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Steel
Furnace Slag contains approximately 40% calcia, 10% magnesia, 30% iron oxide and a few
percent manganese oxide.
These
are beneficial elements in ironmaking.
In an integrated steel
mill, the steel slag can be fed into a blast furnace in limited quantities along with
limestone, ore, or pellets and scrap, with coke for heat and chemical reduction.
How much steel slag can
be recycled depends on the phosphorus content of the steel furnace slag.
The
phosphorus accumulates in the molten iron product of the
blast furnace and then returns in the steel furnace slag
from the steel furnace.
The phosphorus steadily
increases in percentage until the system must be purged by stopping the recycle.
Another direct recycle is the direct
return to (1) the BOF steel furnace where the lime actually required (for
reaction when the molten iron being charged is low in silicon) does not create
adequate slag cover in the furnace, or (2) directly to the EAF where there is
not as much lime required for impurity removal as in the BOF, but more slag
cover is required than the lesser lime amount would contribute
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