disk pelletizer, located at an angle, this machine rotates at a predetermined number of
rotations per minute. Additional water is sprayed onto the disk in which the material is
coagulated and forms pellets in a continuous rotation movement. The resultant pellets
at this stage of the process are called green pellets, because they do not have the
necessary strength.
(ii)
Formation of green balls or pellets. From mixing, the filter cake is sent to the
balling area where the ore is agglomerated on balling discs or balling drums into green
(or unfired) pellets. Both drums and discs ball the ore to the size about 8-16 mm. The
drums typically have very high recycle rates, the same is true for the screens applied in
the process for screening out undersize and oversize pieces to be put back through the
drum. The discs are usually not equipped with separate screens.
(iii)
Induration or heat hardening. Green pellets induration process (Martinez et
al., 2014) consists of four main steps: drying of green pellets; preheating them (Pape,
Frans and Geiger, 1976) at the temperatures of approximately 1000 °C with oxidation
of the magnetite and decomposition of the carbonates present; firing of pellets at
1300
o
C to sinter the iron oxide particles; cooling of hot pellets before discharging. The
pellets larger than the required size are crushed and sent back for pelletizing along with
those of smaller sizes to prepare green pellets from them again.
Figure 1. Schematic of the two principle pelletizing processes: (a) straight grate
pelletizing process (Mourão, 2012); (b) grate-kiln pelletizing process (Metso, 2012)
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