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The influence of iron oxide on the chromium leachability of EAF slag: a full-scale study at Ovako Hofors
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.ORCID iD: 0000-0001-9297-8521
Ovako Hofors.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
2012 (English)In: Scanmet IV: 4th International Conference on Process Development in Iron and Steelmaking, Luleå: MEFOS , 2012, Vol. 2, 329-338 p.Conference paper, Published paper (Refereed)
Abstract [en]

Ovako Hofors has adopted a zero-waste vision. The purpose of this vision is to identify application areas for all residues as alternatives to deposition. In terms of tonnage, the largest residue from the steel production at Ovako in Hofors is the slag from the electric arc furnace, EAF. The properties of EAF slag make it an excellent construction material, for instance, as an aggregate in asphalt. The leaching of chromium must be controlled if the slag is to be used as construction material in an environmentally friendly way. Ovako Hofors is actively working to keep the leaching of chromium at a low level. Progress has been made earlier by introducing dolomite in the slag forming agents. Phases capable of stabilising chromium are spinels and solid solution of MgO. The aim of this work is to investigate if it is possible to completely prevent leaching of chromium by stabilising the solid solution of MgO by increasing the FeO content.All the experiments were performed in the EAF at Ovako Hofors. Three different methods to raise the FeO content in the slag were tried and evaluated. Slag produced earlier was used as reference samples. From each test, three different slag samples were collected and analysed. To evaluate the results SEM, XRD, leaching and chemical analyses were conducted.A new oxygen burner increased the iron oxide content, while the other two methods did not show any additional increase. Leaching of chromium could only be detected in a few of the slag samples. Although this makes correlations harder to see, it indicates that a higher FeO content may affect the leaching in a positive way. It was discovered that the leaching of chromium does not depend on the chromium content in the slag, thereby proving the hypothesis that chromium can be bound in stable phases to prevent it from leaching.

Place, publisher, year, edition, pages
Luleå: MEFOS , 2012. Vol. 2, 329-338 p.
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
URN: urn:nbn:se:ltu:diva-30528Local ID: 4605cd2b-212a-4cce-be3d-40920c878525ISBN: 978-91-637-0859-6 (print)OAI: oai:DiVA.org:ltu-30528DiVA: diva2:1003755
Conference
International Conference on Process Development in Iron and Steelmaking : 10/06/2012 - 13/06/2012
Note
Godkänd; 2012; 20120614 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-28Bibliographically approved
In thesis
1. A Dissolution Study of Common Ferrous Slag Minerals
Open this publication in new window or tab >>A Dissolution Study of Common Ferrous Slag Minerals
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Slag is a vital part of metal production since it removes impurities from the metal. As slag is continuously produced, the options are either to dispose slag in landfill or acknowledge slag as a product. Slag can be used in many different applications, ranging from fertilizer to construction material; in some cases, the properties of slag make it a superior alternative to virgin stone materials. The properties and thereby the field of application is determined by the mineralogical composition of the slag. Slag is considered an environmentally friendly material as long as the leaching of certain elements stay below specified thresholds, for leaching of chromium the limit is at 0.5 mg/kg for slag to be considered inert material.

The most common leaching approach is to compare leaching analyses from slag samples to deduce which elements and/or phases contribute or prevent leaching of specific elements. With this method each slag need to be investigated separately and the result may only apply for that specific slag type. In this thesis the approach is different: individual minerals are synthesized and dissolved separately at various pH to accurately assess their dissolution capabilities. By studying the dissolution of individual minerals the leaching of any type of slag with known mineralogical composition can be anticipated. Slag leaching can then be tailored, for example, chromium leaching can be eliminated if all chromium containing phases are removed or not capable of dissolving.

In this thesis the dissolution of akermanite, β- and γ-dicalciumsilicate, merwinte, monticellite, pseudowollastonite and magnesiowüstite with varying FeO/MgO ratios are studied. Leaching tests of magnesiowüstite with 4 wt% Cr2O3 were also included. The dissolution of each mineral is calculated by the acid addition required to maintain a constant pH with 50 mg of mineral in 100 ml water.

As expected, the dissolution decreases as pH increases, with exception of the dicalcium silicates which dissolved completely at pH 4 to 10. The dissolution of the minerals is largely connected to the elemental composition. In the silica based minerals a high Ca ratio promotes dissolution while a high Si ratio impedes the dissolution rate. Both dissolution and chromium leaching of magnesiowüstite depends on the FeO content, with increasing FeO content the dissolution and leaching decreases, magnesiowüstite with at least 60 wt% FeO does not dissolve at pH 10. None of the magnesiowüstite compositions were close to the chromium leaching limit of inert material, 0.5 mg/kg, as the highest leaching sample, with 52 wt% FeO, leached 0.069 mg/kg.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2016
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-60227 (URN)978-91-7583-747-5 (ISBN)978-91-7583-748-2 (ISBN)
Presentation
2016-12-16, F341, Luleå tekniska universitet, Luleå, 10:00 (English)
Available from: 2016-11-10 Created: 2016-11-09 Last updated: 2017-11-24Bibliographically approved

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