The Modern Copper Industry
The Modern Copper Industry
Copper is a critical component of modern industry. In the United States, the most important use of copper is in electrical wiring. A breakdown below gives the percentage of copper used in the United States by industry:
Building Wire. . . . . . . . . . . . . . . . . . . . . 16% Plumbing & Heating . . . . . . . . . . . . . . . . . . 14% Automotive . . . . . . . . . . . . . . . . . . . . . . 11% Electric Utilities . . . . . . . . . . . . . . . . . . .9% Air Conditioning & Commercial Refrigeration. . . . . . .8% Telecommunications . . . . . . . . . . . . . . . . . . .7% Factory Equipment. . . . . . . . . . . . . . . . . . . .6% Electronics. . . . . . . . . . . . . . . . . . . . . . .6% Appliances & Extension Cords . . . . . . . . . . . . . .3% Other. . . . . . . . . . . . . . . . . . . . . . . . . 20% TOTAL-----------------------------------------------> 100%
Copper sheets are used in cooking utensils and in roofs. Copper tubes are used to make pipes for plumbing and carrying natural gas. Copper wire is used to carry electric current. Extruded copper, that is, copper that has been squeezed through a hole, forms rods, hinges, tubes, and door handles.
The use of copper is increasing. In the 1970s, a 1,500 square-foot house used about 280 pounds of copper. Today, a 2,200 square-foot house uses about 450 pounds of copper.
A car in the 1970s used about 35 pounds of copper. Now, 50 to 80 pounds of copper will go into one automobile.
A Boeing 727 airplane uses 9,000 pounds of copper.
The following countries are the world's major producers of
copper
(amount produced is 1995 output, given in
tons, from the 1995 Mineral Commodity Summary)
Chile . . . . . . . . . . . . . . . . . . . . . . 2,350,000 United States of America. . . . . . . . . . . . . 1,890,000 Canada. . . . . . . . . . . . . . . . . . . . . . . 740,000 Russia. . . . . . . . . . . . . . . . . . . . . . . 600,000 Indonesia . . . . . . . . . . . . . . . . . . . . . 380,000 Australia . . . . . . . . . . . . . . . . . . . . . 420,000 Peru. . . . . . . . . . . . . . . . . . . . . . . . 400,000 China . . . . . . . . . . . . . . . . . . . . . . . 350,000 Zambia. . . . . . . . . . . . . . . . . . . . . . . 350,000 Poland. . . . . . . . . . . . . . . . . . . . . . . 340,000 Kazakstan . . . . . . . . . . . . . . . . . . . . . 220,000 Philippines . . . . . . . . . . . . . . . . . . . . 115,000 Zaire . . . . . . . . . . . . . . . . . . . . . . . .40,000 Other Countries . . . . . . . . . . . . . . . . . 1,600,000 WORLD TOTAL-------------------------------------> 9,800,000
While the U.S. is the world's second-largest producer of copper, it is the world's largest consumer of copper. The United States imports 830,000 tons of copper. It also exports 850,000 tons.
The largest mining companies are Codelco and Minera Escondida of Chile (of which 57.5% is owned by BHP of Australia), and Phelps Dodge in the United States, followed by RTZ, Asarco, Freeport, ZCCM, Cyprus, and MIM.
In the United States, Arizona is by far the largest producer
of copper, followed by Utah and New Mexico. Montana has been the
fourth largest producing state, but the opening of BHP's Robinson
Project in Ely, Nevada, will move Nevada into fourth place ahead
of Montana. Michigan followed Montana, but the largest of the few
remaining mines in Michigan has closed.
Historic mines
or mining districts discussed in the preceding section are still
producing in these states, especially Bingham Canyon in Utah,
Ely, Nevada, and Butte, Montana.
Nevada had only one copper mine in 1995, Arimetco's MacArthur Mine in Yerington, in Lyon County. MacArthur produced 6,498 tons of copper in 1995. BHP's Robinson Project has reopened the historic copper mine near Ely, Nevada. The planned production per year will total 142,000,000 pounds or 71,000 tons.
Used copper can be recycled by resmelting it. Last year, 460,000 tons of copper, or 18% of U.S. copper use, was recycled.
Copper is traded around the world. Producers store it in warehouses until it is sold and shipped to the buyer. The price changes daily, depending on the supply of copper and the demand for copper. The principal place where the trading takes place is in London, at the London Metal Exchange. There, copper sellers try to find a buyer who will pay the highest price for shipment at a certain time, while buyers look for the lowest priced copper. The average price per pound has fallen in 1995, going from a high of $1.37 per pound to around $.91 per pound.
Other metals can substitute for copper in some uses. For example, aluminum may be used in electrical equipment, automobile radiators and refrigerator tubing. Titanium and steel are used in heat exchangers. Steel is used for artillery shell casings. Plastics substitute for copper in water pipe and plumbing fixtures.
Mining
Most modern copper mining is done in open pits with explosives, giant shovels, and huge trucks to haul the ore to a mill or smelter.
The method of extracting copper from ore rock has been
improved with modern technology, but the ideas behind it
developed directly from past experience. Since every ore is at
least a little different from every other ore, the exact process
varies with the type of ore. Sometimes the copper ore mineral is
different; for example, chalcocite (copper sulfide) is very
different from malachite (copper carbonate with water). The
non-copper minerals in the ore, called gangue,
vary as well.
Transportation and Crushing
In most cases, the mined ore must first be carried to a mill. Still in large boulder-sized pieces, it is transported in trucks, in railroad cars or in a pipeline. It is brought to a crusher, where it is crushed into small pieces.
The small pieces are mixed with water until they form a chunky soup called slurry. The slurry is poured into a ball mill. A ball mill is a barrel-shaped container that rotates while holding steel balls that clash together to grind the ore into tiny pieces. These pieces are small enough to pass through a screen with 10,000 openings per square inch.
The next step is a flotation process, where soap-like bubbles hold the tiny particles of copper minerals, while the unwanted parts of the ore sink into the liquid. The slurry is placed in a flotation cell. Chemicals are added to coat the copper particles and to make the bubbles stronger. Then paddles or air jets make the whole thing bubble. The bubbles containing the copper rise to the top of the liquid where they can be skimmed off. The unwanted parts, now called tailings, sink to the bottom to be poured off. The froth containing the copper is dried, and the product is called copper concentrate. It contains about 15 to 33 percent copper.
Sometimes part of the copper ore, or even all of it, does not separate out in the flotation cell. Then another process named leaching is used. As we learned previously, this process was discovered by the Romans. They could not smelt the sulfide copper ores (ore made of the minerals chalcocite, chalcopyrite, bornite, and other minerals in which copper is bonded to sulfur). The Romans collected water from deep in the mines that had seeped through the sulfide ore. They let the water dry, and collected the copper minerals from it. We also saw that the Moors figured out how to pile the sulfide copper ore in heaps and drip acidic water through the heaps, then smelt the results. This process was the first use of heap leaching.
Nowadays, after leaching has removed the copper from the ore and dissolved it into a sulfuric acid-water solution, the solution is placed in containers holding pieces of iron. Some of the iron dissolves and replaces the copper in the solution. The copper, meanwhile, is deposited on the remaining pieces of iron. The resulting copper concentrate is called precipitate copper and is from 60 to 90 percent pure copper. From this point, usually it must be smelted or refined to remove the rest of the impurities.
Smelting, too, is an ancient process made more efficient and precise through modern technology. The typical furnace now used is called a reverberatory furnace. A large amount of concentrate, up over 300 tons, may be placed in the furnace at one time. The flames from one end of the furnace melt the concentrate. Bubbles rise to the surface releasing some impurities in the form of gas. Other impurities form a less dense liquid, like salad oil floating on top of vinegar, that rises to the top of the copper melt. These impurities include iron, calcium oxide (a mixture known as lime), and silicon and oxygen (a mixture known as silica). The impurities are called slag. The slag is skimmed off the top. The melted material is now a mixture of impurities and up to 50 percent copper. It is called copper matte. The remaining impurities include iron and sulfur.
The copper matte goes through a converter to blow forced air into it. The air forces silica back into the copper matte to gather up the impurities and make more slag. The slag is skimmed off again. Now, the matte is up to 99.5 percent pure copper. It has a bubbly surface and so is known as blister copper.
For use in electrical wire and instruments, copper must be even more pure. A technique that the ancient copper smelters and the medieval smelters, and even the Renaissance smelters could not use, is electrolytic refining. The blister copper is poured into molds to make cakes about 3 feet on a side and about 3 inches thick. These cakes will form positive poles called anodes.
The copper anodes are lowered into tanks containing a solution containing more copper in the form of copper sulfate, and nitric acid. They are arranged so that hanging between them are sheets of pure copper that will be the cathodes or negative poles. An electric current is passed through the tank. The anode copper cakes dissolve. Impurities sink to the bottom as sludge. Pure copper deposits on the cathode sheets. These pure copper sheets can be remelted and cast into whatever form is needed.
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