Dolomite
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: 10346–1982) 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              Al2O           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. Sea–water 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