Val. 4, NO.9
CHEMISTRY rn THE MININGINDUSTRY
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CHEMISTRY IN THE MINING INDUSTRY AS EXEMPLIFIED BY THE LEACHING PROCESS OF THE NEW CORNELIA COPPER COMPANY* That we are living in an age of invention, an age of science, an age of research is a thought impre:;sed upon our minds every hour, every moment of our daily existence. The wonders of the twentieth century surround us on all sides and a hlost confound our senses with their numb a s alone. They dazzle our eyes, fill our minds with amazement, and instill in us a thirst for a knowledge and an uuderstanding of these exploits of science. Research work in the natural sciences has been of the utmost consequence to the industrial advancement of the world. . In many different fields of production has it been of great value; for example: in the development of the manufacture of coal-tar dyes, which touches the whole field of the textile manufacturing industry; of steel; and of bakelite. To all of the research work in the natural sciences, chemistry is indispensable. Chemistry is the science of the composition of all matter and, as such, is of paramount worth to the progress of the world. All industries of production-agriculture, manufacturing, and mining-are vitally dependent on chemistry for success, both in a financial way and in relation to the quality of their products. In the mining industry, chemistry is of prime importance. Our country is exceptionally rich in the extent and value of its natural resources, particularly mineral, and even more particularly the metallic minerals. By mining, these metallic ores are extracted from the earth, sometimes from shafts extending many thousands of feet below the surface of the earth and sometimes from open pit mines. When these ores are found
* Prize-winning high-school essay, 192627.
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JOURNAL OF
CHEMICAL EDUCATION
SEPTEMBER. 1927
in the mines, rough estimates may be formed of their values, but it is by chemistry that samples of the ores are assayed and the richness and percentage of each of the elements to be found in the samples accurately ascertained. The chemical assay determines beyond any doubt whether or not a body of ore may be mined a t a profit or at a loss. In this way, every car of ore shipped from a mine can be accurately analyzed by the chemical assay of only a few samples of the ore. In all ore reduction plants-smelters and leaching plantschemistry is most necessary, for without chemistry it would be impossible to reduce the metals from ores to the forms in which we desire them, except by very crude methods and with very impure and unsatisfactory results. Since only by means of chemistry can ores be accurately and thoroughly analyzed, and since it is only with the aid of chemistry that metallic ores can be reduced to pure metals, it is an unquestionable fact that chemistry is absolutely essential to the mining industry. Whereas, chemistry has profoundly affected the whole mining industry, the great changes wrought by the use of chemical processes in mining are nowhere more in evidence than in copper mining. Copper, because it is corrosion-resisting, and because it is found in enormous natural deposits, is one of the most extensively used metals, and, consequently, one of the most extensively mined. Indeed, in the year 1926, 1,658,000 tons of copper were produced throughout the world, approximately sixty per cent of this being produced in the United States. About twentyfive per cent of the world's copper production in 1926 came from Arizona. (Statistics taken from the Engineering and Mining Journal, January 22, 1927.) Copper mining, being the greatest of Arizona's industries, is the one which has given her her wealth. The red metal is mined in almost every section of this vast state. At Ajo, Arizona, is found one of the best examples of the value and utility of chemistry to the copper mining industry. The history of Ajo reads like a fairy tale. I t is the story of untold wealth, worthless for centuries because of the lack of a means of turning it from its crude form into a form which could be used. The great Ajo ore bodies were known to the early Spaniards; American mining companies knew of them for generations; and they were slightly mined during the Civil War; but these oxide ore bodies were practically valueless until a chemical process was evolved by which the metallic copper could be extracted cheaply and profitably from the ore. Think of it! Millions upon millions of dollars of potential wealth in copper, lying dormant! -and all because of the lack of a practical means of converting that wealth into usable form! Mining company after mining company took an option on the property, only to give it up as "a bad job." At length, another company heard of the Ajo district. Its directors became in-
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terested. They took an option. Its representatives made estimates of the millions of tons of ore contained in these great ore bodies. There was the orel How were they going to develop it? They began to experiment and, as a sure expedient, resorted to chemistry. Then, figuratively, Aladdin rubbed his magic lamp; and the genie, a t the command of Aladdin, went to the aid of the great corporation. This genie was chemistry. Chemistry, the science of unlimited powers, of unparalleled achievements, in truth, showed them the way. A chemical process was worked out in 1914 and was named the Greenway Process, its originator being the late General John C. Greenway. Knowing that the huge bodies of low-grade copper oxide ore could be reduced by this process to metallic copper, the New Cornelia Copper Company began to develop an immense open pit mine, founded the town of Ajo, erected a 5000-ton leaching plant and later a 5000-ton concentrator. The Greenway Process is a leaching process by which copper is removed from low-grade oxide ore. Leaching is a method by which copper is extracted from oxide ore as a sulfate in solution. The action of sulfuric acid on the copper oxide changes it to copper sulfate, the chemical equation being HzS04 CuO --+ CuSOr H20. The sulfuric acid, however, acts upon the copper carbonates, the cuprite, and a basic sulfate of copper in much the same way as upon the black oxide of copper, (CuO), forming in each case copper sulfate, (CuSO,). This process, one of the marvels of chemistry, is the principal one by which copper can be taken from low-grade oxide ores profitably. The plant and process as used a t Ajo are briefly described below. There are, in the leaching plant, twelve tanks, each eighty-eight feet square and sixteen feet deep. They are arranged in rows of six. Of these tanks, eleven are used as leaching tanks and one as a settling tank. Seven tanks always contain ore which is being leached; the tailings in one tank are always being washed; one tank is always being excavated, i. e., the ore which has been leached and washed is being removed; one tank is always ready to be excavated; and one tank is always being charged. Charging a tank means filling it with finely aushed ore. Each of the tanks a t Ajo is charged with 5200 tons of ore. After a tank has been charged the actual leaching begins. A sulfuric acid solution, 0.9 per cent a t first but later increased to 3 per cent, is pumped through holes in the floors of the' tanks and thence up through the ore. The normal flow of the acid solution through the tanks is one thousand gallons per minute. The solution is circulated in a clockwise motion through the tanks containing ore which is being leached. An excellent feature of this process is that any per cent solution can be circulated through any tank or series of tanks a t any time. Approximately seventy tons of 60° Baume sulfuric acid, on an average, are used every day in the Ajo plant. The
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copper sulfate solution formed by this process is one from which the copper may be removed by electrolytic methods. The solution, after passing through seven tanks in a series, goes from the seventh, which is also the tank containing the newest ore, to the reduction towcrs. There are six towers arranged in pairs. They are built of sheet lead supported on a steel framework. Lead is used because of its resistance to the action of sulfuric and sulfurous acids. All the towers are filled with boards 3/8 in. thick and 11 in. wide. These boards are placed on edge, the width of a board apart, and in layers. Each layer is laid a t right angles to the one immediately below it. The solution is distributed through the tops of the towers in a showerlike spray, while sulfur dioxide gas is forced, by means of fans, up through the bottoms. The sulfur dioxide gas reduces the ferric iron in the solution to ferrous iron, the chemical equation being: H20 HzS08 + 2PeS04 $ 2HzSOa. Pez(SO& Perrlc
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Ferrous
Ferric iron, because it tends to reoxidize the copper in the solution and since it necessitates an excessive use of power in the electrolytic plant, is harmful to the success of the process. Ferrous iron is not. Nowhere in the leaching process is the value of chemistty to the copper mining industry better illustrated than here. When the reduction of the ferric iron to ferrous iron has been completed, the solution flows into the settling tanks where the solid matter settles out. Prom the settling tanks the solution is pumped into the electrolytic plant. I n this plant the copper in the solution, by means of electrolysis, is removed and built up into sheets of electrolytic copper weighing about one hundred and forty pounds each. Electrolysis is a process involving the discharge of the positive and negative ions in the solutions a t their respective electrodes (anodes or cathodes). In the case of Ajo, thin copper sheets form the cathodes (electrodes having negative charges), and lead sheets form the anodes (electrodes having positive charges). When an electric current is passed through the solution, metallic copper is deposited a t the cathodes. The solution, discarded from the electrolytic plant but still containing some copper, is directed to a group of fourteen reinforced concrete launders -troughs-containing scrap iron. This process takes advantage of the law that one metal higher than another in the electro-potential series of metals will replace fi-om its solution the one below it. Thus, in this SOn-Fe -+ Cu Fe++ SOa--. The copper case, Cu++ left in the solution is precipitated by the scrap iron in the form of cementcopper. This is washed from the iron, loaded into box cars, and shipped to the smelter. The leaching plant and precipitation plant (plant for making cementcopper), a t Ajo have been in continuous operation since June, 1917.
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From that date until November, 1926, a period of eight and one-half years, 248,620,278 lb. of cathode copper were produced, in addition to 29,970,063 lb. of cement-coppet.. An enormous, production, bud jLst one more achievement due to chemistry. The work of the New Cornelia Copper Company, +hen viewkd al'one;, is of great magnitude; but, when viewed as a part of the entire copper mining industry it is found to be only a minute portion of the whole; all of which is dependent on chemistry for commercial success. But' then the copper mining industry, however extensive i t may be, is only a part of the mining industry taken as a whole, a whole to which chemistry is of the most signal worth. Yet the vastness of mining business is but a portion of the whole field of industry necessary t o supply the needs of all the peoples of the world. Chemistry is in some way responsible for the advancement of each and every one of these industries. Chemistry, industry; industry, chemistry-they are as one. They cannot be separated. For, since chemistry is the science of the composition of all matter, and since all industry has to do with matter and its composition, chemistry and industry are interwoven, are interlocked in a grip which will be strengthened and added t o in the centuries t o come. The maintenance of our civilization is dependent upon industry. The old processes would be incapable of the large scale production so necessary to feed, clothe, and house the multitudinous population of the modern world. Industry has had, and continues to have, great demands made upon it-demands that, without the practical application of the laws of chemistry, it could not meet. Bibliography 1. Technical papers by: John C. Greenway, H. A. Tabelman, James A. Potter, Stuart Croasdale,
H. w. Morse. 2. Personal interview with Mr. M. Curley, Manager of New Cornelia Copper Company. 3. Flow sheet of leaching plant made by draftsmen of New Cornelia Copper Company.
