148 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Synergistic Use of Glycine with Other Lixiviants and
Reagents
The lixiviating potential of glycine can be enhanced by the
addition of small amounts of synergistic reagents, such as
ammonia, cyanide, ferricyanide, permanganate, thiourea
and others, often where the added reagents does not act
as a “free” reagent, but through the formation of a glycine-
reagent associated couple. For example, in the GlyCat ™
technology, when small amounts of cyanide is added in
glycine leaches, no free cyanide is detectible (nor should it
be), but the starved amounts of cyanide (often a small frac-
tion of what would be required for the same recovery when
used on its own) aids in lowering the temperature for the
leach and accelerates the leach rate (Eksteen et al., 2018
Oraby and Eksteen, 2015a). Similarly, small amounts of
ammonia can significantly enhance the leach rates and
capacity during base metals leaching, e.g., copper leaching
(Deng et al., 2022). It is essential to understand that these
synergistic reagents do not act independently, and adding
more does not necessarily lead to better results (but often
the opposite).
Solid-Liquid Separation Post Leaching
Glycine is typically used in dilute solutions of mild alkalin-
ity like cyanide leaching of gold. It doesn’t pose particu-
lar viscosity challenges during solid-liquid separation post
leaching. Settling of solids is similar to what is experienced
in alkaline cyanide systems and is more a function of the
solid properties (e.g., some clays) than liquid chemistry.
Washing of settled residues or filter cakes may be neces-
sary where lixiviant concentrations are high, such as in base
metal leaching operations and the wash water may recon-
centration and recycle. This should be contrasted to more
recent interest in Deep Eutectic Solvents (DES), where sig-
nificant amounts of reagents may adhere to solid surfaces
and washing of the residues are problematic (Binnemans
and Jones, 2023b).
METAL RECOVERY FROM
GLYCINATE LEACHATES
Glycine forms moderately strong complexes with base and
precious metals, but often not as strong as cyanide or EDTA
complexes. Consequently, metals can often be stripped as
their cations from the glycinate complexes through stronger
complexing agents such as solvent extraction (SX) extract-
ants or various ion exchange (IX) functional groups grafted
onto resins. The metals can also be precipitated through sul-
fide precipitation or adsorbed through activated carbon (in
the case of precious metals). Thus, a diverse range of metal
recovery technologies can be effectively applied which will
be discussed below.
Sulfide Precipitation of Base Metals From
Glycinate Solutions
Base metals such as Cu, Ni, Co and Zn can be efficiently pre-
cipitated from their alkaline glycine solutions using NaHS,
Na2S or H2S once the solutions are stripped of residual
oxygen (e.g., by nitrogen bubbling) and under appropri-
ate control of the reaction conditions (temperature, resi-
dence time). Operating under alkaline conditions mitigates
against the risk of uncontrolled H2S release. Deng, Oraby
and Eksteen (2019a, 2019b) has studied the precipitation
of copper sulfide from glycinate leachates in the presence of
gold, established both the optimal thermochemical condi-
tions, and the precipitate characteristics based upon operat-
ing parameters. This research has also now been completed
for the precipitation of nickel, cobalt and zinc sulfides
(research not yet published) from glycinate leaches, and
which was funded by the Future Battery Industries CRC.
SX Recovery of Base Metals from Glycinate Leachates
The recovery of Cu, Ni and Co have been demonstrated
using LIX 84 and Cyanex 272 extractants Mohammed et
al. 2024). Tanda, Oraby &Eksteen (2017b) has shown that
Cu could effectively be extracted from glycinate leachate
and stripped with 180 g/L sulfuric acid using 2 extraction
stages and a single stripping stage.
IX Recovery of Base and Precious Metals from
Glycinate Leachates
Deng Oraby and Eksteen (2020a and 2020b) have shown
that both copper and gold can be individually and selec-
tively recovered from glycine-starved cyanide leachates with
tailored IX resins and molecularly imprinted resin (IXOS-
AuC) respectively. Similarly, Eksteen, Oraby and Nguyen
(2020) have demonstrated that ion exchange can be used to
recovery of nickel and cobalt from alkaline glycine leachates
derived from low grade, serpentine-rich sulfide ores.
Adsorption of Precious Metals Onto Activated Carbon
The recovery of gold and silver glycinates onto activated
carbon was initially demonstrated by Oraby and Eksteen
(2015b), Eksteen et al. (2018), with in-depth studies of the
thermodynamic isotherms for gold and copper adsorption
from gold-copper glycinates (Tauetsile, Oraby &Eksteen,
2018a) and glycine-starved cyanide solutions (Tauetsile,
Oraby &Eksteen, 2019a). This was followed by kinetic
studies on gold-copper glycinate solution (Tauetsile, Oraby
&Eksteen, 2018b and 2019b). It was shown that activated
Synergistic Use of Glycine with Other Lixiviants and
Reagents
The lixiviating potential of glycine can be enhanced by the
addition of small amounts of synergistic reagents, such as
ammonia, cyanide, ferricyanide, permanganate, thiourea
and others, often where the added reagents does not act
as a “free” reagent, but through the formation of a glycine-
reagent associated couple. For example, in the GlyCat ™
technology, when small amounts of cyanide is added in
glycine leaches, no free cyanide is detectible (nor should it
be), but the starved amounts of cyanide (often a small frac-
tion of what would be required for the same recovery when
used on its own) aids in lowering the temperature for the
leach and accelerates the leach rate (Eksteen et al., 2018
Oraby and Eksteen, 2015a). Similarly, small amounts of
ammonia can significantly enhance the leach rates and
capacity during base metals leaching, e.g., copper leaching
(Deng et al., 2022). It is essential to understand that these
synergistic reagents do not act independently, and adding
more does not necessarily lead to better results (but often
the opposite).
Solid-Liquid Separation Post Leaching
Glycine is typically used in dilute solutions of mild alkalin-
ity like cyanide leaching of gold. It doesn’t pose particu-
lar viscosity challenges during solid-liquid separation post
leaching. Settling of solids is similar to what is experienced
in alkaline cyanide systems and is more a function of the
solid properties (e.g., some clays) than liquid chemistry.
Washing of settled residues or filter cakes may be neces-
sary where lixiviant concentrations are high, such as in base
metal leaching operations and the wash water may recon-
centration and recycle. This should be contrasted to more
recent interest in Deep Eutectic Solvents (DES), where sig-
nificant amounts of reagents may adhere to solid surfaces
and washing of the residues are problematic (Binnemans
and Jones, 2023b).
METAL RECOVERY FROM
GLYCINATE LEACHATES
Glycine forms moderately strong complexes with base and
precious metals, but often not as strong as cyanide or EDTA
complexes. Consequently, metals can often be stripped as
their cations from the glycinate complexes through stronger
complexing agents such as solvent extraction (SX) extract-
ants or various ion exchange (IX) functional groups grafted
onto resins. The metals can also be precipitated through sul-
fide precipitation or adsorbed through activated carbon (in
the case of precious metals). Thus, a diverse range of metal
recovery technologies can be effectively applied which will
be discussed below.
Sulfide Precipitation of Base Metals From
Glycinate Solutions
Base metals such as Cu, Ni, Co and Zn can be efficiently pre-
cipitated from their alkaline glycine solutions using NaHS,
Na2S or H2S once the solutions are stripped of residual
oxygen (e.g., by nitrogen bubbling) and under appropri-
ate control of the reaction conditions (temperature, resi-
dence time). Operating under alkaline conditions mitigates
against the risk of uncontrolled H2S release. Deng, Oraby
and Eksteen (2019a, 2019b) has studied the precipitation
of copper sulfide from glycinate leachates in the presence of
gold, established both the optimal thermochemical condi-
tions, and the precipitate characteristics based upon operat-
ing parameters. This research has also now been completed
for the precipitation of nickel, cobalt and zinc sulfides
(research not yet published) from glycinate leaches, and
which was funded by the Future Battery Industries CRC.
SX Recovery of Base Metals from Glycinate Leachates
The recovery of Cu, Ni and Co have been demonstrated
using LIX 84 and Cyanex 272 extractants Mohammed et
al. 2024). Tanda, Oraby &Eksteen (2017b) has shown that
Cu could effectively be extracted from glycinate leachate
and stripped with 180 g/L sulfuric acid using 2 extraction
stages and a single stripping stage.
IX Recovery of Base and Precious Metals from
Glycinate Leachates
Deng Oraby and Eksteen (2020a and 2020b) have shown
that both copper and gold can be individually and selec-
tively recovered from glycine-starved cyanide leachates with
tailored IX resins and molecularly imprinted resin (IXOS-
AuC) respectively. Similarly, Eksteen, Oraby and Nguyen
(2020) have demonstrated that ion exchange can be used to
recovery of nickel and cobalt from alkaline glycine leachates
derived from low grade, serpentine-rich sulfide ores.
Adsorption of Precious Metals Onto Activated Carbon
The recovery of gold and silver glycinates onto activated
carbon was initially demonstrated by Oraby and Eksteen
(2015b), Eksteen et al. (2018), with in-depth studies of the
thermodynamic isotherms for gold and copper adsorption
from gold-copper glycinates (Tauetsile, Oraby &Eksteen,
2018a) and glycine-starved cyanide solutions (Tauetsile,
Oraby &Eksteen, 2019a). This was followed by kinetic
studies on gold-copper glycinate solution (Tauetsile, Oraby
&Eksteen, 2018b and 2019b). It was shown that activated