KYANITE
Kyanite is an important mineral used for the production of super duty refractory material mullite (3Al2O3 2SiO2) used mostly in non-ferrous metallurgical and glass industries. Kyanite has the chemical composition Al2O3 SiO2. It is converted in to mullite and free silica when heated to about 1350o C. This conversion takes place with about 20% increase in volume and hence it is necessary to calcine kyanite before use. The outstanding advantages of refractory bricks made from kyanite are: - (i) Higher modules of rupture, (ii) lower Co-efficient of expansion, (iii) increased firing range and temperature, (iv) increased durability (v) negligible change in volume after prolonged heating, (vi) negligible change in volume and (vii) very low co-efficient of spelling.

The only industry in which kyanite is used is refractory industry. The BIS has not standardized any specifications. However, various specifications and terminology have ben in use by the refractory makers and the kyanite producers. Recently the Sub-Committee on Refractory Raw Material appointed by the Directorate General of Technical Development (DGTD) has recommended the following specifications.

 

 

Grade - I

Grade - II

1.

Al2O3

58% (min.) (Preferably 60%)

54% (min.)

2.

Fe2O3  

1.5% (max.)

1.5% (max.)

3.

P. C. E. (Orton)          

37 (min.)

36 (min.)

4.

Size

25mm to 300mm

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There is presently no technology for using granular kyanite either in refractory industry or in any other industry.

Future Trend: -
With the gradual depletion of high-grade limply kyanite, the need to beneficiate low-grade quartz kyanite, rock and use the concentrate, has been felt. The Indian Bureau of Mines have successfully beneficiated low-grade kyanite of Singhbhum district provides by Hindustan Copper Ltd., and have already supplied over 3 tonnes of the beneficiated product to CCCRI to make high alumina bricks and test their suitability there is also possibility of utilizing beach and kyanite in the manufacture of refractory.

The following basis has been followed for the classification of reserves in the inventory as on 01.01.1985.

High-grade

(+) 58% Al2O3

Medium-grade

50 to 58% Al2O3

Low-grade

40 to 50% Al2O3

Conditional reserves

Low-grade quartz kyanite rock.

After examining the specification prescribed by the Sib-Committee on refractory Raw Material of the DGTD, the group recommends the following end use classification of reserves.

Refractory Grade:

Al2O3: 54% (min.)
Fe2O3: 1.5% (max.)

P. C. E.: 36% (min.) (Orton)

Size: 25mm to 300mm

Conditional:   

Quartz kyanite rock and beach sand kyanite.

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