XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2995
Despite the existence of a few experimental studies in
this domain, there remains a notable dearth of mechanistic
understanding, underscoring the need for molecular mod-
eling to elucidate the underlying processes. In this study,
we performed density functional theory (DFT) calculations
to gain insights into the interaction between Isopropyl
Ethylthiocarbamate (IPETC) and the surfaces of Asp (001)
and Py (100). Initially, we computed quantum chemical
descriptors, including the Highest Occupied Molecular
Orbital (HOMO), Lowest Unoccupied Molecular Orbital
(LUMO), and the energy gap (Egap), for both IPETC
and its deprotonated form (IPETCdp). Subsequently, we
explored the adsorption behavior of both the neutral and
deprotonated molecules on pristine Py and Asp surfaces, as
well as in the presence of copper (Cu) ions.
This comprehensive study provides valuable insights
into the molecular interactions at the mineral surfaces,
shedding light on the adsorption mechanisms of IPETC
and IPETCdp. Moreover, the investigation extended to the
presence of Cu ions, which is crucial given the influence
of copper ions in flotation processes. The outcomes of this
study contribute valuable insights into the intricacies of the
adsorption process and offer an atomic scale perspective to
surface chemistry of flotation processes.
COMPUTATIONAL METHODOLOGIES
DFT calculations were carried out using the PWscf code of
the Quantum Espresso-6.7 software package.13 The elec-
tron exchange and correlation interactions were described
using Perdew and Wang (PW91) XC functional.1 The elec-
tronic wavefunction was expanded in a basis of plane waves
upto a kinetic energy cut off 30 Ry and a charge density
cutoff of 300 Ry. The Brillouin Zone (BZ) integrations
were performed using Methfessel-Paxton smearing15 using
a smearing parameter of 0.025 Ry. Bulk structures of Py
and Asp were fully optimized with a well converged 8×8×4
gamma centered Monkhorst-Pack16 k-point grid. Increase
in the k-point grid size resulted in negligible changes to the
lattice parameters as well as the total energy of these mate-
rials. Detailed calculations on the Py and Asp surfaces are
presented in an earlier work by Kumar et al. (2022)17 and
Kumar et al. (2023).18 For adsorption energies calculation,
the most stable surfaces for Asp (001), and Py (100) were
selected based on our earlier computations. A vacuum gap
of at least 15 Å was used along the surface normal direc-
tion to avoid any spurious interaction between periodic
images of the slabs. The geometry optimization was car-
ried out using the BFGS algorithm and the calculations
were deemed to have converged when the force on each
atom and total energy difference between successive steps
dropped below 10–3 Ry/bohr and 10–4 Ry, respectively.
Various initial conformations were considered for the
adsorption of IPETC on the most stable surface of the two
minerals. The interaction energies were computed using the
following expression:
ΔE= Ecomplex – (Esurface +Ecollector) (1)
where Ecomplex, Esurface, and Ecollector are the total energies of
the optimized mineral-collector complex, mineral surface,
and the isolated collector molecule respectively.
Quantum chemical calculations of IPETC and
IPETCdp in a vacuum were carried using the NWChem
6.8 software.19 Both IPETC and IPETCdp were created
using the Avogadro software20 and subsequently subjected
to minimization using the B3LYP exchange-correlation
functional[21 in conjunction with the 6-311++G** basis
set.22 The geometry optimization process was carried out
with an SCF (Self-Consistent Field) convergence criterion
of 0.0027 meV, and a force cutoff of 0.015 meV/Å.
RESULTS AND DISCUSSIONS
Quantum Chemical Descriptors
Quantum chemical descriptors play a pivotal role in unrav-
eling the intricate details of a molecule’s electronic structure,
stability, and reactivity. These descriptors offer invaluable
insights into the molecular properties that govern a spec-
trum of chemical and physical processes. In our investiga-
tion, we optimized both IPETC (Figure 1, upper panel)
and IPETCdp (Figure 1, lower panel), and the resulting
HOMO-LUMO plots are depicted in Figure 1. Analysis of
Figure 1 reveals that in the neutral case, the HOMO is pre-
dominantly localized at the =S group, indicating a region
with high electron density. In contrast, for the IPETCdp,
the HOMO is distributed over both the =S and N groups,
showcasing a distinct electronic structure. Additionally,
the LUMO is observed to be primarily situated above
the hydrogen atoms in both cases. This spatial distribu-
tion implies that, in scenarios involving the interaction of
IPETC with mineral surfaces, there is a high likelihood of
electron donation from the =S atom in the neutral state.
Meanwhile, in the IPETCdp, both the =S and N atoms
exhibit a propensity to contribute electrons. These findings
shed light on the potential electron-donating behavior of
IPETC under different conditions, offering valuable guid-
ance for understanding its reactivity and interactions in
various chemical environments.
Despite the existence of a few experimental studies in
this domain, there remains a notable dearth of mechanistic
understanding, underscoring the need for molecular mod-
eling to elucidate the underlying processes. In this study,
we performed density functional theory (DFT) calculations
to gain insights into the interaction between Isopropyl
Ethylthiocarbamate (IPETC) and the surfaces of Asp (001)
and Py (100). Initially, we computed quantum chemical
descriptors, including the Highest Occupied Molecular
Orbital (HOMO), Lowest Unoccupied Molecular Orbital
(LUMO), and the energy gap (Egap), for both IPETC
and its deprotonated form (IPETCdp). Subsequently, we
explored the adsorption behavior of both the neutral and
deprotonated molecules on pristine Py and Asp surfaces, as
well as in the presence of copper (Cu) ions.
This comprehensive study provides valuable insights
into the molecular interactions at the mineral surfaces,
shedding light on the adsorption mechanisms of IPETC
and IPETCdp. Moreover, the investigation extended to the
presence of Cu ions, which is crucial given the influence
of copper ions in flotation processes. The outcomes of this
study contribute valuable insights into the intricacies of the
adsorption process and offer an atomic scale perspective to
surface chemistry of flotation processes.
COMPUTATIONAL METHODOLOGIES
DFT calculations were carried out using the PWscf code of
the Quantum Espresso-6.7 software package.13 The elec-
tron exchange and correlation interactions were described
using Perdew and Wang (PW91) XC functional.1 The elec-
tronic wavefunction was expanded in a basis of plane waves
upto a kinetic energy cut off 30 Ry and a charge density
cutoff of 300 Ry. The Brillouin Zone (BZ) integrations
were performed using Methfessel-Paxton smearing15 using
a smearing parameter of 0.025 Ry. Bulk structures of Py
and Asp were fully optimized with a well converged 8×8×4
gamma centered Monkhorst-Pack16 k-point grid. Increase
in the k-point grid size resulted in negligible changes to the
lattice parameters as well as the total energy of these mate-
rials. Detailed calculations on the Py and Asp surfaces are
presented in an earlier work by Kumar et al. (2022)17 and
Kumar et al. (2023).18 For adsorption energies calculation,
the most stable surfaces for Asp (001), and Py (100) were
selected based on our earlier computations. A vacuum gap
of at least 15 Å was used along the surface normal direc-
tion to avoid any spurious interaction between periodic
images of the slabs. The geometry optimization was car-
ried out using the BFGS algorithm and the calculations
were deemed to have converged when the force on each
atom and total energy difference between successive steps
dropped below 10–3 Ry/bohr and 10–4 Ry, respectively.
Various initial conformations were considered for the
adsorption of IPETC on the most stable surface of the two
minerals. The interaction energies were computed using the
following expression:
ΔE= Ecomplex – (Esurface +Ecollector) (1)
where Ecomplex, Esurface, and Ecollector are the total energies of
the optimized mineral-collector complex, mineral surface,
and the isolated collector molecule respectively.
Quantum chemical calculations of IPETC and
IPETCdp in a vacuum were carried using the NWChem
6.8 software.19 Both IPETC and IPETCdp were created
using the Avogadro software20 and subsequently subjected
to minimization using the B3LYP exchange-correlation
functional[21 in conjunction with the 6-311++G** basis
set.22 The geometry optimization process was carried out
with an SCF (Self-Consistent Field) convergence criterion
of 0.0027 meV, and a force cutoff of 0.015 meV/Å.
RESULTS AND DISCUSSIONS
Quantum Chemical Descriptors
Quantum chemical descriptors play a pivotal role in unrav-
eling the intricate details of a molecule’s electronic structure,
stability, and reactivity. These descriptors offer invaluable
insights into the molecular properties that govern a spec-
trum of chemical and physical processes. In our investiga-
tion, we optimized both IPETC (Figure 1, upper panel)
and IPETCdp (Figure 1, lower panel), and the resulting
HOMO-LUMO plots are depicted in Figure 1. Analysis of
Figure 1 reveals that in the neutral case, the HOMO is pre-
dominantly localized at the =S group, indicating a region
with high electron density. In contrast, for the IPETCdp,
the HOMO is distributed over both the =S and N groups,
showcasing a distinct electronic structure. Additionally,
the LUMO is observed to be primarily situated above
the hydrogen atoms in both cases. This spatial distribu-
tion implies that, in scenarios involving the interaction of
IPETC with mineral surfaces, there is a high likelihood of
electron donation from the =S atom in the neutral state.
Meanwhile, in the IPETCdp, both the =S and N atoms
exhibit a propensity to contribute electrons. These findings
shed light on the potential electron-donating behavior of
IPETC under different conditions, offering valuable guid-
ance for understanding its reactivity and interactions in
various chemical environments.