TREATMENT OF TAILINGS WITH DEIONIZED SILICATE

SOLUTIONS

FIELD OF THE INVENTION The present invention relates to processes of treating tailings streams produced in mining operations to provide a trafficable deposit.

BACKG ROU N D OF THE .INVENTION

Tailings, as a general term, refers to byproducts from mining operations and processing of mined materials in which a valuable materia] such, as a metal, mineral, coal, and the like, is separated, for example, extracted, from a mined material, that is, material which has been removed from the earth. Tailings typicalty comprise one or more of rock, clay, silt, and sand. Tailings further comprise water. Water is used in combination with mechanical and/or chemical processes for removing the valuable material from the mined material. Mining operations include those for precious metals, base metals, ores, clays and coal. In addition, mining operations include recovery of bitumen from oil sands.

Tailings treatment and disposal are major issues for mining operations. Water recovery from the tailings for re-use in extraction processes and transportation is often desired. Tailings solids, such as rock, clay, silt, sand, and other solid materials are generally sent to a storage facility or disposal area local to the mining operation. Management of such storage facilities or disposal areas is an enormous task.

Storage or disposal of tailings involves construction of a facility that is safe for storage (including permanent storage), sufficiently large and stable to contain the tailings within the facility, and protecting the local environment. It may be desirable to access water from the tailings storage facility for use in mining operations such as extracting and other treatments.

Various tailings streams are produced in extraction processes. A tailings stream is an aqueous stream (slurry, suspension) containing components requiring further treatment, which may include extraction of valuable material or solids removal and/or purification to enable recycle of the water content of the tailings stream. Some tailings streams will be deposited in a tailings pond for long periods of time, including permanently. Coarse solids may settle quickly. The top layer of the pond may clarify with time to make water that is suitable for reuse in the extraction process. A layer may comprise water and fine solids, which solids settle very slowly. This layer may ultimately become mature fine tailings (MFT).

MFT is a stable composite slurry comprising one or more of clay, sand, silt, rock, and water. MFT has little strength, no vegetative potential and may be toxic to animal life, so it must be confined and prevented from contaminating water supplies. Typically, several years of settling time are required to make MFT, which may be stable with little additional settling or consolidation occurring for decades.

MFT ponds pose an environmental concern. For example, the Energy Resources Conservation Board of Alberta (ERCB) has issued Directive 074, which mandates a reduction of MFT ponds and the formation of traffi cable deposits for MFT produced in mining and extraction of bitumen from oil sands by all oil sands operators.

Moffett disclosed, in US 2010/0104744 Al, a process to treat tailings streams with a silicate source and an activator. The silicate source is an alkali metal silicate, poiysilicate microgel, or combinations thereof. The activator may be an acid, alkaline earth metal salt, aluminum salt, organic ester, dialdehyde, organic carbonate, organic phosphate, amide, or a combination thereof.

Alkali metal silicate solutions are distinct from colloidal silica sols by their ratio of silica to metal oxide (Si02:M2.0). For example, solutions of sodium silicate have S of less than 4: 1, as disclosed by ller, "The Chemistry of

Silica", Wiley mterscience ( 1979), page 116. Her further recited that "silicate solutions of higher ratios were not available."

Moffett disclosed in U.S. Patent No. 8,815,004, a process to treat tailings streams with a gelling agent and an activator. The gelling agent is selected from the group consisting of colloidal silica, aluminum-modified colloidal silica, de- ionized colloidal silica, polysiloxane, siliconate, acryfamide, acrylate, urethane, phenoplast, aminoplast, vinyl ester-styrene, polyester-styrene, furfuryl alcohol- based furol polymer, epoxy, vulcanized oil, lignin, lignosulfonate, lignosulfite, montan wax, polyvinyl pyrrolidone, and combinations of two or more thereof. The activator can be any compound or mixture of compounds that will initiate gelation.

An important aspect of tailings management is consolidation of the tailings solids - that is, to produce a dense material containing the solids in the tailings, for example to minimize storage space required upon disposal. According to Kotylar, et al, in Clay and Clay Minerals, Vol. 44, No. 1, pp. 121-131 (1996), in reference to oil sands fine tailings, sodium chloride is "the dominant contributor to the aggregation of nano-sized clay particles present in the tailings." Similarly, EP 1353876B1 claims silica sols with reduced quantity of salt has reduced agglomeration or aggregation.

While there have been many advances in the treatment of tailings, there remains a need to improve one or more of de-watering (less water in the tailings), consolidation (reduction of volume of the tailings), and strengthening of the tailings. There is also a need to reduce the amount of sodium added into the tailings stream to limit the sodium that may be introduced into the environment. There is also a need to return the mined area close to its original condition. The present invention meets these needs.

SUMMARY OF THE INVENTION

The present invention also provides a process for treating a tailings stream comprising, consisting essentially of, or consisting of water and solids. The process comprises: (a) contacting a poiyacrylamide and a gelling agent with the tailings stream whereby the solids are entrapped within a gel produced from the gelling agent; and (b) allowing the gel to strengthen and solidify. In some embodiments, the tailings stream comprises, consists essential!)' of, or consists of water, solids, and poiyacrylamide.

The present invention further provides a process for treating a tailings stream comprising, consisting essentially of, or consisting of water, solids, and poiyacrylamide. The process comprises: (a) contacting a gelling agent with the tailings stream whereby the solids are entrapped within a gel produced from the gelling agent; and (b) allowing the gel to strengthen and solidify.

The gelling agent employed in the present invention comprises, consists essentially of, or consists of a deionized silicate solution having a molar ratio of Si:M of at least 2.6, wherein M is an alkali metal. In some embodiments of this mvention, the deiomzed silicate solution is added in an amount equal to 0.01 to 20 kg on a SiCb basis per metric tonne of solids in the tailings stream. In some embodiments of thi s invention, the deionized si licate solution is added in an amount equal to 0.1 to 10 kg on a S1O2 basis per metric tonne of solids in the tailings stream.

In some embodiments of this mvention, the deionized silicate solution is prepared by contacting a solution of sodium silicate with a strong cation exchange resin. In some embodiments of this mvention, the deionized silicate solution is prepared by contacting a solution of sodium silicate with a weak cation exchange resin. In some embodiments of this invention, the deionized silicate solution is prepared by removing alkali metal from a solution of alkali metal silicate using bipolar electrolysis.

In some embodiments of this invention, the tailings stream is produced in a process to extract bitumen from oil sands ores. In some embodiments of this invention, the process of treating the tailings stream further comprises adding an accelerator in the contacting step (a). In some embodiments, the accelerator is a multivalent metal compound or an oxidizer. In some embodiments, the accelerator is added in an amount equal to 0.01 to 5% by weight, based on the total weight of the tailings stream. In some embodiments of this invention, the process of treating the tailings stream further comprises adding a reinforcing agent in the contacting step (a). In some embodiments, the reinforcing agent is selected from the group consisting of gravel, sand from mining operations, waste rock from mining operations, petroleum coke, coal particles, elemental crystalline sulfur, inorganic fibers, organic fibers, and combinations of two or more thereof. In some embodiments, the reinforcing agent is treated with a surface-active agent. In some embodiments, the reinforcing agent is organic fibers. In some embodiments, the remforcing agent is added in an amount equal to 0.01 to 700 kg/tonne, based on the total weight of the tailings stream.

In some embodiments of this invention, the process of treating the tailings stream further comprises adding both an accelerator and a reinforcing agent in the contacting step (a).

In some embodiments of this invention, the process of treating the tailings stream further comprises spreading the gel produced in step (a) over a surface. In some embodiments, such surface is a sloped surface. In some embodiments of this invention, the process of treating the tailings stream further comprises depositing the gel produced in step (a) in a dewatering pit.

In some embodiments of this invention, in the step (b) of the process of treating the tai lings stream, the gel is allowed to be dewatered to strengthen and solidify. In some embodiments, the gel is allowed to strengthen and solidify to produce a traffieabie deposit. In some embodiments, dewatering occurs by air drying (evaporation), water run-off, compression, syneresis, exudation, freeze/thaw, sublimation, or combination thereof. In some embodiments, dewatering occurs by evaporation. In some embodiments, dewatering occurs by water run-off. In some embodiments, the water run-off is recovered and recycled.

The present invention further provides a traffieabie deposit produced from the above tailings stream treatment processes. Such traffieabie deposit has a minimum undrained shear strength of 5 kPa one year after deposition, and a minimum undrained shear strength of 10 kPa five years after deposition. In some embodiments, the traffieabie deposit is produced from the above tailings stream treatment processes wherein an accelerator is also added in the contacting step (a). In some embodiments, the traffieabie deposit is produced from the above tailings stream treatment processes wherein a reinforcing agent is also added in the contacting step (a). DETAILED DESCRIPTION OF THE INVENTION

The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims. Other features and benefits of any one or more of the embodiments will be apparent from the following detailed description, and from the claims.

As used herein, the terms "comprises," "comprising," "includes,"

"including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily iimited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or' refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, use of "a" or "an" are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control . Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, suitable methods and materials are described below. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and/or lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. The present invention is useful for treating tailings streams and

particularly useful for treatment of tailings stream produced in processes to extract bitumen from oil sands ores. Oil sands ores are large deposits of naturally occurring mixtures comprising bitumen, sand, clays, and other inorganic materials, such as titanium or zirconium ores. Herein, bitumen refers to hydrocarbons and other oils found in oil sands, tar sands, crude oil and other petroleum sources. The oil sands ores typically comprise about 2 to 18 wt% bitumen, based on the total weight of the oil sands ore. Oil sand ores containing greater than 6 to 7 wt % bitumen, based on the total weight of the ore, are mined commercially today. The oil sands ores further comprise water, sand and clay. Generally the oil sands ores comprise about 2 to 5 wt% water.

Definitions

Certain terms as used herein have the definitions as provided below.

Clay is any naturally occurring material composed primarily of hydrous aluminum silicates. Clay may be a mixture of clay minerals and small amounts of nonclay materials or it may be predominantly one clay mineral. The type is determined by the predominant clay mineral.

The term coarse particle refers to a single particle or a collection of particles. It will be appreciated by those skilled in the art that that coarse particle size may vary depending on the source of the tailings stream. For example, in oil sands tailings, coarse particles are defined as particles larger than 44 μιη.

Alternatively, in coal mine tailings, coarse particles are defined as particles larger than 2.5 μτη.

Entrap solids means the solid particles, such as clay, sand, silt, and rock, are trapped within the gel structure while the water is not permanent!)' retained within the structure. The term fine particle refers to a single particle or a collection of particles. It will be appreciated by those skilled in the art that that fine particle size may vary depending on the source of the tailings stream. For example, in oil sands tailings, fine particles are defined as particles smaller than 44 um. Alternatively, in coal mine tailings, fine particles are defined as particles smaller than 2.5 um.

Mineral is a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties.

Rock is any consolidated or coherent and relatively hard, naturally formed mass of mineral matter; stone, with the majority consisting of two or more minerals.

Sand is an unconsolidated or moderately consolidated sedimentary deposit, most commonly composed of quartz (silica), but may include particles of any mineral composition or mixture of rock or minerals, such as coral sand, which consists of limestone (calcium carbonate). (Source: AGI American Geosciences Institute)

Silt is a mixture of fine particulate rock and/or mineral.

Tailings Stream Tailings stream is an aqueous fluid (slurry, suspension) comprising, consisting essentially of, or consisting of water and solids. In some embodiments of this invention, the tailings stream comprises, consists essentially of, or consists of water, solids, and polyacrylamide. In some embodiments of this invention, the polyacrylamide is from a tailings treatment process. For example, fresh tailings can be thickened with a polyacrylamide. In some embodiments of this invention, the tailings stream comprises, consists essentially of, or consists of water, solids, and poiysilicate microgel. In some embodiments of this invention, the polvsilicate microgel is from the oil sands bitumen recovery process. In some embodiments of this invention, the tailings stream comprises, consists essentially of, or consists of water, solids, polyacrylamide, and poiysilicate microgel. in some embodiments of this invention, the tailings stream solids comprise clay, sand, rock, silt, or any combinations thereof. Solids may further comprise unextracted particles of mmeral in the mined material. A portion or all of the solids in the tailings stream may be suspended in th e water. The suspended solids are typically not easy to be separated from the water.

The solids have a particle size typically less than 0.5 mm, and in some embodiments less than 0.05 mm. The tailings stream typically comprises at least 5% by weight solids, in some embodiments greater than 10%, and in some other embodiments greater than 20% by weight solids, based on the total weight of the tailings stream. The rest parts of the tailings stream are typically water and/or dissolved materials such as salts and processing aids (e.g., organic solvent, extraction aids such as polysilicate microgel, and poryacrylarnide). The tailings stream may comprise less than 70%> solids, or less than 50%> solids, or less than 40% solids, based on the total weight of the tailings. For a particular application, oil sands tailings streams may comprise solids wherein 10%> to 100% by volume of the solids have a particle size of less than 0.5 mm, in some embodiments, 20% by volume to 100% by volume of the solids have a particle size less than 0.5 mm, based on the total volume of the solids. In some embodiments of this invention, oil sands tailings streams may comprise solids wherein 5% to 100% by volume of the solids have a particle size of less than 0.05 mm, and in some embodiments, 20% by volume to 100% by volume of the solids have a particle size less than 0.05 mm, based on the total volume of the solids.

Tailings stream solids from mining and mineral processing operations have varied size distributions. Most tailings stream solids comprise a high percent of fine particles. For example, most tailings stream solids produced from mining and processing of copper, gold, iron, lead, zinc, molybdenum and taconite have 50% by weight or more of the particles passing a 0.075 mm (No. 200) sieve. Tailings stream solids from iron ore mining and mineral processing may have a slighter larger particle size. For properties of a number of tailings, see, for example http://www.rmrc.unh.edu/tools/uguidelines/mwstl , asp, accessed June 21 , 2012. The tailings stream is typically produced from a mining operation or mineral processing plant. In a mining operation a material is removed from the earth, in a mineral processing plant, such material is treated to extract a valuable mineral such as coal, oil (such as from oil sands), precious metal ore, base metal ore, clay, gemstone. Mined materials include, for example, coal, uranium, potash, clay, phosphate, gypsum, precious metals and base metals. The generated tailings stream may comprise valuable mineral content (e.g., bitumen, coal, precious or base metal, gemstone) as part of the solids. Thus, there may be steps in advance of entrapping the solids (herein, step (a)) to remove the valuable mineral content. Essentially any mining or mineral processing operation that uses water to convey or wash materials will generate a tailings stream.

In a mining operation, there may be interest to recover and recycle the water content of the tailings stream. Alternatively, in an industrial mineral processing operation, water may be recycled to the processing operation such as milling, refining, smelting, and other manufacturing processes. Refining operations, for example, include extraction of oil, nickel or copper from the mined material.

Precious metals include gold, silver, platinum, palladium, ruthenium, rhodium, osmium, iridium. Gold, silver, platinum, and palladium are the most commonly mined precious metals. Base metals include nickel, copper, aluminum, lead, zinc, tin, tungsten, molybdenum, tantalum, cobalt, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium. Nickel, copper, aluminum, lead, and zinc are the most commonly mined base metals. Gemstones include diamond, emeralds (beryl), rubies, garnet, jade, opal, peridot, sapphire, topaz, turquoise, and others.

Other mining and mineral processing operations include oil sands mining and bitumen extraction and recovery processes.

The tailings stream may be a tailings pond, ore or ore mining process wafers, chemically thickened tailings, fresh tailings, MFT, consolidated composite tailings (CCT), or a combination thereof. CCT may be referred to as composite tailings (CT) and non-segregating tailings (NST). Tailings streams useful in the present invention are also described in U.S. Patent Application Serial No.

13/329,375.

Deionized Silicate Solution

In some embodiments of this invention, the tailings stream is contacted with a gelling agent comprising, consisting essentially of, or consisting of a deionized silicate solution. A deionized silicate solution may be prepared by deionizing a silicate solution.

A deionized silicate solution may be prepared by means known in the art, for example, by an electrolytic process and/or by use of an ion exchange resin. Ion exchange methods are disclosed, for example, by Bird, in U.S. Patent 2,244,325. The deionized silicate solution may be prepared by contacting a solution of alkali metal silicate with a strong cation exchange resin. The deionized silicate solution may alternatively be prepared by contacting a solution of alkali metal silicate with a weak ion exchange resin. Her, in U.S. Patent 3,668,088, discloses a process to remove sodium anions from sodium silicate in an electrodialysis process wherein sodium silicate aqueous solution is electro lyzed while separated from an acid anolyte by a cation- permeable, anion-impermeabie membrane.

A deionized silicate solution may be prepared by removing alkali metal from a solution of alkali metal silicate using bipolar electrolysis.

Other processes to prepare deionized silicate solutions include processes which rely on a combination of electrolysis and ion exchange membranes or ion- permeable membranes have been disclosed, for example, in JP2003236345A, JP2004323326A, JP07000803A, JP2002220220A, JP2003311130A and

JP2002079527A.

More specifically, a sodium silicate (or water glass) solution may be contacted with a strong cation exchange resin. Strong cation exchange resins have sulfonic acid functionality, R-SO3H, wherein R is the backbone of the resin or the matrix. The resin or matrix can be, for example, functionalized styrene divmylbenzene copolymers. Strong cation exchange resins are commercially available, for example, from Dow Chemical Company.

The deionized silicate solutions may be modified by alumina before or during or after the deionization process. Processes such as those disclosed in US Patents 5,482,693; 5,470,435; 5,543,014; and 5,626,721 can be used. Care must be taken when the process uses sodium aiuminate so that the added sodium does not provide a Si:Na molar ratio less than 2.6 after such treatment.

The deionized si licate solution may be stabilized by methods known in the art, such as by control of pH or temperature. A deionized silicate solution is an aqueous (water-based) solution. The solution has a molar ratio of Si:M of at least 2.6. M is an alkali metal, such as lithium, sodium, potassium, or combinations thereof. Preferably the molar ratio is 4 or greater, more preferably 5 or greater. The upper limit of Si:M molar ratio may be set by practical considerations, for example capacity of an ion exchange resin for a given quantity of silicate solution, or alternatively, a minimum threshold for sodium in a particular tailings treatment system, in particular when recovered water is recycled for re-use.

The concentration of silica in the solution after deionization is 1-15% by- weight, as "SiCH", preferably 2-10%, more preferably 4-7%. The deionized silicate solution may comprise particles, anions, and oligomers of silica. The silica specific surface area is greater than 500 nWg, typically greater than 750 m^/g.

Poiyaerylamide

In some embodiments of this invention, the tailings stream is contacted with a poiyaerylamide and a gelling agent.

Polyacrylamides (PAMs) useful in the present invention include anionic, cationic, non-ionic and amphoteric polyacrylamides, Polyacrylamides are polymers formed by polymerization of acryiamide, CH2=CHC(0)NH2.

Polyacrylamides of the present invention typically have a molecular weight greater than one million, Polyacrylamides can be linear or branched molecules. Preferably the PAM is an anionic polyacrylamide (APAM) or eationie polyacrylamide (CPAM). APAM and CPAM are the generic names for a group of very high molecular weight macromolecules produced by the free-radical polymerization of acrylamide and an aniomcaily or a cationically charged co- monomer. APAM and CPAM can be prepared by techniques known to those skilled in the art, including but not limited to the Mannich reaction. Both the charge density (ionicity) and the molecular weight can be varied in APAM and CPAM. By varying the acrylamide/ ^' iomc monomer ratio, a charge density from 0 (nonionic) to 100% along the polymer chain can be obtained. The molecular weight is determined by the type and concentration of the reaction initiator and the reaction parameters.

Typically, a polyacrylamide is dissolved in a solvent before contacting with a tailings stream. Preferably, the solvent comprises, consists essentially of, or consists of water in this disclosure. In some embodiments of this invention, polyacrylamide is added to the tailings stream to facilitate early water release. The polyacrylamide can be added together with the deionized silicate solution, or prior to or after the deionized silicate solution addition. For example, the deionized silicate solution addition can occur in or before a polyacrylamide thickener or after discharge from the polyacrylamide thickener. The deionized silicate solution can also be added prior to, in or after a centrifuge operation that also uses polyacrylamide. In-line injection of polyacrylamide and the deionized silicate solution are also possible. In some embodiments of this invention, an aqueous polyacrylamide solution is mixed with a deionized silicate solution before being added to the tailings stream. Accelerator

The process of this invention optionally uses an accelerator. Accelerators are useful to increase speed and decrease the time for the solids to become immobile. Accelerating agents are particularly useful for environments where temperatures are below 40°F (4.4°C). Examples of accelerators include multivalent metal compounds, acids, and esters. The multivalent metals may be calcium, magnesium, aluminum, iron, titanium, zirconium, cobalt or a combination of two or more thereof. Preferably, the multivalent metal compound is soluble in water and is used as an aqueous solution. Preferred multivalent metal compounds may be selected from the group consisting of calcium chloride, calcium sulfate, calcium hydroxide, aluminum sulfate, magnesium sulfate, aluminum chloride, polyaluminum chloride, polyaluminum sulfate, and aluminum chlorohydrate. More preferably the multivalent metal compound is calcium sulfate, aluminum sulfate, polyaluminum sulfate, polyaiuminum chloride, aluminum chlorohydrate, or combinations thereof. Acids include mineral acids, organic acids, sulfuric acid, hydrochloric acid, carbon dioxide, acetic acid, and giyco lie acid. Salts of acids may be included. Esters, include, for example, acetic esters of glycerol.

Use of salts to control pH must be limited so as to not result in a molar ratio of Si:M of less than 2.6. Use of acid or base may depend on the pH of the tailings stream when combined with the deionized silicate solution. Preferably pH is between 4 and 8, with most rapid gelling to occur around pH 6.

Reinforcing Agent

The process of this invention optionally uses a reinforcing agent.

Reinforcing agents are compounds that act as fillers and mechanically strengthen the treated tailings stream. Reinforcing agents can be used in an amount up to about 70 weight percent of the total weight of the trafficable deposit.

Reinforcing agents are selected from the group consisting of fine gravel, sand from mining operations, waste rock from mining operations; petroleum coke, coal particles; elemental crystalline sulfur; inorganic fibers; organic fibers, and combinations of two or more thereof. Particle size definitions for gravel is determined by ASTM D2488 (2009) "Standard Practice for Description and Identification of Soils (Visual-Manual Procedure)" DOI: 10.1520/D2488-09A, available from ASTM International, West Conshohocken, P A. Inorganic fibers can be, for example, steel fibers or fiberglass. Organic fibers can be, for example, pulp waste, paper waste, wood waste, and waste paper. In addition, the surface of the reinforcing agent may be untreated or the surface may have been treated with a surface-active agent. A typical surface- active agent is an organic silane. Surface-active agents strengthen interfacial bonds between the reinforcing agent and the treated tailings.

Trafficable deposit

Trafficable deposit is a solid or semi-solid material that is deposited on or over a surface. The trafficable deposit in this disclosure has a minimum undramed shear strength (yield stress) of 5 kPa one year after deposition, and/or a minimum undrained shear strength of 10 kPa five years after deposition.

Treatment of Tailings Stream

The present invention also provides a process for treating a tailings stream comprising, consisting essentially of, or consisting of water and solids. The process comprises: (a) contacting a poiyacrylamide and a gelling agent with the tailings stream whereby the solids are entrapped within a gel produced from the gelling agent; and (b) allowing the gel to strengthen and solidify; wherein the gelling agent comprises, consists essentially of, or consists of a deionized silicate solution having a molar ratio of Si:M of at least 2.6, wherein M is an alkali metal. In some embodiments of this invention, the tailings stream comprises, consists essentially of, or consists of water, solids, and poiyacrylamide.

The present invention further provides a process for treating a tailings stream comprising, consisting essentially of, or consisting of water, solids, and poiyacrylamide. The process comprises: (a) contacting a gelling agent with the tailings stream whereby the solids are entrapped within a gel produced from the gelling agent; and (b) allowing the gel to strengthen and solidify; wherein the gelling agent comprises, consists essentially of, or consists of a deionized silicate solution having a molar ratio of Si:M of at least 2.6, wherein M is an alkali metal. It is noted herein that in contrast to flocculation, in which suspended particles coalesce to form a precipitate, in the process of this invention, upon contact with the gelling agent, the tailings stream becomes viscous, then develops rigidity as it strengthens and solidifies.

By "strengthen and solidify", it is meant herein that the gel has formed a solid mass, which separates from the water present in the tailings stream. In some embodiments of thi s invention, the soli d mass wi ll develop a minimum undrained shear strength of 5 kPa one year after deposition, and a minimum undrained shear strength of 10 kPa five years after deposition. In the step of allowing the gel to strengthen and solidify, the gel may be dewatered and/or dried, in some embodiments of this invention, the gel is allowed to strengthen and solidify to produce a traffi cable deposit.

As used herein, separation of water includes partial separation of water from the gel. Separation may occur or be performed by means such as evaporation, drainage, mechanical dewatering, run-off, compression, exudation, percolation of water to underlying surface, freeze/thaw, sublimation, syneresis. It shoul d be understood that the gel may retain a poxtion of the total amount of water from the tailings stream and the treatment solutions (e.g., deionized silicate solutions and poiyacrylamide solutions) as all traces would be nearly impossible to remove and water from natural precipitation or run-off from higher elevation of material may become part of the gel. Typically, after the dewatering step, the gel comprises less than 5 % of the tailings water, or less than 3%, or less than 2%, on a weight basis, based on total water weight of the tailings stream. Preferably at least some of the water from the tailings is recovered and recycled into mining and/or mineral processing operations. By "run-off it is meant that water is exuded from the gel-entrapped solids, or alternatively water from natural precipitation (rain, snow) that passes over the gel-entrapped solids and runs off the tailings. Run-off is generally captured in a water collection area (e.g., a pond), if water run-off occurs, one may recover the water from this process and recycle the run-off water. For

compression, the solids can be deposited into a dewatering pit, where one or more sides allow water run-off to be recovered. For example, the water run-off or recovered water can be re-used in either bitumen extraction or in the flocculation of the tailmgs streams discussed infra. Advantageously, use of deiomzed silicate solution provides lower alkali metal ion concentration in the recovered water. The gel comprising entrapped solids may undergo "forced drying" using piate-and-frarne filter press, or other mechanical dewatering means. Following a forced drying step the dried product may then be spread on a surface, preferably a sloped surface or deposited in a dewatering pit.

Optionally, the process further comprises adding an accelerator in the contacting step (a). Optionally the process further comprises adding a reinforcing agent in the contacting step (a). Optionally, the process further comprises spreading the gel produced in step (a) over a surface. Optionally, the process further comprises depositing the gel produced in step (a) on and/or over a surface. The difference between "on" or "over" a surface may be a matter of degree, but is meant herein to indicate the gel is deposited on a surface in a particular location, whereas depositing over a surface involves spreading or flowing of the gel. There may be many instances of partial spreading or flow that is best described as a combination of depositing on a surface and depositing over a surface. Preferably, the surface is sloped or in a dewatering pit.

In some embodiments of this invention, a trafficable deposit is produced from the process to treat tailings streams. The trafficable deposit comprises, consists essentially of, or consists of the product of the treatment process, optional!)' after full or partial dewatering and/or drying, optionally wherein the process comprises adding a reinforcing agent in the contacting step (a).

The deionized silicate solution, polyacrylamide, optionally accelerator, and optionally reinforcing agent employed in the tailings streams treatment process are used in an effective amount to produce a gel, entrapping solids, such as sand, clay, and other solids in the stream, and to provide a trafficable deposit after strengthening, dewatering and drying.

The tailings stream can be any tailings stream such as, for example, those described hereinabove. A preferred tailings stream is produced in a bitumen extraction process. The tailings stream may be or comprise mature fine tailings.

The deionized silicate solution is added to the tailings stream in an amount equal to 0.01 to 20 kilograms ("kg"), on a Si(>2 basis per metric tonne ("tonne")

(kg/tonne) based on the total weight of the tailings stream. In some embodiments of this invention, the deionized silicate solution is added in an amount equal to 0.1 to 10 kg on a S1O2 basis per metric tonne based on the total weight of the tailings stream.

The polyacrylamide is added to the tailings stream in an amount of 50- 10,000 grams PAM/1000 kg of fine particles (particles smaller than 44 urn). When used, an accelerator is added in an amount equal to 0.01 to 5% by weight, based on the total weight of the tailings stream.

When used, a reinforcing agent is added in an amount equal to 0.1 to 700 kg/tonne based on the total weight of the tailings stream. Preferably the reinforcing agent is added in an amount equal to 0.1 to 100 kg/tonne based on the total weight of the tailings stream. More preferably the reinforcing agent is added in an amount equal to 0,1 to 10 kg/tonne based on the total weight of the tailings stream.

The contacting step (a) can be performed in various ways. The tailings stream, gelling agent, and polyacrylamide, with the optional accelerator and/or reinforcing agent may be contacted in a vessel and deposited on a surface and allowed to dry. The tailings stream, gelling agent and polyacrylamide, with optional accelerator and/or reinforcing agent may be contacted and centrifuged to enhance separation with a reduced amount of the gelling agent needed. In some embodiments, the gelling agent, polyacrylamide, and optional accelerator and/or reinforcing agent are contacted with the tailings stream in a transfer line to initiate gelation, whereas gel matrix formation occurs outside the line to avoid plugging of the line. In some embodiments, the gel matrix is spread on a surface and allowed to de -water and dry. in some embodiments, the gelling agent, polyacrylamide, and optional accelerator and/or reinforcing agent may be added directly to a tailings pond. When added to a tailings pond, water is allowed to evaporate or is separated by other means to dewater the tailings. In some embodiments, separation of water may occur or be performed by the dewater means cited above, including mechanical de watering, run-off, freeze-thaw, etc.

The process for treating a tailings stream comprising contacting a gelling agent, polyacrylamide, and optional accelerator and/or reinforcing agent with a tailings stream may be adjusted to vary gelation times. As used herein, gelation means the rapid increase in viscosity and yield strength. Adjustments include, but not limited to, varying the order of addition and/or concentration of the deiomzed silicate solution, polyacrylamide, accelerators, and/or reinforcing agents. Gelation time can be varied by making adjustments to pH (adding acid to lower pH, adding base to raise pH).

The concentration of the deionized silicate solution will allow for adequate handling prior to formation into an immobile solid. This is important, for example, for applications where the tailmgs stream will be contacted with the deionized silicate solution, polyacrylamide, and optional accelerators) and/or reinforcing agents in pipes then pumped to the desired area, where the

combination will be discharged onto a surface for gelling.

The gel matrix comprising the tailings stream, gelling agent,

polyacrylamide, and optional accelerator and/or reinforcing agent may be deposited such as by pumping or spraying, on a surface. Gel time may be controlled by means such as addition or lack of accelerators, concentrations, residence time, pH, temperature. As will be appreciated by those skilled in the art, it is important to pump, spray or transfer the gel in a time before the gel solidifies to avoid forming a solid that may plug a pump, a spray nozzle or transfer line. Also, spraying the combination of tailings stream and gelling agent onto a slope, before the gelation process is initiated is also a problem as the "ungelled" mixture may run off the slope and not set in the d esired location.

The tailings stream comprises, consists essential!)' of, or consists of water, solids, and optionally polyacrylamide. Contacting the tailings stream with the gel ling agent, polyacrylamide, and optional accelerator and/or reinforcing agent produces a gel matrix, which entraps the solids. The polyacrylamide, accelerator, reinforcing agents, or combinations thereof, may be a) premixed with the deionized silicate solution prior to contacting with the tailings streams, b) added simultaneously with the deiomzed silicate solution while the deionized silicate solution is contacting the tailings stream, or c) added sequentially following contacting the deiomzed silicate solution with the tailmgs stream provided that it is prior to producing a gel matrix. Moreover, as stated above, the polyacrylamide may already be present in the tailings stream prior to adding the gelling agent and optional accelerator and/or reinforcing agent.

The gei matrix is then allowed to strengthen and solidify, in some embodiments with dewatering and/or drying. In some embodiments of this invention, the gel matrix is allowed to strengthen and solidify to produce a trafficable deposit.

The gel with entrapped solids formed from the process of this invention may be deposited on a surface, preferably a sloped surface, and allowed to solidify. This step of applying the product of the contacting step to a surface may be repeated numerous times, producing a lift of several layers of solid surface that encompass the solids including the fines of the tailings stream.

The gel with entrapped solids formed from the process of this invention may be deposited into a dewatering pit in one or more layers. When deposited in more than one layer, the weight of multiple layers produces a compression effect which then presses out water of the multiple layer deposit. Sand or porous media may be inserted beneath a layer to enhance dewatering and drying.

EXAMPLES

The following examples demonstrate that the combination of polyacrylamide and deionized silica solution when added to mature fine tailings (MFT) improves dewatering and yield strength over that of either polyacrylamide or deionized silica alone.

Preparation of polvacrylamlde solution

A 0.2 wt% anionic polyacrylamide (APAM) solution was prepared by dissolving 2 grams of MAGNAFLOC® 1011 anionic fluid (BASF SE, Ludwigshafen Germany) in 998 grams of deionized water.

Preparation of deionized sil ica solution

A 4 wt% deionized silica solution was prepared by mixing 72.73 grams of 3.2 ratio sodium silicate solution in 500 grams of deionized water and then deionizing this solution by addition of 1 10 grams of DOWEX® HCR-W2 cation exchange resin (The Dow Chemical Company, Midland, MI, purchased from VWR International, LLC) . The resin was removed from the solution by filtration after the pH stabilized.

Mature Fine Tailings (M FT)

MFT was obtained from an Alberta, Canada oil sands producer. The solids content of the MFT was 36.6 wt%. Sodium concentration in the MFT was increased to approximately 800 ppm by addition of sodium sulfate to be similar to the equilibrium sodium concentration reported for mature oil sands producers ( Jeeravipoolvarn, Geotechnical Behavior of In- Line Thickened Oil Sands Tailings, Doctoral Thesis, University of Alberta, 2010). Measurement of Peak Yield Stress

Treated MFT was placed in a consolidation cell fabricated from a section of vertically oriented stainless steel tubing having an internal diameter of 9.73 cm. The lower end of the tubing was equipped with a flange supporting a wire mesh screen and a Whatman #40 filter paper. A hole was bored into the flange to allow water to drain from the tailings. 1 day after the MFT was placed in the consolidation cell a load of 40 kPa was applied to the upper surface of the MFT by means of an air cylinder and piston which closely fit the internal diameter of the stainless steel tubing. The height of the MFT sample was monitored with time. Consolidation of the sample was deemed to be complete when no change was observed in the sample height. For comparison between samples, time to 90% of final consolidation height is used since the final consolidation is asymptotic and small changes in height result in large changes in time.

After consolidation was complete the samples were removed from the consolidation cell and peak yield stress of the treated sample was determined using a Brookfiekl rheometer equipped with a varied spindle rotating at 0.1 rpm. The rheometer was interfaced to a PC running Brookfield's rheocalc software.

Example 1

1200 grams of the above MFT were treated by addition of 70.2 grams of 0.2 wt% of the above A RAM solution (added by syringe at the rate of about 1 ml per second) followed by 95.2 grams of the above 4 wt% deiomzed silica solution. 362 grams of MFT solids (1126.3 grams of the treated tailings) were placed in the consolidation cell. 90% of final consolidation height was achieved in 278 hours. The peak yield stress of the sample at the end of consolidation was measured using the Brookfieid rheometer and found to be 19 kPa.

Comparative Example A

1200 grams of the above MFT were treated by addition of 70.2 grams of 0.2 wt% of the above APAM solution (added by syringe at the rate of about 1 ml per second). 363 grams of MFT solids (1049 grams of the treated tailings) were placed in the consolidation cel l. 90% of final consolidation height was achieved in 601 hours. The peak yield stress of the sample at the end of consolidation was measured using the Brookfieid rheometer and found to be 13 kPa.

Comparative Example B

1200 grams of the above MFT were treated by addition of 95.2 grams of the 4 wt% deionized silca solution. 362 grams of MFT solids (1068.4 grams of the treated tailings) were placed in the consolidation cell . 90% of final consolidation height was achieved in 303 hours. The peak yield stress of the sample at the end f consolidation was measured using the Brookfieid rheometer and found to be 17

1000 grams of untreated MFT (366 grams of MFT solids) were placed in the consolidation cell. 90%> of the final consolidation height was achieved in 622 hours. The peak yield stress of the untreated sample at the end of consolidation was measured using the Brookfieid rheometer and found to be 12 kPa.

As demonstrated by the above, the combination of polyaeryl amide solution and deionized silica solution resulted in faster consolidation rates and higher final yield strength than either chemical alone.