Copper extraction techniques

Pyrometallurgical extraction

The following is a process of copper extraction from chalcopyrite ore into pure metal. While oxide ores can be processed using hydrometallurgical methods are more cost effective.

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

Most high grade copper sulfide ores are concentrated using the hydrophobic on its surface. (Besides xanthates, dithiophosphates and thionocarbamates are commonly used.)

The sulfide ore is crushed and ground to increase the surface area of the ore for subsequent processing. The powdered ore is mixed with chemicals (the 'collector chemical') and introduced to a water bath (aeration tank) containing elements.

• An example collector chemical is potassium amyl xanthate.
• An example frother chemical is methylisobutyl carbinol or, for short, MIBC, an alcohol.

To improve the process efficiency, pyrite (FeS₂) - iron exists in both primary zone minerals.

The product from this pyrometallurgical methods are used to produce copper metal. Copper concentrate is sometimes traded either via spot contracts or under long term contracts as an intermediate product in its own right.

Smelting

The calcine is then mixed with exothermic reaction) to form a liquid called copper matte. This temperature allows reactions to proceed rapidly, and allow the matte and slag to melt, so they can be tapped out of the furnace. In copper recycling, this is the point where scrap copper is introduced.

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.SiO_{2 (l)}

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

2FeS_(l) + 3O₂ + 2SiO_{2 (l)} → 2FeO.SiO_2(l) + 2SO_2(g)

The slag is discarded or reprocessed to recover any remaining copper.

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:

2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂

Cu₂S + 2Cu₂O → 6Cu + SO₂

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

2FeS + 3O₂ → 2FeO + 2SO₂

2FeO + 2SiO₂ → 2FeSiO₃

The end product is (about) 98% pure copper known as blister because of the broken surface created by the escape of sulfur dioxide gas as the copper ingots are cast. By-products generated in the process are sulfur dioxide and slag.

Reduction

The blistered copper is put into an anode furnace (a furnace that makes anodes) 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. The anodes produced from this are fed to the electrorefinery.

Electrorefining

  The copper is refined by zinc remain in solution.^[1] The reactions are:

At the anode: Cu_(s) → Cu²⁺_(aq) + 2e^–

At the cathode: Cu²⁺_(aq) + 2e^– → Cu_(s)

Copper cathode is 99.99% copper in sheets of dimensions: 96 cm x 95 cm x 1 cm, with a mass of about 100 kg. It is a true commodity, deliverable to the metal exchanges in New York, London and Shanghai. The chemical specification for electrolytic grade copper is ASTM B 115-00 (a standard that specifies the purity and maximum electrical resistivity of the product).

See also

• Copper mining in the United States
• Metallurgy
• Extractive metallurgy
• Smelting
• Category:Copper minerals
• In-situ leach

Notes

1. ^ ^{a b} Samans, Carl H. Engineering Metals and their Alloys MacMillan 1949