HK1162455B - Treatment of tailings streams - Google Patents

Description

Treatment of tailings streams

Technical Field

The present invention relates to a process for extracting bitumen from oil sands, flocculating/dewatering tailings after extraction, and treating tailings streams.

Background

To meet the global demand for petroleum, oil sands have become an attractive source for oil recovery. Oil sands are naturally occurring mixtures of vast reserves of bitumen, water, sand, clay, and other inorganic materials found on the earth's surface. Bitumen is a highly viscous form of crude oil. The largest oil sands deposits are found in canada and venezuela. In particular, Athabasca oil sands deposits correspond to 1.6 to 2.7 trillion barrels of oil, and are located in Alberta and Saskatchewan, canada. About 10% of the Athabasca oil sands reserves can be mined. After oil sands are mined, it can be processed by extracting bitumen.

Bitumen must be extracted and separated from the water, sand and fine clay of the oil sands. Today, oil sands are mined, crushed, and then mixed with hot water and optional chemicals to facilitate the extraction of bitumen from sand and fine clays. The extracted bitumen is separated from the sand and fine clay and then refined. The remaining sand, clay and water are commonly referred to as "tailings". The tailings are further treated to dewater the sand and clay. Sand and clay are typically placed in, for example, tailings ponds and precipitated into mature fine tailings. Mature fine tailings are stable slurries comprising fine clay with sand, silt, water and bitumen. Mature fine tailings are not strong, do not grow plants, and may be toxic to animals, so they must be sealed to prevent them from contaminating water supplies. The water recovered from the dehydration step may be reused in the extraction process. When this water is reused in the extraction process, faster recovery of the water can reduce energy requirements.

The bitumen recovered from the process is present in the form of a froth. The froth comprises concentrated bitumen (typically 50% or more), water, fine clay and sand. The froth is treated in a froth treatment unit that can recover bitumen with a purity of greater than 95% using steam (for degassing the froth) and a naphthenic or paraffinic solvent. The by-product of the foam treatment process is foam treated tailings. The froth treatment tailings comprise water, residual solvent, and fine solids having a particle size substantially less than 44 microns. The foam treatment tailings are typically treated in a tailings pond. The froth treatment tailings contribute to the formation of mature fine tailings.

Tipman et al, in U.S. patent 5,876,592, disclose a process for recovering bitumen from oil sands that includes: adding an aqueous caustic to the oil sand slurry to produce an emulsion; separating the emulsion into three layers, a top layer of a first foam comprising bitumen; a bottom layer known as tailings, comprising water, precipitated sand and fine clay; and an intermediate layer known as middlings that contains residual bitumen, suspended fine clay and water. The middlings are further processed to recover additional bitumen in the same manner as the oil sand slurry, producing a second foam. The second foam may be combined with the first foam and the bitumen recovered by diluting with a solvent and removing sand and fine clay.

Yuan et al inCanadian Metallurgical Quarterly2007, vol.46, No.3 pp.265-272(Canadian Metallurgical Quartely, 2007, Vol.46, No.3, pp.265 to 272) discloses a process for removing sand and fine clay in tailings in a specific order using a multi-step process. The first step, known as flocculation-coagulation-flocculation (FCF), is the addition of a flocculant. This flocculates to produce larger particles, leaving the fines in solution. In the second step, a coagulant is added. The coagulant destabilizes the finesThereby forming small flocs. In the third step, a small amount of flocculant is added to combine the larger floes in the first step with the smaller floes in the second step, thereby creating larger floes and increasing the settling rate for faster dewatering.

According to Masliyah inInd.Eng.Chem.Res2005, vol.44, pp.4753-4761(ind. eng. chem. res., 2005, volume 44, pages 4753 to 4761), acidified silicates have been used to facilitate extraction of bitumen. The divalent metal ions can be chelated by acidifying the silicate, thereby promoting bitumen extraction while maintaining the pH constant. This process has similar disadvantages as WO 2005/028592, namely that the solids are dispersed.

Li is inEnergy & Fuels，2005，vol.19，pp.936-943(Energy &Fuels, 2005, volume 19, pages 936 to 943) discloses the effect of Hydrolyzed Polyacrylamide (HPAM) on bitumen extraction and tailings disposal in oil sands. In order to achieve both the efficiency of bitumen extraction and flocculation of solid fines, it is necessary to carefully control the amount of HPAM used.

Chaiko et al, in U.S. patent 6,153,103, disclose a method for separating and recovering ultra-fine particles and soluble salts from dilute process streams by a syneresis process using sodium silicate and an organic gelling agent. The process is used for dilute solutions and solids having a ratio to silicate of 0.4: 1 or less.

For so-called "low quality ores," the separation of bitumen from sand and fine clay, and the dewatering of sand and fine clay for disposal is particularly difficult. Generally, in the case of oil sands, low quality ores refer to oil sands containing a large amount of fines that not only hinder the extraction of bitumen, but also affect the dewatering process of sand and fine clays. Low quality mines extract bitumen in acceptable yields using conventional methods. In addition, more bitumen remains in the tailings stream when extracted from low quality ores, and is then sent to tailings ponds as a yield loss.

The yield loss of low quality ore is as high as 35% to 50%, avoiding the use of low quality ore where possible. Alternatively, a limited number of low quality ores are mixed with high quality ores in order to process them more efficiently. As the demand for oil increases year by year, it is necessary to recover such low quality ores and produce high yields of bitumen. The tailings should be substantially bitumen free and separated from water to enable reuse of the water and return of the bitumen free solids to the environment within environmental limits.

It is desirable to have a lower extraction temperature (e.g., less than about 50 ℃) to conserve heat energy. For example, the heat supply cost of the extracted water may be increased when no upgrading plant is nearby that can process the extracted bitumen.

Mature fine tailings ponds also present environmental concerns. It is often necessary to build ponds for disposal of tailings where the clay and fines will be suspended in the water and eventually become mature fine tailings. The canadian Energy Resources Conservation Board has issued a command No. 074 that requires all oil sand operators to reduce the fine tailings pond and form a trafficable deposit. Currently, these mature fine tailings are treated with gypsum/lime and centrifugation. The gypsum/lime treatment process is undesirable because calcium ions are added in and around the tailings pond and the remaining solids are too soft to pass on for long periods of time. Centrifugation is also undesirable because of the large investment and the necessity to transport mature fine tailings to a location where a centrifuge is installed.

While many advances have been made in oil sands extraction and tailings treatment, there remains a need to increase bitumen recovery (yield) from oil sands, improve tailings dewatering (i.e., make the water content in the tailings less), and reduce the need for freshwater bitumen recovery processes. In addition, there is a need to improve bitumen extraction in low quality mines, and it is desirable to achieve this without significantly increasing capital equipment and bitumen yield losses. In addition, there is a need for mature fine tailings ponds that reduce or eliminate residual solids that may be useful. The present invention meets these needs.

Summary of The Invention

The present invention is a process for extracting/recovering bitumen from oil sands and treating tailings. In one embodiment of the invention, the method comprises: (a) providing an aqueous slurry of the placer ore; and (b) contacting the slurry with the polysilicate microgel to produce a froth comprising bitumen and a tailings stream comprising sand and fine clay. Preferably, the process further comprises (c) dewatering the tailings. Bitumen is recovered from the froth. Optionally, an anionic polyacrylamide and/or caustic, such as sodium hydroxide, sodium silicate, sodium citrate, may be added after step (b) and before step (c). Alternatively, polyacrylamide and one or both of the following may be added after step (b) and before step (c): (i) a polyvalent metal compound; and (ii) a low molecular weight cationic organic polymer. Surprisingly, the process improves the recovery of bitumen without adversely affecting tailing flocculation, as compared to processes using sodium silicate instead of polysilicate microgel. The polysilicate microgel is retained to the dewatering step and may promote flocculation in the tailings.

In an alternative embodiment of the invention, there is a process for treating a tailings stream comprising water, sand and fine clay to flocculate the sand and fine clay, wherein the process comprises (a) contacting the tailings stream with a polysilicate microgel, an anionic polyacrylamide and one or both of: (i) a polyvalent metal compound, (ii) a low molecular weight cationic organic polymer to produce flocculated solids; and (b) separating the flocculated solids from the tailings stream. Surprisingly and advantageously, in this second embodiment, flocculation is promoted compared to the use of polyacrylamide alone.

In a third alternative embodiment of the invention, there is a process for treating a tailings stream, the process comprising: (a) contacting the tailings stream with a silicate source and an activating agent; (b) embedding fine clay and sand in silica gel; (c) spreading the silica gel on the surface; and (d) drying the silica gel to produce a trafficable surface, wherein the silicate source is an alkali metal silicate, a polysilicate microgel, or a combination thereof, and wherein the tailings stream comprises water, fine clay, and sand, wherein 20% to about 100% by volume of the fine clay and sand have a particle size of less than 0.05 mm. Optionally, the tailings stream also comprises polysilicate microgels. Optionally, the treated tailings prepared after step (b) may be centrifuged or treated with other known dewatering techniques before spreading the embedded fine clay and sand on the surface.

Brief Description of Drawings

Figure 1 is a process flow diagram of the bitumen extraction process and tailings flocculation according to the present invention.

Detailed Description

In a first embodiment of the invention, a process for recovering bitumen from oil sands is provided that includes providing an aqueous slurry of oil sands ore, and contacting the slurry with a polysilicate microgel to facilitate bitumen separation, thereby preparing foam and tailings. The slurry of oil sands can be prepared by extracting the oil sands, grinding the ores, and adding water. Optionally, anionic polyacrylamide and/or caustic, such as sodium hydroxide, sodium silicate and sodium citrate, may be added to the mixture of oil sands ore and microgel. The foam comprises bitumen, fine clay and water. The tailings contain sand, fine clay, unreacted polysilicate microgel and water. Preferably, the process further comprises dewatering the tailings. The polysilicate microgel in the tailings may be retained with the water in a dewatering step, wherein the microgel may promote flocculation in the tailings.

In an alternative embodiment, a process for flocculating a tailings stream is provided, wherein the tailings stream is prepared from an oil sands ore and comprises water, sand, and fine clay. The method includes contacting a tailings stream with a polysilicate microgel, an anionic polyacrylamide, and a polyvalent metal compound and/or a low molecular weight cationic organic polymer to flocculate solids.

In a third alternative embodiment of the invention, there is a process for treating a tailings stream, the process comprising: (a) contacting the tailings stream with a silicate source and an activating agent; (b) embedding fine clay and sand in silica gel; (c) spreading the silica gel on the surface; and (d) drying the silica gel to produce a trafficable surface, wherein the silicate source is an alkali metal silicate, a polysilicate microgel, or a combination thereof, and wherein the tailings stream comprises water, fine clay, and sand, wherein 20% to about 100% by volume of the fine clay and sand have a particle size of less than 0.05 mm. Optionally, the tailings stream also comprises polysilicate microgels. Optionally, the treated tailings from step (b) may be centrifuged or treated with other known dewatering techniques before spreading the embedded fine clay and sand on the surface.

Oil sand ore

Oil sands are vast reserves of naturally occurring mixtures containing bitumen, sand, clay and other inorganic materials. Bitumen, as used herein, refers to hydrocarbons and other oils found in oil sands, tar sands, crude oil, and other petroleum sources. The oil sands used in the present invention are mined material and typically contain about 5 to 15 weight percent bitumen. Oil sands also contain water, sand and fine clay. Generally, oil sands ore contains about 2 to 5 weight percent water.

The inorganic material may be a naturally occurring ore, such as titanium ore and zirconium ore present in oil sands.

The method of the present invention may advantageously be used to treat low quality ores. The "lower" the quality of the oil sands, the higher the content of fine clay. Surprisingly, the process of the present invention is effective in extracting bitumen from low quality oil sands while simultaneously dewatering a tailings stream.

Low quality ore is defined herein as oil sands ore having one or more of the following properties: (a) the content of fine clay is more than 15 percent; (b) the montmorillonite clay content is more than 1 wt% of the total weight of the oil sand ore; (c) the content of calcium and magnesium is more than 10 ppm; and (d) the ore is less than 25 meters from the surface and has been oxidized.

Polysilicate microgels

The process of the present invention comprises contacting the polysilicate microgel with the oil sands. Polysilicate microgels are aqueous solutions formed by partial gelation of alkali metal silicates or polysilicates (e.g., sodium polysilicate). In contrast to commercially available colloidal silica, microgels can be referred to as "active" silica, which constitute a solution of bonded silica particles having a diameter of from 1 to 2nm, typically having a diameter of at least about 750m²Surface area in g. Polysilicate microgels are commercially available from e.i. du Pont DE Nemours and Company (Wilmington, DE).

The polysilicate microgel has a SiO of from 4: 1 to about 25: 1₂∶Na₂O molar ratio, and is discussed at pages 174 to 176 and pages 225 to 234 of "The Chemistry of Silica" by Ralph K.Iller, published by John Wiley and Sons (N.Y.) in 1979. A general method for preparing polysilicate microgels is described in U.S. patent No. 4,954,220, the teachings of which are incorporated herein by reference.

Polysilicate microgels include microgels which have been modified by the addition of alumina to their structure. Such alumina-modified polysilicate microgels are known as polyaluminosilicate microgels and are readily prepared by the basic process of modifying the polysilicate microgels. A general method for preparing polyaluminosilicate microgels is described in U.S. Pat. No. 4,927,498, the teachings of which are incorporated herein by reference.

Polysilicic acid is a form of polysilicate microgel and generally refers to those silicic acids having a pH in the range of 1 to 4 which have been formed and partially polymerized, including silica particles having a diameter of approximately less than 4nm which then polymerize into chains and three dimensional networks. Polysilicic acids may be prepared according to the methods disclosed in, for example, U.S. patent 5,127,994, which is incorporated herein by reference.

In addition to the silica microgels described above, the term "polysilicate microgel" as used herein includes silica sols having a low S value (e.g., an S value of less than 50%). "Low S-value silica sols" are described in European patents EP 491879 and EP 502089. EP 491879 describes silica sols having an S value in the range from 8 to 45%, in which the silica particles have a size of from 750 to 1000m²Specific surface area per gram and has been surface modified with 2 to 25% alumina. EP 502089 describes SiO with a ratio of 6: 1 to 12: 1₂∶M₂Silica sol of molar ratio O, wherein M is an alkali metal ion and/or an ammonium ion, and comprising a specific surface area of 700 to 1200M²Silica particles per gram.

Polyacrylamide

Polyacrylamides (PAM) useful in the present invention include anionic polyacrylamides, cationic polyacrylamides, nonionic polyacrylamides, and amphoteric polyacrylamides. The polyacrylamide is prepared from acrylamide CH₂＝CHC(O)NH₂A polymer formed by polymerization. The polyacrylamides of the present invention typically have a molecular weight greater than one million.

Preferably, the PAM is an Anionic Polyacrylamide (APAM) or a Cationic Polyacrylamide (CPAM). APAM and CPAM are generic names for a group of very high molecular weight macromolecules that are prepared by free radical polymerization of acrylamide and anionically or cationically charged comonomers. APAM and CPAM can be prepared by techniques known to those skilled in the art, including but not limited to Mannich (Mannich) reactions. Both the charge density (ionization degree) and the molecular weight in APAM and CPAM can be varied. By varying the acrylamide/ionic monomer ratio, charge densities from 0 (non-ionic) to 100% along the polymer chain can be obtained. The molecular weight is determined by the concentration and type of reaction initiator and the reaction parameters.

Low molecular weight cationic organic polymers

The low molecular weight cationic organic polymers useful in the present invention have a number average molecular weight of less than 1,000,000. Preferably, the molecular weight is in the range of between about 2,000 to about 500,000, more preferably between 10,000 and 500,000. The low molecular weight polymer is typically selected from: polyethyleneimine, polyamine, polycyanulamine formaldehyde polymer, diallyldimethylammonium chloride polymer, diallylaminoalkyl (meth) acrylate polymer, dialkylaminoalkyl (meth) acrylamide polymer, copolymer of acrylamide and diallyldimethylammonium chloride, copolymer of acrylamide and diallylaminoalkyl (meth) acrylate, copolymer of acrylamide and dialkyldiaminoalkyl (meth) acrylamide, and copolymer of dimethylamine and epichlorohydrin. Such polymers are described, for example, in U.S. Pat. nos. 4,795,531 and 5,126,014. Low molecular weight cationic organic polymers are commercially available, for example, as FLOQUAT FL 2250 and FLOQUT FL 2449 from SNF Floeger (Andre zieux, France) and as WT-530 from FCT-Water Treatment (Greeley, Colorado).

Polyvalent metal compound

Polyvalent metal compounds that can be used in the process of the present invention are compounds of metals having more than one valence state. Examples of polyvalent metals include calcium, magnesium, aluminum, iron, titanium, zirconium, and combinations thereof. Preferably, the polyvalent metal compound is soluble in water and is used as an aqueous solution. Examples of suitable polyvalent metal compounds include calcium chloride, calcium sulfate, calcium hydroxide, aluminum sulfate, magnesium sulfate, aluminum chloride, polyaluminum sulfate, and aluminum chlorohydrate. Preferably, the polyvalent metal compound is calcium sulfate, aluminum sulfate, polyaluminum chloride, aluminum chlorohydrate. Polymeric polyvalent metal compounds are particularly useful in the present invention.

Activating agent

The activators of the present invention include any compound or mixture of compounds that can initiate the gelation of an alkali metal silicate. Activators can include acids, alkaline earth metal and aluminum salts, as well as organic esters, dialdehydes, organic carbonates, organic phosphates, amides, and combinations thereof. Examples of acids that can be used as activators include, but are not limited to, sulfuric acid, carbon dioxide, phosphoric acid, sodium phosphate, sodium bicarbonate, hydrochloric acid, sodium bisulfate, and acetic acid. Examples of alkaline earth metal and aluminum salts include, but are not limited to, calcium chloride, calcium oxide, calcium carbonate, calcium sulfate, magnesium chloride, aluminum sulfate, sodium aluminate. Examples of organic esters, dialdehydes, organic carbonates, organic phosphates, and amides include, but are not limited to, acetate esters of glycerol, glyoxal, ethylene carbonate, propylene carbonate, and formamide. Preferably, the activator is an acid, an alkaline earth metal salt, or a combination thereof. Preferred acids are sulfuric acid or carbon dioxide. Preferred alkaline earth metal salts are calcium sulfate and calcium chloride. One or more activators may be employed.

Extraction and flocculation

Oil sands ores are typically mined from soil and processed to remove bitumen, which is then further processed as crude oil. In a first embodiment, an oil sands ore is provided. Oil sands ore is mined from oil sands ore deposits and subjected to crushing to provide a material suitable for extracting bitumen from the ore. Mining and crushing may be carried out using conventional methods. Oil sands ore is typically processed as an aqueous slurry. The recovered water from the downstream dewatering step (see below) can be used to prepare an aqueous slurry of oil sands ore.

The process of the present invention comprises providing an aqueous slurry of oil sands ore and contacting the slurry with a polysilicate microgel to extract bitumen from the oil sands ore. Prior to or during this contacting (extracting) step, water and optionally air may be added to the slurry at a temperature in the range of 25 to 90 ℃ (77 to 194 ° f), preferably 35 to 85 ℃ (95 to 185 ° f). Advantageously, the contacting step is carried out at a temperature of 50 ℃ or less, for example, 35 to 50 ℃ (95 to 122 ° f).

The amount of the slurry components can vary. An aqueous slurry of oil sands can be prepared by contacting the oil sands with water in an amount of 10% to 500% (preferably 50% to 200%) by mass of the ore. The water may be recovered water from the extraction process. The amount of water added may depend on the extraction efficiency and the limitations of the transfer line used to efficiently transfer the mineral-containing slurry to the extraction unit.

Polysilicate microgels are typically added in amounts of 25 to 5000g per metric ton of oil sands.

Prior to contacting with the polysilicate microgel (extraction step (b)), one or more of the following additives may be added to the oil sand slurry: anionic polyacrylamide and other polymeric flocculants with coagulants; caustic alkalis such as sodium hydroxide, sodium silicate and sodium citrate; organic acids and salts of organic acids (e.g., glycolic acid and sodium glycolate), surfactants, buffers (e.g., bicarbonate), and antimicrobial agents.

In the extraction step (b), the oil sands, microgel and water are mixed and optionally contacted with air, typically in the form of bubbles, in a reaction vessel or transfer line. The contact of the bubbles with the slurry causes the bitumen to float to the top of the slurry, thereby forming a top layer known as froth or first froth (if the process generates multiple froth). The (first) froth comprises bitumen that has floated to the top of the slurry and also comprises fine clay.

After the formation of the foam, the remaining slurry is separated in the reaction vessel or transferred from the transfer line to a separation vessel. Most of the sand and fine clay settle to the bottom of the slurry forming a bottom layer, called coarse tailings. An intermediate layer is also formed in the slurry. The middle layer is the dilute portion of the slurry, which contains bitumen that does not float to the top and sand and fine clay that does not settle to the bottom, called middlings.

Middlings can be removed from the middle of the reaction vessel or the separation vessel. The removed middlings can also be further processed by contacting air in the form of bubbles or passing through one or more air flotation cells, wherein the bubbles help to separate bitumen droplets from solids (sand and fine clays) and water of the middlings, thereby producing a (second) froth. The second froth may be recovered, for example, from the air flotation cell and may be combined with the first froth. Polysilicate microgels may be added in this process, typically in an amount of 25 to 5000g per tonne of oil sands. Alternatively, the second foam may be added to the slurry comprising the oil sands and water prior to processing the slurry to produce the first foam.

After the second foam is formed, the remaining slurry is separated in the reaction vessel or transferred to a separation vessel. Most of the sand and fine clay settles to the bottom of the slurry to form a bottom layer, called fine tailings, which contains less sand and more fines than coarse tailings. An intermediate layer may also be formed in the slurry. Both the middle and bottom layers may be combined and treated as fine tailings downstream of the dewatering step.

Optionally, the second foam-forming intermediate layer is removed as a second middling and further treated with air in the same way as the (first) middling, i.e. treated with air to generate a third foam. The third froth can be combined with the first froth and the second froth to recover the bitumen. The third foam may be added to the slurry comprising the oil sands and water prior to preparing the first foam, optionally after it is combined with the second foam. In another alternative, a third foam may be combined with the middlings prior to contacting the middlings with air. The second fine tailings are also prepared with a third foam.

Each successive froth formation step removes more bitumen from the oil sands. Although only three foams are described herein, subsequent foams (fourth, fifth, etc.) are contemplated within the scope of the present invention.

The method may further comprise removing foam from the top of the slurry in the extraction step and conveying the foam to a foam treatment unit. In the froth treatment unit, the froth is contacted with a solvent to extract bitumen from the froth and concentrate the bitumen. Typically, the solvent is selected from: paraffin group C₅-C₈N-alkane and cycloalkane solvents. Naphthenic solvents are typically coker naphtha with a final boiling point of less than 125 ℃ and hydrogenationAnd (4) naphtha. A by-product of the froth treatment unit is froth treatment tailings, which contain very fine solids, hydrocarbons and water.

After the froth is treated in the froth treatment unit, the concentrated bitumen product may be further processed to purify the bitumen.

The froth treatment tailings may be further treated in a dewatering step to remove water from the solids comprising fine clay and sand, and the removed water may be recovered in the process.

The process may also include dewatering the tailings. The tailings can be one or more of any tailings streams prepared in a process for extracting bitumen from oil sands ore. The tailings are one or more of coarse tailings, fine tailings and foam treatment tailings. The tailings may be combined into a single tailings stream for dewatering, or each tailings stream may be dewatered separately. Depending on the composition of the tailings stream, the additives, additive concentrations, and the order of addition of the additives may vary. Such changes may be determined empirically for different composition of the tailings stream.

The tailings stream comprises at least one of coarse tailings, fine tailings, and froth treatment tailings. The dewatering step comprises contacting the tailings stream with polyacrylamide and one or both of: (i) a polyvalent metal compound and (ii) a low molecular weight cationic organic polymer. The tailings stream may contain polysilicate microgels from the extraction step. Additional polysilicate microgel may be added as necessary. Polysilicate microgels facilitate flocculation of sand and fine clay in the dewatering step by: to better separate solids from water, and/or to increase the rate at which solids are separated from water, and/or to allow the dewatering step to withstand a range of operating conditions, yet achieve the desired level of solids separation from water in the desired time.

Dewatering can be achieved by means known to those skilled in the art. These include the use of thickeners, hydrocyclones and/or centrifuges, or by decantation and/or filtration. The dewatered solids should be disposed of according to government regulations. The separated water can be recycled to the process ("recycled water"). For example, reclaimed water may be added to crushed oil sands for extraction of bitumen. The recovered water may also be added to the process at any point where water is added.

Conventionally, it has been difficult to effectively dewater fine tailings and froth treatment tailings. Both of which contain fine clay and unextracted bitumen. Such tailings have been sent to tailings ponds after dewatering and over time become mature fine tailings. In the present invention even the separation of solids from fine tailings and froth treatment tailings is improved.

In an alternative embodiment of the process of the present invention, there is a process for extracting bitumen from a bitumen containing slurry, wherein the process comprises: providing a slurry comprising bitumen, wherein the slurry is middling, fine tailings or froth treatment tailings; the slurry is contacted with the polysilicate microgel to extract the bitumen from the slurry and to produce a froth comprising the bitumen and tailings. Preferably, the tailings are dewatered. The contacting, extracting and dehydrating steps are carried out as described above.

The method of the present invention can be used to treat low quality ores. Alternatively, a higher percentage of low quality ore may be combined with high quality ore in the extraction and dewatering process of the present invention.

In a second embodiment of the invention, there is provided a process for treating a tailings stream comprising sand, fine clay and water, the process comprising: (a) contacting the tailings stream with a polysilicate microgel, an anionic polyacrylamide, and a polyvalent metal compound and/or a low molecular weight cationic organic polymer to form flocculated solids; and (b) separating the flocculated solids from the tailings stream. The separation step may be carried out by dehydration. In this process, sand and fine clay are flocculated to produce flocculated solids. In the separation step, flocculated solids are separated from the tailings stream, for example by dewatering, to obtain solids and recovered water.

The tailings stream may be coarse tailings, fine tailings, foam process tailings, or a combination of two or more thereof. A process for preparing such a tailings stream is described above, except that in this embodiment no polysilicate microgel is added during the extraction process. Accordingly, a tailings stream suitable for use in this embodiment may be prepared from a conventional oil sand process for extracting bitumen. For example, the tailings stream treated herein can be a slurry comprising fine clay recovered from an oil sand solvent recovery unit. Further, as an alternative, the tailings stream may be mature fine tailings that have been removed from a tailings pond.

The purpose of the separation step is to flocculate and dewater the solids, while allowing as much water as possible to be recovered. Surprisingly, the present invention has achieved a faster rate of separation of solids from water and a more adequate degree of separation. Thus, the present invention has a higher process efficiency than conventional processes for treating tailings streams.

The solids can be disposed of, sent to tailings ponds for further precipitation, or when the solids are concentrated mineral sources (e.g., titanium and zirconium ores), the solids can be used as raw materials or feeds to make industrial products such as titanium and zirconium compounds.

The order of addition of the polysilicate microgel, anionic polyacrylamide, and polyvalent metal compound and/or low molecular weight cationic organic polymer may be varied to promote certain desired effects. For example, the polyvalent metal compound and/or the low molecular weight cationic organic polymer may be added first, and then the polyacrylamide may be added to the tailings stream. That is, the metal compound is added first, and then the polymer is added. In an alternative process, the following order of addition is used to add to the tailings stream in sequence: (1) a first polymer which is a polyacrylamide; (2) a polyvalent metal compound and/or a low molecular weight cationic organic polymer; (3) a second polymer which is a polyacrylamide. The first polymer and the second polymer may be the same or different polymers. For example, both the first polymer and the second polymer can be polyacrylamide; however, the first polymer is an anionic polyacrylamide and the second polymer may be a cationic polyacrylamide. In any of the addition methods disclosed herein, the polysilicate microgel may be added at any point in time. That is, the microgel may be added before or after the addition of the anionic polyacrylamide and the polyvalent metal compound and/or the low-molecular-weight cationic organic polymer, i.e., before or after the addition of (1), (2) and (3).

Dewatering can be achieved by means known to those skilled in the art for separating solids from the process water. These include thickeners, hydrocyclones, centrifuges, decantations and filtration. The dewatered solids should be disposed of according to government regulations.

It has surprisingly been found that the polysilicate microgel helps to flocculate sand and fine clay during the step of dewatering tailings prepared during the extraction of bitumen from oil sands ore, relative to known processes using polyacrylamide alone and polyacrylamide in combination with a metal salt. In particular, in the process of the present invention, solids are separated from water at a faster rate than in known processes. Furthermore, the percentage of water recovered from the process is higher and the recovered water can be recycled to the process.

It is desirable to recycle water to the oil sands ore extraction and recovery process to minimize the necessity of using fresh water as the process make-up water. The recovered water may be added to the crushed oil sands ore to produce a slurry for bitumen extraction. Alternatively, if the recovered water exceeds the needs of the process, it may be returned to the environment if the water meets local standards.

Furthermore, the addition of the polysilicate microgel during the extraction step does not adversely affect the dehydration step relative to known methods using sodium silicate. That is, the presence of sodium silicate is reported to hinder flocculation and separation of solids from tailings streams. Surprisingly, in the present invention, the addition of polysilicate microgel does not produce the same effect as sodium silicate. The use of sodium silicate also reduces the amount of water recovered and slows the rate of separation of solids from the water relative to the use of polysilicate microgels.

The process of the present invention is robust and can be used to achieve desired levels of bitumen extraction and water recovery from high and low quality ores. Furthermore, the present invention provides a generally simpler separation method and reduces equipment, for example avoiding the need for mechanical separation equipment. In addition, the process of the present invention can be used to treat fine tailings, recover bitumen from such tailings, and provide a source of mineral, and reduce the need for settling ponds.

Treatment of tailings streams

In a third alternative embodiment of the invention, there is a process for treating a tailings stream, the process comprising: (a) contacting the tailings stream with a silicate source and an activating agent; (b) embedding fine clay and sand in silica gel; (c) spreading the silica gel on the surface; and (d) drying the silica gel to produce a trafficable surface, wherein the silicate source is an alkali metal silicate, a polysilicate microgel, or a combination thereof, and wherein the tailings stream comprises water, fine clay, and sand, wherein 20% to about 100% by volume of the fine clay and sand have a particle size of less than 0.05 mm. Optionally, the tailings stream also comprises polysilicate microgels. Optionally, the treated tailings may be centrifuged or treated with other known dewatering techniques before spreading the embedded fine clay and sand on the surface in step (c).

The tailings stream comprises water, sand and fine clay, and optionally comprises polysilicate microgels. These tailings streams may be from tailings ponds and made from fine tailings that have been dewatered and deposited to tailings ponds and allowed to settle over time and froth treatment tailings. The tailings stream may also be derived from the bitumen recovery process as new tailings. The new tailings are typically thickened with polyacrylamide and may contain sand and/or polysilicate microgels from which the tailings stream is prepared. The tailings stream may also contain residual polysilicate microgels from the bitumen recovery process.

A process for treating a tailings stream comprising contacting the tailings stream with a silicate source and an activator can be adjusted to alter the gelling time. Adjustments include, but are not limited to, changing the order and/or concentration of addition of the silicate source and/or activator. For example, adding more alkali silicate to the tailings stream may reduce the yield stress for a short period (0.5 to 30 hours), but may result in an increase in the overall yield stress of no change or greater over a period of time. The gel time may also be varied by adjusting the pH, changing the order of addition of the activator to the silicate source, and/or the concentration of the activator.

Contacting the tailings stream with a silicate source and one or more activators, and optionally with a polysilicate microgel, to form a silica gel structure. The polysilicate microgel is as described above. After drying, the gel becomes a hard solid with a surface suitable for passage. The process can be adjusted to control the gel time. The gel time is the time required for the silicate source to form a solid gel-like structure. Preferably, the tailings stream is contacted with a silicate source and an activator prior to its application to the surface; gelation occurs at the surface, forming a thin solid surface suitable for traffic. The process of applying the product of contacting the tailings stream with the silicate source and the activator to the surface can be repeated multiple times to form a stack of hard solid silica gel layers comprising sand and fine clay of the tailings stream.

It is desirable to spread the silica embedding the tailings formed by the process over an inclined surface and allow it to dry. Drying is carried out by air drying (evaporation) and/or running off the water. If a run-off process is employed, the process water can be recovered and the run-off water recycled, for example, for reuse in bitumen extraction or tailings stream flocculation processes discussed below.

The process of treating a tailings stream can be carried out in a number of ways. The silicate source and activator may be added directly to the tailings stream in the tailings pond and the water evaporated. The tailings stream, silicate source and activator may be mixed in a vessel and spread on a surface and allowed to dry. The tailings stream, silicate source and activating agent may be mixed and centrifuged to facilitate separation with a reduced amount of silicate source and activating agent required. Preferably, the silicate source, activator and tailings stream may be combined in a transfer line prior to spreading them onto a surface for drying.

In a fourth embodiment of the invention, there is a process for treating a tailings stream comprising contacting said tailings stream with an alkali metal silicate. The addition of only the alkali metal silicate can reduce the solids concentration without gelling the mixture. The tailings stream can be treated using this process when residual bitumen remains in the tailings stream. The addition of only the alkali metal silicate will further disperse the suspended solids and promote the release of residual pitch. This may also be useful in situations where the solid product is not immediately needed, perhaps to be transported to a location for later processing or storage. The promotion of bitumen recovery and solids reduction by silicate addition may also be carried out at higher pH by adding caustic or using lower ratios of alkali metal silicate.

The process of the present invention is robust and can be used to achieve desired levels of bitumen extraction and water recovery from high and low quality ores. Furthermore, the present invention provides a generally simpler separation method and reduces equipment, for example avoiding the need for mechanical separation equipment. In addition, the process of the present invention can be used to treat fine tailings, recover bitumen from such tailings, and provide a source of mineral, and reduce the need for settling ponds.

Drawings

FIG. 1 is a process flow diagram of a bitumen extraction process and a tailings flocculation process according to the present invention.

The polysilicate microgel (PSM) and crushed oil sands (Ore) are combined in line 1 and delivered as feed 2 to a mixing vessel 3. Water is added to the mixing vessel 3 to prepare a slurry. Adding air to the slurry in the mixing vessel 3 to produce (1) a first froth 4, the first froth comprising bitumen and, after separation from the slurry, reaching the top of the mixing vessel 3; (2) coarse tailings 5, which contain most of the sand and fine clay from the feed 2 and which, after separation, reach the bottom of the mixing vessel 3; and (3) a middling 6, which contains bitumen, fine clay and sand and is an intermediate layer within the mixing vessel 3.

The first froth 4 is conveyed to a froth treatment vessel 7. Solvent is added to the treatment vessel 7 to extract bitumen 8 from the first froth while froth treatment tailings 9 are prepared within the treatment vessel 7. Bitumen 8 is conveyed outwardly from the treatment vessel 7 for further treatment. The froth treatment tailings 9 comprise water and fine clay and are further treated with other tailings streams.

The middlings 6 are removed from the middle of the mixing vessel 3 and transferred to a second mixing vessel 3 a. Water is added to the second mixing vessel 3 a. Adding air to the second mixing vessel 3a to produce a second froth 4a and fine tailings 10, wherein the second froth 4a comprises bitumen, fine clay and water, and is separated from the middlings 6 to the top of the mixing vessel 3 a; the fine tailings 10 contain sand, fine clay and water, and are separated into the lower half of the mixing vessel 3 a. The second foam 4a is combined with the first foam 4 and transported to the foam treatment vessel 7.

The coarse tailings 5, comprising sand, fine clay and water, are combined with the froth treatment tailings 9 and the fine tailings 10 to provide a combined tailings stream 11, which is conveyed to a separator 12.

Optionally, metal compounds and/or low molecular weight cationic organic polymers (MC/P), Polyacrylamide (PAM) and polysilicate microgel (PSM) are added to the combined tailings stream in separator 12. The combined tailings stream 11 is precipitated in a separator 12. Solids 13 comprising sand and fine clay are separated from the water 14. The solids 13 are transported to a tailings pond. The water 14 may be recycled by, for example, being delivered to the mixing vessel 3.

Examples

Materials and test methods

Material

Mature fine tailings used in the following examples were obtained from oil sand processing plants of Alberta, canada. The solids concentration was 29.2 to 29.9 wt%. The mature fine tailings had a median particle size of 12.95 μm and an average particle size of 20.9 μm, and 100% of the particles were finer than 0.05 mm. Yield stress measurements of the samples were obtained using a Brookfield rheometer equipped with a paddle rotor, providing results in Pa (pascal). The sodium silicate ratio used in the following examples was 3.22SiO₂:Na₂O。

Examples 1 to 3

Examples 1 to 3 show that the yield stress is increased by the addition of sodium silicate and an activator. Mature fine tailings (1000g) contained 29.9 wt.% solids, had a pH of 7.98, and had an initial yield stress of 3.7. Mature fine tailings were stirred in the reactor with a propeller stirrer at 600rpm while bubbling carbon dioxide activator (6psi) through a porous disc. After 10 minutes, the pH was 6.35. The carbon dioxide continues to bubble within the mature fine tailings for an additional 60 minutes. The pH was measured again and found to be 6.35. The mature fine tailings were then divided into 3 sections for use in examples 1 to 3.

Example 1

Example 1 shows the effect of sodium silicate on mature fine tailings. The carbon dioxide saturated mature fine tailings (200g) and sodium silicate (1.18 g, ratio 3.22 sodium silicate) were mixed in a 100mL Tripour beaker for 30 minutes. After standing for 30 minutes, the pH of the mixture was 7.42. Yield stress was measured at 30 minutes, 18 hours and day 6. The results are shown in Table 1.

Example 2

Example 2 shows the effect of sodium silicate and alkaline earth metal salt on yield stress. The carbon dioxide saturated mature fine tailings (200g), sodium silicate (1.18 g, ratio 3.22 sodium silicate) and calcium sulfate (0.22g) were mixed in a 100mL Tripour beaker for 30 minutes. After standing for 30 minutes, the pH of the mixture was 7.78. Yield stress was measured at 30 minutes, 18 hours and day 6. The results are shown in Table 1.

Example 3

Example 3 shows the effect of increasing sodium silicate on yield stress. The carbon dioxide saturated mature fine tailings (200g), sodium silicate (2.36 g, ratio 3.22 sodium silicate) and calcium sulfate (0g) were mixed in a 100mL Tripour beaker for 30 minutes. After standing for 30 minutes, the pH of the mixture was 8.72. Yield stress was measured at 30 minutes, 18 hours and day 6. The results are shown in Table 1.

TABLE 1

As can be seen from table 1, the yield stress increases over time after the addition of sodium silicate, and optionally calcium sulfate. Example 1 contains only sodium silicate and CO as activator₂. Example 2 contains sodium silicate and CO₂And calcium sulfate. Example 2 had a similar yield stress over the test time. Example 3 contains sodium silicate and CO₂And calcium sulfate. Example 3 shows the effect of increasing sodium silicate resulting in an increase in pH. The yield stress measurements at the first 30 minutes and at 18 hours showed a significant decrease in yield stress, but the yield stress measurements at day 6 remained consistent with those in examples 1 and 2. This result is beneficial if immediate hardening of the treated mature fine tailings is not desired. The increase in pH indicated that the gel fraction of the mixture resulted in a longer flow period.

Example 4

Example 4 shows the effect of adding sodium silicate and an organic compound on yield stress. Mature fine tailings (29.9 wt%, pH 7.98, yield stress 3.7), sodium silicate (21.60g) and ethyl acetate (4.12g) were mixed in a 100mL Tripour beaker. The beaker was left to stand for 20 hours. After 20 hours, the yield stress was 896 Pa.

Examples 5 to 7

Examples 5 to 7 show the effect of contacting mature fine tailings with sodium and calcium salts on gel time and weight loss.

Example 5

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH adjusted to pH 7 with sulfuric acid. The weight loss of the resulting mixture was then measured after 120 hours, 168 hours, 192 hours and 264 hours of storage. The results are shown in Table 2.

Example 6

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH adjusted to pH 7 with sulfuric acid. Calcium chloride (1.78g) was added and mixed well. The resulting mixture had a pH of 7.1, and then weight loss was measured after storage for 120 hours, 168 hours, 192 hours, and 264 hours. The results are shown in Table 2.

Example 7

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH adjusted to pH 7 with sulfuric acid. Calcium sulfate (1.6g) was added and mixed thoroughly. The resulting mixture had a pH of 7.22, and then weight loss was measured after storage for 120 hours, 168 hours, 192 hours, and 264 hours. The results are shown in Table 2.

As can be seen from Table 2, the gel time can be adjusted by adding calcium salt. The gel time after addition of the calcium salt was "instant" compared to the mixture without the calcium salt. The resulting weight loss was similar for all three examples.

TABLE 2

Examples 8 to 11

Examples 8 to 11 show the gelation of mature fine tailings with calcium salts without pH adjustment by addition of acid.

Example 8

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH was recorded in table 3. Calcium chloride (3.56g) was added and mixed well. The resulting mixture had a pH of 7.15, and then gel time and weight loss were measured after storage for 120 hours, 168 hours, 192 hours, and 264 hours. The results are shown in Table 3.

Example 9

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH was recorded in table 3. Calcium sulfate (3.2g) was added and mixed thoroughly. The resulting mixture had a pH of 9.91, and then gel time and weight loss were measured after storage for 120 hours, 168 hours, 192 hours, and 264 hours. The results are shown in Table 3.

Example 10

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH was recorded in table 3. Calcium chloride (1.78g) was added and mixed well. The resulting mixture had a pH of 8.06, and then gel time and weight loss were measured after storage for 120 hours, 168 hours, 192 hours, and 264 hours. The results are shown in Table 3.

Example 11

Mature fine tailings (100g, 29.2 wt% solids) and sodium silicate (1.25g) were mixed in a 100mL Tripour beaker and the final pH was recorded in table 3. Calcium sulfate (1.6g) was added and mixed thoroughly. The resulting mixture had a pH of 9.97, and then gel time and weight loss were measured after storage for 120 hours, 168 hours, 192 hours, and 264 hours. The results are shown in Table 3.

As can be seen from table 3, the mature fine tailings can be gelled with sodium and calcium salts without adjusting the pH. The weight loss amounts to examples 5 to 7 in which the pH was adjusted.

TABLE 3

Gel time could not be determined due to water exudation to the surface.

Examples 12 to 18

Examples 12 to 18 show the weight loss over time of pH adjusted mature fine tailings solutions using different amounts of sodium silicate and calcium sulfate.

Example 12

Mature fine tailings (450g, 29.2 wt% solids) were added to a beaker. The pH is adjusted to pH 7 with sulfuric acid. Sodium silicate (5.63g) and calcium sulfate (0.90g) were added to the beaker. The mixture was divided into 4 separate 100mL Tripour beakers. Two beakers (12a and 12b) were placed in a laboratory fume hood and two beakers (12c and 12d) were stored on a standard laboratory bench. Weight loss was measured on day 2, day 3 and day 6. The results are listed in table 4 as sample averages (samples a and b averaged as fume hood samples and samples c and d averaged as bench samples).

Example 13

Example 13 is a repeat of example 12 except that the calcium sulfate concentration (0.45g) is reduced. The results are shown in Table 4.

Example 14

Example 14 is a repeat of example 12 except that the calcium sulfate concentration (0.23g) is reduced. The results are shown in Table 4.

Example 15

Example 15 is a repeat of example 12 except that the sodium silicate concentration is reduced (2.80 g). The results are shown in Table 4.

Example 16

Example 16 is a repeat of example 15 except that the calcium sulfate concentration (0.45g) is reduced. The results are shown in Table 4.

Example 17

Example 17 is a repeat of example 12 except that the sodium silicate concentration (1.40g) is reduced. The results are shown in Table 4.

Example 18

Example 18 is a repeat of example 17 except that the calcium sulfate concentration (0.45g) is reduced. The results are shown in Table 4.

Example 19

Example 19 is a repeat of example 14 except that gypsum (0.23g) was added before the sodium silicate was added.

Comparative example A

Comparative example a is a water sample divided into 4 samples. The samples were exposed to the same conditions as in example 12 and 2 samples were averaged as fume hood samples and 2 samples were averaged as bench samples. The results are shown in Table 4.

As can be seen from table 4, excellent results can be obtained with various amounts of sodium silicate and calcium sulfate in the present invention. Surprisingly, the weight loss increased when sodium silicate and calcium sulfate were added compared to a water sample exposed to the same air conditions.

Example 20

Example 20 shows that the yield stress of a mixture of mature fine tailings and sand containing sodium silicate and two activators is increased. Mature fine tailings (100g, 29.9 wt% solids) at a pH of 7.98 and a yield stress of 3.7Pa were added to a beaker. Sand (200g, from an oil sands processing plant of Alberta, Canada) was added to the beaker. Sodium silicate (1.25g) was added to the beaker. The pH of the mixture was adjusted to pH 7 with sulfuric acid. Calcium sulfate (0.2g) was added to the mixture, and the mixture was stirred. The pH of the final mixture was 6.83. The yield stress was measured after 1 hour and 3 hours. The results are shown in Table 5.

Comparative example B

Comparative example B shows the yield stress of a mixture of mature fine tailings and sand. Mature fine tailings (100g, 29.9 wt% solids) at a pH of 7.98 and a yield stress of 3.7Pa were added to a beaker. Sand (200g, from an oil sands processing plant of Alberta, Canada) was added to the beaker. The pH of the final mixture was 8.21. The yield stress was measured after 1 hour and 3 hours. The results are shown in Table 5.

Comparative example C

Comparative example C shows the yield stress of a mixture of mature fine tailings and sand adjusted to pH 7 with acid, wherein no sodium silicate was added. Mature fine tailings (100g, 29.9 wt% solids) at a pH of 7.98 and a yield stress of 3.7Pa were added to a beaker. Sand (200g, from an oil sands processing plant of Alberta, Canada) was added to the beaker. The pH of the mixture was adjusted to 7 with sulfuric acid. The yield stress was measured after 1 hour and 3 hours. The results are shown in Table 5.

Comparative example D

Comparative example D shows the yield stress of a mixture of mature fine tailings and sand adjusted to pH 7 with acid, with additional calcium salt added, but no sodium silicate added. Mature fine tailings (100g, 29.9 wt% solids) at a pH of 7.98 and a yield stress of 3.7Pa were added to a beaker. Sand (200g, from an oil sands processing plant of Alberta, Canada) was added to the beaker. The pH of the mixture was adjusted to pH 7 with sulfuric acid. Calcium sulfate (0.2g) was added to the mixture, and the mixture was stirred. The pH of the final mixture was 6.93. The yield stress was measured after 1 hour and 3 hours. The results are shown in Table 5.

As shown in table 5, example 20 shows that yield stress can be significantly increased (by about an order of magnitude or more) by treating a mixture of mature fine tailings and sand with sodium silicate, adjusting its pH to 7, and then adding calcium sulfate. The mixture of untreated mature fine tailings and sand has a low yield stress. The mixture of mature fine tailings and sand adjusted to pH 7 also exhibited the same low yield stress measurement as the untreated mixture. Adjusting the pH of the mixture of mature fine tailings and sand to 7, followed by the addition of calcium sulfate, the yield stress of the mixture increased, but still significantly below the level of example 20.

Example 21

Example 21 shows the effect of adjusting the mixture of mature fine tailings and sodium silicate to pH 8 with acid on gel time. Mature fine tailings (220g, 29.9 wt% solids) at pH 7.98 were added to the beaker. Sodium silicate (2.75g) was added to the beaker. The pH of the mixture was adjusted to pH 8.03 with sulfuric acid (0.5N). The mixture gelled.

Example 22

Example 22 shows the effect of adjusting the mixture of mature fine tailings and sodium silicate to pH9 with acid on gel time. Mature fine tailings (220g, 29.9 wt% solids) at pH 7.98 were added to the beaker. Sodium silicate (2.75g) was added to the beaker. The pH of the mixture was adjusted to pH9.01 with sulfuric acid (0.5N). The mixture was still fluid after 24 hours, but gelled after 2 weeks.

Examples 21 and 22 show that gel formation times can be extended by up to several days by reducing the amount of activator added.

Example 23

Example 23 illustrates the effect of adding sodium silicate to mature fine tailings without the addition of an activating agent. Mature fine tailings (220g, 29.9 wt% solids) at pH 7.98 were added to the beaker. Sodium silicate (2.75g) was added to the beaker. The pH of the mixture was not adjusted. After a few hours, a bottom solid was formed. The resulting suspended solids concentration was 16.3%.

Example 24

Example 24 illustrates the effect of adding sodium silicate to mature fine tailings adjusted to pH 11 without the addition of an activating agent. Mature fine tailings (220g, 29.9 wt% solids) at pH 7.98 were added to the beaker. Mature fine tailings (220g, 29.9 wt% solids) at pH 7.98 were added to the beaker. Sodium silicate (2.75g) was added to the beaker. The pH of the mixture was adjusted to 11.03 with sodium hydroxide (1N). After a few hours, a bottom solid was formed. The resulting suspended solids concentration was 15.6%.

Example 25

Example 25 illustrates the effect of adding sodium silicate to mature fine tailings adjusted to a pH of 12 without the addition of an activating agent. Mature fine tailings (220g, 29.9 wt% solids) at pH 7.98 were added to the beaker. Sodium silicate (2.75g) was added to the beaker. The pH of the mixture was adjusted to 12.01 with sodium hydroxide (1N). After a few hours, a bottom solid was formed. The resulting suspended solids concentration was 15.5%.

As shown in example 23, the mature fine tailings can be modified to have a lower solids concentration than untreated mature fine tailings by the addition of sodium silicate alone. The product was a mixture with reduced solids concentration and the product did not gel. Examples 24 and 25 show that increasing the pH also results in a decrease in the solids concentration of the mixture and does not produce a gelled product. In examples 22, 23, 24 and 25, the surfaces of the tailings treated with silicate had a distinct layer of asphalt.

Claims (11)

1. A process for treating a tailings stream, the process comprising: (ii) (a) contacting the tailings stream with a silicate source and an activator; (b) embedding fine clay and sand in silica gel; (c) spreading the silica gel on a surface; and (d) allowing the silica gel to dry to produce a trafficable surface, wherein the silicate source is an alkali metal silicate, and wherein the tailings stream comprises water, fine clay and sand, wherein 20% to 100% by volume of the fine clay and sand have a particle size of less than 0.05 mm; wherein the activator is any compound or mixture of compounds that can initiate the gelation of the alkali metal silicate.

2. The method of claim 1, wherein the activator is an acid, an alkaline earth metal salt, an aluminum salt, an organic ester, a dialdehyde, an amide, or a combination thereof.

3. The method of claim 2, wherein the organic ester is an organic carbonate or an organic phosphate.

4. The method according to claim 1, wherein the activator is sulfuric acid, carbon dioxide, phosphoric acid, sodium phosphate, sodium bicarbonate, hydrochloric acid, sodium bisulfate, acetic acid, or a combination thereof.

5. The method according to claim 2, wherein the activator is an acetate ester of glycerol, glyoxal, ethylene carbonate, propylene carbonate, formamide, or a combination thereof.

6. The process according to claim 1, wherein the activator is calcium chloride, calcium oxide, calcium carbonate, calcium sulfate, magnesium chloride, aluminum sulfate or sodium aluminate.

7. The process of claim 1 wherein the activator is sulfuric acid or carbon dioxide.

8. The process according to claim 2, wherein the activator is calcium sulfate or calcium chloride.

9. The process according to claim 2, wherein two or more activators are used.

10. The process according to claim 1, wherein the tailings stream is from a tailings pond.

11. The process according to claim 1, wherein the silicate source, activator and tailings streams are combined in a transfer line before being spread on a surface and allowed to dry.