Extraction of Copper

• Copper is a valuable asset to us and has been used for over 5000 years. It is used in plumbing, electrical wires, money (alloys), jewellery, ornaments and many other different objects.
• Copper comes from most continents in the world, but the major contributor to copper is Bingham Canyon, USA; it is one of the largest open cast mines in the world.

• The picture above shows Bingham Canyon, each circular line is a road encircling the open pit.
• There are many different sorts of copper ores, below are a few of them:

• Early civilisations such as the Egyptians could supply their small needs for copper by mining it and reducing it using carbon, but they could only really get the deposits that were less than 15% by mass.
• Miners then did not know how to process the sulphide minerals which lay unaltered 30m underground.
• A way of extracting the copper from the minerals from underground was eventually discovered. It involved “roasting” the sulphide minerals in the air, which converted the elements to their oxides:
  CuS_(s) + 1.5O_2(g) CuO_(s) + SO_2(g)
• The metal oxide can then be reduced to just the metal. More advanced roasting techniques are used today, which are also controlled so that not as much sulphur dioxide is emitted.

Mining and Purification of Copper

• For this process we will focus on Bingham Canyon, Utah.
• The Copper Ore is mined from Bingham canyon and then goes through a four stage process of purification.

1. Crusher

The copper ore is crushed into 250mm pieces, and carried through a tunnel on a 5 mile conveyor belt. This is done so that the segments will be smaller, and therefore more able to float in the next process. At this point the ore is made up of approximately 0.5% of copper

2. Froth Flotation

The purpose of the froth floatation is to separate the 0.5% of copper from the 99.5% of “crud”. There are two different types of minerals in the ore at this point; the chalcopyrite is a sulphide, and the rest are silicates containing anions made from silicon and oxygen atoms.

In this process, a “collector” is added to a water/mineral mixture. The collector binds to the surface of the chalcopyrite grains, giving them a water repellent nature. Detergent is added and air bubbles are blown through the mixture, carrying the water repellent carrier attached to the chalcopyrite. The chalcopyrite is now at the surface, ready to be removed.

The air rises and the copper rises to the top, it can then be scooped off. The slurry of water is then disposed of in tailings pond. At this point the mixture contains 28% copper.

3. Smelting

The smelter separates the copper from the sulphur in CuFeS₂ in one stage:

Copper and Oxygen are reduced, sulphur is oxidised, and iron is oxidised.

The iron oxides combine with silica which is added to the smelter, to form slag- a low density crust, which floats on the surface.

4. Electrolytic Refining

This stage is the final purification of copper; in this stage any copper sulphate is finally separated and the copper is removed. The copper solution is mixed with sulphuric acid. The cathodes are made from pure copper, and the anodes are made from impure copper.

When the electricity is passed through the electrolyte, the copper ions on the anode dissolve into the solution, and are attracted to the cathode. At the cathode they pick up 2 electrons and become copper metal.

Some of the insoluble impurities in the solution are valuable (silver and gold), these are extracted from the sludge which forms. The copper is now 99.98% pure.

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