Purification of oil sands pond water

1. A method of purifying oil sand process water, comprising:

(a) sending utilized process water from a bitumen extraction process to a tailings setting pond;

(b) treating water from the tailings settling pond with an effective amount of one or more water-soluble cationic polymers, amphoteric polymers, zwitterionic polymers, or a combination thereof, wherein the tailings settling pond water contains total suspended solids (TSS) from about 2 to about 1,000 ppm prior to said treatment;

(c) passing the treated water through a membrane separation system at a sustainable flux, wherein the sustainable flux is 60-70% of a critical flux determined for the water from the tailings settling pond treated with one or more of said polymers;

(d) optionally, passing the permeate from step (c) through an additional membrane filtration system that is a submerged membrane system, an external membrane separation system, or a combination thereof; and

(e) sending the permeate back for use in a bitumen extraction process;

wherein said effective amount of cationic polymers is from about 0.05 ppm to about 400 ppm active solids;

wherein said effective amount of amphoteric polymers is from about 1 ppm to about 500 ppm of active solids;

wherein the effective amount of zwitterionic polymers is from about 1 ppm to about 500 ppm active solids;

wherein the critical flux is determined for the water from the tailings settling pond treated with one or more of said polymers by monitoring trans-membrane pressure for 15 minutes at a first lowest flux of 30 liters per square meter per hour (LMH), and then after 15 minutes monitoring trans-membrane pressure at a next higher flux, continuing the procedure of increasing flux and measuring trans-membrane pressure until a trans-membrane pressure of 2.5-3 pounds per square inch is reached.

2. The method of claim 1 , wherein said membrane separation system has at least one membrane selected from the group consisting of: an ultrafiltration membrane; a microfiltration membrane; and a combination thereof.

3. The method of claim 1 , wherein said additional membrane separation system has at least one membrane selected from the group consisting of: an ultrafiltration membrane having a pore size smaller than for a different ultrafiltration membrane used in said membrane separation system; a nanofiltration membrane; a reverse osmosis membrane; and a combination thereof.

4. The method of claim 1 , wherein the membrane separation system is a submerged membrane system, an external membrane separation system, or a combination thereof.

5. The method of claim 1 , wherein the amphoteric polymers are selected from the group consisting of at least one of the following: dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylic acid copolymer, diallyldimethylammonium chloride/acrylic acid copolymer, dimethylaminoethyl acrylate methyl chloride salt/N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine copolymer, acrylic acid/N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine copolymer and DMAEA.MCQ/Acrylic acid/N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine terpolymer.

6. The method of claim 1 , wherein the amphoteric polymers have a weight average molecular weight of about 5,000 to about 2,000,000 daltons.

7. The method of claim 1 , wherein the amphoteric polymers have a cationic charge equivalent to an anionic charge equivalent ratio of about 4.0:6.0 to about 9.8:0.2.

8. The method of claim 1 , wherein the cationic polymers are selected from the group consisting of at least one of the following: polydiallyldimethylammonium chloride; polyethyleneimine; polyepiamine; polyepiamine crosslinked with ammonia or ethylenediamine; condensation polymer of ethylenedichloride and ammonia; condensation polymer of triethanolamine and tall oil fatty acid; poly (dimethylaminoethylmethacrylate sulfuric acid salt); and poly(dimethylaminoethylacrylate methyl chloride quaternary salt).

9. The method of claim 1 , wherein the cationic polymers are copolymers of acrylamide and one or more cationic monomers selected from the group consisting of: diallyldimethylammonium chloride, dimethylaminoethylacrylate methyl chloride quaternary salt, dimethylaminoethylmethacrylate methyl chloride quaternary salt and dimethylaminoethylacrylate benzyl chloride quaternary salt.

10. The method of claim 1 , wherein the cationic polymers have a cationic charge of at least about 5 mole percent.

11. The method of claim 1 , wherein the cationic polymers have a cationic charge of 100 mole percent.

12. The method of claim 1 , wherein the cationic polymers have a weight average molecular weight of about 100,000 to about 10,000,000 daltons.

13. The method of claim 1 , wherein the zwitterionic polymers are composed of about 1 to about 99 mole percent of N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine and about 99 to about 1 mole percent of one or more nonionic monomers.

14. The method of claim 1 , wherein the tailings settling pond water contains TS from about 10 to 10,000 ppm; oil and grease from about 1 to about 100 ppm; TOC from about 1 to about 100 ppm; pH from about 7 to about 9; turbidity from about 2 to about 500 NTU; and color from about 5 to about 100 Pt-Co units.

15. The method of claim 1 , wherein the method provides a more than 100% enhancement in sustainable flux over sustainable flux of the process water before treatment with said polymers.

16. The method of claim 1 , wherein the method reduces turbidity and color of the treated water.