CA3048272A1 - Bubble extraction of a residual light hydrocarbon solvent and residual bitumen from tailings settled in a tailings pond - Google Patents

Abstract

Techniques are described herein for treating froth treatment tailings located in a tailings pond and generated from an oil sands extraction operation. The froth treatment tailings include a hydrocarbon solvent and residual bitumen. The process includes generating gas bubbles within at least one layer of the froth treatment tailings located below a water layer capping the froth treatment tailings in the tailings pond, contacting the gas bubbles with at least a portion of the hydrocarbon solvent and the residual bitumen during ascension of the gas bubbles to extract at least a portion of the hydrocarbon solvent and the residual bitumen from the at least one layer of the froth treatment tailings to the water layer capping the froth treatment tailings, thereby obtaining floating hydrocarbon aggregates and treated froth treatment tailings free of the at least a portion of the hydrocarbon solvent and the residual bitumen.

Description

TREATMENT OF RESIDUAL HYDROCARBONS IN FLUID TAILINGS
FIELD
[001] The technical field generally relates to the treatment of fine tailings derived from mining operations, and more particularly relates to the treatment of thick fine tailings and froth treatment tailings derived from oil sands mining.
BACKGROUND

[002] Tailings derived from oil sands mining operations are often placed in disposal ponds for settling. The settling of fine solids from the water in tailings ponds can be a relatively slow process and can form a stratum of thick fine tailings.

[003] Certain techniques have been developed for dewatering fine tailings.
Dewatering of fine tailings can include contacting with a flocculating agent and then depositing the flocculated material onto a sub-aerial deposition area where the deposited material can release water and eventually dry. Other techniques for treating thick fine tailings include addition of gypsum and sand to produce consolidated tailings.

[004] In some scenarios, it can be desirable to pre-treat the fine tailings stream prior to dewatering and adding the flocculating agent. However, there are a number of challenges related to pre-treating the fine tailings stream and to processing the material to facilitate efficient reclamation.
SUMMARY

[005] In one aspect, there is provided a process for treating froth treatment tailings located in a tailings pond and generated from an oil sands extraction operation, the froth treatment tailings comprising a hydrocarbon solvent and residual bitumen, the process comprising: generating gas bubbles within at least one layer of the froth treatment tailings located below a water layer capping the froth treatment tailings in the tailings pond, contacting the gas bubbles with at least a portion of the hydrocarbon solvent and the residual bitumen during ascension of the gas bubbles to extract at least a portion of the hydrocarbon solvent and the residual bitumen from the at least one layer of the froth treatment tailings to the water layer capping the froth treatment tailings, thereby obtaining floating hydrocarbon aggregates and treated froth treatment tailings free of the at least a portion of the hydrocarbon solvent and the residual bitumen.

[006] In some implementations, the gas bubbles comprise air bubbles.

[007] In some implementations, the gas bubbles consist of air bubbles.

[008] In some implementations, the process further comprises settling a froth treatment tailings material in the tailings pond to obtain the water layer capping the froth treatment tailings and the at least one layer of the froth treatment tailings located below the water layer.

[009] In some implementations, the at least one layer of the froth treatment tailings located below the water layer is at least one of a mature fine tailings layer of the froth treatment tailings and a coarse layer of the froth treatment tailings.

[010] In some implementations, the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

[011] In some implementations, generating the gas bubbles comprises sparging gas into the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings.

[012] In some implementations, the process further comprises at least one of dredging and pumping the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings, to generate fluid movement between layers of the froth treatment tailings.

[013] In some implementations, the process further comprises providing gas sparging units at a plurality of locations within the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings, for generating the gas bubbles.

[014] In some implementations, the gas bubbles are introduced at a volume of at least 20 m3 of gas per m3 of froth treatment tailings.

[015] In some implementations, the gas bubbles are introduced at a volume of at least 50 m3 of gas per m3 of froth treatment tailings.

[016] In some implementations, the froth treatment tailings comprises untreated froth treatment tailings obtained from an output of a froth treatment process.

[017] In some implementations, the gas bubbles comprise at least one of coarse bubbles, fine bubbles and micro-bubbles.

[018] In some implementations, the process further comprises: adding an immobilization chemical to the treated froth treatment tailings in order to chemically immobilize remaining contaminants of concern (CoCs); adding flocculating agent to the treated froth treatment tailings in order to flocculate remaining suspended solids, thereby producing a flocculated material; and dewatering the flocculated material to produce an aqueous component depleted in the COCs and the suspended solids, and a solids-enriched component comprising the chemically immobilized COCs and flocculated solids.

[019] In some implementations, the process further comprises providing an in-line flow of the treated froth treatment tailings.

[020] In some implementations, the immobilization chemical and the flocculating agent are added in-line into the in-line flow of the treated froth treatment tailings.

[021] In some implementations, the immobilization chemical is added as an aqueous immobilization solution into the in-line flow of the treated froth treatment tailings, the process further comprising in-line mixing of the aqueous immobilization solution and the treated froth treatment tailings.

[022] In some implementations, the process further comprises in-line conditioning of the flocculated material prior to dewatering to form a conditioned flocculated material in a water release zone.

[023] In some implementations, the immobilization chemical is selected from multivalent organic salts.

[024] In some implementations, the dewatering of the flocculated material comprises depositing the flocculated material onto a sub-aerial deposition area, thereby allowing drainage of the aqueous component away from the solids-enriched component.

[025] In some implementations, the dewatering of the flocculated material comprises depositing the flocculated material into a pit, thereby allowing separation of the aqueous component from the solids-enriched component that settles to a bottom of the pit.

[026] In some implementations, the process further comprises forming a permanent aquatic storage structure (PASS) for retaining the solids-enriched component and a water cap, wherein the solids-enriched component: forms a consolidated solids-rich lower stratum below the water cap; and retains the immobilized CoCs and inhibits migration of the immobilized CoCs into the water cap.

[027] In some implementations, adding the immobilization chemical is performed prior to adding the flocculating agent.

[028] In some implementations, adding the flocculating agent is performed prior to adding the immobilization chemical.

[029] In some implementations, the immobilization chemical and the flocculating agent are added simultaneously.

[030] In some implementations, the treated froth treatment tailings are subjected to pre-shearing to reduce a yield stress thereof prior to addition of the immobilization chemical and the flocculating agent.

[031] In some implementations, the treated froth treatment tailings are subjected to screening to remove coarse debris therefrom prior to addition of the immobilization chemical and the flocculating agent.

[032] In some implementations, the process further comprises: removing the floating hydrocarbon aggregates from the water layer capping the froth treatment tailings to produce recovered hydrocarbon aggregates.

[033] In some implementations, removing the floating hydrocarbon aggregates comprises skimming the floating hydrocarbon aggregates.

[034] In some implementations, the process further comprises treating the recovered hydrocarbon aggregates to recover at least one of the residual bitumen and the hydrocarbon solvent.

[035] In some implementations, treating the recovered hydrocarbon aggregates comprises subjecting the recovered hydrocarbon aggregates to a solvent separation step.

[036] In some implementations, the process further comprises intercepting a gas phase at the surface of the tailings pond.

[037] In another aspect, a system for treating froth treatment tailings generated from an oil sands extraction operation is provided. The froth treatment tailings comprises a hydrocarbon solvent and residual bitumen. The system comprises a tailings pond into which the froth treatment tailings are deposited for settling, to obtain a water layer and at least one layer of the froth treatment tailings located below the water layer; and a gas bubbling assembly to generate gas bubbles within the at least one layer of the froth treatment tailings and comprising at least one gas bubbles generating unit located below the water layer, the gas bubbling assembly being configured to enable extraction of at least a portion of the hydrocarbon solvent and the residual bitumen from the at least one layer of the froth treatment tailings to the gas bubbles during ascension of the gas bubbles towards a surface of the tailings pond, to obtain floating hydrocarbon aggregates and treated froth treatment tailings free of the at least a portion of the hydrocarbon solvent and the residual bitumen.

[038] In some implementations, the at least one gas bubbles generating unit comprises a plurality of air diffusers that generate air bubbles.

[039] In some implementations, the gas bubbles consist of air bubbles.

[040] In some implementations, the gas bubbling assembly further comprises: a compressor assembly located outside the tailings pond for producing compressed gas; and a network of pipes in fluid communication with the compressor for conveying the compressed gas to the at least one layer of the froth treatment tailings located below the water layer.

[041] In some implementations, the at least one layer of the froth treatment tailings located below the water layer is at least one of a mature fine tailings layer of the froth treatment tailings and a coarse layer of the froth treatment tailings.

[042] In some implementations, the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

[043] In some implementations, the gas bubbling assembly comprises gas sparging units located within the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings.

[044] In some implementations, the system further comprises at least one of a dredging unit and a pump located in the at least one layer of the froth treatment tailings located below the water layer, to generate fluid movement between layers of the froth treatment tailings.

[045] In some implementations, the gas sparging units are located at a plurality of locations within the at least one layer of the froth treatment tailings located below the water layer, for generating the gas bubbles.

[046] In some implementations, the gas bubbling assembly is configured to introduce gas into the at least one layer of the froth treatment tailings located below the water layer at a volume of at least 20 m3 of gas per m3 of froth treatment tailings.

[047] In some implementations, the gas bubbling assembly is configured to introduce gas into the at least one layer of the froth treatment tailings located below the water layer at a volume of at least 50 m3 of gas per m3 of froth treatment tailings.

[048] In some implementations, the froth treatment tailings comprise untreated froth treatment tailings obtained from an output of a froth treatment process.

[049] In some implementations, the gas bubbles comprise at least one of coarse bubbles, fine bubbles and micro-bubbles.

[050] In another aspect, there is provided a process for treating fine tailings generated from an oil sands extraction operation, the fine tailings being flocculant-free and comprising residual hydrocarbons, the process comprising: aerating the fine tailings in a gravity aerator to obtain aerated fine tailings comprising the residual hydrocarbons and air bubbles; and settling the aerated fine tailings in a tailings pond, thereby enabling the residual hydrocarbons to rise to a surface layer of the tailings pond to produce floating hydrocarbon aggregates and treated fine tailings free of at least a portion of the residual hydrocarbons.

[051] In some implementations, the fine tailings comprise at least one of thin fine tailings, thick fine tailings, mature fine tailings (MFT), froth treatment tailings (FTT) and froth treatment mature fine tailings (FTMFT).

[052] In some implementations, the residual hydrocarbons comprise at least one of a hydrocarbon solvent and residual bitumen.

[053] In some implementations, the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

[054] In some implementations, the process further comprises at least one of dredging and pumping at least one layer of the aerated fine tailings located below the surface layer of the tailings pond, to generate fluid movement between layers of the aerated tailings.

[055] In some implementations, the process further comprises: adding an immobilization chemical to the treated fine tailings to chemically immobilize remaining contaminants of concern (COCs); adding a flocculating agent to the treated fine tailings to flocculate remaining suspended solids, thereby producing a flocculated material; and dewatering the flocculated material to produce an aqueous component depleted in the COCs and the suspended solids, and a solids-enriched component comprising the chemically immobilized COCs and flocculated solids.

[056] In some implementations, the process further comprises providing an in-line flow of the treated fine tailings.

[057] In some implementations, the immobilization chemical and the flocculating agent are added in-line into the in-line flow of the treated fine tailings.

[058] In some implementations, the immobilization chemical is added as an aqueous immobilization solution into the in-line flow of the treated fine tailings, the process further comprising in-line mixing of the aqueous immobilization solution and the treated froth treatment tailings.

[059] In some implementations, the process further comprises in-line conditioning of the flocculated material prior to dewatering to form a conditioned flocculated material in a water-release zone.

[060] In some implementations, the immobilization chemical is selected from multivalent organic salts.

[061] In some implementations, the dewatering of the flocculated material comprises depositing the flocculated material onto a sub-aerial deposition area, thereby allowing drainage of the aqueous component away from the solids-enriched component.

[062] In some implementations, the dewatering of the flocculated material comprises depositing the flocculated material into a pit, thereby allowing separation of the aqueous component from the solids-enriched component that settles to a bottom of the pit.

[063] In some implementations, the process further comprises forming a permanent aquatic storage structure (PASS) for retaining the solids-enriched component and a water cap, wherein the solids-enriched component: forms a consolidated solids-rich lower stratum below the water cap; and retains the immobilized CoCs and inhibits migration of the immobilized CoCs into the water cap.

[064] In some implementations, adding the immobilization chemical is performed prior to adding the flocculating agent.

[065] In some implementations, adding the flocculating agent is performed prior to adding the immobilization chemical.

[066] In some implementations, the immobilization chemical and the flocculating agent are added simultaneously.

[067] In some implementations, the treated from fine tailings are subjected to pre-shearing to reduce a yield stress thereof prior to addition of the immobilization chemical and the flocculating agent.

[068] In some implementations, the treated fine tailings are subjected to screening to remove coarse debris therefrom prior to addition of the immobilization chemical and the flocculating agent.

[069] In some implementations, the process further comprises removing the floating hydrocarbon aggregates from the surface layer of the tailings pond to produce recovered hydrocarbon aggregates.

[070] In some implementations, removing the floating hydrocarbon aggregates comprises skimming the floating hydrocarbon aggregates.

[071] In some implementations, the process further comprises treating the recovered hydrocarbon aggregates to recover at least one of the residual bitumen and the hydrocarbon solvent.

[072] In some implementations, treating the recovered hydrocarbon aggregates comprises subjecting the recovered hydrocarbon aggregates to a solvent separation step.

[073] In some implementations, the gravity aerator comprises at least one of a cascade aerator, an inclined apron aerator, a slat tray aerator and a gravel bed aerator.

[074] In some implementations, the gravity aerator comprises a cascade aerator.

[075] In some implementations, the gravity aerator consists of a cascade aerator.

[076] In some implementations, the fine tailings comprise an untreated froth treatment tailings stream originating from a froth treatment process.

[077] In some implementations, the fine tailings comprise a settled fine tailings stream originating from a first tailings pond, and wherein the aerated fine tailings are settled in a second tailings pond.

[078] In some implementations, the settled fine tailings comprise at least one of mature fine tailings and froth treatment mature fine tailings.

[079] In some implementations, the first tailings pond is a tailings pond receiving thin fine tailings obtained after a sand dump process.

[080] In some implementations, the first tailings pond is a froth treatment tailings pond receiving froth treatment tailings from a froth treatment process.

[081] In another aspect, there is provided a system for treating fine tailings generated from an oil sands extraction operation, the fine tailings being flocculant-free and comprising residual hydrocarbons, the system comprising: a gravity aerator for aerating the fine tailings, thereby obtaining aerated fine tailings comprising the residual hydrocarbons and air bubbles; and a tailings pond in fluid communication with the gravity separator to receive the aerated fine tailings and settle the aerated fine tailings, thereby enabling the residual hydrocarbons to rise to a surface layer of the tailings pond to produce floating hydrocarbon aggregates and treated fine tailings free of at least a portion of the residual hydrocarbons.

[082] In some implementations, the fine tailings comprise at least one of thin fine tailings, thick fine tailings, mature fine tailings (MFT), froth treatment tailings (FTT) and froth treatment mature fine tailings (FTMFT).

[083] In some implementations, the residual hydrocarbons comprise at least one of a hydrocarbon solvent and residual bitumen.

[084] In some implementations, the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

[085] In some implementations, the system further comprises at least one of a dredging vessel and a pump in at least one layer of the aerated fine tailings located below the surface layer of the tailings pond, to generate fluid movement between layers of the aerated tailings.

[086] In some implementations, the gravity aerator comprises at least one of a cascade aerator, an inclined apron aerator, a slat tray aerator and a gravel bed aerator.

[087] In some implementations, the gravity aerator comprises a cascade aerator.

[088] In some implementations, the gravity aerator consists of a cascade aerator.

[089] In some implementations, the fine tailings comprise an untreated froth treatment tailings stream originating from a froth treatment process.

[090] In some implementations, the tailings pond is a second tailings pond, the system further comprising a first tailings pond in fluid communication with an inlet of the gravity aerator, wherein a settled fine tailings stream originating from the first tailings pond is fed into the gravity aerator, and wherein the aerated fine tailings are settled in the second tailings pond.

[091] In some implementations, the settled fine tailings comprise at least one of mature fine tailings and froth treatment mature fine tailings.

[092] In some implementations, the first tailings pond is a tailings pond receiving thin fine tailings obtained after a sand dump process.

[093] In some implementations, the first tailings pong is a froth treatment tailings pond receiving froth treatment tailings from a froth treatment process.

[094] In some implementations, the hydrocarbon solvent comprises naphthenic solvent.

[095] In some implementations, the hydrocarbon solvent comprises naphthenic solvent.

[096] In some implementations, the hydrocarbon solvent comprises paraffinic solvent.

[097] In some implementations, the hydrocarbon solvent comprises paraffinic solvent.

[098] In some implementations, the at least one layer of the froth treatment tailings located below the water layer is a mature fine tailings layer.

[099] In some implementations, the at least one layer of the froth treatment tailings located below the water layer is a mature fine tailings layer.

[100] In some implementations, the at least one layer of the froth treatment tailings located below the water layer is a coarse layer.

[101] In some implementations, the at least one layer of the froth treatment tailings located below the water layer is a coarse layer.
BRIEF DESCRIPTION OF THE DRAWINGS

[102] Figure 1 is a process flow diagram of an oil sands mining operation, including gas bubbling within tailings ponds.

[103] Figure 2 is a schematic representation of a tailings pond, where gas bubbles are provided in a mature fine tailings layer below the water cap layer.

[104] Figure 3 is a schematic diagram showing oil sands tailings that do not include light hydrocarbons.

[105] Figure 4 is a schematic diagram showing oil sands tailings including light hydrocarbons.

[106] Figures 5A to 5C are schematic diagrams showing oil sands tailings including light hydrocarbons migrating to gas bubbles rising through the oil sands tailings.

[107] Figure 6 is a flow diagram of an exemplary froth treatment tailings dewatering operation, wherein gas bubbles are provided in a mature fine tailings layer, below the water cap layer, prior to dewatering operations.

[108] Figure 7 is a schematic top plan view of a tailings pond wherein several air diffusers are provided.

[109] Figure 8A is a flow diagram of an exemplary cascade aeration step performed on a froth treatment tailings stream.

[110] Figure 8B is a flow diagram of an exemplary cascade aeration step performed on a thin fine tailings stream.

[111] Figure 9A is a flow diagram of an exemplary cascade aeration step performed on a froth treatment tailings stream obtained from a first tailings pond.

[112] Figure 9B is a flow diagram of an exemplary cascade aeration step performed on a thin fine tailings stream obtained from a first tailings pond.

[113] Figure 10 is a flow diagram of a gravity aeration process.

[114] Figure 11A and 11B are schematic diagrams showing exemplary cascade aerators.

[115] Figure 12 is a schematic top plan view of a tailings pond wherein an oxygenated flow is conveyed to several entry points around the tailings pond.
DETAILED DESCRIPTION

[116] Various aspects and implementations of the processes and systems described herein relating to the treatment of tailings materials will be described below.
Overview of the process

[117] Various techniques that are described herein enable the treatment of fine tailings streams, such as thick fine tailings (e.g., mature fine tailings) or froth treatment tailings (FTT), that include residual hydrocarbons. The fine tailings can include residual hydrocarbons such as residual hydrocarbons from primary or secondary separation, or diluent and residual bitumen from a froth treatment process.

[118] For example, residual light hydrocarbons can be found in part of some of the fluid tailings generated from mineable oil sands processing ¨ for example in froth treatment tailings obtained from a froth treatment process. It should be understood that the term "light hydrocarbons" as used herein refers to hydrocarbon solvents or diluents such as Naphthenic solvent or paraffinic solvent. It should also be understood that the terms "light hydrocarbons", "diluent" and "hydrocarbon solvent" can be used interchangeably in the present description. These light hydrocarbons can support microbial activity, and may as such negatively impact aquatic closure performance, as well as add to greenhouse gas (GHG) and volatile organic component (VOC) loading. The techniques described herein can allow for the in-situ removal of the residual light hydrocarbons, or for the in-situ reduction of their overall concentration to a level compatible with aquatic closure requirements.

[119] The fine tailings can be contacted with gas bubbles directly in the tailings pond in which the fine tailings are stored, to remove residual hydrocarbons, prior to sending the treated tailings stream to dewatering operations. Contacting the fine tailings stream with gas bubbles can include flotation. In some scenarios, most of the organic material that migrates to the gas bubbles is light hydrocarbons (e.g., diluent). In other scenarios, the organic material that migrates to the gas bubbles includes both residual bitumen and light hydrocarbons. Froth treatment tailings typically has three classes of "constituents of concern" (CoCs) when considering long term closure performance of tailings fluid. Two out of those three classes (i.e. Acid Rock Drainage potential and Naturally Occurring Radioactive Materials) can be compatible with permanent aquatic storage structure (PASS) treatment or aquatic reclamation. The techniques described herein enable the one remaining CoC (i.e., residual hydrocarbons such as light hydrocarbons) to be targeted specifically, while leaving the others generally unmodified. Over-processing, excessive re-handling and/or an additional ex-situ separation step can be avoided by treating the material within the tailings pond itself.

[120] The techniques described herein can use any diluent-affected fluid tailings inside a tailings containment area as feedstock. The material can first be contacted with gas bubbles (e.g., air bubbles) through a combination of sparging, pumping and dredging. When air bubbles are used, the following effects can be achieved:
1) Introduction of air can promote stripping of light hydrocarbons from the fluids and into the gas phase, through natural partitioning of light hydrocarbons between the fluid and gas phase. As a result, gas bubbles can progressively extract light hydrocarbons from the fluid tailings.
2) Introduction of air can further promote floatation of residual bitumen present in the fluid tailings. Since light hydrocarbons are in part associated with the bitumen phase, removal of bitumen can result in proportional removal of light hydrocarbons.
3) Introduction of air can also increase in-situ oxygen levels, thereby promoting biodegradation of light hydrocarbons into CO2 (aerobic degradation). This is opposed to anaerobic degradation, where the primary degradation product would be methane. Since methane is a significantly more potent greenhouse gas, aerobic degradation can reduce GHG loading.

[121] After removal of residual light hydrocarbons is substantially complete, the remainder of the tailings stream can exhibit characteristics compatible with PASS
treatment and can therefore be treated in a way similar to conventional fluid tailings (i.e., fluid tailings that do not include residual light hydrocarbons). In this context, PASS type treatment can be viewed as a process where an immobilization chemical and a flocculating agent are added to the tailings, and the resulting flocculated material is deposited within a mine pit or similar containment structure such that the flocculated solids settle and a water layer forms above the settled solids, thereby forming a PASS.

[122] It is understood that the "organic materials" found in oil sands include bitumen and other "insoluble organic materials". It is understood that the term "bitumen" as used herein, can include bitumen components such as maltenes and/or asphaltenes in varying proportions. It is understood that the maltenes consist of the fraction of the bitumen which is soluble in n-alkane solvents, including pentane, hexane and/or heptane. It is also understood that the asphaltenes consist of the fraction of the bitumen which is soluble in light aromatic solvents, such as benzene or toluene, and precipitates in n-alkane solvents. The "insoluble organic materials" (also referred to herein as "tightly bound organic materials") can for example include humic materials (i.e., humins) which can form chemical complexes with some of the heavy minerals.
It is understood that the "insoluble organic materials" consist of the organic materials which are insoluble in n-alkane solvents and light aromatic solvents at atmospheric pressure and at the boiling temperature of the solvents and can also be understood as being non-bitumen components.

[123] It should be understood that the term "fine tailings" (also referred to in the art as "fluid tailings") as used herein, may refer to various types of oil sands tailings, such as thin fine tailings (i.e., extraction tailings that have formed from run-off of sand dump operations or similar treatments), thick fine tailings (i.e., settled tailings from a tailings pond ¨ an example of which being mature fine tailings), or froth treatment tailings (or streams derived from froth treatment tailings such as froth treatment mature fine tailings, froth treatment centrifuge cake, etc.). It is understood that the term "froth treatment tailings", as used herein, encompasses froth treatment tailings exiting a froth treatment process (i.e., froth treatment tailings that have not yet settled), froth treatment tailings having settled in a tailings pond for a certain amount of time, or a stream derived from froth treatment tailings. For example, it should be understood that froth treatment tailings having settled in a tailings pond for a certain amount of time may include a top water layer capping the froth treatment tailings, a middle froth treatment mature fine tailings layer, and a bottom layer that can be rich in solid materials.
Integration in oil sands extraction operation

[124] Referring to Figure 1, in a bitumen extraction operation, oil sands ore 10 is mined and crushed in a crushing unit 12 to obtain a crushed ore 13. The crushed ore 13 is then mixed with water 14 (e.g., hot water) in a mixing unit 16 (for example, a rotary breaker) to form an aqueous slurry 18. The aqueous slurry 18 is conditioned (for example during transport) to prepare the bitumen for separation from the aqueous slurry 18 by adding additives (for example, caustic soda) to the aqueous slurry 18.
The aqueous slurry 18 is then transported to a primary separation vessel 20 for separation into primary bitumen froth 22 and coarse tailings 24 (also referred to as primary tailings).

[125] In some scenarios, the primary separation vessel 20 can also produce middlings 26 which can be sent to a secondary separation vessel 28 to be separated into secondary bitumen froth 30 and secondary tailings 32. The secondary bitumen froth 30 can be fed back to the primary separation vessel 20, as shown in the Figure or, alternatively, can be directly added to the primary bitumen froth 22.

[126] The bitumen froth 22 typically includes between about 40 wt% and about wt% bitumen, between about 20 wt% and about 50 wt% water, and between about 5 wt% and about 15 wt% solid materials. The solid materials in the bitumen froth typically include hydrophobic mineral materials and heavy minerals which can include adsorbed insoluble organic material.

[127] The primary tailings 24 and secondary tailings 32 generally include between about 45 wt% and about 55 wt% solid materials, between about 45 wt% and about 55 wt% water, and residual bitumen (typically between about 1 wt% and about 3 wt%
bitumen). The solid materials in the primary and secondary tailings 24, 32 are mainly sand and other fine hydrophilic mineral materials and can include residual heavy minerals. The primary tailings 24 and secondary tailings 32 (that can be generally referred to or combined as extraction tailings or whole tailings 29) can be further treated and dewatered, as will be described further below.

[128] The bitumen froth 22 is treated in a froth treatment process 34 in which the bitumen froth 22 is diluted with a diluent 36 to obtain a diluted bitumen froth. The diluent 36 can be either a naphthenic type diluent or a paraffinic type diluent and can also be referred to herein as "light hydrocarbons". The naphthenic type diluent can for example include toluene, naphtha or other light aromatic compounds. The paraffinic type diluent can for example include 04 to C8 aliphatic compounds and/or natural gas condensate. The diluted bitumen froth is then separated into a bitumen product (which can be further upgraded or used as is) and froth treatment tailings 40 including contaminants of concern (CoCs, such as residual bitumen, residual diluent, naphthenic acids, various salts, Acid Rock Drainage potential, Naturally Occurring Radioactive Materials etc.) and suspended solid materials (such as hydrophilic mineral materials, heavy minerals and insoluble organic materials), and water.
The froth treatment tailings 40 can be further treated and dewatered, as will be described further below.

[129] Still referring to Figure 1, in some implementations, froth treatment tailings 40 are deposited in a froth treatment tailings pond 42 for settling, to form a top water region 43 and a bottom froth treatment mature fine tailings region 44 in the tailings pond 42. Gas bubbles 45 can be generated within the froth treatment mature fine tailings 44 such that at least a portion of the light hydrocarbons and residual bitumen present in the froth treatment mature fine tailings can be extracted from the froth treatment mature fine tailings 44 to the gas bubbles. The extraction can occur as the gas bubbles rise from the froth treatment mature fine tailings 44 layer up to the water layer 43 capping the froth treatment mature fine tailings. As the gas bubbles 45 rise and reach the surface of the tailings pond 42, the extracted light hydrocarbons and residual bitumen can form floating hydrocarbon aggregates 46 and a treated froth treatment tailings stream 47 that is substantially free of light hydrocarbons and residual bitumen.

[130] The floating hydrocarbon aggregates 46 can be recovered from the tailings pond (e.g., by skimming), and the recovered hydrocarbons 49 can be subjected to further extraction and treatment operations 50 (e.g., solvent extraction, filtration, drying) to recover residual bitumen and/or light hydrocarbons.

[131] The treated froth treatment tailings stream 47 includes CoCs other than the residual bitumen and light hydrocarbons, and also includes suspended solids.
The treated froth treatment tailings stream 47 can be treated and dewatered 48 in an effort to further clean the stream. For example, the treatment and dewatering operation 48 can include the injection of an immobilization chemical to chemically immobilize the remaining CoCs and/or injection of a flocculating agent to flocculate the suspended solids and form a flocculated material. Dewatering of the flocculated material can then produce an aqueous component depleted in the CoCs and the suspended solids, and a solid-enriched component including the chemically immobilized and flocculated solids.

[132] While Figure 1 depicts separate tailings pond 54 for thin fine tailings 53 and tailings pond 42 for froth treatment tailings 40, it should be understood that a single tailings pond can be used to recover both the thin fine tailings 53 and the froth treatment tailings 40. Gas bubbles can then be generated in the single tailings pond, followed by treatment and dewatering steps similar to treatment and dewatering 48, similarly as described above. Alternatively, it is also understood that the fine tailings can be deposited in more than two tailings ponds.

[133] Still referring to Figure 1, the extraction tailings 29 are subjected to a sand dump step 52 prior to obtain thin fine tailings 53 that can be deposited into a tailings pond 54 for settling. After settling, the thin fine tailings 53 can produce a water top layer 55 and mature fine tailings 56. Gas bubbles 45' can be generated in the mature fine tailings layer 56 of tailings pond 54 and be subjected to a treatment and dewatering operation 48'. In some implementations, the water top layer 55 can be reused as recycle water 155 in the oil sands extraction operation, for example as input water in the mixing unit 16, for forming aqueous slurry 18.

[134] The gas bubbles 45' can extract at least a portion of residual light organic materials that are present in the mature fine tailings 56, and a light organic-free mature fine tailings stream 47' can be extracted from the pond 54 and subjected to further treatment and dewatering 48'. Floating organics 46' can be recovered as recovered hydrocarbons 49' and subjected to a hydrocarbon recovery process 50'. In some implementations, the fine tailings that have been settling in a tailings pond for some time (e.g., what can be referred to as "legacy tailings") can be subjected to a flotation step, followed by treatment and dewatering operations 48, 48'.

[135] The material to be treated and dewatered in the treatment and dewatering operations 48, 48' can be deposited onto a sub-aerial deposition area or into a pit, for allowing the aqueous component and the solids-enriched component to separate.
Overtime, a permanent aquatic storage structure (PASS) 58 can be formed for retaining the solids-enriched component and a water cap 62. The solids-enriched component can form a consolidated solids-rich lower stratum 60 below the water cap 62, such that the immobilized CoCs are retained by the solids-enriched component and migration of the CoCs into the water cap 62 is inhibited. The treatment and dewatering operation 48, 48', as well as the formation of the PASS 58 will be described in further detail below.
Gas bubbling in tailings pond

[136] Now referring to Figure 2, gas bubbling within a froth treatment tailings pond 42 is shown. In the implementation shown on Figure 2, the tailings deposit is froth treatment tailings obtained from a froth treatment process. The froth treatment tailings include light hydrocarbons that are added to the bitumen froth during the froth treatment process. However, it should be understood that the techniques described herein can be applied to other types tailings generated during the oil sands extraction process, so long as the tailings include hydrocarbons that are able to migrate to the gas bubbles upon bubbling gas in the tailings pond.

[137] Tailings are left over material derived from a bitumen extraction process. Many different types of tailings can be treated using one or more of the techniques described herein. In some implementations, the techniques described herein can be used for "thick fine tailings" where thick fine tailings mainly include water and fines, "thin fine tailings" or "froth treatment tailings", so long as these tailings fluids include hydrocarbons that can migrate to the gas bubbles upon bubbling gas in the tailings pond in which the tailings are stored.

[138] The fines are small solid particulates having various sizes up to about microns. The thick fine tailings have a solids content with a fines portion sufficiently high such that the fines tend to remain in suspension in the water and the material has slow consolidation rates. More particularly, the thick fine tailings can have a ratio of coarse particles to the fines that is less than or equal to one. The thick fine tailings have a fines content sufficiently high such that flocculation of the fines and conditioning of the flocculated material can achieve a two-phase material where release water can flow through and away from the flocs. For example, thick fine tailings can have a solids content between 10 wt% and 45 wt%, and a fines content of at least 50 wt% on a total solids basis, giving the material a relatively low sand or coarse solids content. The thick fine tailings can be retrieved from a tailings pond, for example, and can include what is commonly referred to as "mature fine tailings"
(MFT). A mature fine tailings layer can also form upon depositing the other types of tailings fluids in a tailings pond. For example, the middle layer of froth treatment tailings after settling in the pond for an appropriate time, can be referred to as a "froth treatment mature fine tailings" (FTMFT) layer. Such FTMFT layer includes water, fines (such as sand particles), light hydrocarbons left over from the froth treatment process and residual bitumen. For example, the FTMFT layer can form after several months of settling the froth treatment tailings in a tailings pond, after exiting a froth treatment process. In some scenarios, the FTMFT layer forms after a period between 2 months and a year, or between 4 months and 8 months, or between 6 months and 8 months, or after about 6 months. It should be understood that the settling time required for forming the FTMFT layer can vary depending on the physical-chemical properties of the froth treatment tailings, on the type of diluent used and on the environmental parameters (i.e., temperature, wind, tailings pond geometry) in the vicinity of the tailings pond in which the froth treatment tailings are settling.

[139] More generally, MFT or FTMFT refer to tailings fluids that typically form as a middle or intermediate layer in a tailings pond and contains water and an elevated content of fine solids that display relatively slow settling rates. For example, when whole tailings (which include coarse solid material, fine solids, and water) or thin fine tailings (which include a relatively low content of fine solids and a relatively high water content) are supplied to a tailings pond, the tailings separate by gravity into different layers over time. The bottom layer is predominantly coarse material, such as sand, and the top layer is predominantly water. The middle layer is relatively sand depleted, but still has a fair amount of fine solids suspended in the aqueous phase.
This middle layer is often referred to as MFT. MFT can be formed from various different types of mine tailings that are derived from the processing of different types of mined ore.
While the formation of MFT typically takes a fair amount of time (e.g., between 1 and 3 years under gravity settling conditions in the pond) when derived from certain whole tailings supplied from an extraction operation, it should be noted that MFT
and MFT-like materials can be formed more rapidly depending on the composition and post-extraction processing of the tailings, which can include thickening or other separation steps that can remove a certain amount of coarse solids and/or water prior to supplying the processed tailings to the tailings pond.

[140] In the implementation shown on Figure 2, the froth treatment tailings deposited in the tailings pond 42 has settled into a coarse layer (or bottom layer) 244 that mainly contains coarse material or sand, a middle layer or FTMFT layer 44 and a water layer 43 capping the froth treatment tailings in the tailings pond 42. Depending on the physical/chemical properties of the froth treatment tailings, on the type of light hydrocarbons added during the froth treatment process, and on the other types of CoCs present, it is understood that the properties, relative depth and settling rate of each one of the layers can differ. In the implementation shown, gas spargers 64 are provided in the bottom layer 244 and in the middle layer 44. The gas spargers generate gas bubbles 45 in the bottom layer and the middle layer, and the gas bubbles 45 rise towards the water layer 43. During the rise 47, at least a portion of the hydrocarbon lights and the residual bitumen present in the bottom layer 244 and the middle layer 44 are extracted to the gas bubbles. Upon reaching the water layer 43 and the surface of the tailings pond 42, the extracted organic material and the gas bubbles 45 can form floating hydrocarbon aggregates 46. The extraction of organic material from the middle layer 44 and bottom layer 244 also enables the formation of a treated froth treatment tailings that contains less light hydrocarbons and residual bitumen than the froth treatment tailings initially deposited in the tailings pond 42.

[141] In some implementations, the gas bubbling can be complemented by at least one of dredging and pumping of the bottom layer 244 and/or middle layer 44 to enable a large-scale fluid motion 66 between the layers of the tailings. In some scenarios, the large-scale fluid motion can help the extraction of the organic materials to the gas bubbles 45 by providing more contact between the gas bubbles 45 and the organic materials. The gas bubbles 45 can include air bubbles or can consist of air bubbles.
The floating hydrocarbon aggregates 46 can optionally be recovered at the surface of the tailings pond 42, for example by skimming, and the treated froth treatment tailings can be sent for further processing and dewatering. These optional additional operations will be described in further detail herein.
Effect of gas bubbling on light hydrocarbons and residual bitumen

[142] Now referring to Figure 3, a schematic view of a tailings fluid that does not include light hydrocarbons is shown. The tailings fluid is mainly composed of water and includes several inorganic particles such as sand and clay particles.
Residual bitumen particles are also present in the tailings fluid of Figure 3.

[143] Now referring to Figure 4, a schematic view of a tailings fluid that includes light hydrocarbons is shown (e.g., a naphthenic solvent or a paraffinic solvent). It is understood that the schematic view can for example be representative of the particles present in the middle layer of a tailings pond, such as a FTMFT layer. The light hydrocarbons are typically dispersed in the water phase, for example as discrete droplets of solvent, and can also adhere to some of the clay particles and some of the residual bitumen particles. The light hydrocarbons typically do not adhere to sand particles, which are generally more hydrophilic than the clay particles.

[144] Now referring to Figures 5A to 5C, gas bubbles are introduced in the tailings fluid of Figure 4, in a layer that is below the water layer capping the tailings. The bubbles then rise towards the surface of the tailings pond and come into contact with several hydrocarbon-containing particles and droplets of solvent during the rise. As the gas bubbles rise, droplets of solvent, as well as clay particles and residual bitumen onto which light hydrocarbons have adhered are extracted to the gas bubbles.
As the gas bubbles rise towards the surface of the tailings pond, the gas bubbles become partially saturated with light hydrocarbons. In some scenarios where the concentration of light hydrocarbons in the gas bubble reaches a certain level, particles of residual bitumen and/or clay particles can start forming aggregates with the gas bubbles. Floating hydrocarbon aggregates that float at the surface of the tailings pond can then be obtained. These floating hydrocarbon aggregates can increase in size as more and more gas bubbles are released into the bottom and/or middle layers of the tailings fluid, and as the light hydrocarbons are extracted from the bottom and/or middle layers.
Potential impact of gas bubbling

[145] In some scenarios, the tailings pond can temporarily lose its clear water cap during gas bubbling, and mitigating measures can be implemented. For example, floating booms and/or silt curtains (also referred to as turbidity curtains) can be used as flexible sediment or aggregate control barriers. Such aggregate control barrier can prevent the spread of the floating organic materials throughout the tailings pond or prevent the spread of floating organic materials to specific portions of the tailings pond (e.g., close to the shore). The aggregate control barrier can be made of permeable or non-permeable material. The aggregate control barrier can be suspended vertically in the tailings pond with a flotation material enclosed in a top pocket or region thereof, and a ballast material (e.g., a ballast chain) enclosed in a lower pocket or region thereof. In some scenarios, the water cap returns to its clear (i.e., low turbidity) state within days after stopping gas bubbling.

[146] In some scenarios, the gas bubbling can generate increased volatile organic compound emission and/or increased undesirable odors in the vicinity of the tailings pond. Mitigating measures can be implemented, for example by intercepting the gas phase at the surface of the tailings pond. In some implementations, a catalytic converter or combustion chamber can be used to remove the volatile organic compounds. In other implementations, light hydrocarbons can be recovered through condensation.

[147] In some scenarios, bitumen can build up at the surface of the tailings pond as a result of gas bubbling. Such build-up may require being removed or skimmed from the tailings pond as gas bubbling is still ongoing.
Design and placement of gas bubbler assembly

[148] The gas bubbler assembly that can be used to implement the techniques of the present description can be similar to the gas bubbler assemblies used to keep water bodies ice-free, or to aerate sludge in municipal waste water treatment plants. In some implementations, the gas bubbler assembly includes at least one gas bubbles generating unit. For example, the at least one gas bubbles generating unit can include is a diffused aeration system including a plurality of air diffusers (or air spargers or air bubblers). Compressed air can be pumped from a shore-mounted compressor and pushed through submerged lines to a diffuser located in a bottom or middle layer of the tailings pond. The air diffusers can then continuously release bubbles of any type, such as coarse bubbles, fine bubbles or micro-bubbles that rise to the surface, carrying with them large volumes of water from the bottom and/or middle layer, as well as extracting a portion of the residual light hydrocarbons and residual bitumen present in the tailings. As used herein, the terms "fine bubbles", "coarse bubbles" and "micro-bubbles" refer to bubbles having a diameter between about 1 mm and about 5 mm (fine bubbles), a diameter of at least 5 mm, or preferably between about 5 mm and about 50 mm (coarse bubbles), and a diameter smaller than about 1 mm (micro-bubbles), respectively.

[149] Now referring to Figure 7, a schematic top plan view of a tailings pond 42 is shown, in which several air diffusers 68 are located. The air diffusers 68 are spaced apart from one another and linked via a pipe 72 that also connects the air diffusers 68 to a compressor 70 that compresses air. In the implementation shown on the Figure, several compressors 70 are each connected to a plurality of air diffusers 68 via a pipe 72. In some implementations, each air diffuser assembly includes at least one compressor, at least one pipe and at least one air diffuser. It should be understood that other configurations can be used. For example, the air diffusers can be spaced apart further in the tailings pond and the total number of air diffusers can be lower. Similarly, the air diffusers can be provided closer to one another, and their number can be increased. An aggregate barrier 71 can be provided in the tailings pond 42, for example to surround the area where the air diffusers 68 are provided. In some scenarios, the aggregate barrier 71 acts as a barrier between a central area of the tailings pond 42 and a shore region of the tailings pond. In the embodiment shown, the gas bubbler assembly is partially located within the tailings pond and below the water layer ¨ the compressors 70 are located outside the tailings pond to have direct access to air while the air diffusers 68 are located within the tailings pond and below the water layer. The pipes connect the compressors 70 to the air diffusers and therefore run from the location of the compressors 70 to within the tailings pond and below the water layer, where the air diffusers 68 are located.

[150] In some implementations, the air diffusers can be selected from the group consisting of fine bubble diffusers, coarse bubble diffusers or intermediate bubble diffusers. For example. The fine bubble diffuser can generate bubbles having a diameter ranging from about 0-3 mm. The intermediate bubble diffuser can generate bubbles having a diameter ranging from 3-5 mm. The coarse bubble diffuser can generate bubbles having a diameter ranging from 5-50 mm. In some implementations, holes can be provided in the pipes to generate air bubbles without having to provide air diffusers. For example, holes can be provided at the end of a pipe, where all the air remaining in the pipe can be expelled in the tailings pond. In some implementations, at least 20 m3, or between 20 m3 and 50 m3, or at least 50 m3 of air per m3 of tailings material is diffused in the tailings pond. For example, the amount of air added can depend on the amount of treatment that may be required to clean the tailings stream.
Further processing of the treated tailings

[151] After having removed the light hydrocarbons or residual light organic materials from the tailings pond, the treated tailings thereby obtained (e.g., the treated froth treatment tailings 47) can be further processed to immobilize remaining CoCs and to flocculate remaining solids before dewatering the flocculated material. The long-term result of further processing and dewatering the treated tailings 47 tailings can be a permanent aquatic storage structure (PASS) that includes a water cap suitable for supporting aquatic life and recreational activities.

[152] Techniques are described to facilitate the deposition of treated tailings at a deposition site that over time becomes the PASS. In some implementations, the solids separated from water during the dewatering of the treated tailings do not need to be relocated, e.g., from a drying area, as can be the case for other known techniques for dewatering tailings. Rather, the solids remain in place and form the basis of a sedimentary layer of solids at the bottom of the PASS. Previous techniques for processing tailings are known to use polymer flocculation for dewatering.
However, the PASS technique additionally provides for processing the tailings to provide chemical immobilization of remaining CoCs that would otherwise remain in or transfer into the water, such that the water layer that inherently forms over the solid, sedimentary layer has CoCs removed allowing for the water cap to be of such a quality it can support aquatic life.

[153] Although the size of a PASS can vary, in some implementations the PASS
can contain a volume of 100,000,000 to 300,000,000 cubic metres and can be approximately 100 metres deep at its greatest depth. With a PASS of this scale, flocculated material from the treated thick fine tailings can be directly deposited onto a sub-aerial deposition area that is proximate and/or forms part of the PASS
footprint.
Within a relatively short period of time following closure of a mine that is reclamation of the tailings is complete. That is, the solids feeding treated thick fine tailings into the PASS, e.g., 10 years, are contained in the base of the PASS and CoCs are immobilized within the solid layer. The water cap is of a quality to support aquatic life and/or recreational activities.

[154] For example, in the context of oil sands mature fine tailings (MFT) (such as the treated FTMFT stream 47) that can include CoCs such as dissolved metals, metalloids and/or non-metals, naphthenic acids, Acid Rock Drainage potential and Naturally Occurring Radioactive Materials, the chemical immobilization can include the addition of compounds enabling the insolubilization of the metals, metalloids and/or non-metals, as well as naphthenic acids, in addition to chemical bridging of bitumen droplets with suspended clays. The MFT can also be subjected to flocculation, which can include the addition of a flocculating agent solution followed by pipeline conditioning. In some scenarios, the flocculation includes polymer flocculation, and the flocculating agent includes a polymer flocculant. The MFT that has been subjected to immobilization and flocculation can then be dewatered.
The dewatering can be performed by supplying the flocculated tailings material to a dewatering device and/or a sub-aerial deposition site. While MFT derived from oil sands extraction operations will be discussed and referred to in herein, it should be noted that various other contaminant-containing tailings and slurry streams can be treated using techniques described herein.

[155] It should be noted that the term "constituents" in the expression "constituents-of-concern" can be considered to include or correspond to substances that are considered as "contaminants" by certain institutions, regulatory bodies, or other organizations, which can vary by jurisdiction and by evaluation criteria. n some scenarios, the tailings can first subjected to chemical immobilization, followed by flocculation, and then dewatering to produce a solids-enriched tailings material in which CoCs are immobilized. CoCs can sometimes be referred to as contaminants in the sense that the presence of certain constituents can be undesirable for various reasons at certain concentrations, within certain matrices, and/or in certain chemical forms.

[156] In some implementations, subjecting the tailings to chemical immobilization and flocculation facilitates production of a reclamation-ready material, which can enable disposing of the material as part of a permanent aquatic storage structure (PASS).
Chemical immobilization

[157] In some implementations, the tailings can be treated with an immobilization chemical, which can include multivalent cations (e.g., trivalent or divalent).
The multivalent cation can be added as part of an inorganic salt. The multivalent salts can be added to the tailings pre-dissolved in an aqueous solution, which can be acidic or neutral for example. Various multivalent inorganic salts can be used as immobilization chemicals. For example, aluminum sulphate (e.g., in acid solution which can be sulfuric acid), aluminum potassium sulphate, iron sulphate, or chloride or hydrated calcium sulphate (gypsum) can be used for chemical immobilization of certain CoCs.
For example, the trivalent cation Fe3+ can be added as part of iron (III) sulphate Fe2(SO4)3. Addition of ferric sulphate to the thick fine tailings can provide certain advantages, such as lower potential H25 emissions.

[158] The multivalent cation added to tailings can perform various functions.
One function is that the multivalent cation can form a cation bridge between negatively charged bitumen droplets and negatively charged clay particles in the tailings. This bitumen droplet bridging can help immobilize the bitumen within the solids-enriched material that is formed after dewatering of the tailings. Chemical bridging of bitumen droplets with clays can decrease the potential for gas bubbles to adsorb onto bitumen and migrate out of the solids-enriched material; or chemical bridging of bitumen droplets with clays can increase the density and viscosity of the bitumen droplet and prevent upward migration in the deposit through buoyancy effects as the deposit densifies. Thus, the bitumen can remain immobilized within the solid material and thus inhibiting its migration into adjacent water regions.

[159] Another function of the multivalent inorganic salt is to insolubilize certain CoCs present in the tailings. For instance, surfactants, metals, non-metals, metalloids and other compounds can be present in soluble form in the water of the tailings material.
In tailings derived from oil sands, surfactants such as naphthenic acids can be considered CoCs in terms of water toxicity. In addition, compounds such as selenium and arsenic can also be present and subject to certain regulatory requirements. The addition of the multivalent inorganic salt enables such dissolved CoCs to be precipitated and to remain insolubilized so that the CoCs cannot re-solubilize.
Insolubilization decreases the risk of the CoCs migrating out of the solid material or entering the water column.

[160] In some implementations, chemical immobilization is performed with addition of a coagulant that destabilizes particles in the tailings through double-layer compression and modifies the pore water chemistry. In this sense, the immobilization chemical can include or be a coagulant for coagulating CoCs from the tailings to form coagulated CoCs. The coagulant can include a multivalent inorganic salt as described above and can include other various conventional coagulant species. Chemical immobilization by addition of the coagulant to the tailings can be performed before, during or after flocculation, although pre-addition can be a preferred mode of operation in many cases.

[161] Certain chemicals referred to herein can be known as coagulants in the field of water treatment and can therefore can be referred to as "coagulants" in the present application. However, it should be noted that such chemicals are used herein for the purpose of immobilization in PASS techniques rather than mere coagulation as would be understood in the water treatment industry, for example. In this sense, the terms "coagulant" and "immobilization chemical" can be used interchangeably as long as the coagulant performs the function of immobilization as described in the present application. It should still be noted that certain immobilization chemicals described herein can or cannot perform the function of coagulation. In some implementations, the so-called coagulant is added to the fine tailings in quantities superior to what is known in the water treatment industry for coagulation, e.g., superior to 350 ppm, which is used for purpose of mere coagulation rather than immobilization. It is noted that in many cases the immobilization chemical that is added will in effect cause some or substantial coagulation. It is also noted that immobilization chemicals that generally do not cause coagulation can be used in conjunction with a separate coagulant chemical that provides coagulation effects.
Flocculation

[162] A flocculating agent can be added to the tailings in order to flocculate suspended solids and facilitate separation of the water from the flocculated solids.
The flocculating agent can be selected for the given type of tailings to be treated and also based on other criteria. In the case of oil sands MET (such as MTMFT), the flocculating agent can be a medium charge (e.g., 30%) high molecular weight anionic polymer. The flocculating agent can be a polyacrylamide-based polymer, such as a polyacrylamide-polyacrylate co-polymer. The flocculating agent can have various structural and functional features, such as a branched structure, shear-resilience, water-release responsiveness to fast-slow mixing, and so on.

[163] It should be noted that flocculating agent is not limited to a medium charge, as altering the pH can influence the charge requirements. In some implementations, the flocculating agent charge is selected in accordance with pH.

[164] In some implementations, the overall flocculation and dewatering operations can include various techniques described in Canadian patent application No.
2,701,317; Canadian patent application No. 2,820,259; Canadian patent application No. 2,820,324; Canadian patent application No. 2,820,660; Canadian patent application No. 2,820,252; Canadian patent application No. 2,820,267; Canadian patent application No. 2,772,053; and/or Canadian patent application No.
2,705,055.
Such techniques¨including those related to flocculant selection; rapid dispersion;
pipeline flocculation and water-release condoning; Camp Number-based design and operation; injector design and operation; sub-aerial deposition and handling;
pre-shearing; pre-thinning; and pre-screening¨can be used or adapted for use with techniques described herein related to chemical immobilization, flocculation and dewatering. The above documents are incorporated herein by reference. It should also be noted that various techniques described in such documents can be adapted when included with techniques described in the present application, such as chemical immobilization and coagulation as well as post-flocculation handling, discharging and management.

[165] In some implementations, the flocculating agent is added as part of an aqueous solution. Alternatively, the flocculating agent can be added as a powder, a dispersion, an emulsion, or an inverse emulsion. Introducing the flocculating agent as part of a liquid stream can facilitate rapid dispersion and mixing of the flocculant into the tailings.

[166] In some implementations, the flocculating agent can be injected into a pre-treated tailings fluid using a flocculating agent injector. For example, static injectors and/or dynamic injectors can be used to perform flocculant addition. The injection can be performed in-line, that is, into the pipeline for example. A length of the pipeline downstream of the flocculant injection point can be dedicated to dispersion of the flocculating agent into the pre-treated thick fine tailings, thereby producing a tailings fluid that is ready for conditioning and eventual dewatering.

[167] As mentioned further above, the incoming pre-treated tailings fluid that has been subjected to coagulation can arrive at the flocculant injector with certain pH, yield stress, and flow regime characteristics that facilitate flocculant dispersion, mixing and reaction with suspended solids.

[168] Immediately after flocculant injection (e.g., via a co-annular injector where flocculant inlets are spaced away from the pipe side wall and are distributed around an annular ring through which the pre-treated tailings flow), there can be a dispersion pipe section that receives the flocculating material and imparts pipe shear energy to the material. The dispersion pipe length as well as flocculating agent dosage can be provided based on various factors, which can include the density and/or clay content of the thick fine tailings as well as the flocculant injector design. In some scenarios, for a given injector design and density of the thick fine tailings, optimum ranges of flocculating agent dosage and dispersion pipe length can be determined, particularly when the target pH, yield stress, and flow regime characteristics have been provided.
More regarding process modelling will be discussed in further detail in the experimentation section below.
Dewatering

[169] Various dewatering techniques described in several Canadian patent applications can be used in the context of the techniques described herein. It should be noted that the overall process can include several dewatering steps, which will be discussed in greater detail in relation to Figure 6, for example. In general, dewatering can be done by a solid-liquid separator (SLS) or by sub-aerial deposition/discharge.
A combination of SLS and sub-aerial dewatering can also be performed.

[170] Various types of SLS's can be used. For example, belt filters and/or thickeners can be used to separate a solids-depleted water stream from a solids-enriched tailings material, both of which can be subjected to further processing after dewatering.

[171] In the case of dewatering by sub-aerial deposition, various dewatering mechanisms can be at work depending on the deposition and post-deposition handling methods that are used. For instance, thin lift deposition can promote release water flowing away from the deposited material followed by dewatering by freeze-thaw, evaporation, and permeation mechanisms. For deposition that is performed to promote the formation of a much thicker lower stratum of treated fine tailings with an upper water cap, the lower stratum can dewater with consolidation as a significant dewatering mechanism.
Characteristics of PASS landform

[172] In some implementations, as mentioned above, a permanent aquatic storage structure (PASS) can be built via in situ and/or ex situ dewatering of tailings that has been subjected to chemical immobilization and flocculation. A summary of some characteristics of the PASS landform is provided below.

[173] The containment structure of the PASS can be a former mine pit, which can include various in-pit structural features such as benches and in-pit dykes.
After mining is complete, preparation of in-pit structures and landforms (e.g., dykes, dumps, temporary dams, pit walls) can be undertaken. Placement of the treated fine tailings can then begin. The treated fine tailings can be discharged in various ways at different stages of forming the PASS. The treated fine tailings can be discharged within the pit in accordance with tailings management and reclamation considerations. During or after placement of the treated fine tailings, additional landforms, surface water inlets and outlets, and operational infrastructure can be constructed as part of the overall PASS system.

[174] The PASS can be seen as a type of end pit lake ¨ but how it is formed and its target characteristics are different than a conventional end pit lake. For example, the discharged fine tailings are pre-treated before depositing into the landform that will become the end pit lake, to enhance dewatering and stability of the landform.
Conventional end pit lakes are formed by placing tailings into the mine pit (i.e., the landform), capping with water, and treating the water within the landform. In an oil sands application, a conventional end pit lake directly deposits untreated MFT
into the landform. In contrast, the PASS is formed from pre-treated material such that the MFT is dewatered at deposition and the water released from the MFT is pre-treated to remove residual hydrocarbons (such as light hydrocarbons by bubbling in the tailings pond) and chemically immobilize CoCs in the solids layer formed at the base of the PASS. Thus the PASS has several advantages over conventional end pit lakes, such as more consistent immobilization characteristics throughout the sediment layer, accelerated dewatering, and mitigation of long-term risks related to CoCs in the tailings.

[175] In a PASS, the CoCs are immobilized prior to deposition in the landform.
Fresh water dilution can be used in the aquatic reclamation process, in addition to the chemical immobilization of CoCs in the sedimentary layer. Note that fresh water dilution, meaning dilution of the already present pre-treated water cap, is different than relying on a fresh water cap to overlay fluid fine tails that were deposited untreated into the landform (i.e., as in a conventional end pit lake). The PASS in a reclaimed state will have no persistent turbidity, no (or negligible) bitumen in the water cap and toxicity and metals below guidelines required to support aquatic life.
By contrast, a conventional end pit lake uses a fresh water cap and microbial activity as the aquatic reclamation process, and steps are not taken specifically to remove bitumen from water released from the fine tailings. A conventional end pit lake will have low persistent turbidity.
Process implementations

[176] Referring to Figure 6, an implementation of a process for immobilization, flocculation and dewatering of a treated FTMFT stream 47 is shown. Figure 6 illustrates an ex situ process, wherein the dewatering includes supplying a flocculated tailings material to a solid-liquid separator (SLS) to obtain a depositable tailings material that can be deposited onto a dedicated disposal area. It should be understood the process shown on Figure 6 is not limiting and that other configurations can be implemented. For example, an in situ process can be used, where the dewatering includes directly depositing a flocculated tailings material onto a dedicated disposal area and optionally forming a permanent aquatic storage structure (PASS).

[177] An immobilization chemical 124 is added to the treated FTMFT stream 47 to produce a pre-immobilized tailings stream 126. The pre-immobilized tailings stream 126 is then combined with a flocculating agent 128 (e.g., a polymer flocculant), which can be added in-line via a co-annular injector. The flocculating agent 128 can be added so as to rapidly disperse into the tailings, forming a flocculating tailings material 130. The flocculating tailings material 130 can then be subjected to shear conditioning in order to develop a flocculated material 132 suitable for dewatering.

[178] Still referring to Figure 6, the flocculated material 132 can be supplied to an SLS
156 for the main dewatering step. The SLS 156 can be various types of separators.
The SLS 156 produces a water stream 158 and a solids-enriched stream 160. In some implementations, the immobilization chemical can be added upstream of the SLS
156, as stream 124 for example. In other implementations, a downstream immobilization chemical stream 162 can be added into the solids-enriched stream 160, to produce a depositable tailings material 164 that can be deposited into a sub-aerial dedicated disposable area (DDA) 136. It should also be noted that the immobilization chemical can be added at both upstream and downstream points (e.g., streams 124 and 162).

[179] In the scenario illustrated in Figure 6, the DDA 136 can be managed such that over time a PASS 138 is formed. Due to the upstream separation of water 158 in the SLS 156, the water cap 142 of the PASS in the ex situ dewatering scenario can be thinner than that of in situ scenarios that are described below. Indeed, in the ex situ scenario, a portion of the release water, which can be the primary source of water for the water cap 142, is withdrawn from the solid-liquid separator as recycle water 158, thereby reducing the water level of the water cap 142 in comparison to the in situ scenarios. Depending on a desired water cap depth, water from other sources can be added to the water cap in the ex situ implementation if there is insufficient water from the remaining tailings pore water.

[180] In other implementations not shown in the Figures, the flocculating tailings material 130 is subjected to pipeline conditioning, which can be the only conditioning that causes the flocculated material 132 to attain a state in which release water readily separates and flows away from the flocs (i.e., the solid/liquid separator of Figure 6 can be omitted in some implementations). Alternatively, other shear mechanisms can be provided. The flocculated material 132 can then be dewatered. The dewatering can include depositing the flocculated material 132 directly onto the DDA 136, which can be a beach or built using earthwork techniques. Each DDA 136 can have a deposition region that has a sloped base to facilitate release water flowing away from the deposited material and promote such rapid separation of the release water from the flocs.

[181] Over time, the structure and operation of the DDA 136 can be managed such that a PASS 138 is formed. The PASS 138 includes containment structures 140 for containing the material, a water cap 142, and a solids-rich stratum 144 below a water cap. During formation of the PASS 138, the water cap 142 results from the dewatering of the treated material. The release water separating from the flocs can be the primary source of water for the water cap 142 such that the quality of the water in the water cap is directly related to the immobilization of CoCs. It is also possible to add fresh water 137 or another source of water into the PASS as it is forming such that the water cap includes water from sources other than the pore water of the tailings. The solids-rich stratum includes flocculated solids as well as the immobilized CoCs, which can include bitumen-clay complexes, insolubilized surfactants (e.g., naphthenic acids), insolubilized metals (e.g., arsenic and selenium) and thus inhibits migration of the CoCs into the water cap or water column.

[182] Once the PASS 138 is substantially formed, an outlet water stream 139 can be withdrawn from the PASS as fresh water 137 is added, so as to create a flow-through within the water cap 142, to maintain the water level and/or gradually reduce certain CoC levels to facilitate supporting freshwater plants and/or phytoplankton. In some implementations, the PASS 138 can be formed by expelling treated tailings therein for a period of time (e.g., 20 years) in order to fill the PASS to a desired level. During this formation period, the water cap 142 can be substantially composed of tailings pore water that has separated out, as well as precipitation and optionally some other water sources that can be used to account for evaporation. Then, after the formation period (e.g., 20 years), water flow-through is implemented. The water flow-through can include connecting the PASS 138 with existing waterways. The water flow-through provides certain inlet and outlet flows of water into and out from the water cap, and gradually reduces salt levels in the water cap. The water flow-through can be provided such that the water cap has a certain salt content below a threshold in a predetermined period of time (e.g., below a desired value within 10 years after initiating the flow-through), and salt levels can be monitored in the water cap, the inlet flow and the outlet flow.

[183] The recycle water stream 139 can also be withdrawn from the PASS for recycling purposes. In addition, recycle water 139 can be withdrawn from the water cap 142 to be supplied to various processing units, e.g., as polymer solution make-up water 150 and water 152 for use in extraction operations 154.

[184] Experimentation and calculations regarding chemical immobilization compounds, flocculation and other process parameters related to treating and dewatering tailings can be found in Canadian patent applications Nos.
2,921,835 and 2,958,873.
Gravity aeration

[185] Now referring to Figure 10, in some implementations, a process is provided for treating fine tailings 74 generated from an oil sands extraction operation, wherein the fine tailings 74 are aerated prior to being introduced into a tailings pond for settling.
The fine tailings 74 are flocculant-free and include residual hydrocarbons.
The tailings stream 74 are aerated in a gravity aerator 76, to obtain aerated fine tailings 78 that include the residual hydrocarbons and air bubbles. The aerated fine tailings 78 can then be deposited in a settling area such as a tailings pond 80 to be settled.
In some scenarios, the settling of the aerated fine tailings 78 enable the residual hydrocarbons to rise to a surface layer of the tailings pond 80 and form floating hydrocarbon aggregates that can be recovered as recovered hydrocarbons 82 and treated fine tailings 84 that are free of at least a portion of the residual hydrocarbons.
Recycle water 86 can also be recovered from the tailings pond 80. It should be understood that the term "flocculant-free" refers to the tailings stream being subjected to aeration prior to introducing a flocculating agent, or prior to a flocculation step.

[186] It should be understood that by "free of at least a portion of the residual hydrocarbons", it is meant that the concentration of residual hydrocarbons in the treated fine tailings 84 is lower than the concentration of residual hydrocarbons in the fine tailings 74. For example, the concentration of residual hydrocarbons in the treated fine tailings 84 can be of about 80% or less, or about 70% or less, or about 60% or less, or about 50% or less, or about 40% or less, or about 30% or less, or about 20%
or less, or about 10% or less, or about 5% or less, or about 1% or less than the concentration of residual hydrocarbons in the fine tailings 74. The reduction in residual hydrocarbon concentration can depend on various operational parameters, such as degree of aeration, temperature, type of residual hydrocarbons, type of fine tailings stream etc.

[187] It should be understood that the term "gravity aerator", as used herein, refers to aerators that utilize the potential energy of water to be aerated (e.g., a tailings stream) to create interfaces for gas transfer from surrounding air into the water to be aerated.
For example, the splashing of the water typically creates turbulence and water droplets that can allow for air to be introduced into the water. It should also be understood that the "gravity aerator" excludes spray aerators (e.g., orifices or nozzles to discharge water), diffused air aerators (e.g., jet aerator, aspirating aerators) and mechanical aerators (e.g., vertical or horizontal shaft aerators).

[188] Non-limiting examples of gravity aerators include cascade aerators, inclined apron aerators, slat tray aerators and gravel bed aerators. The gravity aerator preferably includes a cascade aerator. The cascade aerator can have various configurations. For example, the cascade aerator can include at least one of a simple weir, a weir with splashboard, a corrugated sheet, a corrugated sheet with holes and a lattice configuration. In some implementations, the gravity aerator consists of a cascade aerator.

[189] Now referring to Figure 11A, a non-limiting example of a cascade aerator 77 is shown. The tailings stream 74 is provided to an elevated section of the cascade aerator 77 and the tailings stream falls down the steps 88 under the effect of gravity.
Upon exiting the cascade aerator 77 via a lower section of the aerator, the tailings 74 become oxygenated tailings 90. In this particular example, the cascade aerator includes a plurality of steps and does not include overflow weirs. The cascade aerator 77 is provided at an inclination angle a that can vary between about 50 and .

[190] Now referring to Figure 11B, another non-limiting example of a cascade aerator 77' is shown. Compared to the embodiment of Figure 11A, the cascade aerator 77' includes several overflow weirs 89 at each of the steps 88. Each overflow weir enables a corresponding receiving gutter 87 that receives liquid until the liquid overflows down to the next receiving gutter 87.

[191] Now referring to Figure 8A, froth treatment tailings 40 are provided to a cascade aerator 77 to introduce air bubbles therein. The froth treatment tailings 40 cascades down the cascade aerator 77 under the effect of gravity as cascading flow 85, to obtain an oxygenated flow 90. The oxygenated flow 90 is then deposited into a froth treatment tailings pond 42 for settling, to form a top water region 43 and a bottom froth treatment mature fine tailings region 44 in the tailings pond 42. Gas bubbles 45 that are generated in the cascade aerator 77 enable at least a portion of the light hydrocarbons and residual bitumen present in the froth treatment mature fine tailings 40 to migrate to a top water layer 43. The gas bubbles 45 stay at the surface of the tailings pond 42 and the extracted light hydrocarbons and residual bitumen can form floating hydrocarbon aggregates 46 and treated froth treatment tailings 47 that can be substantially free of light hydrocarbons and residual bitumen. The hydrocarbon aggregates 46 can be recovered as recovered hydrocarbons 49 and be subjected to a hydrocarbon recovery process 50. The treated froth treatment tailings 47 can then be subjected to further treatment and dewatering. It should be understood that while one particular configuration of cascade aerator 77 is shown on Figure 8A, other types of cascade aerators, and more generally other types of gravity aerators can be used.

[192] Now referring to Figure 8B, thin fine tailings 53 are provided to a cascade aerator 77 to introduce air bubbles therein. The thin fine tailings stream 53 cascades down the cascade aerator 77 under the effect of gravity as cascading flow 85, to obtain an oxygenated flow 90. The oxygenated flow 90 is then deposited into a tailings pond 54 for settling. After settling, the thin fine tailings 53 can produce a top water layer 55 and mature fine tailings 56. Gas bubbles 45' that are generated in the cascade aerator 77 enable floating organics 46' to migrate to the surface layer. The floating organics 46' can then be recovered as recovered hydrocarbons 49' and subjected to a hydrocarbon recovery process 50'. A light organic-free mature fine tailings stream 47' can be extracted from the tailings pond 54 and subjected to further treatment and dewatering.

[193] Now referring to Figures 9A and 9B, a cascade aerator 77 can be provided between two settling areas. In other words, the cascade aerator 77 can receive an inlet stream (e.g., a fine tailings stream) directly from a first tailings pond. The inlet stream is then oxygenated in the cascade aerator 77 under the effect of gravity, and the oxygenated stream obtained can then be provided to a second tailings pond for further settling and for separating out residual hydrocarbons.

[194] Referring now to Figure 9A, froth treatment tailings 40 are deposited in a froth treatment tailings pond 42 for settling, to form a top water region 43 and a bottom froth treatment mature fine tailings region 44 in the tailings pond 42 (with optionally a coarse layer 244 at the bottom of the tailings pond 42). The froth treatment mature fine tailings 44 can then be provided to a cascade aerator 77 to introduce air bubbles therein. The froth treatment mature fine tailings 44 cascades down the cascade aerator 77 under the effect of gravity as cascading flow 85, to obtain an oxygenated flow 90. The oxygenated flow 90 is then deposited into a further tailings pond 342 for settling, to form a top water region 343 and a bottom froth treatment mature fine tailings region 344 (with optionally a coarse layer 444 at the bottom of the tailings pond 342) in the tailings pond 342. Gas bubbles 345 that are generated in the cascade aerator 77 enable at least a portion of the light hydrocarbons and residual bitumen present in the froth treatment mature fine tailings 44 to migrate to a top water layer 343. The gas bubbles 345 stay at the surface of the tailings pond 342 and the extracted light hydrocarbons and residual bitumen can form floating hydrocarbon aggregates 346 and treated froth treatment tailings 47 that can be substantially free of light hydrocarbons and residual bitumen. The hydrocarbon aggregates 346 can be recovered as recovered hydrocarbons 349 and be subjected to a hydrocarbon recovery process 50. The treated froth treatment tailings 47 can then be subjected to further treatment and dewatering.

[195] Referring now to Figure 9B, thin fine tailings 53 are deposited into a tailings pond 54 for settling. After settling, the thin fine tailings 53 can produce a top water layer 55 and mature fine tailings 56 (with optionally a coarse layer 256 at the bottom of tailings pond 54). The mature fine tailings 56 can then be provided to a cascade aerator 77 to introduce air bubbles therein. The mature fine tailings 56 cascades down the cascade aerator 77 under the effect of gravity as cascading flow 85, to obtain an oxygenated flow 90. The oxygenated flow 90 is then deposited into a further tailings pond 354 for settling, to form a top water region 355 and a bottom froth treatment mature fine tailings region 356 (with optionally a coarse layer 456 at the bottom of the tailings pond 356) in the tailings pond 356. Gas bubbles 345' that are generated in the cascade aerator 77 enable at least a portion of floating organics 346' to migrate to the surface layer 355. The floating organics 346' can then be recovered as recovered hydrocarbons 349' and subjected to a hydrocarbon recovery process 50.
A light organic-free mature fine tailings stream 47' can be extracted from the tailings pond 354 and subjected to further treatment and dewatering.

[196] Now referring to Figure 12, the oxygenated flow 90 obtained from cascading flow 85 can be introduced into a tailings pond 42 in various ways. In some implementations, the oxygenated flow 90 can simply be introduced into the tailings pond 42 at the time of exiting the cascade aerator, from a single general location. The oxygenated flow 90 and the air bubbles contained therein can then diffuse overtime into the tailings pond 42.

[197] In other implementations, the oxygenated flow 90 can be provided to an oxygenated flow distribution system 92 to be transported and distributed 94 at multiple injection points of the tailings pond 42. The oxygenated flow distribution system can for example include a system of gutters or pipes collecting the oxygenated flow 90 from a lower section of the cascade aerator and delivering the oxygenated flow to selected injection points. In some scenarios, this configuration can allow for a more uniform distribution of the air bubbles throughout the tailings pond 42.

Claims (112)

43

1 . A process for treating froth treatment tailings located in a tailings pond and generated from an oil sands extraction operation, the froth treatment tailings comprising a hydrocarbon solvent and residual bitumen, the process comprising:
generating gas bubbles within at least one layer of the froth treatment tailings located below a water layer capping the froth treatment tailings in the tailings pond, contacting the gas bubbles with at least a portion of the hydrocarbon solvent and the residual bitumen during ascension of the gas bubbles to extract at least a portion of the hydrocarbon solvent and the residual bitumen from the at least one layer of the froth treatment tailings to the water layer capping the froth treatment tailings, thereby obtaining floating hydrocarbon aggregates and treated froth treatment tailings free of the at least a portion of the hydrocarbon solvent and the residual bitumen.

2. The process of claim 1, wherein the gas bubbles comprise air bubbles.

3. The process of claim 1 or 2, wherein the gas bubbles consist of air bubbles.

4. The process of any one of claims 1 to 3, further comprising:
settling a froth treatment tailings material in the tailings pond to obtain the water layer capping the froth treatment tailings and the at least one layer of the froth treatment tailings located below the water layer.

5. The process of any one of claims 1 to 4, wherein the at least one layer of the froth treatment tailings located below the water layer is at least one of a mature fine tailings layer of the froth treatment tailings and a coarse layer of the froth treatment tailings.

6. The process of any one of claims 1 to 5, wherein the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

7. The process of any one of claims 1 to 6, wherein generating the gas bubbles comprises sparging gas into the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings.

8. The process of claim 7, further comprising at least one of dredging and pumping the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings, to generate fluid movement between layers of the froth treatment tailings.

9. The process of any one of claims 1 to 8, further comprising providing gas sparging units at a plurality of locations within the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings, for generating the gas bubbles.

10. The process of any one of claims 1 to 9, wherein the gas bubbles are introduced at a volume of at least 20 m3 of gas per m3 of froth treatment tailings.

11. The process of any one of claims 1 to 9, wherein the gas bubbles are introduced at a volume of at least 50 m3 of gas per m3 of froth treatment tailings.

12. The process of any one of claims 1 to 11, wherein the froth treatment tailings comprises untreated froth treatment tailings obtained from an output of a froth treatment process.

13. The process of any one of claims 1 to 12, wherein the gas bubbles comprise at least one of coarse bubbles, fine bubbles and micro-bubbles.

14. The process of any one of claims 1 to 13, further comprising:
adding an immobilization chemical to the treated froth treatment tailings in order to chemically immobilize remaining contaminants of concern (CoCs);
adding flocculating agent to the treated froth treatment tailings in order to flocculate remaining suspended solids, thereby producing a flocculated material; and dewatering the flocculated material to produce an aqueous component depleted in the COCs and the suspended solids, and a solids-enriched component comprising the chemically immobilized COCs and flocculated solids.

15. The process of claim 14, further comprising providing an in-line flow of the treated froth treatment tailings.

16. The process of claim 15, wherein the immobilization chemical and the flocculating agent are added in-line into the in-line flow of the treated froth treatment tailings.

17. The process of claim 16, wherein the immobilization chemical is added as an aqueous immobilization solution into the in-line flow of the treated froth treatment tailings, the process further comprising in-line mixing of the aqueous immobilization solution and the treated froth treatment tailings.

18. The process of any one of claims 15 to 17, further comprising in-line conditioning of the flocculated material prior to dewatering to form a conditioned flocculated material in a water release zone.

19. The process of any one of claims 14 to 18, wherein the immobilization chemical is selected from multivalent organic salts.

20. The process of any one of claims 14 to 19, wherein the dewatering of the flocculated material comprises depositing the flocculated material onto a sub-aerial deposition area, thereby allowing drainage of the aqueous component away from the solids-enriched component.

21. The process of any one of claims 14 to 20, wherein the dewatering of the flocculated material comprises depositing the flocculated material into a pit, thereby allowing separation of the aqueous component from the solids-enriched component that settles to a bottom of the pit.

22. The process of claim 21, further comprising forming a permanent aquatic storage structure (PASS) for retaining the solids-enriched component and a water cap, wherein the solids-enriched component:
forms a consolidated solids-rich lower stratum below the water cap; and retains the immobilized CoCs and inhibits migration of the immobilized CoCs into the water cap.

23. The process of any one of claims 14 to 22, wherein adding the immobilization chemical is performed prior to adding the flocculating agent.

24. The process of any one of claims 14 to 22, wherein adding the flocculating agent is performed prior to adding the immobilization chemical.

25. The process of any one of claims 14 to 22, wherein the immobilization chemical and the flocculating agent are added simultaneously.

26. The process of any one of claims 14 to 22, wherein the treated froth treatment tailings are subjected to pre-shearing to reduce a yield stress thereof prior to addition of the immobilization chemical and the flocculating agent.

27. The process of any one of claims 14 to 22, wherein the treated froth treatment tailings are subjected to screening to remove coarse debris therefrom prior to addition of the immobilization chemical and the flocculating agent.

28. The process of any one of claims 1 to 27, further comprising:
removing the floating hydrocarbon aggregates from the water layer capping the froth treatment tailings to produce recovered hydrocarbon aggregates.

29. The process of claim 28, wherein removing the floating hydrocarbon aggregates comprises skimming the floating hydrocarbon aggregates.

30. The process of claim 28 or 29, further comprising treating the recovered hydrocarbon aggregates to recover at least one of the residual bitumen and the hydrocarbon solvent.

31. The process of claim 30, wherein treating the recovered hydrocarbon aggregates comprises subjecting the recovered hydrocarbon aggregates to a solvent separation step.

32. The process of any one of claims 1 to 31, further comprising intercepting a gas phase at the surface of the tailings pond.

33. A system for treating froth treatment tailings generated from an oil sands extraction operation, the froth treatment tailings comprising a hydrocarbon solvent and residual bitumen, the system comprising:
a tailings pond into which the froth treatment tailings are deposited for settling, to obtain a water layer and at least one layer of the froth treatment tailings located below the water layer; and a gas bubbling assembly to generate gas bubbles within the at least one layer of the froth treatment tailings and comprising at least one gas bubbles generating unit located below the water layer, the gas bubbling assembly being configured to enable extraction of at least a portion of the hydrocarbon solvent and the residual bitumen from the at least one layer of the froth treatment tailings to the gas bubbles during ascension of the gas bubbles towards a surface of the tailings pond, to obtain floating hydrocarbon aggregates and treated froth treatment tailings free of the at least a portion of the hydrocarbon solvent and the residual bitumen.

34. The system of claim 33, wherein the at least one gas bubbles generating unit comprises a plurality of air diffusers that generate air bubbles.

35. The system of claim 33 or 34, wherein the gas bubbles consist of air bubbles.

36. The system of any one of claims 33 to 35, wherein the gas bubbling assembly further comprises:
a compressor assembly located outside the tailings pond for producing compressed gas; and a network of pipes in fluid communication with the compressor for conveying the compressed gas to the at least one layer of the froth treatment tailings located below the water layer.

37. The system of any one of claims 33 to 36, wherein the at least one layer of the froth treatment tailings located below the water layer is at least one of a mature fine tailings layer of the froth treatment tailings and a coarse layer of the froth treatment tailings.

38. The system of any one of claims 33 to 37, wherein the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

39. The system of any one of claims 33 to 38, wherein the gas bubbling assembly comprises gas sparging units located within the at least one layer of the froth treatment tailings located below the water layer capping the froth treatment tailings.

40. The system of claim 39, further comprising at least one of a dredging unit and a pump located in the at least one layer of the froth treatment tailings located below the water layer, to generate fluid movement between layers of the froth treatment tailings.

41. The system of claim 39, wherein the gas sparging units are located at a plurality of locations within the at least one layer of the froth treatment tailings located below the water layer, for generating the gas bubbles.

42. The system of any one of claims 33 to 41, wherein the gas bubbling assembly is configured to introduce gas into the at least one layer of the froth treatment tailings located below the water layer at a volume of at least 20 m3 of gas per m3 of froth treatment tailings.

43. The system of any one of claims 33 to 41, wherein the gas bubbling assembly is configured to introduce gas into the at least one layer of the froth treatment tailings located below the water layer at a volume of at least 50 m3 of gas per m3 of froth treatment tailings.

44. The system of any one of claims 33 to 43, wherein the froth treatment tailings comprise untreated froth treatment tailings obtained from an output of a froth treatment process.

45. The system of any one of claims 33 to 44, wherein the gas bubbles comprise at least one of coarse bubbles, fine bubbles and micro-bubbles.

46. A process for treating fine tailings generated from an oil sands extraction operation, the fine tailings being flocculant-free and comprising residual hydrocarbons, the process comprising:
aerating the fine tailings in a gravity aerator to obtain aerated fine tailings comprising the residual hydrocarbons and air bubbles; and settling the aerated fine tailings in a tailings pond, thereby enabling the residual hydrocarbons to rise to a surface layer of the tailings pond to produce floating hydrocarbon aggregates and treated fine tailings free of at least a portion of the residual hydrocarbons.

47. The process of claim 46, wherein the fine tailings comprise at least one of thin fine tailings, thick fine tailings, mature fine tailings (MFT), froth treatment tailings (FTT) and froth treatment mature fine tailings (FTMFT).

48. The process of claim 46 or 47, wherein the residual hydrocarbons comprise at least one of a hydrocarbon solvent and residual bitumen.

49. The process of claim 48, wherein the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

50. The process of any one of claims 46 to 49, further comprising at least one of dredging and pumping at least one layer of the aerated fine tailings located below the surface layer of the tailings pond, to generate fluid movement between layers of the aerated tailings.

51. The process of any one of claims 46 to 50, further comprising:
adding an immobilization chemical to the treated fine tailings to chemically immobilize remaining contaminants of concern (COCs);
adding a flocculating agent to the treated fine tailings to flocculate remaining suspended solids, thereby producing a flocculated material; and dewatering the flocculated material to produce an aqueous component depleted in the COCs and the suspended solids, and a solids-enriched component comprising the chemically immobilized COCs and flocculated solids.

52. The process of claim 51, further comprising providing an in-line flow of the treated fine tailings.

53. The process of claim 52, wherein the immobilization chemical and the flocculating agent are added in-line into the in-line flow of the treated fine tailings.

54. The process of claim 53, wherein the immobilization chemical is added as an aqueous immobilization solution into the in-line flow of the treated fine tailings, the process further comprising in-line mixing of the aqueous immobilization solution and the treated froth treatment tailings.

55. The process of any one of claims 52 to 54, further comprising in-line conditioning of the flocculated material prior to dewatering to form a conditioned flocculated material in a water-release zone.

56. The process of any one of claims 51 to 55, wherein the immobilization chemical is selected from multivalent organic salts.

57. The process of any one of claims 51 to 56, wherein the dewatering of the flocculated material comprises depositing the flocculated material onto a sub-aerial deposition area, thereby allowing drainage of the aqueous component away from the solids-enriched component.

58. The process of any one of claims 51 to 57, wherein the dewatering of the flocculated material comprises depositing the flocculated material into a pit, thereby allowing separation of the aqueous component from the solids-enriched component that settles to a bottom of the pit.

59. The process of claim 58, further comprising forming a permanent aquatic storage structure (PASS) for retaining the solids-enriched component and a water cap, wherein the solids-enriched component:
forms a consolidated solids-rich lower stratum below the water cap; and retains the immobilized CoCs and inhibits migration of the immobilized CoCs into the water cap.

60. The process of any one of claims 51 to 59, wherein adding the immobilization chemical is performed prior to adding the flocculating agent.

61. The process of any one of claims 51 to 59, wherein adding the flocculating agent is performed prior to adding the immobilization chemical.

62. The process of any one of claims 51 to 59, wherein the immobilization chemical and the flocculating agent are added simultaneously.

63. The process of any one of claims 51 to 59, wherein the treated from fine tailings are subjected to pre-shearing to reduce a yield stress thereof prior to addition of the immobilization chemical and the flocculating agent.

64. The process of any one of claims 51 to 59, wherein the treated fine tailings are subjected to screening to remove coarse debris therefrom prior to addition of the immobilization chemical and the flocculating agent.

65. The process of any one of claims 46 to 64, further comprising removing the floating hydrocarbon aggregates from the surface layer of the tailings pond to produce recovered hydrocarbon aggregates.

66. The process of claim 65, wherein removing the floating hydrocarbon aggregates comprises skimming the floating hydrocarbon aggregates.

67. The process of claim 65 or 66, further comprising treating the recovered hydrocarbon aggregates to recover at least one of the residual bitumen and the hydrocarbon solvent.

68. The process of claim 67, wherein treating the recovered hydrocarbon aggregates comprises subjecting the recovered hydrocarbon aggregates to a solvent separation step.

69. The process of any one of claims 46 to 68, wherein the gravity aerator comprises at least one of a cascade aerator, an inclined apron aerator, a slat tray aerator and a gravel bed aerator.

70. The process of any one of claims 46 to 68, wherein the gravity aerator comprises a cascade aerator.

71. The process of any one of claims 46 to 68, wherein the gravity aerator consists of a cascade aerator.

72. The process of any one of claims 46 to 71, wherein the fine tailings comprise an untreated froth treatment tailings stream originating from a froth treatment process.

73. The process of any one of claims 46 to 71, wherein the fine tailings comprise a settled fine tailings stream originating from a first tailings pond, and wherein the aerated fine tailings are settled in a second tailings pond.

74. The process of claim 73, wherein the settled fine tailings comprise at least one of mature fine tailings and froth treatment mature fine tailings.

75. The process of claim 73, wherein the first tailings pond is a tailings pond receiving thin fine tailings obtained after a sand dump process.

76. The process of claim 73, wherein the first tailings pond is a froth treatment tailings pond receiving froth treatment tailings from a froth treatment process.

77. A system for treating fine tailings generated from an oil sands extraction operation, the fine tailings being flocculant-free and comprising residual hydrocarbons, the system comprising:
a gravity aerator for aerating the fine tailings, thereby obtaining aerated fine tailings comprising the residual hydrocarbons and air bubbles; and a tailings pond in fluid communication with the gravity separator to receive the aerated fine tailings and settle the aerated fine tailings, thereby enabling the residual hydrocarbons to rise to a surface layer of the tailings pond to produce floating hydrocarbon aggregates and treated fine tailings free of at least a portion of the residual hydrocarbons.

78. The system of claim 77, wherein the fine tailings comprise at least one of thin fine tailings, thick fine tailings, mature fine tailings (MFT), froth treatment tailings (FTT) and froth treatment mature fine tailings (FTMFT).

79. The system of claim 77 or 78, wherein the residual hydrocarbons comprise at least one of a hydrocarbon solvent and residual bitumen.

80. The system of claim 79, wherein the hydrocarbon solvent comprises one of a naphthenic solvent and a paraffinic solvent.

81. The system of any one of claims 77 to 80, further comprising at least one of a dredging vessel and a pump in at least one layer of the aerated fine tailings located below the surface layer of the tailings pond, to generate fluid movement between layers of the aerated tailings.

82. The system of any one of claims 77 to 81, wherein the gravity aerator comprises at least one of a cascade aerator, an inclined apron aerator, a slat tray aerator and a gravel bed aerator.

83. The system of any one of claims 77 to 81, wherein the gravity aerator comprises a cascade aerator.

84. The system of any one of claims 77 to 81, wherein the gravity aerator consists of a cascade aerator.

85. The system of any one of claims 77 to 84, wherein the fine tailings comprise an untreated froth treatment tailings stream originating from a froth treatment process.

86. The system of any one of claims 77 to 84, wherein the tailings pond is a second tailings pond, the system further comprising a first tailings pond in fluid communication with an inlet of the gravity aerator, wherein a settled fine tailings stream originating from the first tailings pond is fed into the gravity aerator, and wherein the aerated fine tailings are settled in the second tailings pond.

87. The system of claim 86, wherein the settled fine tailings comprise at least one of mature fine tailings and froth treatment mature fine tailings.

88. The system of claim 86, wherein the first tailings pond is a tailings pond receiving thin fine tailings obtained after a sand dump process.

89. The system of claim 86, wherein the first tailings pong is a froth treatment tailings pond receiving froth treatment tailings from a froth treatment process.

90. The process of any one of claims 1 to 32 or 46 to 76, wherein the hydrocarbon solvent comprises naphthenic solvent.

91. The system of any one of claims 33 to 45 or 77 to 86, wherein the hydrocarbon solvent comprises naphthenic solvent.

92. The process of any one of claims 1 to 32 or 46 to 76, wherein the hydrocarbon solvent comprises paraffinic solvent.

93. The system of any one of claims 33 to 45 or 77 to 86, wherein the hydrocarbon solvent comprises paraffinic solvent.

94. The process of any one of claims 1 to 32, 46 to 76, 90 or 92, wherein the at least one layer of the froth treatment tailings located below the water layer is a mature fine tailings layer.

95. The system of any one of claims 33 to 45, 77 to 86, 91 or 93, wherein the at least one layer of the froth treatment tailings located below the water layer is a mature fine tailings layer.

96. The process of any one of claims 1 to 32, 46 to 76, 90 or 92, wherein the at least one layer of the froth treatment tailings located below the water layer is a coarse layer.

97. The system of any one of claims 33 to 45, 77 to 86, 91 or 93, wherein the at least one layer of the froth treatment tailings located below the water layer is a coarse layer.

98. The process of any one of claims 1 to 32, 46 to 76, 90, 92, 94 or 96, wherein the gas bubbles comprise coarse bubbles.

99. The process of any one of claims 1 to 32, 46 to 76, 90, 92, 94 or 96, wherein the gas bubbles comprise fine bubbles.

100. The process of any one of claims 1 to 32, 46 to 76, 90, 92, 94 or 96, wherein the gas bubbles comprise micro-bubbles.

101. The system of any one of claims 33 to 45, 77 to 86, 91, 93, 95 or 97, wherein the gas bubbles comprise coarse bubbles.

102. The system of any one of claims 33 to 45, 77 to 86, 91, 93, 95 or 97, wherein the gas bubbles comprise fine bubbles.

103. The system of any one of claims 33 to 45, 77 to 86, 91, 93, 95 or 97, wherein the gas bubbles comprise micro-bubbles.

104. The process of any one of claims 46 to 76, wherein the fine tailings comprise thin fine tailings.

105. The process of any one of claims 46 to 76, wherein the fine tailings comprise thick fine tailings.

106. The process of any one of claims 46 to 76, wherein the fine tailings comprise mature fine tailings (MFT).

107. The process of any one of claims 46 to 76, wherein the fine tailings comprise froth treatment tailings (FTT).

108. The process of any one of claims 46 to 76, wherein the fine tailings comprise froth treatment mature fine tailings (FTMFT).

109. The process of any one of claims 46 to 76, wherein the residual hydrocarbons comprise a hydrocarbon solvent.

110. The process of claim 109, wherein the hydrocarbon solvent comprises naphthenic solvent.

111. The process of claim 109, wherein the hydrocarbon solvent comprises paraffinic solvent.

112. The process of any one of claims 46 to 76, wherein the residual hydrocarbons comprise residual bitumen.