2
those studies utilized feed materials with significantly lower
Se concentrations than those used in this study (Lu et al.,
2015).
The Se leaching process developed in this study was
designed to oxidize Se and selenides, thereby making
them easier to leach (Dong et al., 2020). Several oxidation
methods can be applied, including soda roasting at 600°C
and oxidative alkaline leaching. The approach utilized in
this research was oxidative alkaline atmospheric leaching.
Oxygen gas and hydrogen peroxide were used as oxidizing
agents, and the expected reaction is shown in equation 1
(Lee et al., 2021).
2Se 2NaOH 2
7 O 2NaSeO H2O
2 4 "+++(1)
MATERIALS AND METHODS
Materials
Sodium hydroxide (NaOH, 98.5%) from Acros Organics,
USA was used to prepare a 4M NaOH solution. Hydrogen
peroxide (H2O2, 30%) from Taylor Scientific, USA was
used to prepare a 90 g/L solution. Lastly, oxygen gas
(99.2%) was purchased from Airgas, USA and was used
at 2 L/min. The metallurgical byproduct, commercially
known as Crude Selenium, was supplied by a mine located
in North America.
METHODS
Reactor
The reactor used in this research was a 1,000 mL jacketed
glass reactor manufactured by Ace Glass, USA. The reactor
is shown in Figure 2.
Eh and pH Measurements
Pourbaix diagrams (Eh-pH) are very useful in aqueous
chemistry because they provide fundamental insights about
the leaching process as they can predict the most stable spe-
cies under specific Eh and pH conditions (Huang, 2016).
In this research, Eh and pH were measured using pH/Eh
meter (Hanna HI98191), using the HI72911 electrode and
a 3.5M KCl solution. A Se Pourbaix Diagram is shown in
Figure 3.
Elemental Analysis
Elemental Analysis was conducted using Inductively
Coupled Plasma Mass Spectrometry (ICP-MS). The sam-
ples analyzed included the feed (crude Se), pregnant leach
solutions (PLS), rinse solution (deionized water used to
rinse the reactor), and solid residue. The elements analyzed
were Se, Te, Au, Ag, Pd, Pt, Cu, Pb, Zn, iridium (Ir), arse-
nic (As), bismuth (Bi), iron (Fe), gallium (Ga), sulfur (S),
and antimony (Sb).
Figure 1. Periodic table highlighting in blue the critical elements defined by the U.S. Department of Energy
those studies utilized feed materials with significantly lower
Se concentrations than those used in this study (Lu et al.,
2015).
The Se leaching process developed in this study was
designed to oxidize Se and selenides, thereby making
them easier to leach (Dong et al., 2020). Several oxidation
methods can be applied, including soda roasting at 600°C
and oxidative alkaline leaching. The approach utilized in
this research was oxidative alkaline atmospheric leaching.
Oxygen gas and hydrogen peroxide were used as oxidizing
agents, and the expected reaction is shown in equation 1
(Lee et al., 2021).
2Se 2NaOH 2
7 O 2NaSeO H2O
2 4 "+++(1)
MATERIALS AND METHODS
Materials
Sodium hydroxide (NaOH, 98.5%) from Acros Organics,
USA was used to prepare a 4M NaOH solution. Hydrogen
peroxide (H2O2, 30%) from Taylor Scientific, USA was
used to prepare a 90 g/L solution. Lastly, oxygen gas
(99.2%) was purchased from Airgas, USA and was used
at 2 L/min. The metallurgical byproduct, commercially
known as Crude Selenium, was supplied by a mine located
in North America.
METHODS
Reactor
The reactor used in this research was a 1,000 mL jacketed
glass reactor manufactured by Ace Glass, USA. The reactor
is shown in Figure 2.
Eh and pH Measurements
Pourbaix diagrams (Eh-pH) are very useful in aqueous
chemistry because they provide fundamental insights about
the leaching process as they can predict the most stable spe-
cies under specific Eh and pH conditions (Huang, 2016).
In this research, Eh and pH were measured using pH/Eh
meter (Hanna HI98191), using the HI72911 electrode and
a 3.5M KCl solution. A Se Pourbaix Diagram is shown in
Figure 3.
Elemental Analysis
Elemental Analysis was conducted using Inductively
Coupled Plasma Mass Spectrometry (ICP-MS). The sam-
ples analyzed included the feed (crude Se), pregnant leach
solutions (PLS), rinse solution (deionized water used to
rinse the reactor), and solid residue. The elements analyzed
were Se, Te, Au, Ag, Pd, Pt, Cu, Pb, Zn, iridium (Ir), arse-
nic (As), bismuth (Bi), iron (Fe), gallium (Ga), sulfur (S),
and antimony (Sb).
Figure 1. Periodic table highlighting in blue the critical elements defined by the U.S. Department of Energy