More important emissions arise from the sintering plants. These counts, also measured in Germany, for about 300 g per year. Only the dust from the blast furnaces is recycled that way.
Scrap metal has no use there, it is used in steel furnaces and reclamation plants.
In fact no external industrial sources of chlorine are introduced, neither in the sintering process, nor in blast furnaces. Simply from nature. All natural materials contain salt in small quantities. So it is in coal and thus in coke. In general this is already a million times more than necessary to form all dioxins you will form.