TALC/ STEATITE/ SOAPSTONE

Steatite, talc and soapstone are the three terms used in trade for one and the same mineral. Steatite is designated to indicate a purer variety of compact and massive talc while the use of word soapstone is restricted to a slightly impure variety of steatite containing 50 to 80% talc. Talc is a hydrated silicate of magnesium 3MgO, 4SiO2H2O.

In India steatite is mainly consumed in paper insecticide, cosmetic, fertilizer and ceramic industry. Steatite slabs are employed as linings for various kinds of stoves, ovens and fireboxes. Bricks made from crushed steatite, bonded with silicate for soda are used for the manufacture of furnaces in which crude lead bullion is softened before being de-silvered.

Over 90% of the world’s output of talc is marketed in the form of line powder and is widely employed in the paint industry as an extender, as filler in rubber, plastic, linoleum asbestos products, pesticides and insecticide dusts. It is also used in manufacture of ceramic required for the boards and spark plugs. It is also used as a refractory material. The pure white talc powder is used as a talcum powder.

During recent times, pure talc after calcining, called, ‘Lava’ has assumed a new importance in the manufacture of low loss ceramic materials required for high frequency insulation in all kinds of radio, radar, television and related instruments.

BIS has prescribed specifications for this mineral (IS: 380 – 1978) for use in paper, textile, filler for insecticide for preservation of rubber goods (French Chalk). French Chalk is largely used in the preservation of rubber goods, as filler for insecticides, in the manufacture of paper and as a sizing material in textile.

French Chalk shall be obtained from the natural mineral (talc/steatite or soapstone). While powder, free from extraneous impurities, except small quantities of substance naturally occurring in the mineral. It shall have a smooth and soapy feel. The free moisture and volatile matter in the material shall not exceed 0.5% by mass. The material shall have no residue when passed through 75 micron IS sieve of as mutually agreed to between the purchaser and supplier. The following requirements are to be adhered to:

1.

L. O. I. Percent by mass

4% (max.)

2.

Matter insoluble in HCL Percent by mass

95% (min.)

3.

Relative density at 27/27° C

2.7 to 2.9

4.

Chlorides as NaCl Percent by mass

0.5% (max.)

5.

pH of 10% solution      

8.5 (max.)

In addition to these, the French chalk for use in paper and textile should be also be following requirements.

6.

Grit percent by mass

0.02% (max.)

7.

Iron (as Fe2O3) Percent by mass          

0.3% (max.)

8.

Whiteness reflectance to blue light of wavelength 5040A

805 (min.)

9.

Copper or manganese by mass

0 - 0.5% (max.)

* This requirement should be tested only when required by the purchaser.

Specifications of talc for use in cosmetic, ceramics and paints are prescribed by different industries are as below:

Cosmetics: -   Finely pulverized talc of very high purity fineness should be retainable 0.1% max. on 150 microns IS sieves. Color should not changes when heated at 200° C for content acceptable up to 2ppm LOI 7% (max.) MgO to 30% (max.) Fe2O3 0.75% (max.) CaO should not before than 1.5%.

Ceramics: - Size required for this industry is 100 – 200 mesh size, LOI should be 2.5 to 6.0% free from and Al2O3, SiO2 up to 62 – 63% and MgO 30 – 31% preferred. Color may be white or of light cream color.

Paint: - Foliated, fibrous or smeller talc of preferable 300 mesh size preferred. It is used as a paint extender to paint. Talc for this purpose should have volatile matter preferably below 1%, LOI 4 to 7% SiO2 and MgO should be 40 – 56% and 20 – 32% respectively.

No end use classification of reserves was done in 1980 and 1985 inventory due to lack of data from exploration/exploitation agencies. Only the total reserves were given for 01.01.1980 and 01.01.1985.

The following end use specifications for estimation of reserves is recognized.

1.

Paper & Textile

Brightness
Fe2O3
L. O. I.
Color
Grit     

80% (min.) for blue light of wavelength 5040A
0.3% (max.)
4% (max.)
White
0.03% (max.)

2.

Cosmetic

Fe2O3
Grit    
pH

Heavy metal
Arsenic (as Al2O3)
Magnesium (as MgO % by mass)
L. O. I.
Acid soluble iron % by mass

0.3% (max.)
Nil
9.5 (max.)
20 (ppm) (max.) (As Pb)
2 ppm (max.)
20 (max.)
7.05 (max.)
1.5 (max.)

3.

Insecticide

L. O. I.
Fe2O3
Matter soluble in HCL

7% (max.)
1.5% (max.)
3% (max.)

4.

Ceramic

Color
L. O. I.
SiO2% by mass
Al2O3 % by mass
Fe2O3 % by mass
CaO % by mass
MgO % by mass

White or light Cream
6.5% (max.)
56% (max.)
2.5% (max.)
1.5% (max.)
3.5% (max.)
28 (min.)


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