XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1909
The four samples were taken for IR spectra, but there
were no comprehensive spectra due to the dilute nature of
the samples since water peaks were dominating. Due to
this, the water was removed from all four samples using
slow evaporation using a Rotavapor ® R-300, and four
whitish powder samples were obtained. The samples were
mixed with potassium bromide and compressed to form a
pellet that would be analyzed. A potassium bromide pellet
was also made as a baseline correction to mitigate the KBr
influence on the samples. All the samples were subjected to
analysis using Nexus 470 FT-IR Spectrometer for Fourier
Transform Infra-red analysis, and the spectra were gener-
ated and analyzed using the Thermo Scientific OMNIC ™
Specta ™ software 7.3 (Nunn and Nishikida 2008).
Computational details
The structures of gold-alanine complexes, considering both
the neutral and deprotonated forms, as well as individual
alanine, were built. These structures comprised the gold
di-alanine complexes, where one gold atom was intricately
linked to two alanine molecules through various bond-
ing modes such as N-Au-N, O-Au-O, and N-Au-O (see
Additional Information). The generated structures were
transferred to the Gaussian 16 C01 (Frisch et al., 2003) for
computational calculations. The calculations were done in
explicit solvent water using def2svp m062x level of theory,
which is one of the reliable levels of theory in computa-
tion theory. Geometric optimization was done to obtain
the structure with the lowest energy representing a prac-
tically attainable configuration. The complexation energy
was determined by obtaining the energy of the complex
and then subtracting the energies of the two ligands and
the gold atom, as outlined in Equation 4 (Abdalmoneam
et al., 2017).
E Ecomplex E
complexation ligand gold =-72^E h+ A (4)
After achieving the stable configurations through geo-
metric optimization, the next step involved subjecting these
complexes and respective ligands to frequency calculations.
This process aimed to predict the thermodynamic proper-
ties of the complexes, leading to the calculation of the sta-
bility constant.
Pure Gold Dissolution Experiments
All experiments were carried out using solutions prepared
from analytical grade reagents and deionized water. In all
experiments, the pure gold powder (75 mg of 99.98%
purity) and deionized water (400 mL) were placed in a
500 mL volumetric Flask. After pH adjustment, either iso-
electric pH or deprotonated pH, alanine was added to the
solution to give a concentration of 0.5 M. Also, 1% hydro-
gen peroxide was added as an oxidant in all experiments.
The contents of the volumetric flask were placed on top of
a magnetic stirrer and agitated by a magnet with a rotation
speed of 300 rpm. The volumetric flask was left open with-
out a lid to allow for oxygen transfer. At different sampling
times, solution samples (5 mL) of the leach solution were
obtained after filtration using 0.45 μm filter syringes. The
filtrates and the final leach residues were ten times diluted
and analyzed for gold by Thermo ICap 6200 Inductively
coupled plasma atomic emission spectroscopy.
RESULTS AND DISCUSSION
Fourier-Transform Infrared Analysis
FTIR was used to investigate the functional groups that
have been reported to be involved in gold and amino acids
interactions. This was done by targeting specific functional
groups known to be involved in such interactions, namely
the carboxylic and amine groups. In this study, alanine
served as the subject of investigation, and peaks corre-
sponding to symmetrical [ν(COO–)sym, and ν(NH3+)sym]
and antisymmetric [ν(COO–)anti, and ν(NH3+)anti] rota-
tions were examined.
The distinctive peaks were identified through the
comparison with previous research on alanine (Barth, A.
2000 Barth and Zscherp 2002 Justi et al., 2021 Sebben
and Pendleton 2014 Wolpert and Hellwig 2006). Figure 3
illustrates the FTIR spectra pattern, portraying the shifts in
extracted alanine solids (in red) and extracted gold-alanine
complexes (in blue) at the isoelectric pH. The ν(NH3+)
anti peak at 1625.99 cm–1 shifted to 1632.96 cm–1 upon
complexation, while the ν(NH3+)sym peak experienced
a significant shift from 1499.64 cm–1 to 1485.55 cm–1.
These shifts indicated the potential binding of alanine with
gold at isoelectric pH, with involvement of the nitrogen
from the amine end. Again, there is a probability of the
neutral alanine binding with gold at the same pH using
the carboxylic end. This was illustrated in the ν(COO–)anti
which appeared at 1593.45 cm–1 and disappeared upon
complexation, whereas on the symmetrical one appeared at
1412.08 cm–1 and shifted to 1409.60 cm–1, which trans-
lated to 2.48 cm–1 peak shifts.
Moreover, Figure 4 shows the FTIR spectra at the
deprotonated pH, where NH3+ peaks were absent due
to proton loss. The ν(NH2)scissoring band appeared at
1494.14 cm–1 and shifted to 1500.20 cm–1 upon com-
plexation, resulting in a 6.06 cm–1 shift. Simultaneously,
the ν(COO-)anti exhibited a significant shift from
1591.46 cm–1 to 1637.97 cm–1, indicating a substantial
The four samples were taken for IR spectra, but there
were no comprehensive spectra due to the dilute nature of
the samples since water peaks were dominating. Due to
this, the water was removed from all four samples using
slow evaporation using a Rotavapor ® R-300, and four
whitish powder samples were obtained. The samples were
mixed with potassium bromide and compressed to form a
pellet that would be analyzed. A potassium bromide pellet
was also made as a baseline correction to mitigate the KBr
influence on the samples. All the samples were subjected to
analysis using Nexus 470 FT-IR Spectrometer for Fourier
Transform Infra-red analysis, and the spectra were gener-
ated and analyzed using the Thermo Scientific OMNIC ™
Specta ™ software 7.3 (Nunn and Nishikida 2008).
Computational details
The structures of gold-alanine complexes, considering both
the neutral and deprotonated forms, as well as individual
alanine, were built. These structures comprised the gold
di-alanine complexes, where one gold atom was intricately
linked to two alanine molecules through various bond-
ing modes such as N-Au-N, O-Au-O, and N-Au-O (see
Additional Information). The generated structures were
transferred to the Gaussian 16 C01 (Frisch et al., 2003) for
computational calculations. The calculations were done in
explicit solvent water using def2svp m062x level of theory,
which is one of the reliable levels of theory in computa-
tion theory. Geometric optimization was done to obtain
the structure with the lowest energy representing a prac-
tically attainable configuration. The complexation energy
was determined by obtaining the energy of the complex
and then subtracting the energies of the two ligands and
the gold atom, as outlined in Equation 4 (Abdalmoneam
et al., 2017).
E Ecomplex E
complexation ligand gold =-72^E h+ A (4)
After achieving the stable configurations through geo-
metric optimization, the next step involved subjecting these
complexes and respective ligands to frequency calculations.
This process aimed to predict the thermodynamic proper-
ties of the complexes, leading to the calculation of the sta-
bility constant.
Pure Gold Dissolution Experiments
All experiments were carried out using solutions prepared
from analytical grade reagents and deionized water. In all
experiments, the pure gold powder (75 mg of 99.98%
purity) and deionized water (400 mL) were placed in a
500 mL volumetric Flask. After pH adjustment, either iso-
electric pH or deprotonated pH, alanine was added to the
solution to give a concentration of 0.5 M. Also, 1% hydro-
gen peroxide was added as an oxidant in all experiments.
The contents of the volumetric flask were placed on top of
a magnetic stirrer and agitated by a magnet with a rotation
speed of 300 rpm. The volumetric flask was left open with-
out a lid to allow for oxygen transfer. At different sampling
times, solution samples (5 mL) of the leach solution were
obtained after filtration using 0.45 μm filter syringes. The
filtrates and the final leach residues were ten times diluted
and analyzed for gold by Thermo ICap 6200 Inductively
coupled plasma atomic emission spectroscopy.
RESULTS AND DISCUSSION
Fourier-Transform Infrared Analysis
FTIR was used to investigate the functional groups that
have been reported to be involved in gold and amino acids
interactions. This was done by targeting specific functional
groups known to be involved in such interactions, namely
the carboxylic and amine groups. In this study, alanine
served as the subject of investigation, and peaks corre-
sponding to symmetrical [ν(COO–)sym, and ν(NH3+)sym]
and antisymmetric [ν(COO–)anti, and ν(NH3+)anti] rota-
tions were examined.
The distinctive peaks were identified through the
comparison with previous research on alanine (Barth, A.
2000 Barth and Zscherp 2002 Justi et al., 2021 Sebben
and Pendleton 2014 Wolpert and Hellwig 2006). Figure 3
illustrates the FTIR spectra pattern, portraying the shifts in
extracted alanine solids (in red) and extracted gold-alanine
complexes (in blue) at the isoelectric pH. The ν(NH3+)
anti peak at 1625.99 cm–1 shifted to 1632.96 cm–1 upon
complexation, while the ν(NH3+)sym peak experienced
a significant shift from 1499.64 cm–1 to 1485.55 cm–1.
These shifts indicated the potential binding of alanine with
gold at isoelectric pH, with involvement of the nitrogen
from the amine end. Again, there is a probability of the
neutral alanine binding with gold at the same pH using
the carboxylic end. This was illustrated in the ν(COO–)anti
which appeared at 1593.45 cm–1 and disappeared upon
complexation, whereas on the symmetrical one appeared at
1412.08 cm–1 and shifted to 1409.60 cm–1, which trans-
lated to 2.48 cm–1 peak shifts.
Moreover, Figure 4 shows the FTIR spectra at the
deprotonated pH, where NH3+ peaks were absent due
to proton loss. The ν(NH2)scissoring band appeared at
1494.14 cm–1 and shifted to 1500.20 cm–1 upon com-
plexation, resulting in a 6.06 cm–1 shift. Simultaneously,
the ν(COO-)anti exhibited a significant shift from
1591.46 cm–1 to 1637.97 cm–1, indicating a substantial