1. Chinmaya Joshi (110911075)
Guide: Prof. N. B. Dhokey
ENHANCING THE KINETICS OF MILL SCALE
REDUCTION: AN ECO-FRIENDLY APPROACH

2. • Introduction
• Literature Review
• Objectives
• Experimental Work
• Results and Discussions
• Conclusions
• Future Line of Actions
ENHANCING THE KINETICS OF MILL SCALE REDUCTION:
AN ECO-FRIENDLY APPROACH

3. • What is Mill Scale?
• Why Mill Scale is a nuisance even as an waste
product?
• Techniques of treating mill scale.
• Why recovery of iron ore powder is of advantage?
• What are advantages of using hydrogen gas as
reducing agent over coke and charcoal?
• Importance of Thermodynamic Study
• Barriers
INTRODUCTION

4. What is Mill Scale?
• Mill Scale is a Steel Making By-Product and mainly consists of iron
ore and metallic iron with variable oil and grease content
• Hot Rolling Process is the main source of mill scale with a specific
production of around 35-40 kg/ton of hot rolled product
• Problems with mill scale:
– High Oil Content
– Fine Sludge having particles smaller than 0.1 mm
INTRODUCTION: What is Mill Scale?

5. 1. Why Mill Scale is a nuisance even as an waste
product?
2. Techniques Used earlier to remove mill scale
• Removes the applied paint
• Shipbuilders used to leave the steel to allow the scale to
weather off.
• Flame cleaning, pickling, abrasive blasting also have
been used to remove mill scale from steel surfaces
• Reduction with charcoal, coke and hydrogen
respectively
INTRODUCTION

6. Advantages of producing sponge iron powder:
• Powder Metallurgy Applications
• Pelletization and Sintering possible
• Can be used in DRI plant after forming
suitable pellets
INTRODUCTION

7. Advantages of Hydrogen Gas:
• Endothermic Reduction
• Also, thermodynamics are more favorable with
hydrogen than with carbon monoxide at
temperatures greater than 8000C
• Kinetics have been reported to be faster
• Whisker formation prevented
INTRODUCTION

8. Barriers:
• Determining the energy balances
• Lack of knowledge about the behavior of impurities. (eg.
sulfur and phosphorous)
• Lack of knowledge of the complete kinetics of hydrogen
reduction of iron oxide as a function of particle size
Pathways:
• Detailed Material and Energy Balances
• Thermochemical and Equilibrium Calculation
• Bench – Scale test work
INTRODUCTION

9. LITERATURE REVIEW

10. • Lin et.al: “The mechanism of reduction of iron oxide by hydrogen”
• Introduces the concept of Temperature Programmed Reduction (TPR)
• Reaction performed with 5%H2/N2. Consumption of H2 measured by change in
thermal conductivity with heating rates of 3, 7 and 210C/min
TPR patterns of different heating rates (a) 3
(K min-1) (b) 7 (K min-1) (c) 21 (K min-1)
Indicates a two step reduction process
consisting of Hematite to Magnetite and then to
Iron
LITERATURE REVIEW

11. Temperature programmed Arrhenius plot for the
two-step reduction. (a) Fe2O3 to Fe3O4 (b) Fe3O4 to
Fe
TPR patterns of different heating rates compared with the
calculated data. Solid lines are measured data and dash-dot
lines are the calculated data by unimolecular model for peak
1 and two dimensional nucleation model for peak 2. (a) 3 (K
min-1) (b) 7 (K min-1) (c) 21 (K min-1)
LITERATURE REVIEW

12. • Sha et.al: “Thermodynamic Calculation on the reduction of Iron
Oxide in an H2 atmosphere”
• Detailed thermodynamic study of the reactions involved
• Gave relationship of standard free energy change, H2 content
percentage and equilibrium constant with temperature
Relationship of the standard free energy change (a), equilibrium constant (b) and H2 content percentage (c) for reaction (1) with the temperature.
LITERATURE REVIEW

13. Relationship of the standard
free energy change (a),
equilibrium constant (b) and
H2 content percentage (c)
for reaction (1) and (2) with
the temperature.

14. Higher Temperature:
3Fe2O3 (s) + H2 (g) =2Fe3O4 (s) + H2O (g)
Fe3O4 (s) + H2 (g) =3FeO (s) + H2O (g)
FeO (s) + H2 (g) =Fe (s) + H2O (g)
Lower Temperature:
3Fe2O3 (s) + H2 (g) =2Fe3O4 (s) + H2O (g)
Fe3O4 (s) + 4H2 (g) =3Fe (s) + 4H2O (g)
LITERATURE REVIEW

15. • Martin et.al: “Production of Sponge Iron Powder by reduction of
rolling mill scale”
• Studied reduction of rolling mill scale to sponge iron powder using
coke as reducing agent.
• Conventional mixing and grinding in planetary ball mill with ball/load
ratio = 10:1 with a speed = 400 rev/min
• Subjected to reduction at elevated temperatures in tubular furnace for
different reduction times
• Important Results: Temperature of 11000C was most effective with
reaction times of 3 to 6 hours
LITERATURE REVIEW

16. • Sponge Iron powder was produced in covered crucibles in air
atmosphere furnace
LITERATURE REVIEW

17. Sr.
No.
Sample Initial
Weight (g)
Final
Weight (g)
Weight
Loss (g)
Chemical
analysis
XRD
Analysis
1 Mill scale reduced
by carbon
15 12.160 2.84 78.14% Fe Fe mostly
present
2 Mill scale reduced
by hydrogen
15 12.2780 2.722 84.89% Fe N/A
3 Mill scale reduced
by carbon and
hydrogen
15 10.419 4.581 83.77% Fe N/A
LITERATURE REVIEW

18. Current Work: Aim
• To recover metallic iron powder from mill scale using hydrogen gas as
the reducing agent
• Increasing the efficiency to 90 – 95% from current achieved efficiency
of 84.89%
• Study of Material and Energy balances associated with the chemical
reactions
• Study of kinetics of the entire process
• Study the compressibility of the powder
OBJECTIVES

19. EXPERIMENTAL WORK

20. Mill Scale
Laboratory Ball Mill
PROCESS FLOWCHART
Planetary Ball Mill
Tubular Furnace
10/90 H2/N2
9500C
1 hour
2 hour
3 hour
4 hour
7000C
8000C
9000C
10000C
11000C
Chemical Analysis
Determination of Ideal time for
Reaction : x hrs.
X-Ray Fluorescence
Determination of Ideal temperature
for Reaction : y 0C
Laser particle Size Analysis

21. Grinding
• Course Mill Scale obtained from Rolling Mill Rajasthan.
• Laboratory Ball Milling (4 hours, 72 RPM)
• Planetary Ball Milling (2 hours, 250 RPM)
EXPERIMENTAL WORK

22. Grinding
• Laser Particle Size Analysis of blended
powder: 5.28 µm average particle size
EXPERIMENTAL WORK

23. Reduction
EXPERIMENTAL WORK
Gas
Output
Gas
Input
H2 N2
Control Unit
Tubular Furnace
Sample Boat Mill Scale Sample

24. • Chemical Weight Analysis
To determine percentage by weight or metallic iron in the reduced
powder.
• X-Ray Fluorescence
To determine the presence of impurities like S, Si, P, etc in the
reduced powder as well as powdered mill scale sample
EXPERIMENTAL WORK

25. • Sintering of Powdered Mill Scale sample and
Reduced Mill Scale sample was performed
separately at 11200 C for 4 hrs. in an
atmosphere of 10/90 H2/N2
• Density of the sample was measured to
determine the physical properties
• Chemical Analysis performed to determine the
wt. % Fe in each of the samples
EXPERIMENTAL WORK

26. Time (Hrs) Initial
Weight (g)
Final Weight
(g)
Weight Loss (g) Percentage Weight
Loss (%)
0.5 8.0167 7.9434 0.0733 0.914
1 8.0263 7.7846 0.2417 3.011
1.5 8.022 7.7408 0.2812 3.505
2 8.0157 7.4533 0.5624 7.016
2.5 8.0225 6.8304 1.1921 14.859
3 8.0154 6.1777 1.8377 22.927
3.5 8.0254 6.7457 1.2797 15.945
4 8.023 6.3144 1.7086 21.296
RESULTS AND DISCUSSIONS
Table: Reduction at fixed temperature and variable time

27. RESULTS AND DISCUSSIONS
Reduction at fixed temperature and variable time
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0.5 1 1.5 2 2.5 3 3.5 4
WeightLoss(g)
Time (Hours)

28. Temperature
(0C)
Initial
Wt. (g)
Final Wt. (g) Weight Loss (g) Degree of
Reduction (%
weight loss)
1100 14.9991 11.3003 3.6988 24.660
1000 15.0084 11.6112 3.3972 22.635
900 8.023 6.3144 1.7086 21.296
800 15.0064 11.9188 3.0876 20.575
700 15.0593 14.0239 1.0354 6.8754
RESULTS AND DISCUSSIONS
Table: Reduction at fixed time and variable temperature

29. RESULTS AND DISCUSSIONS
Reduction at fixed holding time and variable temperature
5
10
15
20
25
700 750 800 850 900 950 1000 1050 1100
PercentageWeightLoss(%)
Temperature(0C)

30. Time (hrs) Temp (0C) Percentage of Iron(%)
Powdered and
Blended Mill
Sale Powder
25 58.60
0.5 900 70.37
1.5 900 78.29
2.5 900 81.6
4 900 83.35
RESULTS AND DISCUSSIONS
Table: Chemical Analysis of Samples reduced with variable time and fixed
temperature

31. Time (hrs) Temperature(0C) Percentage of Iron (%)
4 1100 90.477
4 1000 86.009
4 900 83.35
4 800 79.27
4 700 68.17
RESULTS AND DISCUSSIONS
Table: Chemical Analysis of Samples reduced with variable temperature and fixed
time

32. Sr. no. Element Actual Values (%)
1 Fe 96.89
2 Si 0.99
3 Mn 0.79
4 Ca 0.56
5 S 0.35
6 Cu 0.29
7 Cr 0.12
RESULTS AND DISCUSSIONS
Table: XRF Analysis Results

33. RESULTS AND DISCUSSIONS
Degree of Reduction vs. Time superimposed on Grinstling-Brounshtein equation

34. Vantoff Equation
V=k Cn
Where rate of reaction „v‟ can be related to the concentration of a reactant
„C‟ and „n‟ is the order of reaction
log v = log k + n.log c
RESULTS AND DISCUSSIONS

35. RESULTS AND DISCUSSIONS
Vantoff Equation
Time (min) Time (sec) %Fe (c) Log c Slope (v) Log v
0 0 58.6 1.767898 3.88499 0.58939
30 1800 70.37 1.847388 6.07289 0.783395
90 5400 78.29 1.893706 10.1834 1.007893
150 9000 81.6 1.91169 21.6957 1.336374
240 14400 83.39 1.921114 37.6317 1.575554
Table: XRF Analysis Results.

36. RESULTS AND DISCUSSIONS
y = 50.805x0.0935
R² = 0.9932
55
60
65
70
75
80
85
90
0 50 100 150 200 250 300
Calculation for Vantoff Equation

37. • Chemical Analysis of Sintered Samples:
• 81% by wt. metallic Fe in sintered sample from powdered mill
scale
• 93% by wt. metallic Fe in sintered sample from reduced mill
scale
RESULTS AND DISCUSSIONS

38. 1. The reduction results sow increased weight loss at 9000C with
increase in time duration
2. The reduction results also show increased weight loss as the
temperature is increased from 700 to 11000C
3. Chemical Analysis also reveals the increase in the total Fe
percentage as the time duration is increased. It also indicates that
the total Fe percentage increases as the temperature is increased
with the maximum efficiency of 90.477% at a temperature of
11000C and 4 hours duration
4. The degree of reduction vs. time graph when compared with the
Grinstling-Brounshtein equation reveals that the reduction reaction
follows a first order kinetics
5. The use of Vantoff equation determines that the reaction has first
order kinetics
CONCLUSIONS

39. 1. To determine the weight loss of the reduction
reaction with a sample bed of 50g
2. FESEM analysis of the mill scale powder to
determine the morphology of the powder
FUTURE LINE OF ACTIONS

40. 1. Philipp, J. and Endell, R., “How German Steel In­dustry is Managing Waste Disposal”, Steel Technol­ogy, 275-279, 1996.
2. Szekely, J., “Steelmaking and Industrial Ecology Is Steel a Green Material ?”, ISIJ International, 36, (1), 121-132, 1996.
3. Mookherjee, s. Ray, H.S. and Mukherjee, A., “Isothermal Reduction of Iron Ore Fines Surrounded by Coal or Char
Fines”, Ironmaking and Steelmaking, 13, (5), 229-235, 1986.
4. L. Camci, S. Aydin, C. Arslan, “Reduction of Iron Oxides in Solid Wastes Generated by Steel Works”, Turkish. J. Eng. Env.
Sci. 26 (2002), 37-44.
5. H. Lin, Y. Chen, C. Li, “The mechanism of reduction of iron oxide by hydrogen”, Thermochemica Acta 400 (2003 61-67).
6. L. Sha, Z. Qiu, “Thermodynamic Calculation on the Reduction of Iron Oxide in an H2 Atmosphere”, International Journal of
Thermodynamics, vol.10 (No. 3), pp. 113-119, September 2007.
7. R. Longbottom, L. Kolbeinsen, “Iron Ore Reduction with CO and H2 Gas Mixtures- Thermodynamic and Kinetic
Modelling”, Ulcos, New Direct Reduction, 2008.
8. Schlebushch, D.W., “K om ure Dayalı SL/RN Direkt Red uksiyon Y ontemi”, Symposium on Direct Re­duction of Iron
Ores, Middle East Technical Uni-versity, 1984.
9. Wagner, Devisme, Patisson, Ablitzer, “A Laboratory Study of the Reduction of Iron Oxides by Hydrogen”, Sohn International
symposium, 27-31 Aug. 06, San diego, TMS, vol.2. pp. 111-120.
10. Kinoshita, Takatsuki, Murakami, Settsu, Ohta, Sakai, “Furnace for the heat treatment of scale covered steel”, United States
Patent 4,397,451, Aug 9, 1983.
11. Koros, Bajaj, Daiga, Hegde, “Treatment of steel mill waste metal oxides”, United States Patent 6,120,577. Sep.19, 2000.
12. Martin, Lopez, Torralba, “Production of sponge iron powder by reduction of rolling mill scale”, Institute of
Materials, Minerals and Mining, DDI 10.11 79 /174 3281211Y. 00 00 00 00 78, Vol. 39, No.3, pp. 155 – 162, 2012.
13. DeGarmo, p. 461
14. Jones, W. D. (1960). Fundamental Principles of Powder Metallurgy. London: Edward Arnold Ltd..
15. Suspension Hydrogen Reduction of Iron Oxide Concentrate, Industrial Technologies Program, U.S. Dept. of Energy, Energy
Efficiency and Renewable Energy
16. Halley et.al “Reduction of Iron Ore with Hydrogen”, United States Patent 3,140,168, May 31, 1961
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