3472 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
as part of their long-term sustainability plans and to reduce
risks associated with tailings storage. Part of the long-term
sustainability associated with filtered tailings is the recy-
cling of water to reduce the demand for fresh water. There
is an expectation that this water may be different from that
which is historically recycled from the tailings impound-
ment as it has not been exposed to UV light, has had time
for particles to naturally settle out or for foreign contami-
nants (organics, etc.) to enter the water.
Operators want to understand the difference in quality
to determine if it can be reused as is or if it will need further
treatment prior to being introduced back into upstream
processes. This paper will focus on the suspended solids
found in the water that is recycled from the filtration pro-
cess. One source of suspended solids in the recycled water
comes from those found in the filtrate. These suspended
solids pass through the filter media during the fill and filtra-
tion steps of the pressure filter process.
Filtration has many different methods of separating
components. A couple examples are 1) surface filtration
-where solids larger than the filter medium pore size are
retained on the media and those smaller pass through 2)
cake filtration—solids build up on the filter medium and in
which the bed or cake of solids becomes the filter medium
and 3) reverse osmosis—separating sub-micron particles
using membranes. This paper will focus on cake filtration,
which is the method use in tailings. A side image of filter
media typically used in the industry is shown in Figure 1.
All cake filtration starts out as surface filtration (exclud-
ing the use of filter aid prior to filtration). When the slurry
encounters the filter medium, those particles smaller than
the pore size of the medium will pass through it, this is
called “bleed through” in which small particles will pass
through the media and follow the filtrate stream. Once
the particles in the slurry begin to pack against each other
and the filter medium forming a filter cake. Once the cake
begins to form, it becomes the predominant medium that
particles need to travel through to reach the filtrate. As cake
filtration proceeds, the quantity of solids bleeding through
the medium lessens and the filtrate becomes clearer than
in the start. Due to the variation in solids concentration
throughout the cycle, an average filtrate solids concentra-
tion is typically used for design and mass balances. A car-
toon of cake filtration is shown in Figure 2.
The filter medium is one of the variables that can affect
solids in the filtrate. Several other variables can include
1. Feed slurry solids concentration—the higher the
feed solids concentration, the faster the cake forms
on the media which affects the filtrate solids con-
centration. If a cake forms rapidly, the cake begins
to act as the filtration medium. When the solids
concentration is low, small particles follow the
filtrate through the medium until enough solids
build a cake on the filter medium.
2. Particle size distribution—a well graded particle
size with a significant portion of the particles larger
than the media pore size is required to initiate the
cake filtration process. If the media pore size is too
large relative to the solids size, the filter medium
will allow a high amount of solids to flow through
the media
3. Feed pressure—the higher the feed pressure, the
higher the pressure drop across the filter medium
4. allowing more solids to move through during sur-
face filtration
5. Particle Shape—particles with a high L/D ratio
CASE STUDY
This case study is based on laboratory testing using a bench-
scale filtration testing unit. The benchscale testing unit
can simulate FLSmidth’s recessed chamber configuration
Figure 1. Filter medium close-up
Figure 2. Cake filtration
as part of their long-term sustainability plans and to reduce
risks associated with tailings storage. Part of the long-term
sustainability associated with filtered tailings is the recy-
cling of water to reduce the demand for fresh water. There
is an expectation that this water may be different from that
which is historically recycled from the tailings impound-
ment as it has not been exposed to UV light, has had time
for particles to naturally settle out or for foreign contami-
nants (organics, etc.) to enter the water.
Operators want to understand the difference in quality
to determine if it can be reused as is or if it will need further
treatment prior to being introduced back into upstream
processes. This paper will focus on the suspended solids
found in the water that is recycled from the filtration pro-
cess. One source of suspended solids in the recycled water
comes from those found in the filtrate. These suspended
solids pass through the filter media during the fill and filtra-
tion steps of the pressure filter process.
Filtration has many different methods of separating
components. A couple examples are 1) surface filtration
-where solids larger than the filter medium pore size are
retained on the media and those smaller pass through 2)
cake filtration—solids build up on the filter medium and in
which the bed or cake of solids becomes the filter medium
and 3) reverse osmosis—separating sub-micron particles
using membranes. This paper will focus on cake filtration,
which is the method use in tailings. A side image of filter
media typically used in the industry is shown in Figure 1.
All cake filtration starts out as surface filtration (exclud-
ing the use of filter aid prior to filtration). When the slurry
encounters the filter medium, those particles smaller than
the pore size of the medium will pass through it, this is
called “bleed through” in which small particles will pass
through the media and follow the filtrate stream. Once
the particles in the slurry begin to pack against each other
and the filter medium forming a filter cake. Once the cake
begins to form, it becomes the predominant medium that
particles need to travel through to reach the filtrate. As cake
filtration proceeds, the quantity of solids bleeding through
the medium lessens and the filtrate becomes clearer than
in the start. Due to the variation in solids concentration
throughout the cycle, an average filtrate solids concentra-
tion is typically used for design and mass balances. A car-
toon of cake filtration is shown in Figure 2.
The filter medium is one of the variables that can affect
solids in the filtrate. Several other variables can include
1. Feed slurry solids concentration—the higher the
feed solids concentration, the faster the cake forms
on the media which affects the filtrate solids con-
centration. If a cake forms rapidly, the cake begins
to act as the filtration medium. When the solids
concentration is low, small particles follow the
filtrate through the medium until enough solids
build a cake on the filter medium.
2. Particle size distribution—a well graded particle
size with a significant portion of the particles larger
than the media pore size is required to initiate the
cake filtration process. If the media pore size is too
large relative to the solids size, the filter medium
will allow a high amount of solids to flow through
the media
3. Feed pressure—the higher the feed pressure, the
higher the pressure drop across the filter medium
4. allowing more solids to move through during sur-
face filtration
5. Particle Shape—particles with a high L/D ratio
CASE STUDY
This case study is based on laboratory testing using a bench-
scale filtration testing unit. The benchscale testing unit
can simulate FLSmidth’s recessed chamber configuration
Figure 1. Filter medium close-up
Figure 2. Cake filtration