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Blast furnace slag (from iron making) and
steel furnace slag (from steel refining) are distinct types of slag
produced in ferrous metallurgy. When molten, slags float on the metal.
Separating is not exact, so it is preferable to have some metal in the
slag rather than slag in the metal.
They are so different that some aggregate
applications can use one, but not both.
However, the processing
techniques are often similar.
The molten slag is allowed to cool and
solidify. Sometimes the cooling of blast furnace slag is very rapid, with water or air to
make granulated or pelletized blast furnace slag, or somewhat less rapid with limited
water quantity to make expanded slag.
Slowly cooled blast furnace slag and
steel furnace slag are crushed and screened to make the sizes needed for construction or
specialty products.
It is especially important that the
metal be removed to avoid problems during the end use of slag and also to recover the
higher value scrap for return to the iron and steel making processes.
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