite and hematite lattices were measured. All the microstructures were analyzed in a scanning electron microscope equipped with a detector for electron backscatter diffraction allowing the complete analysis of crystallographic orientations of hematite and magnetite on a local scale. The results show that the orientations of the basal planes of hematite coincide with the orientations of the octahedral planes of magnetite, indicating that the hematite crystals are a direct product from the magnetite transformation.
Texture (cosmology)
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Citations (40)