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Experimental studies to overcome the recycling barriers of stainless-steel and BOF slags
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process.ORCID iD: 0000-0002-8452-4295
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents several studies aimed at improving the recycling of steel slag. The studies are based on a first evaluation of the state-of-the-art

of the recycling applications both with respect to their possibilities and limitations. In addition, an analysis that highlights several properties of all

kinds of ferrous slags, such as bulk chemical composition and common mineral phases, is presented to aid the discussion. Specifically, the studies

presented in this thesis cover two main topics: a new recycling application for stainless-steel slags and a theoretical study on the hydration of

ferropericlase, which is a mineral often present in basic oxygen furnace slags. Most of the studies presented in this thesis focus on the exploration of a

new use of stainless-steel slags, aimed at increasing their recycling rate. In fact, this kind of materials are the most problematic slags to recycle, as

most are not viable for most of the state-of-the-art applications. Therefore, the potential to use them as a substitute for lime in the neutralization of

acidic waste waters is investigated. The studies cover a wide range of trials, from test performed at both laboratory and industrial scale with acidic

waste waters collected from stainless-steel plants, to more fundamental studies on the dissolution of slag minerals in acid environment. Overall,

the substitution of lime with stainless-steel slags is proved to be successful both in terms of the obtained final pH values as well as in terms of

obtaining an efficient removal of metal ions dissolved in waters. In the last part of the thesis, a theoretical study on the hydration of

ferropericlase is conducted. This study proposes a possible technical solution to reduce the volumetric expansion of steel slags, which contain

high percentages of periclase. Specifically, it is seen that ferropericlase with high percentages of FeO adsorbs less water. Thus, they expand less

compared to regular periclase. Therefore, the formation of such a phase during the solidification of slag can provide a higher volumetric stability,

which is highly beneficial when the material later is employed in outdoors applications

Abstract [sv]

Denna avhandling presenterar flera studier som syftar till att förbättra återvinningen av stålslagger. Studierna är baserade på en första

utvärdering av den senaste tekniken för återvinningsapplikationer både med avseende på möjligheter och begränsningar. Dessutom presenteras en

studie som belyser flera egenskaper hos alla typer av järnslagger, såsom bulk-kemisk sammansättning och vanliga mineralfaser, för att underlätta

diskussionen. Specifikt, så omfattar studierna som presenteras i denna avhandling två huvudämnen: en ny återvinningsapplikation för slagger

från tillverkning av rostfritt stål och en teoretisk studie om hydrering av ferroperiklas, vilket är ett mineral som ofta förekommer i konverterslagger.

De flesta av de studier som presenteras i denna avhandling fokuserar på utforskningen av en ny användning av slagger från tillverkning av rostfritt

stål, i syfte att undersöka hur det är möjligt att öka deras återvinningsgrad. Faktum är att denna typ av material är de mest problematiska slaggerna

att återvinna, eftersom de flesta inte kan behandlas med användandet av de flesta av de senaste slaggåtervinningsteknikerna. Därför undersöks

deras potential att kunna användas som ersättning för kalk vid neutralisering av surt avloppsvatten. Studierna omfattar ett brett spektrum

av försök, från laboratorietester till industriella tester med surt avloppsvatten som samlats från rostfria ståltillverkningsanläggningar, till

mer grundläggande studier om hur upplösning av slaggmineraler sker i en sur miljö. Sammanfattningsvis, så visar resultaten att ersättningen av kalk

med slagg av rostfritt stål är framgångsrik både med avseende på att slutliga pH-värden som erhållits samt med avseende på att erhålla ett

effektivt avlägsnande av metalljoner som är lösta i vatten. I sista delen av avhandlingen så behandlas en teoretisk studie om

hydrering av ferroperiklas. Denna studie föreslår en möjlig teknisk lösning för att minska den volymetriska expansionen av stålslagg som

innehåller höga halter av periklas. Specifikt så visar resultaten att ferroperiklas med höga andelar FeO adsorberar mindre vatten och därför

så expanderar dessa slagger mindre i jämförelse med vanlig ferroperiklas. Därför kan bildandet av en sådan fas under stelning av slagg ge en högre

volymetrisk stabilitet, vilket är mycket fördelaktigt när materialet senare används i applikationer utomhus.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2022. , p. 105
Series
TRITA-ITM-AVL ; 2022:1
Keywords [en]
stainless steel, slag, recycling, sustainability
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-309501ISBN: 978-91-8040-123-4 (print)OAI: oai:DiVA.org:kth-309501DiVA, id: diva2:1642366
Public defence
2022-03-11, Sal Sefström, Brinellvägen 23/ https://kth-se.zoom.us/webinar/register/WN_7j8wKLOWStOF7dpspLSvWA, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2022-03-07 Created: 2022-03-05 Last updated: 2022-06-25Bibliographically approved
List of papers
1. A Study of Treatment of Industrial Acidic Wastewaters with Stainless Steel Slags Using Pilot Trials
Open this publication in new window or tab >>A Study of Treatment of Industrial Acidic Wastewaters with Stainless Steel Slags Using Pilot Trials
2021 (English)In: Materials, E-ISSN 1996-1944, Vol. 14, no 17, p. 4806-Article in journal (Refereed) Published
Abstract [en]

Different stainless steel slags have been successfully employed in previous experiments, for the treatment of industrial acidic wastewaters. Although, before this technology can be implemented on an industrial scale, upscaled pilot experiments need to be performed. In this study, the parameters of the upscale trials, such as the volume and mixing speeds, are firstly tested by dispersing a NaCl tracer in a water bath. Mixing time trials are used to maintain constant mixing conditions when the volumes are increased to 70, 80 and 90 L, compared to the 1 L laboratory trials. Subsequently, the parameters obtained are used in pH buffering trials, where stainless steel slags are used as reactants, replicating the methodology of previous studies. Compared to laboratory trials, the study found only a minor loss of efficiency. Specifically, in previous studies, 39 g/L of slag was needed to buffer the pH of the acidic wastewaters. To reach similar pH values within the same time span, upscaled trials found a ratio of 43 g/L and 44 g/L when 70 and 90 L are used, respectively. Therefore, when the kinetic conditions are controlled, the technology appears to be scalable to higher volumes. This is an important finding that hopefully promotes further investments in this technology.

Place, publisher, year, edition, pages
MDPI AG, 2021
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-301057 (URN)10.3390/ma14174806 (DOI)000694276800001 ()34500896 (PubMedID)2-s2.0-85114040658 (Scopus ID)
Note

QC 20220322

Available from: 2021-09-03 Created: 2021-09-03 Last updated: 2024-07-04Bibliographically approved
2. Study of the Dissolution of Stainless-Steel Slag Minerals in Different Acid Environments to Promote Their Use for the Treatment of Acidic Wastewaters
Open this publication in new window or tab >>Study of the Dissolution of Stainless-Steel Slag Minerals in Different Acid Environments to Promote Their Use for the Treatment of Acidic Wastewaters
Show others...
2021 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 11, no 24, article id 12106Article in journal (Refereed) Published
Abstract [en]

Several stainless-steel slags have been successfully employed in previous studies as substitutes for lime in the treatment of industrial acidic wastewaters. This study deepens the knowledge of such application, by analyzing the neutralizing capacity of different slags related to their mineral compositions. To do so, firstly the chemical and mineral compositions of all the slag samples are assessed. Then, 0.5 g, 1 g, 2 g of each slag and 0.25 g and 0.5 g of lime are used to neutralize 100 g of 0.1 M HCl or HNO3 solutions. After the has neutralization occurred, the solid residues are extracted and analyzed using XRD spectroscopy. Then, the solubility of the minerals is assessed and ranked, by comparing the XRD spectra of the residues with the obtained pH values. The results show that minerals such as dicalcium silicate and bredigite are highly soluble in the selected experimental conditions, while minerals such as merwinite and akermanite, only partially. Moreover, Al-rich slags seem to perform poorly due to the formation of hydroxides, which generate extra protons. However, when the weight of slag is adequately adjusted, Al-rich slags can increase the pH values to higher levels compared to the other studied slags.

Place, publisher, year, edition, pages
MDPI AG, 2021
Keywords
steelmaking slag, solubility, minerals, wastewater treatment, leaching
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-307015 (URN)10.3390/app112412106 (DOI)000735476100001 ()2-s2.0-85121443057 (Scopus ID)
Note

QC 20220112

Available from: 2022-01-12 Created: 2022-01-12 Last updated: 2022-06-25Bibliographically approved
3. Study of the Hydration Behavior of Synthetic Ferropericlase with LowIron Oxide Concentrations to Prevent Swelling in Steel Slags
Open this publication in new window or tab >>Study of the Hydration Behavior of Synthetic Ferropericlase with LowIron Oxide Concentrations to Prevent Swelling in Steel Slags
Show others...
2021 (English)In: Journal of Sustainable Metallurgy, ISSN 2199-3831Article in journal (Refereed) Published
Abstract [en]

Steel slags generally swell when subjected to water or humidity, which prevents proper recycling in the cement or asphaltindustries. The MgO and CaO phases in steel slags are responsible for this phenomenon, as both minerals easily absorb waterto form their respective hydroxides. MgO is often present in steel slags in a solid solution with several oxides, constitutingthe so-called RO phase. This study investigates the hydration rate of an RO phase consisting of FeO and MgO called ferropericlase.The material was synthesized in a laboratory furnace by sintering a FeO–MgO powder mixture with varying initialFeO contents (approximately 10, 15, and 20 wt%). Thereafter, electron probe micro-analyzer (EPMA) and X-ray diffraction(XRD) spectroscopies were used to characterize the structure of the samples, which were mainly composed of ferropericlaseand an exsolution of magnesioferrite. Also, Mössbauer spectra showed that the total ferrous iron proportion (Fe2+/ΣFe) ofthe sintered samples was in the range of 0.55–0.72. To measure the hydration behavior, the samples in powder form werecured in an autoclave at an H2Opartial pressure of 2 atm. Thereafter, thermal gravimetric analysis (TGA) was performed tomeasure the amount of water absorbed during the autoclave curing from the mass drop associated with the dehydration ofthe hydroxide. The study found a linear correlation between the initial FeO content and the weight loss after TGA, with areduction down to 6% in the sample with an initial FeO content of 20 wt% content compared to pure MgO.

Place, publisher, year, edition, pages
Springer Nature, 2021
Keywords
Ferropericlase, Hydration, Slag, Recycling, RO phase, Free MgO
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-292867 (URN)10.1007/s40831-021-00359-x (DOI)000639627600001 ()2-s2.0-85104123688 (Scopus ID)
Note

QC 20210426

Available from: 2021-04-15 Created: 2021-04-15 Last updated: 2022-06-25Bibliographically approved
4. The Use of High-Alloyed EAF Slag for the Neutralization of On-Site Produced Acidic Wastewater: The First Step Towards a Zero-Waste Stainless-Steel Production Process
Open this publication in new window or tab >>The Use of High-Alloyed EAF Slag for the Neutralization of On-Site Produced Acidic Wastewater: The First Step Towards a Zero-Waste Stainless-Steel Production Process
Show others...
2019 (English)In: Applied Sciences, ISSN 2076-3417, Vol. 9, no 19, article id 3974Article in journal (Refereed) Published
Abstract [en]

Recycling of steelmaking slags has well-established applications, such as their use in cement, asphalt, or fertilizer industries. Although in some cases, such as the electric arc furnace (EAF) high-alloyed stainless-steel production, the slag’s high metal content prevents its use in such applications. This forces companies to accumulate it as waste. Using concepts such dematerialization, waste management, industrial symbiosis, and circular economy, the article drafts a conceptual framework on the best route to solving the landfilling issue, aiming at a zero-waste process re-design. An experimental part follows, with an investigation of the use of landfill slag as a substitute of limestone for the neutralization of acidic wastewater, produced by the rinsing of steel after the pickling process. Neutralization of acidic wastewater with both lime and slag samples was performed with two different methods. Two out of four slag samples tested proved their possible use, reaching desired pH values compared to lime neutralizations. Moreover, the clean waters resulting from the neutralizations with the use of both lime and slag were tested. In terms of hazardous element concentrations, neutralization with slag yielded similar results to lime. The results of these trials show that slag is a potential substitute of lime for the neutralization of acidic wastewater.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
EAF slag; recycling; re-use; wastewater treatment; sustainable production; dematerialization; zero waste; circular economy
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-260091 (URN)10.3390/app9193974 (DOI)000496258100033 ()2-s2.0-85073266415 (Scopus ID)
Note

QC 20191001. QC 20200103

Available from: 2019-09-25 Created: 2019-09-25 Last updated: 2024-03-18Bibliographically approved

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