Note: Descriptions are shown in the official language in which they were submitted.
CA 02910470 2015-10-28
METHOD AND DEVICE FOR MANAGEMENT AND TREATMENT
OF FLUID TAILINGS IN TAILINGS POND
TECHNICAL FIELD
The technical field relates to management and treatment of fluid tailings in
tailings pond, and
speeding up reclamation of tailings pond.
BACKGROUND
Fluid tailings are generated from various mine-processing operations that
extract the valuable
components from the mined ore and leave various solid-water slurry wastes as
tailings in tailings
management facilities (TMF), known as tailings ponds. Over the years the
volume of tailings has
grown dramatically as the demand for metals, minerals, and fossil fuels has
increased. In recent
years, more lower grade ores are being mined using advanced processing
technologies to increase
the recovery of valuable fractions from the ore, resulting in more fluid
tailings in tailings pond. It
was estimated that in 2000 there were about 3500 active tailings ponds in the
world (T E Martin, M
P Davies, (2000), hup://www.infomine.com/publications/docs/Martin2000), and
the amount of fluid
tailings generated by an individual mine was about 100,000 tones per day (A
Jakubick, G McKenna,
et al. (2003), Stabilization of Tailings Deposits: International Experience,
Mining and the
Environment III, Sudbury, Ontario, Canada, May 25-28, 2003. pp. 1-9.). A new
estimate in 2012
predicted the amount of fluid tailings generated by an individual mine in
excess of 200,000 tones in
a single day (J Engels, (2014), http://www.tailings.info/about.htm). The oil
sands industry in
Northern Alberta, Canada is one of the examples that generate and hold a huge
amount of fluid
tailings in its tailings ponds. The oil sands mining operation started in late
1960s, the bitumen in oil
sands ore is extracted through hot water extraction process. The extraction
process requires about
0.6 to 0.7 cubic meters of water to process per ton of oil sands ore, and the
demand of fresh make-up
water for the extraction process is in the range of 3 to 4 cubic meters per
cubic meter of bitumen
CA 02910470 2015-10-28
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produced, although most of the process water is recycled. It was estimated
that by 2012 the existing
tailings ponds water covered about a 77 square kilometer area (Government of
Alberta, (2013), Fact
Sheets Tailings, http://www.oilsands.alberta.ca/FactSheets/Tailings_FSht Sep
2013Online), and
contained over 720 million cubic meters of fluid tailings (Pembina, (2010),
Backgrounder: Oil
Sands Tailings and Directive 074, https://www.pembina.org/reports/tailings-
directive-074-
backgrounder).
Conventionally, fluid tailings are stored in various surface impoundments
using natural landscapes,
dams and dykes to confine the fluid tailings in tailings ponds for years with
or without further
treatment, and the mine operators are always to seek the most cost-effective
ways possible to meet
regulations and mine site specific factors. In recent years, some new
technologies have been
employed to improve water release from fluid tailings, such as in plant
thickening, centrifuging, and
filtration, that make the fluid tailings into paste or cake-like tailings for
direct landfills or backfills
with or without further drying treatment, however, the handling and
transportation of the paste and
cake-like tailings are difficult, and the costs for the treatment and handling
of high solids content
tailings are much higher than the ponding process. In addition to the
technical and economical
concerns, the challenges for design of fluid tailings management facilities
grow from regulatory
bodies, governments, and publics, focusing on safety, environmental
protection, ecological balance,
and sustainable development. The challenges are forcing the mine operators to
find more innovative
ways to solve the issues on fluid tailings management and realize cost-savings
in their operations.
The objective of the present invention is to provide mining operators with
methods and devices at a
much low cost to realize: a) a revolutionary conversion of tailings ponds from
single-function
tailings storage facilities into multi-function tailings and water handling,
treatment, and management
facilities, b) simultaneous reclamation of tailings ponds during the mining
operations, and c)
complete the reclamation right after the mine closure.
SUMMARY OF THE INVENTION
This invention discloses a method and relevant devices for handling and
treatment of fluid tailings in
tailings pond, and in-situ deposition of the treated tailings, so as to speed
up the reclamation of the
tailings pond.
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In some embodiments, there is a method to achieve easy handling and treatment
of fluid tailings in
tailings pond, deposition of the treated tailings in-situ, and complete
reclamation of the tailings pond
during the handling, treatment, and deposition of the fluid tailings. The said
method comprises
multi-steps, including: a) using a floating dyke to separate a tailings pond
into two sections, b) using
one of the sections as runoff collection pond to collect the runoff fluid
tailings that are overflow
from the above-water-beach area, and developing an under-water-beach within
the runoff collection
pond, c) using a floating divider and combining with the floating dyke to form
a bottomless
thickener along the deeper side of the floating dyke, d) flocculating various
fluid tailings that are
derived from the processing plant and/or from the runoff collection pond
through a flocculation
station, e) thickening and depositing the flocculated tailings within the
bottomless thickener, f)
recovering water from the top of the bottomless thickener, and developing an
under-water-beach by
the thickened tailings deposits at the tailings pond bottom below the
bottomless thickener, g)
relocating the bottomless thickener along the floating dyke, and repeating the
steps c to f to
continue the development of the under-water-beach along the deeper side of the
floating dyke until
the depth of deposits meets the reclamation requirements, h) setting up a
dividing and treatment
system by relocating the floating dyke and the floating bottomless thickener
downstream in the
tailings pond, and developing the above-water-beach to cover the under-water-
beach formed in
previous steps a to g for tailings pond reclamation, and i) repeating steps a
to h until the completion
of the tailings pond reclamation.
In some embodiments, the said method can be used for handling and treatment of
all types of fluid
tailings that are generated from various mine processing plants and tailings
storage facilities, such as
coarse sand tailings, flotation tailings, mature fine tailings, fluid fine
tailings, off-spec recycle water,
and the combinations of the above-mentioned tailings. The said method can also
be used for
reclamation of all types of tailings ponds that are used to manage and store
various fluid tailings,
such as in-pit tailings pond, out-of-pit tailings pond, new tailings pond
without old fluid tailings in
it, existing active tailings pond with old fluid tailings in it, and existing
inactive tailing pond with
old fluid tailings in it, but without fresh tailings input into it.
In some embodiments, the said floating dykes and floating dividers are major
devices for
management, handling, and treatment of fluid tailings in tailings pond. The
floating dykes and
floating dividers are similar in structure and materials, both the floating
dykes and floating dividers
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include two major parts: a) the floating device at the top of water surface,
and b) the dividing sheet
with its top attached to the floating device and its bottom falling down close
to the bottom of the
tailings pond. The floating dykes have more floating devices on the water
surface for various
functions, including: a) walkways for operation and maintenance, b) working
platforms for specific
operations, such as flocculation stations, pump stations, utilities and
materials supply and storage, c)
pipe rack and pipeline supports, and d) connections for positioning and
locating various operation
devices, such as guiding cables, poles, pillars, lockers, and other devices
for water surface
positioning. The major function of floating dykes and floating dividers are to
provide isolation
media to form various closed cells within the tailings pond. The closed cells
can be used for water
holding, fluid tailings holding, fresh incoming tailings holding, and treated
tailings holding.
Although the bottom of the dividing sheet is designed to touch the bottom of
the tailings pond to
form completely closed cells, however, in some situations, the lowest edge of
the dividing sheet is
designed not to touch the bottom of the tailings pond, that is, there is a gap
between the bottom of
the closed cells and the bottom of the tailings pond. The size of the closed
part of the cells along the
depth of the floating devices is carefully designed in most operation cases to
meet the requirements
for the isolation or treatment. The design of bottomless closed cells is used
for fluid tailings
handling and transportation through the bottom connection, and for the top
water handling and
transportation through the top connection. The design of bottomless closed
cells can also be used
for: a) thickening of the fluid tailings at the closed section of the cells,
b) in-situ depositing the
thickened tailings down to the bottom of the tailings pond just below the
thickening area, and c)
building up the under-water-beach with the thickened tailings deposits. The
thickening also includes
the clarification process for a low solids content stream.
In some embodiments, the size and shape of the floating dykes and floating
dividers are adjustable
to meet the requirements of different operations, including: a) complete
isolation of fluid materials
in tailings pond, b) partial isolation of fluid materials in tailings pond, c)
gradual change of the gap
between the bottom of the dividing sheet and the bottom of the tailings pond
for the development of
under-water-beach, d) various shapes of the closed cells to fit the space
available, and e) various
zoned shapes to match the requirements of rotating treatment operations. In
some embodiments, any
combinations between floating dykes and/or floating dividers can be used to
form closed cells in
different sizes and shapes in the tailings pond, and the sizes and shapes are
flexible and adjustable.
CA 02910470 2015-10-28
In some embodiments, the sizes and shapes of the dividing sheets of the
floating dykes and floating
dividers are also flexible and adjustable along the depth of the closed cells.
In some embodiments, the gap between the bottom of the dividing sheet and the
bottom of tailings
pond is changed accordingly in terms of the elevation change of water surface.
The elevation may
increase due to the increase of fluid volume in tailings pond, resulting from
planned dam elevation
increase, followed by the fluid volume increase. The elevation may decrease
due to the decrease of
fluid volume in tailings ponds, resulting from planned withdraw of water or
fluid tailing out of the
tailings pond.
In some embodiments, the floating devices of the floating dykes and floating
dividers are
commercially available devices, including: a) floating docks, b) floating
platforms, c) floating
working structures, d) chained barges or boats, e) chained pipe bundles, and
f) chained drum
bundles.
In some embodiments, the floating devices of the floating dykes and floating
dividers can be mobile
devices that are used to hang the dividing sheets above the water surface at
required locations. The
supporting devices include: a) suspending cable systems, b) above water
working platforms, c)
above water walkways or access roads, d) mobile pillars and poles hanging
systems, and e) any
combinations of a to d.
In some embodiments, the floating devices of the floating dykes and the
floating dividers can be any
combinations of the floating devices and the mobile supporting devices that
are listed above.
In some embodiments, the materials for the dividing sheets of the floating
dykes and the floating
dividers include: a) woven or non-woven geotextile, b) woven or non-woven
cloth, c) non-
permeable and semi-permeable polymer membrane or thin film, including
plastics, rubber, and
composite materials, d) water permeable networks, including metal and non-
metal meshes, nets,
webs, and filter media, and e) any combinations of a and d.
In some embodiments, the materials for the dividing sheets of the floating
dykes and the floating
dividers are thermal insulations that are used in cold seasons to avoid heat
loss or water surface
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freezing. The thermal insulation materials include: a) thin polymer foams, b)
thin polymer fiber
layers, c) thin polymer coatings, and d) any combinations of a to c.
In some embodiments, the dividing sheets can be made from a single piece of
materials that are
listed above into large piece by the following means: a) zippers, b)
adhesives, c) sewing, d) Velcro
strips or patches, and e) any combinations of a to d.
In some embodiments, the structure of a bottomless thickener has a simple
configuration, including:
a) a peripheral border to define the settling area of the thickening operation
and control the depth of
the thickened tailings deposits, b) one or more feedwells with distributors at
the outlets of the
feedwells to improve the dewatering of thickened tailings evenly across the
settling area, c) a
skimming mechanism to collect the free bitumen or free floats at the top of
water surface, and free
bitumen and floats collection well, and d) a water transport well for water
recovery from the
bottomless thickener. In some embodiments, the bottomless thickener can be
further simplified to
have: a) a peripheral border to define the settling area and the depth of the
thickener, and b) a feed
pipe with a distributor at the outlet of the pipe.
In some embodiments, the peripheral border of the bottomless thickener can be
form by: a) a
floating dyke, b) a floating divider, c) a combination of a floating dyke and
a floating divider, and d)
other floating devices with dividing sheet hanging below the floating devices.
The shape of the
bottomless thickener can be: a) circles, b) squares, c) rectangles, d)
triangles, and e) any
combinations of a to d. The preferred shape is rectangular.
In some embodiments, the size of the bottomless thickener is flexible,
depending on the treatment
required. The size is in a range of 100 m2 to 100000 m2, and the preferred
size is in the range of
5000 m2 to 10000 m2.
In some embodiments, the size and shape of the bottomless thickener are
adjustable through the
change in connections and positioning of various floating devices. As
mentioned before, in most
cases, the floating dykes and/or the floating dividers form the bottomless
thickener, so the height of
the sidewall has been pre-determined. The depth for thickening and depositing
operations is in a
range of 5 m to 65 na, the preferred depth is in the range of 8 m to 35 m. The
height of the sidewall
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of the bottomless thickener can be adjusted within the range of 5 in to 35 m
in terms of the progress
of the thickening and deposition operations.
In some embodiments, there is a method to enhance the dewatering and
strengthening of thickened
tailings deposits during the thickening and deposition operations within the
bottomless thickener.
The method comprises: a) splitting the bottomless thickener into two zones, b)
starting from zone 1
with flocculation, thickening, and deposition of fluid tailings to build up 2
m to 3 in thickened
tailings deposits, c) moving to zone 2 to continue the flocculation,
thickening, and deposition of
fluid tailings to build the same depth of deposits, at the same time in zone
1, using coarse tailings to
do flocculation, thickening, and deposition to build up 0.5 in to 1 m
thickened coarse tailings
deposits as sand-cap on top of the thickened fine tailings deposits, d)
repeating the operation in the
sequence to build up the deposits layers until the total depth of the deposits
reaches the operation
limit, and e) relocating the thickener to another location. The depth of the
deposits is in a range of 15
to 45 m, the preferred depth of deposits is in the range of 8 m to 35 m.
In some embodiments, the bottomless thickener can be split into multi-zones by
the floating
dividers, the number of zones depends on the minimum settling area required,
the actual settling
area in each zone should be one to ten times of the minimum settling area. The
preferred zone area
is in the range of two to five times of the minimum settling area. The
bottomless thickener can be
split into multi-zones by adding a group of floating dividers.
In some embodiments, there is a method to further enhance the dewatering and
strengthening of the
thickened tailings deposits. In this method, the floating dividers work
parallel to form a series of
narrow gaps between each thickening zone, the thickening and deposition
operations within the
thickening zones are the same as previously mentioned, while the gaps between
the floating dividers
are used to deposit the coarse tailings with or without flocculation. The
coarse tailings deposits form
a series of coarse sand walls between each thickening zone. This operation
forms a sand network
within the deposits, and the sand network enhances the dewatering and
strengthening process of the
thickened fine tailings. The distance between two nearest sand walls is in a
range of 5 in to 50 in, the
preferred distance is in the range of 10 in to 35 The thickness of each
vertical sand wall is in a
range of 0.5 to 5 in, the preferred thickness is in the range of 1 m to 2 in.
The floating dividers can
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be relocated after the operation, however, the whole dividing sheets or a part
of the dividing sheets
can be left in place as reinforcement structure after the operation.
In some embodiments, the bottomless thickener can be split into multiple
thickening zones, the
thickening and deposition operations can be done the same as mentioned before,
while a group of
thin columns that are formed from the floating dividers are placed evenly into
the bottomless
thickener. When the thickening and deposition operation continue in the
thickening zones, the
coarse tailings are deposited into the columns with or without flocculation.
When the thickening and
deposition operations are completed, a coarse sand network is formed within
the deposits, and the
sand network enhances the dewatering and strengthening of thickened fine
tailings. The interval of
sand columns is in a range of 5 m to 50 m, the preferred interval is in the
range of 10 in to 30 m. The
shape of the sand columns can be circle, square, rectangle, and triangle, or
irregular shapes. The
cross-sectional area of the sand columns can be in a range of 1 m2 to 10 m2,
the preferred cross-
sectional area is in the range of 2 m2 to 4 n-12. The dividing sheets can be
removed from the deposits
after the operation for reuse.
In some embodiments, there is a method for handling and treatment of fluid
tailings in an existing
active tailings pond that has old fluid tailings in it and accepts new fluid
tailings from processing
plant at the same time. Although the method for handling and treatment of new
fluid tailings
reporting to the existing active tailings pond is the same as mentioned
before, extra steps are needed
to deal with the old fluid tailings in order to set up a fluid tailings
treatment and deposition system in
the tailings pond. Furthermore, the old fluid tailings in this type of
tailings pond can be treated in
different ways that will be described below.
In some embodiments, in addition to the steps for fresh tailings treatment and
deposition, there are
extra steps needed to set up the bottomless thickener for quickly starting up
the thickening operation
in the existing tailings pond. The extra steps comprise: a) using a floating
divider to set up a closed
cell next to the floating dyke, b) withdrawing the top water from the tailings
pond and feeding the
water into the closed cell from the top until the water level is higher than
the top water level of the
tailings pond and reaches constant, c) converting the closed water holding
cell to a thickening cell
by discharging the flocculated tailings into the closed water holding cell,
and d) starting normal
thickening and deposition operations as mentioned for the new tailings pond.
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I some embodiments, there is a method for handling and treatment of fluid
tailings in an existing
inactive tailings pond that has old fluid tailings in it. The method for
handling and treatment of fluid
tailings in an existing inactive tailings pond comprises: a) using two
floating dividers to set up two
closed cells linked together, b) leaving the bottom of the two closed cell
open and connected to the
existing fluid tailings, c) choosing one cell for water holding, and the other
one for fluid tailings
holding, d) withdrawing top water from fluid tailings holding cell to the
water holding cell until the
top water layer disappears in the fluid tailings holding cell, e) withdrawing
top water from the
tailings pond and feeding into the water holding cell until the water level is
higher than the top water
level of the tailings pond and becomes constant, f) taking the fluid tailings
in the fluid tailings
holding cell to do the flocculation treatment, and depositing the flocculated
tailings into the water
holding cell for thickening and dewatering, g) discharging water from the
water holding cell to
tailings pond through overflow, and depositing the thickened tailings to the
bottom of the tailings
pond below the water holding cell, h) relocating the water holding cell after
the deposits reach the
upper limit of the operation, i) repeating steps a to h until the completion
of the fluid tailings
treatment in the whole tailings pond, and j) starting tailings pond
reclamation during or after step i
through reducing top water volume, sand-capping the thickened tailings
deposits, and landfilling
with solid materials along the shoreline of the tailings pond.
In some embodiments, there is a method for handling and treatment of fluid
tailings in an existing
active or inactive tailings pond in terms of seasonal conditions. In warm
regions where no freezing
happens year-round, and/or in wat in seasons when freezing does not happen,
the fluid tailings can
be flocculated and thickened in the water holding cell and deposited within
the tailings pond below
the water holding cell, or flocculated and deposited in the beach area close
to the shoreline below or
above water surface. In cold region and/or in freezing seasons, the fluid
tailings can be treated
through freezing-thawing cycles year-by-year by spreading the fluid tailings
on top of the deposits
that were deposited during the warm seasons, or on the ice surface close to
the shoreline. The ice
layer will be thawed in the coming year, and the thawed tailings will form a
new tailings deposition
layer on the top. The process cycle can be repeated to add more flocculated
tailings on top of the
thawed tailings layer during the warm seasons, and add more freezing tailings
on top of the
flocculated tailings layer during the freezing seasons until the fluid
tailings in the tailings pond are
treated completely, and further operations for tailings pond reclamation can
follow.
CA 02910470 2015-10-28
In some embodiments, the handling and treatment of fluid tailings in an
existing active and/of
inactive tailings pond can be done in a periodical manner. The rotating period
of time can be a
month, three months, six months, and 12 months, or in terms of seasonal
weather conditions.
Particularly in warm region, the flocculation, thickening, and deposition can
be done in a whole year
without a operation switch. In cold regions with freezing time longer than 3
months, the operation
can be pre-determined accordingly for a flocculation, thickening, and
deposition operation, then
switching to a freezing-thawing cyclic operation which needs some time next
year for the thawing
operation.
In some embodiments, there is a method to improve the settling and water
recycle within the runoff
collection pond. The method includes: a) Splitting the runoff collection pond
into more than one
runoff collection cells by a number of floating dividers, one floating divider
can separate the runoff
collection pond into two cells, two floating dividers for three cells, and
three floating dividers for
four cells, and so on. b) Connecting one of the two ends of the floating
dividers perpendicularly to
the floating dyke, and locating the other end to the coarse tailings beach
area. c) Operating the
separated runoff collection cells rotationally to develop required beach area
and split the runoff fluid
tailings for water recycle and fluid tailings treatment after settlement for a
certain time.
In some embodiments, there is a method for the fluid tailings treatment by
flocculation. The
flocculation operation is carried out at a flocculation station. The
flocculation station comprises: a) a
flocculant solution preparation unit, b) a set of flocculant solution storage
vessels, c) a set of
flocculation pipelines, and d) an operation platform with a set of equipment
skids. The flocculation
station can be located on shore area, or on a floating platform attaching to
the floating dyke.
In some embodiments, the fluid tailings can be treated through flocculation
include: a) fine tailings
from processing plant, b) fine tailings from the runoff collection cell, c)
fluid tailings from the
tailings pond, d) coarse tailings from the processing plant, e) off-spec
recycle water from the
treatment systems within the tailings pond, and f) any combinations of
tailings from a to e.
In some embodiments, there is a method to provide tailings ponds with multi-
functions: a)
separating the storage and management of fluid tailings and water, b) rapid
treating fluid tailings and
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recovering classified process waters, c) in-situ depositing treated tailings,
d) simultaneously
reclaiming tailings pond during mining operation and completing the
reclamation right after the
mine closure, and e) providing a great flexibility for planning of short- to
mid-term tailings and
water management and tailings pond development.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a side view of conventional tailings pond.
Figure 2 is a side view of new tailings pond with floating dyke and floating
bottomless thickener.
Figure 3 is a plan view of new tailings pond with floating dyke and floating
thickener.
Figure 4 is a side view of existing active tailings pond with floating dyke,
floating bottomless
thickener, water holding cell, and fluid tailings holding cell.
Figure 5 is a side view, of new tailings pond after the first relocation of
floating dyke and floating
bottomless thickener.
Figure 6 is the structure of floating dyke and dividing sheets across the
tailings pond.
Figure 7 is the structure of single piece of dividing sheet hanging below the
floating dyke.
Figure 8 is the operation sequence of a zoned bottomless thickening area.
Figure 9 shows a network of sand-caps and sand-walls in thickened tailings
deposits in bottomless
thickener.
DETAILED DESCRIPTION OF THE INVENTION
In the following detailed description section, specific embodiments of the
present invention are
described. However, to the extent that the following description is specific
to a particular
embodiment or a particular use of the present invention, this is intended to
be for exemplary purpose
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only, and simply provides a description of the exemplary embodiments. It is
worth noting that the
methods and devices of the present invention are not limited to the specific
embodiments described
below, but rather, include all alternatives, modifications, and equivalents
falling within the scope of
the appended claims.
As mentioned before, the mining industry is facing a great challenge to deal
with the fluid tailings in
tailings pond. The present invention provides a new solution to achieve
handling and treatment of
fluid tailings, management of treated tailings depositions, and management of
recycle water and
fresh make up water in tailings pond, and simultaneous reclamation of tailings
pond. There is no
similar approach as the present invention in the mining industry, or in the
R&D areas for the
handling, treatment, and management of fluid tailings in tailings pond, and
the reclamation of
tailings pond.
The following provides some exemplary details of the invention. Figure 1 is
the side view of a
conventional tailings pond with its major structure and tailings materials in
it. The tailings pond is
impounded by the dams 101 and 106, there are two fresh tailings streams fed
into the tailings pond,
that is, the coarse tailings 110 that is discharged on the coarse tailings
beach 102, and fine tailings
109 that is discharged into the fluid body of the tailing pond. Two types of
beaches form during
tailings deposition, including: a) the above-water-beach 102 that is formed
above the water surface
by the coarse sands in the coarse tailings, and b) the under-water-beach 103
that is formed below the
water surface by the combination of the coarse part of the runoff of coarse
tailings stream 110 and
the coarse part of the fine tailings stream 109. The very fine particles
remaining in fluid tailings
from the runoff of coarse tailings 110 and fine tailings 109 join together to
form a slow flowing and
diffusive suspending fluid tailings body 104 in tailings pond. Over the time
after diffusion, settling,
and segregation of solid minerals in fluid tailings, the rest fluid tailings
body in tailings pond
becomes stable and three distinct layers are observed, including a
consolidated tailings layer 105 at
the bottom of the pond, a fluid tailings layer 107 in the middle of the pond,
and a thin water layer
108 at the top of the pond. It is the middle fluid tailings layer that retains
a huge amount of water
with fine mineral particles, and takes the most volume of the tailings pond.
And the quality of the
top water that is used as recycle water 111 is affected significantly by the
middle fluid tailings
because the top water layer is thin, and the composition of the water varies
with various conditions
that bring fine particles from the fluid tailings into the top water layer,
such as seasonal and daily
CA 02910470 2015-10-28
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temperature fluctuations, strength of wind, relocation of fresh tailings
discharge points, and ore
quality fluctuations. Therefore, the major challenge for the conventional
tailings pond is how to deal
with the fluid tailings middle layer 107 in order to improve the top water
quality, reduce the volume
of fluid tailings in the pond, and start up the reclamation of the pond.
The.present invention discloses a method to solve the problem that the
conventional tailings pond
has. Figure 2 shows the side view of the tailings pond with the embodiments of
the method in
details. The tailings pond is a new pond, meaning there are no old fluid
tailings in the pond; instead,
the tailings pond is pre-filled with only fresh water 108 for starting up a
mining operation. The
major difference in arrangements of tailings pond between the conventional and
the invention is the
addition of two devices, that is, a) the floating dyke 201, and b) the
floating bottomless thickener
202 in the tailings pond. The floating dyke separates the tailings pond into
two sections: a) the
runoff collection section 205, and b) the remaining fresh water section 108.
After the coarse tailings
110 is discharged onto the coarse tailings beach, the runoff part of the
coarse tailings 110 that flows
into the fluid body of the tailings pond is stopped by the floating dyke 201
from flowing further into
the fresh water body. After certain times, the runoff collected in the runoff
collection section
separates into three layers: a) the under-water-beach 103 on the top of the
old beach 102, b) the high
solids content fluid tailings 205, and c) the low solids content top water
208. Although the solids
content in the top water 208 is still high for processing reuse, the quality
is good enough for the top
water to be used as process dilution 208 for tailings transportation purpose.
The high solids content
fluid tailings 207 in the runoff collection section combines with the fine
tailings 109 from the
processing plant to report to the flocculation station 204 for flocculation
treatment, and then report
to the floating bottomless thickener 202 for thickening. The flocculated fluid
tailings are thickened
within the bottomless thickener; the thickened tailings are settled downward
to the bottom of the
tailings pond just below the bottomless thickener to from a new part of the
under-water-beach 206.
The released wann water 203 within the bottomless thickener is directly
recycled back to the
processing plant as recycle water 209. There are several advantages for the
arrangements of the
invention: a) cutting down the flow path of the runoff and the fine tailings
into the main fresh water
body of the tailings pond, so as to avoid adding fine particles into the
existing fresh water body, b)
fixing down the fine particles within the pre-determined areas through
flocculation, thickening, and
in-situ deposition processes within the bottomless thickener, at the same
time, recover the warm
water through the thickening process, c) using different tailings deposits to
build up the under-water-
CA 02910470 2015-10-28
14
beaches for preparation of tailings pond reclamation, and d) reducing the
tailings pond size and
increasing the flexibility of operation planning through reducing the fluid
tailings volume,
improving the water quality, and reclaiming the tailings pond simultaneously.
Figure 3 further shows some details of the arrangements in plan view of the
tailings pond. There are
several features in the arrangement: a) the floating dyke 201 goes across the
whole pond surface at
one corner of the tailings pond, with its two ends next to the shoreline, b)
the runoff collection
section 205 is further separated into three cells by two floating dividers
301, each of the floating
dividers 301 has one end connected perpendicularly to the floating dyke 201,
the other end fixed to
the shoreline, so the two parallel floating dividers form three runoff
collection cells in parallel
arrangements toward the coarse tailings beach, c) a common connection pipeline
207 is set across
the three runoff collection cells 205 to transport the runoff fluid tailings
207 into the flocculation
station 201, d) two types of the floating bottomless thickeners, one in round
shape 202b, the other in
rectangular or square shape 202a, are set next to the floating dyke 201. The
arrangements provide
more advantages for the operation, including: a) the multiple runoff
collection cells allow for the
coarse tailings beaching at different beach areas for beach development, and
for the runoff settling
in different cells for a long time for sufficient separation, b) the two
bottomless thickeners allow for
more flexible fluid tailings thickening, such as different tailings treatment
at the same time in
different thickeners, or in a sequential operation in the same thickener; a
staged treatment from the
first thickener to the second thickener if the water quality in the first
stage does not meet the
requirements. Furthermore, the arrangement makes the water management easy to
classify the water
bodies in terms of water quality and flow rates required.
For more common scenarios in current mining operations, there would be
existing active tailings
ponds before the present invention is used for improvement of tailings and
water management in the
operations. Figure 4 depicts the embodiments of the method, and some more
detailed exemplary
descriptions are given below. The difference between the existing active
tailings pond and the new
tailings pond is in that the new tailings pond holds only fresh water, while
the existing active pond
holds fluid tailings in most of its fluid body. The new tailing pond can be
easily to start up the
thickening process after the bottomless thickener is installed, however, the
existing active tailings
pond needs to be arranged to get rid of the fluid tailings out of the
bottomless thickener, and fill up
the bottomless thickener with process water. As shown in Figure 4, the
operation is realized by the
CA 02910470 2015-10-28
following steps: a) setting up the floating dyke 201 to separate the runoff
collection section 205 and
the main tailings pond section 107 and108, b) starting up the runoff
collection, settling, recycling
dilution water 208 back to the processing plant, transferring the fluid
tailings 207 into the main
tailings pond, and building up the under-water-beach 103 below the runoff
collection section 205, c)
using the floating dividers 202 and combining with the floating dyke 201 to
form at least one of the
floating bottomless thickener 202, d) filling up the floating bottomless
thickener 202 by pumping the
top water 108 of the tailings pond until the water level in the bottomless
thickener 202 is higher than
the water level of the tailings pond or achieves constant high level, e)
starting up the flocculation
and thickening process from the runoff collection section or cells 205,
recycling walui process water
209 for process reuse, and depositing the thickened tailings in-situ down to
the bottom of the tailings
pond to form the under-water-beach 206, and f) relocating the floating
bottomless thickener 202
along the floating dyke 201 to continue the flocculation and thickening
process, and building up the
under-water-beach 206 along the floating dyke 201 until the building of the
under-water-beach is
completed.
Because the fluid tailings is still holding the major volume of the main
tailings pond, the present
invention proposes some embodiments to speed up the treatment of fluid
tailings in the main tailings
pond, and improve the recycle water quality, so as to eliminate or mitigate
the impact of the fluid
tailings on the mining operation. Figure 4 depicts some details with two
floating closed cells for the
treatment and management purpose. The operation steps include: a) setting up
two floating closed
cells 401 and 402 by using floating dividers 202, and choosing one of the
floating closed cell as a
water-holding cell 401, and the other as a fluid tailings-holding cell 402, b)
withdrawing the top
water out of the fluid tailings-holding cell 402 until the top water layer
disappears, then transferring
the fluid tailings 403 in the fluid tailings-holding cell to the flocculation
station 204 for treatment, c)
filling up the top water into the water-holding cell 40 luntil the water level
is higher than the water
level in the main tailings pond or achieves a constant high level, then
transferring the water for
process recycle 111. There are many other alternatives through combinations of
the floating dykes
201 and floating dividers 202 to form various open or closed cells for fluid
tailings treatment, fluid
tailings holding, recycle water holding, treated tailings in-situ deposition,
in-pond deposition, or out-
of-pond deposition, and to make the tailings and water management more
flexible at a low cost.
The continuous development of the above-water beach and the under-water-beach
can be looked as
a part of tailings pond reclamation, the volume reduction of tailings pond
follows simultaneously.
CA 02910470 2015-10-28
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The operation steps for the tailings pond reclamation include: a) determining
the area to be
reclaimed, setting up the boundary, b) installing the floating dyke to cover
the area to be reclaimed,
and installing the floating bottomless thickener next to the floating dyke, c)
starting up the coarse
tailings beaching process to build up the above-water-beach, collecting the
runoff, building up the
under-water-beach in the runoff collection section, and treating the runoff
fluid tailings, d) starting
up the flocculation, thickening, and treated tailings deposition process, and
building up the under-
water-beach in the deeper side of the floating dyke, e) continuing the beach
construction in the three
areas until the under-water-beaches are fully developed along the two sides of
the floating dyke, and
0 relocating the floating dyke forward for a new round of operation, and
moving the coarse tailings
discharge point forward to develop the above-water-beach to cover the under-
water-beach that was
built up during the last round of operation. The exemplary description for the
beach status after the
completion of the first round of tailings pond reclamation is shown in Figure
5. A new beach layer
501 formed from the combination of the new above-water-beach and the old under-
water-beach
moves forward and deposits on the top of old beach layer 102. The new under-
water-beaches 103
and 502 are developed in the same way as the previous round of operation. The
old under-water-
beach 206 developed from the treated tailings deposits is next to the new
beach layer 501 and
becomes a part of the under-water-beach 103 in the new runoff collection
section 205. Although
there is no direct indication for the reduction of the pond size, it is
obvious that the tailings pond
volume is reduced due to the beach moving forward to the fluid pond end. It is
worth noting that the
arrangements are flexible and ready for changes to meet the requirements for
different purposes.
The floating dyke is one of the key devices in the present invention. There
are many ways for the
construction of a floating dyke, such as using floating docks, barges or
boats, suspending cables, and
supporting poles, to hang the dividing sheets. Figure 6 is an exemplary design
for the floating dyke.
The floating dyke comprises: a) a hanging cable 602, b) group of dividing
sheets 604, c) a group of
floating dock modules 606, and d) a group of height adjusting mechanisms 605.
A pair of pillars 601
that are fixed on the shore fixes the hanging cable 602, and the hanging cable
602 hangs the dividing
sheets 604 and guides the floating dock modules 606 in positions required. The
dividing sheets 604
are connected together through adhesive strips or patches 607 that are
attached on the edges of the
dividing sheets. The whole dividing sheet hangs below the hanging cable, left
about 0.5 in to 1.0 in
above water surface, and about 1.0 m to 3.0 m gap at the bottom of the
tailings pond 608. The side
edge of the dividing sheet is trimmed to tightly connect to the slope of the
dam 609. The height
CA 02910470 2015-10-28
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adjusting mechanisms 605 are used to adjust the gap between the pond bottom
608 and the dividing
sheet 604. During the relocation, the adjusting mechanisms are used to pull
the whole dividing sheet
up close to the water surface, and to set up a new height required in a new
location.
Figure 7 shows more details for a single piece of dividing sheet hanging below
the floating dyke, as
well as the arrangement of floating devices at the water surface level. As an
exemplary design in
Figure 7, the floating devices 606 form a walkway 703 at the water surface
level, and there are
handrails 702 on both sides of the walkway. The dividing sheet 604 hangs on
one side of the
handrail 702 through a set of hooking mechanism 701. There is a group of
Velcro patches 607 on
one side of the dividing sheet 604 for connection to another dividing sheet.
Below the dividing sheet
is a group of heavy balls 704 that are used to stretch the dividing sheet by
the weight of the balls.
The height adjusting mechanism 605 links to the bottom of the dividing sheet
604, and controls the
height of the dividing sheet 604 from the handrail level 702 where the hanging
mechanism is
located.
As mentioned before, the design of floating dividers is similar to the
floating dykes, although there
is no walkway attached to the floating dividers. In most scenarios, the
floating dividers form various
open or closed cells for different purposes, such as cell dividers, zone
dividers, bottomless
thickeners, water-holding cells, fluid tailings-holding cells, and the
combinations of above
mentioned cells or zones. The combinations of floating dykes and floating
dividers are also flexible,
and can be used for any kind of applications as mentioned above.
Another key device in the present invention is the floating bottomless
thickener. As a matter of fact,
a floating bottomless thickener is an operational area that is enclosed by a
floating device and a
dividing sheet. Although the top of the area is open, the fluid in the
surrounding area cannot flow
into the enclosed area, neither from the top, nor from the side-dividing
sheet. However, the
bottomless design provides the opportunity for fluid flow through the bottom
area, the present
invention makes use of the design to realize the fluid management and
treatment within a single
operational area, particularly for operations of tailings treatment and
tailings pond reclamation. The
present invention discloses a method for design and use of a floating
bottomless thickener, the
method includes two aspects: a) determination of the bottomless thickening
area, and b) the
thickening operation within the pre-determined area. Because the purpose of
thickening process is to
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improve water release from fluid tailings, the thickening area can be anywhere
within the tailings
pond, however, if there are more goals to be targeted, the selection of
thickening area is constrained
to certain areas. Taking the tailings pond reclamation as an exemplary case,
the best location for the
thickening operation is close to the beach area where the upcoming reclamation
will occur. In this
case, the floating dykes and the floating dividers can be located to the said
area to start up the
construction of the under-water-beach through the thickening and in-situ
deposition operation that
the present invention discloses. Taking the reclamation of an existing
inactive tailings pond as
another exemplary case, the objective of the operation is to release water
from the pond without
reduction of the pond volume. In this case, the thickening area can be
anywhere in the tailings pond,
however, the best location is the deepest area where the thickening operation
will last longest time
before the bottom is filled up for relocation.
The thickening operation is also important for the bottomless thickener to
achieve the highest
efficiency. Figure 8 shows an exemplary embodiment for a zoned thickening
area, and the
thickening operation within the enclosed area. As shown in Figure 8, the shape
of the thickening
area is rectangular, in order to achieve the best performance of the
thickening devices, the area is
split into eight zones in two parallel rows with four zones in each row. There
are two feedwells for
the thickening operation at the same time. The two feedwells 801 and 804 are
arranged in diagonal
positions in zone 1 and zone 5 respectively, so there is the least impact
between the two feedwells
during the thickening operation. Each feedwell follows the pre-determined
directions 802 to move.
The thickening operation will take certain time at each zone to build up the
thickened tailings
deposits layer, then move to the next zone. There may be more feedwells
required for different
purposes.
Figure 9 shows an exemplary result from a periodic thickening and sand-capping
operation. The
resulting network of sand-caps 905 and sand-walls 906 within the thickened
tailings deposits 904 is
constructed after the rotating operation. The detailed operation steps are
described below: a) using
the feedwell 901 for thickening and sand-capping operation, b) starting up the
thickening first to
build up the bottom layer of the thickened tailings deposits that is placed on
the old deposits 908, c)
capping sands layer on top of the thickened tailings deposits, d) setting up a
set of paired floating
dividers within the bottomless thickener to split the thickening area into
isolated zones by the paired
floating dividers, e) depositing coarse sands within the paired floating
dividers to form sand-walls
CA 02910470 2015-10-28
19
progressively, f) repeating the thickening, sand-capping, and sand-wall
building until the deposits
reach the feedwell, and g) remove the floating dividers from the sand-walls
and relocating the
thickening area for next round of operation. Although there is only one
feedwell 901 in Figure 9,
more feedwell in different types or different sizes may be needed for
different feed streams at the
same time within different zones as mentioned in the case of Figure 8.
