ORIGINAL PAPER
Polymorphic transformations of dicalcium silicates in steel slags used in the production of road aggregates
1
Silesian University of Technology, Faculty of Mining, Safety Engineering and Industrial Automation
2
Silesian University of Technology, of Civil Engineering
Submission date: 2021-07-16
Final revision date: 2021-09-10
Acceptance date: 2021-11-12
Publication date: 2021-12-22
Corresponding author
Iwona Jonczy
Silesian University of Technology, Faculty of Mining, Safety Engineering and Industrial Automation, Gliwice, Poland
Silesian University of Technology, Faculty of Mining, Safety Engineering and Industrial Automation, Gliwice, Poland
Gospodarka Surowcami Mineralnymi – Mineral Resources Management 2021;37(4):97-116
KEYWORDS
TOPICS
Rational and efficient development and utilization of mineral resourcesImpact of mineral raw materials industries on the environmentUtilization of recycled mineral raw materials and substitutes
ABSTRACT
This paper presents results of mineralogical and chemical research connected with the polymorphic transformations of dicalcium silicates in aggregate based on open-hearth slag and also slags from the current production of EAF (electric arc furnaces), and LF (ladle furnaces). Particular attention was paid to the transformation of the polymorph β-Ca2[SiO4] into the variant γ-Ca2[SiO4], which is undesirable from the perspective of using steel slags in road construction. A full mineralogical characterization of the tested metallurgical slags enabled the verification of the effectiveness of detecting the decomposition of dicalcium silicate in observations in UV light in line with the PN-EN 1744-1+A1:2013-05 standard. On the basis of the conducted research, it was found that in the aggregate based on open-hearth slags and in the EAF furnace slag, dicalcium silicates are mainly represented by the β-Ca2[SiO4] polymorph, accompanied by α’-Ca2[SiO4]. The slag from the LF furnace was characterized by a different composition, with a strong advantage (57%) of the α’-Ca2[SiO4] variety, with a 1% share of the β-Ca2[SiO4] and 15% of the γ-Ca2[SiO4].
It was found that the transformation of β-Ca2[SiO4] into γ-Ca2[SiO4] can take place only under certain conditions in the metallurgical process, but the process is not influenced by hyperergenic factors, as evidenced by the fact that after more than 100 years of storage of open-hearth slag, on the basis of which the aggregate was produced, it was primarily marked with all the variants of β-Ca2[SiO4], without the polymorph γ-Ca2[SiO4].
The comprehensive characterization of the slag phase composition requires use of an appropriately selected research methodology; this is of key importance prior to the secondary use of this material, especially in the presence of the γ-Ca2[SiO4] polymorph. It has been determined that the most accurate test results are obtained using the XRD technique. The method of determining the decomposition of dicalcium silicate according to the PN-EN 1744-1+A1:2013-05 standard proved to be unreliable. It seems that in the situation of using LF slag as an artificial aggregate, taking the test results according to the method described in the PN-EN 1744-1+A1:2013-05 standard as being decisive is very risky, especially on a large scale (e.g. in communication construction).
ACKNOWLEDGEMENTS
The work is partially supported by the Ministry of Science and Higher Education funding for statutory activities of young researchers BKM-693/RB7/2020.
We would like to thank the Management Board of the EkoProHut sp. z o.o. company for providing research materials and consultations during the research andthe preparation stage of this paper.
METADATA IN OTHER LANGUAGES:
Polish
Przemiany polimorficzne krzemianów dwuwapniowych w żużlach stalowniczych stosowanych do produkcji kruszywa drogowego
żużel stalowniczy, krzemiany dwuwapniowe, kruszywa sztuczne
W artykule przedstawiono wyniki badań mineralogiczno-chemicznych dotyczące przemian polimorficznych krzemianów dwuwapniowych w kruszywie na bazie żużli martenowskich, a także w żużlach z bieżącej produkcji pieca elektrycznego EAF (Electric Arc Furnace) oraz pieca kadziowego LF (Ladle Furnace). Szczególną uwagę zwrócono na przeobrażenia polimorfu β-Ca2[SiO4] w odmianę γ-Ca2[SiO4], co jest niepożądanym zjawiskiem z punktu widzenia wykorzystania żużli stalowniczych w budownictwie drogowym. Pełna charakterystyka mineralogiczna badanych żużli posłużyła do weryfikacji skuteczności wykrywania rozkładu krzemianu dwuwapniowego w obserwacjach w świetle UV zgodnie z normą PN-EN 1744-1+A1:2013-05. Na podstawie przeprowadzonych badań stwierdzono, że w kruszywie na bazie żużli martenowskich oraz w żużlu z pieca EAF krzemiany dwuwapniowe są reprezentowane przede wszystkim przez odmianę β-Ca2[SiO4], której towarzyszy α’-Ca2[SiO4]. Żużel z pieca LF charakteryzował się natomiast odmiennym składem, z silną przewagą (57%) odmiany α’-Ca2[SiO4], przy 1% udziale odmiany β-Ca2[SiO4] oraz przy 15% zawartości odmiany γ-Ca2[SiO4].
Stwierdzono, że przemiana β-Ca2[SiO4] w γ-Ca2[SiO4] może zachodzić tylko w określonych warunkach w procesie metalurgicznym, na proces ten nie mają natomiast wpływu czynniki hipergeniczne, o czym może świadczyć fakt, że po około 100-letnim okresie składowania żużla martenowskiego, na bazie którego wyprodukowano kruszywo, oznaczono w nim przede wszystkim odmianę β-Ca2[SiO4], nie stwierdzając polimorfu γ-Ca2[SiO4].
Kompleksowa charakterystyka składu fazowego żużla wymaga zastosowania odpowiednio dobranej metodyki badawczej, zwłaszcza pod kątem obecności polimorfu γ-Ca2[SiO4], co ma kluczowe znaczenie przed wtórnym wykorzystaniem tego materiału. Stwierdzono, że najdokładniejsze wyniki badań uzyskuje się przy użyciu techniki XRD. Metoda oznaczania rozkładu krzemianu dwuwapniowego wg normy PN-EN 1744-1+A1:2013-05 okazała się zawodna. Wydaje się, że w sytuacji wykorzystania żużla po produkcji pieca LF jako kruszywa sztucznego, zwłaszcza na dużą skalę, np. w budownictwie komunikacyjnym, przyjęcie wyników badań zgodnie z metodą opisaną w normie PN-EN 1744-1+A1:2013-05 jako decydujące jest bardzo ryzykowne.
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