Other Asbestos-Like Minerals

There are many more minerals that could be discussed ranging from wollas-tonite, to attapulgite clays, or zeolites. Some mineral zeolites are fibrous asbestos types of crystals. Natrolite, Na2Al2Si30io-2H20, is called Fibrous Zeolite. Zeolites are used extensively in detergents, throughout the world, as a poor substitute for phosphates, but it is unlikely that synthetic zeolites will cause problems as an 

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Desired minerals are always mixed with other rocks that must be separated. In many cases, particularly for more valuable metals, the mineral that is sought is less than 1% of the ore. This requires processing of the ore, a procedure called beneficiation, which produces relatively large amounts of finely divided by-product rock. For economic reasons, beneficiation is usually carried out at the mine site with the residues returned to the mine or left in piles at the site. As a result, water pollution problems may develop from the leaching of mine spoils. Some communities in the vicinity of lead mines have been contaminated by lead from mine residues, with particular concern over the health of exposed children. Spoils from iron mining in Minnesota have contaminated water with an asbestos-like mineral associated with the iron ore, requiring remedial action that has cost millions of dollars. Enormous piles of tar-contaminated sand are left over from the extraction by hot water of heavy crude oil from tar sands in the Canadian province of Alberta. 

Figure 9 Plots showing the calculated mineral saturation indices as a function of pH for hydroxylapatite, quartz, and various asbestos-forming minerals in electrolyte solutions approximating the electrol)he compositions of lung fluids (approximated by interstitial fluids, upper plot) and intracellular fluids (lower plot). Electrolyte concentrations used as input were taken from Table 4. The CO2 partial pressure was fixed at the value for venous plasma for each speciation at a different pH. Organic species such as amino acids and other organic acids were not included in the calculations, but likely would have the effect of decreasing the calculated saturation indices somewhat due to their...

Many properties of silicates can be understood in terms of the type of network lattice formed. In the one-dimensional networks, shown in Figure 17-8, the atoms within a given chain are strongly linked by covalent bonds but the chains interact with each other through much weaker forces. This is consistent with the thread-like properties of many of these silicates. The asbestos minerals are of this type. 

Asbestos It is not the name of a distinct mineral species but is a commercial term applied to fibrous varieties of several silicate minerals such as amosite and crocido-lite. These extremely fine fibers are useful as fillers and/or reinforcements in plastics. Property performances include withstanding wear and high temperatures, chemical resistance, and strengths with high modulus of elasticity. When not properly handled or used, like other fibrous materials, they can be hazardous. 

The structural variety of the compounds that form fibers is as diverse as their chemistries. From glasses (fiberglass), and partially crystalline materials (carbon), to special three-dimensional arrays, including polymers, the small, elongate solids may have aspect ratios up to 5000. From our research and compilation (Appendices 1, 2) we noted many mineral and synthetic compounds that have structures characterized by basic linear units. Amphi-boles, the major mineral group mined as asbestos, are characterized as doublechain structures. Many of the minerals in Appendix 1 are polymorphic (di-or trimorphs), and where one member of a mineral series has been described as fibrous the others in the same series are likely to be able to grow as fibers as well. Probably all compounds with similar structures and compositions, mineral or synthetic, can form fibers, even though they are not presently listed. It is also clear that fibrous formation is not confined to compounds with linear structural units indeed the variety of crystalline structure patterns is remarkably diverse. 

Curved structures are not only limited to carbon and the dichalcogenides of Mo and W. Perhaps the most well-known example of a tube-like structure with diameters in the nm range is formed by the asbestos mineral (chrysotil) whose fibrous characteristics are determined by the tubular structure of the fused tetrahedral and octahedral layers. The synthesis of meso-porous silica with well-defined pores in the 2-20 nm range was reported by Beck and Kresge.6 The synthetic strategy involved the self-assembly of liquid crystalline templates. The pore size in zeolitic and other inorganic porous solids is varied by a suitable choice of the template. However, in contrast to the synthesis of porous compounds, the synthesis of nanotubes is somewhat more difficult. 

CaCOs compounds. Wollastonite s fiber-like shape provides similar properties as those of the glass fibers discussed below, and also like glass, its abrasiveness can damage processing equipment. However, unlike other mineral fiber, asbestos, its particles are nonhazardous [1-1, 3-4, 7-6, 7-13, 7-15]. 

The serpentine form of asbestos, known as chrysotile, is mined chiefly in Canada and the former Soviet Union more than 90% of the asbestos used in the United States is in this form. The amphi-bole crocidolite is mined in small quantities, mainly in South Africa. The two minerals differ greatly in composition, color, shape, solubility, and persistence in human tissue. Crocidolite is blue, relatively insoluble, and persists in tissue. Its fibers are long, thin, and straight and they penetrate narrow lung passages. In contrast, chrysotile is white, and it tends to be soluble and disappear in tissue. Its fibers are curly they ball up like yarn and are more easily rejected by the body. Scientific studies of many types and by groups in many countries have shown that chrysotile asbestos is significantly less of a health hazard than other types. It is important to note that almost all manufactured materials in the United States contain only this form of asbestos. 

A second class of silicate mineral called asbestos is a serpentine mineral, chrysotile. It is a magnesium silicate hydrate, Mg6[Si40n(0H)6]H20, with a chemical composition similar to talc, Mg3Si40io(OH)2. There is at least a plausible argument that chrysotile should not have been included with other minerals named asbestos from chemical, health, and legal considerations. There is small doubt that the amphiboles are much more likely to cause difficulties. A study of two cement pipe plants in New Orleans revealed some interesting results. In one... 

Mediators of both the infiammatoiy and fibrotic responses have been associated with exposure to oxidants. Similarly, mediator release after incubation of cells with silica and asbestos can be the result of oxygen-based free radicals catalyzed by iron associated with the mineral oxide (Fig. 1). The increase in arachidonic acid metabolism after exposures of cells to particles and fibers can result from the eooxidation of arachidonate by metal-catalyzed oxidants. This is a lipid peroxidation that can be mediated by free radical production by the dust (83). In support of an association between metal-catalyzed oxidant generation and arachidonic acid products, the release of LTB4 by alveolar macrophages can increase with the eoneentrations of iron complexed to the surface of silica and asbestos (84). Similarly, the eellular release of eytokines postulated to participate in the infiammatory and fibrotic responses ean be associated with exposures to metal-dependent radicals (see Fig. 1). TNF-a produetion by alveolar macrophages after mineral oxide exposure can be inhibited by both the metal chelator deferoxamine and hydroxyl radical scavengers (74). The release of other cytokines pertinent to silica and asbestos exposure ean also be responsive to oxidative stress (85,86). The release of these pertinent mediators after dust exposures is likely to be controlled by oxidant-sensitive promoters such as nuclear factor (NF)-kB (87). After exposure to silica and asbestos, NF-kB can function as a promoter... 

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