XXXI International Mineral Processing Congress 2024 Proceedings Page 487 (511 of 3836)

517
Enrichment of Iron-Bearing Phases in Steel-Making Slag
Through Dry Magnetic Separation
Sunil Kumar Tripathy
Research &Development Division, Tata Steel Limited, Jamshedpur, India
Natural Resources Research Institute (NRRI), University of Minnesota Duluth, Coleraine, MN, USA
Kushagra Singh, Y Rama Murthy, Ranjita Sahu, Gajanan Kapure
Research &Development Division, Tata Steel Limited, Jamshedpur, India
ABSTRACT: Primary steel making is carried out in a basic oxygen converter, and steel slag is generated at a
rate of 90–120 kg/t of steel as a by-product. The utilization of the slag is a challenging task due to complex
elemental and phase analysis. In general, utilization is focused on the recycling of the iron-rich phases of the
steel industry and Ca-rich phases of the cement, clinker, aggregate, etc., industries. One of the major challenges
in the utilization is phosphorous content in the slag, which restricts recycling to the steel industries, and the
presence of iron phases, as well as the un-hydrated lime phase, restricts its use in cement, clinker and aggregate
industries. So, any study focussing on separating these phases is a way forward for the recycling option by
promoting the concept of circular economy in the steel industry.
In the present study, an effort was made to understand the separation amenability of iron-rich phases for
steel slag using magnetic separation techniques. Prior to separation, the steel slag is subjected to detailed
characterization using physical, chemical and mineralogical phase analysis along with magnetic property
evaluation. From the characterization studies, it is evident that slag contains Ca-rich phases such as brownmil-
lerite (Al0.55Ca2Fe1.45O5), hatrurite (Ca3O5Si1),, brownmillerite (Mg, Si-exchanged) (Al0.665Ca2Fe1.052Mg0.133
O5Si0.133), and di-calcium Silicate-α (Ca2O4Si1). Similarly, Fe-rich phases are mostly wuestite (FeO) and di-
calcium di-iron (III) oxide(Ca2Fe2O5). Also, it is found that phosphorous is disseminated in all the phases. Dry
magnetic separation studies were carried out with low, medium and high-intensity separators to separate Fe-rich
phases in the slag. Different magnetic separators such as dry low-intensity magnetic drum separator (LIMS),
medium intensity rare earth drum magnetic separator (REDMS) and high-intensity dry rare earth roll magnetic
separator (RERMS) used for the experimentation and optimization were carried out by varying different process
variables. It is concluded that dry low-intensity magnetic separator iron was found to be enriched up to 29.6%
Fe(T) in the coarser size fractions of –3+0.5 mm from a feed assaying from 17.5% Fe(T). Similarly, the phos-
phorous level in the magnetic fraction has decreased to 2.4% P2O5 from the feed assaying 2.83% P2O5. The
separated iron-rich fraction can be recycled for the iron and steel-making process as a flux, whereas the Ca-rich
phases can be suitable as a feedstock for the clinker and cement manufacturing process.
Keywords: BOF slag, Steel slag, Phosphorous, Di-calcium silicates, Fe-rich phases, Free lime, Characterization,
Low-intensity magnetic separation, Dry beneficiation

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517
Enrichment of Iron-Bearing Phases in Steel-Making Slag
Through Dry Magnetic Separation
Sunil Kumar Tripathy
Research &Development Division, Tata Steel Limited, Jamshedpur, India
Natural Resources Research Institute (NRRI), University of Minnesota Duluth, Coleraine, MN, USA
Kushagra Singh, Y Rama Murthy, Ranjita Sahu, Gajanan Kapure
Research &Development Division, Tata Steel Limited, Jamshedpur, India
ABSTRACT: Primary steel making is carried out in a basic oxygen converter, and steel slag is generated at a
rate of 90–120 kg/t of steel as a by-product. The utilization of the slag is a challenging task due to complex
elemental and phase analysis. In general, utilization is focused on the recycling of the iron-rich phases of the
steel industry and Ca-rich phases of the cement, clinker, aggregate, etc., industries. One of the major challenges
in the utilization is phosphorous content in the slag, which restricts recycling to the steel industries, and the
presence of iron phases, as well as the un-hydrated lime phase, restricts its use in cement, clinker and aggregate
industries. So, any study focussing on separating these phases is a way forward for the recycling option by
promoting the concept of circular economy in the steel industry.
In the present study, an effort was made to understand the separation amenability of iron-rich phases for
steel slag using magnetic separation techniques. Prior to separation, the steel slag is subjected to detailed
characterization using physical, chemical and mineralogical phase analysis along with magnetic property
evaluation. From the characterization studies, it is evident that slag contains Ca-rich phases such as brownmil-
lerite (Al0.55Ca2Fe1.45O5), hatrurite (Ca3O5Si1),, brownmillerite (Mg, Si-exchanged) (Al0.665Ca2Fe1.052Mg0.133
O5Si0.133), and di-calcium Silicate-α (Ca2O4Si1). Similarly, Fe-rich phases are mostly wuestite (FeO) and di-
calcium di-iron (III) oxide(Ca2Fe2O5). Also, it is found that phosphorous is disseminated in all the phases. Dry
magnetic separation studies were carried out with low, medium and high-intensity separators to separate Fe-rich
phases in the slag. Different magnetic separators such as dry low-intensity magnetic drum separator (LIMS),
medium intensity rare earth drum magnetic separator (REDMS) and high-intensity dry rare earth roll magnetic
separator (RERMS) used for the experimentation and optimization were carried out by varying different process
variables. It is concluded that dry low-intensity magnetic separator iron was found to be enriched up to 29.6%
Fe(T) in the coarser size fractions of –3+0.5 mm from a feed assaying from 17.5% Fe(T). Similarly, the phos-
phorous level in the magnetic fraction has decreased to 2.4% P2O5 from the feed assaying 2.83% P2O5. The
separated iron-rich fraction can be recycled for the iron and steel-making process as a flux, whereas the Ca-rich
phases can be suitable as a feedstock for the clinker and cement manufacturing process.
Keywords: BOF slag, Steel slag, Phosphorous, Di-calcium silicates, Fe-rich phases, Free lime, Characterization,
Low-intensity magnetic separation, Dry beneficiation

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516 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Case studies on silica and garnet processing highlight
the effectiveness of high-frequency dry screens in achieving
accurate size classification with high efficiency. Overall, the
evolution of dry fine screening technology bridges a crucial
gap in mineral processing, contributing to a more sustain-
able and efficient future for the mining industry.
REFERENCES
Zhang, B., Mohanty, M.K. Brodzik, P., Improving Fine
Coal Cleaning Performance by High-Efficiency Particle
Size Classification, 2014, International Journal of Coal
Preparation and Utilization, 34:3–4, 145–156.
Mohanty, M.K. Palit, A. Dube, B., 2002. A comparative
evaluation of new fine particle size separation technolo-
gies, Minerals Engineering, 15, 727–736.
Rong, R. Naper-Munn, T.J., 2003. Development of a
more efficient classifying cyclone, Coal Prepartion, 23,
149–165.
Valine, S.B. and Wennen, J.E., 2002. Fine screening in
mineral processing operations, Mineral Processing
Plant Design, Practice, and Control, 917–928, Society
for Mining, Metallurgy &Exploration.
VSMA Vibrating Screen Handbook, 1998, Construction
Industry Manufacturers Association.
Kelly, Errol G, and David J Spottiswood. 1982.
“Introduction to Mineral Processing.”
Napier-Munn, Tim, and Barry A. Wills. 2005. Wills’
Mineral Processing Technology Wills’ Mineral Processing
Technology.
Figure 6. Size distribution of feed, oversize and undersize for Test 7

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518 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
INTRODUCTION
Basic Oxygen Furnace (BOF) slag is one of the most
focused wastes generated in integrated steel plants around
the world. It is a by-product of the Linz-Donawitz pro-
cess and is constantly produced as pig iron is processed
into crude steel and accounts for 15 to 20% of crude steel
output (Tripathy et al., 2021 Zhu, 2020). The schematic
process flow in the BOF steelmaking is shown in Figure 1.
Steel production is increasing every year due to industri-
alization and urbanization. Industrial by-product slag is
generated in another out-size during steelmaking (Netinger
Grubeša et al., 2016). The steel slag is generated in two
different routes, i.e., the BOF route and the Electric Arc
Furnace (EAF) route and is produced at a rate of 12–15%
and 13–20%, respectively. According to a report from the
World Steel Association, 400 Mt of iron and steel slag
are produced annually (Alanyali et al., 2006 WSA, 2021).
Globally, the utilisation of iron-making slag is well prac-
tised, but steel slag is still an issue from an application point
of view. There are several efforts to utilize steel slag in vari-
ous applications, including cement, aggregate, restoration
of marine ecology, etc. However, there is no such sustain-
able use in practice globally.
Recently, there have been numerous research publica-
tions on efficient ways to utilize steel slag. Among these,
high-volume applications were for road infrastructure
(Pasetto, et al., 2017 Aziz et al., 2014), followed by cement
and concrete applications as a replacement for aggregates
and cement (Jiang et al., 2018 Martin et al., 2021) in
shaped products. Apart from utilisation as a supplementary
cementitious product, steel slag has a potential application
in wastewater treatment (Li et al., 2018 Mercado-Borrayo
et al., 2018), soil stabilization, soil conditioner and manu-
facture of Phos-based fertilizer (Ashrit et al., 2020). Many
studies are still in process for its application for CO2 seques-
tration. Nippon Steel and POSCO have been working on
the scientific interpretation of the effectiveness and safety of
using steel slag for the creation of sea forests for the restora-
tion of the marine ecology system (Nippon Steel, 2024).
Numerous investigations are currently being conducted
on the preparation of ceramics from steel slag, and steel
slag ceramic products are diverse, such as porous ceramics
(Wu et al., 2021 Han et al., 2022), all-solid waste ceramics
(Zheng et al., 2020 Tang et al., 2020), and foam ceramics
Wu et al., 2021 Han et al., 2022. However, there is very
little literature on the separation of metallic iron or partially
reduced particles from steel slag. Much of the literature
focuses on the separation of vanadium and phosphorous (Lv
et al., 2023 Wan et al., 2021 Zhang et al., 2017 Iwasaki
et al., 1993). However, the separation of magnetic or par-
tially reduced iron phases can be easily recycled through a
secondary steel-making route or through a sintering route.
However, recycling is completely dependent on the con-
stituents of deleterious gangue components except for iron.
In the present investigation, an effort was made to
understand the separation amenability of iron-rich phases
for steel slag using magnetic separation techniques. Prior
to separation, the steel slag is subjected to detailed char-
acterization using physical, chemical, and mineralogical
phase analysis along with magnetic property evaluation.
Dry magnetic separation studies were carried out with low,
medium and high-intensity separators to separate Fe-rich
phases in the slag. Different magnetic separators such as dry
low-intensity magnetic drum separator (LIMS), medium
intensity rare earth drum magnetic separator (REDMS)
and high-intensity dry rare earth roll magnetic separator
(RERMS) used for the experimentation and optimization
were carried out by varying different process variables.
MATERIALS AND METHODS
BOF Slag
About three tons of BOF slag were collected from the metal
recycling plant of Tata Steel, India. The sample was reported
in the non-magnetic fraction of below 6 mm particle size
Figure 1. Overall process from BOF process to slag utilization

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Page 1126Strategic Minerals click to expand contents

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