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Mitigating the Adverse Effect of Salts on the Recovery of
Fine Particles in Flotation
Brady Wright, Kevin Galvin, Mahshid Firouzi
ARC Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals, Newcastle Institute for Energy and
Resources, University of Newcastle
ABSTRACT: Salts can negatively affect the froth flotation process by increasing the recovery of unwanted gangue
particles. This study investigates the potential of counter-current washing to mitigate this issue. Experiments
were conducted using a Reflux flotation cell and fine hydrophilic silica particles (with a D90 of 68μm) as a
model for gangue particles, and their behaviour was examined across various salt concentrations. To understand
the mechanisms affecting the recovery of these gangue particles, we analysed system hydrodynamics, measuring
factors like bubble size, distribution, and gas holdup under different conditions. Our results showed that the
counter-current washing significantly reduced the gangue recovery.
Keywords: inorganic salts, froth flotation, hydrophilic particles, reflux flotation cell, downcomer, entrainment.
INTRODUCTION
A fundamental problem in the field of froth flotation is
the need to increase the recovery of key minerals in the
wake of decreasing ore grades. Lower grade ores typically
contain a higher proportion of gangue (waste) material,
often with more complex structures. These feed types
often require more grinding, leading to finer particle sizes.
However, recovering finer particles in traditional flotation
devices is challenging, as these particles often lack sufficient
momentum to collide with and adhere to the bubble sur-
face. Additionally, the entrainment of hydrophilic gangue
material can lead to its reporting in the product, reducing
the product grade.
Another significant challenge in industrial flotation
circuits is the substantial freshwater requirement for the
beneficiation of valuable minerals, which varies between
8–55% by mass (Wills &Finch, 2016). With the expected
increase in the demand for metals over the coming years,
water consumption is expected to rise correspondingly.
Given global water scarcity and environmental constraints,
the integration of sea water or recycled process water in the
mining industry has become increasingly crucial.
The effect of salts on different types of ore recovery
has been explored in previous studies. Inorganic salts are
known to affect the particle-particle and particle-bubble
interactions. This behavior can be explained by reducing the
electrostatic double layer repulsions between same charged
particles (Firouzi, Howes, &Nguyen, A quantitative review
of the transition salt concentration for inhibiting bubble
coalescence, 2015), increasing the likelihood of particle
attachment. High salt concentration has been found to
enhance hydrophobicity, increase the mitigation of slime
coatings, increase entrainment, improve froth stability, and
lower bubble sizes (Jeldres, Forbes, &Cisternas, 2016).
Further information regarding the effect of salt on flotation
hydrodynamics is described in the literature, (Castro &
Laskowski, 2011) (Laskowski, Castro, &Gutierrez, 2019),
and (Wang &Peng, 2014).
Mitigating the Adverse Effect of Salts on the Recovery of
Fine Particles in Flotation
Brady Wright, Kevin Galvin, Mahshid Firouzi
ARC Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals, Newcastle Institute for Energy and
Resources, University of Newcastle
ABSTRACT: Salts can negatively affect the froth flotation process by increasing the recovery of unwanted gangue
particles. This study investigates the potential of counter-current washing to mitigate this issue. Experiments
were conducted using a Reflux flotation cell and fine hydrophilic silica particles (with a D90 of 68μm) as a
model for gangue particles, and their behaviour was examined across various salt concentrations. To understand
the mechanisms affecting the recovery of these gangue particles, we analysed system hydrodynamics, measuring
factors like bubble size, distribution, and gas holdup under different conditions. Our results showed that the
counter-current washing significantly reduced the gangue recovery.
Keywords: inorganic salts, froth flotation, hydrophilic particles, reflux flotation cell, downcomer, entrainment.
INTRODUCTION
A fundamental problem in the field of froth flotation is
the need to increase the recovery of key minerals in the
wake of decreasing ore grades. Lower grade ores typically
contain a higher proportion of gangue (waste) material,
often with more complex structures. These feed types
often require more grinding, leading to finer particle sizes.
However, recovering finer particles in traditional flotation
devices is challenging, as these particles often lack sufficient
momentum to collide with and adhere to the bubble sur-
face. Additionally, the entrainment of hydrophilic gangue
material can lead to its reporting in the product, reducing
the product grade.
Another significant challenge in industrial flotation
circuits is the substantial freshwater requirement for the
beneficiation of valuable minerals, which varies between
8–55% by mass (Wills &Finch, 2016). With the expected
increase in the demand for metals over the coming years,
water consumption is expected to rise correspondingly.
Given global water scarcity and environmental constraints,
the integration of sea water or recycled process water in the
mining industry has become increasingly crucial.
The effect of salts on different types of ore recovery
has been explored in previous studies. Inorganic salts are
known to affect the particle-particle and particle-bubble
interactions. This behavior can be explained by reducing the
electrostatic double layer repulsions between same charged
particles (Firouzi, Howes, &Nguyen, A quantitative review
of the transition salt concentration for inhibiting bubble
coalescence, 2015), increasing the likelihood of particle
attachment. High salt concentration has been found to
enhance hydrophobicity, increase the mitigation of slime
coatings, increase entrainment, improve froth stability, and
lower bubble sizes (Jeldres, Forbes, &Cisternas, 2016).
Further information regarding the effect of salt on flotation
hydrodynamics is described in the literature, (Castro &
Laskowski, 2011) (Laskowski, Castro, &Gutierrez, 2019),
and (Wang &Peng, 2014).