CA3013009A1

CA3013009A1 - Method for treating suspensions of solid particles in water using a blend of two anionic water-soluble polymers

Info

Publication number: CA3013009A1
Application number: CA3013009A
Authority: CA
Inventors: Morgan Tizzotti; Trong Dang-Vu; Kirk Thomas; Scott Ramey
Original assignee: SPCM SA
Current assignee: SNF Group
Priority date: 2018-08-01
Filing date: 2018-08-01
Publication date: 2020-02-01

Abstract

The invention relates to a method of treating an aqueous suspension of solid particles, wherein the method comprises the step of:
- preparing a blend in a free flowable powder form of at least two anionic water-soluble polymers, both in particulate form, wherein the blend comprises:
.circle. 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, .circle. 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.

Description

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.

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

2 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 mol% and a weight average molecular weight of at least 3,000,000 g/mol,

3 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.

4 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.

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

6 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

7 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.

8 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

9 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.

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 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.

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, 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.

Claims

1. 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 the said blend comprises:
.circle. 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, .circle. 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.

2. Method according to claim 1, wherein the blend is solubilized or dispersed in water to form respectively an aqueous solution or dispersion before being added to the aqueous suspension of solid particles.

3. Method according to any of claims 1 to 2, wherein the anionic water-soluble monomer is selected from the group consisting of monomers having a carboxylic function; salts of monomers having a carboxylic function; monomer 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.

4. Method according to any of claims 1 to 3, wherein the anionic water-soluble monomer for the first anionic water-soluble polymer is selected from the group consisting of (meth)acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid and salts thereof.

5. Method according to any of claims 1 to 4, wherein the anionic water-soluble monomer for the second anionic water-soluble polymer is acrylic acid.

6. Method according to any of claims 1 to 5, wherein 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.

7 . Method according to any of claims 1 to 6, wherein the second anionic water-soluble polymers is formed from one or more anionic water-soluble monomer in combination with one or more non-ionic water-soluble monomer.

8. Method according to any of claims 6 and 7, wherein non-ionic water-soluble monomer is selected from the group consisting of acrylamide; methacrylamide; N-mono derivatives of acrylamide; N-mono derivates of methacrylamide; N,N derivatives of acrylamide; N,N derivates of methacrylamide, acrylic esters; and methacrylic esters.

9. Method according to claim 8, wherein the non-ionic water-soluble monomer is acrylamide.

10. Method according to any of claims 1 to 9, wherein the second anionic water-soluble polymer has an anionicity ranging from between 20 to 100 mol%.

11. Method according to any of claims 1 to 10, wherein the first and second anionic water-soluble polymers represent 80 to 100 weight % based on the total weight of the blend.

12. Method according to any of claims 1 to 11, wherein the ratio first polymer/ second polymer in the blend is between 1/9 and 1/1.

13. Method according to any of claims 1 to 12, wherein the first anionic water-soluble polymer has a weight average molecular weight ranging from between 5,000,000 g/mol and 40,000,000 g/mol.

14. Method according to any of claims 1 to 13, wherein the second anionic water-soluble polymer has a weight average molecular weight ranging from between 5,000,000 g/mol and 40,000,000 g/mol.

15. Method according to any of claims 1 to 14, wherein the aqueous suspension of solid particles is Mature Fine Tailings resulting from oil sand extraction.

16. Method according to any of claims 2 to 15 wherein the water is at least partially recovered from the treated aqueous suspension of solid particles.