CA3069204A1 - System and method for dewatering tailings deposits in situ using forward osmosis - Google Patents

Abstract

ABSTRACT Provided herein are systems and methods for dewatering tailings deposits in situ using forward osmosis. One of such methods involves concentrating with salt a water cap overlying a tailings deposit to create an osmotic pressure gradient therebetween to draw water out of the tailings deposit. A semipermeable membrane can be provided on the tailings deposit to minimize salt diffusion between the deposit and the water cap, or the semipermeable membrane can be omitted to, for example, promote salt diffusion into the deposit. Methods and systems are also provided for dewatering tailings deposits using semipermeable cells, such as bags or pools, containing a saltwater draw solution. 23828359.1 CA 3069204 2020-01-23

Description

SYSTEM AND METHOD FOR DEWATERING TAILINGS DEPOSITS IN SITU USING
FORWARD OSMOSIS
TECHNICAL FIELD
[0001] The following generally relates to systems and methods for dewatering tailings, particularly for dewatering tailings deposits in situ using forward osmosis.
BACKGROUND

[0002] Mining operations often involve the generation of tailings, after the substance of interest is extracted from the ore. Such tailings can take many forms, including thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings. Remediation or disposal of these tailings often requires consolidation, to separate the solid and liquid components therefrom. In some applications, such as oil sands mining operations, the resulting tailings can be particularly difficult to consolidate.

[0003] Bitumen is generally extracted from oil sands deposits by in situ extraction methods or oil sands mining. In situ extraction techniques can be used to access bitumen reservoirs deep underground, whereas oil sands mining is typically employed for extracting bitumen from deposits that are relatively close to the surface.

[0004] Oil sands mining generally begins with surface mining and subsequently crushing the oil sand ore to reduce large clumps. Water is then added to the crushed ore to create an oil sands slurry comprising sand, clay, bitumen and water, which is aerated and pumped to an extraction plant. In the extraction plant, the oil sands slurry is gravity separated to recover bitumen froth, leaving primary extraction tailings. Primary extraction tailings comprise coarse sand, fines, clays, unrecovered bitumen and process water, and are usually diverted to tailings ponds, wherein the solids (i.e., sand and fines) can settle over time. The bitumen froth requires additional treatment to remove solids and water before the bitumen component of the froth can be upgraded and refined, which produces a further tailings stream comprising residual hydrocarbon, solids (e.g. fine clay) and water. These froth treatment tailings can also be diverted to tailings ponds.

[0005] As tailings are discharged into tailings ponds or other disposal facilities, the coarse sand can settle rapidly and trap a portion of the fine solids. The resulting coarse sand mixture can be useful in applications such as the construction of beaches and dykes.
However, a significant fraction of the fines in the discharged tailings can slowly settle and form a thick fine slurry, referred to as fine fluid tailings ("FFT"). If left undisturbed for a period of time such as 23828359.1 several years, the solids content of the FFT layer can increase, and the tailings can then be referred to as mature fine tailings ("MFT"). MFT can contain approximately 85%
water by volume and can be difficult to dewater. If left untreated, it is estimated that MFT deposits can take hundreds of years to consolidate, at which point they are unlikely to have sufficient strength to support a terrestrial landform. Additional measures can thus be required to further increase the solids content and strength of the tailings deposit, some of which are discussed below.

[0006] One method of accelerating consolidation of tailings is the application of a mechanical surcharge load comprising sand and/or other readily available materials across the surface of the tailings. Typically, a surcharge load of greater than 100 kPa would be required to achieve the required solids content and strength needed for an MFT deposit to support a terrestrial landform. Applying a loading of this magnitude can present a number of challenges, such as building sufficient strength in the surface of the tailings to support the loading and uniformly depositing the loading material.

[0007] Methods have been developed to increase the rate of MFT dewatering to reduce time periods to consolidation. Commonly used methods include, but are not limited to, the use of vertical wick drains, electro-kinetic dewatering, and thin-lift deposition.
However, these methods can be considered expensive, complicated, labor intensive, and/or of limited effectiveness for some applications, such as dewatering of deep MFT deposits.

[0008] It would be advantageous to address at least one of the above-noted issues or disadvantages.
SUMMARY

[0009] Provided herein are systems and methods for dewatering tailings deposits in situ using forward osmosis. One of such methods involves concentrating with salt a water cap overlying a tailings deposit to create an osmotic pressure gradient therebetween to draw water out of the tailings deposit. A semipermeable membrane can be provided on the tailings deposit to minimize salt diffusion between the deposit and the water cap, or the semipermeable membrane can be omitted to, for example, promote salt diffusion into the deposit. Methods and systems are also provided for dewatering tailings deposits using semipermeable cells, such as bags or pools, containing a saltwater draw solution.

[0010] In one aspect, provided herein is a method of at least partially dewatering a tailings deposit, the tailings deposit having a water cap thereover, the method comprising: placing a semipermeable membrane between the tailings and the water cap, the semi-permeable 23828359.1 membrane being permeable to water and nearly impermeable to ions; increasing a water cap molar salt concentration to be greater than a tailings deposit molar salt concentration to dewater the tailings deposit; and maintaining the water cap molar salt concentration above the tailings deposit molar salt concentration until the tailings deposit is dewatered to a desired extent.

[0011] In an implementation of the method, a volume of the water cap is minimized while substantially covering the tailings deposit.

[0012] In another implementation of the method, a volume of the water cap is increased to and/or maintained at a target volume to increase a dewatering rate of the tailings deposit.

[0013] In yet another implementation of the method, the volume is controlled by pumping water out of the water cap.

[0014] In yet another implementation of the method, the water cap molar salt concentration is increased and/or maintained by delivering a brine solution having a higher salt concentration than the water cap molar salt concentration into the water cap.

[0015] In yet another implementation of the method, the water cap molar salt concentration is increased stepwise until the desired extent is reached.

[0016] In yet another implementation of the method, the water cap molar salt concentration is increased to be a continuously increasing amount higher than the tailings deposit molar salt concentration until the desired extent is reached.

[0017] In yet another implementation, the method further comprises providing a plurality of wick drains in the deposit.

[0018] In yet another implementation of the method, each of the wick drains has a first end and a second end, the first end being positioned near the semipermeable membrane, and the second end extending toward a base of the deposit.

[0019] In yet another implementation of the method, the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

[0020] In yet another implementation of the method, the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

[0021] In yet another implementation of the method, the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

23828359.1

[0022] In yet another implementation of the method, the brine solution comprises one or more of Nat, Ca2+, K, Mg2 , S042-, HCO3-, and CI-.

[0023] In yet another implementation of the method, the semipermeable membrane is a forward osmosis ("FO") membrane.

[0024] In yet another implementation of the method, the FO membrane comprises one or more of cellulose triacetate ("CTA"), polyamide, polyamide-innide, or polybenzimidazole.

[0025] In yet another implementation of the method, the semipermeable membrane is a reverse osmosis membrane.

[0026] In yet another implementation of the method, the semipermeable membrane is a nanofiltration membrane.

[0027] In yet another implementation of the method, the semipermeable membrane is a thin-film composite membrane ("TFM").

[0028] In yet another implementation of the method, the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

[0029] In yet another implementation of the method, the porous support layer is made from polysulfone.

[0030] In yet another implementation of the method, the semipermeable membrane is at least partially enclosed in a protective fabric that is permeable to water.

[0031] In yet another implementation of the method, the semipermeable membrane is provided between first and second sheets of the protective semipermeable fabric.

[0032] In yet another implementation of the method, the semipermeable membrane is corrugated.

[0033] In yet another implementation of the method, a plurality of spacers are provided between the semipermeable membrane and the first sheet of protective semipermeable fabric such that a space is defined therebetvveen.

[0034] In yet another implementation of the method, an outer surface of the first sheet is in contact with the tailings deposit.

[0035] In yet another implementation of the method, the protective fabric is a geotextile fabric.

23828359.1

[0036] In another aspect, provided herein is a method of storing salt in and/or at least partially dewatering a tailings deposit, the tailings deposit having a water cap thereover, the method comprising: increasing a water cap molar salt concentration to be greater than a tailings deposit molar salt concentration to induce migration of the water cap salt into the tailings deposit and/or to dewater the tailings deposit; and maintaining the water cap molar salt concentration above the tailings deposit molar salt concentration until the earlier of the tailings deposit has accepted a desired amount of salt or the tailings deposit has been dewatered to a desired extent.

[0037] In an implementation of the method, a volume of the water cap is minimized while substantially covering the tailings deposit.

[0038] In another implementation of the method, a volume of the water cap is increased to and/or maintained at a target volume to increase a dewatering rate of the tailings deposit.

[0039] In yet another implementation of the method, the volume is controlled by pumping water out of the water cap.

[0040] In yet another implementation of the method, the water cap molar salt concentration is increased and/or maintained by delivering a brine solution having a higher salt concentration than the water cap molar salt concentration into the water cap.

[0041] In yet another implementation of the method, the water cap molar salt concentration is increased stepwise until the desired extent is reached.

[0042] In yet another implementation of the method, the water cap molar salt concentration is increased to be a continuously increasing amount higher than the tailings deposit molar salt concentration until the desired extent is reached.

[0043] In yet another implementation, the method further comprises providing a plurality of wick drains in the deposit.

[0044] In yet another implementation of the method, each of the wick drains has a first end and a second end, the first end being positioned near the semipermeable membrane, and the second end extending toward a base of the deposit.

[0045] In yet another implementation of the method, the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

[0046] In yet another implementation of the method, the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

23828359.1

[0047] In yet another implementation of the method, the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

[0048] In yet another implementation of the method, the brine solution comprises one or more of Na, Ca2+, K , Mg2+, S042-, HCO3-, and CI-.

[0049] In yet another aspect, there is provided a method of at least partially dewatering a tailings deposit comprising: a) providing on a surface of the tailings deposit a plurality of semipermeable cells containing a draw solution, the semipermeable cells being permeable to water and nearly impermeable to ions; and b) increasing and/or maintaining a draw solution molar salt concentration above a tailings deposit molar salt concentration until a region of the tailings deposit beneath the cells is dewatered to a desired extent.

[0050] In an implementation of the method, at least one of the semipermeable cells is a semipermeable bag comprising a semipermeable membrane.

[0051] In another implementation of the method, at least one of the semipermeable cells is a containment structure having a floor comprising a semipermeable membrane.

[0052] In yet another implementation of the method, the semipermeable membrane is a forward osmosis ("FO") membrane.

[0053] In yet another implementation of the method, the FO membrane comprises one or more of CTA, polyamide, polyamide-imide, or polybenzimidazole.

[0054] In yet another implementation of the method, the semipermeable membrane is a reverse osmosis membrane.

[0055] In yet another implementation of the method, the semipermeable membrane is a nanofiltration membrane.

[0056] In yet another implementation of the method, the semipermeable membrane is a thin-film composite membrane ("TFM").

[0057] In yet another implementation of the method, the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

[0058] In yet another implementation of the method, the porous support layer is made from polysulfone.

23828359.1

[0059] In yet another implementation of the method, the semipermeable membrane is protected by a protective fabric that is permeable to water.

[0060] In yet another implementation of the method, the protective fabric is a geotextile fabric.

[0061] In yet another implementation of the method, at least one of the semipermeable cells extends at least partially into the tailings deposit.

[0062] In yet another implementation of the method, the plurality of semipermeable cells are provided on a portion of the surface, and the method further comprises: c) after the desired extent is reached, moving the plurality of semipermeable cells to another portion of the surface and repeating the method from step a) to dewater another region of the tailings deposit to the desired extent.

[0063] In yet another implementation of the method, moving the plurality of semipermeable cells comprises sliding the cells along the surface.

[0064] In yet another implementation, the method further comprises repeating the method until the entire tailings deposit is dewatered to the desired extent.

[0065] In yet another implementation of the method, the draw solution molar salt concentration is increased and/or maintained by delivering a brine solution into the plurality of cells through an inlet provided in each cell, and removing the draw solution from the plurality of cells through an outlet provided in each cell.

[0066] In yet another implementation of the method, the draw solution molar salt concentration is increased stepwise until the desired extent is reached.

[0067] In yet another implementation of the method, the draw solution molar salt concentration is increased to be a continuously increasing amount higher than the tailings deposit molar salt concentration until the desired extent is reached.

[0068] In yet another implementation, the method further comprises providing a plurality of wick drains in the deposit.

[0069] In yet another implementation of the method, each of the wick drains has a first end and a second end, the first end is positioned near one of the semipermeable cells, and the second end extends toward a base of the deposit.

[0070] In yet another implementation of the method, the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

23828359.1

[0071] In yet another implementation of the method, the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

[0072] In yet another implementation of the method, the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

[0073] In yet another implementation of the method, the brine solution comprises one or more of Na, Ca2+, K , Mg'', S042-, HCO3-, and CI-.

[0074] In yet another aspect, there is provided a system for at least partially devvatering a tailings deposit having a water cap thereover, the system comprising: a source of a brine solution for increasing a water cap molar salt concentration; and a conduit for conveying the brine solution from the source to the water cap.

[0075] In an implementation, the system further comprises a mechanism for removing water from the water cap.

[0076] In another implementation of the system, the mechanism is at least one pump.

[0077] In yet another implementation of the system, the source is a water treatment plant.

[0078] In yet another implementation, the system further comprises a semipermeable membrane provided between the tailings deposit and the water cap, the semipermeable membrane being permeable to water and nearly impermeable to ions.

[0079] In yet another implementation of the system, the semipermeable membrane is a forward osmosis ("FO") membrane.

[0080] In yet another implementation of the system, the FO membrane comprises one or more of CTA polyamide, polyamide-imide, or polybenzimidazole.

[0081] In yet another implementation of the system, the semipermeable membrane is a reverse osmosis membrane.

[0082] In yet another implementation of the system, the semipermeable membrane is a nanofiltration membrane.

[0083] In yet another implementation of the system, the semipermeable membrane is a thin-film composite membrane ("TFM").

[0084] In yet another implementation of the system, the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

23828359.1

[0085] In yet another implementation of the system, the porous support layer is made from polysulfone.

[0086] In yet another implementation of the system, the semipermeable membrane is at least partially enclosed in a protective fabric that is permeable to water.

[0087] In yet another implementation of the system, the semipermeable membrane is provided between first and second sheets of the protective fabric.

[0088] In yet another implementation of the system, the semipermeable membrane is corrugated.

[0089] In yet another implementation of the system, a plurality of spacers are provided between the semipermeable membrane and the first sheet of protective semipermeable fabric such that a space is defined therebetween.

[0090] In yet another implementation of the system, an outer surface of the first sheet is in contact with the tailings deposit.

[0091] In yet another implementation of the system, the protective fabric is a geotextile fabric.

[0092] In yet another implementation, the system further comprises a plurality of wick drains provided in the deposit.

[0093] In yet another implementation of the system, each of the wick drains has a first end and a second end, the first end is positioned near the semipermeable membrane, and the second end extends toward a base of the deposit.

[0094] In yet another implementation of the system, the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

[0095] In yet another implementation of the system, the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

[0096] In yet another implementation of the system, the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, gold mining, copper mining, aluminum mining or nickel mining.

[0097] In yet another implementation of the system, the brine solution comprises one or more of Nat, Ca2+, K+, Mg', S042-, HCO3-, and Cl.

23828359.1

[0098] In yet another aspect, there is provided a system for at least partially dewatering a tailings deposit, the system comprising: a plurality of semipermeable cells provided on a surface of the deposit; a draw solution contained within the plurality of semipermeable cells; and a source of a brine solution for increasing a draw solution molar concentration.

[0099] In an implementation, the system further comprises an inlet and an outlet provided in at least one of the semipermeable cells, each inlet being connected to a conduit for conveying the brine from the source to the respective cell, and each outlet being connected to a conduit for conveying the brine from the respective cell to the source.

[00100] In another implementation of the system, the source is a water treatment plant.

[00101] In yet another implementation of the system, at least one of the semipermeable cells is a semipermeable bag comprising a semipermeable membrane.

[00102] In yet another implementation of the system, at least one of the semipermeable cells is a containment structure having a floor comprising a semipermeable membrane.

[00103] In yet another implementation of the system, the semipermeable membrane is a forward osmosis ("FO") membrane.

[00104] In yet another implementation of the system, the FO membrane comprises one or more of CTA polyamide, polyamide-imide, or polybenzimidazole.

[00105] In yet another implementation of the system, the semipermeable membrane is a reverse osmosis membrane.

[00106] In yet another implementation of the system, the semipermeable membrane is a nanofiltration membrane.

[00107] In yet another implementation of the system, the semipermeable membrane is a thin-film composite membrane ("TFM").

[00108] In yet another implementation of the system, the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

[00109] In yet another implementation of the system, the porous support layer is made from polysulfone.

[00110] In yet another implementation of the system, the semipermeable membrane is protected by a protective fabric that is permeable to water.

23828359.1

[00111] In yet another implementation of the system, the protective fabric is a geotextile fabric.

[00112] In yet another implementation, the system further comprises a plurality of wick drains in the deposit.

[00113] In yet another implementation of the system, each of the wick drains has a first end and a second end, the first end is positioned near one of the semipermeable cells, and the second end extends toward a base of the deposit.

[00114] In yet another implementation of the system, the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

[00115] In yet another implementation of the system, the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

[00116] In yet another implementation of the system, the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, gold mining, copper mining, aluminum mining or nickel mining.

[00117] In yet another implementation of the system, the brine solution comprises one or more of Na, Ca2+, K, Mg2+, S042-, HCO3-, and Cr.

[00118] In yet another implementation of the system, at least one of the semipermeable cells extends at least partially into the tailings deposit.
BRIEF DESCRIPTION OF THE DRAWINGS

[00119] Embodiments will now be described with reference to the appended drawings wherein:

[00120] FIG. 1A is a cross-sectional view of system for dewatering a tailings deposit wherein a semipermeable membrane is positioned between a tailings deposit and a concentrated saltwater cap.

[00121] FIG. 1B is an expanded cross-sectional view of an example embodiment of a semipermeable membrane.

[00122] FIG. 1C is an expanded cross-sectional view of another example embodiment of a semipermeable membrane.

[00123] FIG. 2 is a flow chart illustrating a method for dewatering a tailings deposit having a water cap.
- 11 -23828359.1

[00124] FIG. 3 is a cross-sectional view of a system for dewatering a tailings deposit wherein a semipermeable membrane is positioned between the tailings deposit and a concentrated saltwater cap, and plurality of wick drains are provided in the tailings deposit.

[00125] FIG. 4A is a cross-sectional view of a system for dewatering a tailings deposit using a plurality of semipermeable bags containing concentrated saltwater.

[00126] FIG. 4B is an expanded view of one of the semipermeable bags shown in FIG. 4A.

[00127] FIG. 5A is a cross-sectional view of a system for incrementally dewatering a tailings deposit using a plurality of semipermeable bags containing concentrated saltwater.

[00128] FIG. 5B is a plan view of the system shown in FIG. 5A.

[00129] FIG. 50 is a plan view of the system shown in FIG. 5B, wherein the deposit is being incrementally dewatered.

[00130] FIG. 6A is a cross-sectional view of another system for incrementally dewatering a tailings deposit using a plurality of semipermeable bags containing concentrated saltwater.

[00131] FIG. 6B is a plan view of the system shown in FIG. 6A.

[00132] FIG. 7 is a flow chart illustrating a method for incrementally dewatering a tailings deposit using semipermeable bags containing concentrated saltwater.

[00133] FIG. 8A is a cross-sectional view of a system for dewatering a tailings deposit using a plurality of open, semipermeable pools containing concentrated saltwater.

[00134] FIG. 8B is an expanded view of one of the semipermeable pools shown in FIG. 8A.
DETAILED DESCRIPTION

[00135] Provided herein are methods and systems for dewatering tailings deposits using forward osmosis ("FO").

[00136] By way of background, FO refers to net water flows driven by an osmotic pressure gradient arising from the separation, with a semipermeable membrane, of a "feed" solution from a "draw" solution of a higher solute concentration. Semipermeable membranes used in FO are permeable to water, and ideally impermeable to solutes or ions. In practice, however, there is often at least some leakage of ions through these semipermeable membranes.

[00137] Osmotic pressure is the pressure which, if applied to the more concentrated, or draw solution, would prevent transport of water across such a semipermeable membrane. Osmotic pressures can be considerably large; for example, sea water can have an osmotic pressure of 23828359.1 up to 3000 kPa, which is approximately equivalent to a sand surcharge load greater than 150 meters high. If this phenomenon is harnessed to apply pressure on tailings deposits, it is anticipated the settling rates, ultimate solids contents and strengths of such deposits can be improved relative to what can be achieved with current consolidation technologies. Additionally, as discussed in greater detail below, the dewatering systems provided herein can trap salt within tailings deposits, which could be of benefit for reclaiming oil sands mining sites.

[00138] The term "tailings deposit" as used herein can refer to a tailings slurry. Such term can also refer to a tailings deposit that is not considered a slurry, but still requires dewatering to achieve sufficient strength for reclamation.

[00139] The term "ppm" as used herein means "mg/kg", unless otherwise indicated.

[00140] The term "salt" as used herein with respect to oil sands tailings refers to a mixture of salts typically found in oil sands mining process water. Such salts include, but are not limited to, Na, Ca2+, K , Mg2+, S042-, HCO3-, and C. An advantage of using these salts to concentrate the draw solution is their abundance in the process water. However, other salts or combinations thereof could be used to concentrate the draw solution. Additionally, when used in the context of a different mining operation (see below), the term "salt" can refer to salts abundant in such mining operation and/or salts from external sources.

[00141] The term "brine" as used herein refers to a high concentration solution of salt in water.

[00142] The term "tailings" as used hereinafter generally refers to tailings that are difficult to consolidate, such as, e.g., thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings. Such tailings can be generated from mining processes including, but not limited to, oil sands, phosphate, sulfide mineral, coal, iron, copper, gold, aluminum, nickel, or other forms of mining that create water based tailings.

[00143] Oil sands mining operations can generate thick fine tailings, often in the form of MFT
or froth treatment tailings. Other tailings that can be generated during oil sands mining include, but are not limited to, previously treated MFT, MFT mixed with other tailings types or materials (e.g., overburden) and coarse tailings.

[00144] Dewatering of tailings deposits in one or more of the above noted processes can, in addition to increasing soil strength, prevent or reduce leaching of contaminants (e.g., toxic chemicals) from the associated tailings into the environment. For instance, mining operations that process phosphate rock can produce phosphate tailings deposits having elevated levels of 23828359.1 toxic heavy metals. Dewatering such deposits can reduce or prevent leaching of these toxic metals. Dewatering of the tailings produced by sulfide mineral mining processes can reduce acid mine drainage which can occur when the tailings react with air in the presence of microorganisms.

[00145] The systems and methods discussed below are applied to dewater tailings generated from oil sands mining. However, it will be understood that these systems and methods can be applied to dewater tailings such as those listed above, preferably when the tailings are deposited and contained in a structure such as, e.g., a tailings dam, raised embankment, or a mined or dug out pit. The semipermeable cells discussed below could also be utilized to dewater tailings that are not surrounded by structural features that can contain a water cap above the tailings deposit.

[00146] One or more of the terms "vertical", "vertically", "horizontal", "horizontally", "top", "bottom", "upwardly", "downwardly", "upper", "lower", "above" and "below" are used throughout this specification. It will be understood that these terms are not intended to be limiting. These terms are used for convenience and to aid in describing the features herein, for instance, as illustrated in the accompanying drawings.

[00147] FIG. 1A illustrates a system 100 for dewatering a tailings deposit 106 similar to those seen in the Canadian oil sands. The system 100 comprises the tailings deposit 106 overlain by a water cap 104, both of which are contained by a containment structure 103, which can be, e.g., a dam. A semipermeable membrane 108 can be positioned above, and preferably on the tailings deposit 106. In this example, the tailings deposit 106 comprises MFT
which can include bitumen, other fines, and various solutes. The water cap 104 has an osmotic pressure that is higher than that of the tailings deposit 106, thereby creating an osmotic pressure gradient which can drive the flow of water from the tailings deposit 106 into the water cap 104 (i.e., dewater the tailings deposit 106). That is, an FO process can be implemented directly in the pond 100, where the water cap 104 is a draw solution, and the tailings deposit 106 is a feed solution.

[00148] The semipermeable membrane 108 can be nearly impermeable to solutes, while allowing water from the tailings deposit to pass therethrough. The semipermeable membrane 108 can be any suitable FO membrane such as, for example, a cellulose triacetate ("CTA") FO
membrane. Optionally, the semipermeable membrane 108 can be an FO membrane enclosed within one or more additional fabric layers, such as geotextiles, (not shown) that can permit the flow of water therethrough while providing the FO membrane with protection to prevent same 23828359.1 from being punctured or compromised. Other FO membranes can include materials such as polyannide, polyamide-imide, or polybenzimidazole. Although not preferable over FO
membranes, it can be appreciated that other membranes including, but not limited to, reverse osmosis and nanofiltration membranes could be used instead of an FO membrane.
Thin-film composite membranes ("TFM"), which can be used for nanofiltration, reverse osmosis or FO, could also be used. An example of a TFM that has been used for desalination applications includes an active thin-film layer of polyamide layered with polysulfone as a porous support layer. In another example embodiment, the semipermeable membrane can include a plurality of sections, in which case a function of additional fabric layers, such as those discussed above, could be to assist in holding the plurality of sections together. It can be appreciated that the membranes used can optionally have structural features such as, for example, corrugations and/or projections to increase membrane surface area. Examples of such membranes are shown in FIGS. 1A and 1B, discussed below. A further benefit of using FO as shown in the system 100 is that salt can be trapped in the deposit 106 as same is dewatered, potentially reducing future requirements for water treatment.

[00149] The salt concentration of the water cap 104 can be controlled to achieve a desired osmotic pressure gradient between the water cap 104 and the tailings deposit 106. It can be appreciated that the desired osmotic pressure gradient can change with time or remain constant. Controlling the osmotic pressure gradient can, in turn, assist in controlling the dewatering rate of the tailings deposit 106. A water treatment facility 111 can supply concentrated saltwater 105, and can receive diluted saltwater 107. More particularly, the osmotic pressure gradient can be maintained and/or increased by directing the concentrated saltwater stream 105 into the water cap 104 and removing diluted saltwater 107 from the water cap 104 at appropriate volumetric flowrates (taking into account the flow of water from the tailings deposit 106 into the water cap 104). For example, the volumetric flowrate of the concentrated saltwater stream 105 can be less than or equal to the volumetric flowrate at which diluted saltwater 107 is removed from the water cap 104 should it be desirable to maintain or reduce the water cap volume. In another example, the volumetric flowrate of the concentrated saltwater stream 105 can be greater than the volumetric flowrate at which diluted saltwater 107 is removed from the water cap, thereby increasing the volume of the water cap (assuming the difference outpaces evaporation). The volumetric flowrates of streams 105 and 107 can also affect whether the volume of the water cap 104 increases, remains the same, or decreases. A
water cap of larger volume will require the addition of more salt as compared to a water cap of lesser volume. Thus, to facilitate controlling the salt concentration in the water cap 104, it can 23828359.1 be desirable to achieve the smallest water cap 104 volume possible while ensuring the water cap 104 completely or almost completely covers the tailings deposit 106.
However, although more salt intensive, it can be desirable to increase the thickness of the water cap 104 for reasons such as those discussed below.

[00150] Establishing an osmotic pressure gradient across the membrane generally reduces pore pressures within the deposit, which can be beneficial for consolidation.
It is believed that such pore pressure reduction initially occurs at the tailings-membrane interface and propagates into the deposit over time. The pore pressure gradient (arising from the osmotic pressure gradient) can increase rates of dewatering and the achievable solids content.
Additionally, it may be noted that the difference between pore pressure and the total pressure is of particular relevance. Since pore pressure cannot be reduced below the saturation pressure of the pore water, a viable route to increasing this difference is using a thicker water cap to increase the total pressure. As noted above, however, adjusting the salt concentration in a thicker water cap requires more salt as compared to a smaller water cap. Additionally, for the same rate of salt addition, increasing salt concentration in a water cap of greater volume will take longer than increasing the salt concentration in a water cap of lesser volume. In practice, when trying to increase the salt concentration of the water cap, it is likely that salt will be added to the water cap at the maximum attainable rate. Therefore, in some cases, the target volume (i.e., volume to be maintained) of the water cap can be dictated at least in part by the availability of salt and/or the rate at which salt can be added to the water cap.

[00151] It can be appreciated that other methods of increasing water cap salt concentration can be used alternatively to, or in combination with the above method. For example, in a net evaporative climate, another method of increasing water cap salt concentration could be to allow natural evaporation of the water cap.

[00152] Oil sands tailings pore water, or process water can have a salt concentration of approximately 500 ppm to approximately 4,000 ppm. Thus, it is postulated that a target water cap 104 salt concentration (for achieving a desired osmotic pressure gradient) could be from approximately 10,000 ppm to approximately 50,000 ppm. However, it can be appreciated that in practice, or when applying the principles discussed herein to other tailings deposits, the target salt content could fall outside this range. For example, it could be desirable to maintain a relatively small osmotic pressure gradient, in which case the salt concentration of the water cap 104 can be slightly higher than that of the tailings deposit 106 pore water.
Additionally, the 23828359.1 target salt concentration of the water cap 104 can change as a function of time. For example, the water cap 104 can initially have the same salt concentration as process, or pore water in the deposit 106, and the salt concentration of the water cap 104 can then increase continuously or in a stepwise fashion.

[00153] It can be appreciated that the tailings deposit 106 could still be dewatered with the semipermeable membrane 108 omitted from the configuration shown in FIG. 1A, provided the water cap 104 can be maintained at a higher salt concentration than the deposit 106. Whether or not desired consolidation rates can be achieved, it may be that the omission of the membrane 108 can accelerate and/or increase salt trapping in the deposit 106, provided the water cap 104 can be maintained at a higher salt concentration than the deposit 106. The system shown in FIG. 1A, but with the membrane 108 omitted, or partially omitted, could thus be particularly useful for salt disposal.

[00154] FIGS. 1B and 1C illustrate example embodiments of semipermeable membrane assemblies 908 and 1008, either of which could replace the semipermeable membrane 108. In FIG. 1B, the semipermeable membrane assembly 908 comprises a semipermeable membrane 907 provided between two protective, semipermeable fabrics 910a and 910b. In this example embodiment, the protective semipermeable fabrics 910a and 910b are geotextile membranes.
As shown, a plurality of spacers 905 can be positioned between the geotextile membrane 910b and the semipermeable membrane 907 to maintain a fluid-filled space 912 therebetween. The fluid can be from a water cap 904 and/or the tailings deposit 906. The purpose of this space 912 is to permit salt to move more freely, thereby reducing salt accumulation against and facilitating flow across the membrane 907. The geotextile membranes 910a and 910b can also provide the membrane 907 with protection from physical damage and/or can reduce clogging of pores (not shown) in the membrane 907.

[00155] Turning to FIG. 1C, the semipermeable membrane assembly 1008 shown comprises a semipermeable membrane 1007 provided between two protective, semipermeable fabrics 1010a and 1010b. In this example embodiment, the protective semipermeable fabrics are geotextile membranes. The upper geotextile membrane 1010a is overlain by a water cap 1008, and the lower geotextile membrane 1010b is underlain by a tailings deposit 1006. The semipermeable membrane 1007 is corrugated such that there are spaces 1012 defined between the membrane 1007 and the geotextile membranes 1010a and 1010b. These spaces 1012 can permit salt to move more freely as discussed above. Additionally, the corrugation of the semipermeable membrane 1007 increases the surface area of the membrane 1007 across 23828359.1 which osmosis and diffusion can occur, as compared to a straight, or flat membrane. This, in turn, can lead to increased rates of diffusion and/or osmosis across the membrane 1007.

[00156] FIG. 2 is a flow chart illustrating a general method for dewatering the tailings deposit 106. First, at step 112, the semipermeable membrane 108, which can ideally substantially prevent the passage of solutes therethrough, can be placed on a surface 109 of the tailings deposit 106. Next, the molar concentration of salt in the water cap 104, can be increased continuously by directing a concentrated saltwater stream 105 into the water cap 104, while removing a diluted saltwater 107 therefrom at appropriate volumetric flowrates (step 114). At step 116, it is determined whether the water cap 104 has reached a desired salt concentration.
The desired salt concentration can be, for example, a pre-determined amount above the concentration of the tailings deposit 106 (i.e., to achieve a desired osmotic pressure gradient).
If the desired salt concentration has not been reached, the process returns to step 114, where the molar concentration of salt in the water cap continues to increase in the manner discussed above. When the molar concentration of salt in the water cap 104 reaches the desired level, the process can proceed to step 118 where the molar concentration of salt in the water cap 104 can be maintained at the desired level. At step 120, it is determined whether the tailings deposit 106 is sufficiently dewatered. As mentioned with respect to FIG. 1A, the desired salt concentration and the desired osmotic pressure gradient can change as a function of time. It can be determined whether the deposit is sufficiently dewatered through known methods such as measuring solids content and yield strength of the deposit.

[00157] If the tailings deposit 106 is sufficiently dewatered, the saltwater cap 104, and optionally the membrane 108, can be removed and the process completed (step 122). If not, the process can return to step 116. The saltwater cap can be at least partially removed by pumping the concentrated saltwater therein to the water treatment facility.
The saltwater cap can also be left to evaporate. After the process completes, reclamation measures can be taken, such as covering the deposit with a cap layer of sand, overburden and/or other materials prior to placing soil and plants thereon.

[00158] In another example embodiment, the capacity of the water treatment plant can dictate the flow rates of diluted water removal and brine addition to the water cap. That is, flow rates of diluted water and brine can be relatively constant based on the size of the water treatment plant and the equipment contained therein. A benefit of this configuration can be low operational complexity. However, it is expected that this configuration can control salt concentration with less precision as compared to, e.g., the process described with respect to 23828359.1 FIG. 2. It may be noted that in practice, the brine can be as concentrated as feasibly possible to maximize the rate at which the water cap salt concentration can be increased.

[00159] Turning to FIG. 3, illustrated is another system 300 for dewatering the tailings deposit 106. The system 300 comprises the tailings deposit 106 and a plurality of vertical wick drains 324 provided in the tailings deposit 106. The vertical wick drains 324 can extend from the semipermeable membrane 108 toward a bottom 110 of the tailings deposit 106.
The vertical wick drains 324 can extend to varying depths in the tailings deposit 106. It can be appreciated that the vertical wick drains can alternatively extend to substantially the same depth within the tailings deposit 106, can be positioned at varying angles with respect to one another, and/or can extend between the semipermeable membrane 108 and the bottom 110 of the tailings deposit 106. The vertical wick drains 324 can accelerate osmotically induced consolidation by decreasing the distance that water travels through the pore spaces within the deposit 106 to be liberated therefrom. The vertical wick drains 324 can be made from a permeable material; thus, the water can flow more easily, or with less resistance upwardly toward the water cap 104 upon entering the wick drains 324. The movement of water from the deposit 106 and through one of the wick drains 324 is shown in an expanded view 307. It may be that combining the vertical wick drains 324 with the concept of continuously increasing the salt concentration of the water cap 104, with or without the semipermeable membrane 108, can accelerate dewatering of the tailings deposit 106 relative to any of these methods alone.

[00160] FIGS. 4A and 4B illustrate another system 400 for dewatering a tailings deposit 406.
The system comprises the tailings deposit 406, and a plurality of semipermeable bags 408 containing a saltwater draw solution 404. The bags 408 can be positioned on the tailings deposit 406. It can be appreciated that the bags can optionally extend at least partially into the tailings deposit 406, increasing the surface area of the bag that is in contact with the deposit 406. It may be that this can increase osmosis and/or diffusion rates between the deposit and the draw solution in the bags. Extension of the bags into the deposit 406 could be induced by, for example, changing the shape, size, weight and/or orientation of the bags.
For example, pillow-shaped bags could be positioned such they extend toward the bottom of a deposit in the direction of their longitudinal axis (i.e., placed substantially vertically).

[00161] Continuing with FIGS. 4A and 4B, the saltwater draw solution 404 has a higher salt concentration than a salt concentration of the tailings deposit 406 (particularly the pore water in the tailings deposit) and can thus draw water from the tailings deposit 406 into the bags 408 to consolidate the deposit 406. The salt concentration of the draw solution 404 can be maintained 23828359.1 and/or increased by controlling the flow rate and/or concentration of a concentrated saltwater feed stream 405 directed into the solution 404, and by controlling the flow rate of a draw solution removal stream 407 which removes the draw solution 404 from the bags 408 (FIG.
4B). Each of the bags 408 can have suitable connections (not shown) for the streams 405 and 407. The streams 405 and 407 can interact with a water treatment facility (not shown) in the manner discussed with respect to FIG. 1A, for example. The semipermeable bags 408 can be, e.g., geobags, geotubes, or other bags comprising one or more suitable semipermeable materials.
Such semipermeable materials can be, for example, one or more of the membranes discussed above with respect to FIGS. 1A-1C, surrounded by protective, permeable fabrics such as geotextiles. During dewatering, the salt concentration of the draw solution 404 can be maintained, continuously increased, or increased in stepwise fashion by adjusting the volumetric flowrates of the concentrated saltwater feed stream 405 and the diluted saltwater draw stream 407.

[00162] FIGS. 5A-5C illustrate another system 500 for dewatering a tailings deposit 506 that does not have a water cap. As shown in FIG. 5B, the system 500 comprises a plurality of semipermeable bags 508 containing a saltwater draw solution 504, the bags 508 being positioned along the periphery of the deposit 508. After sufficiently dewatering the tailings beneath the bags 508, the bags 508 can be moved inwardly, resulting in the configuration shown in FIG. 5C. In this example, the bags 508 are generally tubular in shape and thus can be moved by, for example, being rolled. It can be appreciated that the bags 508 can also be moved by being slid or shimmied along the surface of the deposit 506. For this purpose, the bags 508 could be designed to include points of attachment such as hooks for connecting pull ropes thereto, thereby facilitating sliding or shimmying. When the tailings beneath or near the bags 508 in FIG. 5C are sufficiently dewatered, the bags 508 can be moved inwardly. This process can be repeated a number of times, thereby incrementally dewatering the tailings deposit 500. The salt concentration of the draw solution 504 in each of the bags 508 can be adjusted in, e.g., the manner discussed with respect to FIGS. 4A and 4B.

[00163]
FIG. 6A illustrates another system 600 for dewatering a tailings deposit 606 overlain by a water cap 602. As shown in FIGS. 6A and 6B, the water cap 602 begins near a dam 630 and does not completely cover the deposit 606. A plurality of semipermeable bags 608 containing a saltwater draw solution 604 can be placed on a portion of the deposit 606 not covered by the water cap 602 and requiring dewatering. The plurality of semipermeable bags 608 can be used to incrementally dewater the tailings deposit 606 in a manner similar to that 23828359.1 discussed with respect to FIGS. 5A-50. For example, the bags 608 can be placed as shown in FIGS. 6A and 6B, and periodically moved toward the water cap 602 in the direction of the arrows drawn on FIG. 6B. During and/or after such incremental dewatering, the water cap 602 can be removed in the manner discussed with respect to FIGS. 1-3. The water cap 602 can also be removed before beginning incremental dewatering such that the bags 608 can be used on the entire deposit. It can be appreciated that the bags 608 can be used to drain the water cap 602, which can have a lower salt concentration than the draw solution 604 and the tailings deposit 606, prior to beginning incremental dewatering.

[00164] FIG. 7 is a flow chart illustrating a general method for incrementally dewatering a tailings deposit using FO, particularly using semipermeable bags containing a draw solution.
First, at step 700, a plurality of semipermeable bags containing saltwater (i.e., the draw solution) can be placed on a tailings deposit requiring dewatering (i.e., the feed solution). Next, at step 702, water from the tailings can be drawn into the semipermeable bags due to an osmotic pressure gradient between the draw solution in the bags, and the deposit. The salt concentration of the draw solution in the bags can be maintained, continuously increased, or increased in stepwise fashion. At step 704, it is determined whether the tailings beneath or in proximity to the bags are sufficiently dewatered. If not, the method returns to step 702.
Otherwise, the method moves to step 706. If the entire deposit is dewatered (step 706), the bags can be removed (step 710). If not, the method can move from step 706 to step 708, where the bags can be moved to an area of the deposit requiring dewatering, and the method subsequently returns to step 702.

[00165] FIGS. 8A and 8B illustrate another system 800 for dewatering a tailings deposit 806.
The system comprises the tailings deposit 806, and a plurality of open semipermeable pools 808 (i.e., having an open top), containing a saltwater draw solution 804. The pools 808 can be positioned on the tailings deposit 806 and can each include a semipermeable floor 810 and sidewalls 812 for containing the draw solution 804, as shown in FIG. 8B. Each semipermeable floor 810 can include one or more semipermeable materials, such as those discussed above, and the sidewalls 812 can be made from suitable, relatively stronger materials. For example, the semipermeable materials can include a semipermeable CTA membrane as an active layer, and can be surrounded by geotextiles. As also shown in FIG. 8B, the semipermeable floor 810 can be in contact with the deposit 806, allowing osmotic communication (i.e., water flow) between the deposit 806 and the draw solution 804. In this example embodiment, the tailings deposit 806 does not have a water cap thereon; thus, preferentially drawing cap water over pore 23828359.1 water is not of concern. However, it can be appreciated that the pools could also be used to initially remove a water cap prior to tailings dewatering, as discussed above with respect to the semipermeable bags shown in FIGS. 6A and 6B.

[00166] The salt concentration of the draw solution 804 can be maintained and/or increased by controlling the flow rate and/or concentration of a concentrated saltwater, or brine feed stream 805, and by controlling the flow rate of a draw solution removal stream 807 (FIG. 8B).
The concentrated saltwater feed stream 805 can originate at a water treatment facility (not shown) and can be directed into each of the pools 808. The draw solution removal stream 807 can transport diluted saltwater from the draw solution 804 to the water treatment facility.
Although not shown, the pools 808 can include suitable inlets and outlets for streams 805 and 807, respectively. The concentration of the draw solution 804 can be maintained, continuously increased, or increased in stepwise fashion, by adjusting the volumetric flowrates of the concentrated saltwater feed stream 805 and the diluted saltwater draw stream 807. If possible, the concentration of the concentrated saltwater feed stream 805 can also be adjusted at the water treatment plant to assist in adjusting the concentration of the draw stream 804. Such pools 808 can be used to incrementally dewater a tailings deposit in a manner similar to that discussed with respect to FIGS. 5A-7 or can cover the surface of a tailings deposit and remain in place until dewatering is complete.

[00167] It can be appreciated that combinations of the above methods for dewatering tailings deposits without water caps could be implemented (e.g., some combination of incremental dewatering using pools and bags). It can also be appreciated that the draw solution used in the semipermeable cells discussed above (i.e., the semipermeable bags and pools) can comprise a solvent other than water. Additionally, it may be that wick drains can be used in combination with the semipermeable cells.

[00168] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein.

23828359.1

[00169] The examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles.

[00170] The steps or operations in the flow charts and diagrams described herein are just for example. There may be many variations to these steps or operations without departing from the principles discussed above. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.

[00171] Although the above principles have been described with reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.

23828359.1

Claims (109)

Claims:

1. A method of at least partially dewatering a tailings deposit, the tailings deposit having a water cap thereover, the method comprising:
placing a semipermeable membrane between the tailings and the water cap, the semi-permeable membrane being permeable to water and nearly impermeable to ions;
increasing a water cap molar salt concentration to be greater than a tailings deposit molar salt concentration to dewater the tailings deposit; and maintaining the water cap molar salt concentration above the tailings deposit molar salt concentration until the tailings deposit is dewatered to a desired extent.

2. The method of claim 1, wherein a volume of the water cap is minimized while substantially covering the tailings deposit.

3. The method of claim 1, wherein a wherein a volume of the water cap is increased to and/or maintained at a target volume to increase a dewatering rate of the tailings deposit.

4. The method of claim 2 or 3, wherein the volume is controlled by pumping water out of the water cap.

5. The method of any one of claims 1-4, wherein the water cap molar salt concentration is increased and/or maintained by delivering a brine solution having a higher salt concentration than the water cap molar salt concentration into the water cap.

6. The method of any one of claims 1-5, wherein the water cap molar salt concentration is increased stepwise until the desired extent is reached.

7. The method of any one of claims 1-5, wherein the water cap molar salt concentration is increased to be a continuously increasing amount higher than the tailings deposit molar salt concentration until the desired extent is reached.

8. The method of any one of claims 1-7, further comprising providing a plurality of wick drains in the deposit.

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9. The method of claim 8, wherein each of the wick drains has a first end and a second end, the first end being positioned near the semipermeable membrane, and the second end extending toward a base of the deposit.

10. The method of any one of claims 1-9, wherein the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

11. The method of any one of claims 1-10, wherein the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

12. The method of any one of claims 1-10, wherein the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

13. The method of any one of claims 4-11, wherein the brine solution comprises one or more of Na+, Ca', K+, Mg", S042-, HCO3-, and Cl-.

14. The method of any one of claims 1-13, wherein the semipermeable membrane is a forward osmosis ("FO") membrane.

15. The method of claim 14, wherein the FO membrane comprises one or more of cellulose triacetate ("CTA"), polyamide, polyamide-imide, or polybenzimidazole.

16. The method of any one of claims 1-13, wherein the semipermeable membrane is a reverse osmosis membrane.

17. The method of any one of claims 1-13, wherein the semipermeable membrane is a nanofiltration membrane.

18. The method of any one of claims 1-17, wherein the semipermeable membrane is a thin-film composite membrane ("TFM").

19. The method of claim 18, wherein the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

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20. The method of claim 19, wherein the porous support layer is made from polysulfone.

21. The method of any one of claims 1-20, wherein the semipermeable membrane is at least partially enclosed in a protective fabric that is permeable to water.

22. The method of claim 21, wherein the semipermeable membrane is provided between first and second sheets of the protective semipermeable fabric.

23. The method of claim 22, wherein the semipermeable membrane is corrugated.

24. The method of claim 22, wherein a plurality of spacers are provided between the semipermeable membrane and the first sheet of protective semipermeable fabric such that a space is defined therebetween.

25. The method of any one of claims 23-25, wherein an outer surface of the first sheet is in contact with the tailings deposit.

26. The method of any one of claims 21-25, wherein the protective fabric is a geotextile fabric.

27. A method of storing salt in and/or at least partially dewatering a tailings deposit, the tailings deposit having a water cap thereover, the method comprising:
increasing a water cap molar salt concentration to be greater than a tailings deposit molar salt concentration to induce migration of the water cap salt into the tailings deposit and/or to dewater the tailings deposit; and maintaining the water cap molar salt concentration above the tailings deposit molar salt concentration until the earlier of the tailings deposit has accepted a desired amount of salt or the tailings deposit has been dewatered to a desired extent.

28. The method of claim 27, wherein a volume of the water cap is minimized while substantially covering the tailings deposit.

23828359.1

29. The method of claim 27, wherein a wherein a volume of the water cap is increased to and/or maintained at a target volume to increase a dewatering rate of the tailings deposit.

30. The method of claim 28 or 29, wherein the volume is controlled by pumping water out of the water cap.

31. The method of any one of claims 27-30, wherein the water cap molar salt concentration is increased and/or maintained by delivering a brine solution having a higher salt concentration than the water cap molar salt concentration into the water cap.

32. The method of any one of claims 27-31, wherein the water cap molar salt concentration is increased stepwise until the desired extent is reached.

33. The method of any one of claims 27-31, wherein the water cap molar salt concentration is increased to be a continuously increasing amount higher than the tailings deposit molar salt concentration until the desired extent is reached.

34. The method of any one of claims 27-33, further comprising providing a plurality of wick drains in the deposit.

35. The method of claim 34, wherein each of the wick drains has a first end and a second end, the first end being positioned near the semipermeable membrane, and the second end extending toward a base of the deposit.

36. The method of any one of claims 27-35, wherein the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

37. The method of any one of claims 27-36, wherein the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

38. The method of any one of claims 27-36, wherein the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining copper mining, gold mining, aluminum mining or nickel mining.

23828359.1

39. The method of any one of claims 31-37, wherein the brine solution comprises one or more of Na+, Ca2 , K, Mg2+, S042-, HCO3-, and CI-.

40. A method of at least partially dewatering a tailings deposit comprising:
a) providing on a surface of the tailings deposit a plurality of semipermeable cells containing a draw solution, the semipermeable cells being permeable to water and nearly impermeable to ions; and b) increasing and/or maintaining a draw solution molar salt concentration above a tailings deposit molar salt concentration until a region of the tailings deposit beneath the cells is dewatered to a desired extent.

41. The method of claim 40, wherein at least one of the semipermeable cells is a semipermeable bag comprising a semipermeable membrane.

42. The method of claim 40, wherein at least one of the semipermeable cells is a containment structure having a floor comprising a semipermeable membrane.

43. The method of claim 41 or 42, wherein the semipermeable membrane is a forward osmosis ("FO") membrane.

44. The method of claim 43, wherein the FO membrane comprises one or more of CTA, polyamide, polyamide-imide, or polybenzimidazole.

45. The method of claim 41 or 42, wherein the semipermeable membrane is a reverse osmosis membrane.

46. The method of claim 41 or 42, wherein the semipermeable membrane is a nanofiltration membrane.

47. The method of any one of claims 41-45, wherein the semipermeable membrane is a thin-film composite membrane ("TFM").

23828359.1

48. The method of claim 47, wherein the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

49. The method of claim 48, wherein the porous support layer is made from polysulfone.

50. The method of any one of claims 41-49, wherein the semipermeable membrane is protected by a protective fabric that is permeable to water.

51. The method of claim 50, wherein the protective fabric is a geotextile fabric.

52. The method of any one of claims 40-51, wherein at least one of the semipermeable cells extends at least partially into the tailings deposit.

53. The method of any one of claims 40-52 wherein the plurality of semipermeable cells are provided on a portion of the surface, and the method further comprises:
c) after the desired extent is reached, moving the plurality of semipermeable cells to another portion of the surface and repeating the method from step a) to dewater another region of the tailings deposit to the desired extent.

54. The method of claim 53 wherein moving the plurality of semipermeable cells comprises sliding the cells along the surface.

55. The method of claim 53 or 54 further comprising repeating the method until the entire tailings deposit is dewatered to the desired extent.

56. The method of any one of claims 40-55, wherein the draw solution molar salt concentration is increased and/or maintained by delivering a brine solution into the plurality of cells through an inlet provided in each cell, and removing the draw solution from the plurality of cells through an outlet provided in each cell.

57. The method of any one of claims 40-56, wherein the draw solution molar salt concentration is increased stepwise until the desired extent is reached.

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58. The method of any one of claims 40-56, wherein the draw solution molar salt concentration is increased to be a continuously increasing amount higher than the tailings deposit molar salt concentration until the desired extent is reached.

59. The method of any one of claims 40-58, further comprising providing a plurality of wick drains in the deposit.

60. The method of claim 59, wherein each of the wick drains has a first end and a second end, the first end is positioned near one of the semipermeable cells, and the second end extends toward a base of the deposit.

61. The method of any one of claims 40-60, wherein the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

62. The method of any one of claims 40-61, wherein the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

63. The method of any one of claims 40-61, wherein the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

64. The method of any one of claims 56-62, wherein the brine solution comprises one or more of Na+, Ca2+, K+, Mg2+, S042-, HCO3-, and cr.

65. A system for at least partially dewatering a tailings deposit having a water cap thereover, the system comprising:
a source of a brine solution for increasing a water cap molar salt concentration; and a conduit for conveying the brine solution from the source to the water cap.

66. The system of claim 65 further comprising a mechanism for removing water from the water cap.

67. The system of claim 66 wherein the mechanism is at least one pump.

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68. The system of any one of claims 65-67 wherein the source is a water treatment plant.

69. The system of any one of claims 65-68 further comprising a semipermeable membrane provided between the tailings deposit and the water cap, the semipermeable membrane being permeable to water and nearly impermeable to ions.

70. The system of claim 69, wherein the semipermeable membrane is a forward osmosis ("FO") membrane.

71. The system of claim 70, wherein the FO membrane comprises one or more of CTA, polyamide, polyamide-imide, or polybenzimidazole.

72. The system of claim 69, wherein the semipermeable membrane is a reverse osmosis membrane.

73. The system of any one of claim 69, wherein the semipermeable membrane is a nanofiltration membrane.

74. The system of any one of claims 69-73, wherein the semipermeable membrane is a thin-film composite membrane ("TFM").

75. The system of claim 74, wherein the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

76. The system of claim 75, wherein the porous support layer is made from polysulfone.

77. The system of any one of claims 69-76, wherein the semipermeable membrane is at least partially enclosed in a protective fabric that is permeable to water.

78. The system of claim 77 wherein the semipermeable membrane is provided between first and second sheets of the protective fabric.

79. The system of claim 77 or 78, wherein the semipermeable membrane is corrugated.

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80. The system of claim 78, wherein a plurality of spacers are provided between the semipermeable membrane and the first sheet of protective semipermeable fabric such that a space is defined therebetween.

81. The system of any one of claims 78-80, wherein an outer surface of the first sheet is in contact with the tailings deposit.

82. The system of any one of claims 77-81, wherein the protective fabric is a geotextile fabric.

83. The system of any one of claims 65-82, further comprising a plurality of wick drains provided in the deposit.

84. The system of claim 83, wherein each of the wick drains has a first end and a second end, the first end is positioned near the semipermeable membrane, and the second end extends toward a base of the deposit.

85. The system of any one of claims 65-84, wherein the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

86. The system of any one of claims 65-85, wherein the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

87. The system of any one of claims 65-85, wherein the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

88. The system of any one of claims 65-86, wherein the brine solution comprises one or more of Na+, Ca2+, K+, Mg2+, S042-, HCO3-, and Cr.

89. A system for at least partially dewatering a tailings deposit, the system comprising:
a plurality of semipermeable cells provided on a surface of the deposit;
a draw solution contained within the plurality of semipermeable cells; and a source of a brine solution for increasing a draw solution molar concentration.

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90. The system of claim 89, further comprising an inlet and an outlet provided in at least one of the semipermeable cells, each inlet being connected to a conduit for conveying the brine from the source to the respective cell, and each outlet being connected to a conduit for conveying the brine from the respective cell to the source.

91. The system of claim 89 or 90, wherein the source is a water treatment plant.

92. The system of any one of claims 89-91, wherein at least one of the semipermeable cells is a semipermeable bag comprising a semipermeable membrane.

93. The system of any one of claims 89-91, wherein at least one of the semipermeable cells is a containment structure having a floor comprising a semipermeable membrane.

94. The system of claim 92 or 93, wherein the semipermeable membrane is a forward osmosis ("FO") membrane.

95. The system of claim 94, wherein the FO membrane comprises one or more of CTA, polyamide, polyamide-imide, or polybenzimidazole.

96. The system of claim 92 or 93, wherein the semipermeable membrane is a reverse osmosis membrane.

97. The system of claim 92 or 93, wherein the semipermeable membrane is a nanofiltration membrane.

98. The system of any one of claims 92-97, wherein the semipermeable membrane is a thin-film composite membrane ("TFM").

99. The system of claim 98, wherein the TFM includes an active thin-film layer of polyamide layered with a porous support layer.

100. The system of claim 99, wherein the porous support layer is made from polysulfone.

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101. The system of any one of claims 95-100, wherein the semipermeable membrane is protected by a protective fabric that is permeable to water.

102. The system of claim 101, wherein the protective fabric is a geotextile fabric.

103. The system of any one of claims 89-102, further comprising a plurality of wick drains in the deposit.

104. The system of claim 103, wherein each of the wick drains has a first end and a second end, the first end is positioned near one of the semipermeable cells, and the second end extends toward a base of the deposit.

105. The system of any one of claims 89-104, wherein the tailings deposit comprises one or more of thick fine tailings, slime tailings, composite tailings, coarse tailings, and mixed tailings.

106. The system of any one of claims 89-105, wherein the tailings deposit is from an oil sands mining process, and comprises mature fine tailings and/or froth treatment tailings.

107. The system of any one of claims 89-105, wherein the tailings deposit was generated from phosphate mining, sulfide mineral mining, coal mining, iron mining, copper mining, gold mining, aluminum mining or nickel mining.

108. The system of any one of claims 89-106, wherein the brine solution comprises one or more of Na+, Ca2+, K+, Mg2+, S042-, HCO3-, and cr.

109. The system of any one of claims 89-108, wherein at least one of the semipermeable cells extends at least partially into the tailings deposit.

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