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].
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].