Natural “asbestos

For example, in bulk appHcations as thermal insulation, synthetic mineral fibers (glass or slag fibers) have adequately replaced natural asbestos fibers. In sprayed insulation coatings, asbestos fibers have been replaced, for example, by vermicuhte. As replacement for asbestos textiles, clothing made from aramid fibers or aluminized glass fibers is being offered (see High PERFORMANCE FIBERS). 

Soil may be contaminated with asbestos by the weathering of natural asbestos deposits, or by land-based disposal of waste asbestos materials. While disposal of waste asbestos to landfills was a common practice in the past, current regulations restrict this practice (see Chapters 5 and 8). 

The concentration of asbestos fibers in water (expressed as million TEM fibers per liter, MFL) varies widely. Concentrations in most areas are <1 MFL (EPA 1979b), but values of 1-100 MFL and occasionally higher have been detected in areas contaminated by erosion from natural asbestos deposits (EPA 1976 Kanarek et al. 1980) or from mining operations (Sigurdson et al. 1981). 

Most natural asbestos can deviate a little from this nominal composition. 

From the moment of conception of phosphate fibers, during all research and development of phosphate fibers, it was our expressed purpose to deliver a safe, useful, inexpensive mineral fiber to society. It cannot be questioned that our mission was noble. A profit motive existed a corporation ceases to exist when there is no profit, but profit motive was not the driving force behind this project. Because of our mission it would be both deceitful and cowardly to ignore safety issues that deal with natural asbestos. These issues will be considered for comparison to phosphate fibers when it is deemed necessary. If there were no safety issues a Phosphate Fibers Project should never have existed. Properties built into phosphate fibers, to insure their utility and safety, were chosen to overcome the problems associated with asbestos. The properties of the phosphate fibers must be compared with natural serpentine minerals, both negatively and positively, if this book is to serve a useful purpose. 

If the ore is metamorphic or igneous, are the right minerals present for natural asbestos contamination to be present ... 

The fibrous fluorosilicates obtained in our study from mining rocks did not concede by their properties to the fibrous fluoramphiboles synthesized from chemical reactants. Furthermore, the thermal properties and chemical resistance of fluorosilicates from mining rocks were better than those of natural asbestos croddolite. The decomposition temperature of fluorosilicates from mining rocks was by 120-180°C higher compared with the natural and synthetic hydroxyl amphyboles (Hodgson, 1965 Khachatryan, 1969 Grigor eva et al., 1975). 

We developed the method of synthesis of new fibrous crystalline materials, i.e. fluorosilicates of amphibole group, from natural feedstocks. By their texture these materials resemble natural amphibole asbestos, by chemical resistance in acidic and alkaline media, and by sorptive properties they do not concede to natural asbestos and synthetic fibrous fluoramphiboles obtained from reactants and pure minerals. By thermostability they substantially rank over natural amphibole asbestos (see decomposition temperatures in table 7). 

Silicon makes up 25.7% of the earth s crust, by weight, and is the second most abundant element, being exceeded only by oxygen. Silicon is not found free in nature, but occurs chiefly as the oxide and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, hornblende, asbestos, feldspar, clay, mica, etc. are but a few of the numerous silicate minerals. 

Instrumental Methods for Bulk Samples. With bulk fiber samples, or samples of materials containing significant amounts of asbestos fibers, a number of other instmmental analytical methods can be used for the identification of asbestos fibers. In principle, any instmmental method that enables the elemental characterization of minerals can be used to identify a particular type of asbestos fiber. Among such methods, x-ray fluorescence (xrf) and x-ray photo-electron spectroscopy (xps) offer convenient identification methods, usually from the ratio of the various metal cations to the siUcon content. The x-ray diffraction technique (xrd) also offers a powerfiil means of identifying the various types of asbestos fibers, as well as the nature of other minerals associated with the fibers (9). 

Asbestos fiber > 10 micrometer 7 million fibers per liter 7MFL Increased risk of developing benign intestinal polyps Decay of asbestos cement in water mains erosion of natural deposits... 

Asbestos, V natural fibrous form of several silicate minerals of the following types. 

Fibers in this category are composed of naturally occurring materials. A good example is asbestos. The most common type is chrysotile, representing more than 95% of world asbestos production. Chemically it is magnesium silicate (Mg6(OH)4 Si205). Today, use of this fiber is limited because long exposure to it may cause bronchial cancer. 

The technology of kerosene burners is quite mature. The most popular kerosene heater is the perforated sleeve vaporizing burner or range burner (Figure 1). It consists of a pressed steel base with concentric, interconnected grooves and perforated metal sleeves, between which combustion takes place. Kerosene is maintained at a depth of about 1/4 inch in the grooves. As the base heats up, oil vaporizes from the surface, and the flame lights from asbestos wicks. Combustion air is induced by natural draft. The flame is blue, and the burner is essentially silent, odorless, and smokeless. 

Figures 4-65, 4-66, and 4-67 show several units of the bag. The bags may be of cotton, wool, synthetic fiber, and glass or asbestos with temperature limits on such use as 180°F, 200°F, 275°F, 650°F respectively, except for unusual rnaterials. (See Table 4-12A and B.) These units are used exclusively on dry solid particles in a gas stream, not being suitable for wet or moist applications. The gases pass through the woven filter cloth, depositing the dust on the surface. At intervals the unit is subject to a de-dust-ing action such as mechanical scraping, shaking or back-flow of clean air or gas to remove the dust from the cloth. The dust settles to the lower section of the unit and is removed. The separation efficiency may be 99%-i-, but is dependent upon the system and nature of the particles. For extremely fine particles a precoat of dry dust similar to that used in some wet filtrations may be required before re-establishing the pi ocess gas-dust flow.

Magnesium (eighth most abundant element) is found principally as Mg+2 ion in salt deposits, particularly as the slightly soluble carbonate, MgC03, and also in sea water. The natural deposits of MgCOj with CaC02 are called dolomite. Magnesium is present as a cation in the asbestos silicates. 

Scientists and engineers at the University of Exeter are investigating whether natural fibers tike hemp and sisal could be used to make sustainable and eco-friendly brake pads [39]. The technology of brake pads turned green with the replacement of asbestos by aramids (hke Kevlar of DuPont) in the 1980s. Kevlar is very expensive and eco-friendly alternatives like hemp, jute, sisal, nettle, and flax are much, much cheaper. A breakthrough in this application will revolutionize brake manufacture and protect the environment. 

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