Note: Descriptions are shown in the official language in which they were submitted.
CA 02924305 2016-03-15
,
,
DOCKET NO.: NS-549
IN-SITU TREATMENT OF TAILINGS
INVENTORS: YUAN, Simon; LORENTZ, James
ASSIGNEE: SYNCRUDE CANADA LTD.
Field of the Invention
[0001] The present invention relates generally to in-situ
processes for
dewatering tailings ponds such as oil sands tailings ponds. More particularly,
a mobile
facility is provided which can be located on or near a tailings pond for in-
situ treatment
of tailings.
Background of the Invention
[0002] Oil sand generally comprises water-wet sand grains held
together by a
matrix of viscous heavy oil or bitumen. Bitumen is a complex and viscous
mixture of
large or heavy hydrocarbon molecules which contain a significant amount of
sulfur,
nitrogen and oxygen. The extraction of bitumen from sand using hot water
processes
yields large volumes of tailings composed of sand, fine silts, clays and
residual bitumen
which have to be contained in a tailings pond. Mineral fractions with a
particle diameter
less than 44 microns are referred to as "fines." These fines are typically
quartz and clay
mineral suspensions, predominantly kaolinite and illite.
[0003] Tailings produced during bitumen extraction are
typically 50% water
and 50% solids by weight. The solids fraction can be further defined as being
either fine
or coarse solids. Typically, the solid fraction contains 80% coarse and 20%
fines by
weight. Upon entry into the aqueous tailings storage pond the fines and the
coarse
material segregate. The majority of the coarse material settles rapidly to
form beaches
1
WSLEGAL\053707\00544\ 13236334v 1
CA 02924305 2016-03-15
or pond bottom. However, the fines and a portion of the coarse material settle
slowly
over a period of years to a typical composition of 35% solids by weight, which
composition is sometimes referred to a mature fine tailings or MFT.
Hereinafter, the
more general term of fluid fine tailings (FFT) will be used, which encompasses
the
spectrum of tailings from discharge to final settled state. As used herein,
FFT generally
refers to a suspension of oil sands fines in water with a solids content
greater than 1%
and having less than an undrained shear strength of 5 kPa.
[0004] The fluid fine tailings behave as a fluid colloidal-like
material. The fact
that fluid fine tailings behave as a fluid and have very slow consolidation
rates limits
options to reclaim tailings ponds. A challenge facing the industry remains the
removal
of water from the fluid fine tailings to increase the solids content well
beyond 35 wt%
and strengthen the deposits to the point that they can be reclaimed and no
longer
require containment.
[0005] Various processes have been developed by the industry to
address the
slow consolidation of FFT, for example, centrifugation, the TROT"' process,
atmospheric
fines drying, accelerated dewatering/rim ditching, etc. However, all of these
processes
require prior flocculation of FFT with a polymeric flocculant, hence, require
FFT
dredging, pumping and transporting from a tailings pond to another location
(e.g., FFT
treatment plants). The treated FFT must then be transported back to another
designated deposition site for consolidation and desiccation. Thus, the
capital and
operation costs are a major concern.
[0006] Accordingly, there is a need for an in-situ method of
dewatering tailings
which can reduce capital and operation costs and enhance the effectiveness of
FFT
treatment.
Summary of the Invention
[0007] The current application is directed to a process for dewatering
tailings
ponds such as oil sands tailings ponds in-situ. By being able to treat
tailings in-situ, one
or more of the following benefits may be realized:
2
WSLEGAL\053707\00544\ I3236334v I
CA 02924305 2016-03-15
=
1. Reduction of capital and operation costs of FFT treatment through in-
situ
flocculation of FFT with a dredge or barge;
2. Reduction of the FFT pumping distances and costs;
3. Eliminating the requirement of an external pond/containment area; and
4. Eliminating the requirement to build a fixed FFT treatment plant.
[0008] Thus, broadly stated, in one aspect of the present invention,
a process
for the in-situ treatment of tailings in a containment area having a tailings
layer
comprising fine solids and water is provided, comprising:
= adding a flocculant, a coagulant, a hydrophobicity modifying agent, or
any
combination thereof, into a portion of the tailings layer;
= mixing the portion of the tailings layer and flocculant, coagulant,
hydrophobicity modifying agent, or combinations thereof, to form in-situ
treated
tailings; and
= allowing the in-situ treated tailings to dewater and/or consolidate in-
situ in the
tailings containment area.
[0009] Additional aspects and advantages of the present invention
will be
apparent in view of the description, which follows. It should be understood,
however,
that the detailed description and the specific examples, while indicating
preferred
embodiments of the invention, are given by way of illustration only, since
various
changes and modifications within the spirit and scope of the invention will
become
apparent to those skilled in the art from this detailed description.
Brief Description of the Drawings
[00010] The invention will now be described by way of an exemplary
embodiment with reference to the accompanying simplified, diagrammatic, not-to-
scale
drawings:
3
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
[00011]
FIG. 1 is a schematic of one embodiment of the present invention for
in-situ consolidation of fluid fine tailings (FFT) present in a tailings pond.
[00012]
FIG. 2 is a schematic showing another embodiment of the present
invention for in-situ consolidation of fluid fine tailings (FFT) present in a
tailings pond.
[00013]
FIG. 3 is a schematic showing another embodiment of the present
invention for in-situ consolidation of fluid fine tailings (FFT) present in a
tailings pond.
[00014]
FIG. 4 is a schematic showing an embodiment of the present invention
for in-situ treatment of fluid fine tailings (FFT) present in a tailings pond
designed to float
clays therein for removal.
Detailed Description of Preferred Embodiments
[00015]
The detailed description set forth below in connection with the
appended drawings is intended as a description of various embodiments of the
present
invention and is not intended to represent the only embodiments contemplated
by the
inventor. The detailed description includes specific details for the purpose
of providing
a comprehensive understanding of the present invention. However, it will be
apparent to
those skilled in the art that the present invention may be practised without
these specific
details.
[00016]
The present invention relates generally to a process for dewatering
tailings such as oil sands tailings, which are present in a tailings pond or
other
containment, by in-situ treatment with additives.
Additives useful in the present
invention include a flocculant, a coagulant, a hydrophobicity modifying agent,
or any
combination thereof.
Flocculants and coagulants flocculate/agglomerate particles,
thereby affecting the hydraulic conductivity and porosity. Hydrophobicity
modifying
agents are reagents that may reduce the affinity between clay and water and
may
significantly enhance the dewatering rate and hydraulic conductivity of clays
in the
deposit.
4
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
[00017] As used herein, the term "tailings" means any tailings produced
during
a mining operation and, in particular, tailings derived from oil sands
extraction
operations that contain a fines fraction, which are disposed of at a disposal
site such as
a tailings pond and the like. The term is meant to include fluid fine tailings
(FFT)
present in oil sands tailings ponds.
[00018] As used herein, "in-situ" means in the original, natural, or
existing
place. As used herein, "in-situ treatment" means treating tailings that are
present in a
tailings containment area such as a tailings pond with at least one chemical
additive,
whereby the treated tailings are allowed to dewater and/or consolidate in the
tailings
containment area.
[00019] As used herein, the term "flocculation" refers to a process of
contact
and adhesion whereby the particles of a dispersion form larger-size clusters
in the form
of flocs or aggregates. As used herein, the term "flocculant" refers to a
reagent which
promotes flocculation by bridging colloids and other suspended particles in
liquids to
aggregate, forming a floc. Flocculants useful in the present invention are
generally
anionic polymers, which may be naturally occurring or synthetic, having
relatively high
molecular weights. In one embodiment, the dosage of the anionic polymeric
flocculant
ranges from between about 0 to about 1500 grams per tonne of solids in the
tailings.
[00020] Suitable natural polymeric flocculants may be polysaccharides
such as
guar gum, gelatin, alginates, chitosan, and isinglass. Suitable synthetic
polymeric
flocculants include, but are not limited to, polyacrylamides, for example, a
high
molecular weight, long-chain modified polyacrylamide (PAM). PAM is a polymer (-
CH2CHCONH2-)n formed from acrylamide subunits with the following structure:
_________ CH2 HT ________
C=0
NH2 n
(1)
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
(000211
It can be synthesized as a simple linear-chain structure or cross-linked,
typically using N,N'-methylenebisacrylamide to form a branched structure. Even
though
such compounds are often called "polyacrylamide," many are copolymers of
acrylamide
and one or more other chemical species, such as an acrylic acid or a salt
thereof. The
"modified" polymer is thus conferred with a particular ionic character, i.e.,
changing the
anionicity of the PAM.
Preferably, the polyacrylamide anionic flocculants are
characterized by molecular weights ranging between about 10 to about 24
million, and
medium charge density (about 25-30% anionicity).
[00022)
It will be appreciated by those skilled in the art that various
modifications (e.g., branched or straight chain modifications, charge density,
molecular
weight, dosage) to the flocculant may be contemplated.
(00023)
As used herein, the term "coagulation" refers to a process of
neutralizing repulsive electrostatic charge (often negative) surrounding
particles to
cause them to collide and agglomerate under the influence of Van der Waals's
forces.
As used herein, the term "coagulant" refers to a reagent which neutralizes
repulsive
electrical charges surrounding particles to cause the particles to
agglomerate. The term
includes organic and inorganic coagulants.
[00024]
A suitable organic coagulant useful in the present invention includes,
but is not limited to, a cationic polymeric coagulant. In one embodiment, the
dosage of
the cationic polymeric coagulant ranges between about 0 to about 1000 grams
per
tonne of solids in the tailings. In one embodiment, the cationic polymeric
coagulant
comprises polydimethyldiallylammonium chloride (or polydiallyldimethylammonium
chloride (abbreviated as "polyDADMAC" and having a molecular formula of (C81-
116NCI)n.
In one embodiment, the polyDADMAC has a molecular weight ranging between about
6,000 to about 1 million, and a high charge density (about 100% cationicity).
The
monomer DADMAC is formed by reacting two equivalents of ally' chloride with
dimethylamine.
PolyDADMAC is then synthesized by radical polymerization of
DADMAC with an organic peroxide used as a catalyst. Two polymeric structures
are
6
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
possible when polymerizing DADMAC: N-substituted piperidine structure or N-
substituted pyrrolidine structure, with the pyrrolidine structure being
favored. The
polymerization process for polyDADMAC is shown as follows:
cH, ___________________________________________ CH,
H3C
r-,13u0OH
N ASO-75 C
H3C/ CH3 /N\
H3C Cl-I3
CI CI
-n
(2)
[00025] In one embodiment, cationic polymeric coagulants are more
effective
than inorganic cationic coagulants at the same dosages. However, suitable
inorganic
cationic coagulants useful in the present invention include, but are not
limited to, alum,
aluminum chlorohydrate, aluminum sulphate, lime (calcium oxide), slaked lime
(calcium
hydroxide), calcium chloride, magnesium chloride, iron (II) sulphate (ferrous
sulphate),
iron (III) chloride (ferric chloride), sodium aluminate, gypsum (calcium
sulphate
dehydrate), or any combination thereof. In one embodiment, the inorganic
coagulants
include multivalent cations. As used herein, the term "multivalent" means an
element
having more than one valence. Valence is defined as the number of valence
bonds
formed by a given atom. Suitable multivalent inorganic coagulants may comprise
divalent or trivalent cations. Divalent cations increase the adhesion of
bitumen to clay
particles and the coagulation of clay particles, and include, but are not
limited to,
calcium (Ca2+), magnesium (Mg2+), and iron (Fe2+). Trivalent cations include,
but are
not limited to, aluminium (A13+), iron (Fe3+).
[00026] As used herein, "aggregation" refers to the formation of
clusters, flocs
or aggregates in a colloidal suspension as a result of the addition of a
flocculant, a
coagulant, or both. Aggregation is also referred to herein as coagulation or
flocculation.
[00027] As used herein, the term "hydrophobicity modifying agent"
refers to a
chemical reagent which increases the natural hydrophobicity of a mineral
surface, in
particular, clays, thereby decreasing the mineral's affinity to water. For
example, such
7
WSLEGAL\053707\00544\13236334v I
CA 02924305 2016-03-15
reagents can adsorb physically onto mineral surfaces that possess active sites
having
strong negative charge, thereby rendering the mineral surfaces less water
loving
(hydrophilic) and more water repelling (hydrophobic). A suitable
hydrophobicity
modifying agent is dodecylamine (DDA) having a molecular weight of about 185
Da and
molecular formula of C12H27N. Other suitable hydrophobicity modifying agents
include,
but are not limited to, DDAHCI (dodecylamine hydrochloride, MW = 221.81); DTAC
(dodecyl-trimethylammonium chloride, MW = 263.89); CTAB (cetyl-
trimethylammonium
bromide, MW = 364.45). Other hydrophobicity modifying agents that may be
useful in
the present invention include other ammonium surfactants and phosphonium
surfactants. Some hydrophobicity modifying agents act as collectors.
Collectors are
generally used in froth flotation and, as used herein, "collector" is a
chemical that
attaches to the mineral surface (in particular, clays) and produces a
hydrophobic
surface. The water-repellent surface facilitates the attachment of the mineral
particle to
an air bubble.
Useful collectors may include oils, xanthates, dithiophosphates,
petroleum sulfonates and fatty amines.
Dodecylamine (DDA), dodecylamine
hydrochloride (DDAHCI), dodecyl-trimethylammonium chloride (DTAC) and cetyl-
trimethylammonium bromide (CTAB) can also be used as collectors.
[00028]
As used herein, a "frothing agent" or "frother" refers to chemicals
added to the process which have the ability to change the surface tension of a
liquid
such that the properties of the sparging bubbles are modified. Frothers may
act to
stabilize air bubbles so that they will remain well-dispersed in slurry, and
will form a
stable froth layer that can be removed before the bubbles burst. Ideally the
frother
should not enhance the flotation of unwanted material and the froth should
have the
tendency to break down when removed from the flotation apparatus. Frothers
suitable
for the present invention include alcohols (e.g., MIBC), polypropylene glycol
ethers,
glycol ethers, pine oil, cresol and paraffins.
[00029]
As used herein, a "depressant" refers to a chemical that may depress
quartz/feldspar and enhance the hydrophobicity difference between the clays
and the
quartz/feldspar, and hence increase the clay flotation selectivity. The
typical silica
depressant is sodium silicate (commonly referred to as "water glass"). A
depressant
8
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
may include pH modifying agents that have a strong impact on oxide mineral
surface
charges, and hence, on the adsorption of collectors and selectivity between
silica and
clays. For example, at pH 4 using a cationic collector such as DDA, clays have
the
maximum recovery while silica has the lowest recovery. Thus, pH modifiers also
function as depressants to some extent.
[00030] In one embodiment of the present invention,
flocculation/aggregation of
tailings may be followed by treatment with a collector. Without being bound by
any
theory, treatment of the flocculated/aggregated tailings with a collector
enhances the
particle surface hydrophobicity, thereby reducing the affinity of the
aggregates to retain
water and increasing the hydraulic conductivity of the aggregates. This
results in better
solids liquid separation and a product which becomes more rapidly reclaimable.
[00031] Further, in the present invention, a hydrophobicity modifying
agent,
together with sufficient aeration, may be used to render the clays present in
the tailings
floatable in-situ so that the clays can be collected and removed from the
tailings
containment area for disposal.
[00032] One embodiment of the present invention is shown in FIG. 1.
Generally, a tailings pond 100 is a dam or an impoundment that is commonly
made
using "local materials". For example, tailings pond 100 may comprise berms 10
made
from, for example, packed tailings sand or overburden, and sand 12. It is
understood,
however, that a tailings pond could also an in-pit impoundment or a dug pit.
When oil
sand tailings are impounded in a tailings pond, the coarser and heavier sand
settles out
fairly quickly to form sand beaches 12; however, the fluid fine tailings 14
(FFT 14) will
only consolidate to about 35 wt% solids. Forming on top of the tailings pond
100 is a
substantial layer of water 16. Thus, a dredge or barge 18 can be used, which
floats on
the water 16, to treat the FFT 14 in-situ with various additives to enhance
the
dewatering/consolidation of FFT 14.
[00033] In the embodiment shown in FIG. 1, dredge 18 comprises a first
pipe
28 (also referred to herein as FFT pipe 28), which is submerged into the FFT
layer.
Pump 32 (also referred to herein as re-circulation pump 32) will pump the FFT
14 from
9
WSLEGAL\053707\00544\ I 3236334v1
CA 02924305 2016-03-15
the tailings pond and recirculate the FFT 14 through a second pipe 30 (also
referred to
herein as the additive pipe 30). Tanks of additives are also present on the
dredge 18.
For example, dredge 18 may have two tanks which may contain a flocculant, a
coagulant, or one of each (tanks 20 and 20') and, optionally, a third tank
which contains
a hydrophobicity modifying agent (tank 22). A pump 24 is connected to tank 20
and/or
20' and will inject flocculant, coagulant or both into the FFT 14 that is
present in additive
pipe 30. Similarly, a pump 26 is connected to tank 22 for pumping a
hydrophobicity
modifying agent from the tank and injecting the hydrophobicity modifying agent
into the
FFT 14 present in additive pipe 30. Generally, flocculant/coagulant is added
first,
followed by a hydrophobicity modifying agent. Flocculant/coagulant and
hydrophobicity
modifying agent can be prepared off-shore or can be prepared on dredge 18.
[00034] Thus, re-circulation pump 32 will mix the FFT 14 with the
flocculant/coagulant and hydrophobicity modifying agent and deposit the
treated FFT
back to tailings pond 100. In one embodiment, an in-line static or dynamic
mixer may
be added to additive pipe 30 to aid in the mixing of the FFT and additives.
Once the
treated FFT is deposited back to the tailings pond, the flocs/aggregates will
rapidly
settle to the bottom of the tailings pond and release water to the surface of
the tailings
pond. The dredge 18 can then be slowly moved forward or backward from one
place in
the tailings pond to another.
[00035] Another embodiment of the present invention is shown in FIG. 2.
Once
again, tailings pond 200 comprises berms 210 made from, for example, packed
tailings
sand or overburden, and sand 212. It is understood, however, that a tailings
pond could
also an in-pit impoundment or a dug pit. When oil sand tailings are impounded
in a
tailings pond, the heavier sand settles out fairly quickly to form sand
beaches 212;
however, the fluid fine tailings 214 (FFT 214) will only consolidate to about
35 wt%
solids. Forming on top of the tailings pond 200 is a substantial layer of
water 216.
Thus, a dredge or barge 218 can be used, which floats on the water 216, to
treat the
FFT 214 in-situ with various additives to enhance the dewatering/consolidation
of FFT
214.
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
[00036] In the embodiment shown in FIG. 2, dredge 218 comprises an
auger
240, which is submerged into the FFT layer. Auger 240 is designed to inject an
additive
such as a flocculant into the FFT 2014 in-situ and mix FFT 214 and flocculant
in-situ, as
well. In one embodiment, auger 240 comprises a hollow shaft wherein flocculant
is
introduced. In another embodiment, auger 240 comprises multiple injection
points for
injecting the flocculant into the FFT. Dredge 218 further comprises tanks of
additives,
for example, flocculant tanks 220. It is understood, however, that other
additives can be
added to the FFT 214, such as coagulants and/or a hydrophobicity modifying
agent. A
pump 224 (flocculant pump 224) is connected to flocculant tanks 220 and will
pump
flocculant into the auger 240, which is designed to inject flocculant/other
additives into
the FFT 214. As previously mentioned, auger 240 is also a mixer, which will
mix the
flocculant with the FFT 214 in-situ.
[00037] The flocs/aggregates that are formed in-situ will rapidly
settle to the
bottom of the tailings pond and release water to the surface of the tailings
pond. The
dredge 218 can then be slowly moved forward or backward from one place in the
tailings pond to another.
[00038] Another embodiment of the present invention is shown in FIG. 3.
Tailings pond 300 comprises berms 310 and sand 312. As previously mentioned,
when
oil sand tailings are impounded in a tailings pond, the heavier sand settles
out fairly
quickly to form sand beaches 312; however, the fluid fine tailings 314 (FFT
314) will
only consolidate to about 35 wt% solids. Forming on top of the tailings pond
300 is a
substantial layer of water 316. Thus, a dredge or barge 318 can be used, which
floats
on the water 316, to treat the FFT 314 in-situ with various additives to
enhance the
dewatering/consolidation of FFT 314.
[00039] In the embodiment shown in FIG. 3, dredge 318 comprises a first
auger 340 and a second auger 340'. First auger 340 is designed to inject
flocculant into
the FFT 314 and mix the FFT 314 and flocculant in-situ to form flocs or
aggregates.
Pump 324 pumps flocculant from flocculant tanks 320 and 320' to first auger
340.
Pump 326 is connected to tank 322 for pumping a hydrophobicity modifying agent
from
11
WSLEGAL\053707\00544\ 13236334v1
CA 02924305 2016-03-15
the tank and injecting the hydrophobicity modifying agent into the FFT 314 via
second
auger 340'. Generally, flocculant is added first, followed by a hydrophobicity
modifying
agent. Flocculant and hydrophobicity modifying agent can be prepared off-shore
or can
be prepared on dredge 318.
(000401 Thus, first and second augers 340, 340' will mix the FFT 314
with the
flocculant/hydrophobicity modifying agent in-situ in tailings pond 300. Thus,
the
flocs/aggregates are formed in-situ and will rapidly settle to the bottom of
the tailings
pond and release water to the surface of the tailings pond. The dredge 318 can
then be
slowly moved forward or backward from one place in the tailings pond to
another.
(00041J FIG. 4 is a schematic showing an embodiment of the present
invention
for in-situ treatment of fluid fine tailings (FFT) present in a tailings pond
which is
designed to float the clays present in the fluid fine tailings for removal. In
particular,
dredge 418 comprises at least one in-situ agitator 450 comprising a vertical
pipe 454
having a number of agitating devices 452, for example, impellers. The barge
418
further comprises a flocculant tank 42 and a collector tank 422. The in-situ
agitator 450
is designed to inject air 456, flocculant 451 and collector 453 into the FFT
514 and
agitate the FFT 414, flocculant 451, clay surface agent (collector) 453 and
air in-situ.
The clays in the FFT will flocculate/aggregate and the clay surface agent
(collector) will
allow the flocculated/aggregated clays to attach to air bubbles to form froth
bubbles 468,
which will rise to the surface of the water layer 416 and form clay froth 470.
The froth
470 can then be collected in a froth collection and shore transfer station 472
for
removal. A froth collection and shore transfer station may comprise a
mechanical or
vacuum froth collection device and a pump to transfer the froth to a
deposition site. In
the alternative, and overflow weir system can be used. A surface water
skimming
device can be used to collect the froth and the froth can be transferred via a
pump and
pipeline to shore. The remaining non-clay solids will rapidly settle to the
bottom of the
tailings pond and release water to the surface of the tailings pond. The
dredge 418 can
then be slowly moved forward or backward from one place in the tailings pond
to
another.
12
WSLEGAL\053707\00544\ 13236334v1
CA 02924305 2016-03-15
[00042] In one embodiment, a frother can be added to stabilize air
bubbles to
form a stable froth layer. In another embodiment, a depressant can be added to
depress non-clay solids such as quartz/feldspar.
[00043] Example 1
[00044] In this example, fluid fine tailings (FFT) were treated with
either
flocculant alone or flocculant followed by a hydrophobicity modifying agent.
The FFT
used in this example ranged in solids concentrations from about 20-35 wt%
solids and
FFT comprising about 38.66 wt% solids. The flocculant used was an anionic,
high
molecular weight polyacrylamide, which is commercially available as SNF 3338.
The
hydrophobicity modifying agent used was dodecylamine (DDA).
[00045] A mixing tank was used to simulate in-situ mixing. The FFT was
added to the mixing tank and the FFT was first treated with 800 g or 1000 g
flocculant
(SNF 3338) per tonne of tailings solids and mixed for 30 seconds to form large
aggregates (i.e., flocs). The flocculated/aggregated FFT was then either
treated with
DDA at a dosage of 650 g/tonne of tailings solids or no further treatment was
performed. When treated with DDA, the FFT flocculated/aggregated tailings were
mixed for a further 30 seconds, to enhance the hydrophobicity of the
flocs/aggregates.
Several different mix conditions were tested, in particular, various HIT
conditions were
used, i.e., where HIT is the ratio of the slurry (tailings) height in the tank
and the tank
diameter. The mixing speed was also varied (250 rpm, 280 rpm or 300 rpm).
[00046] The dewatering capability of treated FFT was measured using a
Triton
Electronics Ltd. Capillary Suction Time tester to correlate dewatering
efficiency with the
chemical addition sequence. Dewaterability is measured as a function of how
long it
takes for water to travel radially between two ring electrodes through a
filter and low
values indicate rapid dewatering whereas high values indicate slow dewatering
ability.
Thus, a relatively low average capillary suction time (CST, seconds) indicates
good
dewatering. The results are shown in Table 1.
13
WSLEGAL\053707\00544\13236334v1
CA 02924305 2016-03-15
Table 1
Test # Feed Mix Conditions Flocculant Collector
CST (sec) Ave
Solids %
1 20% H/T=0.65, 250 rpm SNF 3338, 800 None
29
g/t
2 25% H/T=0.65, 250 rpm SNF 3338, 800 None
31
g/t
3 30% H/T=0.65, 280 rpm SNF 3338, 800 None
124
g/t
4 35% H/T=0.65, 300 rpm SNF 3338, 800 None
88
g/t
38.66% H/T=0.4, 250 rpm SNF 3338, None 920
1000 g/t
6 20% H/T=0.65, 250 rpm SNF 3338, 800 DDA,
650 g/t 22
g/t
7 25% H/T=0.65, 250 rpm SNF 3338, 800 DDA,
650 g/t 20
g/t
8 30% H/T=0.65, 280 rpm SNF 3338, 800 DDA,
650 g/t 26
g/t
9 35% H/T=0.65, 300 rpm SNF 3338, 800 DDA,
650 g/t 50
g/t
38.66% - H/T=0.4, 250 rpm SNF 3338, DDA, 650 g/t 21
1000 g/t
[00047] It can be seen from the results in Table 1 that, on average,
treatment
of FFT with a flocculant followed by treatment with a collector resulted in
capillary
suction times (CST, seconds) that were generally low, meaning that dewatering
was
occurring fairly rapidly. When FFT was treated with both flocculant and a
collector, CST
was even lower, indicating even better dewatering capability.
[00048] Example 2
[00049] FFT samples having 12.5 wt.% solids were first treated/mixed
with a
high molecular weight, anionic polyacrylamide flocculant, which is
commercially
14
WSLEGAL\053707\00544\ 13236334v1
CA 02924305 2016-03-15
available under the name SNF 3338, at dosages of 0 g/tonne, 50 g/tonne, 100
g/tonne,
500 g/tonne and 800 g/tonne, and mixed for about 0.5 minutes. It is generally
believed
that anionic polyacrylamide polymers are selective for clays. A cationic
collector DDA
was then added at a dosage of 650 g/tonne and the tailings were further
conditioned/mixed for 2 minutes. The thus-treated tailings were then subjected
to 15
minutes flotation in a Denver flotation cell and the clay froth was retrieved.
The total
solids recoveries in the clay froths were then determined.
[00050] At the highest dosage of polymeric flocculant (800 g/t), the
total solids
recovered in the clay froth increased from about 47 wt.% (with no flocculant)
to almost
80 wt%. Even when using very small amounts of polymeric flocculant (50-100
g/t), the
clay/solids recovery increased by more than 10%. Without being bound by
theory, it is
believed that the addition of a clay-specific flocculant causes the clay
particles to form
larger flocs. These flocs can then be rendered hydrophobic by adding a
collector such
as a cationic clay collector, which then allows the clay flocs to separate
from the
silt/sand and float, while the silt/sand sinks to the bottom of the flotation
cell as flotation
tails.
[00051] From the foregoing description, one skilled in the art can
easily
ascertain the essential characteristics of this invention and adapt it to
various usages
and conditions. Reference to an element in the singular, such as by use of the
article
"a" or "an" is not intended to mean "one and only one" unless specifically so
stated, but
rather "one or more". Nothing disclosed herein is intended to be dedicated to
the public
regardless of whether such disclosure is explicitly recited in the claims.
WSLEGAL\053707\00544\ 13236334v1
