Asbestos

Asbestos is a generic term given to a group of fibrous minerals, commercial varieties being (a) Serpentine Group chrysotile and (b) amphibole group Amosite, actinolite, anthophyllite, crocidolite and tremolite. The chemical composition of the asbestos mineral is as follows:

(a) Serpentine Group 

   
  Amosite MgFe6 (OH Si4O11)2
  Actinolite Ca2 (MgFe)5 (OH Si4O11)2
  Anthophyllite (MgFe)7 (OH Si4O11)2
  Crocidolite Na2 Fe5 (OH Si4O11)2
  Tremolite Ca2 (MgFe)5 (OH Si4O11)2

Asbestos owes its commercial utility due to combination of remarkable and unique properties like spinnability, incombustibility, and its resistance to heat, acids and alkalis, filtration property, tensile strength and power to absorb cement. The utility of asbestos is mostly dependent on its physical properties and not so much on its chemical composition.

Chrysotile is the most important commercial variety as it has wide industrial applications. Amosite and crocidolite in amphibole group find larger usage. Chrysotile, amosite and crocidolite can easily be separated in to fibers, thermal insulating sheets, tapes, paper, etc.

There is no BIS standard classification of asbestos. Its industrial use is linked with the type of asbestos. Chrysotile variety is more fibrous than amphibole, possesses good tensile strength and is use in the manufacture of asbestos fabrics, cement sheets, pipes and allied products. These products are used for brakes bands lining, insulation, fireproof clothing, etc. Short fibers are used with cement as binders for the manufacture of asbestos cement products. After chrysotile the other important varsities of commercial importance are amosite and crocidolite both of amphibole group. Amphibole asbestos generally finds use in heat insulation and treatment of acids. The anthophyllite and tremolite fibers even through of considerable length are too weak and brittle to spin. These varieties of amphibole group are generally used for boiler lagging, hard setting magnesia composition and as filler, also in asbestos paints and various asbestos molded articles.

According to the information available with IBM various classifications of chrysotile asbestos are follows in India but these are by and large based on fiber length. This are given below:

1. Grade 

As or A special
1" (24.4mm) fibers or larger.
As1
1" (25.4mm) fibers and larger but brittle compared to As or a special.
A
to 1" (19.05 to 25.4mm) fibers.
Al
to 1" (19.05 to 25.4mm) fibers but brittle compared to A.
A2
to 1" (19.05 to 25.4mm) fibers but brittle compared to Al.
B1
" to (16.35mm to 19.05mm) fibers.
B2
to " (6.35 to 19.05mm) fibers but brittle compared to B1
C
Below " fibers (96.25mm)
2. Special:
GradeA
Above 31.5mm
Grade
Between 19 and 31.5
GradeB
Between 6.3 and 19mm
GradeC
Between 6.3mm including power
GradeD
Dust.
3. Quebec standard asbestos testing machine classification of chrysotile asbestos according to groups.
Group No. 1
Group No. 2

Crude Asbestos

Milled Asbestos
Standard Designation of Grades Guaranteed minimum spinning tests.

Group No. 3 (Spinning fibers)
3 D
3 Z

10.6 3.9 1.3 0.3 0 8 - 6 2

Group No. 4    (Single fibers)
4 D
D Z


0 7 6 - 3
0 1.5 9.5 - 5

Group No. 5 (Paper fibers)
5 D
5 R


0 0.5 5 10.5 5
0 0 10 6

Group No. 6 (Waste)
6 D

0 0 7 9

Group No. 7 (Shorts or refuses)
7 D
7 W


0 - 0 5 11
0 0 0 16

Group No. 7 (Fleats)
7 FF
7 TF


No Test
No Test

Group No. 8 (Sand and gravel)
8 S
8 F


Less than 50 lb. per ft3 loose measure.
Less than 75 lb. per ft3 loose measure.

Group No. 9 (Gravel and Stone)
9 T

More than 75 lb. per ft3 loose measure.

The reserves of asbestos have been classified according to the variety of asbestos i.e., chrysotile, amosite, anthophyllite and mixed grade in the mineral inventory as on 01.01.1985 and earlier. The exploration agencies have not furnished information with regard to fiber length, tensile, strength, etc. Although to some extend the name of the mineral it self reflects its utility, the required specification for different end use ought to be kept in view classifying the reserves.

Due to multifarious uses of asbestos to which it is not a large number of tests have been evolved by the users as well as products to evaluate various physical properties to suit their own requirements. The properties have been mostly specified for chrysotile asbestos that is most extensively used variety. The most commonly used fiber length as given under item (I) above. Grading of other varieties of asbestos is not generally not done.

It is suggested that chrysotile asbestos may be classified in the following three grades depending up on the fiber length for the purpose of classification of reserves.

Grades 

Fiber Length
A Fiber length above 3/4" (19.05mm)
B Fiber length above 3/4" (6.35mm) but below 3/4 " (1905mm)
C Fiber length below 1/4" (6.35mm)
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