Chemistry
Extracting Metals
Extracting metals involves obtaining pure metals from their ores through various processes such as reduction, electrolysis, and smelting. These methods typically involve removing impurities and separating the metal from its ore using chemical reactions and physical processes. The choice of extraction method depends on factors such as the reactivity of the metal and the stability of its compounds.
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eBook - PDFElectrochemistry for Technologists
Electrical Engineering Division
- G. R. Palin, N. Hiller(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER 7 Extraction and Refining of Metals 7.1 Introduction Electrometallurgy is the application of electricity in the extrac-tion of metals from their ores, and in the refining of metals. In arc furnaces and similar units the electricity is merely used to produce the high temperatures required for the extraction process. These systems will not be considered here. In many cases, however, the process is electrochemical. Metals can be refined by the dissolu-tion of the impure metal at the anode of a suitable electrolytic cell, and the deposition of the pure metal at the cathode. The extraction of metals requires the production of a water soluble compound from which the metal is deposited in an electrolytic cell, or the production of a salt which can be fused to provide the electrolyte of a cell from which the metal is deposited electro-lytically. Electrochemical processes may be the only suitable means of extraction and refining, or they may be alternatives to thermo-chemical and other processes. In a number of extractions the electrochemical process is only one stage in the sequence, and many metals are refined electrochemically after extraction by other means. Only the electrochemical processes will be discussed here. 7.2 Electrolysis of Fused Salts Cells for the electrolysis of fused salts are usually designed so that the applied electrical energy maintains the required tempera-ture in the cell, as well as decomposing the electrolyte. This means 181 182 EXTRACTION AND REFINING OF METALS that voltages several times greater than the decomposition voltage must be used, and energy efficiencies are low. The temperatures used are such that in most cases the liberated metal is in liquid form. The Alkali Metals Metallic lithium and sodium are produced exclusively by electrolysis of fused salts. Potassium metal is also produced in this way, but non-electrolytic processes are also used.
eBook - PDFAn Introduction to Chemical Metallurgy
International Series on Materials Science and Technology
- R. H. Parker, D. W. Hopkins(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER 7 Extraction and Refining of Metals 7.1. Introduction Metals occur as minerals in the earth —a mineral being a naturally occurring element or compound —and minerals are the constituents of rocks. A rock which contains a mineral from which the metal may be extracted at a profit is called an ore, and the extraction metallurgist is concerned with the theory, development and control of the methods of Extracting Metals from ores and refining the crude extract. This chapter aims to introduce the chemistry of some of the methods in current use and to indicate how the principles outlined in earlier chapters may be applied to the solution of the riddle of the rocks —as it is so aptly termed in the commentary to a well-known film on nickel extraction. (1) No attempt will be made to give a descriptive treatment of the subject, and several references are available with details of plant and operation should the reader find them necessary. (2) It has been estimated (3) that the earth's crust contains nearly 50% oxygen and over 25% silicon by weight. Alumin-ium, iron, calcium, sodium, potassium and magnesium follow in decreasing proportions as the next most abundant elements. It is therefore not surprising to find that whatever the metal-bearing minerals in an ore —called the value minerals — the oxides or compounds between the oxides of the above group of elements are likely to be present in varying quantities as impurities known as gangue minerals. The geological processes by which value minerals were concentrated naturally in ore deposits should be studied elsewhere (4) but usually the metal-263 2 6 4 AN INTRODUCTION TO CHEMICAL METALLURGY bearing minerals are sulphides, oxides or silicates, or, where the original minerals have become chemically altered by the action of oxygen, water and carbon dioxide from the atmos-phere, sulphates, carbonates and hydrated oxides.
eBook - PDF- M. N. Patten(Author)
- 2017(Publication Date)
- De Gruyter Saur(Publisher)
CHAPTER TWO Extraction Metallurgy S. HARRIS Introduction The subject areas covered by this chapter are the processing of as-mined minerals and secondary raw materials for the recovery of metals, i.e. those areas conventionally designated 'mineral pro-cessing' and 'extractive metallurgy'. The boundary between these two fields remains a real one in terms of both the organization of metal production and the sources of information about it, though the distinction is becoming increasingly blurred with the advent of hydrometallurgical extrac-tion techniques for the base, precious and less common metals. A further distinction is found between the organizations and publi-cations concerned with the production of iron and steel on the one hand and non-ferrous metals on the other. A note on terminology is appropriate: 'non-ferrous' is taken to embrace all metals apart from iron and steel, and to include the ferroalloying elements such as vanadium, chromium and manganese. Sources dealing with extractive metallurgy as a whole, rather than those whose scope is restricted to one metal, are emphasized. Reference material: handbooks Extraction metallurgy interacts with and draws on a number of other disciplines - chemistry, physics, chemical engineering - and many works of reference used in the chemical and process industries are standard also in the extractive processing of metals. There is a trend away from the publication of textbooks and Extraction metallurgy 37 handbooks - an inspection of the Institution of Mining and Metallurgy's holdings reveals a number of such works published prior to 1960 and relatively few since. The rapid advance of technology and the increasing volume of literature produced renders large compilations slow to produce and as 'state-of-the-art reviews' they date quickly. There is still however a need for compilations of basic data in all branches of the process industries which ensures a continuing demand for the large chemical data sources.
eBook - PDF- Bernard Moody(Author)
- 2013(Publication Date)
- Arnold(Publisher)
Broadly, metals are found united as oxides, sulphides, chlorides and to widely different extents, as oxosalts, including silicates, phosphates, carbonates, sulphates and nitrates. The less reactive metals, to some extent called noble metals to distinguish them from the more reactive base metals, are sometimes found natively. They include copper, gold, mercury, and also tin. Because oxygen occurs in such abundance and in electronegative character is second only to fluorine, oxides may be readily formed from other compounds. Metals are often extracted by reduc-tion of their oxides. The extraction of a metal from its ore by a process involving melting is called smelting. Because there are far more metals than non-metals, smelting assumes a paramount position in the extraction of elements. In a general way, the extraction of a metal M from a compound MAmay be written: MX + Y ^ M + XY where the left to right process is smelting. The art of working metals and of Extracting Metals from ores forms part of the science of Metallurgy. A comparison of chemical reducing agents: chemical affinities MX + y ^ M + XY The possibility of this reaction proceeding to the right and to completion, with recovery of the metal M, depends on the relative avidities of M and y for X. The discussion need not be confined to the extraction of metals. 134 The principles governing the extraction of elements The tendency of such a reaction to occur is known as the affinity of the reaction. The first concise treatment of this subject came from Geoffroy who published a table of affinities in 1718. This was extended by Bergman in 1775 but the relative nature of affinities and other factors affecting chemical reactions were clearly ex-pounded for the first time by Berthollet in 1801-3. While the tendency of a reaction to proceed in the direction indicated may be determined by the study of energies (Thermodynamics), other reasons may prevent it from happening.
eBook - ePub- Sir Alan Cottrell(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
Chapter 8Extraction of Metals
8.1 Metallic ores
We saw in § 2.6 that many of the familiar metals occur sparsely in the earth’s crust. Fortunately, geological processes have partly concentrated them in workable ore deposits. The value of a mineral ore has, of course, to be judged against the general demand and availability of the metal and of alternative sources of supply as well as on characteristics of the ore itself, such as the chemical state of the metal, nature and content of impurities, physical state of the mineral and accessibility of the deposit. For example, a deposit containing less than 20 per cent Fe has little value as an iron ore since there are many with 30–50 per cent Fe and a few with 70 per cent, but one containing 4 per cent Cu is a good copper ore.Table 8.1 gives the world production and prices of metals. These values are very approximate and subject to wide fluctuations, but they indicate the very large differences that exist. The choice of extraction processes has to be judged in the light of these economic factors. The elaborate chemical solvent treatments used, for example, in the extraction of beryllium would be prohibitively expensive for metals such as iron or lead, where cheap bulk methods have to be used.TABLE 8.1. APPROXIMATE ANNUAL WORLD OUTPUT OF METALS AND UNITED KINGDOM PRICES, 1972We saw in § 2.6 that there is plenty of oxygen on earth to form oxides. However, at the very high temperatures at which the earth is presumed to have formed, most metals would have been chemically uncombined. The heavier metals, particularly much of the iron, would then have been pulled by gravity to the centre, so forming a metallic core about 4000 miles across. At the lower temperatures reached in the surrounding envelope of mainly light elements (O, Si, Al) a semi-molten magma of silica and silicates formed, about 2000 miles thick, and near the surface crystallized into the solid crust. This is about 30 miles deep, although much thinner underneath the oceans, and consists mainly of an upper layer of granite (Al and Ca silicates) and a lower layer of basalt (Mg and Fe silicates). The mantle beneath the crust consists mainly of olivine (Mg and Fe silicates) and other mixed silicates such as garnet
eBook - PDFThe Chemistry of the Metallic Elements
The Commonwealth and International Library: Intermediate Chemistry Division
- David J. Steele, J. E. Spice(Authors)
- 2017(Publication Date)
- Pergamon(Publisher)
For example, titanium chloride is reduced by magnesium: TiCl 4 + Mg - Ti + MgCl 2 , and uranium halides are similarly reduced by calcium. Another common and powerful reducing agent in this type of reaction is mischmetall, an alloy of rare earth metals. Examples of modern smelting and thermit reactions are given at the end of this chapter. Electrolysis. When the compounds of a metal are too stable to be reduced chemically, electrolytic reduction is used and, for reasons already given (page 19), The Metals: their Occurrence and Extraction 25 it is generally the fused salts which are electrolysed in cells designed to prevent the products recombining. The fundamental reaction is the discharge of the cation by the electrons entering the cell at the cathode: M n+ + ne -> M (deposited) A description of the design, construction, and operation of an industrial electrolytic cell is given on page 27. A new technique of extraction is the use of ion exchange resins. This has been applied with particular success to the extraction of uranium by preferential absorption of the complex ion, U0 2 (S0 4 ) n 2 2n . This is now the basis of an important large-scale process. Solvent extraction techniques are also being developed. The use of ion exchange in the separation of the rare earths is discussed fully in Chapter 10. Refining. Many metals when produced contain impurities which seriously impair their mechanical properties. In some cases, already mentioned on page 24, the impurities are best removed from the ore before extraction. Most metals can be purified after extraction: this is the process of refining. Metals with low melting and boiling points are best refined by liquation and distillation. Tin is separated from impurities of high melting points by heating in a sloping hearth, the pure tin (m.p. 232°C) runs down the hearth leaving the unmelted impurities behind: this is liquation.
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