2775
Improving Flotation Efficiency with Low-Frequency
Acoustic Sound
Yujia Guan, Bingyu Yang, Hangil Park, Chun Yong Ng, Liguang Wang
The University of Queensland, School of Chemical Engineering, St Lucia, Queensland, Australia
ABSTRACT: An approach to improving flotation efficiency was developed and tested in mechanical flotation
and column flotation at laboratory scale and pilot scale. With using sound at a frequency below 500 Hz,
significantly improved flotation efficiency was obtained for coal and metalliferous ore, especially in the coarse
size fractions. This approach enables improvement of flotation efficiency at modest additional energy cost and
reduced reagent consumption, mitigating the overfrothing issue if any. The mechanisms of enhancement of
flotation by low-frequency acoustic sound were discussed with respect to bubble-bubble and bubble-particle
interactions studied experimentally through measuring the stability of foam and wetting films.
INTRODUCTION
Froth flotation is a physiochemical process widely used in
the mining industry to separate particles in fine or ultra-
fine size fraction based on the difference in the affinity to
gas bubbles. The hydrophobized or naturally hydrophobic
particles tend to be attached to air bubbles. The bubble-
particle aggregates that have an apparent specific gravity
less than 1 are lifted to the upper froth layer and then dis-
charged from the flotation cell. Important factors affect-
ing the efficiency of this particle separation process include
particle hydrophobicity, bubble size and froth stability
(Farrokhpay, 2011). The froth is preferably metastable—
unstable or overly stable froth is often detrimental to flota-
tion efficiency. Ideally, the froth within the flotation cell is
metastable whereas the froth discharged is unstable with
fast breakdown outside the flotation cell. A fast breakdown
of the discharged froth is wanted for efficient downstream
processes such as pumping and dewatering. On the other
hand, if the discharged froth is overly stable, the efficiency of
froth handling and dewatering will become low and in the
worse scenario the plant needs to be shut down to remove
the bubbles. This overfrothing issue commonly exits in coal
flotation and base metal flotation operations. To avoid this
issue, a common exercise is to reduce the dosage of reagents,
especially frother, but this approach often leads to loss of
valuable particles to the tailing. Alternatively, one can use
physical methods such as exposure to ultrasound, sound,
or vibration or installation of deaeration tanks to resolve
this issue. Extensive work has been done on ultrasound and
mechanical vibrations (e.g., oscillating the flotation cell).
However, these methods have not found industrial applica-
tions, probably owing to high operating cost.
Recent research progress shows that it is possible to
locally stabilise the froth within the flotation cell by using
acoustic sound at a relatively low frequency (e.g., 350 or 400
Hz) (Ng et al., 2020a, 2021, 2022 Yang et al., 2023a) so as
to improve flotation efficiency and overcome the overfroth-
ing issue. This idea originated from the stark contrast in the
experimentally observed tendency of bubble coalescence
(see Figure1). Increasing the salinity of flotation medium
from 1×10–4 M to 0.1 M would reduce bubble coalescence
tendency in a bubble column with continuous bubbling
(a dynamic condition similar to that of a flotation col-
umn) (Craig et al 1993) whereas it would increase bubble
Improving Flotation Efficiency with Low-Frequency
Acoustic Sound
Yujia Guan, Bingyu Yang, Hangil Park, Chun Yong Ng, Liguang Wang
The University of Queensland, School of Chemical Engineering, St Lucia, Queensland, Australia
ABSTRACT: An approach to improving flotation efficiency was developed and tested in mechanical flotation
and column flotation at laboratory scale and pilot scale. With using sound at a frequency below 500 Hz,
significantly improved flotation efficiency was obtained for coal and metalliferous ore, especially in the coarse
size fractions. This approach enables improvement of flotation efficiency at modest additional energy cost and
reduced reagent consumption, mitigating the overfrothing issue if any. The mechanisms of enhancement of
flotation by low-frequency acoustic sound were discussed with respect to bubble-bubble and bubble-particle
interactions studied experimentally through measuring the stability of foam and wetting films.
INTRODUCTION
Froth flotation is a physiochemical process widely used in
the mining industry to separate particles in fine or ultra-
fine size fraction based on the difference in the affinity to
gas bubbles. The hydrophobized or naturally hydrophobic
particles tend to be attached to air bubbles. The bubble-
particle aggregates that have an apparent specific gravity
less than 1 are lifted to the upper froth layer and then dis-
charged from the flotation cell. Important factors affect-
ing the efficiency of this particle separation process include
particle hydrophobicity, bubble size and froth stability
(Farrokhpay, 2011). The froth is preferably metastable—
unstable or overly stable froth is often detrimental to flota-
tion efficiency. Ideally, the froth within the flotation cell is
metastable whereas the froth discharged is unstable with
fast breakdown outside the flotation cell. A fast breakdown
of the discharged froth is wanted for efficient downstream
processes such as pumping and dewatering. On the other
hand, if the discharged froth is overly stable, the efficiency of
froth handling and dewatering will become low and in the
worse scenario the plant needs to be shut down to remove
the bubbles. This overfrothing issue commonly exits in coal
flotation and base metal flotation operations. To avoid this
issue, a common exercise is to reduce the dosage of reagents,
especially frother, but this approach often leads to loss of
valuable particles to the tailing. Alternatively, one can use
physical methods such as exposure to ultrasound, sound,
or vibration or installation of deaeration tanks to resolve
this issue. Extensive work has been done on ultrasound and
mechanical vibrations (e.g., oscillating the flotation cell).
However, these methods have not found industrial applica-
tions, probably owing to high operating cost.
Recent research progress shows that it is possible to
locally stabilise the froth within the flotation cell by using
acoustic sound at a relatively low frequency (e.g., 350 or 400
Hz) (Ng et al., 2020a, 2021, 2022 Yang et al., 2023a) so as
to improve flotation efficiency and overcome the overfroth-
ing issue. This idea originated from the stark contrast in the
experimentally observed tendency of bubble coalescence
(see Figure1). Increasing the salinity of flotation medium
from 1×10–4 M to 0.1 M would reduce bubble coalescence
tendency in a bubble column with continuous bubbling
(a dynamic condition similar to that of a flotation col-
umn) (Craig et al 1993) whereas it would increase bubble