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A Green Technology to Extract Gold from Refractory Ore:
A Combination of Microencapsulation and Thiosulfate Leaching
Ilhwan Park, Takunda Mhandu Joseph, Naoki Hiroyoshi, Mayumi Ito
Hokkaido University
Sanghee Jeon
Akita University
ABSTRACT: Thiosulfate leaching has gained increasing attention as an alternative to the conventional cyanidation
for extracting gold from ores. However, the efficiency of gold extraction by thiosulfate leaching is dramatically
reduced when processing sulfidic gold refractory ores because sulfide minerals accelerate the decomposition of
thiosulfate. To address this problem, this study investigated the applicability of microencapsulation technique
as a pretreatment method for thiosulfate leaching of gold from a simulated gold-bearing arsenopyrite ore. The
application of microencapsulation technique can contribute to not only improving thiosulfate leaching of gold
but also reducing the formation of arsenic-rich mine drainage from leach residue.
INTRODUCTION
Gold (Au) has been widely used for various applications due
to its extremely high electrical conductivity and excellent
corrosion resistance. The global gold demand is consistently
increasing from ~1800 tonnes in 1980 to ~4700 tonnes
in 2022 (World Gold Council, 2018 Statista Research
Department, 2023). Moreover, the demand for gold is pro-
jected to further increase because of its important role as a
key component in low-carbon technologies. Technologies
under development, for instance, include gold catalysts to
help convert CO2 into useful fuels, the use of gold nano-
materials to enhance hydrogen fuel cell performance, and
the incorporation of gold nanoparticles to improve the per-
formance of photovoltaics (Energy Industry Review, 2028
Lin et al., 2020 World Gold Council, 2018).
The extraction of gold from ores is generally accom-
plished by alkaline cyanide leaching process, known as
cyanidation. Although gold is inert to oxidation, cyanide
(CN–) can dissolve gold by forming a cyano complex (i.e.,
[Au(CN)2]–) under oxidizing conditions. Although effec-
tive, environmental protection organizations and govern-
ments are pushing for the ban of cyanide usage in gold
extraction processes due to its toxicity (Grosse et al., 2003
Mhandu et al., 2023 Zoleta et al., 2023). Because of this,
many studies have been conducted to find alternative lix-
iviants to cyanide, such as thiourea, thiocyanate, halogen-
based, and thiosulfate solvents (Aylmore, 2005). Among
them, thiosulfate is the most promising lixiviant due to its
low toxicity, high selectivity to gold, and fast leaching rate
(Jeon et al., 2020 Xu et al., 2017).
Yet despite its prominence, the application of thio-
sulfate leaching to gold-bearing sulfidic ores is limited
due to low extraction efficiency resulting from thiosulfate
decomposition occurring on the surface of sulfide miner-
als and/or passivation of gold by oxidation products of sul-
fide minerals (Mhandu et al., 2023 Xu et al., 2017). This
indicates that passivation of sulfide minerals that limits its
A Green Technology to Extract Gold from Refractory Ore:
A Combination of Microencapsulation and Thiosulfate Leaching
Ilhwan Park, Takunda Mhandu Joseph, Naoki Hiroyoshi, Mayumi Ito
Hokkaido University
Sanghee Jeon
Akita University
ABSTRACT: Thiosulfate leaching has gained increasing attention as an alternative to the conventional cyanidation
for extracting gold from ores. However, the efficiency of gold extraction by thiosulfate leaching is dramatically
reduced when processing sulfidic gold refractory ores because sulfide minerals accelerate the decomposition of
thiosulfate. To address this problem, this study investigated the applicability of microencapsulation technique
as a pretreatment method for thiosulfate leaching of gold from a simulated gold-bearing arsenopyrite ore. The
application of microencapsulation technique can contribute to not only improving thiosulfate leaching of gold
but also reducing the formation of arsenic-rich mine drainage from leach residue.
INTRODUCTION
Gold (Au) has been widely used for various applications due
to its extremely high electrical conductivity and excellent
corrosion resistance. The global gold demand is consistently
increasing from ~1800 tonnes in 1980 to ~4700 tonnes
in 2022 (World Gold Council, 2018 Statista Research
Department, 2023). Moreover, the demand for gold is pro-
jected to further increase because of its important role as a
key component in low-carbon technologies. Technologies
under development, for instance, include gold catalysts to
help convert CO2 into useful fuels, the use of gold nano-
materials to enhance hydrogen fuel cell performance, and
the incorporation of gold nanoparticles to improve the per-
formance of photovoltaics (Energy Industry Review, 2028
Lin et al., 2020 World Gold Council, 2018).
The extraction of gold from ores is generally accom-
plished by alkaline cyanide leaching process, known as
cyanidation. Although gold is inert to oxidation, cyanide
(CN–) can dissolve gold by forming a cyano complex (i.e.,
[Au(CN)2]–) under oxidizing conditions. Although effec-
tive, environmental protection organizations and govern-
ments are pushing for the ban of cyanide usage in gold
extraction processes due to its toxicity (Grosse et al., 2003
Mhandu et al., 2023 Zoleta et al., 2023). Because of this,
many studies have been conducted to find alternative lix-
iviants to cyanide, such as thiourea, thiocyanate, halogen-
based, and thiosulfate solvents (Aylmore, 2005). Among
them, thiosulfate is the most promising lixiviant due to its
low toxicity, high selectivity to gold, and fast leaching rate
(Jeon et al., 2020 Xu et al., 2017).
Yet despite its prominence, the application of thio-
sulfate leaching to gold-bearing sulfidic ores is limited
due to low extraction efficiency resulting from thiosulfate
decomposition occurring on the surface of sulfide miner-
als and/or passivation of gold by oxidation products of sul-
fide minerals (Mhandu et al., 2023 Xu et al., 2017). This
indicates that passivation of sulfide minerals that limits its