3
RESULTS AND DISCUSSIONS
Characterization of Crude Se
A duplicate elemental analysis was performed on the as-
received crude Se material. The samples were analyzed at an
external analytical laboratory in Nevada. Table 1 shows the
characterization of the crude material for all the elements
described in the previous section.
Table 1 indicted that the feed sample had a very high
concentration of precious metals, particularly when com-
pared to the usual cut-off grades of several Cu or Au mines.
Among the elements listed in Table 1, only a few have a sig-
nificant market value. This is illustrated in Figure 4, which
displays only the elements that contribute to more than 1%
of the market value in the crude material. The values were
calculated by multiplying the element concentration with
the market value per kilogram.
Se Leaching Process
During the oxidative alkaline leaching process of Se, the
pH and the ORP were continuously monitored for the
purpose of process optimization. Knowing the model and
brand of the electrode enables the conversion from ORP
(referenced to Ag/AgCl) to Eh (referenced to the standard
hydrogen electrode). All measurements were adjusted to
account for the change in temperature. The only limitation
of the pH and ORP probe is its temperature limit, which
cannot exceed 80°C.
Figure 5 shows a Pourbaix Diagram for a system with a
4 M NaOH concentration and a 10% Se (Mass/Volume).
Both oxidants showed similar behavior (products move
in the same direction with time) on the Eh-pH diagram,
indicating that the reactions followed comparable thermo-
dynamic pathways. As indicated, when using H2O2 leach-
ing, the pH decreased from 13.326 to 12.810, whereas
with oxygen gas, the pH decreased from 11.290 to 10.480.
Regarding Eh, the H2O2 leaching experienced an increase
Figure 2. A photograph of the leaching reactor used in this
study
Figure 3. Pourbaix Diagram (Eh-pH) for a solution with a
10% Se solid/liquid ratio and 4 M NaOH at 80°C
Table 1. Elemental analysis of the crude Se material
Element Concentration [ppm]
Ag 1491
As 698
Au 370.5
Bi 2506.5
Cu 264
Fe 678
Ga Below detection limit
Ir 0.04
Pb 161.5
Pd 517
Pt 62
S 6804
Sb 135.5
Se 904505
Te 27924
Zn 13
RESULTS AND DISCUSSIONS
Characterization of Crude Se
A duplicate elemental analysis was performed on the as-
received crude Se material. The samples were analyzed at an
external analytical laboratory in Nevada. Table 1 shows the
characterization of the crude material for all the elements
described in the previous section.
Table 1 indicted that the feed sample had a very high
concentration of precious metals, particularly when com-
pared to the usual cut-off grades of several Cu or Au mines.
Among the elements listed in Table 1, only a few have a sig-
nificant market value. This is illustrated in Figure 4, which
displays only the elements that contribute to more than 1%
of the market value in the crude material. The values were
calculated by multiplying the element concentration with
the market value per kilogram.
Se Leaching Process
During the oxidative alkaline leaching process of Se, the
pH and the ORP were continuously monitored for the
purpose of process optimization. Knowing the model and
brand of the electrode enables the conversion from ORP
(referenced to Ag/AgCl) to Eh (referenced to the standard
hydrogen electrode). All measurements were adjusted to
account for the change in temperature. The only limitation
of the pH and ORP probe is its temperature limit, which
cannot exceed 80°C.
Figure 5 shows a Pourbaix Diagram for a system with a
4 M NaOH concentration and a 10% Se (Mass/Volume).
Both oxidants showed similar behavior (products move
in the same direction with time) on the Eh-pH diagram,
indicating that the reactions followed comparable thermo-
dynamic pathways. As indicated, when using H2O2 leach-
ing, the pH decreased from 13.326 to 12.810, whereas
with oxygen gas, the pH decreased from 11.290 to 10.480.
Regarding Eh, the H2O2 leaching experienced an increase
Figure 2. A photograph of the leaching reactor used in this
study
Figure 3. Pourbaix Diagram (Eh-pH) for a solution with a
10% Se solid/liquid ratio and 4 M NaOH at 80°C
Table 1. Elemental analysis of the crude Se material
Element Concentration [ppm]
Ag 1491
As 698
Au 370.5
Bi 2506.5
Cu 264
Fe 678
Ga Below detection limit
Ir 0.04
Pb 161.5
Pd 517
Pt 62
S 6804
Sb 135.5
Se 904505
Te 27924
Zn 13