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Slag is the glass-like by-product left over after a desired metal has been separated (i.e., smelted) from its raw ore. Slag is usually a mixture of metal oxides and silicon dioxide. However, slags can also contain other metal oxides or other elements.

General properties

Ferrous and non-ferrous smelting processes produce different slags. The smelting of copper, lead and bauxite in non-ferrous smelting, for instance, is designed to remove the iron and silica that often occurs with those ores, and separates them as iron-silicate-based slags. Slag from steel mills in ferrous smelting, on the other hand, is designed to minimize iron loss and so mainly contains oxides of calcium, silicon, magnesium, and aluminium. Any sandy component or quartz component of the original ore automatically carries through the smelting process as silicon dioxide.

Ground granulated slag is often used in concrete in combination with Portland cement as part of a blended cement.


Slag is found in many foundries.


Slag can be obtained as side product from most thermite reactions.


  • Make cement

Handling and safety

Powdered slag is irritant and harmful for lungs.

See also


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