Zinc Reduction/Vaporisation Behaviour from Metallurgical Wastes
817
mineralogy (Table 3) indicating the reactions taking place. It has been shown that
there is enough carbon present in the BF dust to fully reduce the iron from hematite
to the metallic form. Similarly, in BOF dust, the magnetite present has been reduced
leaving metallic iron and wüstite. It is apparent that there was insufficient carbon
within the sample to fully reduce the iron. In the case of goethite, limited reduction
has been observed with some hematite being formed, this is due to the minimal
carbon within the sample. The ability of the material to undergo self-reduction is of
interest as it can potentially minimise use of virgin carbon sources within the process.
In order to volatilise the remaining zinc and investigate the reducing effect on iron
within the sample, it was decided to mix materials. Goethite and BOF dust were both
mixed in 60:40 ratios with BF dust, a material rich in carbon (41.3 wt%). The ratio
was chosen to allow enough carbon for the theoretical complete reduction of Zn and
Fe. The accentuated effect of the reductant on the sample weight loss is shown in
Fig. 3. After 30 min, there is roughly an extra 10 and 20% weight loss in the BOF/BF
dust and goethite/BF dust mixtures, respectively, when compared to a calculated
cumulative value of the two individual dusts. This can be accounted for by reduction
of iron and zinc and loss of zinc vapour and carbon oxides. Table 4 shows the loss
of carbon and zinc from the material. It can be seen that in both mixtures, the zinc
vaporisation is mostly complete. Similarly, a large proportion of the carbon present
has also been lost from the sample through reduction reactions.
Table 3 Fe-bearing phases
present in industrial waste
dusts before and after heating
in inert atmosphere at
1000 °C
Initial Fe-bearing
phases
30 min Fe-bearing
phases
Goethite
FeOOH
Fe 3 O 4 , Fe 2 O 3
BF dust
Fe 2 O 3
Fe
BOF dust Fe, FeO, Fe 3 O 4
Fe, FeO
Fig. 3 Weight loss of mixed
dusts and the extra weight
loss calculated compared to
the behaviour of individual
dusts
0
300
600
900
1200
1500
1800
0
10
20
30
40
50
60
Weight Loss (%)
Residence Time (s)
Goethite/ BF Dust 60/40
Extra Weight Loss
BOF/ BF Dust 60/40
Extra Weight Loss
817
mineralogy (Table 3) indicating the reactions taking place. It has been shown that
there is enough carbon present in the BF dust to fully reduce the iron from hematite
to the metallic form. Similarly, in BOF dust, the magnetite present has been reduced
leaving metallic iron and wüstite. It is apparent that there was insufficient carbon
within the sample to fully reduce the iron. In the case of goethite, limited reduction
has been observed with some hematite being formed, this is due to the minimal
carbon within the sample. The ability of the material to undergo self-reduction is of
interest as it can potentially minimise use of virgin carbon sources within the process.
In order to volatilise the remaining zinc and investigate the reducing effect on iron
within the sample, it was decided to mix materials. Goethite and BOF dust were both
mixed in 60:40 ratios with BF dust, a material rich in carbon (41.3 wt%). The ratio
was chosen to allow enough carbon for the theoretical complete reduction of Zn and
Fe. The accentuated effect of the reductant on the sample weight loss is shown in
Fig. 3. After 30 min, there is roughly an extra 10 and 20% weight loss in the BOF/BF
dust and goethite/BF dust mixtures, respectively, when compared to a calculated
cumulative value of the two individual dusts. This can be accounted for by reduction
of iron and zinc and loss of zinc vapour and carbon oxides. Table 4 shows the loss
of carbon and zinc from the material. It can be seen that in both mixtures, the zinc
vaporisation is mostly complete. Similarly, a large proportion of the carbon present
has also been lost from the sample through reduction reactions.
Table 3 Fe-bearing phases
present in industrial waste
dusts before and after heating
in inert atmosphere at
1000 °C
Initial Fe-bearing
phases
30 min Fe-bearing
phases
Goethite
FeOOH
Fe 3 O 4 , Fe 2 O 3
BF dust
Fe 2 O 3
Fe
BOF dust Fe, FeO, Fe 3 O 4
Fe, FeO
Fig. 3 Weight loss of mixed
dusts and the extra weight
loss calculated compared to
the behaviour of individual
dusts
0
300
600
900
1200
1500
1800
0
10
20
30
40
50
60
Weight Loss (%)
Residence Time (s)
Goethite/ BF Dust 60/40
Extra Weight Loss
BOF/ BF Dust 60/40
Extra Weight Loss