Phase Evolution During the Oxidation Process of Low …
55
database of FactSage do not contain the relevant data of Zn 4 Si 2 O 7 (OH) 2 ·H 2 O, G
θ
of Eq. (8) is not calculated. Equation (8) belongs to dehydration reaction, which can
occur at a lower temperature. By comparing G
θ of Eqs. (5–7), it can be seen that
the oxygen in the air gives priority to react with FeS 2 , which is followed by ZnS and
PbS.
CaMg(CO 3 ) 2 → CaO + MgO + 2CO 2 ↑
(1)
CaCO 3 → CaO + CO 2 ↑
(2)
ZnCO 3 → ZnO + CO 2 ↑
(3)
PbCO 3 → PbO + CO 2 ↑
(4)
ZnS + 1.5 O 2 → ZnO + SO 2 ↑
(5)
PbS + 1.5 O 2 → PbO + SO 2 ↑
(6)
6/11FeS 2 + 1.5O 2 → 3/11Fe 2 O 3 + 12/11SO 2 ↑
(7)
Zn 4 Si 2 O 7 (OH) 2 · H 2 O → 2Zn 2 SiO 4 + 2H 2 O ↑
(8)
According to the results of TG-DTA curves, the oxidation process of the low
grade lead–zinc oxide ore was divided into five stages. In the first stage, an obvious
endothermic peak appeared at 394.4 K, which was mainly due to the removal of
crystal water from the hemimorphite (Zn 4 Si 2 O 7 (OH) 2 ·H 2 O). In the second stage,
there were two endothermic peaks occurred at 556.3 and 595.6 K, which were due
to the decomposition of smithsonite (ZnCO 3 ) and cerusite (PbCO 3 ). In the third
stage, there were three significant exothermic peaks at 736.0, 824.6, and 857.3 K.
The exothermic peaks were, respectively, caused by the oxidation reactions of pyrite
(FeS 2 ), sphalerite (ZnS), and galena (PbS), which were corresponded to Eqs. (7),
(5), and (6). As the reaction temperature increased, an endothermic peak appeared
at 1060.8 K in the fourth stage. This was caused by the decomposition of dolomite
(CaMg(CO 3 ) 2 ) and calcite (CaCO 3 ). When the reaction temperature was higher than
1150 K, a plateau appeared in the TG curve. There were no obvious endothermic or
exothermic peaks in this stage. It is worth noting that a slight loss of weight appeared
at the end of the TG curve, which would be further discussed with the results of XRD
analyses.
55
database of FactSage do not contain the relevant data of Zn 4 Si 2 O 7 (OH) 2 ·H 2 O, G
θ
of Eq. (8) is not calculated. Equation (8) belongs to dehydration reaction, which can
occur at a lower temperature. By comparing G
θ of Eqs. (5–7), it can be seen that
the oxygen in the air gives priority to react with FeS 2 , which is followed by ZnS and
PbS.
CaMg(CO 3 ) 2 → CaO + MgO + 2CO 2 ↑
(1)
CaCO 3 → CaO + CO 2 ↑
(2)
ZnCO 3 → ZnO + CO 2 ↑
(3)
PbCO 3 → PbO + CO 2 ↑
(4)
ZnS + 1.5 O 2 → ZnO + SO 2 ↑
(5)
PbS + 1.5 O 2 → PbO + SO 2 ↑
(6)
6/11FeS 2 + 1.5O 2 → 3/11Fe 2 O 3 + 12/11SO 2 ↑
(7)
Zn 4 Si 2 O 7 (OH) 2 · H 2 O → 2Zn 2 SiO 4 + 2H 2 O ↑
(8)
According to the results of TG-DTA curves, the oxidation process of the low
grade lead–zinc oxide ore was divided into five stages. In the first stage, an obvious
endothermic peak appeared at 394.4 K, which was mainly due to the removal of
crystal water from the hemimorphite (Zn 4 Si 2 O 7 (OH) 2 ·H 2 O). In the second stage,
there were two endothermic peaks occurred at 556.3 and 595.6 K, which were due
to the decomposition of smithsonite (ZnCO 3 ) and cerusite (PbCO 3 ). In the third
stage, there were three significant exothermic peaks at 736.0, 824.6, and 857.3 K.
The exothermic peaks were, respectively, caused by the oxidation reactions of pyrite
(FeS 2 ), sphalerite (ZnS), and galena (PbS), which were corresponded to Eqs. (7),
(5), and (6). As the reaction temperature increased, an endothermic peak appeared
at 1060.8 K in the fourth stage. This was caused by the decomposition of dolomite
(CaMg(CO 3 ) 2 ) and calcite (CaCO 3 ). When the reaction temperature was higher than
1150 K, a plateau appeared in the TG curve. There were no obvious endothermic or
exothermic peaks in this stage. It is worth noting that a slight loss of weight appeared
at the end of the TG curve, which would be further discussed with the results of XRD
analyses.