6
reacts with NaOH and O2, resulting in the formation of
soluble Na2TeO3, which is then transported to the solu-
tion, while the Cu remains in the residue, forming a layer
of Cu2O. As the reaction time increases, the unreacted
Cu2Te particle core diminishes, and the Cu2O residue layer
slowly thickens. The high-pressure conditions expedite the
diffusion of NaOH and O2 reactants toward the reaction
interface, along with the outward transportation of the
Na2TeO3 product to the solution until the Te selective dis-
solution process from Cu2Te is complete.
Xu et al. [60] introduced an innovative alkaline leach-
ing method utilizing H2O2 as an oxidizing agent for the
effective extraction of Te and Cu from Cu2Te, with no pro-
duction of solid or liquid waste. The process, as illustrated
in Figure 4, involved two stages of atmospheric alkaline
leaching for the separation of Cu and Te, followed by neu-
tralizing precipitation with H2SO4 to recover Te. A com-
prehensive investigation into various factors impacting the
alkaline leaching operation was conducted, resulting in the
identification of optimal conditions: 5 mol/L NaOH, L/S
ratio of 5 mL/g, 25°C, H2O2 /Cu2Te mole ratio of 5 for
5 hours. The optimal alkaline leaching conditions facili-
tated the reduction of Te content in the solid phase from
31.75 wt% to 4.63 wt%, achieving an impressive Te leach-
ing rate of around 91%. Following Te leaching, H2SO4
was employed to modify the pH to 4.5 for effective TeO2
precipitation. TeO2 crystallization was accomplished within
1 hour, leading to an overall Te recovery rate of nearly 90%.
Relying solely on the leaching process is inadequate
for the efficient separation of Te, necessitating additional
steps to obtain pure Te. Selective precipitation stands as
one of the commonly utilized purification techniques for
the separation of Te from leachate solutions. The specific
flowsheets and precipitation agents employed are contin-
gent on the types of leaching processes involved. Notably,
various approaches have been employed to extract Te
from the solution, including copper displacement, reduc-
tion precipitation, pH adjustment through neutralization,
and electrolysis [40, 61, 62]. However, it is important to
note that, with a few exceptions, Te is predominantly pre-
cipitated from a solution in the form of compounds that
demand subsequent extraction and purification to achieve
higher-purity Te. Various chemical agents, including cop-
per, cuprous ions [63], hydrazine hydrate [64], and sodium
sulfite [65], have been employed for the precipitation of Te
from sulfuric acid media. Notably, copper stands out as a
highly cost-effective reducing agent, with reports demon-
strating its effectiveness for Te and Te/Se cementation from
aqueous solutions [55].
After the alkaline leaching process, Te remains in the
leaching solution as sodium tellurite (Na2TeO3), a soluble
compound in the liquid phase, and can be subsequently
Figure 3. Mechanisms of the oxidizing alkaline leaching process at (a)
atmospheric pressure, and (b) pressure at 0.7 MPa. Regenerated from [59]
reacts with NaOH and O2, resulting in the formation of
soluble Na2TeO3, which is then transported to the solu-
tion, while the Cu remains in the residue, forming a layer
of Cu2O. As the reaction time increases, the unreacted
Cu2Te particle core diminishes, and the Cu2O residue layer
slowly thickens. The high-pressure conditions expedite the
diffusion of NaOH and O2 reactants toward the reaction
interface, along with the outward transportation of the
Na2TeO3 product to the solution until the Te selective dis-
solution process from Cu2Te is complete.
Xu et al. [60] introduced an innovative alkaline leach-
ing method utilizing H2O2 as an oxidizing agent for the
effective extraction of Te and Cu from Cu2Te, with no pro-
duction of solid or liquid waste. The process, as illustrated
in Figure 4, involved two stages of atmospheric alkaline
leaching for the separation of Cu and Te, followed by neu-
tralizing precipitation with H2SO4 to recover Te. A com-
prehensive investigation into various factors impacting the
alkaline leaching operation was conducted, resulting in the
identification of optimal conditions: 5 mol/L NaOH, L/S
ratio of 5 mL/g, 25°C, H2O2 /Cu2Te mole ratio of 5 for
5 hours. The optimal alkaline leaching conditions facili-
tated the reduction of Te content in the solid phase from
31.75 wt% to 4.63 wt%, achieving an impressive Te leach-
ing rate of around 91%. Following Te leaching, H2SO4
was employed to modify the pH to 4.5 for effective TeO2
precipitation. TeO2 crystallization was accomplished within
1 hour, leading to an overall Te recovery rate of nearly 90%.
Relying solely on the leaching process is inadequate
for the efficient separation of Te, necessitating additional
steps to obtain pure Te. Selective precipitation stands as
one of the commonly utilized purification techniques for
the separation of Te from leachate solutions. The specific
flowsheets and precipitation agents employed are contin-
gent on the types of leaching processes involved. Notably,
various approaches have been employed to extract Te
from the solution, including copper displacement, reduc-
tion precipitation, pH adjustment through neutralization,
and electrolysis [40, 61, 62]. However, it is important to
note that, with a few exceptions, Te is predominantly pre-
cipitated from a solution in the form of compounds that
demand subsequent extraction and purification to achieve
higher-purity Te. Various chemical agents, including cop-
per, cuprous ions [63], hydrazine hydrate [64], and sodium
sulfite [65], have been employed for the precipitation of Te
from sulfuric acid media. Notably, copper stands out as a
highly cost-effective reducing agent, with reports demon-
strating its effectiveness for Te and Te/Se cementation from
aqueous solutions [55].
After the alkaline leaching process, Te remains in the
leaching solution as sodium tellurite (Na2TeO3), a soluble
compound in the liquid phase, and can be subsequently
Figure 3. Mechanisms of the oxidizing alkaline leaching process at (a)
atmospheric pressure, and (b) pressure at 0.7 MPa. Regenerated from [59]