146 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
leaching, required the production of concentrates of suit-
able high grade (of metals, but also of sulfur, where it is
used as fuel). As ore grades decline, the recovery losses to
produce acceptable smelter or autoclave-leachable concen-
trates, often with other complicating factors such as high
magnesium content, polymetallic nature of the ores, high
nuisance base metal contents, etc., makes many of the
conventional approaches uneconomic. Thus, contempo-
rary hydrometallurgy often seeks solutions to low grade
polymetallic ores, concentrates and tailings within a circu-
lar economy context rather than competing technologies
for concentrates already suitable for pressure leaching or
smelting.
Binnemans and Jones (2023a) proposed as use-
ful guideline which they name the “Twelve Principles of
Circular Hydrometallurgy,” which they identify as:
• Regenerate reagents
• Close water loops
• Prevent waste
• Maximize mass, energy, space, and time efficiency
• Integrate materials and energy flows
• Safely dispose of potentially harmful elements
• Decrease activation energy
• Electrify processes wherever possible
• Use benign chemicals
• Reduce chemical diversity
• Implement real-time analysis and digital process
control
• Combine circular hydrometallurgy with zero-waste
mining
It is within this context that Curtin University empha-
sized the use of benign lixiviants, various organic acids as
well as microbial leach technologies since 2012. In the
hydrometallurgy field, the WA School of Mines Curtin
University has focused on the use of:
1. Organic acids and phosphate-solubilizing micro-
organisms to solubilize rare earths from their phos-
phate mineral resources (Van Alin et al.,2023a,
2023b Fathollahzadeh et al., 2019a,2019b, 2018a,
2018b, Corbett et al., 2018, 2017a, 2017b Lim,
Ibana, Eksteen, 2016, Lazo, Dyer &Alorro, 2017
Lazo et al. 2017a and 2017b).
2. Bioleaching of base metals from PGM ores
(Mwase, Petersen, Eksteen, 2012a, 2012b, 2014)
3. Amino acids, in particular glycine, for selective
leaching of precious metals (Au, Ag, Pd) and base
metals (Cu, Ni, Co, Zn, Pb, Cd) from ores, concen-
trates, and secondary resources such tailings, slags,
residues, battery waste and other waste electronic
and electric equipment (WEEE). The abiotic use
of amino acids under alkaline conditions was first
published in 2015 (Eksteen and Oraby, 2015) and
the priority date of the first patents dates to 2013.
A recent review of the literature is presented by Li
et al., 2023a.
4. Non-cyanide lixiviants such thiosulfate, iodide,
ferricyanide, etc., for the leaching and recovery of
precious metals (Ilankoon et al., 2019, 2020 Li et
al., 2023b, Karrech et al., 2018)
This paper will explore the development glycine as lixiviant
as a case study as one of the approaches developed at the
Western Australian School of Mines at Curtin University.
One of the risks in hydrometallurgy is overemphasizing
the leach step without due consideration of metal recov-
ery from solution or reagent and solvent (water) recovery
or the larger contexts of process monitoring and control,
and reagent and waste logistics and storage. These will be
addressed in turn.
GLYCINE LEACHING
Glycine Attributes
Glycine as a lixiviant has been reviewed by the author and
co-authors (Li et al., 2023a). It is mass produced China
alone had an annual production capacity of more than
1.6 billion pounds in 2020 (U.S. International Trade
Commission, 2022), or about 725,000 metric tons. It is a
free-flowing, non-hygroscopic, sweet, non-toxic, non-vol-
atile, non-flammable, chemically stable, highly water-sol-
uble crystalline powder. It is the simplest amino acid, and
while other amino acids may sometimes outperform it, the
combination of cost, simplicity and stability makes it the
preferred amino acid to use. It is thermally stable in hydro-
metallurgical applications, stable to UV light radiation, and
resistant to bacterial attack above a pH of 9. Strong oxi-
dants at sufficient concentrations can destroy it. It forms a
range of complexes of varying stability with base and pre-
cious metals, depending on pH. It has three ionic states: a
positively charged glycinium cation predominant at pH’s
below 2.4, a neutral but bipolar zwitterion predominant
between the pH’s of 2.4 And 9.8, and a glycinate anion pre-
dominant under alkaline pH’s higher than 9.8. The metal
glycine complexes can occur in both cis- and trans- isomeric
forms and may crystallize as a number of hydrates, lead-
ing to complicated solubility behavior depending on the
configuration of the complexes (Delf, Gillar and O’Brien,
1979). While this is of a lesser concern for precious metals
at ppm concentrations, it makes a significant difference in
base metal leaching circuits, e.g., for copper and nickel.
leaching, required the production of concentrates of suit-
able high grade (of metals, but also of sulfur, where it is
used as fuel). As ore grades decline, the recovery losses to
produce acceptable smelter or autoclave-leachable concen-
trates, often with other complicating factors such as high
magnesium content, polymetallic nature of the ores, high
nuisance base metal contents, etc., makes many of the
conventional approaches uneconomic. Thus, contempo-
rary hydrometallurgy often seeks solutions to low grade
polymetallic ores, concentrates and tailings within a circu-
lar economy context rather than competing technologies
for concentrates already suitable for pressure leaching or
smelting.
Binnemans and Jones (2023a) proposed as use-
ful guideline which they name the “Twelve Principles of
Circular Hydrometallurgy,” which they identify as:
• Regenerate reagents
• Close water loops
• Prevent waste
• Maximize mass, energy, space, and time efficiency
• Integrate materials and energy flows
• Safely dispose of potentially harmful elements
• Decrease activation energy
• Electrify processes wherever possible
• Use benign chemicals
• Reduce chemical diversity
• Implement real-time analysis and digital process
control
• Combine circular hydrometallurgy with zero-waste
mining
It is within this context that Curtin University empha-
sized the use of benign lixiviants, various organic acids as
well as microbial leach technologies since 2012. In the
hydrometallurgy field, the WA School of Mines Curtin
University has focused on the use of:
1. Organic acids and phosphate-solubilizing micro-
organisms to solubilize rare earths from their phos-
phate mineral resources (Van Alin et al.,2023a,
2023b Fathollahzadeh et al., 2019a,2019b, 2018a,
2018b, Corbett et al., 2018, 2017a, 2017b Lim,
Ibana, Eksteen, 2016, Lazo, Dyer &Alorro, 2017
Lazo et al. 2017a and 2017b).
2. Bioleaching of base metals from PGM ores
(Mwase, Petersen, Eksteen, 2012a, 2012b, 2014)
3. Amino acids, in particular glycine, for selective
leaching of precious metals (Au, Ag, Pd) and base
metals (Cu, Ni, Co, Zn, Pb, Cd) from ores, concen-
trates, and secondary resources such tailings, slags,
residues, battery waste and other waste electronic
and electric equipment (WEEE). The abiotic use
of amino acids under alkaline conditions was first
published in 2015 (Eksteen and Oraby, 2015) and
the priority date of the first patents dates to 2013.
A recent review of the literature is presented by Li
et al., 2023a.
4. Non-cyanide lixiviants such thiosulfate, iodide,
ferricyanide, etc., for the leaching and recovery of
precious metals (Ilankoon et al., 2019, 2020 Li et
al., 2023b, Karrech et al., 2018)
This paper will explore the development glycine as lixiviant
as a case study as one of the approaches developed at the
Western Australian School of Mines at Curtin University.
One of the risks in hydrometallurgy is overemphasizing
the leach step without due consideration of metal recov-
ery from solution or reagent and solvent (water) recovery
or the larger contexts of process monitoring and control,
and reagent and waste logistics and storage. These will be
addressed in turn.
GLYCINE LEACHING
Glycine Attributes
Glycine as a lixiviant has been reviewed by the author and
co-authors (Li et al., 2023a). It is mass produced China
alone had an annual production capacity of more than
1.6 billion pounds in 2020 (U.S. International Trade
Commission, 2022), or about 725,000 metric tons. It is a
free-flowing, non-hygroscopic, sweet, non-toxic, non-vol-
atile, non-flammable, chemically stable, highly water-sol-
uble crystalline powder. It is the simplest amino acid, and
while other amino acids may sometimes outperform it, the
combination of cost, simplicity and stability makes it the
preferred amino acid to use. It is thermally stable in hydro-
metallurgical applications, stable to UV light radiation, and
resistant to bacterial attack above a pH of 9. Strong oxi-
dants at sufficient concentrations can destroy it. It forms a
range of complexes of varying stability with base and pre-
cious metals, depending on pH. It has three ionic states: a
positively charged glycinium cation predominant at pH’s
below 2.4, a neutral but bipolar zwitterion predominant
between the pH’s of 2.4 And 9.8, and a glycinate anion pre-
dominant under alkaline pH’s higher than 9.8. The metal
glycine complexes can occur in both cis- and trans- isomeric
forms and may crystallize as a number of hydrates, lead-
ing to complicated solubility behavior depending on the
configuration of the complexes (Delf, Gillar and O’Brien,
1979). While this is of a lesser concern for precious metals
at ppm concentrations, it makes a significant difference in
base metal leaching circuits, e.g., for copper and nickel.