Occurrence of Metals

Most metals come from minerals. A mineral is a naturally occurring substance with a range of chemical composition. A mineral deposit concentrated enough to allow economical recovery of a desired metal is known as ore Table 23.1 hsts the principal types of minerals, and Figitre 23.1 shows a classification of metals according to their minerals. 

Metallurgy is the science and technology of separating metals from their ores and of compounding alloys. An alloy is a solid solution either of two or more metals, or of a metal or metals with one or more nonmetals. 

The three principal steps in the recovery of a metal from its ore are (1) preparation of the ore, (2) production of the metal, and (3) purification of the metal. 

In the preliminary treatment of an ore, the desired mineral is separated from waste materials—usually clay and silicate minerals—which are collectively called the gangue. One very useful method for carrying out such a separation is caS eA flotation. In this process, the ore is finely ground and added to water containing oil and detergent. The liquid mixture is then beaten or blown to form a froth. The oil preferentially 

Halides Cap2 (fluorite), NaCl (halite), KCl (sylvite), Na3AlF6 (cryolite) 

Silicates Be3Al2Si Oig (beryl), ZrSi04 (zircon), NaAlSi308 (albite), Mg3(Si40io)(OH)2 (talc) 

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The discussion will be restricted to cases for which a complete structure-determination exists. Again, as with the niobium compounds, but even more pronouncedly, the occurrence of metal-metal bonds (340) (see Table XIV) is most significant. 

Fig. 6.3 Forms of occurrence of metal species in natural waters (Stumm and Morgan 1996)...

None of the methods described in this chapter utilize a pre-formed metal vinylidene as an active catalyst precursor. The occurrence of metal vinylidene intermediates is instead inferred on the basis of product structure, isotopic labeling experiments, and computational studies. 

This review describes the preparation, characterization, and properties of all nonpolymeric complexes that contain a metal removed from the fullerene also are included. The article does not cover the essentially ionic fullerides MmC (4) or the endohedral metallofullerenes MmC (8), which have been reviewed previously. The extended fullerenes, or so-called carbon nanotubes, which have hollow centers and can be filled with metal salts, also are not discussed. The majority of complexes involve 7r-bonds and, apart from alkyl lithium fullerides, the potentially useful synthetic area of o- complexes has not been explored. Table I shows the occurrence of metal-bound adducts across the periodic table. 

Fig. 13. (a) Schematic representation of the formation of mixed potential, M, at an inert electrode with two simultaneous redox processes (I) and (II) with formal equilibrium potentials E j and E2. Observed current density—potential curve is shown by the broken line, (b) Representation of the formation of corrosion potential, Econ, by simultaneous occurrence of metal dissolution (I), hydrogen evolution, and oxygen reduction. Dissolution of metal M takes place at far too noble potentials and hence does not contribute to EC0Ir and the oxygen evolution reaction. The broken line shows the observed current density—potential curve for the system. 

Mention was made in the introductory section of the occurrence of metal porphyrins in oils and other fossil fuels, thus indicating that the porphyrins were formed early in the evolutionary process. Interestingly, some of the metals found in these porphyrin complexes, Ga, Ni and V, are not found in this form today. Either these originate from early life forms or metal-exchange reactions have occurred. Related to this, the biosynthesis of the naturally occurring porphyrin complexes is known to involve enzyme-catalyzed insertion of the metal ions into the porphyrin rings. 

MJI Sienko, "On the Occurrence of Metallic Character in the Periodic Table of the Elements," /. Chem. Educ., Vol. 60,1983,691-696. 

The dust which is carried down with rain, hail, or snow has been analyzed by many. W. Stark, A. F. Wiegmand, W. L. Zimmermann, R. Braudes, C. Bertels, J. D. Bohlig. etc., noted the presence of calcium salts—chiefly sulphate—in rain-water J. Girardin, in hail-stones and A. F. Wiegmand, in snow-water. The last-named also noted the presence of phosphates in atm. dust—vide infra, chlorides, etc. A. Ditte, and W. N. Hartley and H. Ramage have discussed the occurrence of metals as well as meteoric dusts in the atmosphere. 

Rauser, W.E. (1981). Occurrence of metal-binding proteins in plants. In Heavy Metals in the Environment, ed. W.H.O. Ernst, pp. 281-4. Edinburgh CEP Consultants Ltd. 

Zagury, G.J., Samson, R. and Deshenes, L. (2003) Occurrence of metals in soil and ground water near chromated copper arsenate-treated utility poles. Journal of Environmental Quality, 32(2), 507-14. 

Alcohol dehydrogenases can be subdivided with respect to various criteria, two of which are in particular relevant for the application of these enzymes first structural and protein chemical data, especially subunit size and occurrence of metal ions, and second the stereochemical course of the catalyzed reaction and the consequential chirality of the formed alcohol. 

When the condition (RIV) = 1 is fulfilled, the refractive index/ dielectric constant goes to infinity, and we have a NM-M transition. The Herzfeld criterion when applied to metal-ammonia solutions does indeed predict (67,93) that localized, solvated electrons are set free by mutual action of neighboring electrons at metal concentrations above 4-5 MPM, and measurements (Fig. 20) similarly indicate a dielectric catastrophe in this concentration range. The simple Herzfeld picture has recently been applied by Edwards and Sienko (70) to explain the occurrence of metallic character in the Periodic Table. 

Figure 6. The occurrence of metallic vs nonmetallic character in the periodic table of the elements the variation of R/V for naturally occurring elements of the s, p, and d blocks (adapted from Edwards and Sienko27).

Price s review [145] gives an excellent account of the mode of occurrence of metals in major constituents in paints and some recommended operating conditions for flame atomic absorption. It may be increasingly necessary to add to the list more exotic metals because of their growing use as markers in security paints. 

Szefer, P., Wolowicz, M. Occurrence of metals in the cockle Cerastoderma glaucum from different geographical regions in view of principal component analysis. SIMO-Mar. Pollut. 64, 253-264 (1993)... 

The metals are elements and, as such, are not produced by man. However, the occurrence of metals and their distribution in nature are often related to anthropogenic activities, resulting in high levels in the surrounding environment and/ or bioavailable forms. Of great concern is the natural methylation of Hg, Pb... 

Metals are widely used for structural purposes in buildings, cars, railroads, ships, and aircraft. They also serve as conductors of heat and electricity. Medical and nutritional research during recent decades has provided much insight into important biological functions of metals. The metals Na, K, Ca, and Mg, as well as some nonmetals (C, H, O, N, P, and S), are present in the human body in substantial quantities. Many other metals are present in lesser quantities in the human body, but they are essential to our well-being (see essay Trace Elements and Life in Chapter 23). In this chapter, we shall study the occurrence of metals and examine processes for obtaining metals from their ores. 

QUESTIONS AND PROBLEMS OCCURRENCE OF METALS Review Questions... 

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