CA3134152C - Oil sand tailings treatment using a flocculant, binder, coagulant, and dewatering - Google Patents

Abstract

A method for treating a tailings stream from an oil sands bitumen extraction process, the method comprising: a) adding a flocculant and a binder to the tailings stream to form treated tailings; b) dewatering the treated tailings, to form dewatered tailings, by: i) depositing the treated tailings into layers and allowing for initial dewatering, atmospheric drying, and strength gain through evaporation to form the dewatered tailings; or ii) mechanical dewatering to form the dewatered tailings; and c) either between steps a) and b) or during step b), adding a coagulant to the treated tailings to initiate pozzolanic reactions.

Description

OIL SAND TAILINGS TREATMENT USING A FLOCCULANT, BINDER, COAGULANT, AND DEWATERING
FIELD
[0001] The present disclosure relates generally to the field of processing of mined oil sands. More particularly, the present disclosure relates to the treatment of tailings from an oil sands bitumen extraction process that generates tailings comprising fine particles such as clays.
BACKGROUND

[0002] This section is intended to introduce various aspects of the art, which may be associated with the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure.
Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

[0003] Fluid tailings streams are typically by-products of mining operations that are composed of water and solid particles. In order to recover the water and consolidate the solids, solid/liquid separation techniques must be applied. In oil sands processing, there are different fluid tailings streams with different compositions. For example, a typical fresh tailings stream comprises water, sand, silt, clay and residual bitumen. However, if the tailings stream is derived from a froth treatment process, it will also comprise residual solvents and other hydrocarbonaceous materials (e.g. asphaltenes).

[0004] Oil sands tailings typically comprise a substantial amount of fine particles (defined as solids that are less than 44 microns) and clays. The bitumen extraction process utilizes hot water and chemical additives such as sodium hydroxide or sodium citrate to remove the bitumen from the solid particles. The side effect of these chemical additives is that they change the inherent water chemistry and thus the solids in the aqueous phase acquire a negative charge. Due to strong electrostatic repulsion, the fine particles form a stabilized suspension that does not settle by gravity, even after a considerable amount of time. In fact, if the suspension is left alone for several years, a gel-like layer known as mature fine tailings (MFT) will be formed and this type of tailings is very difficult to consolidate even with current technologies.

Date Recu/Date Received 2021-10-13

[0005] In oil sands tailings treatment, various types of polyacrylamides (PAM) have been tested for the flocculation of tailings solids. While polyacrylamides are generally useful for fast consolidation of tailings solids, they are not selective towards fine particles and clays. As a result, the water recovered from a PAM consolidation process is rarely good enough for recycling because of high fines content in the water. Therefore, this water needs to be placed in a tailings pond where the fine particles eventually turn into fluid fine tailings (FFT).
Additionally, tailings treated with PAM are shear sensitive so transportation of thickened tailings to a dedicated disposal area (DDA) and general materials handling can become a challenge.

[0006] U.S. Patent Application Publication US 2010-0187181 (Sortwell) describes the use of zeolite to assist in the dispersion of components in aqueous mineral slurries to release and separate individual components of the slurry. Upon dispersion, Sortwell describes a process to consolidate residual mineral solids using multivalent cations and polyacrylamide (PAM).

[0007] U.S. Patent Application Publication US 2010-0126910 (Moffett etal.) describes the treatment of a tailings steam by contacting it with a polysilicate microgel, a polyacrylamide, a multivalent metal compound and/or a low molecular weight cationic organic polymer.

[0008] The synthesis of polysilicate microgel was described in a series of patents, including for example, U.S. Patent Nos. 4,927,498 (Rushmere), 4,954,220 (Rushmere), 6,060,523 (Moffett et al.) and 6,274,112 (Moffett et al.).

[0009] Canadian Patent No. 2,515,581 and U.S. Patent Application Publication 2006-0207946 (Scammell et al.) describe a process in which material comprising an aqueous liquid with dispersed particulate solids is transferred as a fluid to a deposition area, then allowed to stand and rigidify, in which rigidification is improved with an effective rigidifying amount of aqueous solution of a water-soluble polymer.

[0010] Canadian Patent No. 2,767,510 (Lin et al.) describes a process for tailings flocculation and dewatering. More particularly, Lin et al. discloses a method for generating chemically-induced micro-agglomerates (CIMA) of fine particles in a fluid tailings stream and using the micro-agglomerates to enhance tailings flocculation and dewatering.

[0011] Canadian Patent No. 3,048,297 (Sakuhuni et al.) describes a method for treating a tailings stream from an oil sands bitumen extraction process. The method includes flocculating the tailings stream with a flocculant to produce a flocculated tailings stream and treating the Date Recu/Date Received 2021-10-13 flocculated tailings stream with a coagulant and a silicate to produce a treated tailings stream and water.
SUMMARY

[0012] It is an object of the present disclosure to obviate or mitigate at least one disadvantage of previous systems or methods.

[0013] According to one aspect, there is provided a method for treating a tailings stream from an oil sands bitumen extraction process, the method comprising:
a) adding a flocculant and a binder to the tailings stream to form treated tailings;
b) dewatering the treated tailings, to form dewatered tailings, by:
i) depositing the treated tailings into layers and allowing for initial dewatering, atmospheric drying, and strength gain through evaporation to form the dewatered tailings; or ii) mechanical dewatering to form the dewatered tailings; and c) either between steps a) and b) or during step b), adding a coagulant to the treated tailings to initiate pozzolanic reactions.

[0014] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures, wherein:

[0016] Figure 1 is a graph of yield stress versus time using alum and lime.

[0017] Figure 2 is a graph of yield stress versus time using different additives.

[0018] Figure 3 is a graph of yield stress versus lime dosage.
DETAILED DESCRIPTION

[0019] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the features illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications, and any Date Recu/Date Received 2021-10-13 further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be apparent to those skilled in the relevant art that some features that are not relevant to the present disclosure may not be shown in the drawings for the sake of clarity.

[0020] At the outset, for ease of reference, certain terms used in this application and their meaning as used in this context are set forth below. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent.
Further, the present processes are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments and terms or processes that serve the same or a similar purpose are considered to be within the scope of the present disclosure.

[0021] Throughout this disclosure, where a range is used, any number between or inclusive of the range is implied.

[0022] As used herein, the term "pozzolanic reaction" refers to a reaction between a coagulant (e.g., calcium hydroxide) and a pozzolan (e.g., silicic acid) to form a cementation matrix. An example of a pozzolanic reaction is the reaction between calcium hydroxide and silicic acid to form calcium silicate in accordance with the following equation: Ca(OH)2 + H2SiO4 ¨> CaH2SiO4-2H20.

[0023] The method described in the above-referenced Canadian Patent No.
2,767,510 (Lin et a/.) for treating tailings from an oil sands bitumen extraction process involves conditioning with an aluminate and treating the conditioned tailings stream with a silicate to produce treated tailings comprising chemically induced micro agglomerates (CIMA) and water.
The method of Lin et a/. requires the addition of a flocculant after the formation of CIMA in order to produce flocculated tailings. The present inventors have surprisingly discovered that reversing the order of chemical addition produces flocculated tailings that dewater comparably to the CIMA treated tailings. CIMA requires a long conditioning time for the aluminate followed by conditioning of the silicate to allow for reaction time. By contrast, the present method does not require conditioning for the flocculant or coagulant. In addition, the coagulant and the silicate can either be co-injected or premixed prior to addition to the tailings. It was also surprisingly discovered that by maintaining the flocculant to aluminate ratio in a given range, the flocculant dosage can be increased without overdosing and inhibiting dewatering. The ability to increase polymer dosage without inhibiting dewatering and gelling the tails opens up Date Recu/Date Received 2021-10-13 a new possibility which is not available with CIMA treatment, i.e., using polymer dosage to control the required yield strength post flocculation. It was also discovered that the treated tailings obtained using the present invention have unique dewatering properties, i.e., substantially clear water can be squeezed out of the treated tailings without losing significant fines. The ability to squeeze out water without losing significant fines opens the possibility of using either surcharge load in a deep deposit or application of mechanical dewatering techniques including pressure filtration, screw classifier or centrifuge to further dewater the tailings and achieve higher solids content enabling faster reduction of fluid fine inventory. It was also discovered that the present treated tailings result in a tailings deposit with significantly improved permeability and strength. Moreover, it was discovered that the present treated tailings have relatively low yield stress at discharge (which is preferred for spreadability) and rapidly gain yield strength after deposition. Additionally, it was discovered that the strength of the treated material can be enhanced even further by replacing alum with lime.

[0024] Generally, the present disclosure provides a method for treating a tailings stream from an oil sands bitumen extraction process, the method comprising:
a) adding a flocculant and a binder to the tailings stream to form treated tailings;
b) dewatering the treated tailings, to form dewatered tailings, by:
i) depositing the treated tailings into layers and allowing for initial dewatering, atmospheric drying, and strength gain through evaporation to form the dewatered tailings; or ii) mechanical dewatering to form the dewatered tailings; and c) either between steps a) and b) or during step b), adding a coagulant to the treated tailings to initiate pozzolanic reactions.

[0025] In certain aspects, the present method may comprise treating an oil sands waste slurry (including fluid fine tailings) by in-line application of a flocculant, a binder, and a coagulant (e.g. lime), and then either (1) disposal in thin layers to allow initial dewatering, atmospheric drying, and strength gain through evaporation (and pozzolanic reactions), and then removal and transportation of dried material by mechanical equipment (e.g. dozers, loaders, or haulers); or (2) introducing into a mechanical dewatering unit (e.g. a filter press) to produce low water content stackable tailings with potential for haul road construction after further strength gain through evaporation.

Date Recu/Date Received 2021-10-13

[0026] By chemically treating and dewatering the tailings stream, one may be able to produce agglomerates that may have low water content, high compressive strength, low swelling, shrinkage potential, and decreased plasticity. Lab tests and field trials have shown there is a potential to use tailings treated by enhanced chemistry to produce construction material. Such construction material may be used as an alternative to aggregates, such as crushed limestone, for a base layer in haul roads in oil sands mining operations.

[0027]
The coagulant may be any suitable coagulant and may comprise lime. The dewatering may be by step b) i). The flocculant, the binder, and the lime may be added to the tailings stream in-line. The lime may comprise hydrated lime, i.e., calcium hydroxide. The lime may comprise quick lime. The method may further comprise adding fly ash to the tailings stream in-line. The flocculant and the binder may be added to the tailings stream in-line; and the lime may comprise lime powder and may be added during step b) i) following the initial dewatering. The method may further comprise adding coarse sand tailings (CST), thickened tailings (TT), or tailings solvent recovery unit tailings (TSRUT), or a combination thereof, to the treated tailings prior to step b) i). The treated tailings may be poured or sprayed over the coarse sand tailings (CST) on a conveyor belt. The method may further comprise using a porous pipe to dewater a mixture of the coarse sand tailings (CST) and the treated tailings in-line prior to the depositing of step b) i). The method may further comprise pouring or spraying the treated tailings along with the hydrated lime over coarse sand tailings (CST) on a conveyor belt prior to step b) i).

[0028]
The lime may comprise lime powder, and the method may further comprise pouring or spraying the treated tailings over coarse sand tailings (CST) on a conveyor belt prior to step b) i); and adding the lime powder after the deposition of step b) i).

[0029]
The method may further comprise mixing the dewatered tailings with a low grade oil sands ore, defined as an oil sands ore having: less than 7 weight %
bitumen, 7-8 weight %
bitumen and a fines content above 18 weight %, 8-9 weight % bitumen and a fines content above 29 weight %, or 9-11 weight % bitumen and a fines content above 35 weight %, to produce a construction material.

[0030]
The method may further comprise removing and transporting the dewatered tailings using any suitable mechanical equipment.

[0031]
The dewatering may be by step b) ii). The mechanical dewatering may comprise using any suitable mechanical dewatering devices or systems, such as a filter press, Date Recu/Date Received 2021-10-13 centrifuge, dewatering screen, screw classifier, vacuum filter, pressure filter, tube press, belt press, screw press, or belt filter. The mechanical dewatering may be performed to produce low water content stackable tailings with potential for haul road construction after further strength gain through evaporation. The "low water content stackable tailings"
may have a water content of between the liquid limit and the plastic limit. The flocculant and the binder may be added to the tailings stream in-line; and the lime may comprise lime powder and may be added to the dewatered tailings to produce stackable tailings.

[0032] The method may further comprise mixing the treated tailings. The mixing may be provided by transporting the treated tailings.

[0033] The tailings stream may comprise fluid fine tailings (FFT), flotation tailings (FT), coarse sand tailings (CST), tailings solvent recovery unit (TSRU) tailings, thickened tailings (TT), or a combination thereof.

[0034] The flocculant may be any suitable flocculant and may comprise an anionic, cationic, or non-ionic polymer. The flocculant may comprise a polyacrylamide (PAM). The flocculant may comprise: a cationic, anionic, non-ionic or amphoteric polyacrylamide, a copolymer of ethylene oxide with ether-based functional groups, a copolymer of acrylamide and diallyl dimethyl ammonium chloride, a copolymer of acrylamide and diallylaminoalkyl (meth)acrylates, a copolymer of acrylamide and dialkyldiaminoalkyl (meth)acrylamide, or a mixture thereof.

[0035] The binder may be any suitable binder and may comprise a silicate.
The silicate may comprise an inorganic silicate. The inorganic silicate may comprise a polysilicate. The polysilicate may comprise sodium silicate, potassium silicate, or a mixture thereof. The inorganic silicate may comprise a colloidal silica. The colloidal silica may comprise cationic silica, anionic silica, modified colloidal silica, ammonium silica, low sodium silicate, or a mixture thereof. The colloidal silica may have a particle size of 7 to 50 nm, with a surface area between 60 and 400 m2/g SiO2. The colloidal silica may have a particle size of 7 nm with a surface area between 320 and 400 m2/g SiO2, 12 nm with a surface area of between 198 and 258 m2/g SiO2, 22 nm with a surface area between 110 and 150 m2/g SiO2, 50 nm with a surface area between 60 and 90 m2/g SiO2, or a combination thereof.

[0036] The flocculant to coagulant weight ratio may be any suitable ratio and may be between 1:1 and 9:1.

Date Recu/Date Received 2021-10-13

[0037] The method may comprise using 100-2000 ppmw of the flocculant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) above 0.2, using 1000-5000 ppmw of the flocculant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) at or below 0.2, using 30-1000 ppmw of the coagulant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) above 0.2, or using 60-10,000 ppmw of the flocculant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) at or below 0.2.

[0038] The method may comprise maintaining a constant colloidal silica dosage.

[0039] Experimental

[0040] Figure 1 is a graph of yield stress versus time using alum and lime.
Two tailings samples with a SFR (sand to fines ratio) below 0.2 were treated in 600 ml beakers with PAM + Binder + Alum and PAM + Binder + Lime in order to assess the effect of lime on yield strength. A vane spindle was used to measure the yield strength at 1 hour, 1 day, 3, 7, 8 and 9 days. As seen in Figure 1, a combination of PAM + Binder + Lime resulted in higher yield stress compared with PAM + Binder + Alum.

[0041] Figure 2 is a graph of yield stress versus time using different additives. Three tailings samples with an SFR below 0.2 were treated in 600 ml beakers with PAM, PAM + Binder and PAM + Binder + Lime in order to distinguish the effect of a binder and PAM
vs. combining PAM + Lime + Binder on yield strength. A vane spindle was used to measure the yield strength at 1 hour, 1 day, 3, 7, 8 and 9 days. As seen in Figure 2, a combination of PAM + Binder + Lime yielded higher strength compared with PAM only and PAM +
Binder.

[0042] Figure 3 is a graph of yield stress versus lime dosage, showing the effect of combining PAM + Lime vs. combining PAM + Binder + Lime on yield stress. Two tailings samples with an SFR below 0.2 were treated in 600 ml beakers with PAM + Lime and PAM + Binder + Lime in order to distinguish the contribution of lime from the combined effect of Lime + Binder on yield strength. A vane spindle was used to measure the yield strength of the samples after 7days. As seen in Figure 3, a combination of PAM with Lime +
Binder yielded higher strength in 7 days than PAM + Lime.

[0043] As seen from Figure 3, by addition of binder (Silica), the dosage of lime can be significantly reduced whilst achieving equivalent yield strength.

[0044] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments.
However, it will be apparent to one skilled in the art that these specific details are not required.

Date Recu/Date Received 2021-10-13

[0045]
The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

Date Recu/Date Received 2021-10-13

Claims (39)

CLAIMS:

1. A method for treating a tailings stream from an oil sands bitumen extraction process, the method comprising:
a) adding a flocculant and a binder to the tailings stream to form treated tailings;
b) dewatering the treated tailings, to form dewatered tailings, by:
i) depositing the treated tailings into layers and allowing for initial dewatering, atmospheric drying, and strength gain through evaporation to form the dewatered tailings; or ii) mechanical dewatering to form the dewatered tailings; and c) either between steps a) and b) or during step b), adding a coagulant to the treated tailings to initiate pozzolanic reactions.

2. The method of claim 1, wherein the coagulant comprises lime.

3. The method of claim 2, wherein the dewatering is by step b) i).

4. The method of claim 3, wherein the flocculant, the binder, and the lime are added to the tailings stream in-line.

5. The method of claim 4, wherein the lime comprises hydrated lime.

6. The method of claim 4 or 5, wherein the lime comprises quick lime.

7. The method of any one of claims 4 to 6, further comprising adding fly ash to the tailings stream in-line.

8. The method of claim 3, wherein:
the flocculant and the binder are added to the tailings stream in-line; and the lime comprises lime powder and is added during step b) i) following the initial dewatering.

Date Recu/Date Received 2021-10-13

9. The method of any one of claims 3 to 8, further comprising adding coarse sand tailings (CST), thickened tailings (TT), or tailings solvent recovery unit tailings (TSRUT), or a combination thereof, to the treated tailings prior to step b) i).

10. The method of claim 9, wherein the treated tailings are poured or sprayed over the coarse sand tailings (CST) on a conveyor belt.

11. The method of claim 9, further comprising using a porous pipe to dewater a mixture of the coarse sand tailings (CST) and the treated tailings in-line prior to the depositing of step b) i).

12. The method of claim 5, further comprising pouring or spraying the treated tailings along with the hydrated lime over coarse sand tailings (CST) on a conveyor belt prior to step b) i).

13. The method of claim 3, wherein the lime comprises lime powder, the method further comprising:
pouring or spraying the treated tailings over coarse sand tailings (CST) on a conveyor belt prior to step b) i); and adding the lime powder after the deposition of step b) i).

14. The method of any one of claims 3 to 8, further comprising mixing the dewatered tailings with a low grade oil sands ore, defined as an oil sands ore having:
less than 7 weight % bitumen, 7-8 weight % bitumen and a fines content above 18 weight %, 8-9 weight % bitumen and a fines content above 29 weight %, or 9-11 weight % bitumen and a fines content above 35 weight %, to produce a construction material.

15. The method of any one of claims 1 to 14, further comprising removing and transporting the dewatered tailings using mechanical equipment.

16. The method of claim 2, wherein the dewatering is by step b) ii).

Date Recu/Date Received 2021-10-13

17. The method of claim 16, wherein the mechanical dewatering comprises using a filter press, centrifuge, dewatering screen, screw classifier, vacuum filter, pressure filter, tube press, belt press, screw press, or belt filter.

18. The method of claim 16 or 17, wherein the mechanical dewatering is performed to produce low water content stackable tailings with potential for haul road construction after further strength gain through evaporation.

19. The method of any one of claims 16 to 18, wherein:
the flocculant and the binder are added to the tailings stream in-line; and the lime comprises lime powder and is added to the dewatered tailings to produce stackable tailings.

20. The method of any one of claims 1 to 19, further comprising mixing the treated tailings.

21. The method of claim 20, wherein the mixing is provided by transporting the treated tailings.

22. The method of any one of claims 1 to 21, wherein the tailings stream comprises fluid fine tailings (FFT), flotation tailings (FT), coarse sand tailings (CST), tailings solvent recovery unit (TSRU) tailings, thickened tailings (TT), or a combination thereof.

23. The method of any one of claims 1 to 22, wherein the flocculant comprises an anionic, cationic, or non-ionic polymer.

24. The method of any one of claims 1 to 22, wherein the flocculant comprises a polyacrylamide (PAM).

25. The method of any one of claims 1 to 22, wherein the flocculant comprises: a cationic, anionic, non-ionic or amphoteric polyacrylamide, a copolymer of ethylene oxide with ether-based functional groups, a copolymer of acrylamide and diallyl dimethyl ammonium Date Recu/Date Received 2021-10-13 chloride, a copolymer of acrylamide and diallylaminoalkyl (meth)acrylates, a copolymer of acrylamide and dialkyldiaminoalkyl (meth)acrylamide, or a mixture thereof.

26. The method of any one of claims 1 to 23, wherein the binder comprises a silicate.

27. The method of claim 26, wherein the silicate comprises an inorganic silicate.

28. The method of claim 27, wherein the inorganic silicate comprises a polysilicate.

29. The method of claim 28, wherein the polysilicate comprises sodium silicate, potassium silicate, or a mixture thereof.

30. The method of any one of claims 27 to 29, wherein the inorganic silicate comprises a colloidal silica.

31. The method of claim 30, wherein the colloidal silica comprises cationic silica, anionic silica, modified colloidal silica, ammonium silica, low sodium silicate, or a mixture thereof.

32. The method of claim 30 or 31, wherein the colloidal silica has a particle size of 7 to 50 nm, with a surface area between 60 and 400 m2/g SiO2.

33. The method of claim 30 or 31, wherein the colloidal silica has a particle size of 7 nm with a surface area between 320 and 400 m2/g SiO2, 12 nm with a surface area of between 198 and 258 m2/g SiO2, 22 nm with a surface area between 110 and 150 m2/g 5i02, 50 nm with a surface area between 60 and 90 m2/g 5i02, or a combination thereof.

34. The method of any one of claims 1 to 33, wherein the flocculant to coagulant weight ratio is between 1:1 and 9:1.

35. The method of any one of claims 1 to 33, using 100-2000 ppmw of the flocculant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) above 0.2.

Date Recu/Date Received 2021-10-13

36. The method of any one of claims 1 to 33, using 1000-5000 ppmw of the flocculant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) at or below 0.2.

37. The method of any one of claims 1 to 33, using 30-1000 ppmw of the coagulant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) above 0.2.

38. The method of any one of claims 1 to 33, using 60-10,000 ppmw of the flocculant on a solids basis where the tailings stream has a sand-to-fines ratio (SFR) at or below 0.2.

39. The method of any one of claims 1 to 33, comprising maintaining a constant colloidal silica dosage.

Date Recu/Date Received 2021-10-13