WO2018141055A1

WO2018141055A1 - Method for consolidating mature fines tailings

Info

Publication number: WO2018141055A1
Application number: PCT/CA2018/050106
Authority: WO
Inventors: Ian D. Gates; Jingyi Wang; Yi Su
Original assignee: Ceda Services And Projects Lp
Priority date: 2017-02-01
Filing date: 2018-01-30
Publication date: 2018-08-09
Also published as: CA3066803C; CA3189213A1; CA3066803A1

Abstract

A method for treating mature fines tailings (MFT) in a tailings pond, comprising injecting a fluid directly into the MFT layer, the fluid comprising an additive for further consolidating the MFT layer. The method may optionally include injecting a gas into the MFT layer to mix the fluid and the MFT and to float oil from the MFT layer for extraction.

Description

METHOD FOR CONSOLIDATING MATURE FINES TAILINGS

FIELD OF THE INVENTION

[001] The present invention relates to treatment of tailings including mature fines tailings. BACKGROUND OF THE INVENTION

[002] In general, tailings ponds arising from oil sands operations consist of three layers. The bottommost layer consists mostly of sand and large particles (>0.5 mm) that fall to the base of the pond under the action of gravity. The middle layer consists of mature fines tailings ("MFT"), a material that has the general consistency of yogurt and which contains a large amount of water and some residual oil trapped within the interstitial space of clays and fine sand. The topmost layer consists of mostly water with very fine solids suspended within the water. MFT is a composite material comprising water, clay, sand, and residual hydrocarbons.

[003] In oil sands operations, tailings including MFT are produced during the oil sands extraction process wherein the clay and solids are separated from the oil sand to yield bitumen.

[004] The tailings including MFT, in typical practice, are deposited into large ponds where the sand component settles to the bottom of the system whereas the next densest material, the MFT, accumulates in a middle layer above the sand layer and below the water layer. The water can contain fine suspended particles that remain in suspension for considerable periods of time. The tailings materials that enter the tailings pond from the oil sands mining processing plant also contain oil. In typical practice, up to 1% of the material that is placed in the tailings pond is oil. However, this oil remains locked within the tailings material in the pond and is not produced from the pond.

[005] The key issue confronted by oil sands mining operations from an environmental point of view is the accumulation of tailings ponds - they are massive and have the potential for leaks of the water contained in the ponds to the environment.

[006] The intention of all oil sands mines is that the tailings ponds are eventually returned to their original state (e.g., boreal forest). [007] A primary issue faced when dealing with MFT is that the porosity is relatively large but the permeability is very low (and water is bound to the clays through electrostatic and van der Waals forces). It is desired that the MFT be consolidated by having the water removed from the layer, but this is complicated by the lack of permeability.

[008] Given the nature of MFT with its fine particles and low permeability, the amount of time it will take for natural (under gravity) consolidation of MFT is widely acknowledged to be on the order of hundreds to thousands of years. This means that practically, there is no present commercial solution for these tailings ponds to quickly consolidate them to enable their return to their original state.

[009] What is needed, therefore, is a method for more quickly consolidating the MFT layer in a tailings pond.

SUMMARY OF THE INVENTION

[010] According to the present invention, consolidation of MFT is achieved by using injection of a first fluid directly into the MFT layer, the fluid consisting of additives that help to achieve consolidation of the MFT. In some exemplary embodiments of the present invention, a second fluid is injected into the MFT to unlock the oil within the MFT. This oil can then be collected at the surface of the MFT for sale.

[011] According to a first broad aspect of the present invention, there is provided a method for treating a mature fines tailings layer in a tailings deposit, comprising the steps of: a. providing an injection system configured for injection of a first fluid, the first fluid comprising an additive effective to increase consolidation of the mature fines tailings layer; b. positioning the injection system so as to deliver the first fluid directly into the mature fines tailings layer; c. injecting the first fluid directly into the mature fines tailings layer; d. ceasing injection of the first fluid and allowing the first fluid and the additive to interact with the mature fines tailings layer; and e. allowing the mature fines tailings to further consolidate.

[012] In some exemplary embodiments of the first broad aspect, the injection system comprises a well, which may be vertical, horizontal, deviated or multilateral. The injection system may alternatively comprise a distribution plate system, which may be a perforated plate system positioned at a base of the mature fines tailings layer or in an underlying sand layer or positioned near a top of the mature fines tailings layer.

[013] The additive in the first fluid preferably comprises at least one metal halide, which is preferably selected from the group consisting of aluminum chloride and iron chloride.

[014] In some exemplary methods, a gas is directly injected into the mature fines tailings layer before or after the step of injecting the first fluid, and the gas is allowed to disturb the mature fines tailings layer and release entrapped hydrocarbon, and allowing the released hydrocarbon to rise to surface for collection. The gas is preferably selected from the group consisting of air, nitrogen, carbon dioxide, and mixtures thereof. The gas is most preferably carbon dioxide, and in such case exemplary methods may further comprise injecting a second fluid comprising an alkaline solution, and allowing the alkaline solution to interact with the carbon dioxide to produce carbonate to further consolidate and strengthen the mature fines tailings layer.

[015] In some exemplary methods, a second fluid may be injected which comprises an additive selected from the group consisting of polymer and nanocrystals. Preferably, the polymer is polyacrylamide and the nanocrystals are a cellulose nanocrystal suspension.

[016] One key advantage of the present invention is that the solids do not have to be mobilized for processing, e.g., transported to a barge, which means that the energy savings and thus cost savings for the present invention may be greater than that of conventional processes where the MFT is moved for processing.

[017] Given the environmental impact of tailings ponds, there is an ongoing need for safe and effective processes to consolidate and strengthen MFT so that the ponds can be emptied of water and recovered back to their original form before the mine was installed. The consolidation of MFT as described herein and the subsequent removal of water may enable a more rapid conversion of these tailings ponds to their original state. The requirement to consolidate the MFT to a particular strength is because after reclamation, soil and trees and plants will be placed on top of the reclaimed MFT layer.

[018] One novel aspect of the present invention lies in the use of wells or distribution systems to directly inject fluids into the reservoir to consolidate the MFT, and for the injection of additional fluids to yield oil from the MFT, and the collection of the oil from the system for sale.

[019] In general, the present specification describes methods to consolidate MFT to a fraction of its present volume by direct injection of a set of water-borne chemicals into the MFT layer in the tailings pond. Furthermore, in some embodiments of the present invention a different set of fluids are optionally injected into the MFT layer to enhance mixing of the chemicals but to also mobilize trapped oil from the MFT to the top surface of the pond.

[020] In a broad aspect of the present invention, mixtures of metal halide (for example, MX where M = aluminum, iron, sodium, potassium or copper, and X = fluoride, chloride, bromide or iodide) solutions with and without acid and/or base (to adjust pH as required to make it more acidic which may aid in consolidation of the MFT) are injected directly into the MFT layer. The mixture may be injected through a well (horizontal, vertical, deviated or multilateral) into the volume of MFT preferably such that the contact of the solution with the MFT is maximized. The well can also take the form of a distribution plate in some embodiments. The advantage of injecting the solution directly into the MFT is that the solid mass of the MFT is not moved (and thus the energy intensity of the process is far less than that of one where the MFT is transported for processing). Thus, this process could be done in an already existing tailings pond with no transportation of the MFT .

[021] In an optional mixing step, gas is also injected into the MFT layer, preferably but not necessarily using the same well, to cause mixing of the solution and the MFT. The gas rises through the MFT causing movement and disturbance of the MFT and solution thus enabling the two to mix. The mixing, however, could be done in alternate manners where, for example, the original solution is jetted into the MFT to achieve the mixing.

[022] After the solution and the MFT mix, the MFT consolidation is enhanced, and with the optional gas injection step some of the oil within the MFT is floated to the top of the water column above the MFT layer. This oil can be collected by skimming the pond.

[023] In one exemplary embodiment, a cellulose nanocrystal suspension or polymer can be injected into the MFT, either before or after the gas injection step, to further consolidate the MFT. Polymers and nanocrystals and nanoparticles and microparticles can be added to either or both of the initial injected fluid and the gas. The nanoparticles/microparticles can consist of, for example, silica or iron oxide particles with or without functional acid/base groups and salts.

[024] The gas injected can consist of air, carbon dioxide, nitrogen, natural gas, or mixtures thereof.

[025] According to one exemplary embodiment of the present invention, the method comprises: a. Drilling or placing a well or distribution system into the MFT layer of the tailings pond. The well is preferably completed using any existing completion technology that promotes uniform injectivity of the solution into the MFT layer, and the preferred embodiment is a horizontal well that sits a few meters above the base of the MFT layer, depending on the layer thickness. b. Preparation of the primary solution on surface (the preferred embodiment being FeCl₃ and A1C1₃, 10% concentration). c. Injection of the primary solution through the well into the MFT layer. The volume of the primary solution injected should be large enough to contact the desired volume of MFT (the preferred embodiment is that at least 1 pore volume of primary solution is injected into the targeted volume of the MFT layer). The pore volume is defined as the volume in the MFT that is not solid - it is the volume of the fluids (water and oil) that is in the MFT . d. If needed, there can be an optional soak period where the primary solution can mix with the MFT layer. e. Next, gas (preferably nitrogen, carbon dioxide, air or a mixture of these components) is injected into the MFT layer. The gas rises through the MFT and mixes the solution and MFT by buoyancy forces. The gas injection step does not need to be long in duration but should be sufficient to sufficiently mix the system (the preferred embodiment is injection of greater than 1 pore volume of the targeted MFT layer). f. After gas injection has stopped, the system is left to sit and consolidate. g. If carbon dioxide is injected into the MFT layer in Step e., then a secondary solution containing alkaline materials can be injected into the MFT layer. This will react with the injected carbon dioxide to form carbonates which will further consolidate and strengthen the MFT layer. The carbon dioxide can be sourced from flue gas or upgrader process streams. In a preferred embodiment, the injection of the alkaline solution can be done directly after the primary solution or together with the primary solution. In other embodiments, other materials such as polymers or cellulose nanocrystal can be injected into the MFT layer, as described above. h. Next, the oil that has floated to the top of the topmost water layer is collected by standard methods to collect oil slicks from the top of water layers.

[026] In certain embodiments, gas injection is not undertaken so as to only consolidate the MFT layer.

[027] In a further embodiment, gas injection may be done prior to the injection of the primary solution (Step b. above) to first release oil from the MFT. Thereafter, the primary solution is injected into the oil-depleted MFT layer.

[028] The present invention can also be used with non-oil sands tailings ponds such as mineral mining tailings ponds. [029] Detailed descriptions of exemplary embodiments of the present invention are given in the following. It is to be understood, however, that the invention is not to be construed as being limited to these embodiments. The exemplary embodiments are directed to particular applications of the present invention, while it will be clear to those skilled in the art that the present invention has applicability beyond the exemplary embodiments set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[030] Features and advantages of embodiments of the present application will become apparent from the following detailed description and the appended drawings, in which:

[031] FIG. 1A-H are diagrams exemplifying one implementation of the methods described herein for treating a MFT layer.

[032] FIG. 2A-B display results of using the method described here.

[033] FIG. 3 shows an example of the resulting MFT after the method described here is applied and the top water is removed.

[034] FIG. 4 shows an additional example of results for mixtures of additives with MFT.

[035] FIG. 5 shows an additional example of results after an exemplary method according to the present invention described herein is applied.

[036] FIG. 6 shows an additional example of results after an exemplary method according to the present invention described herein is applied.

[037] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[038] Throughout the following description, specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. The following description of examples of the invention is not intended to be exhaustive or to limit the invention to the precise forms of any exemplary embodiment. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[039] The below description relates to treatment of MFT to consolidate the MFT and optionally to yield residual oil.

[040] At present, there are no large scale processes that exist to consolidate MFT and produce its residual oil.

[041] The present invention takes a new approach, and instead of moving the MFT to a surface facility for treatment, it is treated in situ within the pond and consolidates in place to allow reclamation.

[042] Processes that transport the MFT to a location for processing consume large amounts of energy not only for transporting MFT to the processing site but also back to the pond for final deposition. In the novel method described herein, none of the solids are transported but rather additives are mixed with the MFT in place and water rejection from the MFT layer occurs vertically due to the gas moving under buoyancy forces. This means that the energy required for this process is much lower than that of other processes. Furthermore, since the energy intensity is lower, so too is the greenhouse gas intensity of the process. If carbon dioxide is injected with the gas, some fraction of it will be fixed within the tailings pond, especially if an alkaline solution is added to the MFT layer.

[043] The reduction of the volume of the tailings material as well as rejection of clear water which can be sent back for recycling and further use or treatment and disposal is a key advantage of the method described herein. Also, the process does not involve moving tailings materials from the pond to a processing site and back which reduces the risk of spills or exposure to the environment. If the gas optionally used includes carbon dioxide, then there is potential that it can be fixed in the consolidated tailings material thus reducing greenhouse gas emissions of other processes if the carbon dioxide is sourced from the other processes, e.g., an upgrader.

[044] Since no tailings solids are moved in the process, the energy required for the process is reduced over that of processes where the tailings have to be moved. This implies that the cost of the process described herein will be significantly lower than that of processes that require tailings transportation.

[045] Throughout this specification, numerous terms and expressions are used in accordance with their ordinary meanings.

[046] FIG. 1A-H illustrates an exemplary implementation of the present invention for consolidation of MFT with residual oil production. The original state of the tailings pond is displayed in FIG. 1 A.

[047] In the first step, a well or distribution system is placed within the tailings layer, preferably within the base section of the MFT layer as shown in FIG. IB. The primary solution consists of salt solutions or preferably metal halides (MX where M = aluminum, iron, sodium, potassium or copper, and X = fluoride, chloride, bromide or iodide) into the MFT layer. Although not essential, the pH can be altered to make the injected primary solution alkaline to enhance consolidation of the MFT layer. The most preferred materials in the primary solution are aluminum chloride and iron chloride.

[048] FIG. 1C displays the preparation of the primary solution on surface. This can also be done on a barge floating on the surface of the tailings pond or offsite.

[049] FIG. ID shows the step of injecting the primary solution into the MFT layer. The targeted volume of primary solution is preferably equal to at least one-half pore volume in the MFT layer. The preferred volume of primary solution is equal to 1 to 2 pore volumes of primary solution injected into the MFT layer. One-half pore volume of primary solution will be enough to achieve the desired effect, but it is preferable to have 1 to 2 pore volumes of primary solution. The greater the volume of primary solution, the greater the reduction of electrostatic charges in the MFT. In this step, the MFT materials will react with the injectants and reduce the static electrical charges within the MFT and allow it to consolidate and release water. Also, in this step a small amount of oil will be released from the MFT materials. This oil is released through the convective mixing of the primary solution and the MFT as well as a reduction of the electrostatic charges in the MFT due to the injection of the primary solution components. [050] FIG. IE displays a 'soak' step where the primary solution is allowed to mix with the MFT layer. In this step the MFT will continue to react with the primary solution and some oil will be further released from the MFT.

[051] FIG. IF shows the next step of the process where a gas is injected into the MFT layer. The gas further mixes the MFT with the primary solution and also adheres to the released oil and due to buoyancy forces lifts the oil from the MFT layer to the top of the water layer above the MFT layer. The oil that is raised to the top of the water layer may be collected by skimming it from the top surface of the water. The preferred gas for this step is carbon dioxide, nitrogen, air or mixtures thereof. The amount of gas injected is preferably between one-half and three pore volumes (of the MFT layer) of gas. The preferred amount is 1-2 pore volumes of the MFT layer of gas. FIG. 1G illustrates another resting period after the gas has risen out of the MFT layer, showing the further-consolidated MFT.

[052] In FIG. 1H, a final step is shown, where if carbon dioxide was injected into the MFT layer in Step f, a secondary solution containing an alkaline base is added to the MFT to further consolidate the layer by having the carbon dioxide react with the alkaline solution to convert it to carbonates. This further consolidates the MFT layer and also strengthens it for future reclamation of the tailings pond. The alkaline solution can be, for example, calcium hydroxide or magnesium hydroxide with solutions of silicates or metal halides. The preferred components are calcium hydroxide and/or magnesium hydroxide.

[053] In another embodiment, polymer or cellulose nanocrystals are added in the last injection step to further consolidate and strengthen the MFT.

[054] An example of experimental results is illustrated in FIG. 2A-B and FIG. 3.

[055] FIG. 2A-B shows an example of the results from using the method described here. FIG. 2A displays an example of the original MFT material. FIG. 2B shows two examples of the results of the consolidation and oil extraction procedure described herein. The results show that the water is rejected from the MFT layer and the MFT solids are consolidated.

[056] FIG. 3 shows the results of the MFT after gas injection and top water removal. In this example, the MFT is consolidated to about 50% of its original volume. In over 200 experiments conducted by the present inventors, the MFT layer was consolidated to between 15 and 50% of its original volume depending on the materials used and the gas injection volume. In the preferred embodiments, the MFT was consolidated to about 50% of its original volume and about 0.6 g of oil were extracted per 100 mL of MFT processed.

[057] When distilled water is injected into the MFT as the primary solution, the tailings solids remain in a suspended state. No consolidation was observed.

[058] The injection system can be located either on land or on a barge. Extended reach wells can be used if done from land.

[059] FIG. 4 shows the results of tests wherein a mixture of iron(III) chloride and polyacrylamide polymer was mixed with MFT (approximately 0.5 gallons) placed within a 2.5 gallon fish tank. Before the mixture was added to the tank, the MFT was either mixed with the iron(III) chloride and polyacrylamide polymer at either 1,000 or 20,000 rpm. The results display the amount of water spontaneously released from the MFT. In the case where water alone was added to the MFT, no water was released from the tailings mixture.

[060] The results show that for the mixtures obtained at 1,000 rpm (Experiments B and C), the addition of C0₂ helps to accelerate the amount of water released from the tailings mixture. At the higher mixing speed of 20,000 rpm (Experiments D and E), the difference of the water released is more pronounced between the case without and with C0₂. Experiment D (20,000 rpm with no C0₂ added) has less water released than that of Experiment B (1,000 rpm with no C02 added); this is likely due to the mixing generating finer clay particles and causing reduction of the polyacrylamide polymer chains which would tend to cause more water retention. One reason why gas might help to yield greater water release is due to the mixing it causes when it bubbles through the tailings mixture layer. As the iron(III) chloride affects the electrical double layer between clay particles and helps to mobilize water within the clay matrix, the gas provides a vertical upward displacement force, due to buoyancy, that moves unbound water to the top of the tailings mixture. The results show that the addition of the metal halide and polymer help to reject water from the MFT. [061] FIG. 5 compares the final solid content of the Experiments A to E (pre-mix tests in 2.5 gallon tanks) to Experiment F (in-situ test in 2.5 gallon tank demonstrating the method described herein). For Experiment F, measurements of solids content were taken on the tailings samples treated by the in-situ method at the side of the tank where treatment solution and air were pumped into the tank from the sparger. The samples were taken after 513 hours (21 days) of time after the treatment solution and air was injected. Further measurements were taken along the length of the sparger. Samples were also taken at the opposite side of the tank where there was no well. The results demonstrate that the in-situ process yielded a tailings material with higher solids content than that of the pre-mixed tests.

[062] The results presented in FIG. 5 demonstrate that the solids content for the in-situ sample reached as high as 50 wt.%. The 50 wt.% sample was taken along the side of the tank with the sparger, near the middle of the sparger length. The results show that the highest solids content in the in-situ experiments were near the bottom of the tailings layer where the injection well was located. A high solids content was also measured near the end of the sparger whereas the measurement taken near the inlet of the sparger had the lowest solids content.

[063] The results of FIG. 5 demonstrate that the in-situ method (Experiment F) is capable of generating higher solids content (and thus, higher water rejection) in the MFT than that of the pre-mixed samples (Experiments A to E). Thus, the in-situ method yields more consolidation than that of pre-mixed samples.

[064] FIG. 6 compares results of consolidation where different amounts of iron(III) chloride and polyacrylamide polymer are injected into a layer of MFT in a 2.5 gallon fish tank by using the method described here. The rate of height decrease was faster initially before about Hour 284 than that beyond Hour 294. It is interesting to note that this is the same time at which the fractures began to develop in the MFT due to the drying of the MFT. The opening of fractures in the deposits still produces a reduction in the volume of the tailings, however, this manifests as a shrinkage also in the lateral area of the tailings as the widths of the fractures extend laterally as well as vertically into the tailings volume.

[065] The results show that consolidation of the MFT may reach above 50% using the in situ method described here.

[066] Unless the context clearly requires otherwise, throughout the description and the claims:

[067] · "comprise", "comprising", and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

[068] · "connected", "coupled", or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof.

[069] · "herein", "above", "below", and words of similar import, when used to describe this specification shall refer to this specification as a whole and not to any particular portions of this specification.

[070] · "or", in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[071] · the singular forms "a", "an" and "the" also include the meaning of any appropriate plural forms.

[072] Words that indicate directions such as "vertical", "transverse", "horizontal", "upward", "downward", "forward", "backward", "inward", "outward", "vertical", "transverse", "left", "right", "front", "back", "top", "bottom", "below", "above", "under", and the like, used in this description and any accompanying claims (where present) depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

[073] Where a component (e.g., a circuit, module, assembly, device, drill string component, drill rig system, etc.) is referred to herein, unless otherwise indicated, reference to that component (including a reference to a "means") should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[074] Specific examples of methods and systems have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to contexts other than the exemplary contexts described above. Many alterations, modifications, additions, omissions and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled person, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

[075] The foregoing is considered as illustrative only of the principles of the invention. The scope of the claims should not be limited by the exemplary embodiments set forth in the foregoing, but should be given the broadest interpretation consistent with the specification as a whole.

Claims

A method for treating a mature fines tailings layer in a tailings deposit, comprising the steps of:

a. providing an injection system configured for injection of a first fluid, the first fluid comprising an additive effective to increase consolidation of the mature fines tailings layer;

b. positioning the injection system so as to deliver the first fluid directly into the mature fines tailings layer;

c. injecting the first fluid directly into the mature fines tailings layer;

d. ceasing injection of the first fluid and allowing the first fluid and the additive to interact with the mature fines tailings layer; and

e. allowing the mature fines tailings to further consolidate.

The method of claim 1 wherein the injection system comprises a well.

The method of claim 2 wherein the well is vertical, horizontal, deviated or multilateral.

The method of claim 1 wherein the injection system comprises a distribution plate system.

The method of claim 4 wherein the distribution plate system comprises a perforated plate system positioned at a base of the mature fines tailings layer or in an underlying sand layer.

The method of claim 4 wherein the distribution plate system comprises a perforated plate system positioned near a top of the mature fines tailings layer.

The method of claim 1 wherein the additive comprises at least one metal halide.

The method of claim 7 wherein the at least one metal halide is selected from the group consisting of aluminum chloride and iron chloride.

The method of claim 1 further comprising: injecting a gas directly into the mature fines tailings layer before or after the step of injecting the first fluid; allowing the gas to disturb the mature fines tailings layer and release entrapped hydrocarbon; and allowing the released hydrocarbon to rise to surface for collection.

The method of claim 9 wherein the gas is selected from the group consisting of air, nitrogen, carbon dioxide, and mixtures thereof.

11. The method of claim 10 wherein the gas is carbon dioxide, comprising the further steps of injecting a second fluid comprising an alkaline solution, and allowing the alkaline solution to interact with the carbon dioxide to produce carbonate to further consolidate and strengthen the mature fines tailings layer.

12. The method of claim 1 further comprising the step of injecting a second fluid comprising an additive selected from the group consisting of polymer and nanocrystals.

13. The method of claim 12 wherein the polymer is polyacrylamide and the nanocrystals are a cellulose nanocrystal suspension.