Grades of asbestos

In the separation of asbestos from gangue by aspiration methods the fluffy particles of asbestos are the ones taken up by the air current, the sand and refuse falling back in the separating devices and either going to waste or being further treated to yield inferior grades of asbestos. 

The yield of retained fraction in the case of irregularly shaped particles was found to be 1.3-1.5 times that for particles with a rounded shape. In crushing operations, for example, particles of barite, quartz, feldspar, and magnetite form rounded particles, decreasing their adhesion. The wastes from low grades of asbestos contain irregularly shaped mineral dust particles, which adhere to the drum surface and are separated as the retained fraction [137]. 

Pads of a mixture of paper pulp and asbestos fiber are used in bacteriological filtrations. In sheet form it is employed in the laboratory for all kinds of filtration. Filter papers are made in many grades of porosity for use in porcelain and glass funnels. Industrially, paper in the form of sheets is used directly or as a precoat in filter presses. 

For firewater, steel pipes are used but corrosion products can block sprinklers. Cement asbestos pipes are utilized but pressure limitations restrict their use. For critical applications, including offshore oil installations, cupronickel alloys and even duplex stainless steels are used. Fire-retardant grades of fiber-reinforced plastics are now available. 

The NIST material SRM 1866a consists of a set of three common bulk mine-grade asbestos materials chrysotile, amosite and crocidolite, and one glass filter sample. SRM 1867 consists of a set of three imcommon mine-grade asbestos materials antophyllite, tremolite and actinohte. The optical properties of SRMs 1866a and 1867 have been characterized so that they may serve as primary calibration standards for the identification of asbestos types in building materials. 

Clays hazardous component of asbestos dust. A great variety of aluminium—silicate bearing rocks, plastic when wet, hard when dry. Used In pottery, stoneware, tile, bricks, cements, fillers and abrasives. Kaolin is one type of clay. Some clay deposits may include appreciable amounts of quartz. Commercial grades of days may contain up to 20% quartz. 

Craighead JE, Abraham JE, Churg A, et al. 1982. The pathology of asbestos-associated diseases of the lungs and pleural cavities Diagnostic criteria and proposed grading schema. Arch Pathol Lab Med 106 544-597. 

Talc ores can also contain a range of other minerals. In the United States, commercial talc is categorized into cosmetic grade, which is free of asbestos, and industrial grade, which may contain other asbestiform or nonasbestiform minerals, depending on intended use. For example, one important U.S. source of industrial-grade talc is a mixture referred to as tremolitic talc. Analysis by OSHA scientists shows that the tremolite in this talc is nonasbestiform. 

Disc, pulp, and sheet filters accomplish extreme clarification. Not infrequently their mission is complete removal of particles above a stipulated cut size, which may be much less than 1 pm. They operate over a particle-size range of four to five orders of magnitude, contrasting with two orders of magnitude for most other filters. It is not surprising, therefore, that they involve a variety of kinds and grades of filter media, often in successive stages. In addition to packs or discs of cellulosic, polymeric, or asbestos fiber, sheets of pulp, paper, asbestos, carded fiber, woven fabrics, and porous cellophane or polymer are employed. Sandwich-pack composites of several materials have been used for viscous-dope filtration. 

It was concluded from this series of experiments that the fire hazard of a building was not increased by a flame-retarded grade of polystyrene foam when covered with sprayed asbestos or mortar. 

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