Note: Descriptions are shown in the official language in which they were submitted.
PILLARING OF CLAY-CONTAINING FINE TAILINGS FOR ENHANCED POST-
DEPOSITION DEWATERING AND CONSOLIDATION
TECHNICAL FIELD
[001] The present techniques relate to dewatering and consolidation of clay-
containing
fine tailings, and more particularly relate to the treatment of clay-
containing fine tailings to
encourage pillaring of clay platelets for enhancing the dewatering and
consolidation of the
treated tailings into a reclaimable landform.
BACKGROUND
[002] Post-deposition management of fluid fine tailings is an ongoing
challenge in oil
sands and mineral extraction industries, where large volumes of fluid fine
tailings are
generated.
[003] Conventionally, tailings are transported to a deposition site generally
referred to as
a "tailings pond" located close to the mining and extraction facilities to
facilitate pipeline
transportation, deposition and management of the tailings. Due to the scale of
operations,
tailings ponds can cover vast tracts of land. In accordance with some standing
regulations,
the land must be reclaimable after a certain period of time which can be a
complex
undertaking given the slow consolidation rates of fluid fine tailings.
[004] Certain methods have been proposed to improve and accelerate the
dewatering
and consolidation of fluid fine tailings, including mature fine tailings
(MFTs) which can be
recovered from oil sands tailings ponds or other sources. MFTs are formed in
the pond
over time and are often characterized as being high in clay content and having
relatively
slow consolidation rates. For example, MFTs can be co-deposited with sand to
encourage
strength development after the end of the deposition to produce consolidated
tailings. In
another example, flocculation of the MFTs has been proposed to aggregate fine
clays,
optionally co-currently with coagulation, thereby providing a rapid initial
dewatering.
[005] However, challenges remain to be overcome to accelerate post-deposition
consolidation of fluid fine tailings and facilitate terrestrial reclamation.
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Date Recue/Date Received 2023-05-11
SUMMARY
[006] The present techniques are directed to treatment of fine tailings
containing clay
platelets by pillaring to form a consolidated deposit that can be reclaimed as
a landform,
that is sufficiently geotechnically and geochemically stable in accordance
with a specific
land use,
[007] More particularly, there is provided a process for treating fine
tailings containing
clay platelets. The process includes treatment of the fine tailings to produce
treated tailings
comprising pillared layered solids. The treatment includes addition of a
pillaring agent
releasing trivalent cations and/or tetravalent cations that intercalate
between basal
surfaces of the clay platelets to form a thermally stable interlayer of
pillars, thereby
converting at least a portion of the clay platelets into pillared layered
solids. The process
further includes deposition of the treated tailings within a dedicated
deposition area to
produce a consolidated deposit by allowing separation of the water from solids
of the
treated tailings to form a pillared deposit comprising the pillared layered
solids; and
consolidation of the pillared deposit into the consolidated deposit over time,
the
consolidation comprising forming additional thermally stable interlayers of
pillars that grow
from the trivalent cations and/or tetravalent cations intercalated between the
basal
surfaces of the clay platelets.
[008] In some implementations, the treating of the fine tailings can include
adjusting a
pH of the fine tailings to a solubilizing pH encouraging diffusion of the
trivalent cations
and/or tetravalent cations between the basal surfaces of the clay platelets.
For example,
the solubilizing pH can be at most 5 or at least 9 in accordance with a nature
of the trivalent
cations and/or tetravalent cations.
[009] In some implementations, the treating of the fine tailings can include
adjusting a
zeta potential of the fine tailings to encourage diffusion of the trivalent
cations and/or
tetravalent cations between the basal surfaces of the clay platelets. For
example, the zeta
potential can be adjusted to at least ¨40 mV, -50 my, or -60 mV.
[010] In some implementations, the treating of the fine tailings can include
adjusting a
concentration of the pillaring agent to a pillaring concentration being at
most 0.06 wt%, at
most 0.08 wt%, at most 0.1 wt%, at most 0.3 wt%, at most 0.5 wt%, at most 0.7
wt%, at
most 0.9 wt%, at most 1.1 wt%, at most 1.3 wt%, at most 1.5 wt%, at most 1.7
wt%, at
most 1.9 wt%, or at most 2 wt% of the total solids content in the fine
tailings.
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Date Recue/Date Received 2022-02-28
[011] In some implementations of the process, the pillaring agent comprises an
exogenous source of silicon. For example, the pillaring agent can be hydraulic
cement,
activated pozzolan, activated silica fume, activated fumed silica, or a
combination thereof.
The pillaring agent can be added at a pH of at least 9, at least 10, at least
11, at least 12
or at least 13 in the treated tailings.
[012] In some implementations of the process, the pillaring agent can be an
acid
coagulant comprising at least one of an aluminum cation and a ferric cation.
For example,
the pillaring agent can include aluminum sulfate, ferric sulfate or a
combination thereof.
The pillaring agent can be added at a pH of at most 3, at most 4, at most 5,
or at most 6.
[013] In some implementations of the process, the treatment of the fine
tailings can
further includes flocculating the fine tailings by adding a flocculation agent
to form
flocculated tailings. For example, the pillaring agent can be added after the
flocculation
agent into the flocculated tailings, and optionally, the flocculation agent
can be an anionic
water-soluble polymer, such as a polyacrylamide, or a non-ionic polymer. In
another
example, the pillaring agent can be added before the flocculation agent to the
fine tailings,
and optionally the flocculation agent can be a non-ionic polymer, such as a
polyethylene
oxide polymer.
[014] In some implementations of the process, the pillaring agent can be a
flocculant
including pillaring moieties releasing the trivalent cations and/or
tetravalent cations for
intercalation between the clay platelets, and the treatment of the fine
tailings thereby
comprises the addition of the pillaring agent to flocculate the fine tailings
into flocculated
fine tailings and pillar the flocculated fine tailings for forming the treated
tailings. For
example, the flocculant can be a polyethylene oxide copolymer comprising
siloxane units.
[015] In some implementations of the process, the fine tailings can include
contaminants
of concern (CoCs) and the treatment further includes immobilizing the CoCs to
produce
the landform comprising the pillared layered solids and immobilized CoCs. For
example,
the immobilizing can be performed by addition of an immobilization agent that
is added
after the pillaring agent. Optionally, the immobilization agent can be an acid
coagulant
comprising at least one of aluminum cations and ferric cations, such as
aluminum sulfate,
ferric sulfate or a combination thereof. Further optionally, the acid
coagulant can be added
at an immobilizing concentration that is at most 5 meq/L, at most 10 meq/L, at
most 15
meq/L, or at most 20 meq/L of a pore water in the fine tailings.
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Date Recue/Date Received 2022-02-28
[016] In some implementations of the process, the fine tailings can include
contaminants
of concern (CoCs) and the pillaring agent can be an acid coagulant releasing
aluminum
and/or ferric cations performing both the pillaring of the clay platelets and
the immobilizing
of the CoCs to produce the landform comprising the pillared layered solids and
immobilized CoCs. Optionally, the acid coagulant can be added at a
concentration
between 20 and 40 meq/L of a pore water in the fine tailings.
[017] In some implementations, the addition of the pillaring agent can be
performed
under a turbulent micro-mixing regime to minimize formation of secondary
products from
the trivalent cations and/or tetravalent cations.
[018] In some implementations of the process, the treated tailings can include
at least
10, 20, 30, 40, 50, 60, 70 or 80 wt% of pillarable clay platelets initially
present in the fine
tailings being pillared into the pillared layered solids.
[019] In some implementations of the process, the consolidated deposit can
include at
least 50, 60, 70, 80 or 90 wt% of pillarable clay platelets initially present
in the fine tailings
being pillared into the pillared layered solids.
[020] In some implementations of the process, the deposition of the treated
tailings can
be performed until the pillared deposit reaches a target height. For example,
the deposition
of the treated tailings can be performed at a deposition rate of at most 20
meters per year.
Optionally, the target height can be between 20 m and 75 m.
[021] In some implementations of the process, the consolidated deposit can be
reclaimed as a landform once the consolidated deposit is geotechnically stable
after a
consolidation period for a given end use. For example, geotechnical stability
of the
consolidated deposit can be achieved by consolidation when the consolidated
deposit has
a shear strength greater than 15, 20, 25, 30 or 35 kPa. For example,
geotechnical stability
of the consolidated deposit can be achieved by consolidation when the
consolidated
deposit has a solids content of at least 50, 55, 60 or 65 wt%. Optionally, the
consolidation
period can be at most 50 years when the pillared deposit is initially at most
75-meter high.
[022] In some implementations of the process, the pillared deposit can have a
post-
deposition hydraulic conductivity greater than 10-9 m/s.
[023] In some implementations of the process, the dedicated deposition area
can be
below or above grade. The process can include capping the consolidated deposit
with a
layer of sand or coke to form a solid top cap. Optionally, the solid top cap
can have a
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Date Recue/Date Received 2022-02-28
thickness between 2 m and 5 m. The process can further include draining a top
layer of
the consolidated deposit for further dewatering of the top layer. The
consolidated deposit
can be reclaimed as a landform that comprises a dryland, or solid ground.
[024] In some implementations of the process, the dedicated deposition area
can be
below grade. Optionally, the dedicated deposition area can include a
containment
structure, such as a mine pit. The process can include capping the
consolidated deposit
with a layer of water to form a top water cap. The top water cap can include
at least a
portion of the water released from the treated tailings during the dewatering.
For example,
the consolidated deposit can be reclaimed as a landform that comprises a floor
or
sediment of a lake, or a wetland.
[025] In some implementations of the process, the fine tailings can have a
clay content
being at least 50, 60, 70, 80 or 90 wt% of a total solids content of the fine
tailings.
[026] In some implementations of the process, the fine tailings can be oil
sands fine
tailings.
[027] In some implementations of the process, the fine tailings can be mature
fine
tailings.
[028] In some implementations of the process, the fine tailings can be thin
fine tailings
[029] In some implementations of the process, the fine tailings can be thick
fine tailings.
[030] There is also provided a method for converting fine tailings containing
clay platelets
and contaminants of concern (CoCs) into a consolidated deposit. The method
includes
forming treated tailings by flocculating the fine tailings to form aggregates
of the clay
platelets; pillaring the clay platelets by intercalating trivalent cations
and/or tetravalent
cations between basal surfaces of the clay platelets to grow pillared layered
solids
comprising thermally stable interlayers of pillars between the clay platelets;
and
immobilizing the CoCs. The method further includes depositing the treated
tailings within
a dedicated deposition area to convert the treated tailings into the
consolidated deposit by
releasing water from the treated tailings pores to produce a pillared deposit
comprising
the pillared layered solids and immobilized CoCs; and consolidating the
pillared deposit
over a consolidation period to produce the consolidated deposit, the
consolidating
comprising forming additional pillared layered solids from the aggregates of
the clay
platelets.
Date Recue/Date Received 2022-02-28
[031] In some implementations, the pillaring of the clay platelets can be
performed at a
solubilizing pH encouraging diffusion of the trivalent cations and/or
tetravalent cations
between the basal surfaces of the clay platelets. For example, the
solubilizing pH can be
at most 5 or at least 9 in accordance with a nature of the trivalent cations
and/or tetravalent
cations.
[032] In some implementations, the flocculating can be performed to achieve a
zeta
potential of the aggregates encouraging diffusion of the trivalent cations
and/or tetravalent
cations between the basal surfaces of the clay platelets. For example, the
zeta potential
can be at least ¨40 mV, -50 my or -60 mV.
[033] In some implementations of the method, the trivalent cations can be at
least one
of aluminum cations and ferric cations, and the tetravalent cations are
silicon cations.
[034] In some implementations of the method, the flocculating can be performed
before
or after the pillaring via separate addition of a flocculation agent and a
pillaring agent to
the fine tailings.
[035] In some implementations, the addition of the pillaring agent can be
performed
under a turbulent micro-mixing regime to minimize formation of secondary
products from
the trivalent cations and/or tetravalent cations.
[036] In some implementations of the method, the pillaring agent can be added
at a
pillaring concentration being at most 0.06 wt%, at most 0.08 wt%, at most 0.1
wt%, at
most 0.3 wt%, at most 0.5 wt%, at most 0.7 wt%, at most 0.9 wt%, at most 1.1
wt%, at
most 1.3 wt%, at most 1.5 wt%, at most 1.7 wt%, at most 1.9 wt%, or at most 2
wt% of the
total solids content in the fine tailings.
[037] In some implementations of the method, the flocculation agent can be an
anionic
polymer. For example, the anionic polymer can be polyacrylamide (PAM).
[038] In some implementations of the method, the flocculation agent can be a
non-ionic
polymer. For example, the non-ionic polymer can be a polyethylene oxide
polymer.
[039] In some implementations of the method, the pillaring agent can be an
acid
coagulant releasing aluminum cations and/or ferric cations. The acid coagulant
can
include aluminum sulfate, ferric sulfate or a combination thereof. For
example, the pillaring
agent can be added at a pH of at most 3, at most 4, at most 5, or at most 6.
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Date Recue/Date Received 2022-02-28
[040] In some implementations of the method, the pillaring agent can be
hydraulic
cement, activated pozzolan, activated fumed silica, activated silica fume, or
any
combinations thereof.
[041] In some implementations of the method, the flocculating and pillaring
can be co-
currently performed via in-line addition of a flocculant to the fine tailings,
with the flocculant
comprising pillaring moieties releasing the trivalent and/or tetravalent
cations. The
flocculant can be a non-ionic polymer comprising pillaring moieties releasing
silicon
cations. For example, the flocculant can be a polyethylene oxide copolymer
comprising
siloxane units. For example, the flocculant can be added at a pH of at least
9, at least 10,
at least 11, at least 12 or at least 13 in the treated tailings.
[042] In some implementations of the method, immobilizing the CoCs can be
performed
via in-line addition of an immobilization agent, wherein the immobilization
agent is added
after the pillaring agent. For example, the immobilization agent can be an
acid coagulant
releasing aluminum and/or ferric cations, such as aluminum sulfate, ferric
sulfate or a
combination thereof. For example, the acid coagulant can be added at an
immobilizing
concentration that is at most 5 meq/L, at most 10 meq/L, at most 15 meq/L, or
at most 20
meq/L of a pore water in the tine tailings.
[043] In some implementations of the method, immobilizing the CoCs can be
performed
via in-line addition of the pillaring agent, wherein the trivalent and/or
tetravalent cations
released by the pillaring agent participate in both the pillaring of the clay
platelets and the
immobilizing of the CoCs. For example, the pillaring agent can be added at a
concentration
between 20 and 40 meq/L of a pore water in the fine tailings.
[044] In some implementations of the method, the treated tailings can include
at least
10, 20, 30, 40, 50, 60, 70 or 80 wt% of pillarable clay platelets initially
present in the fine
tailings being pillared into the pillared layered solids.
[045] In some implementations of the method, the consolidated deposit can
comprise at
least 50, 60, 70, 80 or 90 wt% of pillarable clay platelets initially present
in the fine tailings
being pillared into the pillared layered solids.
[046] In some implementations of the method, the method can include capping
the
consolidated deposit with a layer of sand or coke to form a top cap. The top
cap can have
a thickness between 2 m and 5 m.
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Date Recue/Date Received 2022-02-28
[047] In some implementations of the method, the method can include capping
the
consolidated deposit with a layer of water to form a top water cap. The top
water cap can
include at least a portion of the water released from the treated tailings
following
deposition.
[048] In some implementations of the method, the dedicated deposition area can
be
above grade.
[049] In some implementations of the method, the dedicated deposition area can
be
below grade. Optionally, the dedicated deposition area can include a
containment
structure. For example, the dedicated deposition area can be a mine pit.
[050] In some implementations of the method, the method can include reclaiming
the
consolidated deposit when the consolidated deposit is geotechnically and
geochemically
stable for a given land use after the consolidation period. For example,
geotechnical
stability of the consolidated deposit can be achieved by consolidation when
the
consolidated deposit has a shear strength greater than 15, 20, 25, 30 or 35
kPa. For
example, geotechnical stability of the consolidated deposit can be achieved by
consolidation when the consolidated deposit has a solids content of at least
50, 55, 60 or
65 wt%. Optionally, the consolidation period can be at most 50 years when the
pillared
deposit is initially at most 75-meter high.
[051] In some implementations of the method, the geotechnically and
geochemically
stable consolidated deposit can be reclaimed as a landform that is a floor of
a lake, a
wetland, or a dryland.
[052] In some implementations of the method, the fine tailings can have a clay
content
being at least 50, 60, 70, 80 or 90 wt% of a total solids content of the fine
tailings.
[053] In some implementations of the method, the fine tailings can be oil
sands fine
tailings.
[054] In some implementations of the method, the fine tailings can be mature
fine
tailings.
[055] In some implementations of the method, the fine tailings can be thin
fine tailings.
[056] In some implementations of the method, the fine tailings can be thick
fine tailings.
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Date Recue/Date Received 2022-02-28
[057] It should also be noted that various features, step and implementations
summarized above may be combined with other features, step and implementations
of the
described above or herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[058] Figure 1 is a schematic representation of the crystalline structure of
two adjacent
clay platelets of a 2:1 clay mineral and a cation interlayer, each clay
platelet comprising a
layer of cations in octahedral coordination and cations in tetrahedral
coordination.
[059] Figure 2 is a schematic representation of a pillared layered solid
including oxy-
hydroxide pillars being formed from intercalation of trivalent and/or
tetravalent cations in
clay aggregates from flocculated fluid fine tailings.
[060] Figure 3 is a schematic process flow diagram of treatment and deposition
of MTF
according to an embodiment of the present techniques.
[061] Figure 4 is a schematic process flow diagram of treatment and deposition
of MTF
according to another embodiment of the present techniques.
[062] Figure 5 is a schematic process flow diagram of treatment and deposition
of MTF
according to another embodiment of the present techniques.
[063] Figure 6 is a schematic process flow diagram of treatment and deposition
of MTF
according to another embodiment of the present techniques.
[064] Figure 7 is a graph of deposit elevation versus years after the start of
the deposition
and indicating the elevation at the end of deposition and the elevation when
the deposit is
sufficiently dewatered and consolidated for reclamation, for five different
tailings materials,
two of which being treated according to the present techniques (f/c and
pillared FFT_PEO
and f/c and pillared FFT_pozzolan) and the three remaining streams being
handled
according to conventional techniques (CT 3:1, c/f FFT, and untreated (FFT)).
FFT refers
to fluid fine tailings.
DETAILED DESCRIPTION
[065] The present techniques include treating clay-containing fine tailings to
form treated
tailings, and depositing the treated tailings to dewater and consolidate the
treated tailings
for supporting aquatic and terrestrial reclamation activities. The treatment
particularly
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Date Recue/Date Received 2022-02-28
allows for the conversion of clay platelets into pillared layered solids as
will be explained
in further detail below.
[066] The fine tailings that can be treated by the techniques described herein
include
clay-containing fine tailings, which can be oil sands fine tailings derived
from oil sands
extraction operations. Fine tailings that are notably suitable for treatment
using the pillaring
techniques include a high fines content, e.g., a fines fraction including clay
that is greater
than 60 wt%, 70 wt%, 80 wt%, 90 wt% of the solids content of the fine
tailings. For
example, the oil sands fine tailings can be thin fine tailings having a solids
content below
wt% or thick fine tailings having a solids content above 10 wt% and typically
in the
range of 20 wt% to 45 wt%. The thick fine tailings can be mature fine tailings
(MFT)
retrieved from a tailings pond. The fine tailings that can be treated include
solid
components, such as clays, that are pillarable. It is also noted that,
although the
abbreviation MFT is used herein, it should be understood that the fine
tailings
encompassed in the present description are not necessarily obtained from a
tailings pond
and can be any clay-containing fine tailings that are derived from a mining
operation.
[067] The treatment of the fine tailings is tailored to encourage formation of
heterostructures between clay platelets of the treated fine tailings. Such
heterostructures
can be referred to as pillars, and the resulting partially pillared clays can
be referred to as
pillared layered solids. The pillared layered solids are clay structures of
larger discrete
particle size and of higher porosity than those in untreated fine tailings.
The larger discrete
particle size and greater porosity advantageously enable quicker consolidation
of the
deposit to support reclamation activities.
Solids and clay
[068] The oil sands industry has adopted a convention with respect to mineral
particle
sizing. Mineral fractions with a particle diameter greater than 44 microns are
referred to
as "sand". Mineral fractions with a particle diameter less than 44 microns are
referred to
as "fines". The "clay" mineral fraction is usually characterized as having a
particle diameter
less than 2 microns.
[069] Clay or clay mineral is defined herein as a phyllosilicate comprising
silicate
tetrahedral and aluminum octahedral sheets arranged into platelets, referred
to as clay
platelets. Typically, clay platelets can include repetitive layers of one
tetrahedral sheet and
one octahedral sheet (1:1 structures), or one octahedral sheet sandwiched
between two
Date Recue/Date Received 2022-02-28
tetrahedral sheets (2:1 structures), with the repetitive layers being
chemically bonded to
one another (e.g., via secondary bonds such as hydrogen bonds). Additional
variable
amounts of iron, magnesium, alkali metals, and/or alkaline earth metals can be
further part
of crystalline structure of the clay platelets. Depending on the composition
of the
tetrahedral and octahedral sheets of the clay platelets, different atoms are
available at
basal surfaces of the platelets, which can change the surface chemistry of the
clay
platelets.
Pillaring
[070] Pillaring as described herein includes inserting vertically spaced,
thermally stable,
inorganic molecular compounds/moieties between external layers of adjacent
clay
platelets, so as to form multiple pillars generating a thermally stable
interlayer between
clay platelets. Each pillar is a heterostructure that is formed between basal
surfaces of two
clay platelets, and can include one or more of Fe, Al or Si atoms. Pillaring
can be
understood as intercalating inorganic moieties between clay platelets to
create a porous
structure having an increased interlamellar distance and an increased pore
volume. The
initial layer configuration is thus retained but further pillared and spaced
apart, and the
formed porous structure can be referred to as the pillared layered solid or
pillared
compound.
[071] Tailings treated according to the present techniques can be referred to
as treated
tailings including water and pillared layered solids. Advantageously, upon
deposition of
the treated tailings, the pillared layered solids can maintain an interlayer
spacing thereof
while releasing water from the treated tailings via pores of the pillared
layered solids. The
clay platelets within the pillared layered solids are thus propped apart
vertically (as in a
stack configuration) and the pillared layered solids do not collapse upon
removal of the
water by dewatering of the treated tailings. If the pillaring agent has an
immobilizing effect
with respect to contaminants of concern present in the fine tailings, or if a
separate
immobilization agent is added subsequently to the pillaring agent, the treated
tailings can
further include immobilized contaminants of concern (CoCs), as will be
described in further
detail below.
[072] In some implementations, the techniques include in-line addition of a
pillaring agent
to fine tailings to form thermally stable interlayers between clay platelets,
producing
treated tailings including the pillared layered solids. The treated tailings
are then subjected
to dewatering and consolidation.
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Date Recue/Date Received 2022-02-28
[073] The pillaring agent refers to an inorganic or organic compound having a
pillaring
effect, i.e., being able to intercalate atoms/moieties and serving as a pillar
seed/nuclei to
grow a pillar between external layers of clay platelets. Referring to Figure
1, the pillaring
agent can liberate at least one of a trivalent cation (M3+) and a tetravalent
cation (M4+) for
intercalation between clay platelets to serve as the pillar seed, e.g., a
hydroxy cation
(referred to in Figure 1 as M3+/M4+ hydroxy islands in interlayer). For
example, the pillaring
agent can release at least one of Al, Fe, and Si in ionic form. More
particularly, referring
to Figure 2, the intercalated trivalent (A13+ or Fe3+) and tetravalent (Si4+)
ions can further
react with oxygen to form solid heterostructures comprising oxyhydroxides
distributed in
interlayers between the clay platelets. The interlayers have lower
compressibility than
mere hydrated exchangeable cations while maintaining high permeability.
Pillaring allows
for creation of micropores and mesopores of controlled sizing between stacked
clay
platelets having a lamellar structure, thereby facilitating dewatering of the
clay-containing
tailings. In some implementations, the pillaring is performed via the in-line
addition of an
exogenous source of silicon to fine tailings. When referring to the Si element
from an
exogenous source, it is understood that the provided silicon is not initially
part of the clay
platelet itself or the original tailings material.
[074] Silicon in the clay platelets is available at the basal surfaces and
edges of the
platelets but is not to be considered as a pillaring agent or as having a
pillaring effect. It
should further be noted that pillars as encompassed herein are to be
distinguished from
hydrates, although pillars and hydrates can co-exist within the formed
interlayers.
[075] The present techniques thus include controlling the water chemistry of
the treated
fine tailings prior to deposition to facilitate their diffusion in a pore
water environment
between the clay platelets. The diffused pillaring ions act as pillar
seeds/nuclei (e.g., metal
hydroxy cations) and can then react with oxygen to form solid pillars growing
between clay
platelets of the fine tailings upon deposition and overtime. Controlling the
water chemistry
can include adjusting at least one of a concentration of the pillaring agent,
a pH of the pore
water and a zeta potential of treated fine tailings.
[076] The treated fine tailings formed according to the present techniques can
be
characterized by including at least 10, 20, 30, 40, 50, 60, 70, or 80 wt% of
the pillarable
clay from the fine tailings being pillared in the treated fine tailings, i.e.,
being stabilized as
a pillared layered solid.
Tailings flocculation
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Date Recue/Date Received 2022-02-28
[077] Flocculation of the tailings is used herein to facilitate formation of
the pillars
between clay platelets by bringing the clay platelets closer together into
aggregates, and
to further facilitate dewatering of the treated tailings upon deposition.
[078] It was noted that flocculation of the fine tailings into clay aggregates
can produce
flocculated tailings having a highly negative zeta potential and a good
stability. Such
negative zeta potential can encourage intercalation of the pillaring moieties
(Al, Fe, and/or
Si) of the pillaring agent when added to the flocculated fine tailings.
[079] For example, the pillaring agent can be added to flocculated fine
tailings having a
zeta potential of at least ¨40 mV, -50 mV, or - 60 mV.
[080] The techniques can thus include in-line addition of a flocculation agent
to the fine
tailings to form aggregates of clay platelets that are pillarable into
pillared layered solids.
The flocculation agent can be a non-ionic polymer or an anionic polymer, for
example.
[081] Addition of the flocculation agent can be performed before, after or
simultaneously
with the addition of the pillaring agent. The sequence of the addition can be
selected in
accordance with various factors, such as the nature of the flocculation agent
for
encouraging seeding and growth of the pillars between the clay platelets upon
adding the
pillaring agent. Depending on properties of the tailings, the flocculation
agent and the
pillaring agent along with operating variables of the process, the order of
the pillaring and
flocculation steps can be selected for a given implementation.
[082] The pillaring agent can be added at a pillaring concentration being at
most 0.06
wt%, at most 0.08 wt%, at most 0.1 wt%, at most 0.3 wt%, at most 0.5 wt%, at
most 0.7
wt%, at most 0.9 wt%, at most 1.1 wt%, at most 1.3 wt%, at most 1.5 wt%, at
most 1.7
wt%, at most 1.9 wt%, or at most 2 wt% of the total solids content in the fine
tailings, for
example. The pillaring concentration can also have a lower bound of, for
example, 0.05
wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.25 wt% or 1.5 wt%.
[083] In some implementations, the pillaring agent can be added subsequently
to the
flocculation agent (e.g., anionic polymer), and thus added to flocculated
tailings. Figures
3 and 4 provide two example process implementations including in-line addition
of an
anionic polymer as the flocculation agent, prior to the in-line addition of a
pillaring agent
(Si-based in Figure 3 and Al/Fe-based in Figure 4). The anionic polymer can be
an anionic
polyacrylamide When using an anionic polymer as the flocculation agent to form
clay
aggregates, a highly negative zeta potential is generated around the clay
aggregates.
13
Date Recue/Date Received 2022-02-28
[084] Referring to Figure 3, the pillaring agent can include an exogenous
source of
silicon that can participate in the formation of thermally stable
heterostructures between
clay platelets. For example, the pillaring agent can be an activated pozzolan.
In another
example, the pillaring agent can be hydraulic cement. In another example, the
pillaring
agent can be activated fumed silica or activated silica fume.
[085] Referring to Figure 4, the pillaring agent can include a source aluminum
or ferric
ions that can participate in the formation of thermally stable
heterostructures between clay
platelets. For example, the pillaring agent can be an acid coagulant. The
pillaring agent is
added in an amount avoiding precipitation of the pillaring ions away from the
clay platelets,
and facilitating diffusion of the pillaring ions to intra-aggregate pore water
and basal
surfaces of the clay platelets.
[086] In other implementations, the pillaring agent can be added to the fine
tailings prior
to or with the flocculation agent. Figures 5 and 6 provide two example process
implementations including in-line addition of a non-ionic polymer as the
flocculation agent,
while adding the pillaring agent (e.g., siloxane units of the flocculant in
Figure 5) or after
the in-line addition of the pillaring agent (e.g., acid coagulant in Figure
6). The non-ionic
polymer can be a polyethylene oxide polymer, or a non-ionic polyacrylamide.
[087] It should be noted that simultaneous addition of the pillaring agent and
the
flocculation agent can include the addition of a flocculation agent having a
pillaring effect.
In other words, the flocculation agent and the pillaring agent would be one
and the same
compound with both flocculation and pillaring functionalities. Optionally, the
flocculation
agent can include a pillaring moiety. For example, the flocculation agent can
be a non-
ionic polymer including Si-containing moieties that can participate in the
formation of
thermally stable heterostructures between clay platelets. Referring to Figure
5, the
flocculation agent having a pillaring effect can be a polyethylene oxide
copolymer including
siloxane units. Advantageously, non-ionic polymers can bind to the basal
surface of the
clay platelets (rather than edges for anionic polymers) which brings the
siloxane units to
the adequate locations of the clay platelets for the desired pillaring.
[088] Referring to Figure 6, the pillaring agent can be an acid coagulant that
includes
aluminum cations, ferric cations or a combination thereof, and that is added
prior to the
non-ionic polymer that can be a polyethylene oxide polymer. The acid coagulant
can be
aluminum sulfate, ferric sulfate, or a mixture thereof, for example. When
using a non-ionic
polymer as the flocculation agent to form clay aggregates, the pH can be
lowered by
14
Date Recue/Date Received 2022-02-28
adding an acid coagulant as the pillaring agent before the flocculation agent,
thereby
encouraging the pillaring ions to remain in solution and to diffuse into pore
water between
clay platelets for promoting heterostructure bridges that grow into oxy-
hydroxide pillars
over time. Optionally, the non-ionic polymer can include silicon moieties that
can further
serve as pillaring moieties, in addition to diffused Al and/or Fe moieties, to
participate in
the pillaring reactions (not illustrated), such that the process includes an
initial pillaring
step using a pillaring agent followed by a second pillaring step using
pillaring moieties that
are part of the flocculation agent.
[089] The residence time for the pillaring ions to diffuse to the basal
surfaces of the clay
platelets can be in the order of seconds. To minimize formation of secondary
products
from the pillaring ions that would not thus be involved in pillaring, a
turbulent micro mixing
regime can be sustained to facilitate pillaring, and the process and equipment
can be
designed accordingly.
[090] The process includes adjusting a pH of the fine tailings to a
solubilizing pH, with
the solubilizing pH being selected to ensure solubilization of the pillaring
ions and diffusion
of the pillaring ions between the basal surfaces of the clay platelets. In
accordance with
the nature of the pillaring ions, the solubilizing pH can be of at most 5 or
at least 9.
[091] In some implementations, the pillaring agent is added to the fine
tailings to achieve
a solubilizing pH that favours solubilizing and diffusion of the pillaring
moieties/ions
between clay platelets. For example, depending on the nature of the pillaring
moieties, the
pillaring agent can be added at a solubilizing pH of at most 3, at most 4, at
most 5, at least
9, at least 10, at least 11, at least 12 or least 13. For example, due to the
buffering effect
of MFTs, the pH generally returns to about 8 after some time.
[092] Optionally, the shearing energy provided to the treated tailings during
pipeline
transport can be controlled by an energy dissipation rate to tailor the
aggregate size
required for settlement and consolidation. The shearing energy can be
controlled by
adjusting the flow rate, pipeline diameter, and the presence or absence of in-
line mixing
elements, for example.
Immobilization
[093] The in-line treatment of the fine tailings is performed to generate
pillared layered
solids over time, and the treated tailings are converted into a pillared
deposit after
deposition and dewatering. The content of pillared layered solids in the
pillared deposit
Date Recue/Date Received 2022-02-28
can also increase over time via consolidation to form a reclaimable
geotechnically and
geochemically stable landform. Using techniques disclosed herein, the
reclamation
timelines to terrestrial or aquatic land use can be measured in decades
instead of
centuries as has been the case for some conventional tailings treatment
solutions.
[094] Fine tailings as discussed herein, such as MFT and especially fine
tailings derived
from oil sands processing operations, can include CoCs that include organic
acids,
residual hydrocarbons and regulated dissolved metals. In some implementations
of the in-
line treatment, the quality of the water released from the treated tailings by
dewatering can
be enhanced by immobilizing the CoCs within the pillared deposit.
Immobilization of the
CoCs can be performed via in-line addition of an immobilization agent into the
fine tailings
to achieve insolubilization of dissolved or soluble CoCs. The water released
from the
treated tailings thus has a reduced level of CoCs or is substantially free of
CoCs, and the
resulting pillared deposit comprises the immobilized CoCs. Immobilization of
CoCs in fine
tailings is described in further detail in Canadian patent No. 2,958,873
(Omotoso et al.)
and can be used in conjunction with techniques described herein.
[095] In some implementations, the pillaring agent can differ from the
immobilization
agent that is used to immobilize the CoCs. For example, referring to Figures 3
and 5, the
pillaring agent can be an external source of silicon (e.g., cement in Figure 3
or
polyethylene oxide with siloxane units in Figure 5) and the immobilizing agent
can be an
acid coagulant including aluminum cations, ferric cations or a combination
thereof, that is
added subsequently to the pillaring agent.
[096] In some implementations, the pillaring agent can have an immobilizing
effect and
acts as an immobilization agent. The pillaring agent can indeed release at
least one of a
trivalent cation or a tetravalent cation that can participate in the formation
of the thermally
stable heterostructures between the clay platelets, and/or in the
immobilization of CoCs.
The pillaring trivalent and tetravalent cations that are exemplified herein,
i.e., Al3+, Fe3+,
and Si4+, can concurrently immobilize CoCs from the pore water between the
clay
platelets.
[097] Referring to Figure 4, the pillaring agent having the immobilizing
effect can thus be
an acid coagulant including aluminum cations, ferric cations or a combination
thereof. The
acid coagulant can be added after the flocculation agent (e.g., anionic
polymer) in an
amount tailored to reduce or avoid precipitation of aluminum or ferric
moieties, to facilitate
diffusion of the Al3+ or Fe3+ ions into the pore water between clay platelets,
and to co-
16
Date Recue/Date Received 2022-02-28
currently immobilize CoCs from the pore water. Referring to Figure 6, the same
agent can
be added before and after the flocculation agent so as to be used as a
pillaring agent and
as an immobilization agent, respectively. More particularly, an acid coagulant
including
aluminum cations, ferric cations or a combination thereof can be added before
and after
the non-ionic polyethylene oxide.
[098] It should be noted that the concentration of the acid coagulant can be
controlled
and tailored for use as the immobilization agent or as the pillaring agent.
More particularly,
the concentration of the acid coagulant that is used for immobilization of the
CoCs (e.g.,
when added after the flocculation agent/pillaring agent) can be lower in
comparison to an
implementation where the acid coagulant is used as a pillaring agent (e.g.,
before a non-
ionic polymer flocculant or after an anionic polymer flocculant). For example,
the
immobilizing concentration of the acid coagulant that is used as an
immobilization agent
can be at most 5 meq/L, at most 10 meq/L, at most 15 meq/L, or at most 20
meq/L of the
pore water and can be adjusted according to the extent of contaminant
immobilization
desired, e.g., to a concentration between 1 and 15 meq/L, between 2 and 12
meq/L, or
between 5 and 10 meq/L. The pillaring concentration of the acid coagulant that
is used as
a pillaring agent can be above 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or 70
meq/L of the
pore water, thereby facilitating Al3+ or Fe3+ migration within the pore water
between clay
particles. Optionally, the concentration of the acid coagulant serving as both
pillaring and
immobilizing agent can be between 20 and 40 meq/L of the pore water.
Example process implementations
[099] Referring to the process implementation illustrated in Figure 3, the in-
line treatment
of the fine tailings, such as MFT, can include in-line addition of an anionic
polymer as the
flocculation agent, an external source of silicon as the pillaring agent, and
an acid
coagulant as the immobilization agent to produce treated tailings. The treated
tailings are
transported by pipeline to a deposition site. The MFTs initially have a pH of
8.0 and the
anionic polymer, e.g., anionic polyacrylamide, is added to flocculate the clay
platelets into
aggregates and bring the clay platelets closer together. The anionic polymer
does not
have an impact on the pore water pH, but the anionic polymer creates a highly
negative
zeta potential around the clay aggregates. The anionic polymer addition is
followed by the
addition of an external source of silicon to the flocculated tailings. The
dissolved silicon
ions, Si4+, which are the primary pillaring ions are added at a concentration
of at most 2
wt% of the solids in the MFTs. In this implementation, dissolved Si4+ ions can
be added
17
Date Recue/Date Received 2022-02-28
either through ordinary Portland cement, activated pozzolan, activated fumed
silica or
activated silica fume. Upon addition of the pillaring agent, the pH of the
MFTs increases
to 11, which ensures that Si4+ ions remain in solution during pipeline
transport for diffusion
into the intra-aggregate pore space and specifically diffuse to the basal
surfaces of the
clay platelets. Because the high pH of about 11 mobilizes organic acids in the
bitumen
from the MFTs, the toxicity of the water that is releasable from the treated
tailings
increases as CoCs would remain in solution. The CoCs are thus immobilized by
further
adding an acid coagulant just before deposition (and after Si4+ has diffused
into the pore
space of the clay aggregates) to reduce the pH to below 9 and improve the
water quality.
Optionally, the amount of acid coagulant that is added as immobilization agent
can be at
most 20 meq/L of the pore water and can depend on the level of contaminant
immobilization that is desired. In the implementation schematized in Figure 3,
the
aluminum or ferric cations (Al or Fe) of the acid coagulant do not participate
in the pillar
formation because at pH > 5, they rapidly form hydroxide precipitates. It
should further be
noted that, if added at high concentrations (typically above 1, 1.5, or 2
wt%), and over time
in the deposit, the pillaring agent (ordinary Portland cement, activated
pozzolan, activated
silica fume, or fumed silica) can react with water to form calcium alumina-or-
silicate
hydrate network in the pore space to further strengthen the mineral matrix.
While this
strengthening mechanism is not the primary focus of the present techniques,
the strength
gain through cement reactions can further accelerate the consolidation of the
treated
tailings once deposited.
[100] Referring to the process implementation illustrated in Figure 4, the in-
line treatment
can include the addition of an anionic polymer as the flocculation agent and
an acid
coagulant as the pillaring agent to the MFTs during pipeline transport.
Anionic
polyacrylamide can be used as the flocculation agent to aggregate the clay
platelets. The
addition of the anionic polymer does not have an impact on the pH of the MFTs,
but
creates a highly negative zeta potential around the clay aggregates. This
potential favours
the diffusion of the pillaring cations provided by the subsequent addition of
the acid
coagulant comprising at least one of aluminum ions and ferric ions. The
pillaring ions
intercalate between the clay platelets to serve as seeds for forming
heterostructures
(pillars). The acid coagulant can co-currently immobilize the CoCs that have
solubilized in
the pore water between aggregates due to the pH lowering. Over time and before
deposition, the pH can increase back to about 8 due to the buffering capacity
of MFTs.
18
Date Recue/Date Received 2022-02-28
[101] Referring to the process implementation illustrated in Figure 5, the in-
line treatment
of the MFTs includes addition of a polyethylene oxide copolymer including
siloxane units
as the flocculation agent having a pillaring effect, and of the acid coagulant
as the
immobilization agent during pipeline transport. The polyethylene oxide
copolymer is a non-
ionic polymer that flocculates the clay platelets into clay aggregates by
bonding to the
basal surfaces of the clay platelets. The pillaring ions are provided
simultaneously as the
siloxane units are part of the flocculation agent. Using a Si-containing non-
ionic polymer
can result in a faster Si4+ pillaring action, because the polymer locates the
siloxane units
to the basal clay surface. The acid coagulant is then added in-line to the
flocculated tailings
to immobilize CoCs that are in solution in the water. Due to the lowering of
the pH to below
4, the aluminum and/or ferric cations released by the acid coagulant can co-
currently serve
as pillaring ions by diffusion to the intra-aggregate pore water between clay
platelets.
Although not illustrated, the acid coagulant can be added before the non-ionic
polymer
such that the aluminum and/or ferric ions would become the primary source of
pillaring
ions, and the siloxane units of the non-ionic polymer would become a secondary
source
of pillaring ions.
[102] Referring to the process implementation illustrated in Figure 6, the in-
line treatment
of the fine tailings, such as MFTs, can include successive in-line addition of
the pillaring
agent, the flocculation agent and the immobilization agent. An acid coagulant
is first added
inline to the MTFs during pipeline transport to provide aluminum and/or ferric
pillaring ions.
The presence of the acid coagulant lowers the pH immediately after addition
from about
8 to below about 4. This lower pH is suitable for the Al3+ and/or Fe3+ ions to
diffuse to the
pore space between clay platelets. The Al3+ and/or Fe3+ are added to provide a
pillaring
effect, and their concentration is of at most 30 meq/L, and optionally of at
most 40 meq/L
of the pore water, to ensure that sufficient Al3+ and/or Fe3+ migrate to the
pore space
between clay platelets prior to precipitating as hydroxides as the pH buffers
up during
transport of the treated tailings. The non-ionic polyethylene oxide is then
added as the
flocculation agent to flocculate and aggregate the clay platelets. The non-
ionic PEO can
serve two purposes which are to (i) promote rapid dewatering of the treated
tailings once
deposited and (ii) promote pillaring by adsorbing on the basal surfaces (or
siloxane
surface) of clay platelets, such that a near parallel configuration of the
clay platelets can
favour the growth of heterostructure bridges as oxy-hydroxide pillars over
time. Although
not illustrated in Figure 6, the non-ionic polymer can include silicon in a
backbone thereof,
and the silicon can participate in the pillaring reactions as a secondary
pillaring ion.
19
Date Recue/Date Received 2022-02-28
[103] When using an anionic polymer, the anionic polymer rather adsorbs on the
edges
of the clay platelets and may thus not be as effective as a non-ionic polymer
to seed the
pillars between clay platelets. The nature of the flocculation agent is thus a
key parameter
impacting the order of the addition sequence of the pillaring agent to favour
seeding of the
pillars by intercalation of pillaring ions between clay platelets.
[104] The treatment can be an in-line treatment, including the in-line
addition of at least
one of the agents. Regarding in-line addition, the agents can be added into a
flow of the
fine tailings via a pipe T-junction, a pipe Y-junction, an in-line static
mixer, a co-annular
injection device, or various other addition apparatuses. It could also be
possible in some
implementations to add the agents using a tank mixer that includes a dynamic
mixing
element, such as an impeller. While in-line addition of the pillaring,
flocculation and
immobilization agents is described herein and illustrated in the figures, it
is also noted that
one or more of the agents can be added to the fine tailings in other ways. For
example,
the pillaring agent could be added in a batch addition and mixing stage, in a
vessel or
other containment structure, and the resulting tailings material could then be
pipelined for
in-line addition of the flocculation agent followed by in-line transport to
the deposition site.
For example, batch addition can involve the use of a dynamic mixer or a
continuous
stirred-tank reactor (CSR).
Consolidation and reclamation
[105] The present techniques can further include deposition of the treated
tailings at a
dedicated deposition area to allow water to separate from the treated
tailings, and to
produce a pillared deposit including pillared layered solids. The pillared
deposit is further
allowed to stand within the dedicated deposition area for consolidation into a
consolidated
deposit over time by further pillaring and optionally by other consolidation
mechanisms
(e.g., via placing a sand or coke surcharge on top). Once sufficiently
consolidated, the
consolidated deposit can be reclaimed as at least part of a landform that can
sustain
terrestrial or aquatic activities. The landform should be understood as a man-
made
geostructure within a landscape. For example, the landform can be a sub-aerial
beach-
like structure formed from one or more layers of deposited material or a
lakebed below a
water cap forming an in-pit lake structure.
[106] The consolidated deposit can be characterized as including at least 50
wt%, 60
wt%, 70 wt%, 80 wt%, or 90 wt% of the pillarable clay initially present in the
fine tailings
being pillared, for example.
Date Recue/Date Received 2022-02-28
[107] Deposition can include discharging the treated tailings within the
dedicated
deposition area over a period of time. The discharging can be performed in a
manner to
avoid over-shearing the treated tailings, and thus to maintain the clay
platelets within
flocculated aggregates. One way of managing this is to discharge the treated
tailings close
onto a slope and/or relatively close to the contact point of the deposition
area, and to use
an outlet that is sized sufficiently large to avoid notable acceleration or
spraying of the
discharged material. The discharging can be performed continuously over a
deposition
period at a given rise rate (e.g about 20 meters per year) until a certain
height of the
deposited material is reached. Discharge could also be a seasonal operation
with material
placed until a final elevation is reached.
[108] It should be noted that the treated tailings can be discharged in
various ways, in
accordance with the structure and properties of the chosen dedicated
deposition area, as
well as the long term reclamation strategy for the tailings. The dedicated
deposition area
can be below or above grade, and the consolidated deposit results in a
landform (above
original ground and optionally below a water cap) that can be geotechnically
and
geochemically stable.
[109] For example, the dedicated deposition area can be a subaerial pit, with
the water
being released from the pillared deposit and coming to the surface, while the
solids settle
to the bottom and further consolidate. The pillared deposit provides for a
lower solids-rich
stratum including pillared layered solids below an upper water cap. The lower
solids-rich
stratum can further dewater with consolidation by pillaring as a significant
dewatering
mechanism. The lower solids-rich stratum becomes consolidated into a
consolidated
deposit that can be reclaimed as a lakebed or lake floor, for example. This
structure can
be referred to as a permanent aquatic storage structure (PASS) where a water
cap is
maintained above a consolidated lower stratum including the pillared layered
solids.
[110] In another example, deposition can be performed according to thin lift
deposition
wherein the treated tailings are deposited as "lifts" or layers which are
stacked on top of
each other on a sloped area to form the pillared deposit, which is allowed to
drain in
accordance with an initial water release. The released water flows away from
the pillared
deposit mainly by drainage, and the pillared deposit is allowed to stand and
further
dewater by evaporation and other mechanisms. Once deposition is ceased, the
pillared
deposit is further allowed to stand as a beach-like structure to form
additional pillars
between clay platelets and consolidate the pillared deposit including the
pillared layered
21
Date Recue/Date Received 2022-02-28
solids into the consolidated deposit. Dewatering of the pillared deposit can
further happen
by consolidation (including the further pillaring), freeze-thaw, evaporation,
and/or
permeation mechanisms.
[111] The pillared deposit should thus be understood herein as being formed by
deposition of the treated tailings and as resulting from an initial water
release of the
deposited treated tailings. The treated tailings can already include some
pillared layered
solids, and additional pillars can form over time to densify the pillared
layered solids that
are already present and generate newly formed pillared layered solids. The
pillared
deposit resulting from the initial dewatering of the treated tailings includes
the formed
pillared layered solids, and the level of pillaring of the pillared deposit
varies and can
increase over time after deposition. When referring to the pillared deposit,
one can thus
understand that, upon dewatering, the tailings are partially pillared and the
pillaring is
further encouraged and develops after deposition for consolidation. The
consolidated
deposit can be reclaimed as a landform including the pillared layered solids,
being for
example a lower solid-enriched stratum below a water cap or a solid-enriched
deposit
above ground.
[112] Stability of the consolidated deposit can be achieved when the tailings
are
sufficiently dewatered and consolidated, thereby forming a geotechnically and
geochemically stable landform. Geochemical stability can refer to the
chemistry of the
mineral and pore water released from the consolidated deposit meeting
specifications
allowing a specific land use. Geotechnical stability can refer to the strength
and the density
of the consolidated deposit being sufficient for use as a structural fill
without requiring
additional containment. For example, geotechnical stability of the
consolidated deposit
can be considered to be achieved when the consolidated deposit has a shear
strength
greater than 15, 20, 25, 30 or 35 kPa and/or when the consolidated deposit has
a solids
content of at least 50, 55, 60 or 65 wt%. The required stability can vary
depending on the
planned end use of the consolidated deposit as a landform, that can be a
sediment/floor
of a lake or wetland, or a dryland, for example.
[113] Stability of the consolidated deposit can be achieved faster according
to
techniques described herein than according to various conventional dewatering
and
consolidation methods. The pillaring can thus aid in the acceleration of
tailings
reclamation.
22
Date Recue/Date Received 2022-02-28
[114] Figure 7 provides a comparison of the time after which stability of the
consolidated
deposit can be achieved following the end of the deposition of treated
tailings produced
according to five treatment options. A reference case illustrating behavior
fluid fine tailings
(FFT) is provided, in addition to coagulated and flocculated fluid fine
tailings (c/f FFT) and
consolidated tailings (CT 3:1) which are produced according to conventional
techniques
known in the art. Figure 7 further provides the behavior of flocculated,
coagulated and
pillared fluid fine tailings (f/c and pillared FFT) produced in accordance
with the techniques
described herein with the pillaring ions being Si4+ that were provided with a
polyethylene
oxide polymer (PEO) or with activated pozzolan. Figure 7 shows that the time
in which
sufficient consolidation of the consolidated deposit can be achieved for use
as a stable
landform in accordance with the present treatment techniques is sooner (within
decades)
than for conventional treatment solutions (close to 100 years or several
centuries). For
example, the consolidation period can be at most 50 years when stability is
reached for a
post-deposition pillared deposit of initially 75-meter high, based on an MFT
volume before
dewatering.
[115] One can see that the consolidation rate is generally faster in the
implementation
where activated pozzolan is added than in the implementation where siloxane
units are
added, such that stability of the consolidated deposit is achieved sooner than
in other
studied cases. This could be explained by the fact that pozzolanic reactions
can further
form hydrates that also strengthen the landform.
[116] A more rapid dewatering and consolidation can be explained at least in
part by the
conversion of the clay platelets aggregates into pillared layered solids. The
porosity of the
pillared layered solids confers a permeability and a hydraulic conductivity
that improve the
initial water release upon deposition of the treated tailings, and thus
contributes to the
acceleration the overall dewatering of the treated tailings. For example, the
pillared deposit
can be characterized as having a post-deposition hydraulic conductivity
greater than 10-9
m/s. In addition, the multiplication of the pillars and the lower
compressibility of the
resulting pillared layered solids confer a strength and a density that improve
a
consolidation rate of the treated tailings.
[117] The process steps including treatment, deposition, dewatering and
consolidation,
with a pillaring feature, can be used to convert fine tailings into a stable
reclaimed
landform.
23
Date Recue/Date Received 2022-02-28
[118] Reclamation can be understood herein as resulting from the physical
reconstruction of soils and terrain on a disturbed site to achieve a land use
capability that
can be equivalent as to what existed before disturbance.
[119] In the context of planned terrestrial reclamation, the process can
include deposition
of the treated tailings in a dedicated deposition area below or above grade,
with the
released water being directed away from the treated tailings as the material
dewaters and
further dries. The water can be recovered and reused in the mining and
extraction
operation, either directly or after pre-treatments; the water can be reused in
the context of
in situ recovery operations after pre-treatment; or the water can be treated
and
reintroduced into the environment. The dewatered treated tailings form the
pillared deposit
including the pillared layered solids and the immobilized CoCs. The pillared
deposit further
consolidates over time to form the consolidated deposit that can be reclaimed
as a
geotechnically and geochemically stable landform after a shortened
consolidation period.
Terrestrial reclamation can comprise reclaiming the consolidated deposit as a
landform
including a dryland or other solid ground.
[120] Optionally, other post-deposition strengthening activities can be
performed to
further consolidate the deposit and achieve stability of the landform sooner
for
reclamation. For example, the consolidated deposit can be capped with a layer
of sand or
coke, or another material, to form a top cap. The top cap can have a thickness
between 2
m and 5 m, for example. The top cap can provide weight that enhances
consolidation
and/or enable water absorption into the top cap from the consolidated deposit.
Another
optional post-deposition strengthening activity can include draining a top
layer of the
consolidated deposit, including using wick drains to further dewater the top
layer.
[121] In the context of planned aquatic reclamation, the process can include
deposition
of the treated tailings in a dedicated deposition area below grade, for
example in a
containment structure such as a mine pit, with at least some of the released
water being
maintained above the dewatered treated tailings, thus forming a water cap at
the end of
deposition. The dewatered treated tailings form the pillared deposit which
remains below
the water cap and includes pillared layered solids and immobilized CoCs. Over
time, the
lower pillared deposit can further consolidate which can include further
pillaring, thereby
forming a consolidated deposit being a lower solids-rich stratum below the
water cap.
Once sufficiently consolidated, the consolidated deposit can be reclaimed as a
landform
being, for example, a sediment layer of a lake or a wetland. With the CoCs
being
24
Date Recue/Date Received 2022-02-28
immobilized within the lower stable landform, the quality of the water is such
that aquatic
recreational activities can be performed on site, and/or that aquatic life can
be sustained.
Optionally, fresh water can be added to the water cap to maintain a level and
a quality of
the water cap.
[122] In some implementations, the aquatic reclamation is such that a lake is
formed
where the floor of the lake includes the solids-rich stratum and water is
allowed to flow into
and out of the lake such that the lower solids-rich stratum remains water
capped. For
example, the water cap can be further connected to a surrounding watershed, to
establish
a fresh water flow through the connected watershed.
Date Recue/Date Received 2022-02-28
