What is Slag?

There are two distinct types of slag produced at the BlueScope Steel Port Kembla Site; Blast Furnace Slag and Steel Furnace (or BOS) Slag.



Iron is extracted from iron ore in a blast furnace by a process known as reduction. The raw materials - iron ore, coke and fluxes - are fed into the top of the furnace. Air, which is heated to about 1200°C, is blown into the furnace through nozzles called tuyeres (pronounced 'twee-yers') that are spaced around the lower section of the furnace. The air causes the coke to burn, producing carbon monoxide, which creates the chemical reaction. The iron ore (iron oxide) is reduced to molten iron and slag.

Molten iron runs into torpedo ladle rail cars. Blast Furnace Slag is a co-product of the iron making process. It is removed from the blast furnace and allowed to cool. ASMS then further process the blast furnace slag into useful products for the construction industry such as concrete aggregates and road base products. Generally the products produced from this type of slag are known as Air Cooled Blast Furnace Slag and their product codes commence with 'ABF'.

Blast Furnace Slag can be processed into another form by Granulation. This process introduces the molten slag to water and creates an amorphous granular product which is typically minus 3mm. This product is marketed to the cement industry by ASMS as a cementitious material. Granulated blast furnace slag has product codes commencing with 'GBF'.


The BOS (Basic Oxygen Steel Making) process utilises the molten iron from the blast furnace with the addition of scrap steel and fluxes. These fluxes (burnt lime or dolomite) are fed into a vessel and a lance injects oxygen creating a reaction between the molten iron, fluxes and scrap to create steel and steel slag. The Steel is tapped from the vessel into a steel ladle and the steel slag is poured into a slag pot.

This slag pot is then handled by our specialised equipment and poured into pits for cooling. The steel furnace slag is then removed from the pits. ASMS processes the steel furnace slag into asphalt aggregates, road bases, fill materials and filter materials. Generally the products produced from this type of slag are known as Steel Furnace Slag and their ASMS product codes commence with 'SFS'.