Ferro Manganese(FeMn) is used for alloying & refining of steel. During manufacture of FeMn fines are generated which are not useable (except in small induction furnaces). This paper describes a process for agglomeration of FeMn fines and its use in steel making. Paper submitted for NMD 2012.

1. Ferro Manganese Briquettes - A New & Promising Product for Steel Making
Authors
Prabhash Gokarn, V Singh, A Kumar, B D Nanda & A Bhattcharjee
Tata Steel Ltd., India.
1. Introduction
Manganese alloys are added as deoxidizing agents and additives to increase
strength, elasticity and abrasion resistance of steel. Manganese is usually added in
the form of lumps of high carbon ferro manganese, silico manganese and manganese
metal. In steelmaking, overall consumption is (on an average) 6 to 7 kgs of
manganese (Mn content in Mn alloys) per ton of steel.
According to the National Steel Policy, 2005, projected steel production in
India is likely to double within a decade. With this background, there is likely to be a
huge gap between the availability and demand of Manganese alloys, if the
production of ferro alloys fails to match the growth in production of steel.
Manganese ferro alloys are made by carbo-thermic reduction of manganese ores
in electric arc furnace. Liquid hot metal is cast into cakes and crushed into 10mm to
60mm size lumps. The fines generated during the sizing of metal cake cannot be
used in the LD steel making process. These fines get oxidized quickly and reduce the
overall manganese recovery during steel making [1-2]. Though, ferro manganese in
the size range of 3 to 20mm has 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].
Briquetting 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]. A briquetting
process has been developed in this study to utilize high carbon ferro manganese
fines in the steel making process. The suitability of the produced briquettes was
tested in the laboratory as well as in the plant. The developed product will improve
the utilization of manganese resources, while minimizing the environmental
pollution caused by steel industry.
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2. 2. Lab Scale Studies
2.1. Characterization of Fines: Samples of ferro manganese fines were collected
from Ferro Alloy Plant (FAP), Joda, India. These were classified into three different
size ranges (>10mm; -10+3mm; -3mm). Five important constituents (Mn, C, S, P, and
Si) 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.
Fines and binder were mixed properly. Sixty to seventy grams of the mixture were
compacted in cylindrical die of diameter 3cm at different loads and 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
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3. Sample Preparation
(0-3mm) FeMn fine)
Mixing Binder
Pressing
(1-5ton)
Curing
(100 & 150° C, 60 minutes)
Compressive strength Test
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.
(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
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4. 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
100
80
Comm.Pass
%, Passed
60
40
20
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Particle Size (mm)
Figure-3: Particle Size Analysis
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5. Figure-4: Particle Shape Analysis
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6. SEM analysis shown in Figure 5 reveals that these fines are not oxidized. Some small
slag inclusions were also seen in the briquetted samples.
Pt-1
Pt-2
Pt-1
Pt-2
Figure-5: SEM micrograph of Lumps (Pt1-High carbon Phase, Pt2-Low Carbon Phase) and
Briquettes (Pt1-High carbon Phase, Pt2- Slag particle)
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7. 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.
(a) Mn Ore Particle (b) FeMn Particle
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.
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8. 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
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
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9. 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.
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10. After successful implementation at the plant scale, a vendor was identified
and developed for supply of 200 tpm of ferro manganese briquettes.
Metal Analysis Slag Analysis
Figure-9: Slag-Metal Analysis During Plant Trials
5. Conclusions
High carbon ferro manganese fines cannot be used in LD steel making process as the
small size increases losses, reduces recovery and could 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. Tata Steel produces 25kTPA high
carbon ferro manganese fines. In the current market scenario the developed
product can save Rs 1.2 crore/annum including the improved process performance
and cost difference between lumps and agglomerate. Use of briquettes is
environment friendly and it can significantly reduce the amount of metallic dust and
fines added to environment by foundries using the fines.
A similar method of briquetting can be explored for SiMn fines, noble ferro alloy
fines and manganese metal which will further reduce costs of steel making and
increase competitiveness.
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11. Figure-10: Process flow Sheet to Agglomerate the FeMn Fines
5. Acknowledgements
The authors express their sincere thanks to Dr. D. Bhattachrjee, 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 in the present study.
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(1999),127.
[6] V Singh, S M Rao, B D Nanda and D Srinivas: International Patent Application No.
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12. 7. Abbreviations
Mn Manganese
Fe Ferro / Iron
Si Silicon
C Carbon
P Phosphorus
kg Kilograms
mm Millimeters
kgf Kilogram-force
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