Dolomite
is a double carbonate of calcium and magnesium (CaCO3,
MgCO3). It is one of the important raw materials
used in the iron and steel, ferro-alloys, glass, alloy steels,
fertilizer industry, etc. Dolomite chips are also
used in flooring tiles. Specification of dolomite required
for different industries are given below:(1) Iron and Steel Industry:
Dolomite is used in iron and steel industry as refractory
raw materials and a flux. The BIS (IS: 103461982) has
prescribed following specifications of dolomite for use
in the manufacture of refractory bricks, felting materials
and for the blast furnace and sintering plants.
Grade |
Constituent
CaO MgO
Acid insolubles |
Size |
Grade-I
For making tar bonded Dolomite bricks for LD Converters |
30%
(min.)
|
20%
(min.)
|
4.5%
(max.) out of which SiO2 should not exceed
2%
|
50
- 80m
|
Grade-II
For use at blast furnaces/sintering plants and for
production of sintered dolomite for fettling purpose
in open earth furnaces. |
28%
(min.) |
18%
(min.) |
8%
(max.) out of which Al2O3
should not exceed 2% |
(i)
For blast furnace: 25
- 27m Tolerance: +-10%
(ii) For sintering plant: 0.60m +- 5% (iii)
For refractory: manufacturing plant: 70
80m Tolerance: +- 10% |
The
data pertaining to specifications of BF, SMS and refractory
grade dolomite in respect of each steel plant in the country
is given in table no. 1. The data has been supplied largely
by SAIL & TISCO.
Table
I Specifications of Dolomite Consumed in Different Steel
Plants
S.
No. |
Plant |
Constitute
|
BF |
SMS |
Refractory(%)
|
1. |
Bhilai
Steel Plant |
MgO
CaO
SiO2
Al2O3
Acid
insoluble
Size |
19
(min.)
29
(min.)
--
--
6
(max.)
0
-60m |
20
(min.)
30
(min.)
--
--
5
(max.)
60
100m |
20
(min.)
30
(min.)
1.7
(max.)
2.5
(max.)
--
50
80m |
2. |
Bokaro
Steel Plant |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
Size |
20
(min.)
30
(min.)
5
(max.)
--
--
--
25
to 80m |
--
--
--
--
--
--
-- |
20
(min.)
30
(min.)
1.5
(max.)
1.0
(max.)
--
--
5
to 25m |
3. |
Rourkela
Steel Plant |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
Size |
19
(min.)
--
--
--
--
8.09
(max.)
0
- 6m |
20
(min.)
--
2.5
(max.)
1.5
(max.)
1.5
(max.)
--
40
- 80m |
21
(min.)
--
1.5
(max.)
0.75
(max.)
1.00
(max.)
--
-- |
4. |
Durgapur
Steel Plant
(Dolo-chips) |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
L
O I
Size |
18
(min.)
--
6
(max.)
--
--
10
(max.)
--
-- |
20
(min.)
30
- 35
2.5
(max.)
.08
(max.)
1.0
(max.)
--
44.0
3
- 16m |
--
--
--
--
--
--
--
-- |
5. |
Indian
Iron & Steel
Company |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
Size |
19
(min.)
--
--
--
--
8.7
(max.)
25
to 75m |
19.5
(min.)
--
--
--
--
8.7
(max.)
50
to 125m |
--
--
--
--
--
--
-- |
6. |
Tata
Iron & Steel
Company |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
Size |
20
(min.)
--
--
--
--
6
(max.)
25
to 50m |
20
(min.)
--
--
3.5
(max.)
--
6
(max.)
25
to 50m |
20
(min.)
--
--
1.7
(max.)
--
11.5
(max.)
5
to 25m |
7. |
Vishveswaraya
Iron & Steel Company |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
Size |
--
--
--
--
--
--
-- |
21
- 22
30
31
1.70
(max.)
--
--
--
80
to 120m |
--
--
--
--
--
--
-- |
8. |
Visakhapatnam
Steel Project (Under con- struction) |
MgO
CaO
SiO2
Al2O3
Fe2O3
Acid
insoluble
Size |
19.80
(min.)
29.04
(min.)
3.8
(max.)
1.10
(max.)
1.20
(max.)
44.94
6
80m |
21.2
(min.)
30.5
(min.)
0.90
(max.)
0.30
(max.)
1.10
(max.)
46.00
25
- 50m |
21.20
(min.)
30.50
(min.)
0.90
(max.)
0.30
(max.)
1.10
(max.)
46.00
5
- 25m |
9. |
Kalinga
Iron works |
MgO
CaO
SiO2
Al2O3
Fe2O3
Total
insoluble
Size |
19.50
(min.)
8.00
(max.)
25
to 75m |
-- |
-- |
The
Sub-committee on Refractory Raw Materials appointed by
the DGTD in their report dated August 1985 has suggested
the following specifications of dolomite for its use as
refractory material.
Grade |
Constituents
MgO
SiO2
Al2O3 Fe2O3
|
Physical
Characteristics |
Grade-I
(for use in the LD converters) |
21%
(min.)
|
1%
(max.)
|
1%
(max.)
|
0.5%
|
The
minerals should be compact, homogeneous fine grained
and non decrepitating on calcination. |
Grade-II
(for fettling purpose) |
20%
(min.)
|
2.5%
(max.)
|
1%
(max.)
|
1%
(max.)
|
|
According
to the report mentioned above, the consumer steel plants
have by large agreed to the limitations specified by the
sub-committee. TISCO, however, wanted much more stringencies
in the level of acid insoluble. According to TISCO, the
acid insoluble for Grade-I dolomite should not to exceed
1.25% instead of 2.5% as stipulated by the Sub-Committee.
Dolomite used for fettling purposes by SALY sometimes
contain up to 5% acid insoluble. Use of dolomite containing
higher insoluble than those specified above results in
lower life of the refractory bricks and hinders the productions
of steel due to higher number of shut downs.
The
type of dolomite use in blast furnace, sinter, and pellet
plants is to same quality but it is of inferior grade
as compared to that used in steel melting shop. The BIS
stipulates to that dolomite for use in BF/SP should contain
MgO 18% (min.) CaO 28% (min.) and acid insoluble 8% (max.),
where as steel plants in practice, consume dolomite with
MgO 18% to 19.5%, CaO 29 to 30% and acid insoluble 6 to
10%. The steel melting shop requires superior quality
dolomite for fluxing purposes. The total insoluble should
be below 4%. The silica content should be as low possible
but in no case above 2.5%. The steel plants however use
dolomite with acid insoluble up to 6% and the case of
TISCO it is as high as 8.7%.
2.
Ferro Manganese:
The
specifications of dolomite for use in ferro manganese
are more or less similar to SMS grade dolomite. Physically
dolomite should be hard and fine grained because crystalline
dolomite gives fritting affects in the furnace Ferro alloys
industry actually consumes dolomite with MgO 19 to 20%,
CaO 28 to 30%, SiO2 2 to 5% and R2O3
2 to 2.5%.
3.
Glass:
High-grade
dolomite with as low content as possible is required by
the glass industry. Glass grade dolomite is typified by
its purity and consistency. The MgO and CaO content should
not vary by more than 0.5%. The chief undesirable impurities
are iron followed by chromite, manganese, vanadium and
lead, all of which color glass or they may cause defects
in the glass. For certain commercial colorless
glass, the Fe2O3 content up to 0.25%
is permissible, but for truly colorless glass, Fe2O3
content of 0.04% (max.) is sometimes specification.
The
BIS (IS: 997 - 1973) has prescribed specifications for
limestone and dolomite for glass for glass industry as
given below:
S.
No. |
Characteristics |
Requirement
on dry basis in % |
1. |
Silica
(as SiO2) |
2.5%
(max.) |
2. |
Total
Iron (as Fe2O3)
(a) Calcite or marble
(b)
Limestone
(c) Dolomite limestone & dolomite |
0.05
(max.)
0.10 (max.)
0.15
(max.) |
3. |
Lime
(as CaO) |
53.00
(min.) |
4. |
Total
lime and magnesia (as CaO & MgO) |
54.50
(min.) |
In
case of dolomite limestone or dolomite, requirement of
lime and CaO may be fixed by mutual agreement between
purchaser and the suppliers.
When
the material is supplied in powder form, the grains size
distribution of the materials shall be between the following
limits:
a.Materials rfbf7f3etained on 2.00 mm IS sieve nil.
b.Materials
passing 125 micron IS sieve 25% by mass, max.
4. Fertilizer Industry:
Dolomite
for use in fertilizer industry must have CaCO3
+ MgCO3 90% (min.) and SiO2 5% max.
Inferior
grade dolomite limestone of 15 20% MgO can be used as
soil conditioner. Ground dolomite, 50% of which must be
100 BS mesh size be considered suitable as a soil conditioner
if it is applied at the rate of 2-3 ton per acre.
The
BIS (IS: 5407 Part 2-1985) has prescribed the specifications
of limestone and dolomite to be used as soil amendments.
According to this specification, 90% by mass of the materials
should pass through 2m (10mesh) sieve and 50% by mass
of materials to pass through 250 micron (60
mesh) sieve. The neutralizing value (express as CaCO3)
percent by mass shall not be less than 70%. The total
lime and magnesia (as CaO + MgO) shall not be less than
50% by mass and the materials shall not contain more than
5% moisture by mass.
5.
Lime:
The
dolomite for the manufacture of lime should contain CaCO3
58 75%, MgCO3 28-48% and other constituent
should be less than 3%.
6.
Magnesium Metal:
Calcined
dolomite of 200mesh size is used in the extraction of magnesium
metal. For this purpose calcined dolomite must contain MgO,
40.5%, CaO 58.10%, Fe2O3 0.8% and
insoluble 0.6%.
7.
Fertilizer / Extender:
For this purpose, dolomite must be very pure and in particular
be free from coloring impurities such as oxides of iron,
chromium, Manganese, etc.
8.
Seawater Magnesia:
The
essential requirements of dolomite raw materials in particular
for this purpose are that the impurities of iron oxide and
alumina are kept to minimum.
In
the mineral Inventory as on 01.01.1980, and 01.01.1985
the reserves have been classified in to BF, SMS, BF &
SMS mixed, Refractory, B. F., SMS, Refractory mixed, Glass
and others as reported by exploration and exploitation
agencies. However, in most cases the basis of classification
is not known. It is problems that the only chemical analysis
dates were taken in to consideration.
The
following end use grades for the purpose of
classification of reserves are prevalent.
9.
Refractory:
i |
L.
D. grade:
MgO
SiO2
Al2O3
Fe2O3
|
21%
(min.)
1%
(max.)
1%
(max.)
1%
(max.) |
|
SMS
& Physical: |
Fine
grained & nom decapitating on calcination. |
ii |
Fertilizer
grade:
MgO
SiO2
Total
|