XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 147
Glycine as a Lixiviant
It is particularly the alkaline domain that offers various
advantages with regards to selectivity of leaching, and it has
been shown that the pH ranges from 9.5 to 11.5 optimizes
selectivity towards precious metals (Au, Ag and Pd) and
selected base metals (Cu, Ni, Co, Zn). This pH range is
particularly useful as it corresponds to that of gold leach-
ing, and magnesium minerals, iron minerals and silicate are
all practically insoluble in this pH range. As these are all
predominant and abundant lithophile gangue minerals the
selectivity benefit is substantial. For example, glycine has
been shown to successfully leach nickel and cobalt from
finely disseminated ultramafic sulfide ores and tailings with
nickel grades from 0.2–0.8% nickel. Gold has been leached
from free milling resources, paleochannel resources, copper
gold oxide and sulfide resources. Similarly, silver is leach-
able, zinc, palladium, copper, lead, gold, and silver have
all been showed to be alkaline glycine leachable from elec-
tronic wastes such as waste printed circuit boards.
Examples of glycine leaching applications researched at
Curtin University are summarized in Table 1.
pH Modifiers and Redox Control
The choice of pH modifier, such as calcium hydroxide,
sodium hydroxide, potassium hydroxide or ammonium
hydroxide may have significant impacts of the extent and
kinetics of leaching. Depending on the nature of the sys-
tem, quicklime (calcium hydroxide) may be suitable, e.g.,
for the leaching of gold, silver and copper from oxide ores.
However, in sulfide ores and concentrates the use of lime
may be detrimental due to passivating layers of gypsum
that may form around sulfide mineral surfaces. In such
cases caustic soda may be preferred, despite it increased
costs. Potassium hydroxide may be preferred if a potassium
sulfate by-product can be isolated. Ammonia solution may
have the additive effect of extending the solubility range for
copper bearing solutions (Deng et al., 2022). Redox con-
trol is typically performed using oxygen sparging, although
potassium permanganate (Oraby, Eksteen and O’Connor,
2020) and potassium ferricyanide (Li et al., 2023) has been
used effectively as oxidants, although some glycine oxida-
tion occurs in the presence of permanganate.
Table 1. Examples of glycine leaching developed at Curtin University
Leach System Reference
Gold Eksteen &Oraby, 2015
Oraby &Eksteen, 2015a
Gold/silver Oraby &Eksteen, 2015b
Copper Concentrates Oraby and Eksteen 2014
Gold-Copper Ores and Concentrates Oraby and Eksteen, 2014
Eksteen et al., 2018
Oraby, Eksteen and Tanda, 2017
Li, et al., 2022
Polymetallic Ores Cabri, Wilhelmij, Eksteen, 2017
Aylmore, M., Eksteen, J.J., Wells, M., Jones, M., 2019
Polymetallic e-waste Oraby, Li, &Eksteen, 2019
Li, Oraby, Eksteen, 2018, 2020, 2021a, 2021b, 2022a, 2022b
Nickel and Cobalt Oraby et al., 2023a, 2023b
Eksteen, Oraby &Nguyen, 2020
Chalcopyrite Eksteen, Oraby and Tanda, 2017
Tanda et al., 2019
O’Connor and Eksteen, 2020
O’Connor et al., 2018b
Copper oxide minerals Tanda, Oraby &Eksteen, 2017
Tanda, Oraby &Eksteen, 2021
Chalcocite Tanda, Oraby and Eksteen, 2018
Zinc and Lead Sulfides Saba, M., 2019
Copper Metal O’Connor et al., 2018a Li, Oraby &Eksteen, 2021b
Glycine as a Lixiviant
It is particularly the alkaline domain that offers various
advantages with regards to selectivity of leaching, and it has
been shown that the pH ranges from 9.5 to 11.5 optimizes
selectivity towards precious metals (Au, Ag and Pd) and
selected base metals (Cu, Ni, Co, Zn). This pH range is
particularly useful as it corresponds to that of gold leach-
ing, and magnesium minerals, iron minerals and silicate are
all practically insoluble in this pH range. As these are all
predominant and abundant lithophile gangue minerals the
selectivity benefit is substantial. For example, glycine has
been shown to successfully leach nickel and cobalt from
finely disseminated ultramafic sulfide ores and tailings with
nickel grades from 0.2–0.8% nickel. Gold has been leached
from free milling resources, paleochannel resources, copper
gold oxide and sulfide resources. Similarly, silver is leach-
able, zinc, palladium, copper, lead, gold, and silver have
all been showed to be alkaline glycine leachable from elec-
tronic wastes such as waste printed circuit boards.
Examples of glycine leaching applications researched at
Curtin University are summarized in Table 1.
pH Modifiers and Redox Control
The choice of pH modifier, such as calcium hydroxide,
sodium hydroxide, potassium hydroxide or ammonium
hydroxide may have significant impacts of the extent and
kinetics of leaching. Depending on the nature of the sys-
tem, quicklime (calcium hydroxide) may be suitable, e.g.,
for the leaching of gold, silver and copper from oxide ores.
However, in sulfide ores and concentrates the use of lime
may be detrimental due to passivating layers of gypsum
that may form around sulfide mineral surfaces. In such
cases caustic soda may be preferred, despite it increased
costs. Potassium hydroxide may be preferred if a potassium
sulfate by-product can be isolated. Ammonia solution may
have the additive effect of extending the solubility range for
copper bearing solutions (Deng et al., 2022). Redox con-
trol is typically performed using oxygen sparging, although
potassium permanganate (Oraby, Eksteen and O’Connor,
2020) and potassium ferricyanide (Li et al., 2023) has been
used effectively as oxidants, although some glycine oxida-
tion occurs in the presence of permanganate.
Table 1. Examples of glycine leaching developed at Curtin University
Leach System Reference
Gold Eksteen &Oraby, 2015
Oraby &Eksteen, 2015a
Gold/silver Oraby &Eksteen, 2015b
Copper Concentrates Oraby and Eksteen 2014
Gold-Copper Ores and Concentrates Oraby and Eksteen, 2014
Eksteen et al., 2018
Oraby, Eksteen and Tanda, 2017
Li, et al., 2022
Polymetallic Ores Cabri, Wilhelmij, Eksteen, 2017
Aylmore, M., Eksteen, J.J., Wells, M., Jones, M., 2019
Polymetallic e-waste Oraby, Li, &Eksteen, 2019
Li, Oraby, Eksteen, 2018, 2020, 2021a, 2021b, 2022a, 2022b
Nickel and Cobalt Oraby et al., 2023a, 2023b
Eksteen, Oraby &Nguyen, 2020
Chalcopyrite Eksteen, Oraby and Tanda, 2017
Tanda et al., 2019
O’Connor and Eksteen, 2020
O’Connor et al., 2018b
Copper oxide minerals Tanda, Oraby &Eksteen, 2017
Tanda, Oraby &Eksteen, 2021
Chalcocite Tanda, Oraby and Eksteen, 2018
Zinc and Lead Sulfides Saba, M., 2019
Copper Metal O’Connor et al., 2018a Li, Oraby &Eksteen, 2021b