How does smelting remove impurities from copper ore?

Smelting removes impurities from copper ore through a multi-stage process designed to separate the metal from unwanted minerals and elements.12

The Smelting Process

In modern copper processing, the ore is first concentrated and often roasted to drive off volatile impurities like arsenic, mercury, and some sulfur. The concentrate is then heated in a furnace—such as a reverberatory, electric-arc, or modern flash furnace—along with a flux, typically silica or limestone.21

This heating produces two distinct layers:
* Matte: A molten mixture of copper, iron, and sulfur.13
* Slag: A fluid layer containing gangue minerals and oxidized impurities (especially iron) that have reacted with the flux.23

Converting and Refining

Because the matte still contains iron and sulfur, it undergoes a second stage called converting. In a converter, air or oxygen is blown through the molten matte, oxidizing the remaining iron and sulfur. The iron forms oxides that combine with flux to create more slag, while sulfur is removed as gas. This results in "blister" copper, which is further purified through fire refining to reach the high levels of purity required for electrolytic refining.123