Note: Descriptions are shown in the official language in which they were submitted.
CA 02954574 2017-01-13
MULTI-ACRYLATE ANIONIC FLOCCULANTS
FIELD:
The invention relates generally to polymers and the use thereof for
aggregating mineral or organic components in aqueous slurries to separate
out individual components of the slurry, which may then be recovered from
the slurry.
BACKGROUND:
Many industrial or municipal processes involve the dispersion of
minerals and/or organic matter in water to assist in the separation and
recovery of the mineral or organic components.
For mineral processing, the mining industry is the predominant user of
such processes, wherein mineral ores are ground and slurried in water to
allow separation and recovery of desired components. The residual mineral
components in the slurry, referred to as gangue or tailings, are then often
deposited in pits or ponds, often called tailings ponds, where solids are
expected to settle to allow recovery of the supernatant water, and ultimate
consolidation of the remaining mineral solids. Coal, copper and gold mining
are but a few of the mining processes that employ this technology. An
important use, discussed below, is in bitumen processing from oil sands
formations.
The slow rate of mineral solids setting in tailings ponds is often a
serious economic and environmental problem in mining operations. If an
objective of such processes is to recover water for reuse or disposal, lengthy
pond residence times, often measured in years, can cripple process economics.
Further, huge volumes of slurry can be environmentally and physically
dangerous. Occasional dike failures of coal slurry ponds attest to both these
dangers.
If the ponded slurry is predominantly composed of coarse minerals, the
settling rate in tailings in such ponds is not generally an environmental or
economic problem. In this instance, solids settle quickly and consolidate to
disposable consistencies, and water is easily recovered. However, when the
solid components of the ponded slurry are very fine, settling is often
hindered
and, in some instances, may take years to occur.
A major undesired component of many mineral slurries is often clay.
Clays have a variety of chemical compositions but a key determinant in how a
clay behaves in a mineral slurry is whether it is predominantly in a
monovalent (usually sodium) form or in a multivalent (usually calcium) form.
The effects of the varying chemical compositions of clays are well known to
those in the industry. Monovalent clays tend to be water-swelling and
dispersive, whereas multivalent clays generally are not.
Water-swelling and dispersive clays cause many of the problems in
mineral processing and tailings dewatering. These clays tend to be
monovalent sodium clays, such as bentonite, which is largely composed of
montmorillonite. These clays can be expressed as Na.Al2.SiO3.4Si02.H20.
Further, if the clays are very finely divided, the problem is often
magnified. If the clay particles are easily broken down to even finer
particles
through shearing in processing, problems can be compounded. Layered,
platelet, or shale-like forms of clay are particularly sensitive to mechanical
breakdown to even finer particles during processing.
In mineral processing, additives are often used to facilitate removal of
specific components. Frothers used to separate and float ground coal particles
are an example of this. In this instance, the desired component to be
recovered is an organic material such as coal, but similar processes are used
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for mineral recoveries. In almost all mining processes the remaining slurry
must be separated to recover water and consolidated solids.
Since the late 1960s, a new mining industry has been operating in the
northeast of the Canadian province of Alberta. The deposits being mined are
referred to as the Athabasca oil sands. These deposits are formed from a heavy
hydrocarbon oil (called bitumen), sand, clay, and water. In processing the
deposit, the ore is slurried in warm or hot water with the objective of
separating the bitumen from the sand and clay, recovering the bitumen by
flotation, recovering the water for reuse, and disposing of the dewatered
residual mineral solids in site reclamation. Canada's oil sand deposits
contain
the second largest quantity of oil in the world, second only to Saudi
Arabia's.
Consequently, separation, water recovery, and solids disposal are carried out
on an industrial scale never before seen.
The first objective in oil sands processing is to maximize bitumen
recovery. Slurrying in warm or hot water tends to release bitumen from the
minerals in the ore, in a pipeline process called hydrotransport, while the
slurry is transported via pipeline to a primary separation unit. Various
chemical additives, including caustic soda or sodium citrate, have been used
to
improve dispersion of the ore's components into the process water and to
accelerate separation of the bitumen from the sand and clay for greater
bitumen recovery. In the hydrotransport process, sand is relatively easily
stripped of bitumen and readily drops out and is removed through the bottom
of the primary separation unit; the clays are the principal problem. Clays,
associated with divalent or other multivalent cations, particularly calcium
and
magnesium, contributed by, for example, process waters are recognized to
deter efficient separation and flotation of the bitumen. The use of additives
such as caustic soda or sodium citrate aid in the dispersion to inhibit clay's
deleterious effects. Sodium citrate is a known dispersant and also acts as a
water-softening agent, to sequester calcium and magnesium ions.
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While improving recovery, these additives often have residual negative
effects following bitumen separation by inhibiting subsequent water removal
from the clay. A great deal of research has gone into studying the various
types
of clays found in the oil sands deposits. Different clays affect bitumen
separation differently, often in ways not completely understood, and
differences in the clays affect the clays' subsequent separation from the
process water. Since ore is a natural deposit, the separation process is at
the
mercy of clay type and content, and the level of divalent ions. Pump and
pipeline shear acting on the slurry also break down clay into finer clay
particles, which further negatively affects the separation process. Various
ore
sources are often blended prior to hydrotransport in an attempt to mitigate
the effects of clays. Compressed air may be introduced into the hydrotransport
pipeline. The air dissolves under pressure and, as pressure is released ahead
of the primary separation vessel, bubbles form to help float the bitumen.
In the separation process, the floated bitumen overflows to further
processing. Typically, the sand and any coarse clays settle quickly into the
base of a conical primary separation unit. The withdrawal rate of this coarse
segment can be controlled. The largest volumetric component, called
middlings, is the middle stratum above the coarse layer and below the
bitumen float. The middlings consist of a dispersion of the fine clays. The
industry considers these fine clays to be any size less than 44 microns in
diameter. These clays usually form a very stable dispersion. Any dispersive
additives further increase the stability of the clay slurry. If the
dispersant, or
any other additive, increases middlings viscosity in the primary separation
unit, then bitumen flotation and recovery may be hindered.
In existing processes, the conditions that promote efficient dispersion
and bitumen recovery appear to be diametrically opposed to the conditions
that subsequently promote downstream fine clay separation, solids
consolidation, and water recovery. The longer it takes to recover and reuse
the
process water, the more heat and evaporative losses occur. The tradeoff
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between efficient bitumen extraction and downstream disposal of mineral
solids is an expensive problem for the oil sands industry.
In the extraction process, middlings are continuously withdrawn from
the center of the primary separation unit. Both the heavy, easily settled
sand/coarse clay component, withdrawn from the conical bottom of the
primary separation unit, and the middlings component are usually subjected
to additional cleaning and mechanical devvatering steps to recover any
bitumen that is not floated off in the primary separation unit. The middlings
may be hydrocycloned to increase density. The middlings then generally
report to a thickener, where high molecular weight
sodium/potassium/ammonium-acrylate/acrylamide-based copolymers (called
flocculants) are added to coagulate and flocculate the dispersed middling's
fine clays. Four to five hours of residence time are generally required in the
thickener to produce a thickened underflow (to begin to increase clay solids
for use in final solids consolidation) and to produce clarified overflow water
for reuse in the process. Thickeners are immense, expensive mechanical
separators with massive holding volumes.
The final objective of the oil sands process is to produce dense,
trafficable solids for site reclamation and to recover water for process use.
The
two mineral process streams, sand/coarse clay from the primary separation
unit, and middlings (often thickened as described above) are either pumped to
separate containment areas (called ponds) or are combined and then sent to
ponds. Both approaches have created problems, with which the industry is
grappling. The combined streams (called combined tailings, or CT) have
produced a condition wherein the coarse sand and clays have settled relatively
quickly in the ponds, but the fine clays have not. Instead of the desired
settling
and recovery of supernatant water, the upper layer in these- ponds forms an
almost permanent layer of suspended fine clays, referred to as mature fine
tails (MFT). The clay content in this relatively fluid, almost permanent layer
of
MFT generally ranges from 30 wt% to 50 wt% solids. When the middlings are
pumped separately to ponds, the same condition is immediately created. The
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existence and size of these ponds threaten the very future of the industry.
Government has ordered that these ponds of MFT must be reprocessed, water
recovered for reuse, and dewatered solids consolidated to restore the mined
sites.
The oil sands industry has made a concerted effort to reprocess the MFT
into what arc called non-segregating tailings (NST). By this is meant sand and
clay tailings of varying particle sizes that, when pumped to ponds, do not
segregate by particle size upon settling but rather, settle in a non-
segregating
manner, more quickly releasing supernatant and/or undcrflow drainage
waters, and ultimately producing a trafficable solid that can be used for mine
site restoration. Heat is still lost after the NST slurry is pumped to ponds
and
the warm water still evaporates. Methods or procedure that can recover more
warm water within the operating process, and that could produce easily-
dewatered, non-segregating tailings immediately after the separation process,
would be of great benefit to the oil sands industry.
Monovalent anionic polymer flocculants have been in use for several
years for separating components within an aqueous slurry, recovering specific
components within an aqueous slurry, and/or dewatering residual
components of an aqueous slurry. Recently introduced calcium diacrylate /
acrylamide copolymers have reached new performance levels in these
applications. Nevertheless, given the concerns outlined above, further
performance improvements are of interest to the oil sands and other
industries.
SUMMARY:
We disclose anionic polymeric flocculants that combine monovalent and
multivalent acrylate monomers in a single polymer or a mixture of polymers.
In some applications, this may allow the ratio of monovalent and multivalent
acrylate monomers in the polymer or polymer mixture to be tailored to match
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substrate demand, particularly where the substrate in question consists of a
mixture of materials.
We further disclose an anionic flocculant comprising a heteropolymer
which includes: a monovalent acrylate monomer; a multivalent acrylate
monomer; and an acrylamide monomer. This polymer may be a terpolymer of
the aforementioned components. Thus, the monomer composition of the
polymer may be varied by modifying the ratio of monomers included during
catalysis.
We further disclose an anionic flocculant comprising a mixture of a first
copolymer and a second copolymer. The first copolymer includes a
monovalent acrylate monomer and an acrylamide monomer. The second
copolymer includes a multivalent acrylate monomer and an acrylamide
monomer. Thus, the monomer composition of the mixture may be varied by
changing the proportion of each copolymer added to the mixture.
Polymeric compounds, terpolymers, and copolymer mixtures as
described herein may be used to treat bentonite/montmorillonite clay, which
is prevalent in MFTs resulting from Athabasca oil sands processing. The
following ratios of monomers may be used in a flocculant composition,
wherein the respective compositions may comprise a mixture composed of
distinct polymers or a single polymer that combines all three monomers:
Table 1. Exemplary Monomer Composition of the Flocculant
Polymer Mixtures Terpolymer
Monovalent acrylates 4-90 wt% 4-90 wt%
Multivalent acrylates 5-70 wt % 5-70 wt %
Acrylamide 10-90 wt % 10-90 wt %
Molecular Weight 1,000 ¨ 16,000 1,000 ¨ 16,000
(kDa)
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The monovalent acrylate monomer may be sodium acrylate, potassium
acrylate, ammonium acrylate, or a combination thereof. Likewise, the
multivalent acrylate may be calcium diacrylate, magnesium diacrylate, iron
diacrylate, iron triacrylate, aluminum diacrylate, or a combination thereof.
We further disclose a low-molecular weight copolymer (Copolymer L)
for use as a pre-treatment prior to the addition of the terpolymer or polymer
mixture described above. Copolymer L comprises a polymer of monovalent
acrylate monomer and divalent acrylate monomer, at a 50/50 ratio.
to Copolymer L may have a molecular weight of between 80 to 250 kDa, go to
200 kDa, loo kDa to 150 kDa, or about loo kDa.
A terpolymer, copolymer mixture, and/or Copolymer L according to the
present invention may be a water soluble gel, emulsion, or dry granular solid.
Polymers may be manufactured by solution, emulsion, or dispersion
polymerization.
We further disclose a method of water recovery or solids reclamation.
The steps include: (a) providing an aqueous slurry of suspended particles; and
(b) adding to said slurry a heteropolymer or copolymer mixture as described
above, to flocculate the slurry. The heteropolymer or copolymer mixture may
be added in solution at a dosage of between loo and 2000 grams of polymer
active per ton of solids in the slurry, between 700 and 1200 grams of polymer
active per ton, or about 764 grams per ton.
We further disclose a method in which the slurry in step (a) is first pre-
treated with the Copolymer L described above. Copolymer L may be added
during pre-treatment at a dosage of between 50 and 1200 grams of polymer
active per ton of solids, such as 207 grams per ton.
The aqueous slurry can be of various types. In some applications the
slurry may comprise 30% to 50% solids by weight and/or particle sizes may be
less than 50 microns or less than 44 microns. The slurry may be a mineral
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slurry, such as a mineral slurry containing bitumen. The particles in the
slurry
may be sand or clay particles, which may include water-swelling sodium clays,
non-water swelling calcium clays, bentonite/montmorillonite clays, and/or
Na.Al2.SiO3.4Si02.H20. In some cases, the slurry is derived from oil sands
processing, such as MET.
We further disclose the use of polymeric flocculants, or mixtures of
polymeric flocculants, as described above for water recovery or solids
reclamation from an aqueous slurry. We further disclose the use of the
Copolymer L described above as a pre-treatment during water recovery or
solids reclamation from an aqueous slurry.
DRAWINGS:
FIG 1 compares the amount of polymer required to treat the MET
sample (in grams per ton of solids) for Copolymer X alone, Copolymer Y
alone, Mixture 1, and Terpolymer 1.
FIG 2 compares the drainage performance for MET treated with
Copolymer X alone, Copolymer Y alone, Mixture 1, and Terpolymer 1.
FIG 3 compares the dewatering performance (CST) for MET treated
with Copolymer X alone, Copolymer Y alone, Mixture 1, and Terpolymer 1.
FIG 4 compares the dewatering performance (CST) of Terpolymer 1
with and without pre-treatment with the Copolymer L.
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DETAILED DESCRIPTION:
Defmitions
The terms identified below shall be defined in the specification and
claims in accordance with the following definitions, unless otherwise
specified
or the context clearly requires otherwise.
Low molecular weight polymer: a polymer which is in the range of
about 80-250 kDa.
High molecular weight polymer: a polymer which has a molecular
weight which is above about 1,000 kDa.
Fines: Fine particle mine tailings waste (usually in an aqueous slurry)
of less than 44 microns size.
Mature fine tailings (MFT): Ponded fines, usually in concentrations
from 30-50%.
Monomer: A single reactable species.
Copolymer: A polymer from two monomers.
Terpolymer: A polymer comprising three or more monomers.
Polymer mixture: A physical blend of two or more polymers, either in
solid form or in aqueous solution
Pretreatment: A treatment that is performed prior to flocculating the
solids within a slurry to enhance to the performance of the flocculating
agent.
The invention will now be described in further detail with reference to
certain preferred embodiments set out in Examples 1 to 6 below. These
embodiments are exemplary in nature and are not intended to limit the scope
of the invention.
EXAMPLE 1: Monovalent / Multivalent Acrylate
Copolymers
Copolymers "X" and "Y" were obtained from commercial sources. In the
present examples, copolymer "X" is A-3338TM (SNF Holding Co.) and
copolymer "Y" is 1047TM (BASF-SE).
Copolymer "L" was prepared using 28 wt% stock solutions of each
monomer. Monomer solutions were deoxygenated before catalysis. Catalysts
were added separately to each monomer solution and the resulting solutions
were combined instantly. Ammonium persulfate (o.o6 wt%) was added to the
sodium acrylate and calcium diacrylate solutions. Sodium bisulfite (0.06 wt%)
and 2,2'-Azobis(2-amidinopropane) dihydrochloride (V50 TM by Wako
Chemical) (o.oi wt%) were added to the acrylamide monomer solution. The
initiation temperature was 15 C. The final molecular weight was ioo kDa. All
catalyst wt.%'s are based on total weight of monomer in the composition.
The molecular weight and monomer compositions of copolymers
X, Y, and L are provided in Table 2 below.
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Table 2. Monomer Composition of Copolymers X, Y, and L
Monomer Copolymer X Copolymer Y Copolymer L
(A-3338TM (1047Th
SNF Holding Co.) BASF-SE)
Sodium acrylate
25% o% 50%
(wt%)
Calcium diacrylate
o% 40% 50%
(wt%)
Acrylamide
75% 6o% o%
(wt%)
Molecular Weight
12,500 10,000 100
(wt%)
EXAMPLE 2: Preparation of Copolymer Mixtures 1-5
Monovalent / multivalent acrylate mixtures were prepared for use with
MFT containing bentonite/montmorillonite clay. Copolymers X and Y were
combined to provide Mixtures 1-5, having the final monomer proportions
shown in Table 3 below.
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Table 3. Monomer Composition of Copolymer Mixtures 1-5
Mixture Mixture Mixture Mixture Mixture
Monomer
1 2 3 4 5
Copolymer X:Y Ratio
1:1 2:1 51 1:2 1:5
(wt%)
Sodium Acrylate
12% 17% 21% 8% 4%
(wt%)
Calcium Di Acrylate
20% 13% 7% 27% 33%
(wt%)
Acrylamide
68% 70% 72% 65% 63%
(wt%)
Molecular Weight
11,500 11,600 12,100 10,800 10,400
(kDa)
EXAMPLE 3: Preparation of Monovalent / Multivalent
Terpolymers 1-5
Terpolymers 1-5 were synthesized using the monomer proportions
shown in Table 4 below.
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Table 4. Monomer Composition of Terpolymers
Ter- Ter- Ter- Ter- Ter-
Monomer polymer polymer polymer polymer polymer
1 2 3 4 5
Sodium Acrylate
12% 17% 21% 8% 4%
wt%
Calcium Di Acrylate
20% 13% 7% 27% 33%
wt%
Acrylamide
68% 70% 72% 65% 63%
wt%
As seen in Tables 3 and 4 above, the monomer composition of
Mixtures 1-5 in Example 2 and Terpolymers 1-5 in this Example 3 were
substantially the same.
Mixtures 1-5 (table 3) provided monovalent and multivalent
acrylate monomers using a mixture of two molecules. Terpolymers 1-5
(table 4) provided such monomers in a single polymeric compound
comprising the three monomers listed above within a single molecule.
Terpolymers 1-5 were prepared using the methods described for
Copolymer L above in Example 1, with some amendments. The
catalysis and reaction conditions for Terpolymers 1-5 are summarized
in Table 5 below.
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Table 5. Catalysis of Terpolymers 1-5
Ter- Ter- Ter- Ter- Ter-
Catalyst polymer polymer polymer polymer polymer
1 2 3 4 5
Ammonium
0.003571 0.003652 0.003652 0.00357 0.00357
PerSulfate
(wt%)
Sodium
BiSulfite 0.0017860.001799 0.001799 0.001786 0.0025
(wt%)
VSOTM 0.002143 0.002132 0.002052 0.002243 0.0024
(wt%)
Initiation
4 C 4 C 4 C 4 C 4 C
Temperature
Molecular
Weight 10,000 10,000 10,500 10,000 9,500
(kDa)
All catalyst wt.%'s are based on total weight of monomer in the
composition.
EXAMPLE 4: Performance of Copolymer Mixtures 1-5 and
Terpolymers 1-5
The Copolymer Mixtures 1-5 and Terpolymers 1-5 of Examples 2
and 3 were subjected to various performance tests using MFT containing
33.8% solids and having a methylene blue index (MBD of
Tests were performed at room temperature. MFT samples were mixed
with Copolymers X, Y, Mixtures 1-5, and Terpolymers 1-5 after which
performance tests were conducted.
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Polymer solutions were reconstituted at 0.4% active polymer in process
water. Prior to each performance test, a 40 ml sample of MFT was placed
within a clear 300 ml tall plastic cup and then mixed by hand with an initial
dose of the respective polymer mixture or terpolymers for about 10-20
seconds. The mixture was hand-stirred with a stainless steel spatula.
The initial dose of polymer was about 2 ml, which was about half of the
expected total quantity. At this level of polymeric additive, the MFT mixture
adhered to the spatula. Additional polymeric flocculant was added in 0.5 ml
doses and stirred until the spatula could be withdrawn without MV!' adhering
to the surface of the spatula.
In tests where a well-defined flocculate was formed, the MFT/polymer
mixture solidified into a well-defined water breakout from the flocculate when
the cup was tipped wherein free-flowing water would flow out of solidified
flocculate.
Free Drainage Test:
Free drainage tests were conducted in accordance with the
following procedure:
1. 0.4 wt.% acqueous polymer solution was added to a 40 ml sample of
homogenous MFT.
2. The polymer solution was added to the MFT in aliquots, with
mixing, until the MFT formed a distinct flocculate and no longer
adhered to the stainless steel spatula.
3. The treated 40m1 MFT sample was dropped quickly onto a 4.4 cm
diameter screen (having 0.18 cm openings).
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4. Filtrate was collected over a period of 1 minute. This volume is
reported as "Free Drainage".
Higher values indicate greater dewatering, and hence better
performance.
Capillary Suction Timer (CST) Test:
The Capillary suction timer (CST) test measures a combination of
drainage and filtrate clarity. The test measures the time (in seconds)
for filtrate to pass through a filter pad between two electrodes. The
automatic timer starts when the filtrate touches the first electrode and
the timer stops when the filtrate reaches the second electrode.
Filtrate quality is a key factor in rapid movement of the fluid
front. A shorter time indicates better fine particulate retention within
the flocculate structure (i.e. better flocculant performance).
CST tests were conducted in accordance with standard procedures
using a FANN Model 440 CST apparatus (Fann Instrument Company,
Houston, Texas). CST tests were conducted as follows:
1. 0.4 wt.% acqueous polymer solution was added to a 40 ml sample of
homogenous MFT.
2. The polymer solution was added to the MFT in aliquots, with
mixing, until the MFT formed a distinct flocculate and no longer
adhered to the stainless steel spatula.
3. The treated 40 ml MFT sample was dropped immediately into the
top of the transition tube of the CST apparatus and measurements
were taken in accordance with standard techniques.
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Results:
The results of drainage and CST tests on MFT treated with
Copolymers X-Y only, Mixtures 1-5, and Terpolymers 1-5 are provided
in Table 6 below, along with the amount added (i.e. dosage) to the MFT
to produce a flocculate, in grams of polymer per metric ton of solids.
Table 6. Performance of Copolymer Mixtures and Terpolymers
Dosage (g/ton) Free Drainage (m1s) CST (s)
Copolymer X 1035 8 163
Copolymer Y 962 11 129
Mixture 1 814 14 115
Terpolymer 1 764 16 75
Mixture 2 814 14 132
Terpolymer 2 764 16 79
Mixture 3 814 14 186
Terpolymer 3 764 19 119
Mixture 4 764 17 179
Terpolymer 4 764 17 134
Mixture 5 764 16 245
Terpolymer 5 764 17 189
As seen in Table 6, mixtures of monovalent and multivalent acrylamide
co-polymers outperformed the individual components of the mixtures (i.e.
Copolymers X and Y). Terpolymers having the same monomer ratios as the
mixtures further improved flocculation and dewatering performance.
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Both the mixtures and the tcrpolymers formed flocculates at lower
dosages while also providing superior performance over the individual anionic
copolymers X or Y alone. More specifically, mixtures 1-5 performed as well
or better than either Copolymer X or Y alone, using less polymer.
Terpolymers 1-5 also outperformed Copolymers X or Y alone, using less
polymer. Terpolymers also outperformed mixtures 1-5.
FIG 1 compares the amount of polymer required to treat the MFT
sample for Copolymer X alone, Copolymer Y alone, Mixture 1, and
Terpolymer 1. As seen therein, the amount of polymer used progressively
decreased.
FIG 2 compares the drainage from MFT treated with Copolymer X
alone, Copolymer Y alone, Mixture 1, and Terpolymer 1. As seen therein,
the drainage progressively increased, with Terpolymer 1 providing the best
performance despite using the least amount of polymer.
FIG 3 compares the CST values for MFT treated with Copolymer X
alone, Copolymer Y alone, Mixture 1, and Terpolymer 1. As seen therein,
the CST values progressively decreased, with Terpolymer i providing the
best performance despite using the least amount of polymer.
EXAMPLE 5: Performance of Terpolymers A-E
Terpolymers A-E were produced using the methods described in
Example 3 above, with differing amounts of sodium acrylate and calcium
diacrylate monomer solution, so as to achieve the monomer compositions
shown in Table 7 below.
The resulting Terpolymers A-E contained higher levels of sodium
acrylate and calcium acrylate monomers than can be produced from
mixtures of copolymer X and copolymer Y.
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Table 7. Monomer Composition of Terpolymers A-E
Ter- Ter- Ter- Ter- Ter-
Monomer polymer polymer polymer polymer polymer
A B C D E
Sodium Acrylate
55% 25% 40% 15% 35%
wt%
Calcium Di Acrylate
15% 35% 25% 5o% 15%
wt%
Acrylamide
30% 40% 35% 35% 50%
wt%
Terpolymers A-E were subjected to the same tests described in
Example 4 above, using the same testing conditions. The results of such
testing are provided in Table 8 below.
Table 8. Performance of Copolymer Mixtures and Terpolymers
Dosage (g/ton) Free Drainage (mls) CST (s)
Copolymer X 1035 8 163
Copolymer Y 962 11 129
Terpolymer A 764 17 92
Terpolymer B 764 18 79
Terpolymer C 764 15 121
Terpolymer D 764 16 115
Terpolymer E 764 18 84
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EXAMPLE 6: Pretreatment with Low-Molecular Weight
Copolymer L
Additional testing was performed by subjecting an MFT slurry to a
pre-treatment, by contacting the slurry with Copolymer L of Example 1
prior to contacting the slurry with the high molecular weight anionic
flocculants described herein.
Room temperature MFT samples were pre-treated with a 0.4% (w/v)
solution of Copolymer L at 207 grams of polymer per ton of solids. Samples
were hand stirred for 20-30 seconds during pre-treatment.
After pre-treatment, samples were treated with Terpolymer 1 and
tested for performance, using the methods described in Example 4. The
dosage, drainage, and CST values for such testing is provided in Table 9
below, which compares a control sample (Copolymer L only) versus
terpolymer treated samples with and without pre-treatment.
Table q. Performance of Terpolymer 1 With and Without Pre-Treatment
Dosage Free Drainage CST
(g/ton) (mls) (s)
Copolymer L Only no 8 0co
Terpolymer 1
764 17 71
(untreated)
Terpolymer 1 after
pre-treatment with 557 17 59
207 g/ton Copolymer L
As seen in Table 9, pre-treatment with the Copolymer L improved
dewatering (CST) performance of Terpolymer 1. Pre-treatment with
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Copolymer L also reduced the amount of Terpolymer 1 required to form a
stable flocculate, which was of higher quality.
These improvements could not be attributed to the Copolymer L, on
its own, which provided no useful characteristics when used without the
terpolymer. Indeed, dosages of Copolymer L up to 11 o8 grams of polymer
per ton of solids did not generate a flocculate. Instead, a synergistic effect
was observed between Copolymer L and the terpolymer flocculants.
FIG 4 compares the dewatering performance (CST) of Terpolymer
with and without pre-treatment with Copolymer L. As seen therein, pre-
treatment improved dewatering performance.
The foregoing arc examples only. The scope of the claims should not be
limited by the preferred embodiments set forth in the examples, but should be
given the broadest interpretation consistent with the description as a whole.
The claims are not to be limited to the preferred or exemplified embodiments
of the invention as described herein, which may be combined or modified
without departing from the scope of the present invention.
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