XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3449
generally operate below this point and the bulk of the mud
transport is hydraulic flow. With yield stress muds, some
force is needed to start the mud moving. The inner spi-
ral blade concept keeps the mud moving for much longer,
reducing the force needed and torque required.
Some minerals like Copper and Iron are frequently
processed at much higher tonnages. Handling those higher
tonnages has traditionally been achieved through using
large diameter high-rate thickeners, up to 128 m in diam-
eter. One option used for a 96,000 tpd plant was 12 × 24
m DCTs, as the customer wanted the largest proven size.
This was generally successful, although the feed splitter
and underflow pumping systems are relatively complex to
design. DCTs are limited in size due to torque and floor
slope. They generally use 30-degree floors to help with mov-
ing thick mud to the outlets. These steep floors in conjunc-
tion with deep sidewalls make large DCTs very tall, and
hence expensive. There are designs for intermediate floor
slope and torque, providing more than high-rate thickeners
but less than DCTs that are labeled high density or high
compression designs. These have often had mixed success,
performing better than standard HRTs but mostly under-
performing in terms of hitting underflow density targets.
More recently a large Copper concentrator with an
existing plant was looking to double production by add-
ing a second plant. Their existing tailings thickeners were
2 × 65 m high compression thickeners achieving roughly
61 wt%. They requested a design to hit 68 wt%. There are
several aspects of the thickener design that can be modi-
fied to improve underflow density performance, includ-
ing floor slope and rake design. Knowing the existing 3:12
floor slope with truss rake design was only able to achieve
61 wt%, using a similar design with a low drag rake arm
could potentially achieve close to 65 wt%. A similar rake
arm retrofit done in 2008 at Esperanza in Chile achieved
a 2–3 wt% improvement in density. Based on other high
density thickening projects, features like low drag rakes and
increased floor slope would improve the underflow density,
but not enough to get from 61 wt% to 68 wt%. Lab testing
was used to characterize the settling and thickening of the
mud. Testing showed the ability to thicken to high densi-
ties, 68 wt% up to 72 wt%, with significant mud retention
time. Based on that as well as knowing how the existing
equipment was performing, (3) × 45 m DCTs were selected
to handle 86,000 tpd. The inner spiral blade design was
included to provide the raking capacity needed for high
yield stress mud.
RESULTS AND DISCUSSION
The (3) × 45 m DCTs were quickly able to hit 68 wt% and
handle the tonnage, but a variety of issues prevented consis-
tent operation. Initial operation was at relatively high floc-
culant dosages, leading to large island formation issues and
loads causing high rake arm deflections and mechanical
damage. Both process and mechanical issues needed to be
worked out including improved guide bearings, instrument
maintenance, adding armoring for abrasion resistance, and
modifying clearances.
The process performance before modifications was
generally 65 – 68 wt%. After modifications the thickeners
are able to hit 68 wt% consistently. The customer’s TSF is
in a relatively flat area, requiring a long dam and relatively
high cost, making the value of every extra percent of under-
flow density quite substantial.
The added water recovery from producing 68 wt%
instead of 61 wt% at 86,000 tpd is about 500 m3/h.
Preventing that from flowing to the TSF results in higher
deposited density and a big savings in TSF capacity, as the
final deposited density is higher when placed at higher con-
centrations (Reid, et al).
One of the more remarkable outcomes is the low torque
these machines run at. Most DCTs operate at much higher
relative torques when compared to high-rate thickeners.
The inner spiral blade technology allows these machines to
run at ⅓ to ½ the expected torque levels without the spiral
blades. This leaves a lot of capacity to handle upsets and
should result in a longer drive life.
The inner spiral blade technology is currently in the
process of being retrofitted to an existing large diameter
Copper tailings thickener with the objective of increasing
underflow density. Results of this will be presented if they
are available.
CONCLUSIONS
The advent of the Deep Cone Thickeners (DCTs) has
impacted the industry by achieving significantly higher
underflow densities when compared to traditional sedi-
mentation methods. While hundreds of these machines
have been installed, most of them are less than 25 meters in
diameter and are suitable for many applications, including
most alumina refineries and underground mines. However,
some markets operate at much larger capacities, such as
copper and iron processing, which require much higher
tonnages. For instance, a copper mine requested a design to
handle over 80,000 tons per day, thickening the underflow
generally operate below this point and the bulk of the mud
transport is hydraulic flow. With yield stress muds, some
force is needed to start the mud moving. The inner spi-
ral blade concept keeps the mud moving for much longer,
reducing the force needed and torque required.
Some minerals like Copper and Iron are frequently
processed at much higher tonnages. Handling those higher
tonnages has traditionally been achieved through using
large diameter high-rate thickeners, up to 128 m in diam-
eter. One option used for a 96,000 tpd plant was 12 × 24
m DCTs, as the customer wanted the largest proven size.
This was generally successful, although the feed splitter
and underflow pumping systems are relatively complex to
design. DCTs are limited in size due to torque and floor
slope. They generally use 30-degree floors to help with mov-
ing thick mud to the outlets. These steep floors in conjunc-
tion with deep sidewalls make large DCTs very tall, and
hence expensive. There are designs for intermediate floor
slope and torque, providing more than high-rate thickeners
but less than DCTs that are labeled high density or high
compression designs. These have often had mixed success,
performing better than standard HRTs but mostly under-
performing in terms of hitting underflow density targets.
More recently a large Copper concentrator with an
existing plant was looking to double production by add-
ing a second plant. Their existing tailings thickeners were
2 × 65 m high compression thickeners achieving roughly
61 wt%. They requested a design to hit 68 wt%. There are
several aspects of the thickener design that can be modi-
fied to improve underflow density performance, includ-
ing floor slope and rake design. Knowing the existing 3:12
floor slope with truss rake design was only able to achieve
61 wt%, using a similar design with a low drag rake arm
could potentially achieve close to 65 wt%. A similar rake
arm retrofit done in 2008 at Esperanza in Chile achieved
a 2–3 wt% improvement in density. Based on other high
density thickening projects, features like low drag rakes and
increased floor slope would improve the underflow density,
but not enough to get from 61 wt% to 68 wt%. Lab testing
was used to characterize the settling and thickening of the
mud. Testing showed the ability to thicken to high densi-
ties, 68 wt% up to 72 wt%, with significant mud retention
time. Based on that as well as knowing how the existing
equipment was performing, (3) × 45 m DCTs were selected
to handle 86,000 tpd. The inner spiral blade design was
included to provide the raking capacity needed for high
yield stress mud.
RESULTS AND DISCUSSION
The (3) × 45 m DCTs were quickly able to hit 68 wt% and
handle the tonnage, but a variety of issues prevented consis-
tent operation. Initial operation was at relatively high floc-
culant dosages, leading to large island formation issues and
loads causing high rake arm deflections and mechanical
damage. Both process and mechanical issues needed to be
worked out including improved guide bearings, instrument
maintenance, adding armoring for abrasion resistance, and
modifying clearances.
The process performance before modifications was
generally 65 – 68 wt%. After modifications the thickeners
are able to hit 68 wt% consistently. The customer’s TSF is
in a relatively flat area, requiring a long dam and relatively
high cost, making the value of every extra percent of under-
flow density quite substantial.
The added water recovery from producing 68 wt%
instead of 61 wt% at 86,000 tpd is about 500 m3/h.
Preventing that from flowing to the TSF results in higher
deposited density and a big savings in TSF capacity, as the
final deposited density is higher when placed at higher con-
centrations (Reid, et al).
One of the more remarkable outcomes is the low torque
these machines run at. Most DCTs operate at much higher
relative torques when compared to high-rate thickeners.
The inner spiral blade technology allows these machines to
run at ⅓ to ½ the expected torque levels without the spiral
blades. This leaves a lot of capacity to handle upsets and
should result in a longer drive life.
The inner spiral blade technology is currently in the
process of being retrofitted to an existing large diameter
Copper tailings thickener with the objective of increasing
underflow density. Results of this will be presented if they
are available.
CONCLUSIONS
The advent of the Deep Cone Thickeners (DCTs) has
impacted the industry by achieving significantly higher
underflow densities when compared to traditional sedi-
mentation methods. While hundreds of these machines
have been installed, most of them are less than 25 meters in
diameter and are suitable for many applications, including
most alumina refineries and underground mines. However,
some markets operate at much larger capacities, such as
copper and iron processing, which require much higher
tonnages. For instance, a copper mine requested a design to
handle over 80,000 tons per day, thickening the underflow