2264 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Biosurfactants produced from renewable sources
by non-pathogenic microbes are promising candidates as
future substitutes of toxic/hazardous petroleum-based col-
lectors due to their promising unconventional molecular
structures that can underpin their selectivity [1]. In particu-
lar, sophorolipids, which are a subgroup of glycolipids, have
a wide structural variety and can be easily functionalized
further. The most common sophorolipids are acidic sopho-
rolipid (ASL) and lactonic sophorolipid (LSL) (Figure 1).
From the scaling-up viewpoint, an important advantage of
sophorolipids is that they hold the largest share of the bio-
surfactant market while their economic and environmental
sustainability is enhanced by their production from food
waste [6–8].
Although ASL and LSL share similar structural units
(Figure 1), they have different solution and interfacial
properties due to their anionic and nonionic characters,
respectively. ASL is soluble and effective in reducing sur-
face tension, which makes it a good emulsifier and foamer
[9]. Static surface tension estimates critical micelle concen-
tration (CMC) of diacetylated ASL as 0.18 mM at pH 6
and 10 [10]. Due to the absence of a carboxylic functional
group, LSL has a lower solubility compared to ASL, with
diacetylated LSL having a maximum solubility of 70 mg/L
(equivalent to 100 µM) [11, 12]. Even at 50 µM LSL is
present in solution as colloids [10].
The goal of this study is to compare the collecting
properties of ASL and LSL with conventional bench-
marks—sodium oleate (NaOl) and benzohydroxamic acid
(BHA)—in the flotation of ultrafine iron, copper, and
cerium oxide particles (hematite, malachite, and cerium
oxide, respectively). In the case of hematite and malachite,
we also compare the biosurfactants with a non-ionic green
surfactant n-dodecyl-β-D-maltoside (DDM). Given the
limited information about the collecting properties of ASL
and LSL, the study was conducted on artificial mineral
mixtures. To interpret flotation results, we measure single-
mineral flotation, zeta-potential, solubility, adsorption den-
sity, and X-ray photoelectron spectra (XPS).
MATERIALS AND METHODS
Diacetylated LSL and diacetylated ASL were provided by
Bio Base Europe Pilot Plant, Ghent, Belgium. Hematite
was provided by Rana Gruber, Norway. Malachite was pur-
chased from Richard Tayler Minerals, United Kingdom.
The origin of quartz was Khystym, South Ural, Russia.
X-ray diffraction (XRD) and XPS show that the natural
minerals have a very high purity with foreign inclusions
(aluminosilicates) less than 1%. Reduced cerium oxide
particles CeO2(red) were purchased from VWR and used
as received. Oxidized cerium oxide particles CeO2(°x) were
synthesized by sintering commercial 10-nm (99.9%) CeO2
nanoparticles provided by Meliorum Technology.
Flotation was conducted using a 100-mL XFG II flo-
tation machine in 90 mL MilliQ water (Figure 2). The
weight of minerals in single-mineral flotation of ultrafine
and coarse particles was 1 g and 1.5 g, respectively. In two-
mineral and three-mineral flotation, the ratio of miner-
als was 1:1 and 1:1:1, respectively. Since quartz does not
adsorb the collectors, in the two-mineral flotation of hema-
tite and malachite against quartz, the weight of each oxide
was maintained as 1 g. In the two-mineral and three-min-
eral flotation including CeO2, the weight of each oxide was
0.5 g. We did not use a frother in the case of biosurfactants
due to their good intrinsic foaming properties. As BHA
lacks these properties, 50 µM DowFrothTM 200 was used
as a frother in the flotation with BHA. In the case of NaOl,
which also does not have foaming properties, we collected
the hydrophobic layer of particles on the surface of the flo-
tation cell. pH was adjusted with NaOH and HNO3. pH
a b
acidic sophorolipid (ASL) lactonic sophorolipid (LSL)
Figure 1. Examples of diacetylated sophorolipids: (a) acidic sophorolipid (ASL) and (b) lactonic
sophorolipid (LSL). Copyright (C) 2023, Slabov, Jain, Larsen, Rao Kota, and Chernyshova

Previous Page Next Page

Extracted Text (may have errors)

2264 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Biosurfactants produced from renewable sources
by non-pathogenic microbes are promising candidates as
future substitutes of toxic/hazardous petroleum-based col-
lectors due to their promising unconventional molecular
structures that can underpin their selectivity [1]. In particu-
lar, sophorolipids, which are a subgroup of glycolipids, have
a wide structural variety and can be easily functionalized
further. The most common sophorolipids are acidic sopho-
rolipid (ASL) and lactonic sophorolipid (LSL) (Figure 1).
From the scaling-up viewpoint, an important advantage of
sophorolipids is that they hold the largest share of the bio-
surfactant market while their economic and environmental
sustainability is enhanced by their production from food
waste [6–8].
Although ASL and LSL share similar structural units
(Figure 1), they have different solution and interfacial
properties due to their anionic and nonionic characters,
respectively. ASL is soluble and effective in reducing sur-
face tension, which makes it a good emulsifier and foamer
[9]. Static surface tension estimates critical micelle concen-
tration (CMC) of diacetylated ASL as 0.18 mM at pH 6
and 10 [10]. Due to the absence of a carboxylic functional
group, LSL has a lower solubility compared to ASL, with
diacetylated LSL having a maximum solubility of 70 mg/L
(equivalent to 100 µM) [11, 12]. Even at 50 µM LSL is
present in solution as colloids [10].
The goal of this study is to compare the collecting
properties of ASL and LSL with conventional bench-
marks—sodium oleate (NaOl) and benzohydroxamic acid
(BHA)—in the flotation of ultrafine iron, copper, and
cerium oxide particles (hematite, malachite, and cerium
oxide, respectively). In the case of hematite and malachite,
we also compare the biosurfactants with a non-ionic green
surfactant n-dodecyl-β-D-maltoside (DDM). Given the
limited information about the collecting properties of ASL
and LSL, the study was conducted on artificial mineral
mixtures. To interpret flotation results, we measure single-
mineral flotation, zeta-potential, solubility, adsorption den-
sity, and X-ray photoelectron spectra (XPS).
MATERIALS AND METHODS
Diacetylated LSL and diacetylated ASL were provided by
Bio Base Europe Pilot Plant, Ghent, Belgium. Hematite
was provided by Rana Gruber, Norway. Malachite was pur-
chased from Richard Tayler Minerals, United Kingdom.
The origin of quartz was Khystym, South Ural, Russia.
X-ray diffraction (XRD) and XPS show that the natural
minerals have a very high purity with foreign inclusions
(aluminosilicates) less than 1%. Reduced cerium oxide
particles CeO2(red) were purchased from VWR and used
as received. Oxidized cerium oxide particles CeO2(°x) were
synthesized by sintering commercial 10-nm (99.9%) CeO2
nanoparticles provided by Meliorum Technology.
Flotation was conducted using a 100-mL XFG II flo-
tation machine in 90 mL MilliQ water (Figure 2). The
weight of minerals in single-mineral flotation of ultrafine
and coarse particles was 1 g and 1.5 g, respectively. In two-
mineral and three-mineral flotation, the ratio of miner-
als was 1:1 and 1:1:1, respectively. Since quartz does not
adsorb the collectors, in the two-mineral flotation of hema-
tite and malachite against quartz, the weight of each oxide
was maintained as 1 g. In the two-mineral and three-min-
eral flotation including CeO2, the weight of each oxide was
0.5 g. We did not use a frother in the case of biosurfactants
due to their good intrinsic foaming properties. As BHA
lacks these properties, 50 µM DowFrothTM 200 was used
as a frother in the flotation with BHA. In the case of NaOl,
which also does not have foaming properties, we collected
the hydrophobic layer of particles on the surface of the flo-
tation cell. pH was adjusted with NaOH and HNO3. pH
a b
acidic sophorolipid (ASL) lactonic sophorolipid (LSL)
Figure 1. Examples of diacetylated sophorolipids: (a) acidic sophorolipid (ASL) and (b) lactonic
sophorolipid (LSL). Copyright (C) 2023, Slabov, Jain, Larsen, Rao Kota, and Chernyshova

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2263
Flotation of Ultrafine Metal Oxides with Sophorolipids
Irina Chernyshova
Department of Geoscience and Petroleum, Norwegian University of Science and Technology (NTNU)
Department of Earth and Environmental Engineering, Columbia University
Vladislav Slabova, Hanumantha Rao Kota
Department of Geoscience and Petroleum, Norwegian University of Science and Technology (NTNU)
ABSTRACT: Toward developing more sustainable flotation processes, we study two sophorolipid biosurfactants
as collectors of ultrafine hematite, malachite, and ceria against quartz, in comparison with conventional
collectors. In the flotation of hematite and malachite against quartz, the sophorolipids achieve similarly high
grades and recoveries for the conventional (+38–90 µm) and ultrafine (–20 µm) particle sizes. Notably, the
sophorolipids also demonstrate efficacy in the separation of ceria or hematite from quartz, with the recovery of
ceria being influenced by its oxidation state—an additional critical factor. To interpret the trends, we measure
zeta-potential, single-mineral flotation, solubility of the minerals, adsorption density of the collectors, and ex
situ XPS. Our findings underscore that sophorolipids hold a promise as environmentally-friendly substitutes of
conventional petroleum-based collectors in addressing the persistent problems of fines in oxide flotation as well
as the recovery of rare earth minerals (REM).
INTRODUCTION
In common with other separation technologies, froth flota-
tion is facing the grand challenge of increasing separation
efficiency while minimizing the environmental impact.
In particular, there is a growing concern about the envi-
ronmental impact of traditional, chemically intensive
separation methods that rely heavily on petroleum-based
reagents. The latter are associated with a number of prob-
lems including the dependence on non-renewable sources
and their production using non-green synthesis routes. In
addition, many conventional petroleum-based reagents or
their decomposition products pose occupational or envi-
ronmental hazards [1]. Flotation already heavily employs
two important classes of green reagents – fatty acids and
polysaccharide polymers, which are mainly used as col-
lectors and depressants of iron oxides and Ca minerals.
However, further research is needed to expand the list of
greener flotation reagents that not only mitigate the envi-
ronmental and safety problems, but also improve separa-
tion efficiency.
A new generation of green reagents can also help tackle
another persisting problem of froth flotation—the so-called
‘problem of fines’ [2]. Flotation is optimized for particle
sizes in the 38–150 µm (‘conventional’) range, losing its
selectivity for fine and ultrafine particles (smaller than
10–30 µm), which inflates the cost. The problem of fines
is especially pressing in the processing of mechanically soft
oxide ores, the grinding of which immanently produces a
high fraction of ultrafine particles. Ultrafine particles are
also produced during grinding of low grade ores and are
also anticipated during re-processing of flotation tailings
that require overgrinding to liberate small grains of valu-
able minerals. Furthermore, rare earth minerals (REM) are
often highly dispersed in ores and tailings [3–5].

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2263
Flotation of Ultrafine Metal Oxides with Sophorolipids
Irina Chernyshova
Department of Geoscience and Petroleum, Norwegian University of Science and Technology (NTNU)
Department of Earth and Environmental Engineering, Columbia University
Vladislav Slabova, Hanumantha Rao Kota
Department of Geoscience and Petroleum, Norwegian University of Science and Technology (NTNU)
ABSTRACT: Toward developing more sustainable flotation processes, we study two sophorolipid biosurfactants
as collectors of ultrafine hematite, malachite, and ceria against quartz, in comparison with conventional
collectors. In the flotation of hematite and malachite against quartz, the sophorolipids achieve similarly high
grades and recoveries for the conventional (+38–90 µm) and ultrafine (–20 µm) particle sizes. Notably, the
sophorolipids also demonstrate efficacy in the separation of ceria or hematite from quartz, with the recovery of
ceria being influenced by its oxidation state—an additional critical factor. To interpret the trends, we measure
zeta-potential, single-mineral flotation, solubility of the minerals, adsorption density of the collectors, and ex
situ XPS. Our findings underscore that sophorolipids hold a promise as environmentally-friendly substitutes of
conventional petroleum-based collectors in addressing the persistent problems of fines in oxide flotation as well
as the recovery of rare earth minerals (REM).
INTRODUCTION
In common with other separation technologies, froth flota-
tion is facing the grand challenge of increasing separation
efficiency while minimizing the environmental impact.
In particular, there is a growing concern about the envi-
ronmental impact of traditional, chemically intensive
separation methods that rely heavily on petroleum-based
reagents. The latter are associated with a number of prob-
lems including the dependence on non-renewable sources
and their production using non-green synthesis routes. In
addition, many conventional petroleum-based reagents or
their decomposition products pose occupational or envi-
ronmental hazards [1]. Flotation already heavily employs
two important classes of green reagents – fatty acids and
polysaccharide polymers, which are mainly used as col-
lectors and depressants of iron oxides and Ca minerals.
However, further research is needed to expand the list of
greener flotation reagents that not only mitigate the envi-
ronmental and safety problems, but also improve separa-
tion efficiency.
A new generation of green reagents can also help tackle
another persisting problem of froth flotation—the so-called
‘problem of fines’ [2]. Flotation is optimized for particle
sizes in the 38–150 µm (‘conventional’) range, losing its
selectivity for fine and ultrafine particles (smaller than
10–30 µm), which inflates the cost. The problem of fines
is especially pressing in the processing of mechanically soft
oxide ores, the grinding of which immanently produces a
high fraction of ultrafine particles. Ultrafine particles are
also produced during grinding of low grade ores and are
also anticipated during re-processing of flotation tailings
that require overgrinding to liberate small grains of valu-
able minerals. Furthermore, rare earth minerals (REM) are
often highly dispersed in ores and tailings [3–5].

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2265
in the flotation machine was adjusted to the required value
after dispersing the mineral particles in water for 2 min,
followed by adding the surfactant solution at the same pH.
pH was readjusted after 4 min followed by the flotation in
1 minute. The reported pH values were measured under
flotation conditions.
Hematite, malachite, and quartz were crushed and
milled in a planetary mill with a stainless-steel jar and stain-
less steel 30 mm balls, followed by wet sieving to obtain
a –20 µm fraction. The coarse (+38–90 µm) fraction was
prepared by dry sieving. To remove contaminations, hema-
tite and quartz particles were cleaned in a 0.01 M HCl
solution followed by washing in MilliQ water until neutral
pH is reached. The cleaning procedure for malachite was
eliminated due to its dissolution at acidic pH. Oxidized
cerium oxide particles, which we call CeO2(°x) hereafter,
were synthesized by sintering commercial 10-nm (99.9%)
CeO2 nanoparticles provided by Meliorum Technology. To
synthesize CeO2(°x), a 60:50 (w/w) mixture of the CeO2
nanoparticles with water was placed in a corundum jar and
dried overnight at 80 °C, followed by the calcination at
1000 °C in air for 3 h with a heating rate of 250 °C/h. The
final porous sample was crushed in a hand mill to obtain a
visually homogeneous powder which was used for the fur-
ther study.
The mineral particles were characterized using XRD,
SEM, and zeta-potential. The adsorption of the collectors
was studied using their adsorption density and the solubil-
ity of the minerals in the collector solutions measured after
2h of equilibration using total organic carbon (TOC) and
inductively coupled plasma mass spectrometry (ICP-MS),
respectively. Molecular-level insights were gained using
XPS. The spectra were measured after 2h of equilibration
and was aligned by setting the C 1s peak of adventitious
carbon at 285 eV. More technical details can be found else-
where [10, 13].
RESULTS
Flotation of Ultrafine Hematite and Malachite with
ASL, LSL, NaOl, and DDM
In this part, we compare ASL, LSL, NaOl, and DDM as
collectors in the two-mineral flotation of hematite and
malachite against quartz for ultrafine (–20 µm) and con-
ventional (+38 − 90 µm) particle size at pH 5–6 and 10.
For brevity, the conventional size fraction is called ‘coarse’
hereafter. The surfactant concentration is 50 µM, which is
lower than their CMC.
In the flotation of coarse hematite against ultrafine
quartz at pH 5 and 10, NaOl, LSL, and ASL produce hema-
tite grades of 65–70% (Figure 3a,b). The coarse malachite
grade is somewhat higher, being 75–80% and 65–75% at
Figure 2. Flotation flowsheet
c d a b
Figure 3. Recovery and grade in the flotation of a 1:1 (wt) mixture of ultrafine (–20 mm) and coarse (+38 − 90 µm) (a,b)
hematite and (c,d) malachite with ultrafine quartz with 50 µM () ASL, () LSL, () DDM, and () NaOl as
collectors at (a) pH 5 ± 0.3 and (b) pH 10 ± 0.3. The filled and empty symbols correspond to ultrafine and coarse hematite
particles, respectively. The error of the grade and recovery data points without the error bars is less than 5%. Copyright ©
2023, Slabov, Jain, Larsen, Rao Kota, and Chernyshova

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2265
in the flotation machine was adjusted to the required value
after dispersing the mineral particles in water for 2 min,
followed by adding the surfactant solution at the same pH.
pH was readjusted after 4 min followed by the flotation in
1 minute. The reported pH values were measured under
flotation conditions.
Hematite, malachite, and quartz were crushed and
milled in a planetary mill with a stainless-steel jar and stain-
less steel 30 mm balls, followed by wet sieving to obtain
a –20 µm fraction. The coarse (+38–90 µm) fraction was
prepared by dry sieving. To remove contaminations, hema-
tite and quartz particles were cleaned in a 0.01 M HCl
solution followed by washing in MilliQ water until neutral
pH is reached. The cleaning procedure for malachite was
eliminated due to its dissolution at acidic pH. Oxidized
cerium oxide particles, which we call CeO2(°x) hereafter,
were synthesized by sintering commercial 10-nm (99.9%)
CeO2 nanoparticles provided by Meliorum Technology. To
synthesize CeO2(°x), a 60:50 (w/w) mixture of the CeO2
nanoparticles with water was placed in a corundum jar and
dried overnight at 80 °C, followed by the calcination at
1000 °C in air for 3 h with a heating rate of 250 °C/h. The
final porous sample was crushed in a hand mill to obtain a
visually homogeneous powder which was used for the fur-
ther study.
The mineral particles were characterized using XRD,
SEM, and zeta-potential. The adsorption of the collectors
was studied using their adsorption density and the solubil-
ity of the minerals in the collector solutions measured after
2h of equilibration using total organic carbon (TOC) and
inductively coupled plasma mass spectrometry (ICP-MS),
respectively. Molecular-level insights were gained using
XPS. The spectra were measured after 2h of equilibration
and was aligned by setting the C 1s peak of adventitious
carbon at 285 eV. More technical details can be found else-
where [10, 13].
RESULTS
Flotation of Ultrafine Hematite and Malachite with
ASL, LSL, NaOl, and DDM
In this part, we compare ASL, LSL, NaOl, and DDM as
collectors in the two-mineral flotation of hematite and
malachite against quartz for ultrafine (–20 µm) and con-
ventional (+38 − 90 µm) particle size at pH 5–6 and 10.
For brevity, the conventional size fraction is called ‘coarse’
hereafter. The surfactant concentration is 50 µM, which is
lower than their CMC.
In the flotation of coarse hematite against ultrafine
quartz at pH 5 and 10, NaOl, LSL, and ASL produce hema-
tite grades of 65–70% (Figure 3a,b). The coarse malachite
grade is somewhat higher, being 75–80% and 65–75% at
Figure 2. Flotation flowsheet
c d a b
Figure 3. Recovery and grade in the flotation of a 1:1 (wt) mixture of ultrafine (–20 mm) and coarse (+38 − 90 µm) (a,b)
hematite and (c,d) malachite with ultrafine quartz with 50 µM () ASL, () LSL, () DDM, and () NaOl as
collectors at (a) pH 5 ± 0.3 and (b) pH 10 ± 0.3. The filled and empty symbols correspond to ultrafine and coarse hematite
particles, respectively. The error of the grade and recovery data points without the error bars is less than 5%. Copyright ©
2023, Slabov, Jain, Larsen, Rao Kota, and Chernyshova