2326 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
of the oxygen present within the aliphatic chain on the
adsorption.
The present work considers two angles: (i) a macro-
scopic angle, with isotherms acquisition at three tempera-
tures, and fitting with adsorption models (ii) a microscopic
angle investigating the adsorption of collectors on kaolinite
basal surfaces, using molecular modelling. Molecular mod-
elling has already proven to be a relevant tool to understand
and highlight the adsorption mechanisms of organic mol-
ecules onto mineral surfaces (Foucaud et al., 2019 Silva et
al., 2021) and has already proved to be in good accordance
with experimental results (Foucaud et al., 2021a, 2021b).
Herein, our objectives are to compare the adsorption
behaviour of the two molecules, and at a much larger scale,
to pinpoint the best reagents for kaolinite recovery depend-
ing on their chemical structure and on the chemical envi-
ronment of the system.
MATERIALS &METHODS
Material
A natural kaolinite was purchased from Sigma-Aldrich.
Modal mineralogy showed that the material contains 87%
kaolinite with quartz, orthoclase, and muscovite impuri-
ties. The specific surface is 10.12 m2·g–1 as estimated with
argon adsorption. The d80 of the material is 15 µm and
thus, requires no further grinding.
Dodecylammonium chloride (C12H28N+··Cl–) (DDA)
was acquired from Acros Organics with a purity superior to
98 wt.%. 3-dodecyloxypropylamine (C15H33NO) (EA)
was acquired from Sigma Aldrich (purity 99 wt. %).Being
non soluble under this form, the salt was synthesized by
solubilising pure EA in ethanol under mild agitation and
by adding hydrochloric acid. After evaporation of the etha-
nol, a powder of hydrochloric EA was formed, which was
perfectly soluble in water.
Methods
A Total Organic Carbon (TOC) analyser from AnalytikJena
(2100 TOC analyser) was used for analysing the concen-
tration of flotation reagents remaining in solution after
the adsorption experiment. Adsorption isotherms were
acquired at 25°C, 35°C, and 45°C (±0.1°C). Initial con-
centrations of reagents in the conditioning solution ranged
from 10 to 3000 ppm, in an effort to not cross the critical
micellar concentration (CMC). Each test tube was filled
with 200 mg of mineral powder and 10 mL of adsorbate
solution. The tubes were set horizontally and agitated at
285 rpm in a shaker-incubator for 16 h. The solution con-
taining the mineral was then centrifugated for 10 min at
4900 rpm and the recovered solution was directly analysed
using the TOC analyser.
To complete isotherm analysis, the variation of the
theoretical coverage θ was calculated using Eq. 1, where
A is the number of adsorbed molecules (mol·m2), NA is
the Avogadro number (6.022×1023 mol–1), and SCS is the
packing area (or cross-section) of one molecule on kaolinite
surface. It has been shown that the packing area of DDA
cations is 25 Å2 (Yoon and Ravishankar, 1994). As EA mol-
ecule only differs in its structure by its oxygen and a longer
chain than DDA, the package area of EA is supposed to be
the same as DDA.
A N S
A CS ##i =(1)
From the experimental monolayer, it is possible to estimate
the actual packing area of the molecules using Eq. 2 (Sabah
et al., 2002) where Γm and A are the adsorbed amount at
the monolayer (in mol·m–2), and the Avogadro number (in
mol–1), respectively.
A
1 Packing area
m #C =t (2)
The isotherms were fitted with different usual adsorp-
tion isotherms: Langmuir (Langmuir, 1918), Freundlich
(Freundlich, 1907), Langmuir-Freundlich, Dual-site
Langmuir (Mathias et al., 1996), Dual-Site Langmuir
Freundlich (Nuhnen and Janiak, 2020), Toth (Toth, 1971)
and Redlich-Peterson (Redlich and Peterson, 1959) (see
Table 1).
The enthalpy of adsorption was estimated using the
affinity parameter k in the Langmuir isotherm expressed
including the temperature dependency following Arrhenius
equation (Eq. 3). k A/ T =
3 ,is the affinity at infinite
temperature, usually ranging between 1 and 10, A is a pre-
factor described by the Langmuir theory (Delachaux et al.,
2023) and Q is the isosteric heat of adsorption, which is
equal to –ΔH (Do, 1998).
k Th k e /RT Q #=
3 ^(3)
Fourier Transform Infrared (FTIR) spectroscopy analyses
were carried out using the Diffuse Reflectance Infrared
Fourier Transform (DRIFT) method (Thomas and Kelley,
2008) .Spectra were acquired using an IFS 55 spectrometer
from Bruker. Samples were then conditioned for 15 min
under vigorous agitation to ensure an efficient diffusion of
chemical species in the solution. Kaolinite particles were
then filtered using a Buchner device to remove the condi-
tioning solution and dried at ambient temperature before
the DRIFT analyses.
of the oxygen present within the aliphatic chain on the
adsorption.
The present work considers two angles: (i) a macro-
scopic angle, with isotherms acquisition at three tempera-
tures, and fitting with adsorption models (ii) a microscopic
angle investigating the adsorption of collectors on kaolinite
basal surfaces, using molecular modelling. Molecular mod-
elling has already proven to be a relevant tool to understand
and highlight the adsorption mechanisms of organic mol-
ecules onto mineral surfaces (Foucaud et al., 2019 Silva et
al., 2021) and has already proved to be in good accordance
with experimental results (Foucaud et al., 2021a, 2021b).
Herein, our objectives are to compare the adsorption
behaviour of the two molecules, and at a much larger scale,
to pinpoint the best reagents for kaolinite recovery depend-
ing on their chemical structure and on the chemical envi-
ronment of the system.
MATERIALS &METHODS
Material
A natural kaolinite was purchased from Sigma-Aldrich.
Modal mineralogy showed that the material contains 87%
kaolinite with quartz, orthoclase, and muscovite impuri-
ties. The specific surface is 10.12 m2·g–1 as estimated with
argon adsorption. The d80 of the material is 15 µm and
thus, requires no further grinding.
Dodecylammonium chloride (C12H28N+··Cl–) (DDA)
was acquired from Acros Organics with a purity superior to
98 wt.%. 3-dodecyloxypropylamine (C15H33NO) (EA)
was acquired from Sigma Aldrich (purity 99 wt. %).Being
non soluble under this form, the salt was synthesized by
solubilising pure EA in ethanol under mild agitation and
by adding hydrochloric acid. After evaporation of the etha-
nol, a powder of hydrochloric EA was formed, which was
perfectly soluble in water.
Methods
A Total Organic Carbon (TOC) analyser from AnalytikJena
(2100 TOC analyser) was used for analysing the concen-
tration of flotation reagents remaining in solution after
the adsorption experiment. Adsorption isotherms were
acquired at 25°C, 35°C, and 45°C (±0.1°C). Initial con-
centrations of reagents in the conditioning solution ranged
from 10 to 3000 ppm, in an effort to not cross the critical
micellar concentration (CMC). Each test tube was filled
with 200 mg of mineral powder and 10 mL of adsorbate
solution. The tubes were set horizontally and agitated at
285 rpm in a shaker-incubator for 16 h. The solution con-
taining the mineral was then centrifugated for 10 min at
4900 rpm and the recovered solution was directly analysed
using the TOC analyser.
To complete isotherm analysis, the variation of the
theoretical coverage θ was calculated using Eq. 1, where
A is the number of adsorbed molecules (mol·m2), NA is
the Avogadro number (6.022×1023 mol–1), and SCS is the
packing area (or cross-section) of one molecule on kaolinite
surface. It has been shown that the packing area of DDA
cations is 25 Å2 (Yoon and Ravishankar, 1994). As EA mol-
ecule only differs in its structure by its oxygen and a longer
chain than DDA, the package area of EA is supposed to be
the same as DDA.
A N S
A CS ##i =(1)
From the experimental monolayer, it is possible to estimate
the actual packing area of the molecules using Eq. 2 (Sabah
et al., 2002) where Γm and A are the adsorbed amount at
the monolayer (in mol·m–2), and the Avogadro number (in
mol–1), respectively.
A
1 Packing area
m #C =t (2)
The isotherms were fitted with different usual adsorp-
tion isotherms: Langmuir (Langmuir, 1918), Freundlich
(Freundlich, 1907), Langmuir-Freundlich, Dual-site
Langmuir (Mathias et al., 1996), Dual-Site Langmuir
Freundlich (Nuhnen and Janiak, 2020), Toth (Toth, 1971)
and Redlich-Peterson (Redlich and Peterson, 1959) (see
Table 1).
The enthalpy of adsorption was estimated using the
affinity parameter k in the Langmuir isotherm expressed
including the temperature dependency following Arrhenius
equation (Eq. 3). k A/ T =
3 ,is the affinity at infinite
temperature, usually ranging between 1 and 10, A is a pre-
factor described by the Langmuir theory (Delachaux et al.,
2023) and Q is the isosteric heat of adsorption, which is
equal to –ΔH (Do, 1998).
k Th k e /RT Q #=
3 ^(3)
Fourier Transform Infrared (FTIR) spectroscopy analyses
were carried out using the Diffuse Reflectance Infrared
Fourier Transform (DRIFT) method (Thomas and Kelley,
2008) .Spectra were acquired using an IFS 55 spectrometer
from Bruker. Samples were then conditioned for 15 min
under vigorous agitation to ensure an efficient diffusion of
chemical species in the solution. Kaolinite particles were
then filtered using a Buchner device to remove the condi-
tioning solution and dried at ambient temperature before
the DRIFT analyses.