Copper from Chile1 NANCY BROWER
\
Mary Hardin-Baylor College, Belton, Texas
OPPER, a key metal in both war and peace, is a grft of earth's great depths. Probably one of the fundamental discoveries of the cave man which made possible our tremendously complex machine age was the finding of a lump of pure copper. Our knowledge of copper has been derived from all races and nations, but directly and largely from the Romans who gave i t the name by which we know it today. Prehistoric men nsed copper for axes and knives, in place of stone; for pins, in place of bone or splinters of wood; for necklaces and other ornaments, in place of shells or bright pebbles. Early Egyptians used copper for their temples, drains, plates, lamps, chains, cooking utensils, and doors. The early American Indians were taking the first step away from the Stone Age culturally when they used copper to make their fish hooks, knives, and pins. In the Orient, methods were invented of casting statues of bronze, life size or even larger, but it was the Greeks who brought this method to perfection. The Romans constructed their temples and public buildings out of copper when they conquered and ruled the Western world. Copper had a great part to play in the development of civilization in the use of copper coins, or of bars as a means to pay for the necessities of life in the ancient days. Although the Egyptians used copper for money, they had to weigh i t and test its purity. It is believed that the Chinese were the first people to use coinage. Chinese coins were made of brass cut in the shape of miniature knives and other articles. The Greeks were the first to use coinage in any way similar to ours. These coins, too, were made of brass as well as of silver and gold. Today, all of our coins contain c o p per. The copper deposit with which I am familiar, and near which I lived most of my life until three years ago, is located in Chuquicamata, Chile. This city is on the west slope of the Andes, 10,000 feet above sea level, about 150 miles north and east of the city and sea port of Antofagasta. It is a tiny civilization transplanted in the center of the Atacama Desert, 150 miles away from any sort of civilization. Of the 25,000 citizens, 7500 are employed by the copper mine.= This mine is the largest open-pit copper mine in the world. The reserve is estimated a t 134,000,000,000 pound^.^ The deposit is 2500 meters long, 700 meters wide; and, although the depth has not been finally determined, there are several prospect drill holes
C.
-
1 Presented before the Division of Chemical Education of the American Chemical Society, 103rd meeting, Memphis, Tennessee, April 22. 1942. Fortune, January, 1942, p. 148. a "Encyclopedia Britannica." Val. 5. p. 491.
600 meters deep which were discontinued while still in ore. In other words, it is one and a half miles long and almost a half mile wide and deep. Even in our back yard, copper ore could be found. When as a child I used to go to the seashore, I used to brag to my playmates as we made sand cakes and pies, that a t home I made cakes and pies out of copper, or green mud. When asked what copper was, I said, "Oh, something, more valuable than gold." Little did I know then the real value of this metal. Because this deposit can be worked as an open-pit mine, the copper can be mined with much less expense than the underground mines of Montana. The deposit is owned and operated by an American company, Anaconda. Today i t furnishes a large share of the copper nsed in the United States' defense industries. The slopes of the copper mine are beautiful. If you can imagine hills of these bright green minerals in a solid mass a mile long, you will have an idea of what they are like. may wish to know how such a large deposit of copper came to be in one place. All mineral deposits are found on what is termed the "crust" of the earth, or within five to ten miles from the surface. Mineral deposits of this type can be formed in many different ways. Geologists describe them as "local accumulations or concentrations of ores," but geologists themselves cannot always prove how these ores happened to become concentrates. They have theories and often enough proof to back these theories. They believe that the Chuquicamata deposits of copper were formed from volcanic eruptions near the surface of the earth and as veins and replacement deposits above and near intrusions of igneous rocks. This theory is supported by the fact that the deposit is located about 30 miles from two volcanoes which are now active and have frequent eruptions. It is believed that the copper ore originated in the hot molten material in the interior of the earth. First, it was the magna itself, as this molten material is called, that carried the copper mineral up to the crust. The magna intruded itself into the rocks. The copper and other minerals either stayed with the rocks or just separated as pure ore. The cooling and crystallizing gave off aqueous solutions that carried the minerals upward to be deposited in cracks. When the molten rock and its gases no longer rose from the interior of the earth, hot water took up the task of elevating the minerals to the surface. In deeper parts of the earth, the waters are under great pressure which allows them to take into solution compounds that we usually believe and know to be difficult to dissolve in water. As the
water rose to the surface, the pressure decreased and the water could no longer hold the dissolved compounds. They dropped them and ore deposits formed.' The ore a t Chuquicamata was worked by the Spaniards as early as 1601, and by the Indians long before this; but, of course, they did not apply our modem methods of mining the copper.' The mine is now worked as an open pit or quarry, in benches each 12 meters high. The ore is broken down by blasting chum drill holes drilled parallel to the face. An average blast breaks about 100,000 tons in rock. The broken ore is then loaded into 70-ton standard gage railroad cars by revolving electric shovels each having a capacity of 3600 tons in eight hours. The cars are hauled to the plant a distance of 3.5 kilometers by 80-ton electric locomotives. The ore occurs in three distinct classes, namely,' the oxide, the mixed ore, and the sulfide. The principal oxide ore in this deposit is Antlerite. It is the only type of ore that has been treated up to date. The steps used in obtaining the copper metal from the impure oxide are crushing the ore, roasting it, extracting the copper, precipitating i t from solution, and purifying i t by electrolysis. The ore is crushed a t the plant until 90 per cent of i t passes through a J/kinch sieve. The ore is then roasted a t a temperature varying from 300 to 800 degrees. In the leaching extraction method, which is practiced in Chuquicamata to separate the copper ore from the rock and other minerals, the roasted ore in suitable vessels called vats is subjected to the action of a dilute solution of sulfuric acid which acts as a solvent for the copper. In the next step the copper sulfate solution obtained is removed from the pulp, scrap iron is added, and the copper is deposited in a finely crystalline form, the equivalent amount of iron replacing it in the solution. This form of copper is impure, and therefore must be melted down and rcfincd hy electrolysis. For thiq process the in suitimpure comer is cast in slabs which- are- nlnced r -- --- ~ ~ abie tanks a n d act as anodes, while sheets of refined copper are used as cathodes. The tanks are filled with a copper sulfate solution that serves as the electrolyte and must contain some free acid. The passing of a direct current through the solution causes copper to be deposited a t the cathode with the release of a corresponding quantity of sulfuric acid which attacks copper sulfate. This action is continued until the anode has been consumed with a minimum waste. The impurities in the anode solution fall and collect on the tank bottom in the form of a sludge, which contains a high concentration of precious metals. The refined copper cathodes are removed from the tank when built up to a convenient thickness, washed and dried, and melted down under proper oxidizing and reducing conditions in a reverberatory furnace or casting furnace. The molten copper is cast into ~
~
' LINDGREN, "Mineral Deposits," 4th ed., McGraw-Hill Book Company. Inc.. New York. 1933. pp. 112-26. "'Encvclo~edia Britannica." Vol. 5.. o. 491. ~ r i v a i ecbmmunication. '
.
sheets or bars which are then ready to be shipped to the smelters. In the laboratory I have tried to use a small piece of ore, and change i t to copper by following the abovementioned steps. I placed a rock that contained the green oxide ore in dilute sulfuric acid. After the green part was extracted, I filtered the mixture and obtained a copper sulfate solution. To this I added iron nails. The iron displaced the copper from the solution in a powder-like or finely crystalline form. When the molten copper is made into bars, i t is used chiefly for making wire; when i t is made into slabs or square cakes, i t is used for rolling purposes; when it is made into circular cakes, i t is used for making seamless cylindrical products such as tanks and hot water heaters; when it is made in round billets, i t is used for seamless copper tubing; and the copper that is cast in ingots is used for casing or for the manufacture of alloys. These are just some of the present-day uses of copper. One of the most important uses is in electrical appliances, chiefly because its conductivity stands only second to silver. Robert E. McConnd, chairman of the Engineers Defense Board, New York City, has said, "The shortage of copper will cause more inconvenience and dislocations than will be caused by any other shortage." He believes that because of the shortage of copper, silver could be economically substituted in electrical wiring and equipment of the new magnesium and aluminum plants. The Government owns 100,000 tons of silver which now lie idle in vaults. The silver will be safe because these plants will work 24 hours a day and will always be guarded, and because the wires will be charged with a high voltage all the time. When the emergency is over the silver conductors may once again he replaced by the copper ones. Exactly 25,000 tons of copper could he saved in this way in the new plants and about -50,000 tons in other plants.' Cornelius Kelly, Anaconda's Board Chairman, suggested in 1933 that, because half a million tons of refined copper were available, the Government should begin to stockpile it, as it had done silver and gold, against the contingency of war. This was not done. In fact, copper was neglected entirely. The great potential stockpile available a t that time was large enough to supply the equipment for 600 battleships, 2,400,000 bombers, and 66 power developments. This copper has vanished and in its place is the shortage that is now facing us.8 Recent estimates are that the total productive capaaty of Chilean copper will be required for military purposes alone. Amidst the great copper shortage, the Chuquicamata deposit becomes a powerful instrument of war. In 1942 i t will produce one-third of the United States' supply. Chile produces 85 per cent of the copper in Latin America. The Chuquicamata mine and two other deposits are American owned.
-
' Science News Ldler, Nov. 22. 1941, p. 332. Fortune. January 1942. p. 53.
There has been no public confirmation as yet of the rumor that the United States Government has reached an agreement to purchase copper from the mines of Chile, but the owners of the mines see strong support for i t in Washington's attitude toward assuring sufficient copper to satisfy defense needs. No decision has been reached as to what method of purchase will be followed, or as to what ties are involved. Chilean copper was shipped to France. After the fall of
France it was shipped to Japan but now i t is shipped under lend-lease to England. Indeed, in the United States, we can be glad that the people in Chile are friendly toward us, for the copper mines in this country cannot possibly furnish enough material to satisfy our needs of defense. The fact that the copper from the mine a t Chuquicamata is available to us and not to the Japanese or totalitarian powers is a decided advantage in fighting this war.
