METHOD FOR TREATING SUSPENSIONS OF SOLID PARTICLES IN WATER USING COMB LIKE POLYMERS

Abstract

The invention relates to a method for treating an aqueous suspension of solid particles, wherein at least one water-soluble polymer is added to the suspension, and wherein said polymer is obtained by polymerizing at least a non-ionic monomer, optionally at least one anionic and/or at least one cationic monomer, in the presence of a multifunctional free radical transfer agent. This method is particularly useful for the treatment of mineral tailings and especially for tailings resulting from oil sand extraction.

Claims

1- A method for treating an aqueous suspension of solid particles, comprising the following steps: preparing a water-soluble polymer by polymerizing: at least one non-ionic monomer; optionally at least one anionic and/or at least one cationic monomer; in the presence of from between 0.05% and 10% by weight, of at least one multifunctional free radical transfer agent, said weight percentage being related to the total amount of monomers; and adding said water-soluble polymer to the aqueous suspension of solid particles; wherein the multifunctional free radical transfer agent is a polymer having a molecular weight ranging from between 2,000 g/mol and 500,000 g/mol.

2- The method according to claim 1, wherein the multifunctional free radical transfer agent is selected from the group consisting of polyamine; polyvinyl alcohol; polyvinyl alcohol copolymer; hydrolyzed vinyl acetate-based polymer; hydrolyzed vinyl acetate-based copolymer; polythiol; polyether imine; polycarboxylic acid; salts of polycarboxylic acid; and polyaldehyde.

3- The method according to claim 1, wherein the multifunctional free radical transfer agent is selected from the group consisting of polyvinyl alcohol; polyvinyl alcohol copolymer; hydrolyzed vinyl acetate-based polymer; and hydrolyzed vinyl acetate-based copolymer.

4- The method according to claim 1, wherein the multifunctional free radical transfer agent is a partially hydrolyzed vinyl acetate-based polymer or a partially hydrolyzed vinyl acetate-based copolymer.

5- The method according to claim 4, wherein the degree of hydrolysis of the partially hydrolyzed vinyl acetate-based polymer or copolymer is between 60% and 99%.

6- The method according to claim 1, wherein the multifunctional free radical transfer agent is an ionic partially hydrolyzed vinyl acetate-based copolymer, said ionic copolymer comprising: between 1 and 40 mol % of at least one anionic monomer relative to the total amount of monomers; and optionally at least one non-ionic monomer present at about 0 to 10 mol % relative to the total amount of monomers.

7- The method according to claim 1, wherein the amount of multifunctional free radical transfer agent is comprised between 0.1% and 6% by weight, as compared to the total weight of the monomers.

8- The method according to claim 1, wherein the water-soluble polymer is anionic and has an anionicity ranging from between 10 to 55 mol %.

9- The method according to claim 1, wherein the water-soluble polymer contains at least 30 mol % of at least one non-ionic monomer.

10- The method according to claim 1, wherein the non-ionic monomer is selected from the group consisting of acrylamide; methacrylamide; N-mono derivatives of acrylamide; N-mono derivatives of methacrylamide; N,N derivatives of acrylamide; N,N derivatives of methacrylamide; acrylic esters; and methacrylic esters.

11- The method according to claim 1, wherein the anionic monomer is selected 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; and salts of monomers having a phosphonic acid function.

12- The method according to claim 1, wherein the water-soluble polymer is obtained by emulsion polymerization or gel polymerization.

13- The method according to claim 1, wherein the polymer is added into a thickener containing the aqueous suspension of solid particles to treat.

14- The method according to claim 1, wherein the polymer is added to the aqueous suspension of solid particles during the transport of the said suspension to a deposition area.

15- The method according to claim 1, wherein the aqueous suspension of solid particles is a suspension resulting from mineral ores processes.

16- The method according to claim 1, wherein the aqueous suspension of solid particles is Mature Fine Tailings resulting from oil sand extraction.

Description

FIGURES

[0091] FIG. 1 relates to the preparation of the water-soluble polymer according to the invention, wherein the monomers M are polymerized in the presence of a multifunctional free radical transfer agent.

EXAMPLES

Example 1Polymer Preparation (FIG. 1)

[0092] A 1.5 L reactor equipped with a mechanical stirrer, a thermometer and a nitrogen inlet is charged with 1050 g of distilled water, 317.14 g acrylamide (AM), 132.86 g acrylic acid (AA) and X g of partially hydrolyzed poly vinyl acetate (degree of hydrolysis 90%). X is calculated according to the following formula: X (g)=[C]/450, where [C] is the concentration of partially hydrolyzed poly vinyl acetate as a function of active monomers. [C] is expressed in ppm.

[0093] The resulting mixture is homogenized and then cooled, neutralized with sodium hydroxide to pH=7.6-7.7, and finally degassed under a nitrogen flow. The polymerization is then initiated using a redox system (initiator). The resulting, gel obtained after polymerization, is then grinded and dried in a drying oven so as to afford a powder.

[0094] The different polymers prepared according to the above method are listed in Table 1 below:

TABLE-US-00001 TABLE 1 Properties of polymer 1 to 15. [C] Mw partially hydrolyzed UL viscosity Polymer (ppm) poly vinyl acetate (g/mol) (cps) 1 0 6.16 2 1000 25,000-30,000 5.61 3 2000 25,000-30,000 5.51 4 5000 25,000-30,000 5.46 5 1000 120,000-130,000 5.76 6 2000 120,000-130,000 5.61 7 5000 120,000-130,000 5.46 8 10,000 120,000-130,000 5.00 9 15,000 120,000-130,000 5.10 10 20,000 120,000-130,000 5.00 11 25,000 120,000-130,000 5.30 12 30,000 120,000-130,000 4.30 13 35,000 120,000-130,000 4.40 14 40,000 120,000-130,000 4.40 15 50,000 120,000-130,000 5.05 Mw: Molecular Weight in g/mol. UL Viscosity: Brookflield viscosity with UL module, 1 g/L in NaCl 1M at 25 C.

Example 2Flocculation of Sludge 1 (MFT 1)

[0095] Polymers 1-7 are stirred into tap water in order to afford aqueous solutions having a concentration of 0.4 wt % of polymer with respect to the total weight of the solution. All of these solutions are mechanically stirred at 500 rpm until complete solubilization of the polymers and obtaining clear and homogeneous solutions. Flocculation tests have been carried out using Mature Fine Tailings (MFT) having a solid content of 33.7 wt %.

[0096] For each test, the appropriate volume of polymer solution was added into 200 g of MFT and then the whole mixture was mixed manually until flocculation and water release were observed.

[0097] Results displayed in Table 2 show that the use of partially hydrolyzed poly vinyl acetate of example 1 as multifunctional free radical transfer agent increases the water release from the flocculated sludge when compared to the reference (Polymer 1). Polymers prepared from partially hydrolyzed poly vinyl acetate having a molecular weight of 120,000-130,000 g/mol are more efficient than polymers prepared from partially hydrolyzed poly vinyl acetate having a molecular weight of 25,000-30,000. Significant improvements are obtained when [C] is around 5,000 ppm of HPVOH having a molecular weight of 120,000-130,000 g/mol (polymer 7).

TABLE-US-00002 TABLE 2 Performances of polymer 1 to 7 in terms of Net Water Release in MFT 1. Polymer dosage Water release (mL) Polymer (g/dry ton) 30 min 1 h 24 h 24 h NWR 1 1128 18.55 20.89 23.56 4.56 2 1128 23.01 27.47 32.24 13.24 3 1128 23.73 27.90 32.51 13.51 4 1128 23.14 27.51 32.32 13.32 5 1128 23.92 28.69 32.77 13.77 6 1128 24.37 29.32 32.50 13.50 7 1128 26.91 32.24 36.39 17.39 NWR = Net Water Release. It corresponds to the total amount of water recovered during the flocculation test.

Example 3Flocculation of Sludge 2 (MFT 2)

[0098] Polymers 1 and 7-15 are stirred into tap water in order to afford aqueous solutions having a concentration of 0.4 wt % of polymer with respect to the total weight of the solution. All of these solutions are mechanically stirred at 500 rpm until complete solubilization of the polymers and obtaining clear and homogeneous solutions.

[0099] Flocculation tests have been carried out using Mature Fine Tailings (MFT) having a solid content of 35.1 wt %.

[0100] For each test, the appropriate volume of polymer solution was added into 200 g of MFT and then the whole mixture was mixed manually until flocculation and water release were observed.

[0101] Results displayed in Table 3 show that an optimum in partially hydrolyzed poly vinyl acetate dosage exists and strongly impacts the flocculation. In this particular case, polymer 12 containing 30,000 ppm of high molecular weight partially hydrolyzed poly vinyl acetate (120,000-130,000 g/mol) exhibits the best flocculating properties.

TABLE-US-00003 TABLE 3 Performances of polymer 1 and 7-15 in terms of Net Water Release in MFT 2. Polymer dosage Water release (mL) Polymer (g/dry ton) 30 min 1 h 24 h 24 h NWR 1 1009 12.45 15.46 19.55 2.55 7 1009 12.09 16.28 21.11 4.11 8 1009 12.31 14.82 20.04 3.04 9 1009 11.93 15.26 21.77 4.77 10 1009 16.95 19.83 25.58 8.58 11 1009 18.82 22.08 27.15 10.15 12 1009 23.76 27.79 32.80 15.80 13 1009 18.23 22.06 27.66 10.66 14 1009 17.33 22.02 26.96 9.96 15 1009 16.91 19.05 23.99 6.99

Example 4Evidence of Improvement Due to the Comb-Like Macromolecular Architecture of the Water-Soluble Polymer

[0102] Blend A is a mixture of 2 linear polymers (97 wt % of polymer 1+3 wt % of partially hydrolyzed poly vinyl acetate 120,000-130,000 g/mol). It has the same chemical composition as polymer 12, but polymer 12 has been prepared by polymerization of acrylamide and acrylic acid in the presence of partially hydrolyzed poly vinyl acetate. Polymer 12 has therefore a comb-like structure while polymer 1 and partially hydrolyzed poly vinyl acetate are linear polymers.

Blend A has been mixed according to the method described in example 3 and carried out in order to flocculate sludge 2 having a solid content of 35.1 wt %.

[0103] Results presented in Table 4 show that the partially hydrolyzed poly vinyl acetate needs to be added to the monomers before the polymerization starts in order to initiate the comb-like macromolecular architecture. The blend of a linear flocculant (i.e. Polymer 1) and the unreacted partially hydrolyzed poly vinyl acetate exhibits the same dewatering properties as the sole flocculant (polymer 1).

TABLE-US-00004 TABLE 4 Performances of polymers 1, 12, and Blend A in terms of Net Water Release in MFT 2. Polymer dosage Water release (mL) Polymer (g/dry ton) 30 min 1 h 24 h 24 h NWR 1 1009 12.45 15.46 19.55 2.55 12 1009 23.76 27.79 32.80 15.80 Blend A 1009 10.52 14.55 20.34 3.34