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A Dissolution Study of Common Ferrous Slag Minerals
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
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: urn:nbn:se:ltu:diva-60227ISBN: 978-91-7583-747-5ISBN: 978-91-7583-748-2 (pdf)OAI: oai:DiVA.org:ltu-60227DiVA: diva2:1045500
Presentation
2016-12-16, F341, Luleå tekniska universitet, Luleå, 10:00 (English)
Available from: 2016-11-10 Created: 2016-11-09 Last updated: 2016-11-25Bibliographically approved
List of papers
1. Synthesis and dissolution of slag minerals: A study of β-dicalcium silicate, pseudowollastonite and monticellite
Open this publication in new window or tab >>Synthesis and dissolution of slag minerals: A study of β-dicalcium silicate, pseudowollastonite and monticellite
2015 (English)In: Canadian metallurgical quarterly, ISSN 0008-4433, E-ISSN 1879-1395, Vol. 54, no 4, 446-454 p.Article in journal (Refereed) Published
Abstract [en]

Leaching of slag must be limited when slag is used in other areas than landfill. As slag is composed of different minerals, the properties of slag, inter alia the dissolution, depend on these minerals. If the leaching properties of each mineral are known, counter measurements can be taken to prevent the leaching of unwanted elements. In this study, the dissolution of three common slag minerals will be examined. The three minerals; boron-stabilised β-dicalcium silicate, pseudowollastonite and monticellite were synthesised. The dissolution was measured by setting pH to 4, 7 or 10 and adding 0.05 g mineral in the size range 20-38 μm, and the HNO3 consumption required 3 to maintain the pH level was recorded during 40 h. As expected, the dissolution increases for all minerals when pH decreases. The boron- stabilised β-dical cium silicate was the only mineral fully dissolved at all pH levels, while pseudowollastonite and monticellite only dissolved completely at pH 4.

Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-9171 (URN)10.1179/1879139515Y.0000000022 (DOI)7bca281c-f98d-4457-97f4-0a2b34fc3fb6 (Local ID)7bca281c-f98d-4457-97f4-0a2b34fc3fb6 (Archive number)7bca281c-f98d-4457-97f4-0a2b34fc3fb6 (OAI)
Note
Validerad; 2016; Nivå 2; 20160329 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-11-09Bibliographically approved
2. Chromium leaching from low-alloy EAF slag: Influence of ageing and FeO content
Open this publication in new window or tab >>Chromium leaching from low-alloy EAF slag: Influence of ageing and FeO content
2013 (English)Conference paper (Refereed)
Abstract [en]

Slag produced as a by-product from steelmaking is not utilized to the extent that could be possible. In Sweden and Europe, too much steelmaking slag is still deposited in landfills. Of the slag that is re-used, most is used in road construction, whereas the amount used in other more high-value applications is very low. The main technical reasons for the limited re-use of steelmaking slags are usually: slag disintegration, slag expansion and leaching from the slag, of which the latter is the most difficult to control. This paper discusses the relationships between the mineralogy of steelmaking slag and factors such as leaching of chromium and ageing of the slag. Examples from laboratory experiments and full-scale trials to modify the slag are given.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-60225 (URN)
Conference
The ISIJ-VDEh-Jernkontoret Joint Symposium, (The 14th ISIJ-VDEh Seminar, The 8th Japan-Nordic Countries Joint Symposiumm, on Science and Technology of Process Metallurgy), Osaka, Japan, 15-16 April, 2013
Available from: 2016-11-09 Created: 2016-11-09 Last updated: 2016-12-06Bibliographically approved
3. The influence of iron oxide on the chromium leachability of EAF slag: a full-scale study at Ovako Hofors
Open this publication in new window or tab >>The influence of iron oxide on the chromium leachability of EAF slag: a full-scale study at Ovako Hofors
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 (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
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-30528 (URN)4605cd2b-212a-4cce-be3d-40920c878525 (Local ID)978-91-637-0859-6 (ISBN)4605cd2b-212a-4cce-be3d-40920c878525 (Archive number)4605cd2b-212a-4cce-be3d-40920c878525 (OAI)
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: 2016-11-09Bibliographically approved

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