56
H.-P. Gou et al.
XRD Analyses
XRD patterns of the oxidation products obtained at different reaction temperatures
are shown in Fig. 4. When the reaction temperatures were 1173, 1223, and 1273 K,
the main phases of the products were CaSO 4 , Fe 3 O 4 , MgFe 2 O 4 , ZnFe 2 O 4 , Zn 2 SiO 4 ,
ZnO, and PbFe 4 O 7 . It is obviously seen that the element of S did not escape from
the ore in the form of SO 2 . Since the content of Ca in the ore was 13.14%, the element of S combined with the element of Ca to form CaSO 4 during the oxidation
process. Therefore, the oxidation reactions of the sulfide occurred as Eqs. (9), (10),
and (11). When the reaction temperature was higher than 1173 K, the sulfide in the
ore turned into the oxide after 2 h. When the reaction temperature reached 1323 K,
the diffraction peaks of Zn 2 SiO 4 disappeared. It means that Zn 2 SiO 4 decomposed
at this temperature. When the reaction temperature was 1373 K, a new phase of
Ca 2 (Mg,Fe,Al) 6 (Si,Al) 6 O 20 appeared in the products. When the reaction temperatures were 1423 K, the diffraction peaks of Ca 2 (Mg,Fe,Al) 6 (Si,Al) 6 O 20 disappeared
and a new phase of Ca 2 Fe 2 O 5 appeared. When the reaction temperatures were 1473 K,
the intensities of diffraction peaks of CaSO 4 obviously weakened. It is confirmed
that the element of S could be removed from the low grade lead–zinc oxide ore when
the reaction temperature reached 1473 K. This explained the reason for the slight
loss of weight appeared at the end of the TG curve.
ZnS + 2O 2 + CaCO 3 → ZnO + CaSO 4 + CO 2 ↑
(9)
PbS + 2O 2 + CaCO 3 → PbO + CaSO 4 + CO 2 ↑
(10)
FeS 2 + 3.75O 2 + 2CaCO 3 → 0.5Fe 2 O 3 + 2CaSO 4 + 2CO 2 ↑
(11)
Figure 5 is the appearance of the products obtained at 1173 K and 1473 K, respectively. It is obvious that the sintering phenomenon of the product obtained at 1473 K
was more serious than the other one. It is because that the acicular calcium ferrites
(SFCA-I) was quickly formed by the reaction between Fe 2 O 3 and CaO, absorbing
a small amount of SiO 2 and Al 2 O 3 . When the reaction temperature was 1473 K, a
melt formed and covered the ore surface, which led to the sintering phenomenon [9].
The Percentages of Mass Loss
The percentages of mass loss obtained at different reaction temperatures are shown
in Fig. 6. With the increase of reaction temperature, the percentages of mass loss
increased obviously. The percentage of mass loss obtained at 1473 K was 29.36%,
which was much higher than the maximum mass loss in the TG curve. Combined
with the XRD spectrum, it is found that the decomposition of CaSO 4 led to the
increase of the mass loss.
H.-P. Gou et al.
XRD Analyses
XRD patterns of the oxidation products obtained at different reaction temperatures
are shown in Fig. 4. When the reaction temperatures were 1173, 1223, and 1273 K,
the main phases of the products were CaSO 4 , Fe 3 O 4 , MgFe 2 O 4 , ZnFe 2 O 4 , Zn 2 SiO 4 ,
ZnO, and PbFe 4 O 7 . It is obviously seen that the element of S did not escape from
the ore in the form of SO 2 . Since the content of Ca in the ore was 13.14%, the element of S combined with the element of Ca to form CaSO 4 during the oxidation
process. Therefore, the oxidation reactions of the sulfide occurred as Eqs. (9), (10),
and (11). When the reaction temperature was higher than 1173 K, the sulfide in the
ore turned into the oxide after 2 h. When the reaction temperature reached 1323 K,
the diffraction peaks of Zn 2 SiO 4 disappeared. It means that Zn 2 SiO 4 decomposed
at this temperature. When the reaction temperature was 1373 K, a new phase of
Ca 2 (Mg,Fe,Al) 6 (Si,Al) 6 O 20 appeared in the products. When the reaction temperatures were 1423 K, the diffraction peaks of Ca 2 (Mg,Fe,Al) 6 (Si,Al) 6 O 20 disappeared
and a new phase of Ca 2 Fe 2 O 5 appeared. When the reaction temperatures were 1473 K,
the intensities of diffraction peaks of CaSO 4 obviously weakened. It is confirmed
that the element of S could be removed from the low grade lead–zinc oxide ore when
the reaction temperature reached 1473 K. This explained the reason for the slight
loss of weight appeared at the end of the TG curve.
ZnS + 2O 2 + CaCO 3 → ZnO + CaSO 4 + CO 2 ↑
(9)
PbS + 2O 2 + CaCO 3 → PbO + CaSO 4 + CO 2 ↑
(10)
FeS 2 + 3.75O 2 + 2CaCO 3 → 0.5Fe 2 O 3 + 2CaSO 4 + 2CO 2 ↑
(11)
Figure 5 is the appearance of the products obtained at 1173 K and 1473 K, respectively. It is obvious that the sintering phenomenon of the product obtained at 1473 K
was more serious than the other one. It is because that the acicular calcium ferrites
(SFCA-I) was quickly formed by the reaction between Fe 2 O 3 and CaO, absorbing
a small amount of SiO 2 and Al 2 O 3 . When the reaction temperature was 1473 K, a
melt formed and covered the ore surface, which led to the sintering phenomenon [9].
The Percentages of Mass Loss
The percentages of mass loss obtained at different reaction temperatures are shown
in Fig. 6. With the increase of reaction temperature, the percentages of mass loss
increased obviously. The percentage of mass loss obtained at 1473 K was 29.36%,
which was much higher than the maximum mass loss in the TG curve. Combined
with the XRD spectrum, it is found that the decomposition of CaSO 4 led to the
increase of the mass loss.