816
T. Kerry et al.
Table 2 Weight loss of zinc and carbon from individual dust samples
Goethite
BF dust
BOF dust
Element
Residence
time
(min)
Mass of
element
(g)
Weight
loss (%)
Mass of
element
(g)
Weight
loss (%)
Mass of
element
(g)
Weight
loss (%)
Zn
0
0.12
8.33
0.06
96.67
0.007
71.43
30
0.11
0.002
0.002
C
0
0.0007
57.14
0.4
27.5
0.023
95.65
30
0.0003
0.29
0.001
lost in this time indicating the self-reducing behaviour of the dust. On the contrary,
in goethite, there is extremely low quantity of carbon to facilitate the zinc reduction reaction. Zinc will be present in the varying industrial waste dusts in different
mineralogical forms but primarily as zinc oxide (ZnO) and franklinite (ZnFe 2 O 4 )
[6–8]. These compounds will undergo simultaneous reduction and vaporisation at
the temperatures studied in the presence of a reducing agent [8].
The reduction of ZnO primarily takes place through the mechanism described by
reactions 1–3. The overall mechanism is given by 1 which is mediated by reactions 2
and 3 [13].
ZnO(s) + C(s) ↔ CO(g) + Zn(g)
(1)
C(s) + CO 2 (g) ↔ 2CO(g)
(2)
ZnO(s) + CO(g) ↔ CO 2 (g) + Zn(g)
(3)
In the case of franklinite, it has been shown that at 1000 °C franklinite decomposes into zinc oxide and hematite through reaction 4 [14]. Concurrently, direct
reaction with carbon can lead to the release of zinc vapour (reaction 5 as mediated
by reaction 2) [14].
ZnFe 2 O 4 (s) ↔ ZnO(s) + Fe 2 O 3 (s)
(4)
3ZnFe 2 O 4 (s) + 4C(s) ↔ 3Zn(g) + 2Fe 3 O 4 (s) + 4CO(g)
(5)
In the case of reaction 4, this is obviously followed by the previously described
reduction process given by reactions 1–3. It can be seen that by increasing the carbon content of the material the reduction and hence, vaporisation of zinc can be
realised and kinetics increased. However, excess carbon should be accounted for
when looking at the carbon balance of the process.
The reducing behaviour of carbon also has an impact on the oxidation states of
iron found in the various materials. XRD analysis has shown the starting and final
T. Kerry et al.
Table 2 Weight loss of zinc and carbon from individual dust samples
Goethite
BF dust
BOF dust
Element
Residence
time
(min)
Mass of
element
(g)
Weight
loss (%)
Mass of
element
(g)
Weight
loss (%)
Mass of
element
(g)
Weight
loss (%)
Zn
0
0.12
8.33
0.06
96.67
0.007
71.43
30
0.11
0.002
0.002
C
0
0.0007
57.14
0.4
27.5
0.023
95.65
30
0.0003
0.29
0.001
lost in this time indicating the self-reducing behaviour of the dust. On the contrary,
in goethite, there is extremely low quantity of carbon to facilitate the zinc reduction reaction. Zinc will be present in the varying industrial waste dusts in different
mineralogical forms but primarily as zinc oxide (ZnO) and franklinite (ZnFe 2 O 4 )
[6–8]. These compounds will undergo simultaneous reduction and vaporisation at
the temperatures studied in the presence of a reducing agent [8].
The reduction of ZnO primarily takes place through the mechanism described by
reactions 1–3. The overall mechanism is given by 1 which is mediated by reactions 2
and 3 [13].
ZnO(s) + C(s) ↔ CO(g) + Zn(g)
(1)
C(s) + CO 2 (g) ↔ 2CO(g)
(2)
ZnO(s) + CO(g) ↔ CO 2 (g) + Zn(g)
(3)
In the case of franklinite, it has been shown that at 1000 °C franklinite decomposes into zinc oxide and hematite through reaction 4 [14]. Concurrently, direct
reaction with carbon can lead to the release of zinc vapour (reaction 5 as mediated
by reaction 2) [14].
ZnFe 2 O 4 (s) ↔ ZnO(s) + Fe 2 O 3 (s)
(4)
3ZnFe 2 O 4 (s) + 4C(s) ↔ 3Zn(g) + 2Fe 3 O 4 (s) + 4CO(g)
(5)
In the case of reaction 4, this is obviously followed by the previously described
reduction process given by reactions 1–3. It can be seen that by increasing the carbon content of the material the reduction and hence, vaporisation of zinc can be
realised and kinetics increased. However, excess carbon should be accounted for
when looking at the carbon balance of the process.
The reducing behaviour of carbon also has an impact on the oxidation states of
iron found in the various materials. XRD analysis has shown the starting and final