CHAPTER-4: RESULTS & DISCUSSION: CHARACTERIZATION AND...
28
CHAPTER-4: RESULTS & DISCUSSION: CHARACTERIZATION AND GREEN PELLETIZING STUDIES
Transcript of CHAPTER-4: RESULTS & DISCUSSION: CHARACTERIZATION AND...
CHAPTER-4:
RESULTS & DISCUSSION:
CHARACTERIZATION AND
GREEN PELLETIZING STUDIES
72
4. RESULTS & DISCUSSION: CHARACTERIZATION AND GREEN
PELLETIZING STUDIES
This chapter presents the results of the detailed characterization studies
of iron ore and fluxes. Effect of pelleting feed fineness on the green pellet
growth and quality is also presented in detail.
4.1 Characterization of the iron ore fines and fluxes
Chemical analysis of the as-received Noamundi iron ore fines is given in
Table 8. LOI of the sample is on dry basis.
Table-8 Chemical analysis of the as- received iron ore fines from Noamundi
mines
Element Fe (t) SiO2 Al2O3 CaO MgO P S LOI
Wt.% 66.64 1.46 2.05 0.1 0.08 0.055 0.04 2.2
Size analysis and cumulative particle distribution of the iron ore fines is
shown in Fig.34 (a) and 34 (b) respectively. From the results, it is understood
that the amount of ready-to-pelletize fines in the as-received ore is up to about
25%, which is an indication of friable nature of this ore. Table 9 and 10 shows
the chemical analysis and size analysis of bentonite, limestone, dolomite,
magnesite, pyroxenite and coal fines used in the preparation of green pellets
respectively.
Bentonite is a hydrous alumino-silicate, largely composed of
montmorillonite mineral. Pyroxenite is a magnesium silicate rock composed
largely of pyroxene (MgSiO3) with small amounts of olivine (Mg2SiO4) and
serpentine (3MgO.2SiO2.2H2O). It contains more amount of silica as compared
to its MgO content. Magnesite is a naturally occurring magnesium carbonate
mineral (MgCO3), found in two different forms, crystalline and cryptocrystalline.
Coal used was anthracite with medium volatile matter.
73
Fig. 34 (a) Size analysis of the as-received Noamundi iron ore fines
Fig. 34 (b) Size distribution of as-received Noamundi iron ore fines
Ta
ble
-9 C
he
mic
al a
naly
sis
of
flu
xe
s a
nd
ad
ditiv
es u
se
d in
pelle
tizin
g
B
en
ton
ite
L
ime
sto
ne
Do
lom
ite
Py
rox
en
ite
M
ag
ne
sit
e
Co
al
Fe
(t)
14
.2
0.1
0
.1
11
.0
1.0
0
.5
SiO
2
55
.5
1.5
0
.7
52
.2
4.3
8
.0
Al 2
O3
17
.6
0.2
0
.3
0.9
2
0.4
3
.9
CaO
1
.5
51
.3
29
.7
0.7
6
6.0
0
.15
Mg
O
2.9
2
.8
21
.3
29
.5
45
.0
0.1
6
LO
I 3
.1
43
.7
46
.2
- 4
9.1
6
.7
TiO
2
1.3
-
- 0
.02
0.1
0
.2
Na
2O
2
.4
- -
- -
-
K2O
0
.3
- -
- -
-
Fix
ed
C
arb
on
- -
- -
- 7
7.0
Ta
ble
-10
Siz
e a
naly
sis
of flu
xe
s a
nd
ad
ditiv
es u
se
d in
pelle
tizin
g
Sie
ve
M
es
h
No
Op
en
ing
, m
icro
ns
B
en
ton
ite
L
ime
sto
ne
Do
lom
ite
Py
rox
en
ite
M
ag
ne
sit
e
Co
al
+1
00
1
50
0
15
.4
10
.1
29
.3
12
.8
7.7
+2
00
7
5
2.2
1
4.8
1
3.4
2
7.2
1
1.1
2
8.8
+2
40
6
3
97
.8
5.8
6
8
.2
4.9
1
2.1
+3
50
4
5
- 3
.6
6.2
2
.9
5.9
1
5
+4
00
3
7
- 5
.7
5.8
4
.1
8.8
3
+5
00
2
5
- 5
.3
9.2
6
.4
8.3
4
.5
-50
0
-25
- 4
9.4
4
9.3
2
1.9
4
8.4
2
8.9
75
4.1.1 QEMSCAN characterization of iron ore fines
Fraction wise characterization of the as-received and ball mill ground
sample was carried out to understand the distribution of iron ore and gangue
minerals across different size fractions. The mineral phases present in the
sample are hematite and goethite as iron ore minerals and kaolinite, limonite,
gibbsite and quartz as gangue minerals. Hematite and goethite are present in
the proportion of 68% and 30% respectively. 90% of the alumina in the sample
is associated with goethite, gibbsite and kaolinite.
4.1.1.1 Mineralogy of as-received iron ore fines
The as-received iron ore sample was subjected to chemical analysis,
mineralogical constituents determined by XRF and QEMSCAN (Table 11).
Table-11 Chemical assay & mineral mass % in the as-received sample
Chemical Assay
Al Fe O Si H
QEMSCAN 1.18 65.75 32.38 0.31 0.37
XRF 1.11 67.57 30.61 0.71
Mineral mass %
Goethite Hematite Kaolinite Gibbsite Limonite Quartz
29.78 68.39 0.1 0.73 0.41 0.58
The rock is massive in nature showing no clear layering described by
different mineral phases. Goethite is mostly associated with hematite. Hematite
is present as inclusion within goethite and vice versa. Goethite is randomly
present within hematite matrix and sometimes hematite is rimmed by goethite
as shown in Fig.35.
Goethite grains also include gibbsite, kaolinite and quartz, which are
visible in the particle analysis of the as-received samples, as shown in Fig.36.
But hematite grains show no such relationship with the gangue minerals.
76
Fig.35 (a) Goethite inclusion in Hematite (b) Gibbsite and Hematite inclusion in
Goethite
Fig. 36 Particle analysis of some size fractions of as-received sample
(a=+3mm, b=+0.5mm, c=+0.045mm)
77
4.1.1.2 Size-wise mineral liberation of as-received sample
As-received sample was screened at different size fractions to carry out
the fraction wise characterization and reported in Table 12. Mean grain size of
each mineral in different size fractions is also reported.
Texturally hematite and goethite are mutually associated with each
other. Goethite is apparently more in finer fractions whereas coarser fractions
are rich in hematite.
4.1.1.3 Liberation analysis of as-received iron ore fines
Liberation analysis indicated that goethite is found to be more liberated
in finer fractions as compared to coarser fractions. In case of hematite, majority
of grains are associated with other minerals, mostly goethite. It was observed
that in +12.5mm and +0.150mm fractions, most of the hematite grains were
within the range of <=80% and <=90% liberation can be seen in Table 13.
Concentration of gangue minerals like gibbsite, limonite, quartz are more in
finer size fraction.
4.1.1.4 Deportation analysis of as-received iron ore fines
Table 14 shows the deportment (contribution) of Fe and Al in different
size fractions of the as-received sample. The major contributory minerals of iron
are hematite and goethite but the ratio between hematite and goethite is
distributed bimodal. Al is mostly contributed by goethite. Al is considered to be
present in goethite with average of 3%, which cannot be separated by physical
beneficiation process. In addition to goethite, gibbsite also contributes to Al in
considerable amounts.
Ta
ble
-12
Min
era
l m
ass a
nd
gra
in s
ize o
f a
s-r
ece
ive
d s
am
ple
Min
era
l m
as
s %
+
12
.5m
m
+1
0m
m
+8
mm
+
6m
m
+3
mm
+
1m
m
+0
.50
mm
+
0.1
5m
m
+0
.04
5m
m
-0.0
45
mm
Go
eth
ite
18
.18
36
.52
34
.73
40
.76
34
.44
49
.21
27
.9
18
.86
36
.32
39
.15
He
ma
tite
8
1.7
2
60
.96
65
.04
58
.05
64
.2
48
.9
70
.93
80
.18
62
.46
57
.82
Ka
olin
ite
0.0
3
0.0
8
0.0
2
0.0
6
0.0
4
0.5
7
0.0
7
0.0
4
0.1
1
0.2
6
Gib
bsite
0.0
1
1.4
6
0.1
2
0.6
0
.8
0.5
9
0.6
1
0.5
9
0.5
7
1.4
9
Lim
on
ite
0.0
4
0.9
5
0.0
8
0.5
2
0.2
2
0.6
5
0.4
3
0.2
5
0.3
4
0.8
9
Qu
art
z
0.0
1
0.0
1
0.0
1
0
0.2
7
0.0
8
0.0
4
0.0
1
0.1
8
0.3
8
Me
an
Gra
in S
ize
(M
icro
ns
)
Min
era
l +
12
.5m
m
+1
0m
m
+8
mm
+
6m
m
+3
mm
+
1m
m
+0
.50
mm
+
0.1
5m
m
+0
.04
5m
m
-0.0
45
mm
Go
eth
ite
41
.2
68
.16
53
.8
51
.09
43
.54
55
.8
36
.3
8.6
2
18
.01
6.1
8
He
ma
tite
1
13
.78
84
.15
64
.71
49
.22
61
.53
45
.07
67
.62
24
.83
31
.78
9.1
Ka
olin
ite
20
1
7.7
8
19
.79
24
.19
20
.45
53
.08
29
.98
7.7
3
17
.02
6.7
3
Gib
bsite
17
.77
26
.92
22
.13
34
.32
49
.67
27
.81
28
.59
13
.72
19
.82
7.8
2
Lim
on
ite
15
.15
17
.16
15
.16
18
.61
15
.67
19
.35
17
.24
4.9
7
8.0
2
4.7
5
Qu
art
z
17
.12
17
.01
17
.22
20
.87
53
.99
40
.34
28
.17
7.2
1
44
.23
10
.86
Pa
rtic
le s
ize
26
48
.7
24
57
.7
24
71
.1
18
76
79
8.4
7
03
.7
39
8.5
7
1.5
6
6.6
1
1.3
Ta
ble
-13
Lib
era
tio
n p
att
ern
of
go
eth
ite
& h
em
atite
fo
r a
s-r
eceiv
ed
sa
mp
le
Lib
era
tio
n o
f G
oeth
ite
(%
)
+
12
.5m
m
+1
0m
m
+8
mm
+
6m
m
+3
mm
+
1m
m
+0
.50
mm
+
0.1
50
mm
+
0.0
45
mm
-0
.04
5m
m
<=
20
%
20
.28
7.4
3
3.1
3
0.0
0
2.3
7
0.0
0
6.2
6
20
.19
2.6
5
1.0
9
<=
40
%
38
.35
2.3
3
24
.31
13
.58
18
.77
3.9
4
26
.75
40
.90
17
.71
17
.97
<=
60
%
37
.33
24
.79
23
.63
35
.03
40
.00
32
.53
30
.92
16
.67
30
.65
33
.08
<=
80
%
4.0
4
8.2
5
3.2
3
15
.75
29
.99
46
.48
23
.88
5.7
7
27
.24
21
.90
<=
90
%
0.0
0
40
.47
0.0
0
17
.63
8.8
8
13
.55
8.1
4
5.6
2
9.7
2
4.4
6
<=
10
0%
0
.00
16
.73
45
.70
18
.00
0.0
0
3.5
0
4.0
5
10
.84
12
.03
21
.50
Lib
era
tio
n o
f H
em
ati
te (
%)
+
12
.5m
m
+1
0m
m
+8
mm
+
6m
m
+3
mm
+
1m
m
+0
.50
mm
+
0.1
50
mm
+
0.0
45
mm
-0
.04
5m
m
<=
20
%
0.0
0
2.8
4
1.8
8
5.4
1
1.0
7
4.8
8
1.4
2
0.6
8
2.6
0
2.0
1
<=
40
%
0.8
6
0.0
0
1.8
7
9.9
5
15
.42
42
.91
7.7
3
1.3
8
12
.68
13
.59
<=
60
%
17
.90
31
.13
21
.81
40
.71
34
.98
43
.20
21
.37
8.7
5
30
.41
39
.97
<=
80
%
36
.22
8.7
3
61
.78
43
.92
36
.76
9.0
1
45
.74
43
.68
39
.78
39
.05
<=
90
%
45
.02
40
.77
12
.66
0.0
0
11
.76
0.0
0
21
.17
39
.02
12
.40
4.0
9
<=
10
0%
0
.00
16
.53
0.0
0
0.0
0
0.0
0
0.0
0
2.5
7
6.4
8
2.1
3
1.3
0
Ta
ble
-14
Resp
on
sib
le m
ine
rals
and
th
eir
co
nce
ntr
atio
n (
Dep
ort
me
nt)
fo
r F
e &
Al in
th
e a
s-r
ece
ive
d s
am
ple
Fe
De
po
rtm
en
t (m
as
s %
in
fra
cti
on
)
+
12
.5m
m
+1
0m
m
+8
mm
+
6m
m
+3
mm
+
1m
m
+0
.50
mm
+
0.1
50
mm
+
0.0
45
mm
-0
.04
5m
m
Go
eth
ite
15
.87
33
.41
31
.16
37
.16
31
.21
45
.79
24
.93
16
.59
32
.94
36
.20
Hem
ati
te
84
.08
65
.72
68
.77
62
.37
68
.56
53
.62
74
.68
83
.12
66
.74
62
.99
Lim
on
ite
0.0
3
0.8
5
0.0
7
0.4
6
0.2
0
0.5
9
0.3
8
0.2
2
0.3
0
0.8
0
Ma
gn
eti
te
0.0
2
0.0
2
0.0
1
0.0
0
0.0
3
0.0
0
0.0
1
0.0
7
0.0
2
0.0
1
Al
Dep
ort
me
nt
(ma
ss
% i
n f
rac
tio
n)
+
12
.5m
m
+1
0m
m
+8
mm
+
6m
m
+3
mm
+
1m
m
+0
.50
mm
+
0.1
50
mm
+
0.0
45
mm
-0
.04
5m
m
Gib
bs
ite
0.4
9
30
.50
3.9
5
14
.25
20
.79
11
.43
19
.59
25
.99
15
.08
29
.22
Go
eth
ite
98
.54
66
.11
95
.46
83
.52
78
.02
83
.19
77
.66
71
.88
82
.72
66
.63
Lim
on
ite
0.3
2
2.8
7
0.3
5
1.7
8
0.8
5
1.8
3
2.0
2
1.6
0
1.3
1
2.5
2
Kao
lin
ite
0.6
5
0.5
2
0.2
4
0.4
5
0.3
4
3.5
5
0.7
4
0.5
4
0.8
9
1.6
3
81
4.1.1.5 Mineralogy of the iron ore fines after ball mill grinding
After grinding the iron ore fines in ball mill to mean particle size of 55
microns, goethite and hematite grains show no inclusions of gangue as clearly
shown in Fig.37. Quartz grains were also found free of other minerals as
inclusions.
4.1.1.6 Size-wise mineral liberation of iron ore fines after ball mill grinding
Mineralogical analysis showed that goethite is apparently more in finer fractions
whereas coarser fractions are rich in hematite as shown in Table 15.
4.1.1.7 Liberation analysis of iron ore fines after ball mill grinding
Goethite is found to be more liberated (46%) in finer size fractions,
whereas hematite is more liberated in coarser size fractions (+0.25 mm). After
grinding, goethite, being softer than hematite, has been more liberated as
compared to hematite, as shown in Table 16.
4.1.1.8 Deportation analysis of iron ore fines after ball mill grinding
Table 17 shows Al and Fe deportment of ground sample. Goethite is the
highest contributory mineral for Al and hematite is the highest contributory
mineral for Fe.
82
;
Fig. 37 Particle analysis of some size fractions of ground sample (a=+1.4mm,
b=+0.25mm, c=+0.15mm)
Ta
ble
-15
Min
era
l m
ass a
nd
me
an
gra
in s
ize o
f d
iffe
rent
siz
e f
ractio
ns
+2.3
6m
m+1
.4m
m+1
mm
+0.2
5m
m+0
.15
mm
+0.0
75
mm
+0.0
63
mm
+0.0
45
mm
+0.0
37
mm
-0.0
37
mm
Go
eth
ite
29
.22
16
.84
44
.33
14
.71
43
.92
17
.81
22
.73
67
.32
38
.64
58
.15
Hem
ati
te6
9.7
28
2.8
15
5.0
28
4.1
25
4.9
80
.77
75
.44
29
.96
58
.51
38
.46
Lim
on
ite
0.2
80
.16
0.4
50
.31
0.5
90
.51
0.8
41
.11
1.2
41
.68
Ka
oli
nit
e0
.71
0.0
50
.13
0.0
70
.06
0.1
10
.14
0.2
0.2
40
.25
Qu
art
z0
.01
0.0
10
0.2
30
.17
0.1
40
.17
0.3
0.3
10
.25
Gib
bsi
te0
.02
0.1
30
.08
0.5
50
.37
0.6
10
.65
1.1
11
.05
1.2
1
+2.3
6m
m+1
.4m
m+1
mm
+0.2
5m
m+0
.15
mm
+0.0
75
mm
+0.0
63
mm
+0.0
45
mm
+0.0
37
mm
-0.0
37
mm
Go
eth
ite
32
.02
34
.86
38
.61
27
.96
35
21
.11
9.5
82
0.8
91
8.4
29
.8
Hem
ati
te4
5.1
21
02
.51
29
.78
97
.87
36
.84
52
.13
41
.65
17
.98
22
.99
10
.58
Lim
on
ite
17
.08
15
.96
19
.62
16
.07
18
.81
6.3
41
5.3
11
5.3
41
5.2
77
.71
Ka
oli
nit
e3
1.5
82
2.6
62
7.9
82
6.9
62
3.5
32
2.5
92
0.4
51
8.0
22
0.0
29
.16
Qu
art
z1
8.9
18
.07
15
.86
52
.65
0.2
33
2.9
33
9.5
62
0.5
52
5.3
71
1.0
6
Gib
bsi
te1
5.9
42
4.1
62
7.6
43
1.4
83
1.2
92
8.7
42
2.4
81
8.2
22
1.7
59
.5
Pa
rtic
le s
ize
11
03
.11
36
9.7
10
16
.42
51
.31
47
.67
5.3
50
.42
5.3
26
.81
2.7
Gra
in S
ize
(Mic
rom
eter
)
Min
era
l m
ass
%
Ta
ble
-16
Lib
era
tio
n p
att
ern
of
go
eth
ite
& h
em
atite
fo
r g
roun
d s
am
ple
Lib
era
tio
n o
f H
em
ati
te (
%)
+
2.3
6m
m
+1
.4m
m
+1
mm
+
0.2
5m
m
+0
.15
mm
+
0.0
75
mm
+
0.0
63
mm
+
0.0
45
mm
+
0.0
37
mm
M
inu
s
0.0
37
mm
<=
20
%
0
0
2.5
9
0.4
7
3.2
5
0.3
6
14
.75
0.3
2
1.6
5
6.0
5
<=
40
%
4.8
6
0
25
.4
1.5
4
19
.98
2.8
2
42
.84
1.8
5
12
.3
28
.68
<=
60
%
51
.33
9.2
5
61
.63
5.4
9
49
.88
12
.79
25
.19
10
.29
32
.98
38
.9
<=
80
%
43
.81
48
.01
10
.38
23
.21
22
.99
54
.35
5.6
3
44
.06
34
.8
19
.29
<=
90
%
0
33
.71
0
39
.11
3.2
5
22
.56
0.2
1
32
.93
7.9
3
1.8
1
<=
10
0%
0
9
.02
0
30
.18
0.6
6
7.1
2
11
.38
10
.55
10
.36
5.2
7
Lib
era
tio
n o
f G
oeth
ite
(%
)
+
2.3
6m
m
+1
.4m
m
+1
mm
+
0.2
5m
m
+0
.15
mm
+
0.0
75
mm
+
0.0
63
mm
+
0.0
45
mm
+
0.0
37
mm
M
inu
s
0.0
37
mm
<=
20
%
0.0
1
19
.51
0
30
.19
0.5
4
10
.52
0.0
7
19
.26
2.3
0
.33
<=
40
%
27
.24
56
.7
4.2
3
29
.37
8.2
1
42
.67
1.3
4
44
.34
16
.12
4.7
<=
60
%
63
.71
23
.79
45
.56
14
.29
37
1
8.8
1
9.5
2
0.8
9
27
.25
17
.49
<=
80
%
9.0
5
0
44
.83
7.7
6
31
.11
8.4
2
29
.39
7.7
8
19
.11
24
.57
<=
90
%
0
0
3.7
3
5.0
6
8.7
5
2.2
6
12
.85
2.1
6
3.4
3
6.9
8
<=
10
0%
0
0
1
.65
13
.32
14
.39
17
.32
46
.86
5.5
6
31
.8
45
.93
Ta
ble
-17
Dep
ort
me
nt
of
Al a
nd F
e in
th
e g
roun
d s
am
ple
Al
Dep
ort
me
nt
(Ma
ss
% i
n F
rac
tio
n)
+
2.3
6m
m
+1
.4m
m
+1
mm
+
0.2
5m
m
+0
.15
mm
+
0.0
75
mm
+
0.0
63
mm
+
0.0
45
mm
+
0.0
37
mm
-0
.03
7m
m
Gib
bsite
0.8
5
8.0
7
1.9
2
9.0
3
8.5
7
26
.79
23
.41
15
.46
22
.63
18
.45
Go
eth
ite
89
.74
89
.57
95
.5
67
.43
88
.98
68
.37
70
.64
81
.42
71
.9
76
.66
Lim
on
ite
1.4
2
1.4
1
.61
2.3
8
1.9
8
3.2
5
4.3
5
2.2
4
3.8
4
3.6
9
Ka
olin
ite
7.9
9
0.9
7
0.9
9
1.1
6
0.4
6
1.5
9
1.5
9
0.8
8
1.6
2
1.2
Fe
De
po
rtm
en
t (M
as
s %
in
Fra
cti
on
)
+
2.3
6m
m
+1
.4m
m
+1
mm
+
0.2
5m
m
+0
.15
mm
+
0.0
75
mm
+
0.0
63
mm
+
0.0
45
mm
+
0.0
37
mm
-0
.03
7m
m
Go
eth
ite
26
.16
14
.69
40
.44
12
.89
40
.22
15
.68
20
.2
64
.92
35
.52
55
.32
He
ma
tite
7
3.5
6
85
.16
59
.16
86
.83
59
.25
83
.82
79
.04
34
.04
63
.37
43
.12
Lim
on
ite
0.2
4
0.1
3
0.4
0
.27
0.5
2
0.4
4
0.7
3
1.0
4
1.1
1
1.5
6
86
4.1.2 XRD analysis of iron ore fines and fluxes
Figure 38(a) shows the XRD analysis of different fluxes viz., limestone,
dolomite, magnesite and pyroxenite used in the pelletizing. Limestone primarily
comprised of calcite whereas dolomite flux contained dolomite and some traces
of quartz. Magnesite and quartz were found to be primary minerals in
magnesite flux. Pyroxenite comprised enstatite and trimolite minerals.
4.1.3 TGA analysis of iron ore fines and fluxes
Figure 38(b) shows the thermo gravimetric analysis of the iron ore,
limestone, dolomite, magnesite, pyroxenite and coal fines. From the results, it
was evident that among all the fluxes, magnesite dissociation occurs at lower
temperatures (around 500oC) followed by dolomite (around 700oC) and
limestone (around 750oC). Magnesite dissociation completes at 800oC,
whereas dolomite at 920oC and limestone at 960oC. Pyroxenite, which is a
magnesium silicate, does not dissociate unlike the above carbonate fluxes.
Minor amount of its weight loss was observed due to the presence of combined
water. Devolatilization of coal was found to start from around 315oC and
completed at around 640oC.
87
Fig. 38 (a) XRD analysis of the iron ore fines and different fluxes
88
Fig. 38 (b) TGA analysis of the iron ore, different fluxes, and coal
89
4.2 Grinding and granulometry studies
Figure 39 shows the effect of grinding time on the P80 and mean particle
size (MPS) of the Noamundi iron ore fines ground in the laboratory ball mill.
Full particle size distribution for the corresponding mean particle sizes are
shown in Fig.40. From the results, it is clear that grinding the ore fines beyond
55 micron MPS, results in more amount of ultrafines (<25 micron), which are
believed to be detrimental to the pelletizing. These ultrafines increase the
surface area of the pelletizing mixture and decrease the porosity inside the
green pellets thus making their drying becomes more difficult at a given
temperature.
Higher surface area attracts more amount of water during balling and
makes them more plastic resulting their deformation in the pellet bed.
Deformed pellets decrease the bed voidage and thereby impede the flow of hot
gases across the bed. Improper drying patterns in the pellet bed results in
undesirable thermal spalling of green pellets generating more fines.
90
Fig. 39 Effect of grinding time on P80 and mean particle size during ball mill
grinding
0
20
40
60
80
100
120
140
2Hr 3Hr 3.5Hr 4Hr 5Hr
Part
icle
siz
e, m
icro
ns
Grinding Time
P80
Geomean particle size
Fig
. 4
0 M
ea
n p
art
icle
siz
e d
istr
ibu
tion
of ir
on
ore
fin
es g
rou
nd
fo
r d
iffe
ren
t
0
10203040506070
+25
0+1
50
+75
+63
+45
+37
+25
-25
Wt.%
Par
ticl
e si
ze, m
icro
ns
70
mic
rons m
ea
n s
ize
55
mic
rons m
ea
n s
ize
38
mic
rons m
ea
n s
ize
26
mic
rons m
ea
n s
ize
92
4.3 Green pelletizing studies
Effect of fineness of the pellet feed on the green pellet growth and quality
was studied by conducting laboratory pelletizing studies at varying fineness,
viz., % minus 45 microns ~ 60%, 65%, 70%, 75% and 80%. Green pellet quality
was estimated in terms of drop number, green compression strength and
moisture content to find out optimum fineness for the pelletizing.
4.3.1 Effect of pelletizing feed fineness on pellet size distribution
Figure 41 shows the effect of pelletizing feed fineness on the d50 of
green pellets for varying pelletizing durations. From the results, it is obvious that
with increasing the pelletizing duration, mean size of the pellet increases.
With increasing feed fineness, pellet mean diameter increases up to 70% minus
45 microns and decreases thereafter. This could be attributed to the fact that
with increasing fineness, the surface area of the feed increases, leading to
improved growth of the pellets due to layering mechanism. Beyond 70%
fineness, substantially high surface area, resulting from high amount of
ultrafines as shown in Fig. 40, promotes the formation of more number of nuclei
leading to decreased mean size of pellets.
93
Fig. 41 Effect of pelletizing feed fineness on the D50 of green pellets
0
5
10
15
20
25
5 10 15 20
D5
0 o
f g
reen
pell
ets
, m
icro
ns
Pelletizing time, minutes
60% <45 microns
65%<45 microns
70%<45 microns
75%<45 microns
80%<45 microns
94
4.3.2 Self-preserving curve of the Noamundi iron ore fines
D50 values for pellet feed with varying fineness, viz., minus 45 microns ~
60%, 65%, 70%, 75% and 80%, at 20 minutes pelletizing time, were found to
be 14.9, 16.4, 19.3, 13.7 and 16.1 microns respectively.
Figure 42 (a) shows the self-preserving behaviour of the Noamundi iron
ore fines with varying fineness. Figure 42 (b) shows the aggregated self-
preserving curve for the Noamundi iron ore fines. This curve can be used to
estimate the size distribution of the green pellets for a given ‘d’ value. A model
equation has been developed to correlate the D50 with the fineness of pellet
feed as below;
D50 = AF4 +BF3 + CF2 +DF + E, where F= Pellet feed fineness
Self-preserving curve is fitted with the following polynomial equation;
Y = aX3 + bX2 +cX + d,
where X= (d/d50), Y= Cumulative wt.% passing size “d”
Fig
. 4
2 (
a)
Self-p
reserv
ing
be
ha
vio
ur
of
the
No
am
un
di ir
on
ore
fin
es
-200
20
40
60
80
100
120
00.5
11.5
2
Cumulative wt. passing, %
d/d
50
60%
<45 m
icro
ns
65%
<45 m
icro
ns
70%
<45 m
icro
ns
75%
<45 m
icro
ns
80%
<45 m
icro
ns
Poly
. (6
0%
<45 m
icro
ns)
Poly
. (6
5%
<45 m
icro
ns)
Poly
. (7
0%
<45 m
icro
ns)
Poly
. (7
5%
<45 m
icro
ns)
Poly
. (8
0%
<45 m
icro
ns)
Fig
. 4
2(b
) A
ggre
ga
ted
self-p
reserv
ing
curv
e o
f th
e N
oa
mu
nd
i ir
on
ore
fin
es
y =
-265.2
1x
3 +
891.9
9x
2 -
845.0
3x +
247.6
9
R²
= 0
.94
0
10
20
30
40
50
60
70
80
90
100
00.5
11.5
2
Cumulative wt. passing, %
d/d
50
97
4.3.3 Effect of pelletizing feed fineness on green pellet quality
To study the effect of fineness on the green pellet quality, ground ore
with four different MPS was selected, viz., 26, 38, 55 and 70 microns. Fig.43
shows the effect of MPS on the green pellet quality. Results indicated that with
increasing fineness (decreasing MPS), the green compression strength (GCS)
of the pellets increased while the drop strength decreased. This could be
attributed to the fact that increased fineness decreases the porosity of the
green pellets thereby increasing their compression strength but at the same
time, associated stiffness leads to poor drop strength. Increased fineness, and
subsequent higher surface area, allowed for higher moisture content in green
pellets up to 38 microns MPS, and slightly decreased beyond as more moisture
leads to viscous or muddy green pellets with sticking/clustering tendency.
98
Fig. 43 Green pellet properties as a function of Mean Particle Size
0.6
0.8
1.0
1.2
1.4
1.6
1.8
4.0
5.0
6.0
7.0
8.0
9.0
10.0
70 55 38 26
Gre
en
co
mp
ressio
n s
tren
gth
, kg
/pel
Dro
p n
o, &
Mo
istu
re %
Mean particle size of pellet feed, microns
Drop No Moisture,% GCS,kg/pellet
