What is slag?
Slag is a byproduct of the melt when converting iron ore or scrap steel
into molten steel. Pulverized limestone is added to the melt to provide an additional
source of carbon monoxide and to
bind to the silicates present to prevent the formation of iron silicates. The slag
with its lower density is skimmed off the top of the ladle, transferred to its own car
and either poured in a waste area
in molten form or after it has cooled and solidified. See diagram. Slag is formed by
nucleation, with a core of calcium oxide surrounded by a layer of calcium hydroxide and
a outer layer of calcium carbonate.
See diagram. Other elemental concentrations vary depending on the furnace and process
used, but slag generally has a high iron concentration.
What good is slag anyway?
For many years slag was treated as a waste material. However, cold poured slag
is a good aggregate material with properties similar to limestone. Due to the high angularity,
it forms a solid
subbase upon which to build (United States Steel). Current slag production is now a revenue
source for the industry.