Agglomeration of Ferroalloy Fines for use in Bulk Steelmaking Processes

Vol 7 No 3 APRIL 2013
Gokarn et al Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process Page 1 of 10

Agglomeration of Ferro Alloy Fines for Use in Bulk Steel Making Process
Authors
Prabhash Gokarn*, Veerendra Singh, A Kumar, B D Nanda & A Bhattcharjee, Tata Steel Ltd., India.
(*corresponding author - prabhash@tatasteel.com)
Abstract
Ferroalloys are added as deoxidizing agents and additives to increase strength, elasticity and abrasion
& corrosion resistance of steel. The preferred size of ferroalloy lumps for steel making is 10mm – 80
mm to optimize the operational efficiency. Ferroalloy lumps are produced by manual breaking of
casted alloy cakes which generates 5-10% fines which cannot be used in bulk steel making process
(like the commonly used LD process) because of handing and operational difficulties. Therefore, we at
Tata Steel developed an agglomeration process for ferroalloy fines and used the briquettes thus
produced for making steel. The developed process described in the paper is an economic, environment
friendly and efficient way to utilize the ferroalloy fines in steel making.
1. Introduction
Ferroalloys are used in Steel Making as deoxidizing agents and additives to increase mechanical
properties (strength, toughness, wear resistance, springiness), high temperature properties(creep
strength, hardness), electrical properties or corrosion resistance.
Most bulk ferroalloys - like FeMn, SiMn, FeSi and FeCr manufactured by carbo-thermic reduction of
ores in submerged arc furnaces. Noble ferroalloys like FeMo, FeV, FeTi etc. manufactured through
the Alumino-Thermic process. In both cases, the ferroalloy is produced in form of liquid metal.
The liquid metal is cast into cakes and crushed into ~10mm to ~60mm size lumps, with co-
generation of fines during sizing.
The fines generated during the sizing of metal cake cannot be used in the bulk steel making
processes like the BOF(LD) process, as these fines get oxidized quickly and this reduces the overall
recovery during steel making [1-2]. Though, ferroalloy fines in the size range of 3 to 20mm have
better dissolution characteristics, the higher surface area (due to small size) also transports
undesirable gases and moisture into the furnace. Small alloy size also increases dust losses and
leads to handling difficulties [3-6].
Agglomeration into lumps is the best method to utilize these fines. Binder composition and physical
strength of the agglomerate are two main constraints to develop a cost effective method. Various
attempts have been made in the past to agglomerate these fines using conventional binders like
molasses, tar, resin, etc [6-10], which failed due to a variety of reasons and could not be adopted
commercially.
A briquetting process has been developed in this study to utilize ferroalloy fines of manganese
alloys (ferro-manganese and silico-manganese) in the steel making process. The briquettes
produced by the patented process developed was tested in the laboratory as well as in
commercially in the LD shops of Tata Steel.
2. Lab Scale Studies
2.1. Characterization of Fines: Samples of ferroalloy fines were collected from Ferro Alloy Plants
being operated by Tata Steel (viz FeMn at Joda, FeCr at Cuttack and SiMn under tolling at
Durgapur). These were classified into three different size ranges (>10mm; -10+3mm; -3mm). Five
important constituents (Mn/Cr, Si C, S, and P) were analyzed using ICP-OES (Spectro-Analytical
Instruments; Ciros) to find the chemical composition of the prepared agglomerate. Particle shape

and surface characteristics were also analyzed using scanning by electron microscope to study the
agglomeration behavior of fines.
2.2 Briquetting of Fines: Selection of binder for alloy fines determines the strength of briquettes
and thus is most important. The binders should not add any unwanted ingredient like sulphur,
phosphorus, nitrogen etc. in the steel, and it should be cost effective. Molasses and other
conventional organic binders were rejected because these binders contain sulphur and phosphorus.
Sodium silicate, Bentonite, Acrylic resins and Phenolic resins were tried as binders and tested, and
the results are given in Table-1. The experimental work plan is described in Table 1 and Fig. 1.
Ferroalloy fines were mixed thoroughly with the binder in a muller mixer. Sixty to seventy grams of
the mixture was compacted in a cylindrical die of diameter 3cm at different loads and the green
compact was cured at different temperatures (100˚ and 150˚ C) for one hour. Briquette density,
compressive strength, tumbling index, abrasion index, shatter index and dissolution characteristics
were studied.
Binder % Load (ton) Curing Condition
Sodium Silicate 5, 7.5 & 10 1 & 5 100 C, 1 hour
Sodium Silicate+ Bentonite 5+2, 7.5+2 & 10+2 1 100 C, 1 hour
Acrylic Resin 5, 8 & 10 1 & 3 100 C, 1 hour
Phenol formaldehyde Resin 5, 8 & 10 1 & 5 100 & 150 C, 1 hour
Table-1: Briquetting conditions
Figure-1: Process Methodology for Binder Selection
2.3. Smelting of Briquettes: Twenty kilograms of steel scrap was melted in a 25 kg induction
furnace and 5 kg of ferro manganese (FeMn) lumps were added. Experiments were repeated for
FeMn fines and FeMn briquettes under the same test conditions for comparison. The mixing
behavior of the materials was observed. Slag and metal samples were collected and the manganese
recovery was calculated. Figure-2 shows the lab scale setup to test the dissolution behavior of
lumps, fines and briquettes. Similar trials were conducted for SiMn and FeCr fines, for reasons of
space and clarity trials with FeMn fines have been described in detail in this paper.
Sample Preparation
(0-3mm) FeMn fine)
Mixing
Pressing
(1-5ton)
Curing
(100 & 150° C, 60 minutes)
Compressive strength Test
Binder

(a) (b) (c)
Figure-2: Lab Scale trials in Induction furnace (a) Induction furnace (25kg) (b) Melting of scrap (c) Sample
collection before and after the addition
3. Results and Discussions
3.1 Characterization Studies: Chemical analysis of various size fractions is given in Table-2.
Despite the slightly lower percentage of silicon (Si) and manganese (Mn) in fines compared to
lumps, fines are suitable for use in steel making. Size analysis of the samples of ferro manganese
fines (0-10mm) was carried out and it was found that ~70 % fines are of 0 to 3mm size (fines) and
30 % are of 3 to 10mm size (chips). Particle size and shape analysis is shown in Figure-3 and 4.
Finer particle sizes are preferred for briquetting, but presence of significant amount of very angular
particles makes the agglomeration process more challenging. Very angular particles enhance the
mechanical interlocking but require high pressure compaction.
Size Range % C Mn S P Si
>10mm 93 6 >68 0.01 0.193 0.54
-10, +3mm 2 6.75 66.30 0.01 0.175 1.72
<3mm' 5 6.7 65.90 0.01 0.188 1.33
Table-2: Size and Size wise chemical analysis of Ferromanganese fines
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
20
40
60
80
100
Comm.Pass
%,Passed
Particle Size (mm)
Figure-3: Particle Size Analysis

Figure-4: Particle Shape Analysis
SEM analysis shown in Figure 5 reveals that these fines are not oxidized. Some small slag inclusions
were also seen in the briquetted samples.
Figure-5: SEM micrograph of Lumps (Pt1-High carbon Phase, Pt2-Low Carbon Phase) and Briquettes (Pt1-
High carbon Phase, Pt2- Slag particle)
Pt-1
Pt-2
Pt-1
Pt-2

3.2 Briquetting Studies: Metallic fines show a different binding behavior compared to
conventional ore particles. Figure 6 shows surface of manganese ore and ferro manganese metal
particles. The ore particles usually contain small cracks and cleavages which play important role in
binder absorption and binding of the particles.
Figure-6: Surface Roughness of Mn ore and FeMn Metal Particle
Three different combination of sodium silicate were tried and it was found that the
prepared agglomerate does not attain the suitable compressive strength and it varies between 90
and 240 kgf/sample. The strength achieved by machine compaction was 700-1150 kgf/sample. The
strength of the briquettes is not suitable for handling and presence of alkalis and silicon are a
concern which prevents its use in the steel making process.
Acrylic resins and phenol based resins were then used and it was found that acrylic resins
produce an agglomerate of strength of 650-1050 kgf/sample and 720 to 1100 kgf/sample at 1 ton
and 3 ton loads, respectively.
Thermosetting resin produces the best agglomerate with minimum compressive strength of
1050 kgf/sample. Agglomerate strength varies between 1600 and 2000 kgf by machine compaction
with a 15 MPa load. This binder produces good strength with manual compaction also and strength
varies between 1050 to 1440 kgf/ sample for 5 and 10 % binder content, respectively.
A comparative analysis of maximum cold compressive strength achieved using different
binders is given in Figure-7 and it shows that phenolic resin based agglomerate achieves maximum
strength. Handling properties of these briquettes were tested and shown in Table 3 for the
briquettes produced with the most suitable binder combination. The physical characteristics of
briquettes are acceptable to existing LD steel making process.
Properties Briquette
Size & Shape Diameter : 30mm, L : 20mm
Apparent Density 5200 kg/m3
Compressive Strength 55Mpa
Tensile Strength (Load Applied in radial direction) 15Mpa
Tumbler Index (Wt 15kg, rpm 200@25) 95% (>6.3mm)
Abrasion Index (Wt: 15kg, rpm 200@25) 3%( <0.5mm)
Shatter Index (Wt : 10 kg, No of Drops : 4, Height : 2m) 98%(<5mm)
Table-3: Properties of briquettes
(a) Mn Ore Particle (b) FeMn Particle

Figure-7: Maximum Cold Compressive Strength of Briquettes Achieved using Different Binders
3.3 Smelting Studies: Initially these briquettes were tested in laboratory and subsequently
larger trials (0.5, 10 & 100 ton) were conducted at the plant. Mixing and other operational
performance parameters were observed during the lab scale induction furnace operations. It was
observed that fines do not mix properly in the liquid steel but get trapped in the foam on top of the
liquid steel. It also generates a significant amount of slag. The slag generation was lowest for lumps
and highest for fines. Mn recovery was lowest for the fines but it was similar for lumps and
briquettes. A comparison is given in Figure 8. Mn recovery was also observed for different types of
briquettes tested for tumbling test. The best recovery was observed for the briquettes of 30mm
diameter and 20mm thickness (Weight: 65gm) and same were used for the plant trial.

Figure-8: Comparative Analysis of Mn Recovery from Lumps, Briquettes and Fines
4. Product Validation
First phase plant trials were carried out using 500 kg of FeMn briquettes. The Plant adds
150 to 600 kg of ferro manganese in ladles of heat size of 155 tons to produce different grades of
steel. 200 kg and 300 kg ferro manganese briquettes were added in two heats. It was found that the
Mn recovery was 5 to 10% higher when using briquettes (over lumps) compensating the lower Mn
content of fines. The improved dissolution characteristic is the likely reason for improved Mn
recovery. Nitrogen level did not show any unexpected variation (and was within ~13ppm). In
second phase of plant trials, 10 ton of ferro manganese briquettes were prepared and added
manually in 20 different heats of different grades of steel in varied quantities. These trials too were
found satisfactory and in further trials 100 tons of FeMn briquettes were filled in the working chute
and added through the actual plant feeding system. These results, presented in figure 9, confirm the
results of the previous trials.
After successful implementation at the plant scale, a vendor was identified and developed
for supply of 200 tpm of ferro manganese briquettes. Later after successful lab and plant scale trials
with briquetting of silico-manganese fines, the capacity at the vendor was increased and
briquetting of silico manganese fines for use at the LD Shops(BOF Steelmaking) was commercially
undertaken. Lab scale trials have also successfully been completed using FeCr fines.

Figure-9: Slag-Metal Analysis During Plant Trials
5. Conclusions
Ferroalloy fines cannot be used in bulk steel making processes like BOF(LD) as the small
size increases losses, reduces recovery and can act as carrier for moisture and gasses. High quality
briquettes can be produced by mixing the resin binder, compaction and by curing at 150˚ C
temperature. The process flow sheet developed for briquetting is shown in Figure-10. The
developed product was tested in the lab and commercialized after successful plant trials.
Apart from financial benefits of using ferroalloy fines, use of briquettes is environment
friendly and it can significantly reduce the amount of metallic dust and fines generated during
handling and use of ferroalloy fines in smaller furnaces.
The method of briquetting developed by Tata Steel for bulk ferroalloys (FeMn, SiMn and
FeCr) can be extended to noble ferro alloy fines and fines of manganese metal which will further
reduce costs of steel making and increase competitiveness.
Figure-10: Process flow Sheet to Agglomerate the FeMn Fines
5. Acknowledgements
The authors express their sincere thanks to Dr. D. Bhattacharjee, Director, RD&T, TATA
Steel, Mr. Rajeev Singhal, EIC, FAMD and Mr. Debashis Das Chief LD#1, Tata Steel for their keen
interest and guidance during the development of the process and its commercialization.
Metal Analysis Slag Analysis

6. References
[1] K.D. Peaslee, D.S. Webber, S. Lekakh and B. Randall: 58th SFSA Technical and Operating
Conference, 4.1, (2005).
[2] P.G. Sismanis and S. A. Argyropoulos: Proc. of the 69th Steelmaking Conf., 69(1986), 315.
[3] Y. Lee, H Berg, B. Jensen, and J. Sandberg: Iron and Steel Society, 54(1996), 237.
[4] M. Tanaka, M. Mazumdar and R.I. L. Guthrie: Metall. Trans. B, 24B, 4, (1993), 639.
[5] H. Berg, H. Laux,, S. T. Johansen and O. S. Klevan: Ironmaking Steelmaking, 26,2, (1999),127.
[6] V Singh, S M Rao, B D Nanda and D Srinivas: International Patent Application No. 2009-
PCT/IN2009/000532.
[7] Vance, L Calbert. : United States Patent 1946-2405278.
[8] Saunders, R. Earle, Pope, L. Richard: United States Patent 1960- 2935397.
[9] L. Robert and Ranke: United States Patent 1975-3898076.
[10] J.P.Beukes, J. Nell and S. D McCullough: South Africa Patent: 2001-4091.
[11] A Ramu, P K Banerjee and B Roy Choudhury: Unpublished Report, R&D Tata Steel, India,
R&D-INV-011-96-1-13-97(1997).
7. Abbreviations
Mn Manganese
Cr Chrome
Fe Ferro / Iron
Si Silicon
C Carbon
P Phosphorus
kg Kilograms
mm Millimeters
kgf Kilogram-force
BOF/LD Basic Oxygen Furnace Processes like LD

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