Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1
TREATMENT OF RESIDUAL HYDROCARBONS IN FLUID TAILINGS
FIELD
[001] The technical field generally relates to the treatment of fine tailings
derived from
mining operations, and more particularly relates to the treatment of thick
fine tailings
and froth treatment tailings derived from oil sands mining.
BACKGROUND
[002] Tailings derived from oil sands mining operations are often placed in
disposal
ponds for settling. The settling of fine solids from the water in tailings
ponds can be a
relatively slow process and can form a stratum of thick fine tailings.
[003] Certain techniques have been developed for dewatering fine tailings.
Dewatering of fine tailings can include contacting with a flocculating agent
and then
depositing the flocculated material onto a sub-aerial deposition area where
the
deposited material can release water and eventually dry. Other techniques for
treating
thick fine tailings include addition of gypsum and sand to produce
consolidated
tailings.
[004] In some scenarios, it can be desirable to pre-treat the fine tailings
stream prior
to dewatering and adding the flocculating agent. However, there are a number
of
challenges related to pre-treating the fine tailings stream and to processing
the
material to facilitate efficient reclamation.
SUMMARY
[005] In one aspect, there is provided a process for treating froth treatment
tailings
located in a tailings pond and generated from an oil sands extraction
operation, the
froth treatment tailings comprising a hydrocarbon solvent and residual
bitumen, the
process comprising: generating gas bubbles within at least one layer of the
froth
treatment tailings located below a water layer capping the froth treatment
tailings in
the tailings pond, contacting the gas bubbles with at least a portion of the
hydrocarbon
solvent and the residual bitumen during ascension of the gas bubbles to
extract at
CA 3048272 2019-06-28
2
least a portion of the hydrocarbon solvent and the residual bitumen from the
at least
one layer of the froth treatment tailings to the water layer capping the froth
treatment
tailings, thereby obtaining floating hydrocarbon aggregates and treated froth
treatment tailings free of the at least a portion of the hydrocarbon solvent
and the
residual bitumen.
[006] In some implementations, the gas bubbles comprise air bubbles.
[007] In some implementations, the gas bubbles consist of air bubbles.
[008] In some implementations, the process further comprises settling a froth
treatment tailings material in the tailings pond to obtain the water layer
capping the
froth treatment tailings and the at least one layer of the froth treatment
tailings located
below the water layer.
[009] In some implementations, the at least one layer of the froth treatment
tailings
located below the water layer is at least one of a mature fine tailings layer
of the froth
treatment tailings and a coarse layer of the froth treatment tailings.
[010] In some implementations, the hydrocarbon solvent comprises one of a
naphthenic solvent and a paraffinic solvent.
[011] In some implementations, generating the gas bubbles comprises sparging
gas
into the at least one layer of the froth treatment tailings located below the
water layer
capping the froth treatment tailings.
[012] In some implementations, the process further comprises at least one of
dredging and pumping the at least one layer of the froth treatment tailings
located
below the water layer capping the froth treatment tailings, to generate fluid
movement
between layers of the froth treatment tailings.
[013] In some implementations, the process further comprises providing gas
sparging
units at a plurality of locations within the at least one layer of the froth
treatment
tailings located below the water layer capping the froth treatment tailings,
for
generating the gas bubbles.
CA 3048272 2019-06-28
3
[014] In some implementations, the gas bubbles are introduced at a volume of
at least
20 m3 of gas per m3 of froth treatment tailings.
[015] In some implementations, the gas bubbles are introduced at a volume of
at least
50 m3 of gas per m3 of froth treatment tailings.
[016] In some implementations, the froth treatment tailings comprises
untreated froth
treatment tailings obtained from an output of a froth treatment process.
[017] In some implementations, the gas bubbles comprise at least one of coarse
bubbles, fine bubbles and micro-bubbles.
[018] In some implementations, the process further comprises: adding an
immobilization chemical to the treated froth treatment tailings in order to
chemically
immobilize remaining contaminants of concern (CoCs); adding flocculating agent
to
the treated froth treatment tailings in order to flocculate remaining
suspended solids,
thereby producing a flocculated material; and dewatering the flocculated
material to
produce an aqueous component depleted in the COCs and the suspended solids,
and a solids-enriched component comprising the chemically immobilized COCs and
flocculated solids.
[019] In some implementations, the process further comprises providing an in-
line
flow of the treated froth treatment tailings.
[020] In some implementations, the immobilization chemical and the
flocculating
agent are added in-line into the in-line flow of the treated froth treatment
tailings.
[021] In some implementations, the immobilization chemical is added as an
aqueous
immobilization solution into the in-line flow of the treated froth treatment
tailings, the
process further comprising in-line mixing of the aqueous immobilization
solution and
the treated froth treatment tailings.
[022] In some implementations, the process further comprises in-line
conditioning of
the flocculated material prior to dewatering to form a conditioned flocculated
material
in a water release zone.
CA 3048272 2019-06-28
4
[023] In some implementations, the immobilization chemical is selected from
multivalent organic salts.
[024] In some implementations, the dewatering of the flocculated material
comprises
depositing the flocculated material onto a sub-aerial deposition area, thereby
allowing
drainage of the aqueous component away from the solids-enriched component.
[025] In some implementations, the dewatering of the flocculated material
comprises
depositing the flocculated material into a pit, thereby allowing separation of
the
aqueous component from the solids-enriched component that settles to a bottom
of
the pit.
[026] In some implementations, the process further comprises forming a
permanent
aquatic storage structure (PASS) for retaining the solids-enriched component
and a
water cap, wherein the solids-enriched component: forms a consolidated solids-
rich
lower stratum below the water cap; and retains the immobilized CoCs and
inhibits
migration of the immobilized CoCs into the water cap.
[027] In some implementations, adding the immobilization chemical is performed
prior
to adding the flocculating agent.
[028] In some implementations, adding the flocculating agent is performed
prior to
adding the immobilization chemical.
[029] In some implementations, the immobilization chemical and the
flocculating
agent are added simultaneously.
[030] In some implementations, the treated froth treatment tailings are
subjected to
pre-shearing to reduce a yield stress thereof prior to addition of the
immobilization
chemical and the flocculating agent.
[031] In some implementations, the treated froth treatment tailings are
subjected to
screening to remove coarse debris therefrom prior to addition of the
immobilization
chemical and the flocculating agent.
CA 3048272 2019-06-28
5
[032] In some implementations, the process further comprises: removing the
floating
hydrocarbon aggregates from the water layer capping the froth treatment
tailings to
produce recovered hydrocarbon aggregates.
[033] In some implementations, removing the floating hydrocarbon aggregates
comprises skimming the floating hydrocarbon aggregates.
[034] In some implementations, the process further comprises treating the
recovered
hydrocarbon aggregates to recover at least one of the residual bitumen and the
hydrocarbon solvent.
[035] In some implementations, treating the recovered hydrocarbon aggregates
comprises subjecting the recovered hydrocarbon aggregates to a solvent
separation
step.
[036] In some implementations, the process further comprises intercepting a
gas
phase at the surface of the tailings pond.
[037] In another aspect, a system for treating froth treatment tailings
generated from
an oil sands extraction operation is provided. The froth treatment tailings
comprises
a hydrocarbon solvent and residual bitumen. The system comprises a tailings
pond
into which the froth treatment tailings are deposited for settling, to obtain
a water layer
and at least one layer of the froth treatment tailings located below the water
layer; and
a gas bubbling assembly to generate gas bubbles within the at least one layer
of the
froth treatment tailings and comprising at least one gas bubbles generating
unit
located below the water layer, the gas bubbling assembly being configured to
enable
extraction of at least a portion of the hydrocarbon solvent and the residual
bitumen
from the at least one layer of the froth treatment tailings to the gas bubbles
during
ascension of the gas bubbles towards a surface of the tailings pond, to obtain
floating
hydrocarbon aggregates and treated froth treatment tailings free of the at
least a
portion of the hydrocarbon solvent and the residual bitumen.
[038] In some implementations, the at least one gas bubbles generating unit
comprises a plurality of air diffusers that generate air bubbles.
CA 3048272 2019-06-28
6
[039] In some implementations, the gas bubbles consist of air bubbles.
[040] In some implementations, the gas bubbling assembly further comprises: a
compressor assembly located outside the tailings pond for producing compressed
gas; and a network of pipes in fluid communication with the compressor for
conveying
the compressed gas to the at least one layer of the froth treatment tailings
located
below the water layer.
[041] In some implementations, the at least one layer of the froth treatment
tailings
located below the water layer is at least one of a mature fine tailings layer
of the froth
treatment tailings and a coarse layer of the froth treatment tailings.
[042] In some implementations, the hydrocarbon solvent comprises one of a
naphthenic solvent and a paraffinic solvent.
[043] In some implementations, the gas bubbling assembly comprises gas
sparging
units located within the at least one layer of the froth treatment tailings
located below
the water layer capping the froth treatment tailings.
[044] In some implementations, the system further comprises at least one of a
dredging unit and a pump located in the at least one layer of the froth
treatment
tailings located below the water layer, to generate fluid movement between
layers of
the froth treatment tailings.
[045] In some implementations, the gas sparging units are located at a
plurality of
locations within the at least one layer of the froth treatment tailings
located below the
water layer, for generating the gas bubbles.
[046] In some implementations, the gas bubbling assembly is configured to
introduce
gas into the at least one layer of the froth treatment tailings located below
the water
layer at a volume of at least 20 m3 of gas per m3 of froth treatment tailings.
[047] In some implementations, the gas bubbling assembly is configured to
introduce
gas into the at least one layer of the froth treatment tailings located below
the water
layer at a volume of at least 50 m3 of gas per m3 of froth treatment tailings.
CA 3048272 2019-06-28
7
[048] In some implementations, the froth treatment tailings comprise untreated
froth
treatment tailings obtained from an output of a froth treatment process.
[049] In some implementations, the gas bubbles comprise at least one of coarse
bubbles, fine bubbles and micro-bubbles.
[050] In another aspect, there is provided a process for treating fine
tailings generated
from an oil sands extraction operation, the fine tailings being flocculant-
free and
comprising residual hydrocarbons, the process comprising: aerating the fine
tailings
in a gravity aerator to obtain aerated fine tailings comprising the residual
hydrocarbons and air bubbles; and settling the aerated fine tailings in a
tailings pond,
thereby enabling the residual hydrocarbons to rise to a surface layer of the
tailings
pond to produce floating hydrocarbon aggregates and treated fine tailings free
of at
least a portion of the residual hydrocarbons.
[051] In some implementations, the fine tailings comprise at least one of thin
fine
tailings, thick fine tailings, mature fine tailings (MFT), froth treatment
tailings (FTT)
and froth treatment mature fine tailings (FTMFT).
[052] In some implementations, the residual hydrocarbons comprise at least one
of a
hydrocarbon solvent and residual bitumen.
[053] In some implementations, the hydrocarbon solvent comprises one of a
naphthenic solvent and a paraffinic solvent.
[054] In some implementations, the process further comprises at least one of
dredging and pumping at least one layer of the aerated fine tailings located
below the
surface layer of the tailings pond, to generate fluid movement between layers
of the
aerated tailings.
[055] In some implementations, the process further comprises: adding an
immobilization chemical to the treated fine tailings to chemically immobilize
remaining
contaminants of concern (COCs); adding a flocculating agent to the treated
fine
tailings to flocculate remaining suspended solids, thereby producing a
flocculated
CA 3048272 2019-06-28
8
material; and dewatering the flocculated material to produce an aqueous
component
depleted in the COCs and the suspended solids, and a solids-enriched component
comprising the chemically immobilized COCs and flocculated solids.
[056] In some implementations, the process further comprises providing an in-
line
flow of the treated fine tailings.
[057] In some implementations, the immobilization chemical and the
flocculating
agent are added in-line into the in-line flow of the treated fine tailings.
[058] In some implementations, the immobilization chemical is added as an
aqueous
immobilization solution into the in-line flow of the treated fine tailings,
the process
further comprising in-line mixing of the aqueous immobilization solution and
the
treated froth treatment tailings.
[059] In some implementations, the process further comprises in-line
conditioning of
the flocculated material prior to dewatering to form a conditioned flocculated
material
in a water-release zone.
[060] In some implementations, the immobilization chemical is selected from
multivalent organic salts.
[061] In some implementations, the dewatering of the flocculated material
comprises
depositing the flocculated material onto a sub-aerial deposition area, thereby
allowing
drainage of the aqueous component away from the solids-enriched component.
[062] In some implementations, the dewatering of the flocculated material
comprises
depositing the flocculated material into a pit, thereby allowing separation of
the
aqueous component from the solids-enriched component that settles to a bottom
of
the pit.
[063] In some implementations, the process further comprises forming a
permanent
aquatic storage structure (PASS) for retaining the solids-enriched component
and a
water cap, wherein the solids-enriched component: forms a consolidated solids-
rich
CA 3048272 2019-06-28
9
lower stratum below the water cap; and retains the immobilized CoCs and
inhibits
migration of the immobilized CoCs into the water cap.
[064] In some implementations, adding the immobilization chemical is performed
prior
to adding the flocculating agent.
[065] In some implementations, adding the flocculating agent is performed
prior to
adding the immobilization chemical.
[066] In some implementations, the immobilization chemical and the
flocculating
agent are added simultaneously.
[067] In some implementations, the treated from fine tailings are subjected to
pre-
shearing to reduce a yield stress thereof prior to addition of the
immobilization
chemical and the flocculating agent.
[068] In some implementations, the treated fine tailings are subjected to
screening to
remove coarse debris therefrom prior to addition of the immobilization
chemical and
the flocculating agent.
[069] In some implementations, the process further comprises removing the
floating
hydrocarbon aggregates from the surface layer of the tailings pond to produce
recovered hydrocarbon aggregates.
[070] In some implementations, removing the floating hydrocarbon aggregates
comprises skimming the floating hydrocarbon aggregates.
[071] In some implementations, the process further comprises treating the
recovered
hydrocarbon aggregates to recover at least one of the residual bitumen and the
hydrocarbon solvent.
[072] In some implementations, treating the recovered hydrocarbon aggregates
comprises subjecting the recovered hydrocarbon aggregates to a solvent
separation
step.
CA 3048272 2019-06-28
10
[073] In some implementations, the gravity aerator comprises at least one of a
cascade aerator, an inclined apron aerator, a slat tray aerator and a gravel
bed
aerator.
[074] In some implementations, the gravity aerator comprises a cascade
aerator.
[075] In some implementations, the gravity aerator consists of a cascade
aerator.
[076] In some implementations, the fine tailings comprise an untreated froth
treatment
tailings stream originating from a froth treatment process.
[077] In some implementations, the fine tailings comprise a settled fine
tailings stream
originating from a first tailings pond, and wherein the aerated fine tailings
are settled
in a second tailings pond.
[078] In some implementations, the settled fine tailings comprise at least one
of
mature fine tailings and froth treatment mature fine tailings.
[079] In some implementations, the first tailings pond is a tailings pond
receiving thin
fine tailings obtained after a sand dump process.
[080] In some implementations, the first tailings pond is a froth treatment
tailings pond
receiving froth treatment tailings from a froth treatment process.
[081] In another aspect, there is provided a system for treating fine tailings
generated
from an oil sands extraction operation, the fine tailings being flocculant-
free and
comprising residual hydrocarbons, the system comprising: a gravity aerator for
aerating the fine tailings, thereby obtaining aerated fine tailings comprising
the
residual hydrocarbons and air bubbles; and a tailings pond in fluid
communication
with the gravity separator to receive the aerated fine tailings and settle the
aerated
fine tailings, thereby enabling the residual hydrocarbons to rise to a surface
layer of
the tailings pond to produce floating hydrocarbon aggregates and treated fine
tailings
free of at least a portion of the residual hydrocarbons.
CA 3048272 2019-06-28
11
[082] In some implementations, the fine tailings comprise at least one of thin
fine
tailings, thick fine tailings, mature fine tailings (MFT), froth treatment
tailings (FTT)
and froth treatment mature fine tailings (FTMFT).
[083] In some implementations, the residual hydrocarbons comprise at least one
of a
hydrocarbon solvent and residual bitumen.
[084] In some implementations, the hydrocarbon solvent comprises one of a
naphthenic solvent and a paraffinic solvent.
[085] In some implementations, the system further comprises at least one of a
dredging vessel and a pump in at least one layer of the aerated fine tailings
located
below the surface layer of the tailings pond, to generate fluid movement
between
layers of the aerated tailings.
[086] In some implementations, the gravity aerator comprises at least one of a
cascade aerator, an inclined apron aerator, a slat tray aerator and a gravel
bed
aerator.
[087] In some implementations, the gravity aerator comprises a cascade
aerator.
[088] In some implementations, the gravity aerator consists of a cascade
aerator.
[089] In some implementations, the fine tailings comprise an untreated froth
treatment
tailings stream originating from a froth treatment process.
[090] In some implementations, the tailings pond is a second tailings pond,
the
system further comprising a first tailings pond in fluid communication with an
inlet of
the gravity aerator, wherein a settled fine tailings stream originating from
the first
tailings pond is fed into the gravity aerator, and wherein the aerated fine
tailings are
settled in the second tailings pond.
[091] In some implementations, the settled fine tailings comprise at least one
of
mature fine tailings and froth treatment mature fine tailings.
CA 3048272 2019-06-28
12
[092] In some implementations, the first tailings pond is a tailings pond
receiving thin
fine tailings obtained after a sand dump process.
[093] In some implementations, the first tailings pong is a froth treatment
tailings pond
receiving froth treatment tailings from a froth treatment process.
[094] In some implementations, the hydrocarbon solvent comprises naphthenic
solvent.
[095] In some implementations, the hydrocarbon solvent comprises naphthenic
solvent.
[096] In some implementations, the hydrocarbon solvent comprises paraffinic
solvent.
[097] In some implementations, the hydrocarbon solvent comprises paraffinic
solvent.
[098] In some implementations, the at least one layer of the froth treatment
tailings
located below the water layer is a mature fine tailings layer.
[099] In some implementations, the at least one layer of the froth treatment
tailings
located below the water layer is a mature fine tailings layer.
[100] In some implementations, the at least one layer of the froth treatment
tailings
located below the water layer is a coarse layer.
[101] In some implementations, the at least one layer of the froth treatment
tailings
located below the water layer is a coarse layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[102] Figure 1 is a process flow diagram of an oil sands mining operation,
including
gas bubbling within tailings ponds.
CA 3048272 2019-06-28
13
[103] Figure 2 is a schematic representation of a tailings pond, where gas
bubbles
are provided in a mature fine tailings layer below the water cap layer.
[104] Figure 3 is a schematic diagram showing oil sands tailings that do not
include
light hydrocarbons.
[105] Figure 4 is a schematic diagram showing oil sands tailings including
light
hydrocarbons.
[106] Figures 5A to 5C are schematic diagrams showing oil sands tailings
including
light hydrocarbons migrating to gas bubbles rising through the oil sands
tailings.
[107] Figure 6 is a flow diagram of an exemplary froth treatment tailings
dewatering
operation, wherein gas bubbles are provided in a mature fine tailings layer,
below the
water cap layer, prior to dewatering operations.
[108] Figure 7 is a schematic top plan view of a tailings pond wherein several
air
diffusers are provided.
[109] Figure 8A is a flow diagram of an exemplary cascade aeration step
performed
on a froth treatment tailings stream.
[110] Figure 8B is a flow diagram of an exemplary cascade aeration step
performed
on a thin fine tailings stream.
[111] Figure 9A is a flow diagram of an exemplary cascade aeration step
performed
on a froth treatment tailings stream obtained from a first tailings pond.
[112] Figure 9B is a flow diagram of an exemplary cascade aeration step
performed
on a thin fine tailings stream obtained from a first tailings pond.
[113] Figure 10 is a flow diagram of a gravity aeration process.
[114] Figure 11A and 11B are schematic diagrams showing exemplary cascade
aerators.
CA 3048272 2019-06-28
14
[115] Figure 12 is a schematic top plan view of a tailings pond wherein an
oxygenated
flow is conveyed to several entry points around the tailings pond.
DETAILED DESCRIPTION
[116] Various aspects and implementations of the processes and systems
described
herein relating to the treatment of tailings materials will be described
below.
Overview of the process
[117] Various techniques that are described herein enable the treatment of
fine
tailings streams, such as thick fine tailings (e.g., mature fine tailings) or
froth treatment
tailings (FTT), that include residual hydrocarbons. The fine tailings can
include
residual hydrocarbons such as residual hydrocarbons from primary or secondary
separation, or diluent and residual bitumen from a froth treatment process.
[118] For example, residual light hydrocarbons can be found in part of some of
the
fluid tailings generated from mineable oil sands processing ¨ for example in
froth
treatment tailings obtained from a froth treatment process. It should be
understood
that the term "light hydrocarbons" as used herein refers to hydrocarbon
solvents or
diluents such as Naphthenic solvent or paraffinic solvent. It should also be
understood
that the terms "light hydrocarbons", "diluent" and "hydrocarbon solvent" can
be used
interchangeably in the present description. These light hydrocarbons can
support
microbial activity, and may as such negatively impact aquatic closure
performance,
as well as add to greenhouse gas (GHG) and volatile organic component (VOC)
loading. The techniques described herein can allow for the in-situ removal of
the
residual light hydrocarbons, or for the in-situ reduction of their overall
concentration
to a level compatible with aquatic closure requirements.
[119] The fine tailings can be contacted with gas bubbles directly in the
tailings pond
in which the fine tailings are stored, to remove residual hydrocarbons, prior
to sending
the treated tailings stream to dewatering operations. Contacting the fine
tailings
stream with gas bubbles can include flotation. In some scenarios, most of the
organic
material that migrates to the gas bubbles is light hydrocarbons (e.g.,
diluent). In other
CA 3048272 2019-06-28
15
scenarios, the organic material that migrates to the gas bubbles includes both
residual
bitumen and light hydrocarbons. Froth treatment tailings typically has three
classes
of "constituents of concern" (CoCs) when considering long term closure
performance
of tailings fluid. Two out of those three classes (i.e. Acid Rock Drainage
potential and
Naturally Occurring Radioactive Materials) can be compatible with permanent
aquatic
storage structure (PASS) treatment or aquatic reclamation. The techniques
described
herein enable the one remaining CoC (i.e., residual hydrocarbons such as light
hydrocarbons) to be targeted specifically, while leaving the others generally
unmodified. Over-processing, excessive re-handling and/or an additional ex-
situ
separation step can be avoided by treating the material within the tailings
pond itself.
[120] The techniques described herein can use any diluent-affected fluid
tailings
inside a tailings containment area as feedstock. The material can first be
contacted
with gas bubbles (e.g., air bubbles) through a combination of sparging,
pumping and
dredging. When air bubbles are used, the following effects can be achieved:
1) Introduction of air can promote stripping of light hydrocarbons from the
fluids
and into the gas phase, through natural partitioning of light hydrocarbons
between the fluid and gas phase. As a result, gas bubbles can progressively
extract light hydrocarbons from the fluid tailings.
2) Introduction of air can further promote floatation of residual bitumen
present
in the fluid tailings. Since light hydrocarbons are in part associated with
the
bitumen phase, removal of bitumen can result in proportional removal of light
hydrocarbons.
3) Introduction of air can also increase in-situ oxygen levels, thereby
promoting
biodegradation of light hydrocarbons into CO2 (aerobic degradation). This is
opposed to anaerobic degradation, where the primary degradation product
would be methane. Since methane is a significantly more potent greenhouse
gas, aerobic degradation can reduce GHG loading.
CA 3048272 2019-06-28
16
[121] After removal of residual light hydrocarbons is substantially complete,
the
remainder of the tailings stream can exhibit characteristics compatible with
PASS
treatment and can therefore be treated in a way similar to conventional fluid
tailings
(i.e., fluid tailings that do not include residual light hydrocarbons). In
this context,
PASS type treatment can be viewed as a process where an immobilization
chemical
and a flocculating agent are added to the tailings, and the resulting
flocculated
material is deposited within a mine pit or similar containment structure such
that the
flocculated solids settle and a water layer forms above the settled solids,
thereby
forming a PASS.
[122] It is understood that the "organic materials" found in oil sands include
bitumen
and other "insoluble organic materials". It is understood that the term
"bitumen" as
used herein, can include bitumen components such as maltenes and/or
asphaltenes
in varying proportions. It is understood that the maltenes consist of the
fraction of the
bitumen which is soluble in n-alkane solvents, including pentane, hexane
and/or
heptane. It is also understood that the asphaltenes consist of the fraction of
the
bitumen which is soluble in light aromatic solvents, such as benzene or
toluene, and
precipitates in n-alkane solvents. The "insoluble organic materials" (also
referred to
herein as "tightly bound organic materials") can for example include humic
materials
(i.e., humins) which can form chemical complexes with some of the heavy
minerals.
It is understood that the "insoluble organic materials" consist of the organic
materials
which are insoluble in n-alkane solvents and light aromatic solvents at
atmospheric
pressure and at the boiling temperature of the solvents and can also be
understood
as being non-bitumen components.
[123] It should be understood that the term "fine tailings" (also referred to
in the art as
"fluid tailings") as used herein, may refer to various types of oil sands
tailings, such
as thin fine tailings (i.e., extraction tailings that have formed from run-off
of sand dump
operations or similar treatments), thick fine tailings (i.e., settled tailings
from a tailings
pond ¨ an example of which being mature fine tailings), or froth treatment
tailings (or
streams derived from froth treatment tailings such as froth treatment mature
fine
tailings, froth treatment centrifuge cake, etc.). It is understood that the
term "froth
CA 3048272 2019-06-28
17
treatment tailings", as used herein, encompasses froth treatment tailings
exiting a
froth treatment process (i.e., froth treatment tailings that have not yet
settled), froth
treatment tailings having settled in a tailings pond for a certain amount of
time, or a
stream derived from froth treatment tailings. For example, it should be
understood
that froth treatment tailings having settled in a tailings pond for a certain
amount of
time may include a top water layer capping the froth treatment tailings, a
middle froth
treatment mature fine tailings layer, and a bottom layer that can be rich in
solid
materials.
Integration in oil sands extraction operation
[124] Referring to Figure 1, in a bitumen extraction operation, oil sands ore
10 is
mined and crushed in a crushing unit 12 to obtain a crushed ore 13. The
crushed ore
13 is then mixed with water 14 (e.g., hot water) in a mixing unit 16 (for
example, a
rotary breaker) to form an aqueous slurry 18. The aqueous slurry 18 is
conditioned
(for example during transport) to prepare the bitumen for separation from the
aqueous
slurry 18 by adding additives (for example, caustic soda) to the aqueous
slurry 18.
The aqueous slurry 18 is then transported to a primary separation vessel 20
for
separation into primary bitumen froth 22 and coarse tailings 24 (also referred
to as
primary tailings).
[125] In some scenarios, the primary separation vessel 20 can also produce
middlings 26 which can be sent to a secondary separation vessel 28 to be
separated
into secondary bitumen froth 30 and secondary tailings 32. The secondary
bitumen
froth 30 can be fed back to the primary separation vessel 20, as shown in the
Figure
or, alternatively, can be directly added to the primary bitumen froth 22.
[126] The bitumen froth 22 typically includes between about 40 wt% and about
70
wt% bitumen, between about 20 wt% and about 50 wt% water, and between about 5
wt% and about 15 wt% solid materials. The solid materials in the bitumen froth
22
typically include hydrophobic mineral materials and heavy minerals which can
include
adsorbed insoluble organic material.
CA 3048272 2019-06-28
18
[127] The primary tailings 24 and secondary tailings 32 generally include
between
about 45 wt% and about 55 wt% solid materials, between about 45 wt% and about
55 wt% water, and residual bitumen (typically between about 1 wt% and about 3
wt%
bitumen). The solid materials in the primary and secondary tailings 24, 32 are
mainly
sand and other fine hydrophilic mineral materials and can include residual
heavy
minerals. The primary tailings 24 and secondary tailings 32 (that can be
generally
referred to or combined as extraction tailings or whole tailings 29) can be
further
treated and dewatered, as will be described further below.
[128] The bitumen froth 22 is treated in a froth treatment process 34 in which
the
bitumen froth 22 is diluted with a diluent 36 to obtain a diluted bitumen
froth. The
diluent 36 can be either a naphthenic type diluent or a paraffinic type
diluent and can
also be referred to herein as "light hydrocarbons". The naphthenic type
diluent can for
example include toluene, naphtha or other light aromatic compounds. The
paraffinic
type diluent can for example include 04 to C8 aliphatic compounds and/or
natural gas
condensate. The diluted bitumen froth is then separated into a bitumen product
38
(which can be further upgraded or used as is) and froth treatment tailings 40
including
contaminants of concern (CoCs, such as residual bitumen, residual diluent,
naphthenic acids, various salts, Acid Rock Drainage potential, Naturally
Occurring
Radioactive Materials etc.) and suspended solid materials (such as hydrophilic
mineral materials, heavy minerals and insoluble organic materials), and water.
The
froth treatment tailings 40 can be further treated and dewatered, as will be
described
further below.
[129] Still referring to Figure 1, in some implementations, froth treatment
tailings 40
are deposited in a froth treatment tailings pond 42 for settling, to form a
top water
region 43 and a bottom froth treatment mature fine tailings region 44 in the
tailings
pond 42. Gas bubbles 45 can be generated within the froth treatment mature
fine
tailings 44 such that at least a portion of the light hydrocarbons and
residual bitumen
present in the froth treatment mature fine tailings can be extracted from the
froth
treatment mature fine tailings 44 to the gas bubbles. The extraction can occur
as the
gas bubbles rise from the froth treatment mature fine tailings 44 layer up to
the water
CA 3048272 2019-06-28
19
layer 43 capping the froth treatment mature fine tailings. As the gas bubbles
45 rise
and reach the surface of the tailings pond 42, the extracted light
hydrocarbons and
residual bitumen can form floating hydrocarbon aggregates 46 and a treated
froth
treatment tailings stream 47 that is substantially free of light hydrocarbons
and
residual bitumen.
[130] The floating hydrocarbon aggregates 46 can be recovered from the
tailings
pond (e.g., by skimming), and the recovered hydrocarbons 49 can be subjected
to
further extraction and treatment operations 50 (e.g., solvent extraction,
filtration,
drying) to recover residual bitumen and/or light hydrocarbons.
[131] The treated froth treatment tailings stream 47 includes CoCs other than
the
residual bitumen and light hydrocarbons, and also includes suspended solids.
The
treated froth treatment tailings stream 47 can be treated and dewatered 48 in
an effort
to further clean the stream. For example, the treatment and dewatering
operation 48
can include the injection of an immobilization chemical to chemically
immobilize the
remaining CoCs and/or injection of a flocculating agent to flocculate the
suspended
solids and form a flocculated material. Dewatering of the flocculated material
can then
produce an aqueous component depleted in the CoCs and the suspended solids,
and
a solid-enriched component including the chemically immobilized and
flocculated
solids.
[132] While Figure 1 depicts separate tailings pond 54 for thin fine tailings
53 and
tailings pond 42 for froth treatment tailings 40, it should be understood that
a single
tailings pond can be used to recover both the thin fine tailings 53 and the
froth
treatment tailings 40. Gas bubbles can then be generated in the single
tailings pond,
followed by treatment and dewatering steps similar to treatment and dewatering
48,
similarly as described above. Alternatively, it is also understood that the
fine tailings
can be deposited in more than two tailings ponds.
[133] Still referring to Figure 1, the extraction tailings 29 are subjected to
a sand dump
step 52 prior to obtain thin fine tailings 53 that can be deposited into a
tailings pond
54 for settling. After settling, the thin fine tailings 53 can produce a water
top layer 55
CA 3048272 2019-06-28
20
and mature fine tailings 56. Gas bubbles 45' can be generated in the mature
fine
tailings layer 56 of tailings pond 54 and be subjected to a treatment and
dewatering
operation 48'. In some implementations, the water top layer 55 can be reused
as
recycle water 155 in the oil sands extraction operation, for example as input
water in
the mixing unit 16, for forming aqueous slurry 18.
[134] The gas bubbles 45' can extract at least a portion of residual light
organic
materials that are present in the mature fine tailings 56, and a light organic-
free
mature fine tailings stream 47' can be extracted from the pond 54 and
subjected to
further treatment and dewatering 48'. Floating organics 46' can be recovered
as
recovered hydrocarbons 49' and subjected to a hydrocarbon recovery process
50'. In
some implementations, the fine tailings that have been settling in a tailings
pond for
some time (e.g., what can be referred to as "legacy tailings") can be
subjected to a
flotation step, followed by treatment and dewatering operations 48, 48'.
[135] The material to be treated and dewatered in the treatment and dewatering
operations 48, 48' can be deposited onto a sub-aerial deposition area or into
a pit, for
allowing the aqueous component and the solids-enriched component to separate.
Overtime, a permanent aquatic storage structure (PASS) 58 can be formed for
retaining the solids-enriched component and a water cap 62. The solids-
enriched
component can form a consolidated solids-rich lower stratum 60 below the water
cap
62, such that the immobilized CoCs are retained by the solids-enriched
component
and migration of the CoCs into the water cap 62 is inhibited. The treatment
and
dewatering operation 48, 48', as well as the formation of the PASS 58 will be
described in further detail below.
Gas bubbling in tailings pond
[136] Now referring to Figure 2, gas bubbling within a froth treatment
tailings pond 42
is shown. In the implementation shown on Figure 2, the tailings deposit is
froth
treatment tailings obtained from a froth treatment process. The froth
treatment tailings
include light hydrocarbons that are added to the bitumen froth during the
froth
treatment process. However, it should be understood that the techniques
described
CA 3048272 2019-06-28
21
herein can be applied to other types tailings generated during the oil sands
extraction
process, so long as the tailings include hydrocarbons that are able to migrate
to the
gas bubbles upon bubbling gas in the tailings pond.
[137] Tailings are left over material derived from a bitumen extraction
process. Many
different types of tailings can be treated using one or more of the techniques
described herein. In some implementations, the techniques described herein can
be
used for "thick fine tailings" where thick fine tailings mainly include water
and fines,
"thin fine tailings" or "froth treatment tailings", so long as these tailings
fluids include
hydrocarbons that can migrate to the gas bubbles upon bubbling gas in the
tailings
pond in which the tailings are stored.
[138] The fines are small solid particulates having various sizes up to about
44
microns. The thick fine tailings have a solids content with a fines portion
sufficiently
high such that the fines tend to remain in suspension in the water and the
material
has slow consolidation rates. More particularly, the thick fine tailings can
have a ratio
of coarse particles to the fines that is less than or equal to one. The thick
fine tailings
have a fines content sufficiently high such that flocculation of the fines and
conditioning of the flocculated material can achieve a two-phase material
where
release water can flow through and away from the flocs. For example, thick
fine
tailings can have a solids content between 10 wt% and 45 wt%, and a fines
content
of at least 50 wt% on a total solids basis, giving the material a relatively
low sand or
coarse solids content. The thick fine tailings can be retrieved from a
tailings pond, for
example, and can include what is commonly referred to as "mature fine
tailings"
(MFT). A mature fine tailings layer can also form upon depositing the other
types of
tailings fluids in a tailings pond. For example, the middle layer of froth
treatment
tailings after settling in the pond for an appropriate time, can be referred
to as a "froth
treatment mature fine tailings" (FTMFT) layer. Such FTMFT layer includes
water,
fines (such as sand particles), light hydrocarbons left over from the froth
treatment
process and residual bitumen. For example, the FTMFT layer can form after
several
months of settling the froth treatment tailings in a tailings pond, after
exiting a froth
treatment process. In some scenarios, the FTMFT layer forms after a period
between
CA 3048272 2019-06-28
22
2 months and a year, or between 4 months and 8 months, or between 6 months and
8 months, or after about 6 months. It should be understood that the settling
time
required for forming the FTMFT layer can vary depending on the physical-
chemical
properties of the froth treatment tailings, on the type of diluent used and on
the
environmental parameters (i.e., temperature, wind, tailings pond geometry) in
the
vicinity of the tailings pond in which the froth treatment tailings are
settling.
[139] More generally, MFT or FTMFT refer to tailings fluids that typically
form as a
middle or intermediate layer in a tailings pond and contains water and an
elevated
content of fine solids that display relatively slow settling rates. For
example, when
whole tailings (which include coarse solid material, fine solids, and water)
or thin fine
tailings (which include a relatively low content of fine solids and a
relatively high water
content) are supplied to a tailings pond, the tailings separate by gravity
into different
layers over time. The bottom layer is predominantly coarse material, such as
sand,
and the top layer is predominantly water. The middle layer is relatively sand
depleted,
but still has a fair amount of fine solids suspended in the aqueous phase.
This middle
layer is often referred to as MFT. MFT can be formed from various different
types of
mine tailings that are derived from the processing of different types of mined
ore.
While the formation of MFT typically takes a fair amount of time (e.g.,
between 1 and
3 years under gravity settling conditions in the pond) when derived from
certain whole
tailings supplied from an extraction operation, it should be noted that MFT
and MFT-
like materials can be formed more rapidly depending on the composition and
post-
extraction processing of the tailings, which can include thickening or other
separation
steps that can remove a certain amount of coarse solids and/or water prior to
supplying the processed tailings to the tailings pond.
[140] In the implementation shown on Figure 2, the froth treatment tailings
deposited
in the tailings pond 42 has settled into a coarse layer (or bottom layer) 244
that mainly
contains coarse material or sand, a middle layer or FTMFT layer 44 and a water
layer
43 capping the froth treatment tailings in the tailings pond 42. Depending on
the
physical/chemical properties of the froth treatment tailings, on the type of
light
hydrocarbons added during the froth treatment process, and on the other types
of
CA 3048272 2019-06-28
23
CoCs present, it is understood that the properties, relative depth and
settling rate of
each one of the layers can differ. In the implementation shown, gas spargers
64 are
provided in the bottom layer 244 and in the middle layer 44. The gas spargers
64
generate gas bubbles 45 in the bottom layer and the middle layer, and the gas
bubbles 45 rise towards the water layer 43. During the rise 47, at least a
portion of
the hydrocarbon lights and the residual bitumen present in the bottom layer
244 and
the middle layer 44 are extracted to the gas bubbles. Upon reaching the water
layer
43 and the surface of the tailings pond 42, the extracted organic material and
the gas
bubbles 45 can form floating hydrocarbon aggregates 46. The extraction of
organic
material from the middle layer 44 and bottom layer 244 also enables the
formation of
a treated froth treatment tailings that contains less light hydrocarbons and
residual
bitumen than the froth treatment tailings initially deposited in the tailings
pond 42.
[141] In some implementations, the gas bubbling can be complemented by at
least
one of dredging and pumping of the bottom layer 244 and/or middle layer 44 to
enable
a large-scale fluid motion 66 between the layers of the tailings. In some
scenarios,
the large-scale fluid motion can help the extraction of the organic materials
to the gas
bubbles 45 by providing more contact between the gas bubbles 45 and the
organic
materials. The gas bubbles 45 can include air bubbles or can consist of air
bubbles.
The floating hydrocarbon aggregates 46 can optionally be recovered at the
surface
of the tailings pond 42, for example by skimming, and the treated froth
treatment
tailings can be sent for further processing and dewatering. These optional
additional
operations will be described in further detail herein.
Effect of gas bubbling on light hydrocarbons and residual bitumen
[142] Now referring to Figure 3, a schematic view of a tailings fluid that
does not
include light hydrocarbons is shown. The tailings fluid is mainly composed of
water
and includes several inorganic particles such as sand and clay particles.
Residual
bitumen particles are also present in the tailings fluid of Figure 3.
[143] Now referring to Figure 4, a schematic view of a tailings fluid that
includes light
hydrocarbons is shown (e.g., a naphthenic solvent or a paraffinic solvent). It
is
CA 3048272 2019-06-28
24
understood that the schematic view can for example be representative of the
particles
present in the middle layer of a tailings pond, such as a FTMFT layer. The
light
hydrocarbons are typically dispersed in the water phase, for example as
discrete
droplets of solvent, and can also adhere to some of the clay particles and
some of the
residual bitumen particles. The light hydrocarbons typically do not adhere to
sand
particles, which are generally more hydrophilic than the clay particles.
[144] Now referring to Figures 5A to 5C, gas bubbles are introduced in the
tailings
fluid of Figure 4, in a layer that is below the water layer capping the
tailings. The
bubbles then rise towards the surface of the tailings pond and come into
contact with
several hydrocarbon-containing particles and droplets of solvent during the
rise. As
the gas bubbles rise, droplets of solvent, as well as clay particles and
residual bitumen
onto which light hydrocarbons have adhered are extracted to the gas bubbles.
As the
gas bubbles rise towards the surface of the tailings pond, the gas bubbles
become
partially saturated with light hydrocarbons. In some scenarios where the
concentration of light hydrocarbons in the gas bubble reaches a certain level,
particles
of residual bitumen and/or clay particles can start forming aggregates with
the gas
bubbles. Floating hydrocarbon aggregates that float at the surface of the
tailings pond
can then be obtained. These floating hydrocarbon aggregates can increase in
size as
more and more gas bubbles are released into the bottom and/or middle layers of
the
tailings fluid, and as the light hydrocarbons are extracted from the bottom
and/or
middle layers.
Potential impact of gas bubbling
[145] In some scenarios, the tailings pond can temporarily lose its clear
water cap
during gas bubbling, and mitigating measures can be implemented. For example,
floating booms and/or silt curtains (also referred to as turbidity curtains)
can be used
as flexible sediment or aggregate control barriers. Such aggregate control
barrier can
prevent the spread of the floating organic materials throughout the tailings
pond or
prevent the spread of floating organic materials to specific portions of the
tailings pond
(e.g., close to the shore). The aggregate control barrier can be made of
permeable or
non-permeable material. The aggregate control barrier can be suspended
vertically
CA 3048272 2019-06-28
25
in the tailings pond with a flotation material enclosed in a top pocket or
region thereof,
and a ballast material (e.g., a ballast chain) enclosed in a lower pocket or
region
thereof. In some scenarios, the water cap returns to its clear (i.e., low
turbidity) state
within days after stopping gas bubbling.
[146] In some scenarios, the gas bubbling can generate increased volatile
organic
compound emission and/or increased undesirable odors in the vicinity of the
tailings
pond. Mitigating measures can be implemented, for example by intercepting the
gas
phase at the surface of the tailings pond. In some implementations, a
catalytic
converter or combustion chamber can be used to remove the volatile organic
compounds. In other implementations, light hydrocarbons can be recovered
through
condensation.
[147] In some scenarios, bitumen can build up at the surface of the tailings
pond as
a result of gas bubbling. Such build-up may require being removed or skimmed
from
the tailings pond as gas bubbling is still ongoing.
Design and placement of gas bubbler assembly
[148] The gas bubbler assembly that can be used to implement the techniques of
the
present description can be similar to the gas bubbler assemblies used to keep
water
bodies ice-free, or to aerate sludge in municipal waste water treatment
plants. In some
implementations, the gas bubbler assembly includes at least one gas bubbles
generating unit. For example, the at least one gas bubbles generating unit can
include
is a diffused aeration system including a plurality of air diffusers (or air
spargers or air
bubblers). Compressed air can be pumped from a shore-mounted compressor and
pushed through submerged lines to a diffuser located in a bottom or middle
layer of
the tailings pond. The air diffusers can then continuously release bubbles of
any type,
such as coarse bubbles, fine bubbles or micro-bubbles that rise to the
surface,
carrying with them large volumes of water from the bottom and/or middle layer,
as
well as extracting a portion of the residual light hydrocarbons and residual
bitumen
present in the tailings. As used herein, the terms "fine bubbles", "coarse
bubbles" and
"micro-bubbles" refer to bubbles having a diameter between about 1 mm and
about 5
CA 3048272 2019-06-28
26
mm (fine bubbles), a diameter of at least 5 mm, or preferably between about 5
mm
and about 50 mm (coarse bubbles), and a diameter smaller than about 1 mm
(micro-
bubbles), respectively.
[149] Now referring to Figure 7, a schematic top plan view of a tailings pond
42 is
shown, in which several air diffusers 68 are located. The air diffusers 68 are
spaced
apart from one another and linked via a pipe 72 that also connects the air
diffusers
68 to a compressor 70 that compresses air. In the implementation shown on the
Figure, several compressors 70 are each connected to a plurality of air
diffusers 68
via a pipe 72. In some implementations, each air diffuser assembly includes at
least
one compressor, at least one pipe and at least one air diffuser. It should be
understood that other configurations can be used. For example, the air
diffusers can
be spaced apart further in the tailings pond and the total number of air
diffusers can
be lower. Similarly, the air diffusers can be provided closer to one another,
and their
number can be increased. An aggregate barrier 71 can be provided in the
tailings
pond 42, for example to surround the area where the air diffusers 68 are
provided. In
some scenarios, the aggregate barrier 71 acts as a barrier between a central
area of
the tailings pond 42 and a shore region of the tailings pond. In the
embodiment shown,
the gas bubbler assembly is partially located within the tailings pond and
below the
water layer ¨ the compressors 70 are located outside the tailings pond to have
direct
access to air while the air diffusers 68 are located within the tailings pond
and below
the water layer. The pipes connect the compressors 70 to the air diffusers and
therefore run from the location of the compressors 70 to within the tailings
pond and
below the water layer, where the air diffusers 68 are located.
[150] In some implementations, the air diffusers can be selected from the
group
consisting of fine bubble diffusers, coarse bubble diffusers or intermediate
bubble
diffusers. For example. The fine bubble diffuser can generate bubbles having a
diameter ranging from about 0-3 mm. The intermediate bubble diffuser can
generate
bubbles having a diameter ranging from 3-5 mm. The coarse bubble diffuser can
generate bubbles having a diameter ranging from 5-50 mm. In some
implementations,
holes can be provided in the pipes to generate air bubbles without having to
provide
CA 3048272 2019-06-28
27
air diffusers. For example, holes can be provided at the end of a pipe, where
all the
air remaining in the pipe can be expelled in the tailings pond. In some
implementations, at least 20 m3, or between 20 m3 and 50 m3, or at least 50 m3
of air
per m3 of tailings material is diffused in the tailings pond. For example, the
amount of
air added can depend on the amount of treatment that may be required to clean
the
tailings stream.
Further processing of the treated tailings
[151] After having removed the light hydrocarbons or residual light organic
materials
from the tailings pond, the treated tailings thereby obtained (e.g., the
treated froth
treatment tailings 47) can be further processed to immobilize remaining CoCs
and to
flocculate remaining solids before dewatering the flocculated material. The
long-term
result of further processing and dewatering the treated tailings 47 tailings
can be a
permanent aquatic storage structure (PASS) that includes a water cap suitable
for
supporting aquatic life and recreational activities.
[152] Techniques are described to facilitate the deposition of treated
tailings at a
deposition site that over time becomes the PASS. In some implementations, the
solids separated from water during the dewatering of the treated tailings do
not need
to be relocated, e.g., from a drying area, as can be the case for other known
techniques for dewatering tailings. Rather, the solids remain in place and
form the
basis of a sedimentary layer of solids at the bottom of the PASS. Previous
techniques
for processing tailings are known to use polymer flocculation for dewatering.
However, the PASS technique additionally provides for processing the tailings
to
provide chemical immobilization of remaining CoCs that would otherwise remain
in or
transfer into the water, such that the water layer that inherently forms over
the solid,
sedimentary layer has CoCs removed allowing for the water cap to be of such a
quality it can support aquatic life.
[153] Although the size of a PASS can vary, in some implementations the PASS
can
contain a volume of 100,000,000 to 300,000,000 cubic metres and can be
approximately 100 metres deep at its greatest depth. With a PASS of this
scale,
CA 3048272 2019-06-28
28
flocculated material from the treated thick fine tailings can be directly
deposited onto
a sub-aerial deposition area that is proximate and/or forms part of the PASS
footprint.
Within a relatively short period of time following closure of a mine that is
reclamation
of the tailings is complete. That is, the solids feeding treated thick fine
tailings into the
PASS, e.g., 10 years, are contained in the base of the PASS and CoCs are
immobilized within the solid layer. The water cap is of a quality to support
aquatic life
and/or recreational activities.
[154] For example, in the context of oil sands mature fine tailings (MFT)
(such as the
treated FTMFT stream 47) that can include CoCs such as dissolved metals,
metalloids and/or non-metals, naphthenic acids, Acid Rock Drainage potential
and
Naturally Occurring Radioactive Materials, the chemical immobilization can
include
the addition of compounds enabling the insolubilization of the metals,
metalloids
and/or non-metals, as well as naphthenic acids, in addition to chemical
bridging of
bitumen droplets with suspended clays. The MFT can also be subjected to
flocculation, which can include the addition of a flocculating agent solution
followed
by pipeline conditioning. In some scenarios, the flocculation includes polymer
flocculation, and the flocculating agent includes a polymer flocculant. The
MFT that
has been subjected to immobilization and flocculation can then be dewatered.
The
dewatering can be performed by supplying the flocculated tailings material to
a
dewatering device and/or a sub-aerial deposition site. While MFT derived from
oil
sands extraction operations will be discussed and referred to in herein, it
should be
noted that various other contaminant-containing tailings and slurry streams
can be
treated using techniques described herein.
[155] It should be noted that the term "constituents" in the expression
"constituents-
of-concern" can be considered to include or correspond to substances that are
considered as "contaminants" by certain institutions, regulatory bodies, or
other
organizations, which can vary by jurisdiction and by evaluation criteria. n
some
scenarios, the tailings can first subjected to chemical immobilization,
followed by
flocculation, and then dewatering to produce a solids-enriched tailings
material in
which CoCs are immobilized. CoCs can sometimes be referred to as contaminants
in
CA 3048272 2019-06-28
29
the sense that the presence of certain constituents can be undesirable for
various
reasons at certain concentrations, within certain matrices, and/or in certain
chemical
forms.
[156] In some implementations, subjecting the tailings to chemical
immobilization and
flocculation facilitates production of a reclamation-ready material, which can
enable
disposing of the material as part of a permanent aquatic storage structure
(PASS).
Chemical immobilization
[157] In some implementations, the tailings can be treated with an
immobilization
chemical, which can include multivalent cations (e.g., trivalent or divalent).
The
multivalent cation can be added as part of an inorganic salt. The multivalent
salts can
be added to the tailings pre-dissolved in an aqueous solution, which can be
acidic or
neutral for example. Various multivalent inorganic salts can be used as
immobilization
chemicals. For example, aluminum sulphate (e.g., in acid solution which can be
sulfuric acid), aluminum potassium sulphate, iron sulphate, or chloride or
hydrated
calcium sulphate (gypsum) can be used for chemical immobilization of certain
CoCs.
For example, the trivalent cation Fe3+ can be added as part of iron (III)
sulphate
Fe2(SO4)3. Addition of ferric sulphate to the thick fine tailings can provide
certain
advantages, such as lower potential H25 emissions.
[158] The multivalent cation added to tailings can perform various functions.
One
function is that the multivalent cation can form a cation bridge between
negatively
charged bitumen droplets and negatively charged clay particles in the
tailings. This
bitumen droplet bridging can help immobilize the bitumen within the solids-
enriched
material that is formed after dewatering of the tailings. Chemical bridging of
bitumen
droplets with clays can decrease the potential for gas bubbles to adsorb onto
bitumen
and migrate out of the solids-enriched material; or chemical bridging of
bitumen
droplets with clays can increase the density and viscosity of the bitumen
droplet and
prevent upward migration in the deposit through buoyancy effects as the
deposit
densifies. Thus, the bitumen can remain immobilized within the solid material
and
thus inhibiting its migration into adjacent water regions.
CA 3048272 2019-06-28
30
[159] Another function of the multivalent inorganic salt is to insolubilize
certain CoCs
present in the tailings. For instance, surfactants, metals, non-metals,
metalloids and
other compounds can be present in soluble form in the water of the tailings
material.
In tailings derived from oil sands, surfactants such as naphthenic acids can
be
considered CoCs in terms of water toxicity. In addition, compounds such as
selenium
and arsenic can also be present and subject to certain regulatory
requirements. The
addition of the multivalent inorganic salt enables such dissolved CoCs to be
precipitated and to remain insolubilized so that the CoCs cannot re-
solubilize.
Insolubilization decreases the risk of the CoCs migrating out of the solid
material or
entering the water column.
[160] In some implementations, chemical immobilization is performed with
addition of
a coagulant that destabilizes particles in the tailings through double-layer
compression and modifies the pore water chemistry. In this sense, the
immobilization
chemical can include or be a coagulant for coagulating CoCs from the tailings
to form
coagulated CoCs. The coagulant can include a multivalent inorganic salt as
described
above and can include other various conventional coagulant species. Chemical
immobilization by addition of the coagulant to the tailings can be performed
before,
during or after flocculation, although pre-addition can be a preferred mode of
operation in many cases.
[161] Certain chemicals referred to herein can be known as coagulants in the
field of
water treatment and can therefore can be referred to as "coagulants" in the
present
application. However, it should be noted that such chemicals are used herein
for the
purpose of immobilization in PASS techniques rather than mere coagulation as
would
be understood in the water treatment industry, for example. In this sense, the
terms
"coagulant" and "immobilization chemical" can be used interchangeably as long
as
the coagulant performs the function of immobilization as described in the
present
application. It should still be noted that certain immobilization chemicals
described
herein can or cannot perform the function of coagulation. In some
implementations,
the so-called coagulant is added to the fine tailings in quantities superior
to what is
known in the water treatment industry for coagulation, e.g., superior to 350
ppm,
CA 3048272 2019-06-28
31
which is used for purpose of mere coagulation rather than immobilization. It
is noted
that in many cases the immobilization chemical that is added will in effect
cause some
or substantial coagulation. It is also noted that immobilization chemicals
that generally
do not cause coagulation can be used in conjunction with a separate coagulant
chemical that provides coagulation effects.
Flocculation
[162] A flocculating agent can be added to the tailings in order to flocculate
suspended solids and facilitate separation of the water from the flocculated
solids.
The flocculating agent can be selected for the given type of tailings to be
treated and
also based on other criteria. In the case of oil sands MET (such as MTMFT),
the
flocculating agent can be a medium charge (e.g., 30%) high molecular weight
anionic
polymer. The flocculating agent can be a polyacrylamide-based polymer, such as
a
polyacrylamide-polyacrylate co-polymer. The flocculating agent can have
various
structural and functional features, such as a branched structure, shear-
resilience,
water-release responsiveness to fast-slow mixing, and so on.
[163] It should be noted that flocculating agent is not limited to a medium
charge, as
altering the pH can influence the charge requirements. In some
implementations, the
flocculating agent charge is selected in accordance with pH.
[164] In some implementations, the overall flocculation and dewatering
operations
can include various techniques described in Canadian patent application No.
2,701,317; Canadian patent application No. 2,820,259; Canadian patent
application
No. 2,820,324; Canadian patent application No. 2,820,660; Canadian patent
application No. 2,820,252; Canadian patent application No. 2,820,267; Canadian
patent application No. 2,772,053; and/or Canadian patent application No.
2,705,055.
Such techniques¨including those related to flocculant selection; rapid
dispersion;
pipeline flocculation and water-release condoning; Camp Number-based design
and
operation; injector design and operation; sub-aerial deposition and handling;
pre-
shearing; pre-thinning; and pre-screening¨can be used or adapted for use with
techniques described herein related to chemical immobilization, flocculation
and
CA 3048272 2019-06-28
32
dewatering. The above documents are incorporated herein by reference. It
should
also be noted that various techniques described in such documents can be
adapted
when included with techniques described in the present application, such as
chemical
immobilization and coagulation as well as post-flocculation handling,
discharging and
management.
[165] In some implementations, the flocculating agent is added as part of an
aqueous
solution. Alternatively, the flocculating agent can be added as a powder, a
dispersion,
an emulsion, or an inverse emulsion. Introducing the flocculating agent as
part of a
liquid stream can facilitate rapid dispersion and mixing of the flocculant
into the
tailings.
[166] In some implementations, the flocculating agent can be injected into a
pre-
treated tailings fluid using a flocculating agent injector. For example,
static injectors
and/or dynamic injectors can be used to perform flocculant addition. The
injection can
be performed in-line, that is, into the pipeline for example. A length of the
pipeline
downstream of the flocculant injection point can be dedicated to dispersion of
the
flocculating agent into the pre-treated thick fine tailings, thereby producing
a tailings
fluid that is ready for conditioning and eventual dewatering.
[167] As mentioned further above, the incoming pre-treated tailings fluid that
has
been subjected to coagulation can arrive at the flocculant injector with
certain pH,
yield stress, and flow regime characteristics that facilitate flocculant
dispersion, mixing
and reaction with suspended solids.
[168] Immediately after flocculant injection (e.g., via a co-annular injector
where
flocculant inlets are spaced away from the pipe side wall and are distributed
around
an annular ring through which the pre-treated tailings flow), there can be a
dispersion
pipe section that receives the flocculating material and imparts pipe shear
energy to
the material. The dispersion pipe length as well as flocculating agent dosage
can be
provided based on various factors, which can include the density and/or clay
content
of the thick fine tailings as well as the flocculant injector design. In some
scenarios,
for a given injector design and density of the thick fine tailings, optimum
ranges of
CA 3048272 2019-06-28
33
flocculating agent dosage and dispersion pipe length can be determined,
particularly
when the target pH, yield stress, and flow regime characteristics have been
provided.
More regarding process modelling will be discussed in further detail in the
experimentation section below.
Dewatering
[169] Various dewatering techniques described in several Canadian patent
applications can be used in the context of the techniques described herein. It
should
be noted that the overall process can include several dewatering steps, which
will be
discussed in greater detail in relation to Figure 6, for example. In general,
dewatering
can be done by a solid-liquid separator (SLS) or by sub-aerial
deposition/discharge.
A combination of SLS and sub-aerial dewatering can also be performed.
[170] Various types of SLS's can be used. For example, belt filters and/or
thickeners
can be used to separate a solids-depleted water stream from a solids-enriched
tailings material, both of which can be subjected to further processing after
dewatering.
[171] In the case of dewatering by sub-aerial deposition, various dewatering
mechanisms can be at work depending on the deposition and post-deposition
handling methods that are used. For instance, thin lift deposition can promote
release
water flowing away from the deposited material followed by dewatering by
freeze-
thaw, evaporation, and permeation mechanisms. For deposition that is performed
to
promote the formation of a much thicker lower stratum of treated fine tailings
with an
upper water cap, the lower stratum can dewater with consolidation as a
significant
dewatering mechanism.
Characteristics of PASS landform
[172] In some implementations, as mentioned above, a permanent aquatic storage
structure (PASS) can be built via in situ and/or ex situ dewatering of
tailings that has
been subjected to chemical immobilization and flocculation. A summary of some
characteristics of the PASS landform is provided below.
CA 3048272 2019-06-28
34
[173] The containment structure of the PASS can be a former mine pit, which
can
include various in-pit structural features such as benches and in-pit dykes.
After
mining is complete, preparation of in-pit structures and landforms (e.g.,
dykes, dumps,
temporary dams, pit walls) can be undertaken. Placement of the treated fine
tailings
can then begin. The treated fine tailings can be discharged in various ways at
different
stages of forming the PASS. The treated fine tailings can be discharged within
the pit
in accordance with tailings management and reclamation considerations. During
or
after placement of the treated fine tailings, additional landforms, surface
water inlets
and outlets, and operational infrastructure can be constructed as part of the
overall
PASS system.
[174] The PASS can be seen as a type of end pit lake ¨ but how it is formed
and its
target characteristics are different than a conventional end pit lake. For
example, the
discharged fine tailings are pre-treated before depositing into the landform
that will
become the end pit lake, to enhance dewatering and stability of the landform.
Conventional end pit lakes are formed by placing tailings into the mine pit
(i.e., the
landform), capping with water, and treating the water within the landform. In
an oil
sands application, a conventional end pit lake directly deposits untreated MFT
into
the landform. In contrast, the PASS is formed from pre-treated material such
that the
MFT is dewatered at deposition and the water released from the MFT is pre-
treated
to remove residual hydrocarbons (such as light hydrocarbons by bubbling in the
tailings pond) and chemically immobilize CoCs in the solids layer formed at
the base
of the PASS. Thus the PASS has several advantages over conventional end pit
lakes,
such as more consistent immobilization characteristics throughout the sediment
layer,
accelerated dewatering, and mitigation of long-term risks related to CoCs in
the
tailings.
[175] In a PASS, the CoCs are immobilized prior to deposition in the landform.
Fresh
water dilution can be used in the aquatic reclamation process, in addition to
the
chemical immobilization of CoCs in the sedimentary layer. Note that fresh
water
dilution, meaning dilution of the already present pre-treated water cap, is
different
than relying on a fresh water cap to overlay fluid fine tails that were
deposited
CA 3048272 2019-06-28
35
untreated into the landform (i.e., as in a conventional end pit lake). The
PASS in a
reclaimed state will have no persistent turbidity, no (or negligible) bitumen
in the water
cap and toxicity and metals below guidelines required to support aquatic life.
By
contrast, a conventional end pit lake uses a fresh water cap and microbial
activity as
the aquatic reclamation process, and steps are not taken specifically to
remove
bitumen from water released from the fine tailings. A conventional end pit
lake will
have low persistent turbidity.
Process implementations
[176] Referring to Figure 6, an implementation of a process for
immobilization,
flocculation and dewatering of a treated FTMFT stream 47 is shown. Figure 6
illustrates an ex situ process, wherein the dewatering includes supplying a
flocculated
tailings material to a solid-liquid separator (SLS) to obtain a depositable
tailings
material that can be deposited onto a dedicated disposal area. It should be
understood the process shown on Figure 6 is not limiting and that other
configurations
can be implemented. For example, an in situ process can be used, where the
dewatering includes directly depositing a flocculated tailings material onto a
dedicated
disposal area and optionally forming a permanent aquatic storage structure
(PASS).
[177] An immobilization chemical 124 is added to the treated FTMFT stream 47
to
produce a pre-immobilized tailings stream 126. The pre-immobilized tailings
stream
126 is then combined with a flocculating agent 128 (e.g., a polymer
flocculant), which
can be added in-line via a co-annular injector. The flocculating agent 128 can
be
added so as to rapidly disperse into the tailings, forming a flocculating
tailings material
130. The flocculating tailings material 130 can then be subjected to shear
conditioning
in order to develop a flocculated material 132 suitable for dewatering.
[178] Still referring to Figure 6, the flocculated material 132 can be
supplied to an SLS
156 for the main dewatering step. The SLS 156 can be various types of
separators.
The SLS 156 produces a water stream 158 and a solids-enriched stream 160. In
some
implementations, the immobilization chemical can be added upstream of the SLS
156,
as stream 124 for example. In other implementations, a downstream
immobilization
CA 3048272 2019-06-28
36
chemical stream 162 can be added into the solids-enriched stream 160, to
produce a
depositable tailings material 164 that can be deposited into a sub-aerial
dedicated
disposable area (DDA) 136. It should also be noted that the immobilization
chemical
can be added at both upstream and downstream points (e.g., streams 124 and
162).
[179] In the scenario illustrated in Figure 6, the DDA 136 can be managed such
that
over time a PASS 138 is formed. Due to the upstream separation of water 158 in
the
SLS 156, the water cap 142 of the PASS in the ex situ dewatering scenario can
be
thinner than that of in situ scenarios that are described below. Indeed, in
the ex situ
scenario, a portion of the release water, which can be the primary source of
water for
the water cap 142, is withdrawn from the solid-liquid separator as recycle
water 158,
thereby reducing the water level of the water cap 142 in comparison to the in
situ
scenarios. Depending on a desired water cap depth, water from other sources
can be
added to the water cap in the ex situ implementation if there is insufficient
water from
the remaining tailings pore water.
[180] In other implementations not shown in the Figures, the flocculating
tailings
material 130 is subjected to pipeline conditioning, which can be the only
conditioning
that causes the flocculated material 132 to attain a state in which release
water readily
separates and flows away from the flocs (i.e., the solid/liquid separator of
Figure 6
can be omitted in some implementations). Alternatively, other shear mechanisms
can
be provided. The flocculated material 132 can then be dewatered. The
dewatering
can include depositing the flocculated material 132 directly onto the DDA 136,
which
can be a beach or built using earthwork techniques. Each DDA 136 can have a
deposition region that has a sloped base to facilitate release water flowing
away from
the deposited material and promote such rapid separation of the release water
from
the flocs.
[181] Over time, the structure and operation of the DDA 136 can be managed
such
that a PASS 138 is formed. The PASS 138 includes containment structures 140
for
containing the material, a water cap 142, and a solids-rich stratum 144 below
a water
cap. During formation of the PASS 138, the water cap 142 results from the
dewatering
of the treated material. The release water separating from the flocs can be
the primary
CA 3048272 2019-06-28
37
source of water for the water cap 142 such that the quality of the water in
the water
cap is directly related to the immobilization of CoCs. It is also possible to
add fresh
water 137 or another source of water into the PASS as it is forming such that
the
water cap includes water from sources other than the pore water of the
tailings. The
solids-rich stratum includes flocculated solids as well as the immobilized
CoCs, which
can include bitumen-clay complexes, insolubilized surfactants (e.g.,
naphthenic
acids), insolubilized metals (e.g., arsenic and selenium) and thus inhibits
migration of
the CoCs into the water cap or water column.
[182] Once the PASS 138 is substantially formed, an outlet water stream 139
can be
withdrawn from the PASS as fresh water 137 is added, so as to create a flow-
through
within the water cap 142, to maintain the water level and/or gradually reduce
certain
CoC levels to facilitate supporting freshwater plants and/or phytoplankton. In
some
implementations, the PASS 138 can be formed by expelling treated tailings
therein
for a period of time (e.g., 20 years) in order to fill the PASS to a desired
level. During
this formation period, the water cap 142 can be substantially composed of
tailings
pore water that has separated out, as well as precipitation and optionally
some other
water sources that can be used to account for evaporation. Then, after the
formation
period (e.g., 20 years), water flow-through is implemented. The water flow-
through
can include connecting the PASS 138 with existing waterways. The water flow-
through provides certain inlet and outlet flows of water into and out from the
water
cap, and gradually reduces salt levels in the water cap. The water flow-
through can
be provided such that the water cap has a certain salt content below a
threshold in a
predetermined period of time (e.g., below a desired value within 10 years
after
initiating the flow-through), and salt levels can be monitored in the water
cap, the inlet
flow and the outlet flow.
[183] The recycle water stream 139 can also be withdrawn from the PASS for
recycling purposes. In addition, recycle water 139 can be withdrawn from the
water
cap 142 to be supplied to various processing units, e.g., as polymer solution
make-
up water 150 and water 152 for use in extraction operations 154.
CA 3048272 2019-06-28
38
[184] Experimentation and calculations regarding chemical immobilization
compounds, flocculation and other process parameters related to treating and
dewatering tailings can be found in Canadian patent applications Nos.
2,921,835 and
2,958,873.
Gravity aeration
[185] Now referring to Figure 10, in some implementations, a process is
provided for
treating fine tailings 74 generated from an oil sands extraction operation,
wherein the
fine tailings 74 are aerated prior to being introduced into a tailings pond
for settling.
The fine tailings 74 are flocculant-free and include residual hydrocarbons.
The tailings
stream 74 are aerated in a gravity aerator 76, to obtain aerated fine tailings
78 that
include the residual hydrocarbons and air bubbles. The aerated fine tailings
78 can
then be deposited in a settling area such as a tailings pond 80 to be settled.
In some
scenarios, the settling of the aerated fine tailings 78 enable the residual
hydrocarbons
to rise to a surface layer of the tailings pond 80 and form floating
hydrocarbon
aggregates that can be recovered as recovered hydrocarbons 82 and treated fine
tailings 84 that are free of at least a portion of the residual hydrocarbons.
Recycle
water 86 can also be recovered from the tailings pond 80. It should be
understood
that the term "flocculant-free" refers to the tailings stream being subjected
to aeration
prior to introducing a flocculating agent, or prior to a flocculation step.
[186] It should be understood that by "free of at least a portion of the
residual
hydrocarbons", it is meant that the concentration of residual hydrocarbons in
the
treated fine tailings 84 is lower than the concentration of residual
hydrocarbons in the
fine tailings 74. For example, the concentration of residual hydrocarbons in
the treated
fine tailings 84 can be of about 80% or less, or about 70% or less, or about
60% or
less, or about 50% or less, or about 40% or less, or about 30% or less, or
about 20%
or less, or about 10% or less, or about 5% or less, or about 1% or less than
the
concentration of residual hydrocarbons in the fine tailings 74. The reduction
in
residual hydrocarbon concentration can depend on various operational
parameters,
such as degree of aeration, temperature, type of residual hydrocarbons, type
of fine
tailings stream etc.
CA 3048272 2019-06-28
39
[187] It should be understood that the term "gravity aerator", as used herein,
refers to
aerators that utilize the potential energy of water to be aerated (e.g., a
tailings stream)
to create interfaces for gas transfer from surrounding air into the water to
be aerated.
For example, the splashing of the water typically creates turbulence and water
droplets that can allow for air to be introduced into the water. It should
also be
understood that the "gravity aerator" excludes spray aerators (e.g., orifices
or nozzles
to discharge water), diffused air aerators (e.g., jet aerator, aspirating
aerators) and
mechanical aerators (e.g., vertical or horizontal shaft aerators).
[188] Non-limiting examples of gravity aerators include cascade aerators,
inclined
apron aerators, slat tray aerators and gravel bed aerators. The gravity
aerator
preferably includes a cascade aerator. The cascade aerator can have various
configurations. For example, the cascade aerator can include at least one of a
simple
weir, a weir with splashboard, a corrugated sheet, a corrugated sheet with
holes and
a lattice configuration. In some implementations, the gravity aerator consists
of a
cascade aerator.
[189] Now referring to Figure 11A, a non-limiting example of a cascade aerator
77 is
shown. The tailings stream 74 is provided to an elevated section of the
cascade
aerator 77 and the tailings stream falls down the steps 88 under the effect of
gravity.
Upon exiting the cascade aerator 77 via a lower section of the aerator, the
tailings 74
become oxygenated tailings 90. In this particular example, the cascade aerator
77
includes a plurality of steps and does not include overflow weirs. The cascade
aerator
77 is provided at an inclination angle a that can vary between about 50 and
500
.
[190] Now referring to Figure 11B, another non-limiting example of a cascade
aerator
77' is shown. Compared to the embodiment of Figure 11A, the cascade aerator
77'
includes several overflow weirs 89 at each of the steps 88. Each overflow weir
enables a corresponding receiving gutter 87 that receives liquid until the
liquid
overflows down to the next receiving gutter 87.
[191] Now referring to Figure 8A, froth treatment tailings 40 are provided to
a cascade
aerator 77 to introduce air bubbles therein. The froth treatment tailings 40
cascades
CA 3048272 2019-06-28
40
down the cascade aerator 77 under the effect of gravity as cascading flow 85,
to
obtain an oxygenated flow 90. The oxygenated flow 90 is then deposited into a
froth
treatment tailings pond 42 for settling, to form a top water region 43 and a
bottom
froth treatment mature fine tailings region 44 in the tailings pond 42. Gas
bubbles 45
that are generated in the cascade aerator 77 enable at least a portion of the
light
hydrocarbons and residual bitumen present in the froth treatment mature fine
tailings
40 to migrate to a top water layer 43. The gas bubbles 45 stay at the surface
of the
tailings pond 42 and the extracted light hydrocarbons and residual bitumen can
form
floating hydrocarbon aggregates 46 and treated froth treatment tailings 47
that can
be substantially free of light hydrocarbons and residual bitumen. The
hydrocarbon
aggregates 46 can be recovered as recovered hydrocarbons 49 and be subjected
to
a hydrocarbon recovery process 50. The treated froth treatment tailings 47 can
then
be subjected to further treatment and dewatering. It should be understood that
while
one particular configuration of cascade aerator 77 is shown on Figure 8A,
other types
of cascade aerators, and more generally other types of gravity aerators can be
used.
[192] Now referring to Figure 8B, thin fine tailings 53 are provided to a
cascade
aerator 77 to introduce air bubbles therein. The thin fine tailings stream 53
cascades
down the cascade aerator 77 under the effect of gravity as cascading flow 85,
to
obtain an oxygenated flow 90. The oxygenated flow 90 is then deposited into a
tailings
pond 54 for settling. After settling, the thin fine tailings 53 can produce a
top water
layer 55 and mature fine tailings 56. Gas bubbles 45' that are generated in
the
cascade aerator 77 enable floating organics 46' to migrate to the surface
layer. The
floating organics 46' can then be recovered as recovered hydrocarbons 49' and
subjected to a hydrocarbon recovery process 50'. A light organic-free mature
fine
tailings stream 47' can be extracted from the tailings pond 54 and subjected
to further
treatment and dewatering.
[193] Now referring to Figures 9A and 9B, a cascade aerator 77 can be provided
between two settling areas. In other words, the cascade aerator 77 can receive
an
inlet stream (e.g., a fine tailings stream) directly from a first tailings
pond. The inlet
stream is then oxygenated in the cascade aerator 77 under the effect of
gravity, and
CA 3048272 2019-06-28
41
the oxygenated stream obtained can then be provided to a second tailings pond
for
further settling and for separating out residual hydrocarbons.
[194] Referring now to Figure 9A, froth treatment tailings 40 are deposited in
a froth
treatment tailings pond 42 for settling, to form a top water region 43 and a
bottom
froth treatment mature fine tailings region 44 in the tailings pond 42 (with
optionally a
coarse layer 244 at the bottom of the tailings pond 42). The froth treatment
mature
fine tailings 44 can then be provided to a cascade aerator 77 to introduce air
bubbles
therein. The froth treatment mature fine tailings 44 cascades down the cascade
aerator 77 under the effect of gravity as cascading flow 85, to obtain an
oxygenated
flow 90. The oxygenated flow 90 is then deposited into a further tailings pond
342 for
settling, to form a top water region 343 and a bottom froth treatment mature
fine
tailings region 344 (with optionally a coarse layer 444 at the bottom of the
tailings
pond 342) in the tailings pond 342. Gas bubbles 345 that are generated in the
cascade aerator 77 enable at least a portion of the light hydrocarbons and
residual
bitumen present in the froth treatment mature fine tailings 44 to migrate to a
top water
layer 343. The gas bubbles 345 stay at the surface of the tailings pond 342
and the
extracted light hydrocarbons and residual bitumen can form floating
hydrocarbon
aggregates 346 and treated froth treatment tailings 47 that can be
substantially free
of light hydrocarbons and residual bitumen. The hydrocarbon aggregates 346 can
be
recovered as recovered hydrocarbons 349 and be subjected to a hydrocarbon
recovery process 50. The treated froth treatment tailings 47 can then be
subjected to
further treatment and dewatering.
[195] Referring now to Figure 9B, thin fine tailings 53 are deposited into a
tailings
pond 54 for settling. After settling, the thin fine tailings 53 can produce a
top water
layer 55 and mature fine tailings 56 (with optionally a coarse layer 256 at
the bottom
of tailings pond 54). The mature fine tailings 56 can then be provided to a
cascade
aerator 77 to introduce air bubbles therein. The mature fine tailings 56
cascades down
the cascade aerator 77 under the effect of gravity as cascading flow 85, to
obtain an
oxygenated flow 90. The oxygenated flow 90 is then deposited into a further
tailings
pond 354 for settling, to form a top water region 355 and a bottom froth
treatment
CA 3048272 2019-06-28
42
mature fine tailings region 356 (with optionally a coarse layer 456 at the
bottom of the
tailings pond 356) in the tailings pond 356. Gas bubbles 345' that are
generated in
the cascade aerator 77 enable at least a portion of floating organics 346' to
migrate
to the surface layer 355. The floating organics 346' can then be recovered as
recovered hydrocarbons 349' and subjected to a hydrocarbon recovery process
50.
A light organic-free mature fine tailings stream 47' can be extracted from the
tailings
pond 354 and subjected to further treatment and dewatering.
[196] Now referring to Figure 12, the oxygenated flow 90 obtained from
cascading
flow 85 can be introduced into a tailings pond 42 in various ways. In some
implementations, the oxygenated flow 90 can simply be introduced into the
tailings
pond 42 at the time of exiting the cascade aerator, from a single general
location. The
oxygenated flow 90 and the air bubbles contained therein can then diffuse
overtime
into the tailings pond 42.
[197] In other implementations, the oxygenated flow 90 can be provided to an
oxygenated flow distribution system 92 to be transported and distributed 94 at
multiple
injection points of the tailings pond 42. The oxygenated flow distribution
system can
for example include a system of gutters or pipes collecting the oxygenated
flow 90
from a lower section of the cascade aerator and delivering the oxygenated flow
to
selected injection points. In some scenarios, this configuration can allow for
a more
uniform distribution of the air bubbles throughout the tailings pond 42.
CA 3048272 2019-06-28
