Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WATER MANAGEMENT SYSTEM
FOR OIL SANDS TAILINGS
TECHNICAL FIELD
[0001] The present invention relates to dewatering oil sands tailings.
BACKGROUND
[0002] Oil sands tailings such as those in Canada are a by-product of a
water-based
extraction of bitumen from oil-sands. They are a mixture of sand, clay, water,
silt, residual
bitumen and other organics, together with salts and trace metals. After
bitumen extraction,
tailings in the form of a slurry with process water is stored in tailings
ponds. Coarse sand settles
quickly and is used to form containment dykes or to form a tailings pond -
beach". Smaller
particles or fines, defined in the industry as having a diameter less than 44
gm, settle much more
slowly but leave a layer of water with some suspended fines near the surface
of the ponds. This
water is recycled and reused in the extraction process. Because of the
elevated levels of
dissolved metals, salts, and organic contaminants such as naphthenic acids and
polycyclic
aromatic compounds, the process affected water is toxic to many aquatic
species.
[0003] Beneath the surface process water layer, an intermediate layer of
so-called fluid
fine tailings (FFT) forms from initial settling of the fines (mainly silica
and clay particles). FFT
has a low solids content of less than 15% and is also referred to as thin fine
tailings (TFT).
[0004] The FFT are transferred to special settling ponds. Over time,
additional settling
occurs, assisted by the freeze-thaw process resulting from the freezing winter
temperature drops,
but the negative surface charge of the mineral particles limits aggregation
and a distinct layer
of so-called mature fine tailings (MFT) is formed below the top water layer in
the ponds.
[0005] The solids content of the MFT component of the tailings ponds is of
the order of
30% to 40% and varies significantly within the pond. Lenses of oil/bitumen
tend to aggregate
within the MFT. MFT has gel-like properties that make it difficult to handle
and dewater. It has
been estimated that under the action of gravity alone this tailings component
could take decades
if not centuries to consolidate and settle and thus allow for land
reclamation. See, e.g., Wang et
al. Minerals Engineering, 2014:58:113-131.
[0006] There is a clear need in the industry for processes to improve the
recovery of
water from the oil sands tailings and to eliminate the MET and oil sands
tailings ponds in a way
that is more environmentally friendly and in an economically feasible manner.
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SUMMARY OF THE DISCLOSURE
[0007] An advantage of the present invention is a process for dewatering
oil sands
tailings which includes using reclaimed surface water from a tailings storage
facility (TSF) and
a solid suspension stream from oil sands tailings to output consolidated
solids and clarified
water.
[0008] These and other advantages are satisfied, at least in part, by a
process for
dewatering oil sands tailings comprising mixing a stream of reclaimed process
water from oil
sands tailings with an indifferent salt and polymer flocculant to form a
functional processing
solution; mixing the functional processing solution with a solids suspension
stream from oil
sands tailings without or with coarse particles to form a treated slurry
stream having
consolidated solids and clarified water; and separating the clarified water
from the consolidated
solids.
[0009] Upon separation from the consolidated solids, the clarified water
optionally can
be treated with materials to remove unwanted components in the water such as
treating with
carbonaceous material (petroleum coke, activated carbon, etc.) to remove
organic impurities
such as bitumen, naphthenic acid, etc. and/or treating with limestone to
remove acidic
components. In addition, or alternatively, the clarified water can be treated
to concentrate the
indifferent salt dissolved therein such as, for example, by reverse osmosis or
nanofiltration,
which can separate the clarified water in to a brine stream including a
concentrated amount of
the indifferent salt and a desalted water stream. The brine steam can be used
to form additional
functional processing solution by combining the brine stream with any one or
all of the process
water, indifferent salt or flocculating polymer. The desalted water can be
used for other
processes or discharged to the environment depending on its quality.
[0010] Additional advantages of the present invention will become readily
apparent to
those skilled in this art from the following detailed description, wherein
only the preferred
embodiment of the invention is shown and described, simply by way of
illustration of the best
mode contemplated of carrying out the invention. As will be realized, the
invention is capable
of other and different embodiments, and its several details are capable of
modifications in
various obvious respects, all without departing from the invention.
Accordingly, the drawings
and description are to be regarded as illustrative in nature, and not as
restrictive.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Reference is made to the attached drawings, wherein elements having
the same
reference numeral designations represent similar elements throughout and
wherein:
[0012] Figure 1 is a schematic illustrating a process for dewatering a
tailings pond
according to aspects of the present disclosure.
[0013] Figure 2 are pictures of vials showing the use of polymer
flocculant
(polyacrylamide) and an indifferent salt (ammonium chloride) in consolidating
MFT. The vial
on left shows MFT plus tap water (control); second from left shows MFT plus a
salt solution;
third from left shows MFT plus a polymer solution; and the vial on right shows
MFT plus the
indifferent salt and polymer containing solution.
[0014] Figure 3 are pictures of a process for dewatering oil sands
tailings according to
aspects of the present disclosure. The pictures on the left shows mixing
mature fine tailings
with a FPS solution followed by mixing with sand in a ribbon mixer. The
pictures on the right
show consolidated solids emerging from the bottom of the ribbon mixer
interspersed with
apparently clear liquid.
[0015] Figure 4 are pictures showing recovered solids after consolidation
of MFT with
sand (1:0.8 tailings solids to sand weight ratio). The picture on the left
shows consolidated solids
one week after draining and the picture on the right shows a worker standing
on the onsolidated
solids three months after draining.
[0016] Figure 5 is a schematic depiction of an in-line mixing step
according to aspects
of the present disclosure.
[0017] Figure 6 shows pictures of a pilot unit for in-line mixing
according to aspects of
the present disclosure. The picture on the left shows, in the back, of tanks
holding MFT and
FPS solutions. The foreground of the picture on the left shows hoses meeting
at a pump to
provide in-line mixing. The middle picture shows the slurry emerging from the
pipes on a flume
to give simple gravity dewatering. The right picture shows the slurry squeeze
by hand to give a
consolidated material with a solids content of about 75%.
[0018] Figure 7 is a schematic illustrating mass flow rates for a process
for dewatering
a tailings pond according to aspects of the present disclosure.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0019] The present disclosure relates to dewatering oil sands tailings
such as coarse or
fine plant tailings, froth treatment tailings, FFT or MFT tailings. The
processes of the present
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disclosure are particularly suited to consolidating fluid fine tailings (FFT)
and mature fine
tailings (MFT) and can advantageously form relatively dry, stackable material
and can allow
discharge of purified water to the environment and/or for reuse in other
processes.
[0020] The process described herein uses one or more indifferent salts,
i.e., a salt highly
soluble in process water that does not hydrolyze or coagulate, together with a
flocculating
polymer to achieve a fast flocculation, dewatering and consolidation of a
solids suspension
stream from oil sands tailings such as a stream of MFT or FFT or both. In
practicing certain
aspects of the present disclosure, a process for dewatering oil sands tailings
includes mixing a
stream of process water from oil sands tailings with an indifferent salt and
polymer flocculant
to form a functional processing solution. An indifferent salt herein means one
or more
indifferent salts and a polymer flocculant means one or more polymer
flocculants.
Advantageously, reclaimed process water from the surface or near the surface
of oil sands
tailings such as in a TSF can be used as the process water. Such process water
generally has a
low suspended solids content, e.g., less than 2 wt%, e.g., less than 1 wt% of
solids.
[0021] In an aspect of the present processes, the process further includes
mixing the
functional processing solution with a solids suspension stream from oil sands
tailings and
optionally coarse particles to form a treated slurry stream having
consolidated solids and
clarified water. The solids suspension stream from oil sands tailings are one
or more streams
from oil sands tailings that includes a relatively high amount of suspended
solids, e.g., greater
than 2 wt%, such as greater than about 10 wt% such as greater than about 25
wt% and higher.
Such solids suspension streams include a stream of fluid fine tailings or
mature fine tailings or
both. Coarse particles are solid particles with sizes greater than 44 gm. The
clarified water in
the treated slurry, and separated therefrom, advantageously includes the
indifferent salt
dissolved therein and thus the indifferent salt can be concentrated and
recycled to form
additional functional processing solution.
[0022] The process further includes separating the clarified water from
the consolidated
solids. The clarified water can be readily separated from the consolidated
material as, for
example, by one or more of sub-aqueous deposition, decanting, thickening,
filtration, electro-
filtration, cross-flow filtration, gravity drainage, vacuuming and other
evaporating techniques,
etc. or combinations thereof and/or by one or more of a device for dewatering
consolidated
material such as a centrifuge, decanting centrifuge, dewatering screw,
hydrocyclone, vacuum
belt filter, filter press or pressing devices, etc. or combinations thereof.
In addition, the
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separated consolidated material can be disposed or deposited in a containment
structure to
further dewater the consolidated material.
[0023] Upon separation from the consolidated solids, the clarified water
optionally can
be treated with materials to remove unwanted components in the water such as
treating with
carbonaceous material (petroleum coke, activated carbon, etc.) to remove
organic impurities
such as bitumen, naphthenic acid, etc. and/or treating with limestone to
remove acidic
components. In addition, or alternatively, the clarified water can be treated
to concentrate the
indifferent salt dissolved therein such as by reverse osmosis or
nanofiltration or other desalting
technologies such as by precipitation, ion exchange, electrolytically
etcetera, which can separate
the clarified water into a brine stream including a concentrated amount of the
indifferent salt
and a desalted water stream. The brine steam can be used to form additional
functional
processing solution by combining the brine stream with any one or all of the
process water,
indifferent salt or flocculating polymer. The desalted water can be used for
other processes or
discharged to the environment depending on its quality.
[0024] The processes of the present disclosure can optionally include
monitoring a
concentration of the indifferent salt or the polymer flocculant or both during
various steps in the
process such as monitoring the concentrations in any one or all of a stream of
the functional
processing solution, a stream of clarified water, a brine stream, or a
desalted water stream.
Amounts of indifferent salt or flocculating polymer or both can be adjusted
based on a
determination of the monitored concentrations of such in one or more streams.
Hence,
managing the indifferent salt and polymer concentrations in the process and
producing purified
water can be integral parts of the process.
[0025] Salts that are useful in practicing the present disclosure include
salts that are
highly soluble in process water and that are non-hydrolyzing. Such highly
water-soluble salts
are referred to as an ``indifferent" salt. As used herein an ``indifferent"
salt is a salt that is highly
soluble in the aqueous phase of the tailings, disassociating in to one or more
cations and anions,
and remains dissolved in the aqueous phase without precipitating from the
tailings throughout
the consolidation process. The disassociated cations or anions of the
indifferent salt further do
not chemically react to form coagulates or chemically react with components of
the tailings
such as polymer flocculant or solid components during the process or undergo
oxidation or
reduction reactions. Such indifferent salts are advantageous since they remain
dissolved in the
water phase of the treated tailings and can be substantially recovered, unlike
hydrolyzing
coagulant salts. Hydrolyzing coagulating salts undergo hydrolysis when added
to process water
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to form metal hydroxides, which precipitate from the solution onto mineral
surfaces, and so
would be depleted in the process and require replacement.
[0026] Hence, the processes of the present disclosure do not include a
substantial
amount of coagulating salts, e.g., less than 20 wt% such as less than 10 wt%,
if any at all, of
coagulating salts relative the total amount of salt added to the functional
processing solution for
consolidating solids in tailings streams. Hydrolyzing, coagulating salts that
are preferably not
included in a substantial amount in the functional processing solution include
aluminum
coagulants such as alum, aluminum sulfate, (Al2(SO4)3), aluminum chloride, and
iron
coagulants such as ferric chloride (FeCl3), ferric sulfate (Fe2(SO4)3), ferric
citrate, ferrous
sulfate (Fe(SO4)), ferrous ammonium sulfate, lime CaO. The indifferent salts
further do not
include a substantial amount, e.g., less than 20 wt% such as less than 10 wt%,
if any at all, of
salts intended to react with minerals such as titanium salts, zinc salts, such
as zinc chloride,
zirconium salts such as zirconium acetate, zirconium oxychloride.
[0027] Indifferent salts that are highly soluble in process water from oil
sands tailings
and useful in practicing the present process include salts having a monovalent
cation, e.g., alkali
halide salts such as sodium chloride, potassium chloride, other monovalent
cationic salts include
sodium nitrate, potassium nitrate, ammonium based salts such as ammonium
chloride (NR4C1),
ammonium bromide, ammonium carbonate, ammonium nitrate (NR4NO3), ammonium
sulfate
((NH4)2SO4), ammonium phosphate, etc., phosphate salts, e.g., sodium,
potassium and
ammonium phosphate (N1141-12PO4), etc. Mixtures of such salts can also be
used. Ammonium
based salts are useful for practicing the present disclosure since residual
ammonium-based salts
on the consolidated solids after mixing the salt with the oil sands tailings
are not harmful to
plant life. In fact, many of the ammonium-based salts are useful as
fertilizers and are in fact
beneficial to plant life, e.g., ammonium chloride and ammonium nitrate are
useful as fertilizers.
[0028] In addition, indifferent salts can be sourced from a functional
processing solution
can be formed from a natural or existing body of water having a high
concentration of dissolved
monovalent ion salts, e.g., seawater, hypersaline lakes, salt lakes, brine
springs, etc. Alberta
has significant amounts of saline water and brine springs occur in the Fort
McMurray area
(Grasby; Geological Survey of Canada, Bulletin 591, 2006, p. 241-254). Western
Canada also
has a significant number of saline lakes (Last and Ginn; Saline Systems 2005,
1:10). Like
seawater, these brines have complex compositions including predominantly
monovalent cations
such as sodium, but various small amounts of divalent cations such as calcium
and magnesium.
The anions are mostly chlorine and sulfate. Salt concentrations in these
sources can be as high
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as 10% (Last and Ginn, cited above), with the brine springs in the Fort
McMurray area averaging
4.5% (Grasby, cited above). These and mixed salt saline systems with similar
compositions can
also be advantageously used.
[0029] Flocculating polymers that can be used in practicing aspects of the
processes of
the present disclosure and include polyacrylamides or copolymers thereof such
as a nonionic
polyacrylamide, an anionic polyacrylamide (APAM) such as a polyacrylamide-co-
acrylic acid,
and a cationic polyacrylamide (CPAM), which can contain co-monomers such as
acryloxyethyltrimethyl ammonium chloride, methacryloxyethyltrimethyl ammonium
chloride,
dimethyldiallyammonium chloride (DMDAAC), etc. Other water soluble
flocculating
polymers useful for practicing the present disclosure include a polyamine,
such as a polyamine
or quaternized form thereof, e.g., polyacrylamide-co-
dimethylaminoethylacrylate in
quaternized form, a polyethyleneimine, a polydiallyldimethyl ammonium
chloride, a
polydicyandiamide, or their copolymers, a polyamide-co-amine, polyelectrolytes
such as a
sulfonated polystyrenes can also be used. Other water soluble polymers such as
polyethylene
oxide and its copolymers can also be used.
[0030] Although most commercial flocculating polymers can be used in the
process
described herein, anionic and cationic polyacrylamide copolymers are commonly
used.
However, anionic and cationic polyacrylamide copolymers can foul membranes in
nanofilters
and reverse osmosis devices, among others. Certain cationic polyacrylamides
are also acutely
toxic to fish. An additional advantage of the process described herein is that
a non-ionic polymer
flocculant, e.g., a non-ionic polyacrylamide or copolymer thereof, works well
in combination
with indifferent salts, such as sodium chloride and ammonium sulfate and other
monovalent
salts, in consolidating oil sands tailings.
[0031] Because the indifferent salt and polymer flocculant are preferably
highly soluble
in the process water, the temperature of the treated slurry need not be
elevated above ambient
to practice the process. In certain embodiments, treating the oil sands
tailings according to the
various embodiments herein can be carried out at a temperature of no more than
50 C, e.g., no
more than about 40 C or about 30 C.
[0032] It will be appreciated that the indifferent salt and polymer
concentrations in the
functional processing solution can be varied over a range. As explained above,
processes of the
present disclosure include mixing a functional process solution with a solids
suspension stream
from oil sands tailings, such as a stream of MFT or FFT, and sand to form a
treated slurry
stream. Upon mixing the streams, the initial concentration of the indifferent
salt in the FPS
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becomes diluted with water in the solids suspension stream and any water
combined with coarse
particles.
[0033] However, it is the concentrations of the indifferent salt and
polymer in the treated
tailings, i.e., treated slurry stream, that is significant in how well the
solids suspended therein
consolidate. We found that when a sufficiently high concentration of the
indifferent salt is
included in the treated tailings, the indifferent salt can destabilize and
consolidate solids in the
tailings. For a relatively short process times with a relatively low energy
input, the
concentration of the indifferent salt in the treated tailings forming a
treated slurry stream should
preferably be at least 0.5 wt% and preferably no less than about 0.70 wt%,
such as at least about
1 wt%, 1.25 wt %, 1.5 wt%, 1.75 wt%, 2 wt% and even at least about 2.5 wt%, 3
wt%, 4 wt%,
wt%, etc. The concentration of the indifferent salt is determined based on the
mass of
indifferent salt to the mass of water and indifferent salt in the treated
tailings forming the treated
slurry as a weight%.
[0034] Advantageously, since the indifferent salt is highly soluble and
non-coagulating,
the indifferent salt remains almost entirely in the water phase of the treated
slurry stream and
can be recovered in the clarified water. The clarified water separated from
the consolidated
solids would have a concentration of the indifferent salt that is similar to
the concentration of
the indifferent salt in the treated tailings forming the treated slurry
stream. Some loss may be
due to loss with the consolidated solids. However, it is preferable that the
clarified water
separated from the consolidated solids have a concentration of the indifferent
salt of at least 0.5
wt% and preferably no less than about 0.70 wt%, such as at least about 1 wt%,
1.25 wt %, 1.5
wt%, 1.75 wt%, 2 wt%.
[0035] In considering the amount of flocculating polymer to include in the
functional
processing solution, it is again the amount of polymer in the treated oil
sands tailings forming
the treated slurry that is significant. However, since the polymer flocculates
with the solids in
the tailings, the dose of is determined based on the amount of solids in the
treated tailings
forming the treated slurry. In some embodiments of the present disclosure, the
suspended solids
stream can be treated with one or more polymer flocculants at a dose (weight
of the polymer
flocculant) to weight of the solids in the tailings) of not less than zero and
up to about 0.001
wt%, e.g., up to about 0.005 wt% such as up to about 0.01 wt% and in some
implementations
up to about 0.015 wt%, 0.020 wt%, 0.025 wt%, 0.03 wt%, or 0.04 wt%.
[0036] Mixing a functional processing solution with appropriate amounts of
indifferent
salt and polymer floccuant with a solids suspension stream from oil sands
tailings and coarse
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particles forms a treated slurry stream having consolidated solids and
clarified water. In some
embodiments, the consolidated material can have a solids content of greater
than about 50%
and at least about 55%, 60%, 65%, 70%, 75% and 80% by weight.
[0037] As an example, Figure 1 illustrates a process for dewatering oil
sands
tailings(100), such as mature fine tailings or fluid fine tailings, from a
tailings storage facility,
in this case a tailings pond (110). As illustrated in the figure, process
water from at or near the
surface (110a) of the tailings pond (110) can be mixed with an indifferent
salt and polymer
flocculant to form a functional processing solution (FPS). The FPS can be
prepared in an FPS
unit (120) in which certain amounts of process water, indifferent salt,
polymer flocculant and
other optional components can be combined and adjusted to appropriate
concentrations for the
indifferent salt and polymer. The functional processing solution (122) is then
mixed with a
solids suspension stream from oil sands tailings (110b) and coarse particles
(140). The solids
suspension stream is obtained from an intermediate layer or lower layer of the
tailings pond
which have oil sands fines in water with a solids content greater than 2 wt%
and higher such as
a solids content greater than or equal to about 30 wt%, e.g., FFT or MFT. The
coarse particles
can be sand from existing tailings storage facilities or in the form of a
slurry from currently
operating oil sands primary separation vessels to mix with the solids
suspension tailings stream
and FPS. Petroleum coke from current upgrading operations could also be used
with the sand
or separately as coarse particles to mix with the solids suspension stream.
The inclusion of
coarse particles (e.g., sand, petroleum coke, limestone) in the process
reduces the time for
consolidation of fines and significantly increased the solids content and
shear strength of the
final consolidated solids.
[0038] In addition to petroleum coke and sand, other coarse particles that
would be
beneficial in the process would include limestone or limestone mixed with sand
or petroleum
coke. MFT and FFT contain significant amounts of sulfide minerals like pyrite
that would result
in acid rock drainage. In addition, such acid leachates can dissolve toxic
trace metals and release
them to the environment. (See Kuznetsova et al.; Science of the Total
Environment 571 (2016)
699-710.) The inclusion of limestone as a coarse particle or a component of a
coarse particle
mixture can minimize this problem by neutralization of any acid species
formed.
[0039] Upon mixing, the initial concentration of the indifferent salt in
the FPS becomes
diluted with water in the MET (or FFT) and any water combined with the coarse
particle
fraction. We have found that to have fast consolidation of the suspended
solids, the
concentration of the indifferent salt in the treated tailings stream forming
the treated slurry
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should be at least 0.5 wt% and preferably higher such as at least about 1 wt%
of the indifferent
salt dissolved in the water portion of the slurry. Under such conditions,
mixing the functional
processing solution (122), tailings (110b) and coarse particles (140) in a
mixing unit (130) forms
a treated slurry stream (132) having consolidated solids and clarified water.
Mixing unit 130
can be an inline mixing unit, one or more dynamic mixers, etc.
[0040] The treated slurry can then be pumped to a solids/liquids
separation unit (150)
where clarified water (152) can be readily separated from the consolidated
material (154). The
solids content of the consolidated material will depend, in part, on the
concentration of
indifferent salt in the treated slurry, dose of flocculating polymer and
amount of sand and time
for dewatering, but can be greater than about 50%. The indifferent salt in the
separated clarified
water (152) can then be concentrated by removing water by desalination. This
step can also
remove organic contaminants present in the clarified water. Figure 1 depicts
the use of a
membrane process such as reverse osmosis or nanofiltration (160). Other
methods can be used.
[0041] As illustrated in Figure 1, clarified water (152) is treated by
reverse osmosis or
nanofiltration (160) to form a brine stream (162) which includes the
indifferent salt, and a
desalted water stream (164). The brine steam, which includes the indifferent
salt, can then be
recycled to the process by mixing the brine stream (162) in the functional
processing solution
unit (120) and combining it with either or all of the process water,
indifferent salt or polymer
flocculant to form additional functional processing solution. Make-up FPS
components
(indifferent salt and polymer) are added as needed.
[0042] The processes of the present disclosure can optionally include
monitoring the
concentration of the indifferent salt or the polymer flocculant or both during
various steps in the
process. For example, one or more monitors (170) can be used to monitor and
determine the
concentrations in any one or all of a stream of the functional processing
solution (170a), a stream
of clarified water (170b), a brine stream (170c), or a desalted water stream
(170d). Amounts of
indifferent salt or flocculating polymer or both can be adjusted based on a
determination of the
monitored concentrations of such in one or more streams. Hence, managing the
indifferent salt
and polymer concentrations in the process and producing purified water can be
integral parts of
the process.
[0043] Figure 2 shows the results of vial tests that demonstrate that a
combination of an
indifferent salt and a flocculating polymer results in a fast consolidation of
MFT. In this
experiment, four vials of MFT were prepared and treated. Each of the four
vials included
approximately 5 grams of MFT. The MFT sample was obtained from Alberta
Innovates Corp.,
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which obtained the samples from oil sands tailings ponds. This MFT sample had
a sludge-like
consistency with an average solids content of about 30 wt%.
[0044] The MFT in the first vial was mixed with an equal weight of tap-
water (as a
control); in the second vial it was mixed with a 5% solution of ammonium
chloride (no
polymer); in the third vial it was mixed with an aqueous solution of
polyacrylamide (0.1% by
weight, no added salt); and in the fourth vial it was mixed with a solution
containing both
ammonium chloride (5%) and polyacrylamide (0.1%). The vials were shaken to
provide mixing
and then centrifuged at 3000 rpm for 30 seconds. It can be seen that the
control vial (addition
of just tap-water) showed little or no settling. Both the salt and
polyacrylamide alone allowed a
degree of consolidation, but residual fines can be seen in the supernatant
water. The combination
of indifferent salt and polymer gave far superior results, with a highly
consolidated solids phase
and a clear supernatant liquid phase.
[0045] Similar vial tests show that an FPS having a concentration of 1 wt%-
5 wt% of
the indifferent salts and 0.01% to 0.1% flocculating polymer works well.
Higher concentrations
work just as well but would involve higher materials costs.
[0046] Mixing of the FPS with MFT (or FFT) pumped from the tailings pond
can be
accomplished by standard methods known to the art. Sand and/or petroleum coke
and/or
limestone can also be mixed with these two streams. Tests of the process where
sand is added
as a solid is shown in Figure 3 and utilized a ribbon mixer. As in laboratory
work, the process
is very simple. First, the MFT is mixed with FPS (2% ammonium sulfate solution
containing
0.1% PAM in this example). This initiates destabilization and partial
flocculation of the fines
(top left picture in Figure 3). Sand is then added as a solid, as shown in the
bottom left picture
in this figure. The proportion of sand to fines in the oil sands tailings
stream in this example
was about 0.8:1.
[0047] Mixing was continued for a few minutes. The resulting treated
slurry had two
phases that were apparent to the naked eye with a semi-solid like material
dispersed in an
apparently clear liquid. This can also be seen in Figure 3, right hand
pictures, which shows two
screen shots from a video of the solids and liquids pouring out of the bottom
of the mixer once
a valve was opened. The solids were captured on a metal sieve, while the
apparently clear liquid
quickly drained into a drum placed beneath.
[0048] The consolidated solids had sufficient cohesion to remain supported
on the mesh
but were wet. A sample was immediately taken and dried in an oven overnight.
The solids
Date Recue/Date Received 2021-03-05
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12
content of the initially formed consolidated MFT/sand was determined to be
53%. Some of this
material was pressed by hand between paper towels. This material had a solids
content of 75%.
[0049] The solids content of the treated slurry from the ribbon mixer
increased rapidly
over time through simple drainage and evaporation. The recovered tailings/sand
mixture was
initially placed on a plastic sheet. After one-week it had a solids content of
75% and could easily
support the weight of a person. The material was then left outside to the
mercy of the elements.
Three months later the recovered tailings/sand mixture was still cohesive and
could still readily
support the weight of a person. However, as with clay-like soils, it could
also be broken apart
using ordinary tools.
[0050] In another embodiment of the process mixing can advantageously be
accomplished by using the tailings stream from the primary oil sands
separation vessel, where
the solids component consists predominantly of coarse sand. Depending on the
slurry
concentration in this process stream, it may be advantageous to partially
thicken this stream first
and recycle the collected water to the process.
[0051] In-line mixing is one method that can be used to mix a sand stream
from a
primary oil sands separation vessel (142) and a solids suspension stream from
oil sands tailings
(110b) and then simultaneously or subsequently mix with a stream of FPS (122).
A schematic
illustration of this part of the process is shown in Figure 5. The FPS can be
added as a single
solution (i.e., a salt and polymer solution) (122) or as separate solutions
added successively. In
this latter embodiment of the process, the salt solution (FPS1)(122a) should
be added first to
destabilize the tailings solids, followed by a polymer solution (FPS2) (122b)
to bind the
destabilized suspension into fast settling flocs. Mixing such streams results
in a treated slurry
having consolidated solids and clarified water.
[0052] Once the clarified water and consolidated solids have been
separated, the
clarified water, diluted with process water from the MFT and coarse particle
slurry, can be
restored to its operating salt concentration for recycling and reuse. This can
be accomplished by
evaporative methods, reverse osmosis etc. In the embodiment of the process
shown in figure 1
reverse osmosis or nanofiltration or a combination of the two can be used.
[0053] The use of membrane processes in this process has the additional
benefit of
removing pollutants such as naphthenic acids (see Wu et al., Fuel 253 (2019)
1229-1246).
Evaporation methods could result in the incorporation of low boiling point
pollutants into the
evaporated water stream. Advantageously, the process is designed to produce a
stream of
purified water that can be returned to the environment.
Date Recue/Date Received 2021-03-05
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13
[0054] Naphthenic acids are considered to be the major source of toxicity
in tailings
ponds process water and pose a significant problem in releasing untreated
water to the
environment. They have limited solubility in water, about 88 mg/L at pH 7.5
(Naphthenic Acid
Category Analysis and Hazard Characterization. Report to the EPA by The
American Petroleum
Institute Petroleum HPV Testing Group; Consortium Registration # 1100997 May
14, 2012.)
The concentration of naphthenic acids in the oil sands tailings ponds varies
but is between 20
mg/L and 80 mg/L. (Li et al.; Science of the Total Environment 601-602 (2017)
1785-1802.)
[0055] Reverse osmosis can reduce the total dissolved solids present to
very low levels
removing heavy metals and dissolved organic material such as polycyclic
aromatics and
naphthenic acids. (Loganathan et al. Desalination 360 (2015) 52-60).
Particular attention has
also been paid to adsorption of naphthenic acids and their salts on petroleum
coke and activated
petroleum cokes. Petroleum coke is a by-product of bitumen upgrading and there
is a large
local supply. However, depending on how much petroleum coke is used and the
method of
contact, adsorption of naphthenic acids is incomplete and can be as low as 18%
of the material
originally present in the water. (See Zubot et al.; Science of the Total
Environment 427-428
(2012) 364-372; Alam et al.; Environmental Technology & Innovation 6 (2016)
141-151.)
[0056] The water processing part of the process can be managed carefully.
If, for
example, reverse osmosis is used to restore the FPS to its original salt
concentration, too high a
feed salt concentration and the requirement for a high salt concentration FPS
would involve the
use of high pressures at correspondingly high cost. There would also be
concentration limits
close to those encountered in seawater desalination (-3.5% salt feed, 7% brine
produced). Thus,
if reverse osmosis is used to produce a brine stream it can be adjusted to
produce an appropriate
concentration of the indifferent salt. The same can be achieved with
nanofiltration.
[0057] Excess polymer remaining in solution would also be problematic as
it can clog
membranes. Stray fines not captured in the consolidated solids would pose a
similar problem.
These problems can be handled by passing the solution through a bed of coarse
particles prior
to reverse osmosis or nanofiltration. Petroleum coke, a by-product of bitumen
upgrading, could
advantageously be used to accomplish this. It would have the additional
benefit of removing a
proportion of pollutants like naphthenic acids from the clarified water
stream.
[0058] Because of these and other factors, a water management system is a
useful part
of the process. The indifferent salt concentration can be readily determined
by conductivity
measurements, while the concentration of polymers like polyacrylamide have
distinct
absorption bands that can be measured at very low (ppm) concentrations using
ultra-violet
Date Recue/Date Received 2021-03-05
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14
spectroscopy. In-line instruments set to the appropriate specific frequency
provide an
inexpensive monitoring tool for this purpose.
[0059] Figure 7 illustrates an aspect of managing water in the process. It
includes many
of the same elements in the schematic flow chart shown in Figure 1 and adds
mass flow numbers
per unit time. These are depicted in tons, which could be tons/hour or
tons/day, depending on
the size of the process. The number shown in parentheses are the solids
contents of the streams
and their salt concentrations. An optional circuit to treat a stream of
clarified water by petroleum
coke or other treatment option is shown between the solids/liquids separation
step and the
reverse osmosis or nanofiltration unit. This would help remove gel-like or
other materials that
could clog membranes. It would also adsorb naphthenic acids and some other
organics and help
prevent the build-up of unwanted species in the recycled water.
[0060] The flow diagram assumes MFT with a 30% solids content and a coarse
sand
slurry stream with a 50% solids content. The initial concentration of
indifferent salt in the FPS
stream is 3.5%. It is diluted to an operating concentration of 1.75% by
process water from the
MFT and coarse sand slurry tailings streams. The reverse osmosis unit restores
the concentration
to 5% while producing desalinated water that is also free of organic
contaminants like
naphthenic acids.
[0061] Upon returning to the FPS storage facility, the saline water is
diluted back to the
3.5% initial concentration by advantageously using process water from near the
surface of the
tailings pond. This process water can also be used to produce FPS make-up
solutions to restore
polymer and salt solution losses on the separated solids. Monitoring of the
flow rates and salt
concentrations allow for control of the process. Essentially, tailings ponds
water is an input to
the process and purified water is an output of the process.
[0062] In summary, the process described herein advantageously dewaters
MFT to form
high solids content, stackable material while using contaminated processing
water. Clean,
desalted water is produced from this process water as an integral part of the
process.
EXAMPLES
[0063] The following examples are intended to further illustrate certain
preferred
embodiments of the invention and are not limiting in nature. Those skilled in
the art will
recognize, or be able to ascertain, using no more than routine
experimentation, numerous
equivalents to the specific substances and procedures described herein.
Date Recue/Date Received 2021-03-05
123170-5016-CA
[0064] Pilot-scale testing of this embodiment of the process is
illustrated in figures 6. A
simple mixing and separation system was constructed. Essentially, two tanks,
one containing
MFT with added sand and the second tank containing the FPS were both connected
to a positive
displacement pump to allow in-line mixing, as shown in the picture on the left
in Figure 6. The
slurry was then pumped through up to 300 ft (-91 m) of pipe to allow mixing.
The length of
pipe could be varied to change mixing time. The slurry was then emptied onto a
simple wooden
flume to allow gravity drainage, as shown in the middle picture in Figure 6.
The proportion of
sand to MFT solids was 1:1.
[0065] Figure 6 shows that as the FPS/MFT slurry emerged from the mixing
pipe onto
the flume the solids had already partially separated from liquids, which
appeared to be a mostly
clear stream with minimal suspended particles. The slurry quickly drained to
give a material
that could be pressed by hand to give a cohesive solid ball with a solids
content of 75%, as
shown in the right-hand picture in Figure 6. This material continued to dry
over the next couple
of days by both draining and evaporation to give a material with a solids
content in excess of
90%.
[0066] Faster separation of the solids and liquids to give a high solids
content material
can be achieved with standard equipment known to the art, such as vacuum drum
filters, belt
filters, plate-and-frame presses, cyclones, screens, dewatering screws,
decanting centrifuges,
etc.
[0067] While the claimed invention has been described in detail and with
reference to
specific embodiments thereof, it will be apparent to one of ordinary skill in
the art that various
changes and modifications can be made to the claimed invention without
departing from the
spirit and scope thereof. Thus, for example, those skilled in the art will
recognize, or be able to
ascertain, using no more than routine experimentation, numerous equivalents to
the specific
substances and procedures described herein. Such equivalents are considered to
be within the
scope of this invention and are covered by the following claims.
Date Recue/Date Received 2021-03-05
