Gangue
Definition and meaning of Gangue in chemistry.
Gangue is the commercially worthless mineral material that occurs mixed with a valuable ore mineral in a deposit and must be separated from it during mineral processing.
In more detail
Gangue typically consists of common rock-forming minerals such as quartz, calcite, feldspar, or clay silicates that have no economic value themselves but are physically intergrown with the desired ore mineral. Before smelting, gangue is largely removed by physical concentration methods like froth flotation, gravity separation, or magnetic separation, since carrying excess gangue into a furnace wastes energy and fuel. Any gangue that remains is handled chemically by adding a flux, a substance that reacts with the gangue at high temperature to form a low-melting, easily removable slag.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Typical minerals | Quartz (SiO2), calcite (CaCO3), feldspar, clays |
| Removed by | Froth flotation, gravity/magnetic separation, or fluxing to slag |
| Contrast | Opposite of the valuable ore mineral in a deposit |
In hematite (Fe2O3) iron ore, silica (SiO2) sand is a common gangue mineral; adding limestone (CaCO3) as a flux in the blast furnace decomposes it to calcium oxide, which reacts with the silica to form calcium silicate slag that floats above the molten iron and is drained off separately.
Frequently asked questions
Is gangue the same as slag?
No. Gangue is the unwanted mineral matter present in the raw ore before processing; slag is the glassy waste product formed after gangue reacts with a flux during smelting.
Why is gangue removed before smelting rather than left in?
Leaving gangue in the charge wastes furnace energy heating non-metal-bearing rock and increases the amount of flux and time needed to form slag, raising overall processing cost.