Iron & Steel thermal process (IS) wastes showed the highest
median value for the heavy metals Cd (14.76 mg/kg), Cr
(166.15 mg/kg) and Hg (2.38 mg/kg) (supplementary material Table
S2). IS mostly uses iron/steel scrap as the raw material which contains
Cd and Hg as contaminants, thus it becomes an important
source of release of these metals. Cd which evaporates during the
process ends up in flue gas cleaning residues due to its tendency to
adhere to particles [20].
The concentration of Hg (BDL–22.79 mg/kg) present in IS waste
was much greater than any other thermal processes (Fig. 1). Hg
is easily captured by wet scrubbers and particle control systems
[21–24] and ends up mainly in the filter cake from the flue gas
cleaning system [20]. The average Hg removal efficiency of the
existing APCDs in Korea was reported to be 23–92% [25]. The mercury
concentrations in the various solid wastes from five capital
steel companies in Japan had been reported to be BDL–28,500 g/kg
by Fukuda et al. [26].