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close this bookAsbestos Overview and Handling Recommendations (GTZ, 1996)
close this folderPart II. Asbestos
close this folder1. Introductory part: Asbestos - Deposits, uses, types, characteristics
View the document(introduction...)
View the document1.1 Types, deposits, and uses of Asbestos, chemical structure
View the document1.2 Mineralogical and mechanical properties of Asbestos
View the document1. 3 Analytical methods of determining Asbestos fibers

(introduction...)

The different Asbestos minerals in the Earth's crust, their deposits and characteristics are presented in detail in this part. In particular, the minerals concerned are: chrysotile, amosite, crocidolite, anthophyllite, tremolite und actinolite, which are categorized on the basis of their chemical composition and fibrous structure as serpentine Asbestos (chrysotile) or amphibole Asbestos.

The following presents a classification of Asbestos minerals and a description of the chemical composition, physical properties and specific figures for Asbestos fibers. In addition, the important mines for the different Asbestos fibers are named.

1.1 Types, deposits, and uses of Asbestos, chemical structure

Asbestos is a collective term for a group of silicate fibers. The aforementioned six different Asbestos minerals can be categorized on the basis of their chemical composition (primary cation) and their crystalline and fibrous structure into the groups amphibole or serpentine Asbestos.

Serpentines have a leafy or layered structure. Amphiboles have a chain-like crystalline structure.


Figure 1: Classification of Asbestos Types


· Serpentine Asbestos:

Serpentine Asbestos (chrysotile, as most important type, and antigorite) is leaf structured and consists of fine fibers. The leaves consist of alternating layers of silicate tetrahedron (SiO4), which are held together by hydroxide groups (OH) and magnesium ions. The structure is similar to that of serpentine minerals.

Chrystolite Asbestos:

Chrysotile Asbestos fibers have a very small diameter, are tubular, very soft and bendable. The individual fibrilles have a diameter of 100 - 250 Angstrom (A). Chrysotile originates from the hydrothermal decomposition of ultra basic, primarily olivine-containing rock; particularly severe weathering occurs in subtropical and tropical climates.

Mines are located primarily in Ural (Bazenovo, Asbest, Dzetygara, Kiembaj), in Canada (Quebec, Ontario, British Columbia, New Foundland), as well as in South Africa (Zimbabwe, Botswana, South Africa).

Chrysotile, or white Asbestos, is the most widely used form of Asbestos. In the USA cat 95 % of all Asbestos types used in buildings is white Asbestos. Of the total German use of Asbestos, 96 % is chrysotile (1976).

· Amphibole:

Amphibole Asbestos types have a chain-like crystal structure, which stipulates their fibrous nature. Individual fibers have larger diameters, are straight, firm and hard, but elastic.

Amosite:

Amosite is a long-fibered Asbestos. Fiber length can reach 35 mm. Due to its needle-like structure it is a very dangerous type of Asbestos. On the basis of quantity (ca. 1% of all used types in Germany in 1976), amosite or brown Asbestos is second to only chrysotile as the most common form in buildings. It is primarily used in the manufacturing of light, fire-proof insulation sheets. The important mining areas are in South Africa.

Crocidolite:

The blue Asbestos is the most hazardous type of Asbestos and is primarily applied in pressure resistant pipes made of Asbestos cement. Economically, it is the most important type of amphibole (amphibole represented 3% of all Asbestos used in Germany in 1976, whereby > 90 % was from the manufacturing of pressure resistant Asbestos cement pipes). The diameter of fibers is very small: 0.1 - 0.2 mm; the surface of crocidolite consists of SiO4 - tetrahedrons. Important deposits are in South Africa and in West Australia.

· Mining:

The world production of Asbestos increased steadily until the early 1980's, since the economic value of the fibers stood in the foreground, although the risks of Asbestos have been known at least in part since cat 1930. The total world production of Asbestos peaked around 1976 at approximately 5.2 million tons (Mt). Currently the trend shows a steep decline (1986: 4.1 Mt, 1991: 3.5 Mt., US Bureau of Mines). The main producing and consuming countries were (see also the maps in Annex 1):

Table 1: Percentage of Asbestos Production among the Main Producing and Consuming Countries

Mining

(1976)

(1979)

(1987)

(1991)

Canada

(30 %)

(27 2 %)

(15.7 %)

(19.7 %)

USSR

(44 %)

(43.9 %)

(60.3 %)

(57.3 %)

South Africa

(12%)

(6.1 %)

(3.2 %)

(4.3 %)

Source: own compilation from different sources

Other important producing countries are currently: Brasil, Zimbabwe, China, Greece, India, Swaziland, Columbia and Japan. Meanwhile, the market shows a surplus of supply. The known worldwide supply of Asbestos ores will be sufficient to last far into the next century.

The largest part of Asbestos production is chrysotile (over 90 %), the remainder primarily crocidolite (ca. 4 %). The types amosite, anthopyllite, tremolite and actinolite are quantitatively (together < 2 %) of subordinate importance.

The annual tonnage, location and type of Asbestos at each mining site can be found in Tables 2 through 4 and the respective references.

Some of the most important Asbestos deposits are listed in Table 2.

Table 2: Asbestos Deposits

Country

Location

Asbestos Type

Rock Formation

References

USSR

S-Central Ural Sverdlosk, Tuva& Kustanay Region

C

US

Harben & Bates (1984)

Canada

Eastern Quebec

C

US

Lamarche & Riordon (1981)


N-E Quebec

C

US

Hanley (1987), Stewart (1981)


Newfoundland

C

US

Williams et al. (1977)


British Columbia

C&T

SP

Burgoyne (1986)

USA

N-Central

C

P&D

Chidester et al. (1978)


Vermont

C

SP

Mumpton & Thompson (1975)


California

C&T

AL

Harben & Bates (1984)


Arizona

An&C

U

Ross (1982), Puffer et al. (1980)


Georgia-Maryland New Jersey

C&T

AM

Germine & Puffer (1981)

Yugoslavia

Croatia

C

SP

Harben & Bates (1984)

Greece

Macedonia

C

H&I

Harben & Bates (1984

South Africa

Transvaal

C

AS

Dryer & Robinson (1981)


Transvaal

A&Cr

BI

Ross (1982)


Lyndenburg N-Cape Province

Cr

BI

Dryer & Robinson (1981)

Swaziland

Northern

Region

C

S&C Harben & Bates (1984)

Zimbabwe

Eastern Bulawayo

C

D&P

Harben & Bates (1984)

Australia

New South Wales

C

H&D

Butt (1981)

Finland

Karelian Mts.

An

US

Ross (1982)

Italy

Western Alps

C&T

S

Ross (1982)

China

Various Locations

C&T

U&Do

Hodgson (1986)

Brasil

Goias State

C

D&P

Beurian & Cassedanne (1981)

Asbestos Type

C = Chrysotile
T = Tremolite
An = Anthophyllite
A = Amosite
Cr = Crocidolite

Rock Formation

Se = Serpentine Rock
P = Periodotite
AS = Altered Sedimentaries
H&I = Harzburgite & Iherzolite
Do = Dolomite
AL = Altered Limestone
BI = Banded Ironstone
SP = Serpentinized Periodotite
D = Dunite
AM = Altered Marble
S&C = Altered Schist&Carbonates
US = Ultramafic Serpentinite
U = Ultramafic Rock

Source: Schreier, H.: Asbestos in the Natural Environment, Studies in Environmental Science, Amsterdam 1989

Table 3: Estimated Production Capacity of Asbestos Useable in Industry

Country

Asbestos (in Tons)

USSR

3.100.000

Canada

1.500.000

South Africa

400.000

China

300.000

Zimbabwe

300.000

Brasil

200.000

Italy

200.000

USA

120.000

Greece

100.000

Australia

100.000

Germany

90.000

Swasiland, Cyprus, India, Japan, Yugoslavia, Columbia, Turkey, etc.

> 50 000

(for each country)


Source: Schreier, H.: Asbestos in the Natural Environment, Studies in Environmental Science, Amsterdam 1989

· Processing:

In the western world 75% of Asbestos rock is produced in openpit mining with blasting, and in total 85% of the worldwide Asbestos rock is produced in this manner. Mining production refers to the amount of fiber gained from Asbestos mills. The mass content of fibers in rock lies around 3 - 10%. The crude rock is crushed in the mines with breaking and pan grinding operations and separated into fiber bundles. This is a largely mechanical process, which consists of many steps of screening and air sifting. These procedures are illustrated in Figure 2.

The conditions in the important Asbestos producing countries in Africa are markedly different. In Simbabwe and Swasiland Asbestos production is performed exclusively through deep mining, in the Republic of South Africa to 95% extent. Asbestos production in China is also 40% underground mining. In Canada the percentage of deep mining for Asbestos lies just above 5%, in the former USSR deep mining is not considered to play a significant role.


Figure 2: Illustration of Asbestos Mining Along a Slope and Dry Processing (Source: 1980)

· Further Processing Asbestos Cement

Asbestos cement is a fiber composite material made of primarily chrysotile Asbestos and cement and in some cases other additives, such as quartz, pigments, etc.. The first technical and economic procedures for manufacturing this construction material were developed by Hatscheck (1900).

Currently, even in the developing countries the large-scale technical procedures used are exclusively variations of that introduced by Hatschek, which is according to paper technology.

The manufacturing of Asbestos cement pipes according to Mazza and Mattei (1913) is also based in principle on the suggestions of Hatscheck.

In a continuous procedure, Asbestos, spread open to fine fibers, is mixed with cement and a great deal of water into a thin liquid suspension and then thickened to paper-like sheets as the excess process water is removed via felt cloth. Depending on the type of production, further manufacturing operations are performed with presses for sheets or with wrapping machines for pipes. (A detailed description of the historical and technological development of Asbestos cement is provided by Klos, 1967)

Table 4: Asbestos Percentages and Types in the Most Important Asbestos Cement Forms

Asbestos Cement Products

Asbestos content in matter wt -% relative to solid

Type of Asbestos

Supplements (outer Cement)

Standard sheets ( flat sheets for walls. roofs, etc., corrugated sheets for roofing) and pipeline fittings

9 -12

Chrysotile

none

Pressed pipes - sewer- and drainage pipes

12 - 15

Chrysotile (approx. 85%);
Crocidolite (approx. 15 %)

none

Light construction sheets (primarily for fire protection purposes)

15 - 30

Chrysotile; Amosite

Cellulose; Pearlite (Calcium silicate)

White sheets

6 - 9

Chrysotile

Quartz

Source: UBA - Report 1/80

· Consumption

In 1979, the countries with the highest consumption of Asbestos in percent of the total were:

Table 5:Asbestos Consumption ( 1979)

USSR

(31.7 %)

USA

(11.3 %)

Source: own compilation

From the maps in Annex [(with 1978-1981 data from the BGR/DIW study), it is apparent that the use of Asbestos materials primarily took place in the industrial nations. From this standpoint it can be argued that Asbestos is not a specific problem of the developing countries. Upon further analysis, however, it becomes clear that the present situation is different from that in 1981. Furthermore, in the study (BGR/DIW) no statements were made regarding how many Asbestos products are exported to the developing countries, leading to health risks there.

1.2 Mineralogical and mechanical properties of Asbestos

The majority of application areas for Asbestos result from the synthesis of different technical properties:

· high tensile strength
· resistance to moisture
· resistance to heat
· flexibility, elasticity
· cability of being spun
· flame retardant, fireproof
· insulation capacity
· good binding capability in many inorganic and organic binding materials
· chemical resistance (depending on Asbestos type, resistant against acids or bases)

The different Asbestos minerals demonstrate different characteristics influencing:

· potential application possibilities,
· the attractiveness of substances for multi-purposes,
· the resulting health hazards from the use.

In view of the above differences, there are different evaluation criteria among Asbestos minerals.

From a technological standpoint, chrysotile or white Asbestos demonstrates the most valuable characteristics, such as very high flexibility, fineness of fibers, capability of being spun, heat resistance, and alkali resistance. White Asbestos is therefore particularly important in addition to blue Asbestos (crocidolite) and amosite.

Table 6 shows an overview of figures for the most important types of Asbestos. More information can be found in the health and safety data sheet for Asbestos cement in the UK (Annex 2), and in an excerpt from the Compendium of Environmental Standards (KUSt, Katalog umweltrelevanter Standards), BMZ/GTZ (Annex 7).

1. 3 Analytical methods of determining Asbestos fibers

A number of techniques have been developed for the analytical determination of Asbestos fibers. The determination is generally performed in three steps: the sampling, fiber counting and determination of the type of fiber. These steps are presented below along with the most widely used determination procedures.

Sampling

For the determination of Asbestos in fluid media (air, water), a defined volume of the media is drawn through a filter, upon which the fibers are deposited. The typical filter materials are gold-coated track-etched membrane filters or cellulose membranes. In order to determine the number of fibers in solids (e.g. in material samples or in dust), the sample can be directly used.

Fiber Counting

Generally, microscopic techniques are applied for fiber counting. The optical counting of fibers proceeds in the simplest case under the phase contrast microscope. Since the optical resolution can at best include structures of 1 mm in size, whereas in airborne particulates the main fraction of fiber bundles has sizes ranging from 2 - 0.2 mm, phase contrast microscopy can at best be used as a screening method in cases of very high fiber concentrations (e.g. for the investigation of material samples). In the case of investigations of drinking water, phase contrast microscopy is totally unsuitable (sizes around 0.06 mm).

Sufficient resolution can be achieved with using scanning electrion microscopy (SEM) or with transmission electron microscopy (TEM). These procedures are relatively expensive, however, and require extensive measures in the preparation of the samples, in addition to well-educated operating personnel.

Asbestos fibers in particulate samples can also be determined on the basis of their characteristic absorption lines using infrared spectroscopy. However, the determination limit lies relatively high at 1-5%, depending on the type of fiber.

Table 6: Data on the Most Important Types of Asbestos


Serpentine

Amphibole


Chrysotile

Anthophyllit

Crocidolite

Actinolite

Tremolite

Amosite

Chemical formula

Mg3(OH)4Si2

(Mg,Fe2+)7

Na2(Fe2+,Mg)

(Ca,Na)2

Ca2(Mg,Fe)5

(Fe2+,Mg.Al)7


O5

(OH)2Si8O22

3Fe23+(OH)2

(Fe,Mg,Al)5

(OH,F)2Si8O22

(OH)2Si, Al)8




Si8O22

(OH, F)2


O22





(Si, Al)8O22



Chemical composition in (%)







SiO2

35 - 44

52 - 64

49 - 57

0 - 63

50 - 63

45 - 56

MgO

36 - 44

25 - 35

3 - 15

18 - 33

18 - 33

4 - 7

Al2O3, Iron oxide

0 - 9

1 - 10

20 - 40

2 - 17

2 - 17

31 - 46

CaO, Na2O

0 - 2

0 - 1

2 - 8

1 - 10

1 - 10

1 - 2

H2O

12 - 15

1 - 5

2 - 4

1 - 4

1 - 4

1 - 3

Physical properties

fine light fibers

prismatic crystal and fibers

long, brittle fibers

prismatic crystal and fibers

prismatic crystal and fibers

prismatic crystal and fibers

Color

white, grey, greenish

grey-white

blue

green

white, grey- white, greenish

ash grey

Texture

soft to rough, mostly silky

rough

soft to rough

rough

rough

rough

Flexibility

very high

low

good

low

low

good

Mohs-strenght

2,5 - 4

5,5 - 6

5,5 - 6

6

5,5 - 6

5,5 - 6

Fiber diamiter (nm)

18 - 30

60 - 90

50 - 90

0 - 90

60 - 90

60 - 90

Resistance (N/nm2)

210 - 560

< 28

280 - 420

7

7 - 56

70 - 140

Modulus of elasticity(N/nm²)

160.000

-

190.000

-

-

160.000

Melting point (C)

1.500

1.480

1.180

1.393

1.320

1.400

Specific heat (kj/kg C)

1,1

0,85

0,8

0,9

0,9

0,8

Surface (m²/g)

10 - 60

7

10



9

Thickness g/cm³

2,2 - 2,6

2,8 - 3,2

2,8 - 3,6

3,0 - 3,2

2,9 - 3,2

2,9 - 3,3

Breeking index







n (alpha)

> 1,53

> 1,59

> 1,68

> 1,61

> 1,60

> 1,64

n (gamma)

< 1,57

< 1,63

< 1,70

< 1,65

< 1,63

< 1,69

pH-Value

9,5 - 10,3

9,4

9,1

9,5

9,5

9,1

Electrical charge in aqueous suspension

+

-

-

-

-

-

Stable towards acids

unstable

very good

good

fairly good

good

good

Alkali resistant

very good

good

good

good

good

very good

capability of being spun

easily spinnable

barely spinnable

mostly spinnable

unspinnable

unspinnable

partially spinnable

Source: Umweltbundesamt (Publ.): Analysis of the Asbestos Industry, written by the Battelle-lnstitut Frankfurt e.V., Report 4/78, Berlin 1978

Determination of the Type of Fiber

The determination of the type of fiber and particularly the differentiation from other inorganic fibers can be directly performed under the transmission electron microscope using small angle electron diffraction (SAED). Another possibility is the energy dispersive X-ray analysis (EDXA). The arising diffraction or energy spectra are evaluated using numerical methods. The required infrastructure is relatively expensive and places high requirements on the operating personnel. The previously common use of phase contrast microscopy to determine the type of fiber in airborne particulates based on fiber geometry is unsuitable, due to low resolution.

The type of fiber can also be identified with infrared spectroscopy based on the characteristic absorption bands of chrysotile and amphibole types. This method is inexpensive, but only applicable if the fiber concentration in the sample exceeds about 1-5 percentage by weight.

In Germany there are two accredited American procedures for the measurment of Asbestos fiber concentrations. These VDI Guidelines are for fiber in particulates and in indoor air and replace the previously common phase contrast microscopy procedures:

VDI Guideline 3861

This guideline specifies a procedure for the determination of the fraction of Asbestos fibers in particulate mass, e.g. as they occur in air vents. The sampling proceeds through deposition of particulates onto a nitro-cellulose filter. This filter undergoes cold ashing, and the fiber concentration is then determined using infrared spectroscopy with the help of the KBr Pressure Technique. The analytical result is obtained as the weight fraction in g/kg.

VDI Guideline 3492

This guideline specifies a procedure for the determination of Asbestos fibers in indoor or outdoor air. The Asbestos fibers from a defined air volume are deposited onto a gold-coated track-etched membrane, which is then cold-ached, and subsequently the fibers are counted under the scanning electron microscope. The type of fiber is determined using energy dispersive X-ray analysis.

Due to the cost of this analytical procedure, it may be assumed that in developing countries at best the phase contrast microscopy and infrared techniques are available (cost of equipment < 50,000 DM). The electron microscopy procedures (costs >>100,000 DM) would currently be applied exclusively in industrial nations. Therefore, in developing countries it is questionable whether any existing limits, e.g. for indoor air concentrations, can be monitored.