54
Application of the Boycott Effect in Maximizing
Grade and Recovery
Kevin P. Galvin
ARC Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals, Newcastle Institute for Energy and
Resources, University of Newcastle, Callaghan, NSW, Australia
ABSTRACT: Ultrafine colloidal particles, otherwise known as slimes, impede gravity and flotation separations
to a degree that is often not widely appreciated. These particles produce exponential increase in suspension
viscosity and contamination of mineral and bubble surfaces. The Boycott Effect, operating with counter current
washing via fluidization provides the essential elements for effective desliming and hence effective beneficiation.
This paper focuses on an improved description of gravity separation in the Reflux Classifier, linking the
partition surface to the hydrodynamics, in turn providing stronger insights into the underpinning separation
mechanisms. The Reflux Classifier forms the basis of a platform technology that includes the Reflux Flotation
Cell, and the Graviton for ultrafine desliming. This paper describes the synergy between the Boycott Effect and
the fluidization, including the synergy between these different technologies.
INTRODUCTION
More than one hundred years ago, A.E. Boycott (1920)
reported in a letter to Nature that blood “corpuscles settle
a good deal faster if the tube is inclined than when it is
vertical”. This observation, referred to as the Boycott Effect,
led to the development of the Lamella settler used in water
treatment and clarification, an early form of process inten-
sification achieved by increasing the effective sedimenta-
tion area through the presence of parallel inclined plates
(Ponder, 1925 Nakamura, and Kuroda, 1937 Acrivos and
Herbolzheimer, 1979).
The present work is focussed on a further development
of the Boycott Effect referred to as a “Reflux Classifier”
(Galvin, 2004). The basic arrangement, shown in Figure 1,
combines two key elements, the first being the system of
parallel inclined channels in the upper section, and the
second, the introduction of an upward current flow of
fluidization water through the lower base to support a flu-
idized bed. Clearly, with the introduction of the fluidiza-
tion water through the base, the motivation here was not
to achieve solid-liquid separation, rather to effect efficient
particle separations, promoting the departure of certain
particles to the overflow, and others to the underflow.
The basic hydrodynamics of the Reflux Classifier have
been described with reference to a simple laminar flow
model under dilute conditions (Galvin and Liu, 2011
Galvin, 2021), while the actual gravity separation perfor-
mance has been described empirically with reference to
the partition surface (Galvin et al., 2020, Rodrigues et
al., 2023). This paper formally brings these two disparate
descriptions into a single analytical description for the first
time, utilising a constitutive description of the hindered
settling, previously described by Asif (1997) and Galvin et
al (1999). While a more complex computational approach
has been developed (Syed et al., 2018) based on the
Application of the Boycott Effect in Maximizing
Grade and Recovery
Kevin P. Galvin
ARC Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals, Newcastle Institute for Energy and
Resources, University of Newcastle, Callaghan, NSW, Australia
ABSTRACT: Ultrafine colloidal particles, otherwise known as slimes, impede gravity and flotation separations
to a degree that is often not widely appreciated. These particles produce exponential increase in suspension
viscosity and contamination of mineral and bubble surfaces. The Boycott Effect, operating with counter current
washing via fluidization provides the essential elements for effective desliming and hence effective beneficiation.
This paper focuses on an improved description of gravity separation in the Reflux Classifier, linking the
partition surface to the hydrodynamics, in turn providing stronger insights into the underpinning separation
mechanisms. The Reflux Classifier forms the basis of a platform technology that includes the Reflux Flotation
Cell, and the Graviton for ultrafine desliming. This paper describes the synergy between the Boycott Effect and
the fluidization, including the synergy between these different technologies.
INTRODUCTION
More than one hundred years ago, A.E. Boycott (1920)
reported in a letter to Nature that blood “corpuscles settle
a good deal faster if the tube is inclined than when it is
vertical”. This observation, referred to as the Boycott Effect,
led to the development of the Lamella settler used in water
treatment and clarification, an early form of process inten-
sification achieved by increasing the effective sedimenta-
tion area through the presence of parallel inclined plates
(Ponder, 1925 Nakamura, and Kuroda, 1937 Acrivos and
Herbolzheimer, 1979).
The present work is focussed on a further development
of the Boycott Effect referred to as a “Reflux Classifier”
(Galvin, 2004). The basic arrangement, shown in Figure 1,
combines two key elements, the first being the system of
parallel inclined channels in the upper section, and the
second, the introduction of an upward current flow of
fluidization water through the lower base to support a flu-
idized bed. Clearly, with the introduction of the fluidiza-
tion water through the base, the motivation here was not
to achieve solid-liquid separation, rather to effect efficient
particle separations, promoting the departure of certain
particles to the overflow, and others to the underflow.
The basic hydrodynamics of the Reflux Classifier have
been described with reference to a simple laminar flow
model under dilute conditions (Galvin and Liu, 2011
Galvin, 2021), while the actual gravity separation perfor-
mance has been described empirically with reference to
the partition surface (Galvin et al., 2020, Rodrigues et
al., 2023). This paper formally brings these two disparate
descriptions into a single analytical description for the first
time, utilising a constitutive description of the hindered
settling, previously described by Asif (1997) and Galvin et
al (1999). While a more complex computational approach
has been developed (Syed et al., 2018) based on the