Technogenic magnetic particles from steel metallurgy and iron mining in topsoil: Indicative characteristic by...

Technogenic magnetic particles (TMPs), produced during various industrial processes, are released into the atmosphere as dust and get deposited on the surrounding topsoil. The mineralogical and structural differences of TMPs produced in different technological processes should be reflected in their magnetic properties and therefore should be indicative for industrial pollution sources. The goal of this study was to characterize the TMPs by novel methodological approach, based on combination of magnetic methods and Mössbauer spectroscopy to indicate parameters that are discriminative enough to be used as environmental indicators for iron metallurgy, steel production, and iron mining. We collected the topsoil samples in the vicinity of 4 European iron- and steelworks, located in three different countries (Poland, Norway, and Czech Republic) and operating for minimum 40 years. We sampled also topsoil close to the opencast iron mine, iron ore dressing plant, and over strongly magnetic natural background. Analysis of the hyperfine parameters of the Mössbauer spectra revealed that TMPs are "magnetite-like" minerals with low stoichiometry. It is indicated by ratio of iron ions contributions in B sites (octahedral) and A sites (tetrahedral) in magnetite spinel structure, which is much lower than 2.0 (theoretical value for stoichiometric magnetite). The characteristic feature of TMPs collected from the vicinity of old metallurgical plants (>180 years) was the high contribution of surface components probably related to the surface oxidation/maghemitization. We found that, TMPs can be easily differentiated from geogenic magnetite based on their magnetic parameters. The TMP produced by the iron and steel metallurgy had relatively narrow ranges of magnetic parameters (saturation ratio Mrs/Ms, <0.15, coercivity ratio Bcr/Bc 2.5-6.0 and saturation to susceptibility ratio Mrs/χ 3.5-15). These magnetic parameters may be indicative for TMPs emitted by these pollution sources and helpful in the study of historical pollution sources in topsoil in urban and post-industrial areas.