Editing Copper extraction (section)

==Refining==
===Fire refining===
[[File:CopperAnodeRejects.jpg|alt=Copper anodes after fire refining and casting.|thumb|Copper anodes after fire refining and casting.]]
The blister copper is put into an [[anode furnace]], a furnace that refines the blister copper to anode-grade copper in two stages by removing most of the remaining sulfur and iron, and then removing oxygen introduced during the first stage. This second stage, often referred to as ''[[poling (metallurgy)|poling]]'' is done by blowing [[natural gas]], or some other reducing agent, 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.

===Electrolysis===
[[File:CuElectrolyticRefineApparatus.png|thumb|upright=1.35|Apparatus for electrolytic refining of copper]]
{{main|Electrowinning}}
The final stage in the production of copper is refining. Refining is achieved by [[electrolysis]], which exploits the easy (low potential) and selective conversion of copper(II) solutions to the metal. The anodes cast from processed blister copper are placed into an [[aqueous]] solution of 3–4% [[Copper(II) sulfate|copper sulfate]] and 10–16% [[sulfuric acid]]. Cathodes are thin rolled sheets of highly pure copper or, more commonly these days, reusable stainless steel starting sheets (as in the [[IsaKidd refining technology|IsaKidd process]]).<ref name="Robinson">Robinson T. (2002). "Electrolytic refining."  pp. 265–288 in: ''Extractive Metallurgy of Copper, Fourth Edition''. Eds Davenport W. G., King M., Schlesinger M., and Biswas A. K. (Elsevier Science Limited: Kidlington, Oxford, England).</ref> A potential of only 0.2–0.4 volts is required for the process to commence. In industrial plants current densities up to 420 A/m<sup>2</sup> are possible.<ref>{{Cite report |vauthors=Filzwieser A, Hanel MB, Filzwieser I, Wallner S |date=May 13, 2019 |title=FAQS with regard to operating a Cu ER tankhouse above 400 A/m<sup>2</sup> |url=https://www.mettop.com/api/cdn/uploads/1474547633_4kktjvcg.pdf}}</ref>

At the [[anode]] ([[redox|oxidation]] reaction), copper and less noble metals [[Dissolution (chemistry)|dissolve]]. More noble metals and less [[solubility|soluble]] elements such as [[silver]], [[gold]], [[selenium]], and [[tellurium]] settle to the bottom of the cell as [[anode slime]], which forms a salable by-product. Copper(II) ions [[electromigration|migrate]] through the [[electrolyte]] to the cathode. At the [[cathode]] ([[redox|reduction]] reaction), {{chem2|Cu(2+)}} ions are reduced in copper metal and Cu<sub>(s)</sub> plates out, but less noble constituents such as [[arsenic]] and [[zinc]] remain in solution unless a higher voltage is used.<ref name="samans">Samans, Carl H. (1949). ''Engineering Metals and their Alloys''. MacMillan.</ref>

The reactions involving metallic copper and {{chem2|Cu(2+)}} ions at the electrodes are the following:
: {|
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|– At the [[anode]]  || (oxidation and dissolution) || : Cu<sub>(s)</sub>  || → Cu<sup>2+</sup>  + 2 e<sup>−</sup>
|-
|– At the [[cathode]]  || (reduction and precipitation) || : Cu<sup>2+</sup>  +  2 e<sup>−</sup>  || → Cu<sub>(s)</sub>
|}