4
gas to eliminate excess oxygen. Following this, the cop-
per is cast into copper anodes through fire refining. These
anodes, comprising 98–99% pure copper, may contain
minor impurities such as Au, Ag, PGE, Se, and Te. Copper
cathode (99.9% pure) can be produced from the copper
anodes via electrorefining in a copper sulfate-sulfuric acid
electrolyte tank. A thorough explanation of the copper pro-
duction processes has been summarized by Moskalyk and
Alfantazi [35].
Anode slimes are collected from the bottom of the elec-
trolytic tanks during the refining of copper [36]. The type
of ore and the method of copper extraction significantly
impact the distribution of elements and the composition
of the anode slimes. Copper anode slimes typically consist
of Cu, Ni, Se, Te, Ag, Au, and PGE metals. The Te con-
tent usually falls within the range of 1–4 wt%, occasion-
ally reaching higher levels, such as 8–9 wt%. A significant
portion of Te (often exceeding 80%) is found as inclusions
at the grain boundaries of silver-copper-selenide-telluride
compounds in the copper anode slimes. The anode slimes
need to be further treated for the extraction of the precious
and critical metals. These slimes are regularly processed to
recover additional Cu and then to recover precious metals,
as well as minor elements including Se and Te.
While Te is considered as an impurity in electrolytic
copper and as a harmful substance in its natural form if
improperly disposed, represents a highly valuable by-prod-
uct when recovered efficiently from copper anode slimes
[37]. From a statistical perspective, 90% of the world’s total
pure Te production is derived from the processing of cop-
per anode slimes. Processing 1000 tons of copper ore gen-
erally results in the production of approximately 1 kg of
Te [38]. Table 1 displays the composition of anode slimes
originating from various copper refinery plants worldwide.
Te present in anode slime can be extracted through
either pyrometallurgical or hydrometallurgical proce-
dures. Pyrometallurgical methods for treating anode slime
encompass processes such as oxidizing roasting, soda ash
smelting, cupellation, and sulphation roasting [41]. Within
the pyrometallurgical techniques, Te can be transformed
into soluble or insoluble forms based on the requirements
of successive operations. Subsequently, in the hydrometal-
lurgical phase, Te is extracted through leaching, purifica-
tion, and electrowinning. Nevertheless, the recovery of Te
is typically below 70% due to the lengthy nature of the
process [42,43].
The leaching process can be broadly categorized into
two main groups: acid leaching and alkaline leaching. In
the treatment of copper anode slime, sulfuric acid-oxygen
pressure leaching stands out as one of the main separation
techniques [43] (Wang, 2011). The use of oxygen as an
oxidizing agent plays a crucial role in enhancing the leach-
ing efficiency. Hoffmann and Wesstrom [44] employed
the typical conditions of selective oxidative acidic leach-
ing, which involved a temperature of 120°C and a partial
oxygen pressure of 345 kPa, for the separation of Te and
Se. Given that Se and seleno-compounds exhibit higher
resistance to oxidation, the majority of Se remained in the
residue, while Te compounds were dissolved in the oxida-
tive acidic environment. The dissolution of Te compounds
can be represented by the following chemical reactions, as
explained by Hoffmann [40]:
CuTe (s) +8H+(aq) +3O2 (g) → Cu2+ (aq)
+H2TeO3(aq) +3H2O (l )(1)
2H2TeO3(aq) +O2 (g) → 2H2TeO4(aq) (2)
Apart from oxygen, various other oxidizing agents,
including H2O2, NaClO3, FeCl3, and MnO2, have been
examined for the leaching of Te with H2SO4 [45–49]. Hait
et al. [45] discovered that the leaching efficiency of Te in
copper anode slime remained consistently below 10% when
using H2SO4 without oxidizing agents, but it significantly
improved manganese dioxide (MnO2) was added. In addi-
tion to the use of oxidative agents, microwave technology
has been employed to reduce leaching time and enhance
solvent heating rates. Ma et al. [50] investigated the
decomposition of copper anode slime when subjected to
microwave energy in H2SO4 environment. They reported
impressive leaching efficiencies, achieving 99.56% for Cu
and 98.68% for Te, all within less than 5 minutes under
the optimized conditions of microwave-assisted leaching.
Despite the widespread use of H2SO4 as a lixiviant
in acid leaching process of Te, other acids have also been
used including HNO3 at high dosage serving as an oxi-
dizing agent as well. In this context, while copper can
be effectively leached by HNO3, the associated Te could
undergo oxidation, forming TeO2, which is soluble in HCl.
Table 1. Anode slime composition in different refineries [34,
39–40]
Plant Country Te (%)
Saganoseki Japan 3.9
Las Ventanas Chile 0.8
Townsville Australia 0.5
Amarillo USA 1.4
Montreal Canada 2
Boliden Sweden 0.9
Kayseri Turkey 0.4
Sarcheshmeh Iran 0.7
Kennecott USA 3.5
gas to eliminate excess oxygen. Following this, the cop-
per is cast into copper anodes through fire refining. These
anodes, comprising 98–99% pure copper, may contain
minor impurities such as Au, Ag, PGE, Se, and Te. Copper
cathode (99.9% pure) can be produced from the copper
anodes via electrorefining in a copper sulfate-sulfuric acid
electrolyte tank. A thorough explanation of the copper pro-
duction processes has been summarized by Moskalyk and
Alfantazi [35].
Anode slimes are collected from the bottom of the elec-
trolytic tanks during the refining of copper [36]. The type
of ore and the method of copper extraction significantly
impact the distribution of elements and the composition
of the anode slimes. Copper anode slimes typically consist
of Cu, Ni, Se, Te, Ag, Au, and PGE metals. The Te con-
tent usually falls within the range of 1–4 wt%, occasion-
ally reaching higher levels, such as 8–9 wt%. A significant
portion of Te (often exceeding 80%) is found as inclusions
at the grain boundaries of silver-copper-selenide-telluride
compounds in the copper anode slimes. The anode slimes
need to be further treated for the extraction of the precious
and critical metals. These slimes are regularly processed to
recover additional Cu and then to recover precious metals,
as well as minor elements including Se and Te.
While Te is considered as an impurity in electrolytic
copper and as a harmful substance in its natural form if
improperly disposed, represents a highly valuable by-prod-
uct when recovered efficiently from copper anode slimes
[37]. From a statistical perspective, 90% of the world’s total
pure Te production is derived from the processing of cop-
per anode slimes. Processing 1000 tons of copper ore gen-
erally results in the production of approximately 1 kg of
Te [38]. Table 1 displays the composition of anode slimes
originating from various copper refinery plants worldwide.
Te present in anode slime can be extracted through
either pyrometallurgical or hydrometallurgical proce-
dures. Pyrometallurgical methods for treating anode slime
encompass processes such as oxidizing roasting, soda ash
smelting, cupellation, and sulphation roasting [41]. Within
the pyrometallurgical techniques, Te can be transformed
into soluble or insoluble forms based on the requirements
of successive operations. Subsequently, in the hydrometal-
lurgical phase, Te is extracted through leaching, purifica-
tion, and electrowinning. Nevertheless, the recovery of Te
is typically below 70% due to the lengthy nature of the
process [42,43].
The leaching process can be broadly categorized into
two main groups: acid leaching and alkaline leaching. In
the treatment of copper anode slime, sulfuric acid-oxygen
pressure leaching stands out as one of the main separation
techniques [43] (Wang, 2011). The use of oxygen as an
oxidizing agent plays a crucial role in enhancing the leach-
ing efficiency. Hoffmann and Wesstrom [44] employed
the typical conditions of selective oxidative acidic leach-
ing, which involved a temperature of 120°C and a partial
oxygen pressure of 345 kPa, for the separation of Te and
Se. Given that Se and seleno-compounds exhibit higher
resistance to oxidation, the majority of Se remained in the
residue, while Te compounds were dissolved in the oxida-
tive acidic environment. The dissolution of Te compounds
can be represented by the following chemical reactions, as
explained by Hoffmann [40]:
CuTe (s) +8H+(aq) +3O2 (g) → Cu2+ (aq)
+H2TeO3(aq) +3H2O (l )(1)
2H2TeO3(aq) +O2 (g) → 2H2TeO4(aq) (2)
Apart from oxygen, various other oxidizing agents,
including H2O2, NaClO3, FeCl3, and MnO2, have been
examined for the leaching of Te with H2SO4 [45–49]. Hait
et al. [45] discovered that the leaching efficiency of Te in
copper anode slime remained consistently below 10% when
using H2SO4 without oxidizing agents, but it significantly
improved manganese dioxide (MnO2) was added. In addi-
tion to the use of oxidative agents, microwave technology
has been employed to reduce leaching time and enhance
solvent heating rates. Ma et al. [50] investigated the
decomposition of copper anode slime when subjected to
microwave energy in H2SO4 environment. They reported
impressive leaching efficiencies, achieving 99.56% for Cu
and 98.68% for Te, all within less than 5 minutes under
the optimized conditions of microwave-assisted leaching.
Despite the widespread use of H2SO4 as a lixiviant
in acid leaching process of Te, other acids have also been
used including HNO3 at high dosage serving as an oxi-
dizing agent as well. In this context, while copper can
be effectively leached by HNO3, the associated Te could
undergo oxidation, forming TeO2, which is soluble in HCl.
Table 1. Anode slime composition in different refineries [34,
39–40]
Plant Country Te (%)
Saganoseki Japan 3.9
Las Ventanas Chile 0.8
Townsville Australia 0.5
Amarillo USA 1.4
Montreal Canada 2
Boliden Sweden 0.9
Kayseri Turkey 0.4
Sarcheshmeh Iran 0.7
Kennecott USA 3.5