4
from -200 mV to -172 Mv, while the oxygen gas process
showed an increase from -88 mV to -43 mV.
A comparable decrease in pH over time was observed,
likely due to the consumption of sodium hydroxide.
Although both reactions remained thermodynamically
favored at lower pH values, the H2O2 reaction appeared to
consume less sodium hydroxide. Regarding Eh, the pres-
ence of an oxidizing agent appears to promote the forma-
tion of sodium selenite over time. The utilization of oxygen
gas increased the Eh by 35 mV compared to 28 mV when
H2O2 was used, which can be attributed to the continuous
supply of oxygen gas into the reactor.
MASS BALANCE OF THE LEACHING
PROCESS
Table 2 presents the concentrations and the recoveries of
metals in the solid residue obtained after alkaline leaching
using both leaching approaches: oxygen gas and H2O2 as
oxidizing agents. The recovery of Ag and Pd were 100%
with both oxidizing agents however, the recovery of Au
and Pt with H2O2 was 84% and 72%, respectively, whereas
with oxygen gas, both metals achieved 100% recovery.
Additionally, oxygen gas proved to be more effective for Te
removal, yielding a Te recovery of only 1% in the residue,
whereas the residue from the H2O2 method retained 11%
Te, over ten times higher, making H2O2 a less attractive
option for this application. Finally, oxygen gas resulted in a
selenium recovery in the residue of 58%, which is superior
to the 64% recovery achieved with H2O2, likely due to the
continuous supply of oxygen gas to the system.
During the leaching process with H2O2, the first 5
minutes were critical due to rapid foam production. This
foam would overflow during the first 5 minutes, if the reac-
tor was not sufficiently tall The foam formation suggests
that H2O2 may be partially decomposing and escaping at
the start of the reaction. This could explain the relatively
smaller increase in Eh, which is only 28 mV, compared to
the 25 mV observed with oxygen gas.
CONCLUSIONS
In this study, Se-rich crude material was characterized for
its potential to recover PGMs, precious metals, and other
critical elements. Characterization results revealed that the
crude Se contained promising concentrations of precious
metals, with 517 ppm Pd, 370 ppm Au, 62 ppm Pt, and
1491 ppm Ag. Additionally, elements such as Ir, As, Bi,
Cu, Fe, Pb, S, Sb, and Zn were detected. Given that Se
constituted most of the sample, this study focused on iden-
tifying a thermodynamic state in the Pourbaix diagram that
favored Se leaching (Michałek et al., 2024).
1%
22%
28%
3% 2%
0%
20%
40%
Ag Au Pd Pt Se Te
Element
Figure 4. Market value percentage of significant elements by
unit of crude material
Figure 5. Pourbaix Diagram (Eh-pH) of Se/H2O system
showing the thermodynamics of the reaction at the start and
the end of the reaction using H2O2 and oxygen as oxidants
Table 2. Elemental concentration and recovery in the solid
leach residue using oxygen gas and H
2 O
2 as oxidizing agents
El.
Con.
(O2)
Recovery
(O2)
Con.
(H2O2)
Recovery
(H2O2)
Ag 0.3% 100% 0.2% 100%
Au 0.1% 100% 0.05% 84%
Pd 0.1% 100% 0.1% 100%
Pt 0.01% 100% 0.01% 72%
Se 92% 58% 91% 64%
Te 0.07% 1% 0.5% 11%
from -200 mV to -172 Mv, while the oxygen gas process
showed an increase from -88 mV to -43 mV.
A comparable decrease in pH over time was observed,
likely due to the consumption of sodium hydroxide.
Although both reactions remained thermodynamically
favored at lower pH values, the H2O2 reaction appeared to
consume less sodium hydroxide. Regarding Eh, the pres-
ence of an oxidizing agent appears to promote the forma-
tion of sodium selenite over time. The utilization of oxygen
gas increased the Eh by 35 mV compared to 28 mV when
H2O2 was used, which can be attributed to the continuous
supply of oxygen gas into the reactor.
MASS BALANCE OF THE LEACHING
PROCESS
Table 2 presents the concentrations and the recoveries of
metals in the solid residue obtained after alkaline leaching
using both leaching approaches: oxygen gas and H2O2 as
oxidizing agents. The recovery of Ag and Pd were 100%
with both oxidizing agents however, the recovery of Au
and Pt with H2O2 was 84% and 72%, respectively, whereas
with oxygen gas, both metals achieved 100% recovery.
Additionally, oxygen gas proved to be more effective for Te
removal, yielding a Te recovery of only 1% in the residue,
whereas the residue from the H2O2 method retained 11%
Te, over ten times higher, making H2O2 a less attractive
option for this application. Finally, oxygen gas resulted in a
selenium recovery in the residue of 58%, which is superior
to the 64% recovery achieved with H2O2, likely due to the
continuous supply of oxygen gas to the system.
During the leaching process with H2O2, the first 5
minutes were critical due to rapid foam production. This
foam would overflow during the first 5 minutes, if the reac-
tor was not sufficiently tall The foam formation suggests
that H2O2 may be partially decomposing and escaping at
the start of the reaction. This could explain the relatively
smaller increase in Eh, which is only 28 mV, compared to
the 25 mV observed with oxygen gas.
CONCLUSIONS
In this study, Se-rich crude material was characterized for
its potential to recover PGMs, precious metals, and other
critical elements. Characterization results revealed that the
crude Se contained promising concentrations of precious
metals, with 517 ppm Pd, 370 ppm Au, 62 ppm Pt, and
1491 ppm Ag. Additionally, elements such as Ir, As, Bi,
Cu, Fe, Pb, S, Sb, and Zn were detected. Given that Se
constituted most of the sample, this study focused on iden-
tifying a thermodynamic state in the Pourbaix diagram that
favored Se leaching (Michałek et al., 2024).
1%
22%
28%
3% 2%
0%
20%
40%
Ag Au Pd Pt Se Te
Element
Figure 4. Market value percentage of significant elements by
unit of crude material
Figure 5. Pourbaix Diagram (Eh-pH) of Se/H2O system
showing the thermodynamics of the reaction at the start and
the end of the reaction using H2O2 and oxygen as oxidants
Table 2. Elemental concentration and recovery in the solid
leach residue using oxygen gas and H
2 O
2 as oxidizing agents
El.
Con.
(O2)
Recovery
(O2)
Con.
(H2O2)
Recovery
(H2O2)
Ag 0.3% 100% 0.2% 100%
Au 0.1% 100% 0.05% 84%
Pd 0.1% 100% 0.1% 100%
Pt 0.01% 100% 0.01% 72%
Se 92% 58% 91% 64%
Te 0.07% 1% 0.5% 11%