Characterization of magnetic particulates in urban and industrial dusts

Abstract

Morphology and mineralogy and magnetic parameters were analysed in atmospheric dust samples collected in 7 cities of Upper Silesia region (South Poland). The study was carried on by means of EDS spectroscopy, SEM technique, X-ray diffraction and Mössbauer spectroscopy. Special attention was paid to the magnetic fraction of studied dusts that is a potential carrier trace elements emitted to the environment. To assess the total content of magnetic fraction in bulk dust samples, mass specific magnetic susceptibility (χ) was measured using a MS2B "Bartington" sensor, then a physical separation of magnetic particles (mostly of technogenic origin) was conducted. The dusts revealed high diversity of χ value, which depended both on the sampling site and the prevailing direction of winds during the period of dust deposition on filters. In the case of atmospheric dusts, the χ value ranged from 10×10-8m3kg-1 to 1577×10 -8m3kg-1. The highest values were detected in samples collected within the range of metallurgical dust emission. The morphological and mineralogical analyses showed that among the technogenic magnetic fraction ferrimagnetic spherules built of iron oxides from magnetite-maghemite series with admixtures of wustite, hematite, goethite and non-stoichiometric Fe-Zn oxides were the predominant structures. Significant differences in magnetic mineralogy of dusts coming from different branches of industry were observed. Magnetic fraction produced by the metallurgy and coke industry were mostly in forms of tightly compacted aggregates with well-formed crystal structure whereas in fly ashes from coal combustion spherical forms (typical ferromagnetic spherules) were mostly observed. Here the predominant magnetic minerals are: magnetite, maghemite, magnesioferrite and hematite that occurred among the silicates, aluminosilicates and amorphic phases. In coke and metallurgical dust distinctive mineral forms are metallic iron (α Fe) and iron sulphides. © 2010 WIT Press.