Spanka, Marina (2018). Minimizing the release of Chromium, Molybdenum, Vanadium, and Fluoride from Steelwork Slags. PhD thesis, Universität zu Köln.
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Abstract
Steelwork slags (SWS) are important by-products of the iron and steel manufacturing. About 87% of SWS are used in qualified fields of application: e.g., for internal use, as construction and building materials, as fertilizer or for metallurgical processes; but the remaining 13% of SWS still have to be deposited in landfills. For use as construction and building material, SWS have to fulfill stringent technical and environmental requirements, which are continuously evolving. In consequence higher amounts of SWS might have to be landfilled in the future. The overall aim of this research project was to improve the leaching behavior of environmentally relevant parameters, i.e., chromium, molybdenum, vanadium and fluoride from SWS and to enhance the knowledge about the release of these parameters from SWS, to ensure the use of SWS as a construction product. Two different approaches were investigated: accelerated carbonization of SWS (project I) and immobilization with additives (project II). In project I the influence of natural and accelerated carbonation on the leaching behavior of SWS was investigated. From the obtained results the outdoor exposed SWS show a distinct increase in Si and V leaching and a decrease of Ca leaching, with lower pH, due to carbonation. The other investigated elements (Al, Cr, Mo, and F−) react differently to carbonation depending on the mineral binding. However, the achieved results show that the German LAGA emplacement category can be improved from Z 2 (restricted appli-cations with defined safeguarding measures) to Z 1 (restricted open applications) due to carbonation. The immobilization of trace elements and fluoride with appropriate additives was investigated in project II. Seven mineral additives were tested for their efficiency to immobilize Cr, Mo, V, and F− in SWS eluates, which were obtained from four different SWS. It was possible to identify two suitable additives: iron oxide hydroxide (a commercial available product) and water work sludge (classified as waste). Both additives show a significant immobilization of the above mentioned parameters. To verify these results, long term studies with these two additives and four SWS were done under practical conditions. The relation of mineralogy and related leaching behavior, i.e., the availability of environmentally relevant elements was also investigated, which is quite lacking in the literature. This issue was investigated with a four-fraction-based sequential extraction procedure in combination with X-ray diffraction. The results showed that Cr and Mo primarily occurred in F4, representing rather immobile elements under natural conditions, which were strongly bound into/onto Fe-minerals (srebrodolskite, magnetite, hematite or wustite). In contrast, V was more mobile with proportional higher findings in F2 and F3, and the X-ray diffraction results reveal that V was not solely bound into Ca-minerals (larnite, hatrurite, kirschsteinite and calcite), but also to Fe-minerals. The results indicated that the total content of elements after digestion is a poor indicator of the availability of elements, and did not correspond to the leaching of elements from basic oxygen furnace slags.
Item Type: | Thesis (PhD thesis) | ||||||||
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URN: | urn:nbn:de:hbz:38-85836 | ||||||||
Date: | March 2018 | ||||||||
Language: | English | ||||||||
Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
Divisions: | Faculty of Mathematics and Natural Sciences > Department of Geosciences > Geographisches Institut | ||||||||
Subjects: | Natural sciences and mathematics Chemistry and allied sciences Earth sciences Geography and travel |
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Date of oral exam: | 16 May 2018 | ||||||||
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Refereed: | Yes | ||||||||
URI: | http://kups.ub.uni-koeln.de/id/eprint/8583 |
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