The refining of metals

Why Do We Need to Know This Material The topics described in this chapter may one day unlock a virtually inexhaustible supply of clean energy supplied daily by the Sun. The key is electrochemistry, the study of the interaction of electricity and chemical reactions. The transfer of electrons from one species to another is one of the fundamental processes underlying life, photosynthesis, fuel cells, and the refining of metals. An understanding of how electrons are transferred helps us to design ways to use chemical reactions to generate electricity and to use electricity to bring about chemical reactions. Electrochemical measurements also allow us to determine the values of thermodynamic quantities. 

Chemical or extractive metallurgy is concerned with the extraction of metals from ores and with the refining of metals. Physical metallurgy is concerned with the physical and mechanical properties of metals as affected by composition, mechanical working, and heat treatment. 

As the third most abundant metal in Earths crust, calcium is widespread in a large number of mineral deposits, relatively inexpensive to recover, and useful in a number of applications. In industry, calcium is used in the refining of metals like lead, aluminum, zirconium, and uranium. Calcium alloyed with iron in steel production reduces surface defects. When alloyed with lead in the manufacture of maintenance-free automobile batteries, it increases battery life. The metal is also used to produce vitamin B5, calcium pantothenate. 

A third industrial use for carbon monoxide is in the refining of metals. Most metal ores exist in the form of oxides or sulfides when extracted from the earth. For example, the two most important ores of iron are magnetite (Fe304) and hematite (Fe203). After an ore has been mined, it is treated to remove the oxygen or sulfur in the ore to obtain a pure metal. Carbon monoxide is often used for this purpose with oxide ores because it combines with oxygen from the ore to form carbon dioxide, leaving the metal behind Metal oxide + CO —> Metal + C02. 

On the industrial scale, carbon monoxide is used as a reducing agent in metallurgical operations, in the refining of metallic nickel, in the synthesis of phosgene, and in the synthesis of a wide variety of organic compounds. In the laboratory, it is used in the preparation of carbonyls and aromatic aldehydes. 

F.D. Richardson, Thermodynamic Principles in the Refining of Metals , Paper 6A in Symposium Physical Chemistry of Metallic Solutions and Inteimetallic Compounds. National Physical Laboratory, Teddington, Middlesex, England, 1958,6A1-23. 

In this chapter, we will see how chemical reactions can be used to produce electricity and how electricity can be used to cause chemical reactions. The practical applications of electrochemistry are countless, ranging from batteries, fuel cells, and biological processes to the manufacture of key chemicals, the refining of metals, and methods for controlling corrosion. Before we can understand such applications, we must first discuss how to carry out an oxidation-reduction reaction in an electrochemical cell and explore how the energy obtained from, or supplied to, an electrochemical cell is related to the conditions under which the cell operates. 

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