Next to aluminum, copper is one of the most-important nonferrous metals. It is a red, ductile, and malleable metal with good resistance to corrosion, but its most outstanding property is high electrical conductivity. After silver, it is the best conductor of electricity and is used widely in the electricity industry for a wide range of applications from overhead power lines carrying mega-watts of power (although aluminum is being used increasingly for this purpose) to domestic wiring. As a structural alloy, copper is an important component of brass and bronze.
Chemistry of copper
Copper is one of the transition elements and comes in Group 1b of the periodic table together with silver and gold. It has a melting point of 1985°F (1085°C) and is only soluble in strong oxidizing acids, such as nitric acid and hot concentrated sulfuric acid.
The majority of copper compounds are divided into cuprous (with a valency of 1, Cu+), which are the most stable in the solid state, and cupric (with a valency of 2, Cu2+). In solution, however, only the cupric ion is stable. Welnown compounds include copper (cupric) sulfate, CuSO4·5H2O, known as blue vitriol, a blue crystalline salt used as a mordant in dyeing and a fungicide; cupric oxide, CuO, a black powder used to give glass a green color; and cuprous oxide, Cu2O, a red insoluble powder used to give a red color to glass.
Extraction
The metal that heralded the Bronze Age can be found in the natural state. Commercially all copper is extracted from either sulfide (copper glance, Cu2S, and copper pyrites, CuFeS2) or oxide (cuprite, Cu2O) ores. Principal sources are the United States, Russia, Canada, Chile, and Zambia. Much of the ore occurs mixed up with rock in what is known as a porphyry deposit.
Sulfide ores, which are the more common, are reduced and purified by higemperature pyrometallurgical (involving strong heating) processes, whereas the metal is extracted from its oxide ores by hydrometallurgical (extraction by aqueous solution) methods involving dissolution.
The first stage in the extraction of the sulfide ores is the removal of as much crushed rock as possible by using a froth flotation method. The mined material is put in a water bath together with specific surfacctive agents, and air is blown through. Helped by the surfacctive agent, the small particles of coppeearing ore cling to the air bubbles and are brought to the surface, where they are removed by skimming off the froth.
Copper sulfide is invariably found in association with iron sulfide, and the initial extraction processes are designed to remove as much iron as possible. They exploit the fact that at high temperatures copper has a lower affinity for oxygen than either iron or sulfur. The first process is known as matte smelting. The ore is melted in a furnace and some oxidation of the iron sulfide takes place. The iron oxide produced dissolves preferentially in the silicatich slag, which floats on the surface, leaving the melt enriched in copper sulfide.
At completion, the melt, or matte as it is called, is then placed into a converter-type furnace designed to enable a blast of air to be blown through the molten charge. The forced air completes the oxidation of iron sulfide to iron oxide, which is absorbed into the slag and periodically poured off by tilting the converter. When most of the iron has been removed as oxide, the air blast iscontinued, and the chemical reaction in which copper sulfide is reduced to copper metal commences. When the reaction is complete, the metal is cast. During solidification, much of the dissolved sulfur dioxide is released, but some of the bubbles are caught in the cooling metal, giving it a blistered appearance. It is called blister copper.
The extraction of copper from oxide ores starts by dissolving the ore in sulfuric acid. The iron content of the solution is reduced by adding other chemicals and the copper extracted by electrodeposition (electrolysis). In comparison with the smelting of sulfide ores, hydrometallurgical extraction from oxide ores is much less used.
