Editing Copper extraction (section)

===Converting===
[[File:Tough-Pitch Copper Containing Antimony And Nickel.jpg|thumb|[[Oxygen-free copper]] aka "Tough-pitch" copper (ca. 98% pure), containing antimony and nickel]]
The matte, which is produced in the smelter, contains 30–70% copper (depending on the process used and the operating philosophy of the smelter), primarily as copper sulfide, as well as iron sulfide. The sulfur is removed at a high temperature as sulfur dioxide by blowing air through molten matte:
:2 CuS + 3 O<sub>2</sub> → 2 CuO + 2 SO<sub>2</sub>

:CuS + O<sub>2</sub> → Cu + SO<sub>2</sub>

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

:2 FeS + 3 O<sub>2</sub> → 2 FeO + 2 SO<sub>2</sub>
:2 FeO + SiO<sub>2</sub> → Fe<sub>2</sub>SiO<sub>4</sub>

The purity of this product is 98%, it is known as ''blister'' because of the broken surface created by the escape of sulfur dioxide gas as blister copper ''pigs'' or [[ingot]]s are cooled. By-products generated in the process are sulfur dioxide and [[slag]]. The sulfur dioxide is captured and converted to sulfuric acid and either sold on the open market or used in copper leaching processes.