XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3477
Repurposing a partial stream of the full plant tailings
by classifying useful particle size fractions has three main
advantages:
1. Reduced stored volume – reduces or eliminates the
need for borrowed material for embankment and
drain construction.
2. Improved short- and long-term stack stability
– adequate removal of water reduces the risk of
liquefaction.
3. Improved water recovery – improved drainage
from the TSF allows recovery of valuable process
water, that would otherwise be locked in as inter-
stitial water.
The total tonnage of free-draining sands that can be recov-
ered from the full plant tailings stream depends on the
tailings’ characteristics and the method of classification. In
plants where coarse particle recovery (CPR) is applied in
the beneficiation plant, the coarse tailings stream can be
used in its entirety, requiring only dewatering and minor
slimes control (see Bruton et al., 2023). On the other hand,
the relatively fine particle size characteristics of ‘traditional’
mine tailings may require more extensive classification,
yielding a lower coarse-solids recovery for reuse as a con-
struction material.
To be useful in dam construction or any design features
that enhance water drainage, the classified tailings product
needs to maintain sufficient hydraulic conductivity under
compaction. Experimental evidence indicates that for well-
classified products, the strength parameters and saturated
hydraulic conductivity or permeability mainly depend on
the degree of compaction and the degree of saturation at
the end of compaction (Tatsuoka, 2015 Scarcella et al.,
2018). It is also known that permeability is easily lost when
medium- or low-permeability particles are mixed with non-
permeable particles (Lu et al., 2024). This is the case with
typical mine tailings due to their relatively high level of fine
particles. The necessity to control the level of saturation
during compaction therefore requires tight control of the
quantity of fine or low-permeability particles in the classi-
fied product.
TAILINGS CLASSIFICATION THROUGH
CYCLONING
Hydrocyclones can be efficiently used for tailings classifica-
tion, specifically for removing the fines fraction from the
tailings (Castro et al., 2009). In conventional hydrocyclone
applications, two stages of cycloning may be required to
achieve the desired partition.
The Cavex ® DE hydrocyclone is a dual classification
technology in a single piece of equipment that achieves
a high degree of particle and water separation. Its design
includes in-built geometric variables and auxiliary features,
such as the wash chamber, which enable control over the
output products.
When using two hydrocyclones in series, the classifi-
cation efficiency is directly impacted, leading to a reduc-
tion in the bypass of fines. The Cavex ® DE classification
technology capitalizes on the synergy between the two units
and the wash chamber to minimize fine bypass. This results
in an underflow product with lower fine content while
simultaneously increasing water recovery to the overflow
(Figure 1).
In the following paragraphs the application of DE
cyclones in discrete tailings applications is expanded upon.
Abbreviations have been used for the solids concentration
by weight and volume, as well for the 80% passing particle
size. A summary of abbreviations and definitions is given
in Table 1.
Table 1. List of abbreviations
Abbreviation Definition
Cw Weight Solid Concentration (%w/w)
Cv Volumetric Solid Concentration (%v/v)
F80 80% passing size of the product (µm)
D50c Particle size of which 50% reports to the
overflow and 50% reports to the underflow.
WASHING CHAMBER
The wash chamber of the Cavex ® DE hydrocyclone is
designed to address one of the main issues in density clas-
sification: the carryover of fine material into the coarse
product due to the viscous layer on the equipment’s walls.
This problem, identified by Bloor and Ingham (1976) and
Concha (1994), is mitigated by the geometry of the wash
chamber, which breaks the viscous layer and releases the
trapped fine material. The injection water then helps trans-
port these fines to the air core of the hydrocyclone, enabling
their classification. Additionally, the wash water dilutes the
slurry, and this diluted slurry, when fed to the second clas-
sification stage, demonstrates the effect of the wash water
on the fine bypass, as illustrated in Figure 2.
INDUSTRIAL APPLICATION
Cavex ® DE hydrocyclones are used for the classification
of sands for dam wall construction at various mine sites
around the world. Their application allows for considerable
Repurposing a partial stream of the full plant tailings
by classifying useful particle size fractions has three main
advantages:
1. Reduced stored volume – reduces or eliminates the
need for borrowed material for embankment and
drain construction.
2. Improved short- and long-term stack stability
– adequate removal of water reduces the risk of
liquefaction.
3. Improved water recovery – improved drainage
from the TSF allows recovery of valuable process
water, that would otherwise be locked in as inter-
stitial water.
The total tonnage of free-draining sands that can be recov-
ered from the full plant tailings stream depends on the
tailings’ characteristics and the method of classification. In
plants where coarse particle recovery (CPR) is applied in
the beneficiation plant, the coarse tailings stream can be
used in its entirety, requiring only dewatering and minor
slimes control (see Bruton et al., 2023). On the other hand,
the relatively fine particle size characteristics of ‘traditional’
mine tailings may require more extensive classification,
yielding a lower coarse-solids recovery for reuse as a con-
struction material.
To be useful in dam construction or any design features
that enhance water drainage, the classified tailings product
needs to maintain sufficient hydraulic conductivity under
compaction. Experimental evidence indicates that for well-
classified products, the strength parameters and saturated
hydraulic conductivity or permeability mainly depend on
the degree of compaction and the degree of saturation at
the end of compaction (Tatsuoka, 2015 Scarcella et al.,
2018). It is also known that permeability is easily lost when
medium- or low-permeability particles are mixed with non-
permeable particles (Lu et al., 2024). This is the case with
typical mine tailings due to their relatively high level of fine
particles. The necessity to control the level of saturation
during compaction therefore requires tight control of the
quantity of fine or low-permeability particles in the classi-
fied product.
TAILINGS CLASSIFICATION THROUGH
CYCLONING
Hydrocyclones can be efficiently used for tailings classifica-
tion, specifically for removing the fines fraction from the
tailings (Castro et al., 2009). In conventional hydrocyclone
applications, two stages of cycloning may be required to
achieve the desired partition.
The Cavex ® DE hydrocyclone is a dual classification
technology in a single piece of equipment that achieves
a high degree of particle and water separation. Its design
includes in-built geometric variables and auxiliary features,
such as the wash chamber, which enable control over the
output products.
When using two hydrocyclones in series, the classifi-
cation efficiency is directly impacted, leading to a reduc-
tion in the bypass of fines. The Cavex ® DE classification
technology capitalizes on the synergy between the two units
and the wash chamber to minimize fine bypass. This results
in an underflow product with lower fine content while
simultaneously increasing water recovery to the overflow
(Figure 1).
In the following paragraphs the application of DE
cyclones in discrete tailings applications is expanded upon.
Abbreviations have been used for the solids concentration
by weight and volume, as well for the 80% passing particle
size. A summary of abbreviations and definitions is given
in Table 1.
Table 1. List of abbreviations
Abbreviation Definition
Cw Weight Solid Concentration (%w/w)
Cv Volumetric Solid Concentration (%v/v)
F80 80% passing size of the product (µm)
D50c Particle size of which 50% reports to the
overflow and 50% reports to the underflow.
WASHING CHAMBER
The wash chamber of the Cavex ® DE hydrocyclone is
designed to address one of the main issues in density clas-
sification: the carryover of fine material into the coarse
product due to the viscous layer on the equipment’s walls.
This problem, identified by Bloor and Ingham (1976) and
Concha (1994), is mitigated by the geometry of the wash
chamber, which breaks the viscous layer and releases the
trapped fine material. The injection water then helps trans-
port these fines to the air core of the hydrocyclone, enabling
their classification. Additionally, the wash water dilutes the
slurry, and this diluted slurry, when fed to the second clas-
sification stage, demonstrates the effect of the wash water
on the fine bypass, as illustrated in Figure 2.
INDUSTRIAL APPLICATION
Cavex ® DE hydrocyclones are used for the classification
of sands for dam wall construction at various mine sites
around the world. Their application allows for considerable