140 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
requiring the basis to address brittle behavior through the
design process.
Geotechnical engineering is thought of as the study
of soil mechanics but is rather, and probably more impor-
tantly, the study of drainage. Water is entrained by the min-
eral processing, and the resulting reclaimed and entrained
water can create challenges. Management of a tailings facil-
ity is the process of dewatering the residuals and placing
tailings at a density that promotes stability. Scenarios, where
dams are constructed of saturated tailings at a loose density
with elevated pore pressures, can result in undrained load-
ing and, in rare cases, result in a tailings flow liquefaction
failure with potentially devastating consequences.
The traditional tailings dam construction methods,
including upstream, centerline, and downstream methods,
provide cost and structural benefits and when properly
designed can produce a stable and robust structure with
consideration for the given environment. The industry
is working diligently to identify methods that can better
extract water from the tailings and place the material at a
density that provides for long-term stability. However, the
use of these traditional construction methods will continue
well into the future, and their selection as an impounding
structure will depend on numerous factors.
Filtered Tailings
Filtered tailings is an emerging technology that applies a
mechanical dewatering process to extract the majority of
water contained in the soil fabric. The filter extraction
process is designed to produce a workable earth fill-type
material. This material, when properly dewatered, is easily
transported by truck or conveyor to a stockpile where it can
be placed in thin lifts and compacted with traditional earth-
moving equipment, creating an inherently stable structure
and inert designed/engineered landform.
The process appears simple on the surface. However,
the technologies for dewatering tailings are varied and have
experienced mixed degrees of success. The biggest challenge
from a dewatering standpoint is the extraction of water from
a tailings composition that is high in clay. The adsorption
of water and the capillary stresses within the tailings matrix
create challenges for the economic filtering of tailings.
Production of filtered tailings is directly controlled by
the rate at which water can be extracted. Fine-grained tail-
ings have a longer extraction period resulting in an increased
dewatering time and an overall reduction in production.
Equipment maintenance cycles indirectly control and affect
production because of the scarcity of filters on the market.
The current challenge is that the dewatering filter produc-
tion is not meeting nameplate designs (production rates are
overstated) and maintenance cycles, leading to, by proxy,
costs, and processing times that are significantly higher and
longer than expected.
The design process for filter stack facilities requires a
robust characterization of the ore body and the genera-
tion of representative tailings sample(s) to initiate labora-
tory testing and field trials. The design process also requires
intensive critical planning to accommodate both normal
operations and upset conditions. A significant financial
commitment is made early on to characterize the tailings,
and these processes at times are not for the faint of heart.
Upset conditions, such as filter press breakdowns, can
shut down the entire operation and cut into production
cycles, reducing operational efficacy. Ineffective dewatering
can also make tailings transport difficult, if not impossible,
because the material becomes flowable, impacting conveyor
or truck transport or generating excess carryback on the
conveyor. Improperly dewatered tailings can also create
conditions that produce a potentially unstable filter stack.
It is the author’s opinion that some filter manufactur-
ers have done a disservice to their industry by extrapolat-
ing successes from small to moderate filter productions and
applying similar principles to larger production operations,
often resulting in an expectation that the filtered facilities
can be proportionally upgraded for higher nameplate pro-
duction values. However, experience to date has shown that
these productions range from optimistic to unachievable.
The rule of thumb, as of this writing, is that the filtering
capacity would need to be twice the nameplate produc-
tion for filtered tailings or, in simpler terms, purchasing
two plants instead of one. While not completely accurate
for all conditions, it does provide a general initial design
consideration.
One aspect of filtered tailings often ignored by pro-
ponents is the significant increase in energy requirements
for both the dewatering and transportation aspects of the
process. Tailings transport can have its inherent challenges,
and the dewatering of the tailings will generate specific
properties that can create challenges with material han-
dling. The use of conveyors, over-the-road trucks, and haul
trucks are the most popular ways of conveying dewatered
tailings. Climatic conditions can also impact the filtered
tailings. For example, high precipitation environments
can reintroduce water into a dewatered tailings-producing
material that initially meets the specification requirements
but exceeds moisture requirements by the time the mate-
rial is placed at the filter stack. Freezing environments can
also create inherent challenges during the conveyance and
placement of the material. As the mining world grapples
with decarbonization and the majority of the jurisdictions
requiring the basis to address brittle behavior through the
design process.
Geotechnical engineering is thought of as the study
of soil mechanics but is rather, and probably more impor-
tantly, the study of drainage. Water is entrained by the min-
eral processing, and the resulting reclaimed and entrained
water can create challenges. Management of a tailings facil-
ity is the process of dewatering the residuals and placing
tailings at a density that promotes stability. Scenarios, where
dams are constructed of saturated tailings at a loose density
with elevated pore pressures, can result in undrained load-
ing and, in rare cases, result in a tailings flow liquefaction
failure with potentially devastating consequences.
The traditional tailings dam construction methods,
including upstream, centerline, and downstream methods,
provide cost and structural benefits and when properly
designed can produce a stable and robust structure with
consideration for the given environment. The industry
is working diligently to identify methods that can better
extract water from the tailings and place the material at a
density that provides for long-term stability. However, the
use of these traditional construction methods will continue
well into the future, and their selection as an impounding
structure will depend on numerous factors.
Filtered Tailings
Filtered tailings is an emerging technology that applies a
mechanical dewatering process to extract the majority of
water contained in the soil fabric. The filter extraction
process is designed to produce a workable earth fill-type
material. This material, when properly dewatered, is easily
transported by truck or conveyor to a stockpile where it can
be placed in thin lifts and compacted with traditional earth-
moving equipment, creating an inherently stable structure
and inert designed/engineered landform.
The process appears simple on the surface. However,
the technologies for dewatering tailings are varied and have
experienced mixed degrees of success. The biggest challenge
from a dewatering standpoint is the extraction of water from
a tailings composition that is high in clay. The adsorption
of water and the capillary stresses within the tailings matrix
create challenges for the economic filtering of tailings.
Production of filtered tailings is directly controlled by
the rate at which water can be extracted. Fine-grained tail-
ings have a longer extraction period resulting in an increased
dewatering time and an overall reduction in production.
Equipment maintenance cycles indirectly control and affect
production because of the scarcity of filters on the market.
The current challenge is that the dewatering filter produc-
tion is not meeting nameplate designs (production rates are
overstated) and maintenance cycles, leading to, by proxy,
costs, and processing times that are significantly higher and
longer than expected.
The design process for filter stack facilities requires a
robust characterization of the ore body and the genera-
tion of representative tailings sample(s) to initiate labora-
tory testing and field trials. The design process also requires
intensive critical planning to accommodate both normal
operations and upset conditions. A significant financial
commitment is made early on to characterize the tailings,
and these processes at times are not for the faint of heart.
Upset conditions, such as filter press breakdowns, can
shut down the entire operation and cut into production
cycles, reducing operational efficacy. Ineffective dewatering
can also make tailings transport difficult, if not impossible,
because the material becomes flowable, impacting conveyor
or truck transport or generating excess carryback on the
conveyor. Improperly dewatered tailings can also create
conditions that produce a potentially unstable filter stack.
It is the author’s opinion that some filter manufactur-
ers have done a disservice to their industry by extrapolat-
ing successes from small to moderate filter productions and
applying similar principles to larger production operations,
often resulting in an expectation that the filtered facilities
can be proportionally upgraded for higher nameplate pro-
duction values. However, experience to date has shown that
these productions range from optimistic to unachievable.
The rule of thumb, as of this writing, is that the filtering
capacity would need to be twice the nameplate produc-
tion for filtered tailings or, in simpler terms, purchasing
two plants instead of one. While not completely accurate
for all conditions, it does provide a general initial design
consideration.
One aspect of filtered tailings often ignored by pro-
ponents is the significant increase in energy requirements
for both the dewatering and transportation aspects of the
process. Tailings transport can have its inherent challenges,
and the dewatering of the tailings will generate specific
properties that can create challenges with material han-
dling. The use of conveyors, over-the-road trucks, and haul
trucks are the most popular ways of conveying dewatered
tailings. Climatic conditions can also impact the filtered
tailings. For example, high precipitation environments
can reintroduce water into a dewatered tailings-producing
material that initially meets the specification requirements
but exceeds moisture requirements by the time the mate-
rial is placed at the filter stack. Freezing environments can
also create inherent challenges during the conveyance and
placement of the material. As the mining world grapples
with decarbonization and the majority of the jurisdictions