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Encyclopedia > Copper mine

The most commonly present source of copper ore is chalcopyrite (CuFeS2), which accounts for about 50% of copper production. Chalcopyrite ore is extensively mined in Chile, the United States, Canada, Zambia, and Poland. In the United States, the states of Arizona, Montana, New Mexico, and Utah lead in ore mining. Indeed, the world's largest copper mine, the Berkeley Pit, is located in Butte, Montana.


The following is a process of copper extraction from chalcopyrite ore into pure metal.

Contents

Method

The copper ore is crushed and ground before it is concentrated to between 20 and 40% copper in a flotation process. The next major step in production uses pyrometallurgical processes to convert the copper concentrate to 99% pure copper suitable for electrochemical refining. These high temperature processes first roast the concentrate, then smelt it in a furnace, oxidise and reduce the molten products to progressively remove sulfur, iron, silicon and oxygen to leave behind relatively pure copper.


Concentration

Ground chalcopyrite is mixed with paraffin oil, which reacts with the copper mineral to make it water repellent, producing copper naphthenate.


This is then sent into a large water basin with detergent. Jets of air from the base of the basin cause the copper mineral to float, from which the copper naphthenate is skimmed off. This dewatering process separates the gangue, the worthless portion of the ore, from the enriched product. The product from this flotation process is known as copper concentrate. It is sometimes traded either via spot contracts or under long term contracts as an intermediate product in its own right.


Roasting

In the roaster, the copper concentrate is partially oxidised to produce calcine and sulfur dioxide gas. The reaction which takes place is:


2CuFeS2(s) + 3O2(g) → 2FeO(s) + 2CuS(s) + 2SO2(g)


Smelting

The calcine is then mixed with silica and limestone and smelted in an exothermic reaction at 1200C to form a liquid called matte. Several reactions occur. For example iron oxides and sulfides are converted to slag which is floated off the matte. The reactions for this are:


FeO(s) + SiO 2 (s) → FeO.SiO2 (l)


2FeS(l) + 3O2 + 2SiO2 (l) → 2FeO.SiO2(l) + 2SO2(g)


Conversion to Blister

The matte, which is produced in the smelter, contains around 70% copper primarily as copper sulfide as well as iron sulfide. The sulfur is removed at high temperature as sulfur dioxide by blowing air through molten matte:


CuS(l) + O2(g) → Cu(l) + SO2(g)


In a parallel reaction the iron sulfide is converted to slag:


2FeS(l) + 3O2 + 2SiO2 (l) → 2FeO.SiO2(l) + 2SO2(g)


This end products of these reactions are sulfur dioxide, more slag and 98% pure copper, known as blister because bubbles of oxygen are present in the sheets which are cast from the liquid product of this furnace.


Reduction

The blistered copper is put into an anode furnace to get rid of most of the remaining oxygen. This is done by blowing natural gas through the molten copper oxide. When this flame burns green, indicating the copper oxidation spectrum, the oxygen has mostly been burned off. This creates copper at about 99% pure.


Refining

The copper is then put into sheets which are refined by electrolysis. The copper sheets (anodes) are placed into a solution of copper sulfate and sulfuric acid. The copper then migrates across the solution to the cathode. The reactions are:


At the anode: Cu(s) → Cu2+(aq) + 2e-


At the cathode: Cu2+(aq) + 2e- → Cu(s)


See also


  Results from FactBites:
 
Mining - Wikipedia, the free encyclopedia (589 words)
Mining is the extraction of valuable minerals or other geological materials from the earth, usually (but not always) from an ore body, vein, or (coal) seam.
Another early mining operation was the turquoise mine operated by the ancient Egyptians at Wady Maghareh on the Sinai Peninsula.
Turquoise was also mined in pre-Columbian America in the Cerillos Mining District in New Mexico, where a mass of rock 200 feet (60 m) in depth and 300 feet (90 m) in width was removed with stone tools; the mine dump covers 20 acres (81,000 m²).
  More results at FactBites »

 
 

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