3006 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The result of surface analysis of the residue after extrac-
tion using SEM-EDS suggests that the residue was PbCl2.
In addition, almost all SO42– was released from PbSO4.
These indicate that extraction of PbSO4 was completed
while the formation of Pb-Cl complexes (e.g., PbCl
3
-and
PbCl
4
2- )was limited due to the saturation of Pb-Cl com-
pounds, such as PbCl2.
Next, the coupled extraction-cementation (CEC)
method was applied to improve Pb extraction efficiency
using NaCl-HCl. The CEC method is a technique that com-
bines two processes: extraction by NaCl-HCl and recovery
of extracted metals on ZVI (Silwamba 2020). Once metals
are extracted by NaCl-HCl, the extracted metals are soon
reductively deposited on ZVI by cementation. Therefore,
this process could keep the concentration of Pb2+ lower
than its saturation concentration in the chloride system.
Figure 3 shows effects of NaCl concentration and time on
distribution of Pb in ZVI, residue, and solution after the
CEC experiments. Almost all of the Pb was recovered on
ZVI after CEC experiments for 24 h irrespective of NaCl
concentration (0.5−5.0 M) (Figure 3a). As can be seen in
Figure 3b, while almost all of the Pb was recovered on ZVI
for 1 h, ~20% of extracted Pb2+ remained in solution for
0.5 h. The surface of the magnetic fraction obtained from
the CEC experiment using NaCl 5.0 M for 24 h was ana-
lyzed using SEM-EDS, and the result indicated that the
extracted Pb2+ was reductively deposited on ZVI via the
following cementation reaction
PbCl Fe Pb 4Cl Fe
4
2 0 0 2+ +=++--
Effects of Pretreatments on ZnS Depression in
Flotation
As described in the previous sections, PbSO4 could be
extracted and removed with CH3COONH4 and NaCl-
HCl. Therefore, the effects of the pretreatments on ZnS
depression in flotation were investigated. Flotation experi-
ments using a model sample (ZnS/PbSO4 mixture) with
and without the pretreatments were conducted. Prior to
the flotation experiments, the mixture of 15 g ZnS and 5 g
PbSO4 was treated with 3.5 M of CH3COONH4 for 30
min or 5 M of NaCl acidified with 0.1 M of HCl and 5 g
of ZVI for 1 h, and then flotation experiments were con-
ducted with ~5 kg/t ZnSO4 (100 ppm Zn2+) and 1 kg/t
Na2SO3 as depressants. The flotation results show that the
floatability of ZnS was clearly depressed from ~80% to
~7% and ~2% with pretreatments using CH3COONH4
or NaCl-HCl, respectively (Figure 4).
To confirm the depression of ZnS floatability with the
pretreatments, pretreated samples reacted with ZnSO4 for
3 min and Na2SO3 for 3 min, a ~5 mL aliquots of the
flotation pulp for each test were collected, and the filtrates
were analyzed by ICP-AES. The concentration of Pb2+ in
the filtrate without the pretreatment was 3.3 ppm which
decreased to 0.09 ppm and 0.20 ppm with pretreatments
using CH3COONH4 or NaCl-HCl, respectively. On the
other hand, the concentrations of Zn2+ in the filtrates
without the pretreatment and with pretreatments using
CH3COONH4 or NaCl-HCl showed 96.5, 95.4, and
95.2 ppm, respectively. Based on thermodynamics calcu-
lation using following equations, the possibility of lead
Figure 3. Effects of NaCl concentration and time on distribution of Pb in ZVI, residue, and
solution: (a) NaCl 0.5−5.0 M for 24 h and (b) NaCl 5.0 M for 0−1 h
The result of surface analysis of the residue after extrac-
tion using SEM-EDS suggests that the residue was PbCl2.
In addition, almost all SO42– was released from PbSO4.
These indicate that extraction of PbSO4 was completed
while the formation of Pb-Cl complexes (e.g., PbCl
3
-and
PbCl
4
2- )was limited due to the saturation of Pb-Cl com-
pounds, such as PbCl2.
Next, the coupled extraction-cementation (CEC)
method was applied to improve Pb extraction efficiency
using NaCl-HCl. The CEC method is a technique that com-
bines two processes: extraction by NaCl-HCl and recovery
of extracted metals on ZVI (Silwamba 2020). Once metals
are extracted by NaCl-HCl, the extracted metals are soon
reductively deposited on ZVI by cementation. Therefore,
this process could keep the concentration of Pb2+ lower
than its saturation concentration in the chloride system.
Figure 3 shows effects of NaCl concentration and time on
distribution of Pb in ZVI, residue, and solution after the
CEC experiments. Almost all of the Pb was recovered on
ZVI after CEC experiments for 24 h irrespective of NaCl
concentration (0.5−5.0 M) (Figure 3a). As can be seen in
Figure 3b, while almost all of the Pb was recovered on ZVI
for 1 h, ~20% of extracted Pb2+ remained in solution for
0.5 h. The surface of the magnetic fraction obtained from
the CEC experiment using NaCl 5.0 M for 24 h was ana-
lyzed using SEM-EDS, and the result indicated that the
extracted Pb2+ was reductively deposited on ZVI via the
following cementation reaction
PbCl Fe Pb 4Cl Fe
4
2 0 0 2+ +=++--
Effects of Pretreatments on ZnS Depression in
Flotation
As described in the previous sections, PbSO4 could be
extracted and removed with CH3COONH4 and NaCl-
HCl. Therefore, the effects of the pretreatments on ZnS
depression in flotation were investigated. Flotation experi-
ments using a model sample (ZnS/PbSO4 mixture) with
and without the pretreatments were conducted. Prior to
the flotation experiments, the mixture of 15 g ZnS and 5 g
PbSO4 was treated with 3.5 M of CH3COONH4 for 30
min or 5 M of NaCl acidified with 0.1 M of HCl and 5 g
of ZVI for 1 h, and then flotation experiments were con-
ducted with ~5 kg/t ZnSO4 (100 ppm Zn2+) and 1 kg/t
Na2SO3 as depressants. The flotation results show that the
floatability of ZnS was clearly depressed from ~80% to
~7% and ~2% with pretreatments using CH3COONH4
or NaCl-HCl, respectively (Figure 4).
To confirm the depression of ZnS floatability with the
pretreatments, pretreated samples reacted with ZnSO4 for
3 min and Na2SO3 for 3 min, a ~5 mL aliquots of the
flotation pulp for each test were collected, and the filtrates
were analyzed by ICP-AES. The concentration of Pb2+ in
the filtrate without the pretreatment was 3.3 ppm which
decreased to 0.09 ppm and 0.20 ppm with pretreatments
using CH3COONH4 or NaCl-HCl, respectively. On the
other hand, the concentrations of Zn2+ in the filtrates
without the pretreatment and with pretreatments using
CH3COONH4 or NaCl-HCl showed 96.5, 95.4, and
95.2 ppm, respectively. Based on thermodynamics calcu-
lation using following equations, the possibility of lead
Figure 3. Effects of NaCl concentration and time on distribution of Pb in ZVI, residue, and
solution: (a) NaCl 0.5−5.0 M for 24 h and (b) NaCl 5.0 M for 0−1 h