Chemical symbol: Cu
Atomic mass: 63.546 g.mol -1
Atomic number: 29
Melting point: 1083.4°C
Boiling point: 2595°C
Specific gravity: 8.93
Density: 8.9 g.cm-3 at 20°C
Crystal form: isometric
Fracture: hackly
Hardness: 21/2 - 3
ID marks: tarnished to green or blue
Lustre: metallic
Copper, the pinkish coloured and comparatively softer metal, is well known to all of us. It is one of the few metals to occur in native metal form as nuggets and masses in nature and is being used prior to iron by mankind since ancient past. Hence, it is the metal that has high cultural significance.
In other languages it is known as Kupfer (German), Cobre (Spanish), Kobber (Norwegian), Rez (Hungarian), Cuivre (French), Med (Russian, Bulgarian and Polish), Baker (Serbian and Bosnian), Varis (Lithuanian), Chalkos (Greek), Mes/ Mess (Farsi and Pashto), Mys (Kazakh), Tembaga (Malay), Dong (Vietnamese) and Rame (Italian). In India, owing to prevalence of many languages, it has attained several names viz. Tamba/ Tama/ Tamad/ Kamal in Hindi, Tamra/ Tamrakam/ Dhastam/ Malechhamukham/ Shulbam/ Varishtam Udumbaram/ in Sanskrit/ Vedic; Tamra in Kannada; Chemb in Malyalam; Zangs in Tibetan; Cheppu Tamil, Tamba in Urdu and Tama in Nepali.
On record this metal was known to some of the oldest civilizations and has a history of use that is at least 10,000 years old. A copper pendant was found in what is now northern Iraq that dates to 8700 BC. Evidence of regular use of copper artifacts also came from Mehrgarh in Baluchistan (earlier part of India) datable to 6500 BC. Use of copper compounds also dates back to before 4000 BC. In the past it was also used in making mirror.
The archaeological studies made on the basis of excavations at Ganeshwar, an old mining town located east of Khetri in north Rajasthan (India), ascribe the earliest Indian copper mining to Indus valley civilization (3000-1500 BC). Large number of the ancient copper mining and metallurgical sites (slag heaps) present in almost all States of the country bear testimony to it. In Kumaun (central Himalaya) copper smithy is considered an old traditional technology.
Mention of copper mining and metallurgy in country exists in several ancient works e.g. Kautilya's Arthsastra (3rd Century BC) to Ain-i-Akbari in 1590 AD.
During the ancient period ‘native copper’ was the initial source of this metal until it was possible to extract copper from its ores, which are far more abundant in nature and, therefore, form the main source of copper today.
Copper possesses some of very special characters such as excellent ductility, high conductivity of heat and electricity, resistance to corrosion, ability to form alloys with other metals and beauty. It is completely soluble with gold. It can be cold-rolled down to one one-thousandth inch in thickness, and by cold drawing, its length can be increased as much as 5,000 times. Hence, it is an ideal metal for making wire. Copper has 29 distinct isotopes ranging in atomic mass from 52 to 80. Two of these, 63Cu and 65Cu, are stable and occur naturally, with 63Cu comprising approximately 69% of naturally occurring copper. The other 27 isotopes are radioactive and do not occur naturally. The most stable of these is 67Cu with a half-life of 61.83 hours
When found in free metallic state it is called ‘native copper’ forming polycrystalline mass, wire, distorted crystals, grains etc. In nature it occurs in mineral form. It forms a primary mineral in basalts, the volcanic rocks. It’s most common mineral forms are sulphides, carbonates and oxides. Copper constitutes 70 parts per million of the Earth's crust and is present to the extent of 0.020-0.001 parts per million in seawater.
Copper-bearing ores fall into three main classes i.e. oxide, carbonate and the sulfide. There are more than 150 ore minerals of copper. The important oxide ores include cuprite (Cu2O) and tenorite (CuO). The carbonate ores are malachite (Cu2CO3(OH)2) and azurite (Cu3(CO3)2(OH)2). The common sulfides of copper include chalcopyrite (CuFeS2), covellite (CuS), chalcocite (Cu2S) and bornite (Cu5FeS4). Fresh copper sulphides form deeper parts of the ore zones or lodes, which are not exposed to weathering. Near the surface, these get altered by oxidation and other chemical actions to native metal, oxides and carbonates. These secondary copper minerals also form rich ore and owing to characteristic green or blue colour, even small amounts of copper ore is identified easily in the rocks.
Cuprite is a secondary mineral, which forms in the oxidized zone of copper sulfide deposits. It has a relatively high specific gravity of 6.1; and is also known as ‘ruby copper’ due to its distinctive red color. The tenorite is dull grey-black colored mineral of copper.
The malachite is a green-colored copper mineral, which crystallizes in the monoclinic system, and most often forms botryoidal, fibrous or stalagmitic masses. Azurite is a soft, deep blue copper mineral produced by weathering of copper ores. It occurs as massive to nodular, and often stalactitic in form. It tends to lighten in color over time due to weathering into malachite. Both the minerals were used as mineral pigment for centuries.
The chalcopyrite is brassy yellow in colour, shows metallic lustre and tarnishes to iridescent blue, green, yellow and purple. Its hardness is 3.5 to 4 on the Mohs scale and specific gravity 4.2. It breaks with conchoidal fracture and becomes magnetic on heating. When exposed to air, it oxidizes to a variety of oxides, hydroxides and sulfates. Chalcopyrite occurs in a variety of ore types such as huge masses, irregular veins and disseminations. Its streak is diagnostic as green tinged black. Half of the world's copper deposits are in the form of chalcopyrite ore. The covellite is a rare copper sulfide mineral of indigo blue colour and was the first discovered natural superconductor. It is commonly found as secondary mineral, rarely as a primary mineral, and very rare as volcanic sublimate. Chalcocite is opaque, dark-gray to black in colour with a metallic lustre. It has a hardness of 2½ - 3 with an orthorhombic crystal system. It is a secondary mineral that forms from the alteration of other minerals; it has been known to form pseudomorphs of different minerals. Bornite is brown to copper-red in colour on fresh surfaces that tarnishes to various shades of blue to purple. Its striking iridescence gives it nickname ‘peacock ore’. It crystallizes in orthorhombic system and occurs mostly as granular masses and disseminations in different rocks. It has of grayish black streak. It is also magnetic after heating.
Copper ores occur in varied forms viz. in native form as wire, grains, crystals etc., in mineral form as disseminations, veins, stock work etc. in variety of rocks.
Copper is extracted from its ores by two principal methods i.e. pyrometallurgical and the hydrometallurgical method. In the first method ore is crushed into powder. Minerals are concentrated into slurry. Copper minerals are separated by flotation. Smelting of concentrate and extraction of metal follow it; by heat, flux and addition of oxygen. Sulfur, iron and other undesirable elements are removed and product is called ‘blister copper’. It is further refined by fire and electro-refining methods. The second method i.e. ‘solvent extraction’ and ‘electro-winning’ is most dominant leaching process in use today in recovering copper by chemical solutions. It involves two major stages: solvent extraction - the process by which copper ions are leached or extracted from the ore using chemical agents; and electro-winning - electrolysis of Cu ions plated onto the cathode and thereafter removed in elemental form.
The most common copper-base alloys are the ‘bronze’ made of copper and tin, and the ‘brass’ made of copper and zinc.
Bronze was the first to be produced by man during ancient period and is of two kinds i.e. wrought bronze and the cast bronze. Alloying it with other elements such as aluminum, silicon, manganese, beryllium, lead etc different types of bronzes are produced, which have different usage. The bronze figure of a dancing girl recovered from Mohenjodaro is a testimony of the knowledge of copper alloying of the Indians during Harappan (Sindhu-Sarasvati) civilization.
Brass is comparatively stronger than bronze; its colour changes with zinc content. German brass looking like gold contains 20 parts zinc in hundred, and is used in making cheaper ornaments by rolling it into thin foils. The naval brass is made of tin, copper and zinc and it strongly resists corrosion in seawater
Copper is one of the oldest metals ever used and has been one of the important materials in the development of civilization. Today it has become a major industrial metal, ranking third after iron and aluminum in terms of quantities consumed. Copper has been fashioned into ornamental objects and cooking utensils. Coins have been made of copper throughout history. Copper is also used in pigments, insecticides, and fungicides. Electrical uses of copper, including power transmission and generation, building wiring, telecommunication, electrical and electronic products account for about three quarters of total copper usage.
Copper is the third most abundant trace mineral in the body. The human body contains approximately 100-500 mg of copper but it's role is important as it serves as a cofactor for enzymes involved in hemoglobin and collagen formation and is involved in incorporating iron into the structure of hemoglobin. It strengthens blood vessels, bones and nerves.
Copper producing localities in the world are too numerous to mention here. Worldwide famous localities are Broken Hill (Australia); Daye, Hubei Chengmenshan, Jiurui, Jiangxi Province (China); Ogonja (Namibia); and Callington District, Cornwall (England). In addition, Bolivia, Kazakhstan also produce significant amount of copper. In India, Hindustan Copper Limited (HCL) under Ministry of Mines carries out mining and production of copper. The Company’s mines and plants are spread across four operating Units, one each in the States of Rajasthan, Madhya Pradesh, Jharkhand and Maharashtra i.e. Khetri Copper Complex (KCC) at Khetri Nagar, Rajasthan; Indian Copper Complex (ICC) at Ghatsila, Jharkhand; Malanjkhand Copper Project (MCP) at Malanjkhand, Madhya Pradesh; and Taloja Copper Project (TCP) at Taloja, Maharashtra as shown in the map.
The Khetri Copper Belt, situated in Aravalli Range in Jhunjhunu and Sikar districts, Rajasthan, hosts several copper deposits. The area comprises of tightly folded Proterozoic metasediments that rest over basement gneisses. The prominent copper deposits in the belt are Khetri, Kolihan, Banwas, Chandmari, Dholamala, Akwali and Muradpur-Pacheri. KCC was established in 1967. It has two mechanized underground mines namely 'Khetri' and 'Kolihan' with capacity of 1.0 million tonnes of ore per annum. It’s ore resources include 26 million tonnes @ 1.13 % Cu at Khetri Mine; 20.64 million tonnes @ 1.35 % Cu at Kolihan Mine; 25.02 million tonnes @ 1.69 % Cu at Banwas Block and 12.10 million tonnes @ 1.03 % Cu at Intervening block. The Malanjkhand copper belt comprises of a large body of copper ore in granitic rocks. Its prominent deposits include Malanjkhand, Shitalpani, Gidhri Dhorli, Jatta and Garhi Dongri. GSI had initiated systematic explorations for this deposit in 1969. MCP was established in 1982. It has an open pit mine, and concentrator plant. It has 221.00 million tonnes @ 1.31% copper resources at Malanjkhand Mine. The Singhbhum copper belt of Jharkhand comprises of Proterozoic volcano-sedimentary sequence with a prominent shear zone called Singhbhum shear zone. Copper mineralisation is localized along this shear zone. Prominent deposits are at Chapri, Rakha, Surda, Kendadih, Pathargora and Dhobani. A British company established the ICC LTD in 1930 at Ghatsila. It was merged with HCL in 1972. It has a cluster of underground copper mines, concentrator plant and smelter. Its operating mine is Surda having 26 MT of ore @ 1.20% Cu. Additional reserves include 47.19 million tonnes @ 0.97% copper at Rakha mine; 12.85 million tonnes @1.73% copper at Kendadih Mine; 63.50 million tonnes @1.14% copper at Chapri Block. The Taloja copper project, set up in 1990, has a plant to produce mainly copper rods (CCR) with ore input from HCL mines. The capacity for the production of primary copper in India has risen from a mere 47,500 t/pa till 1997 to 9,47,000 tonne in 2008-09, with the result that India is now a net exporter of refined copper.
Contributed by: A.K. GROVER, DirectorGSI, Western Region, Jaipur
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