Gangue: definition in chemistry
Gangue: The unwanted rock and minerals mixed with the valuable mineral in an ore, which must be removed when the metal is extracted.
Ores are rarely pure: a valuable mineral such as an iron oxide or a copper sulfide is usually surrounded by worthless material like quartz, silicates and clay. Mining companies first concentrate the ore, for example by froth flotation, magnetic separation or washing, to discard much of the gangue. Any gangue left during smelting is removed by adding a flux, which reacts with it to form a molten waste called slag. The word is pronounced like gang.
Examples
- Silica (SiO₂) in iron ore, removed as calcium silicate slag in a blast furnace
- Quartz surrounding veins of gold
- Clay and sand washed away from tin ore
- Rock separated from copper minerals by froth flotation
On the periodic table
Gangue is usually rich in oxygen, silicon and aluminum, the most common elements in Earth's crust, which is why silica and silicate minerals make up so much of it.