Note: Descriptions are shown in the official language in which they were submitted.
METHOD FOR TREATING SUSPENSIONS OF SOLID PARTICLES IN WATER
USING A BLEND OF TWO ANIONIC WATER-SOLUBLE POLYMERS
FIELD OF THE INVENTION
The invention relates to a method for treating an aqueous suspension of solid
particles,
including mineral tailings such as mature fine tailings (MFT) resulting from
oil sand
extraction. This method comprises using a blend in a free flowable powder form
of at least
two anionic water-soluble polymers, both in particulate form, solubilizing
this blend in water
to form an aqueous solution of said polymers, and adding said aqueous polymer
solution to
the aqueous suspension of solid particles. The aqueous polymer solution can be
added into a
thickener containing the suspension (e.g. tailings) to treat, and/or during
transport of said
suspension to a deposition area for dewatering and solidification, or to the
suspension (e.g.
tailings) to treat followed by a mechanical treatment such as centrifugation,
screw press and
filtration.
BACKGROUND OF THE INVENTION
Flocculants and/or coagulants are commonly used for the treatment of
industrial and
municipal tailings. Different processes and equipment, such as thickeners,
centrifuges, plate
and frame filter presses, screw press, water-capping or thin/thick-lift drying
(beach drying)
are implemented worldwide for this matter. Despite differences between each
industrial site,
the following performances criteria remain the main drivers during the
product/equipment
selection process: dosage, quantitative Net Water Release (NWR) (dewatering
rate), strong
cake/flocs and clean released water.
Nowadays, the most efficient treatment process is called Dual Treatment .
It involves the
use of both anionic and cationic water-soluble polymers. Such a technology is
a robust,
reliable and versatile option for the treatment of most of aqueous streams. It
gives high NWR
with high quality released water. However, it suffers from two main drawbacks.
First, screening various anionic and cationic products is a time-consuming and
compulsory
task for Dual Treatment >> process, involving not only products, dosages,
solution
concentration and mixing but also sequence of products addition.
Second, because Dual Treatment >> processes require both cationic and
anionic polymers,
one must proceed to a dual injection in the tailing stream. As these two
polymers immediately
precipitate/ or gel when mixed together, they must be injected at two separate
injection points.
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This implies also the preparation and storage of two separate polymer
solutions and doubles
the storage tank, dissolution unit, pipeline, etc.
Numerous references report the use of two different polymers for the treatment
of industrial
waste water streams.
For example, one can cite patent CA 2897663, Z. Ying et al. (Canadian J. Chem.
Eng. 95 (1)
3-10), M. Tizzotti et al. (World Heavy Oil Congress, Mar. 5-7 2014, New
Orleans, Louisiana,
USA), T. Dang-Vu et al. (IOSTC, Dec. 7-10 2014, Lake Louise, Alberta, Canada),
T. Dang-
Vu et al. (IOSTC, Dec. 4-7 2016, Lake Louise, Alberta, Canada) and D. Soane et
al. (IOSTC,
Dec 5-8 2010, Edmonton, Alberta, Canada) (IOSTC: International Oil Sands
Tailings
Conference).
Yuan & Shaw have studied the sequence of addition of the two polymers (one
anionic and
one cationic) (Canadian Metallurgical Quaterly, Vol. 46, n 3, 265-272, 2007).
C. Cote et al.
have successfully tried this technology on a frame filter press for the
treatment of oil sands
tailings (Tailings & Mine Waste, Nov. 3-6 2013, Banff, Alberta, Canada). As
expected, one
can substitute the organic coagulant by an inorganic coagulant as described by
Mahmoudkhani et al. (Paste conference, Jun. 17-20 2013, Belo Horizonte,
Brazil).
In patent CA 2364854, R. Sykes describes a mixture of two different anionic
water-soluble
polymers. These polymers must differ in terms of (i) molecular weight (Mw) and
(ii) anionic
charge density. The first anionic water-soluble polymer has a low Mw (less
than 2 million
g/mol) and a medium to high anionicity (between 40 and 100%) while the second
anionic
water-soluble polymer has a high Mw (more than 5 million g/mol) and a low to
medium
anionicity (between 1 and 50%).
In patent WO 2015/173728, S. Adkins describes the use of two different
polymers. This is a
dual treatment when one polymer is added followed by the second one. No
particular details
are given regarding their chemical compositions (these two flocculants can be
anionic,
cationic or neutral), but these flocculants must have significantly different
molecular weight
as the difference of their intrinsic viscosities must be at least 5 dL/g, more
preferably 15 dL/g.
Likewise, a process requiring two cationic products has already been described
in patent
US 7754086.
In SPE 141398 and patent WO 2012/088291, P. Watson et al. describe the use of
two
different anionic water-soluble polymers. As in patent CA 2364854, these must
differ in terms
of (i) molecular weight and (ii) anionic charge density. The first anionic
water-soluble
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polymer has a very low Mw (less than 50,000 g/mol), and an anionicity around
50 mol%
while the second anionic water-soluble polymer has a high Mw (more than 1
million g/mol),
and an anionicity around 30 mol%.
In patent WO 2015/013421, P. Watson et al. describe the use of an anionic
flocculant and a
neutral flocculant. This invention is like a Dual Treatment >> even though
the flocculants
cannot be added simultaneously. The order of addition does not seem to matter,
and so does
the flocculants form (powder, liquid, emulsion, etc.). Despite not being
mentioned in this
patent, it is well known to those skilled in the art that neutral flocculant
solutions are much
longer to prepare than the anionic ones.
Despite great advances over the last 10 years, there is still a need to
develop polymers that
enhance the rate and amount of water released from treated tailings or to
reduce installation
and/or MFT treatment cost. Improvement of the physical characteristics of the
produced
sludge is also sought.
SUMMARY OF THE INVENTION
The applicant has developed a new method of treating an aqueous suspension of
solid
particles using a blend in a free flowable powder form of at least two anionic
water-soluble
polymers, both in particulate form.
This invention offers the similar dewatering performances of a Dual
Treatment >> with only
a single injection process. It is fully compatible with all of the existing
tailings treatment
processes (centrifuge, thickener, plate and frame filter press, screw press,
thin/thick-lift
drying, water capping, etc.) and polymer dissolution units in which incumbent
flocculants are
used (similar dissolution time and shelf-life, both as a powder or in
solution).
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a method of treating an aqueous suspension of solid
particles, wherein
the method comprises the step of:
-
providing a blend in a free flowable powder form of at least two anionic water-
soluble
polymers, both in particulate form,
wherein said blend comprises:
o a first anionic water-soluble polymer having an anionicity ranging from 1 to
20
mol% and a weight average molecular weight of at least 3,000,000 g/mol,
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o a second anionic water-soluble polymer, different from the first polymer,
having a
weight average molecular weight of at least 3,000,000 g/mol,
- adding the blend to the aqueous suspension of solid particles in
order to obtain a treated
aqueous suspension of solid particles.
A blend in a free-flowable powder form corresponds to a mixture of at least
two polymers in
particulate form.
As used herein, the term "water-soluble polymer" refers to a polymer which
gives an aqueous
solution without insoluble particles after it has been appropriately mixed
with water.
In the following of the description, "particulate form" means powder, bead or
a mixture
thereof having a size preferably between 0.1 and 10 millimeters,
advantageously between 0.5
and 4 millimeters. Size refers to the mean size of the largest dimension of
the particulate form
e.g. the mean diameter for spherical particles.
The polymer blend can be added in liquid form or in solid form. Said blend can
be added as
particulate, a dispersion of polymer in oil or in brine, or solubilized in
water to form an
aqueous solution. In a preferred embodiment, the polymer blend is added in
liquid form.
Preferably, the first anionic water-soluble polymer is formed from one or more
anionic water-
soluble monomer in combination with one or more non-ionic water-soluble
monomer.
Preferably, the second anionic water-soluble polymers is formed from one or
more anionic
water-soluble monomer in combination or not with one or more non-ionic water-
soluble
monomer.
The anionic monomer may be chosen from the group consisting of monomers having
a
carboxylic function; salts of monomers having a carboxylic function; monomers
having a
sulfonic acid function; salts of monomers having a sulfonic acid function;
monomers having a
phosphonic acid function; salts of monomers having a phosphonic acid function.
Typical
anionic water-soluble monomers comprise: (meth)acrylic acid; itaconic acid;
crotonic acid;
maleic acid; fumaric acid; 2-acrylamido-2-methylpropane sulfonic acid;
vinylsulfonic acid;
vinylphosphonic acid; allylsulfonic acid; allylphosphonic acid; or
styrenesulfonic acid; and
water-soluble salts thereof. Generally, salts are alkaline salts, alkaline
earth salts or
ammonium salts.
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Preferably, the anionic water-soluble monomer used for the first anionic water-
soluble
polymer is selected from the group consisting of (meth)acrylic acid, 2-
acrylamido-2-
methylpropane sulfonic acid and salts thereof, preferably 2-acrylamido-2-
methylpropane
sulfonic acid and salts thereof.
Preferably, the anionic water-soluble monomer used for the second anionic
water-soluble
polymer is acrylic acid.
The non-ionic water-soluble monomer may be chosen from the group consisting of
(meth)acrylamide; N-mono derivatives of acrylamide; N-mono derivates of
methacrylamide;
N,N derivatives of acrylamide; N,N derivates of methacrylamide, acrylic
esters; and
methaerylic esters.
Preferably, the non-ionic water-soluble monomer used for the first and the
second anionic
water-soluble polymer is acrylamide or methacrylamide, preferably acrylamide.
Monomers having a hydrophobic character can also be used in the preparation of
the water-
soluble polymers used in the method of the invention. They are preferably
selected from the
group consisting of (meth)acrylic acid esters having an alkyl, arylalkyl or
ethoxylated chain;
derivatives of (meth)acrylamide having an alkyl, arylalkyl or dialkyl chain;
anionic
hydrophobic (meth)acryloyl derivatives; and anionic water-soluble monomers
derivatives of
(meth)acrylamide bearing a hydrophobic chain.
When a monomer having a hydrophobic character is used for the preparation of
the water-
soluble polymer(s), its amount preferably ranges from between 0.001 and 1
mor/0 as
compared the total amount of monomers.
In a preferred embodiment, the first anionic water-soluble polymer is a
copolymer of
acrylamide and 2-acrylamido-2-methylpropane sulfonic acid and/or a salt
thereof.
In a preferred embodiment, the second anionic water-soluble polymer is a
copolymer of
acrylamide and acrylic acid and/or a salt thereof.
Advantageously, the first anionic water-soluble polymer is a copolymer of
acrylamide and 2-
acrylamido-2-methylpropane sulfonic acid and/or a salt thereof and the second
anionic water-
soluble polymer is a copolymer of acrylamide and acrylic acid and/or a salt
thereof.
CA 3013009 2018-08-01
According to another preferred embodiment, the first anionic polymer and/or
the second
anionic polymer do(es) not have any cationic monomer.
The anionicity of the first and/or second anionic water-soluble polymers can
result from a
post-hydrolysis reaction of a non-ionic water-soluble monomer. The non-ionic
water-soluble
monomer(s) can be partially or totally post-hydrolyzed.
According to the invention, the anionicity of the anionic water-soluble
polymers corresponds
to the sum of the percentage of anionic water-soluble monomers from which the
polymer is
formed and the potential post-hydrolysis of part of the non-ionic water-
soluble monomers
from which the polymer is formed.
The skilled man in the art definitely knows how to post-hydrolyze a polymer
comprising non-
ionic function(s) such as acrylamide, to transform them in anionic
function(s), such as acrylic
acid.
The first anionic water-soluble polymer has an anionicity preferably of at
least 1 mol%, more
preferably of at least 2 mol%, more preferably of at least 3 mol%, more
preferably of at least
4 mol%, more preferably of at least 5 mol%, more preferably of at least 6
mol%, more
preferably of at least 7 mol%, more preferably of at least 8 mol%, more
preferably of at least
9 mol%, preferably of at least 10 mol% and preferably less than 20 mol%, more
preferably
less than 19 mol%, more preferably less than 18 mol%, more preferably less
than 17 mol%,
more preferably less than 16 mol%, more preferably less than 15 mol%, more
preferably less
than 14 mol%, more preferably less than 13 mol%, more preferably less than 12
mol%, more
preferably less than 11 mol%.
In a preferred embodiment the first anionic water-soluble polymer is a
copolymer of
acrylamide and 2-acrylamido-2-methylpropane sulfonic acid and/or a salt
thereof, having an
anionicity ranging from between 1 to 20 mol%.
The second anionic water-soluble polymer has an anionicity ranging preferably
from between
20 to 100 mol%, more preferably from between 25 to 85 mol%, and even more
preferably
from between 30 to 70 mol%.
In a preferred embodiment, the first anionic water-soluble polymer has a
weight average
molecular weight preferably greater than 3,000,000 g/mol, preferably ranging
from between
5,000,000 g/mol and 40,000,000 g/mol, more preferably between 7,000,000 g/mol
and
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30,000,000 g/mol, and even more preferably between 10,000,000 g/mol and
25,000,000
g/mol.
In a preferred embodiment, the first anionic water-soluble polymer is a
copolymer of
acrylamide and 2-acrylamido-2-methylpropane sulfonic acid and/or a salt
thereof, having an
anionicity ranging from between 1 to 20 mol%, and a weight average molecular
weight
greater than 3,000,000 g/mol.
The second anionic water-soluble polymer has a weight average molecular weight
preferably
greater than 3,000,000 g/mol, preferably ranging from between 5,000,000 g/mol
and
40,000,000 g/mol, more preferably between 7,000,000 g/mol and 30,000,000
g/mol, and even
more preferably between 10,000,000 g/mol and 25,000,000 g/mol.
The "weight average molecular weight" according to the present invention is
determined by
the intrinsic viscosity. The intrinsic viscosity can be measured by methods
known to a skilled
person in the art. Especially, it can be calculated from the values of reduced
viscosity for
different concentrations by a graphical method consisting of plotting the
reduced viscosity
values (on the ordinate axis) against the concentrations (on the abscissa) and
extrapolating the
curve to zero concentration. The intrinsic viscosity value is read off the
ordinate axis or by
using the least square method. Then the weight average molecular weight can be
determined
by the well-known Mark-Houwink equation: [11] = K W
[ii] represents the intrinsic viscosity of the polymer determined by solution
viscosity
measuring method,
K represents an empiric constant,
M represents the molecular weight of the polymer,
a represents the Mark-Houwink coefficient
a and K depend on the particular polymer-solvent system.
In preferred embodiment, the second anionic water-soluble polymer is a
copolymer of
acrylamide and acrylic acid and/or salt thereof, having an anionicity ranging
from between 20
and 70 mol%, and a weight average molecular weight greater than 3,000,000
g/mol.
In preferred embodiment, the first anionic water-soluble polymer is a
copolymer of
acrylamide and 2-acrylamido-2-methylpropane sulfonic acid and/or a salt
thereof, having
preferably an anionicity ranging from between 1 to 20 mol%, and a weight
average molecular
weight greater than 3,000,000 g/mol and the second anionic water-soluble
polymer is a
copolymer of acrylamide and acrylic acid and/or salt thereof, having
preferably an anionicity
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ranging from between 20 and 70 mol%, and a weight average molecular weight
greater than
3,000,000 g/mol.
The first and second anionic water-soluble polymers represent 80 to 100 weight
% based on
the total weight of the blend.
As mentioned thereafter, the blend may comprise other polymers and/or salts as
described
herein.
In a preferred embodiment, the ratio first polymer/ second polymer in the
blend of the
invention is between 1/9 and 1/1.
The water-soluble polymers of the invention are preferably linear or
structured. As it is
known, a structured polymer is a polymer that can have the form of a star, a
comb, or has
pending groups of pending chains on the side of the main chain.
The water-soluble polymers may also be branched. Branching can preferably be
carried out
during the polymerization of the monomers, in the presence of a
branching/crosslinking agent
and possibly a transfer agent other than the multifunctional free radical
transfer agent. A non-
exhaustive list of branching/crosslinking agents includes:
methylenebisacrylamide (MBA);
ethylene glycol diacrylate; polyethylene glycol dimethacrylate; vinyloxyethyl
acrylate;
vinyloxyethyl methacrylate; triallylamine, glyoxal; compounds of the glycidyl
ether type such
as ethylene glycol diglycidyl ether; and compounds having at least one epoxy
function.
The method of polymerization can be carried out according to any
polymerization techniques
well known to a person skilled in the art: solution polymerization, suspension
polymerization,
gel polymerization, precipitation polymerization, emulsion polymerization
(aqueous or
reverse) followed or not by spray drying step, suspension polymerization,
micellar
polymerization followed or not by a precipitation step. Post-hydrolysis of the
polymer of the
invention is possible. Post-hydrolysis consists in reacting the hydrolysable
functional group
with a base.
It is essential that the multifunctional free radical transfer agent is added
before or during the
polymerization. According to a preferred embodiment, it is added to the
monomers before
starting the polymerization.
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It is known that polymerization method leads to different polymers. For
example, the
molecular weight or degree of linearity may vary, all ingredients being equal
(monomers
nature, monomers ratio, etc...).
It is also known that precipitation polymerization leads to the use of solvent
which are not
desired during the production step, transport and use of polymer, for safety
and environmental
considerations. It has also been found that the polymers obtained by this
polymerization
method are less efficient than polymers obtained by other polymerization
method, all
ingredients being equal (monomers nature, monomers ratio, etc...).
The most preferred methods of polymerization are emulsion polymerization and
gel
polymerization.
The polymerization is generally a free radical polymerization preferably by
inverse emulsion
polymerization or gel polymerization. By free radical polymerization, we
include free radical
polymerization by means of U.V. azoic, redox or thermal initiators and also
Controlled
Radical Polymerization (CRP) techniques or template polymerization techniques.
As already mentioned, the invention relates to a method for treating an
aqueous suspension of
solid particles. It involves mixing the suspension with a blend comprising two
anionic water-
soluble polymers.
Such a treatment can be carried out into a thickener, which is a holding area
wherein the
particles may settle at the bottom. According to a specific embodiment, the
blend is added
into the pipe transporting the suspension to a thickener.
According to another specific embodiment, the blend is added into a thickener
that already
contains an aqueous suspension of solid particles to be treated. The blend may
also be added
into the pipe transporting the aqueous suspension of solid particles to the
thickener, or
partially into the pipe transporting the aqueous suspension of solid particles
to the thickener
and partially into the thickener containing the aqueous suspension of solid
particles to be
treated. In a typical mineral processing operation, tailings are often
concentrated by a
flocculation process in a thickener to give higher density underflow, and to
recover some of
the process water. Typically, the addition of the polymer(s) enhances the
concentration of the
underflow and increases the quality of the liquor.
According to another specific embodiment, the blend is added to the aqueous
suspension of
solid particles, during the transport of said suspension to a deposition area.
Preferably, the
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blend of polymers is added into the pipe transporting said suspension to a
deposition area on
which the treated suspension is spread off for dewatering and solidifying,
said treated
suspension may also be deposed under water. Examples of such treatments
include beach
drying, and deep cell (accelerated dewatering). Another example of such
treatment is the thin
bed process which consists of spreading a fluidized treated suspension onto
the ground in thin
layer.
According to another specific embodiment, the blend is added to the suspension
and then
followed by a mechanical treatment such as centrifugation, screw press or
filtration.
The blend may be added simultaneously at different stage of the suspension
treatment, i.e. for
example into the pipe transporting the suspension to a thickener and in the
underflow of the
thickener. In this case a specific blend 1 is preferably added into the pipe
and a specific blend
2 (different from blend 1) is added in the underflow of the thickener.
When the blend is solubilized, it can be partially or totally dissolved in
water with the
Polymer Slicing Unit (PSU) disclosed in WO 2008/107492.
According to another specific embodiment, the blend is added to the suspension
in
combination with another polymer, synthetic or natural. The blend and the said
other polymer
can be added simultaneously or separately. The other polymer can be water-
soluble or water
swellable. It can be a dispersant, a coagulant or a flocculant.
According to another specific embodiment, the blend is added to the suspension
in
combination with at least one salt, for example a calcium and/or a magnesium
salt. The blend
and the salt(s) can be added simultaneously or separately. Salts can be
inorganic or organic.
Suitable salts include calcium chloride, calcium acetate, calcium sulfate,
calcium nitrate,
calcium hydroxide, calcium carbonate, magnesium chloride, magnesium acetate,
magnesium
sulfate, magnesium nitrate, magnesium hydroxide, magnesium carbonate, calcium
formate,
calcium gluconate, calcium propionate, tricalcium phosphate and calcium
succinate.
According to the invention, the blend can comprise other polymers and/or salts
as described
herein.
When added simultaneously, polymers and/or salts can be comprised in the
blend, or not
comprised in the blend. When not comprised into the blend, polymers and/or
salts are added
in the same location, or added in the solution used to dissolve the blend, or
added in the
aqueous solution obtained by dissolution of the blend.
CA 3013009 2018-08-01
When added separately, polymers and/or salts can be added before or after the
addition of the
blend.
When a salt is added in the suspension of solid particles, it can be added in
solid form or in
liquid form. When another polymer is added in the suspension of solid
particles, it can be
added in solid form or in liquid form.
According to the invention, the total dosage of the first and second anionic
water-soluble
polymers added is between 50 and 10,000 g per ton of dry solids of suspension,
preferably
between 250 and 5,000 g/t, and more preferably between 500 and 2,000 g/t,
depending on the
nature and the composition of the tailings to be treated.
According to another preferred embodiment, the blend of anionic polymers does
not comprise
any cationic polymer.
According to another particular embodiment, the method of treating an aqueous
suspension of
solid particles does not involve any cationic polymer.
According to the invention, the method using the polymer blend described in
the invention
allows to treat more efficiently suspension of solid particles and more
preferably of mineral
material.
Suspensions of aqueous solid particles include all types of sludge, tailings,
or waste materials.
The suspensions may result from mineral ores processes. They may consist of,
for instance,
industrial sludge or tailings and all mine wash and waste products from
exploiting mines, such
as, for example, coal mines, diamonds mines, phosphate mines, metal mines
(aluminum,
platinum, iron, gold, copper, silver, etc...). Suspensions are also drilling
mud or tailings
derived from the treatment of oil sand. These suspensions generally comprise
organic and/or
mineral solid particles such as for instance clays, sediments, sand, metal
oxides, etc..., mixed
with water.
Generally, suspensions of aqueous solid particles are concentrated, and
contain between 2%
and 60% in weight of solid particles, preferably between 20 and 50% in weight
of solid
particles, as compared to the total weight of said suspensions.
The method according to the invention is especially useful for the treatment
of tailings
resulting from oil sand extraction. The method is particularly useful for the
treatment of fine
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tailings, Mature Fine Tailings, but may be also used to treat fresh tailings.
According to an
embodiment of the invention, the aqueous suspension of solid particles can be
Mature Fine
Tailings resulting from oil sand extraction.
The treatment of oil sand tailings has recently become an increasing issue in
Canada. The
tailings waste goes to tailings pond or thickeners for further water
management. The oil sands
tailings are alkaline aqueous suspensions which contain residual bitumen,
salts, soluble
organic compounds, sands and clays.
The tailings ponds are also closely regulated by the government. Two to four
barrels of fresh
water are required per barrel of oil produced from the surface mining method.
After the
tailings slurry is discharged to the tailings ponds, the coarse solids
segregate as the dykes
while most of the water and fine solids remain as suspensions in the tailings
pond. A layer of
Mature Fine Tails develops after two to three years. MFT consolidates very
slowly. The
completion of the settling process is predicted to take almost a century.
Using the polymer blend described in the invention for treating MFT increases
the
performances in terms of net water release and yield strength of treated MFT.
It has been discovered that the invention allows a water released after
flocculation much
quicker than traditional treatment. It is possible to recycle this water to
make down new
polymer solutions. No degradation in performances of the new solutions was
observed.
Another aspect of the invention relates to a method of treating an aqueous
suspension of solid
particles, wherein the method comprises the step of:
- providing a blend in a free flowable powder form of at least two anionic
water-soluble
polymers, both in particulate form,
wherein said blend comprises:
o a first anionic water-soluble polymer having an anionicity ranging from 1
to 20
mol% and a weight average molecular weight of at least 3,000,000 g/mol,
o a second anionic water-soluble polymer, different from the first polymer,
having a
weight average molecular weight of at least 3,000,000 g/mol,
- putting the blend in contact with water, wherein, part of or all of, said
water is recovered
from the aqueous suspension of solid particles treated according to the method
described
above, and obtaining a polymeric aqueous mixture,
- adding said polymeric aqueous mixture to the aqueous suspension of
solid particles in
order to obtain a treated aqueous suspension of solid particles.
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In other words, the method comprises advantageously the step of solubilizing
or dispersing
the blend in water, said water being at least partially recovered from the
treated aqueous
suspension of solid particles.
The blend is preferably mixed with the recovered water from a previous
treatment to obtain a
solution in which the polymers of the blends are dissolved or dispersed. This
solution is then
added into the aqueous suspension of solid particles as described above.
The blend may also be mixed with the recovered water to obtain a dispersion.
Obviously, the following figures and examples are only given to illustrate the
subject matter
of the invention and its advantages, which is in no way restricted to them.
Figure 1: compares the dewatering performances of a Dual Treatment to the
method
according to the invention
EXAMPLES
For each test, the appropriate quantity of polymers was added into 200g of MFT
and then the
whole mixture was mixed manually until flocculation and water release were
observed. The
performances of the treatment are measured by the net water released. It
corresponds to the
total amount of water recovered during the flocculation test.
Example 1: Treatment of MFT by a Dual Treatment:
The dual treatment involves the use of a first cationic polymer (100 mol%
Poly(dimethyldiallylammonium chloride) (DADMAC) having a weight average
molecular
weight of 10,000,000 g/mol) mixed with the MFT separately and before the
addition of a
second anionic polymer (copolymer of acrylamide/acrylic acid (70 mol%-30 mol%
having a
weight average molecular weight of 15,000,000 g/mol).
The single treatment involves only one injection of a blend according to the
invention. Three
different blends were tested.
Example 2: Treatment of MFT by a blend according to the invention composed of:
o 25% of a first anionic water-soluble polymer with an anionicity of 5
mol% (copolymer
of acrylamide (95 mol%) and 2-acrylamido-2-methylpropane sulfonic acid (5
mol%)
having a weight average molecular weight of 15,000,000 g/mol,
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o 75 mol% of a second anionic water-soluble polymer with an anionicity of
30 mol%
(copolymer of acrylamide and acrylic acid (70 mol%-30 mol%) having a weight
average molecular weight of 15,000,000 g/mol).
Example 3: Treatment of MFT by a blend according to the invention composed of:
o 25% of a first anionic water-soluble polymer with an anionicity of 10
mol%
(copolymer of acrylamide (90 mol%) and 2-acrylamido-2-methylpropane sulfonic
acid
(10 mol%) having a weight average molecular weight of 15,000,000 g/mol,
o 75 mol% of a second anionic water-soluble polymer with an anionicity of
30mo1%
(copolymer of acrylamide and acrylic acid (70 mol%-30 mol%) having a weight
average molecular weight of 15,000,000 g/mol).
Example 4: Treatment of MFT by a blend according to the invention composed of:
o 25% of a first anionic water-soluble polymer with an anionicity of 13
mol%
(copolymer of acrylamide (87 mol%) and 2-acrylamido-2-methylpropane sulfonic
acid
(13 mol%) having a weight average molecular weight of 15,000,000 g/mol,
o 75 mol% of a second anionic water-soluble polymer with an anionicity of
30 mol%
(copolymer of acrylamide and acrylic acid (70 mol%-30 mol%) having a weight
average molecular weight of 15,000,000 g/mol).
The results displayed in figure 1, show that the blend according to the
invention offers at least
equivalent performances compared to a dual treatment at the same dosage, in
one injection
point instead of two separate injection points.
When the first anionic water-soluble polymer has an anionicity of 5 mol%, the
blend offers
better performances when the dosage used to treat the MFT is above 700 g/t of
polymer.
At an anionicity of 10 mol%, the blend offers better performances regardless
of the dosage
used to treat the MFT.
At an anionicity of 13 mol%, the blend offers equivalent performances but in
only one
injection point, instead of the two required for the dual treatment.
The skilled man of the art will be able to determine and adjust the blend
characteristics
(molecular weight, anionicity and ratio of the two polymers) depending on the
MFT to treat,
in order to obtain the best dewatering performances.
Other advantages of the invention include the reduction of both cost and space
needed for the
MFT treatment plan.
14
CA 3013009 2018-08-01
