Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 67

Like other capital‐intensive activities, glassmaking plants traditionally are local industries so as to minimize transportation costs of both raw materials and finished products. Although not necessarily rare geologically, however, certain minerals are not commonly found in commercially exploitable amounts with the consequence that they have to be procured globally, national policies sometimes applying heavy, protectionist custom fees to limit exportations. This situation applies, for instance, to lithium, boron, and some aluminum carriers.

In glassmaking, lithium occasionally serves as an additive (flux) for the production of standard soda‐lime silica glasses, but it is mainly used for glass‐ceramics to form the β‐spodumene [LiAlSi₂O₆] phase that gives them very low thermal expansion coefficients (Chapter 7.11). But the price of Li₂O raw materials has been boosted – it has actually almost tripled – during the last decade, driven by the dramatically increasing demand for Li‐ion batteries (Chapter 9.5). Among the available Li₂O raw materials (Table 1), Li from brines is mostly used to manufacture Li‐carbonate or hydroxide (battery‐grade raw materials), whereas mineral Li is incorporated into glass and ceramics. Concentrates of both minerals, spodumene and petalite, are actually crucial sources for the glass industry [17, 18], which does not require as high a purity as Li‐ion battery makers. These Li‐silicate sources are abundantly available in Australia, China, the United States, and Canada, but much rarer and mostly unexploited in Europe (Austria, Finland, Ireland, Portugal, and Spain) where most of the glass‐ceramic industries are in fact located.

As for boron, this element is important for the production of reinforcement fibers (Chapter 1.5) and for insulation (Chapter 9.3) and textile glasses. Borates are found in Turkey, the United States, China, Russia, and South America. Turkey is the world's biggest producer and holds the largest reserves. The United States ranks second both in terms of reserves production, with about 40% of the market [19]. In this case too, the heterogeneous distribution of boron sources translates into high transportation costs as a component of the raw‐material supplies.

Figure 7 Increases of iron contamination caused by grinding of quartz made with steel‐bearing jaws to shift the particle size distribution. (a) Iron contents associated with the PSD curves of quartz sand and flour ground. (b) Alignment of steel particles in the magnetic field of the separator during the deferrization step of raw‐material beneficiation. Picture scale of 0.5 m.

Concerning aluminum, bauxites and laterites are used as Al‐carrier in standard industrial glasses. The main and largest exploited ores, representing more than 90% of the reserves, are located in Western Africa (especially Guinea), Brazil, Central America and the Caribbean (Jamaica, Trinidad and Tobago, Suriname) and Australia [20]. In this market, however, glassmakers are very distant followers of alumina‐ceramics makers and especially of metallic aluminum producers whose needs are several orders of magnitude higher than theirs. In instances when relatively high contents of both aluminum and alkalis are required, it may be advantageous to use instead nepheline syenite, a rock consisting mainly of alkali feldspars and nepheline [NaAlSiO₄], which is exploited and exported from Norway, Russia (Kola Peninsula), South‐Africa, Brazil, India, and China.