CA2689684A1 - Processes for treating oil sands tailings - Google Patents

Abstract

Processes for treating oil sands tailings are capable of minimizing or eliminating potential adverse impacts of chemical application to tailing treatment on bitumen extraction within the area of tailing treatment regardless of the types of chemicals (flocculants/
coagulants) used and significantly enhancing in both dewatering and consolidation of the sludge layer in a dynamic thickening pond or a static thickener. Tailing deposits are used to make up loam soil suitable for deep-rooted plants, e.g. alfalfa, to grow and remove water retained in the tailing deposits hydroponically, as a result, the tailing deposit can be reclaimed to trafficable criteria within three years.

Description

PROCESSES FOR TREATING OIL SANDS TAILINGS
Cross reference to related application [0001] This specification includes materials in common with a patent application US
61/149,285 filed on February 2, 2009 and a patent application US 61/242,035 filed on Sep 14, 2009 with the same title, inventor and assignee as this application. This application also includes two additional embodiments.

Field of the Invention

[0002] The invention relates to processes for oil sands tailing treatment with application of different chemicals for different purposes (thickening, settling and consolidation), such as flocculants, coagulants, and pH modifiers (flue gas (mainly for carbon dioxide, CO2) or acetic acid). For thickening, the chemicals can be any kind of high performance flocculants and/or coagulants, regardless of their potential adverse impacts on bitumen extraction. The chemical's adverse impacts on bitumen extraction is minimized and controlled within tailing treatment area. Flue gas or acetic acid is used as a pH modifier to improve dewatering and consolidation of tailing sediment. The invention also relates to a process for tailing deposit reclamation to a trafficable surface using hydroponic power of deep-rooted plants, e.g. alfalfa.
Background

[0003] Oil sand is essentially a matrix of bitumen, mineral material and water. Oil sand deposits are mined for the purpose of extracting bitumen from them, which is then upgraded to synthetic crude oil. First, the oil sand is mined in open-pit mine using trucks and shovels.
The oil sand lumps are crushed and then mixed with recycle process water in mixing boxes, stirred tanks, cyclo-feeders (Syncrude Canada Ltd.) or rotary breakers (Suncor Energy Inc. and Albian Sands Energy Inc.). The conditioned oil sand slurry is introduced to hydrotransport pipelines or to tumblers, where the oil sand lumps are sheared and size reduction takes place.
Within the tumblers or the hydrotransport pipelines bitumen is released, or "liberated", from the sand grains. Chemical additives, used as dispersants, can be added during the slurry preparation stage. Entrained or introduced air attaches to bitumen in the tumblers and hydrotransport pipelines. Second, the slurry is separated by allowing the sand and rock to settle out, and the bitumen, having air entrained within it floats to the top of the slurry and is withdrawn as bitumen froth. Third, the remainder of the slurry, which is referred to as a middling, is then treated further or scavenged by froth flotation techniques to recover bitumen that did not float to the top of the slurry during the separation step.

[0004] To assist in the recovery of bitumen during the separation step, sodium hydroxide (caustic) is typically added to the slurry during the conditioning step in order to disperse the sand grains and maintain the slurry slightly basic, having a pH in the range of 8.0 to 8.5. This has the effect of chemically dispersing the clay in the slurry during the conditioning step, which results in the middling stream a huge disposal problem, since it constitutes a sludge that tends to settle and consolidate very slowly. Current practice for the disposal of the sludge remaining after the scavenging step involves pumping it into huge tailing ponds, where the fines slowly settle and stratify. After several weeks, some of the water forming the sludge will be present at the top of the tailing pond containing only a small amount of suspended fines.

The remaining sludge continues to settle and gradually increases in density over a period of perhaps 10-20 years, the solids concentration of the sludge may increase to up to 50%.
Complete settlement and consolidation of the sludge may take in the order of hundreds of years. It is thought that the reason for the slow consolidation of the sludge is that the clays that become physically and chemically dispersed during the water process partially re-flocculate into a fragile gel network.

[0005] In any event, because of the characteristics of the middling sludge, the tailing ponds can not be completely rehabilitated for many years, and only a portion of the water that enters the tailing ponds can be recovered and reused in the bitumen extraction process, thus creating a requirement that a large amount of make up water be available to make up for the water that is lost to the tailing ponds.

[0006] Some attempts have been made to improve the oil sand process in two ways: 1) modification of the bitumen extraction process to minimize dispersing the clays in middling, such as U.S. Pat. No. 4,414,117 and U.S. Pat. No. 5,723,042; and 2) application of flocculants in tailing treatment, such as U.S. Pat. No. 4.225,433 and U.S. Pat. No.
5,723,042.

[0007] U.S. Pat. No. 4,414,117 and U.S. Pat. No. 5,723,042 disclosed methods to control carbonate and bicarbonate ions in bitumen extraction process to minimize dispersion of clays in middling. U.S. Pat. No. 4,414,117 teaches that the removal of carbonate and bicarbonate ions can be accomplished in several ways, such as by the use of an ion exchange resin, the addition of an ion precipitant, or the use of a mineral acid such as hydrochloric acid to convert the carbonate and bicarbonate ions to CO2. It is stated that best results are obtained when essentially all of the carbonate and bicarbonate ions are removed from the system with the result being that the settlement rate of the sludge is significantly accelerated. U.S. Pat. No.
4,414,117 teaches that the concentration of bicarbonate ions in the warm water should preferably be maintained at less than about 6 Meq/liter. Since bicarbonate ions tend to form in solution when the pH of the solution is higher than about 7 and will leave the solution when the pH is lower than about 7, the bicarbonate ion concentration in the warm water is preferably controlled by adding an acid to the warm water to reduce its pH.

[0008] U.S. Pat. No. 4.225,433 and U.S. Pat. No. 5,723,042 disclosed methods to promote settlement of the dispersed fine material in suspension by adding a flocculant to the suspension, which relates to a process whereby the solid material and the sludge that is generated during the bitumen extraction process is combined together, mixed with a flocculating agent to separate water and solid material. The fines form agglomerates with the coarse particles and that the agglomerates settle at a rate comparable to that of the solid material alone.

[0009] Other efforts have focused on the characteristics of the solids tailings and sludge tailings as a whole in the feasibility of combining them together to create a waste stream that is easier to handle. Cymerman, G. J., Prediction of Viable Tailings Disposal Methods.
Proceedings of a Symposium: Sedimentation Consolidation Models, ASCE/October 1984, San Francisco, Calif.). This paper indicates that tailings typically produced by Syncrude Canada Ltd. at Fort McMurray, Alberta tend to be a segregating mix so that the solid material settles out from the tailings quickly, leaving the sludge. Segregation is detrimental due to the problems associated with the disposal of the sludge. To prevent fines segregation, it is stated that it is necessary to lower the water content of the tailings stream, increase the fines content of the tailings, or do both. Based upon this analysis, the authors conclude that promising proposals include the mixing of mature sludge taken from the bottom of tailing ponds with a thickened sand tailing to produce a non-segregating mix, or the mixing of sand, sludge and overburden stripped from the mine site in order to produce a non-segregating mix.

[0010] To accelerate tailings handling, Suncor and Syncrude are using consolidated (composite) tailings (CT) process. This process entails adding gypsum to mature fine tails to consolidate the fines together with the coarse sand into a non-segregating mixture. CT is disposed of in a geotechnical manner that enhances its further dewatering and eventual reclamation. At Albian Sands, the tailings from the extraction plant are cycloned, with the overflow (fine tailings) being pumped to thickeners and the cyclone underflow (coarse tailings) to the tailing pond. Fine tailings are treated with flocculants, then thickened and pumped to a tailing pond. The three oil sand operators are considering the use of paste technology (addition of flocculants /polyeletrolytes), consolidated or composite tailings, CT, or a combination of the two (i.e., CT and paste technology) for fast water release and recycle of the water in CT to the extraction plant for bitumen recovery from oil sands.

[0011] As a general rule, the higher the fine material content in an oil sand deposit, the more difficult the oil sand is to process for the extraction of bitumen. The higher the content of the fine material in the oil sand, the more sludge that is generated by the extraction process; and the more difficult the disposal problem for the sludge.

[0012] It can therefore be seen that the challenge in extracting bitumen from oil sand is to maximize the recovery of bitumen while minimizing the amount of sludge that is generated, and while controlling the physical characteristics of the sludge so that it may be more easily disposed of in an economical and environmentally acceptable.

Limitation of the existing technologies

[0013] It is imperative to achieve as high bitumen recovery as possible and recycle as much process water as possible so that the amount of makeup water required is minimized. Practice experiences showed that good chemicals (flocculants/coagulants) for tailing treatment normally have an adverse impact on bitumen extraction, and good chemicals for bitumen extraction have adverse impacts on tailing settlement. The adverse impacts do not show up immediately after chemical applications. Because it takes a long time for the added chemicals to reach a dynamical chemical equilibrium in huge tailing ponds and for the adverse effects of chemical addition take place in the use of recycle water. The potential adverse impacts of chemical application in tailing treatment on bitumen extraction must be considered in any attempt of tailing treatment due to their opposite (dispersion for bitumen extraction and sedimentation for tailing treatment) technical natures. It is highly demanded that there is a method available to control the potential adverse impacts within tailing treatment area. The adverse impacts will be enhanced after the Directive 074 is in effect that was release in February 2009, as more recycle water will be available and less fresh water will be required, meaning the residual chemicals in recycle water would be concentrated to negatively influence extraction processes if the adverse impact is not minimized or eliminated within tailing process. This adverse impact will limit the application of some high performance chemicals and lead engineers have to use moderate chemicals for tailing treatment that have lower adverse impacts on bitumen extraction. The use of moderate performance chemicals for tailing treatment results in instability of forming non-segregating tailing deposit, and incapability of meeting the criteria of Directive 074.

[0014] In addition, current available composite tailing (CT) technology has operational instability in forming non-segregating tailings due to insufficient coarse sands for CT, as some sands are used for building tailing pond dykes. To form stable non-segregating tailing deposit, sand to fine ratio needs to be 4-5. The sand to fine ratio in raw oil sands is typically 4.25, meaning that almost all sands are required for capturing fines in CT process.
Using part of coarse sands deposited on beach for tailing pond dykes will make remaining coarse sands impossible to capture all fines, and hence results in CT operation instable.

[0015] Further more, the CT deposit needs more than 10 years to drain its water, and can not reach strength of 10 kPa or the trafficable criteria of Directive 074 within 5 years.

[0016] Some attempts of planting deep-rooted perennials in overburden that covers the CT
deposit as top soil to remove water from CT deposit have failed due to inhomogeneity of the overburdens. Overburdens have a variety of segregated compositions and may be not suitable for plants to grow, such as mainly sands or mainly clay overburden layers.
Sorting overburdens into desirable loam soil textures is a challenging and costly task.

Summary of The Invention

[0017] An adverse impact minimization process (AIMP) is provided, which can minimize or eliminate the potential adverse impacts of chemical addition in tailing treatment on bitumen recovery in bitumen extraction from oil sands. With AIMP, any high performance chemicals (flocculants/coagulants) can be used for tailing treatment to significantly enhance in both i dewatering and consolidation of the sludge layer in a small thickening pond or a vessel regardless of their potential adverse impacts on bitumen extraction. As a result, more process water can be available and recycled for bitumen extraction, and fresh water import can be reduced by 36.6%.

[0018] There are two types of AIMP applications: dynamic pond and static pond.
Dynamic pond processes use a small moving thickening pond and a moving settling pond and are suitable to capture a portion of fines, e.g. 50%. The tailing deposits accumulate at dykes and expend inward to the thickening pond, requiring the thickening pond expansion in the opposite side; at the same time, the un-captured fines accumulate in the settling pond as inventory and requires its pond expansion in size. The static pond processes use a small size-fixed thickener and a size-fixed settling pond and are suitable to capture all fines. The tailing deposits are transported to and stacked in a dedicated disposal area. A
variety of application cases with AIMP are disclosed. A pH modifier (flue gas or acetic acid) could be optionally used to accelerate water drainage from the tailing deposits. Make-up loam soil that is formed by using tailing materials (sands, clays and silts) is placed on top surface of the tailing deposit for deep-rooted plants, such as alfalfa, to grow and remove water hydroponically and make the surface trafficable within 3 years.

[0019] Four cases of the applications with AIMP are disclosed, two of them belong to dynamic pond; they are the base case without a pH modifier (embedment 1) and the case with a pH modifier (embedment 2) for accelerating water drainage from tailing deposits. Another two cases belong to static pond, one is raw tailing split process (RTSP,) and another is fine tailing split process (FTSP). The RTSP (embedment 3) applies AIMP principle to raw tailings directly and split the raw tailing between a thickener and sand collector;
while the FTSP
(embedment 4) applies AIMP principle to fine tailings after coarse sands are removed using a sand collector, the fine tailing is then split between a thickener and a settling pond.

[0020] Each of the four cases can be considered as an independent service process with a tailing receiving line and a recycle water delivering line. The tailing receiving line can receive sludge's from different streams individually as a localized tailing process or any kind of combined sludge of different streams as a whole process.

Brief Description Of The Drawings

[0021] Fig. 1 is a schematic flow diagram of the process (embedment 1) for treating oil sands tailings with a feature of minimizing or eliminating the adverse impacts of chemical (flocculants/coagulants) addition in tailing treatment on bitumen extraction.

[0022] Fig. 2 is a schematic flow diagram of the process (embedment 2) for treating oil sands tailings with a feature of tailing sediment dewatering, compaction and consolidation.

[0023] Fig. 3 is an illustration of sediment placement for compaction (sectional view and bird view).

[0024] Fig. 4 is a schematic flow diagram of the process (variation of embedment 2) for treating oil sands tailings with a feature of tailing sediment compaction and a self contained flue gas generator.

[0025] Fig. 5 is a chart showing dependent carbonate equilibrium i

[0026] Fig. 6 is chart showing total CO2 concentration in water as a function of pH at different CO2 volume percentages.

[0027] Fig. 7 is a raw tailing split process (embedment 3).

[0028] Fig. 8 is a fine tailing split process (embedment 4).

[0029] Fig. 9 is an illustration of the performance for both the raw tailing split process and the fine tailing process.

[0030] Fig. 10 is a site plan option A of the present invention: tailing settling pond in overburden area adjacent to mining area.

[0031] Fig. 11 is a site plan option B of the present invention: tailing settling pond in an external area.

[0032] Fig. 12 is a schematic illustration of the mixed tailing deposit disposal with a layer of make-up loam soil spreading on top surface suitable for deep-rooted plants to grow in a dedicated disposal area.

Detailed Description of Preferred Embodiments

[0033] One of the embedment of the present invention is described below with reference to Fig. 1. Fig. 1 is a schematic illustration of one embedment (embedment 1) of the present invention, including an adverse impact minimization process (AIMP) that minimizes or eliminates the adverse impacts of chemical (flocculants/coagulants) addition in tailing treatment on bitumen extraction. The AIMP process for treating oil sands tailings comprising:
a thickening pond to receive tailings from bitumen extraction units and bitumen froth _10-I

treatment unit via a tailing receiving line, a tailing settling pond to receive and hold a mixture of the fines-containing water, transferred via a water transfer line from the thickening pond to the settling pond, and the tailing received for further solids/water separation, a recycle water line with a chemical injection point for withdrawing recycle water from the settling pond for water reuse in bitumen extraction from oil sands, and a sludge transfer line for transferring sludge/suspension from the settling pond back to the tailing receiving line.
The chemical injection point can accept any kind of high performance chemicals (flocculants/coagulants), regardless of their adverse impacts on bitumen extraction, as the residual amount of added chemicals in the water withdrawn from the thickening pond can be consumed by mixing the tailing received from tailing receiving line before discharging the water to the settling pond.

[0034] Detailed descriptions of the embedment of the present invention are as follows:

[0035] With reference to Fig. 1, showing a schematic flow diagram of the process for treating oil sands tailings, the oil sands are fed into the system through a line 1 and passed to a conditioning drum 10. Water is introduced into the drum through line 2. The total water introduced is a minor amount based on the weight of the oil sands processed.
The conditioned pulp passes through a line 3 to a screen 20. The purpose of the screen 20 is to remove oversize materials 21, such as rocks or oversized lumps of clay from the pulp. The oversize materials are discarded at a suitable site. The conditioned pulp passes through a line 22 to a feed sump 30 which serves as a zone for diluting the pulp with additional water before it enters a separation zone 40.

[0036] The diluted pulp is continuously flushed from the feed sump 30 through a line 31 into the separation zone 40. The settling zone within the separator 40 is relatively quiescent so that i I

bituminous froth rises to the top and is withdrawn through a line 41 while the bulk of the sand component settles to the bottom as a tailing layer which is withdrawn through line 42.

[0037] A relatively bitumen-rich middling stream is withdrawn through line 43 to maintain the middling layer between the froth and the sand layer at a functional viscosity. This middling material is transferred to a flotation scavenger zone 50 where an air flotation operation is conducted to bring about the formation of additional bituminous froth which passes from the scavenger zone 50 through line 51, in conjunction with the primary froth from the separation zone 40 passing through line 41, to a froth settler zone 60. A
bitumen-lean water stream is removed from the bottom of the scavenger zone 50 through line 52. In the froth settler zone 60, some further bitumen-lean water is withdrawn from the froth and removed through line 61 to be mixed with the bitumen-lean water stream from the flotation scavenger zone 50 and the sand tailings stream from the separation zone 40.
The bitumen from the settler 60 is removed through line 62 for further treatment.

[0038] Bitumen-lean water from the froth settler 60, the scavenger zone 50, and the separation zone 40, all of which make up a mixed discharge stream carried by line 44, are split into two tailing streams: branch line 44a and branch line 44b. The line 44 that carries the mixed discharge stream is also referred to as tailing receiving line to the tailing treatment of present invention. The tailing carried in line 44a is discharged into a tailing thickening pond 70 which has a clarified water layer 71 and a sediment layer 72. The sands included in the tailing stream quickly settle in the region 73, and the fines-containing water flows into the body of the pond 70 where settling takes place. The sediment layer 72 of the thickening pond 70 is overlayed i with a clarified water layer 71. A mineral-to-water ratio in the sediment layer 72 increases from top to bottom.

[0039] In a application of high performance chemicals (flocculants/coagulants), the clarified water in the thickening pond consists of some residual high performance chemicals (flocculants/coagulants) and is withdrawn through a water transfer line 75 and mixed with the tailing from the branch line 44b then transferred to the tailing settling pond 80 at an inclined sand pile 81 situated adjacent a dyke 82. The volume ratio of the clarified water to tailing is controlled in a range so that the residual high performance chemicals (flocculants/coagulants) in the clarified water can be consumed to the level at which its adverse impacts on bitumen extraction can be minimized or even eliminated by the mixed excess amount of tailing. To improve the tailing settling in the settling pond, a moderate performance chemical (flocculants/coagulants), such as gypsum or a mixture of gypsum and lime, is added to the clarified water at the chemical injection point 76, denoted as chemical for settling pond (C.S.).
The type of the C.S. must be proven no significant adverse impacts on bitumen extraction; and the amount of the C.S. must be well controlled.

[0040] The sands included in the mixture quickly settle at the inclined sand pile 81 situated adjacent the dyke 82, and the fines-containing water flows into the body of the settling pond, which comprises a clarified water layer 83 on the top and a sludge/ suspension layer 84 at the bottom. The sludge/suspension 84 is commonly referred to as mature fine tailing (MFT). The MFT 84 is withdrawn from the settling pond 80 via a sludge withdrawal mean 90 and is transferred to a line 93 by a pump 92 which is supported by a flotation mean 91 on the surface of the pond 80. The MFT transferred from the line 93 is combined with the tailing material carried by the branch line 44a from the extraction process for recovering bitumen from oil sands.

[0041] The MFT 84 withdrawn from the bottom of the settling pond may be mixed with the clarified water 83 withdrawn from the top of the settling pond by a pump 94 via a water transfer line 95 then a branch line 95a to archive a high water to solids weight ratio for a better solids/water separation in the thickening pond. Preferably, water to solids weight ratio is in a range of 0.5 to 5. The higher the water to solids ratio, the larger the size of the flocs can be formed, hence the quicker settling speed and the denser of the flocs.

[0042] Chemicals (flocculants/coagulants) are capable of enhancing in both solids settling and sediment thickening. High performance chemicals (flocculants/coagulants) can be added at the chemical injection point 100, denoted as chemical for thickening pond (C.T.), to the MFT
being transferred by the line 93. To obtain a very high degree of thickening and dewatering, the high performance chemicals (flocculants/coagulants) can be relatively over dosed;
regardless the potential negative impacts on bitumen extraction due to recycling the clarified water. However, the high performance chemical dosage should be optimized in an ideal fashion. If little chemicals are used, adequate thickening of the sludge may take longer than the desired time. If too much chemicals are used, large, loose flocs tend to be generated, which do not thicken in an ideal fashion. Different amounts of chemicals may be required if different types of chemicals (flocculants/coagulants) are used.

[0043] The clarified water layer 83 in the settling pond only consists of marginal amount of chemicals due to that significant excess amount of tailing from the tailing branch line 44b can consume most of or all of the residual high performance chemicals (flocculants/coagulants) in the clarified water layer 71, minimizing the potential negative impacts of recycling the clarified water 83 back to bitumen extraction.

[0044] Recycle water withdrawn by the pump 94 from the clarified water layer 83 in the settling pond is transferred via the line 95 back to bitumen extraction process for water reuse.
The line 95 comprises three branch lines, one line 95a combines with the MFT
transfer line 93, another two branch lines 95b and 95c for oil sands conditioning and diluting the conditioned oil sands, respectively.

[0045] The embedment of the present invention enclosed in the dashed box as shown in Fig. I
can be considered as an independent service process with one tailing receiving line 44 and one recycle water delivering line 95. The tailing receiving line 44 can receive sludge from different streams individually as a localized tailing treatment process or any kind of combined sludge of different streams as a whole tailing treatment process.

[0046] There is an internal circulation loop in the process of treating oil sands tailings of the present invention to minimize even eliminate the adverse impacts of high performance chemical addition in tailing treatment on bitumen recovery in bitumen extraction from oil sands. The internal circulation comprises the MFT transfer line 93 and the water transfer line 75. The high performance chemicals (flocculants/coagulants) can be slightly over dosed (if required) into the MFT transfer line 93 to achieve better solids/water separation, while excess amount of tailing can be combined into the water transfer line 75 to consume the over dosed or residual chemicals.

i

[0047] A significant difference between the C.T. and the C.S. is that C.T. can be any kind of high performance chemicals (flocculants/coagulants), while C.S. must be proven type that has no significant adverse impacts on bitumen extraction.

[0048] Referring now to Fig. 2, whereby another embedment (embedment 2) of the current invention is employed in combination with a pH modifier (such as flue gas (CO2) or acetic acid) injection and replacement of materials that were settled previously and contain less moisture to improve tailing sediment compaction and eventually consolidation along the dyke of the thickening pond. Flue gas or acetic acid is injected at an injection point 112 to the sediment carried by the sludge line 111 and is withdrawn from the sediment layer 72 in the thickening pond by a sludge pump mounting on a suspension unit 110. The sediment after pH
modification is then discharged along the dyke 73 directly or combined with the materials taken from the outside of the dyke 73 in a mixing mean 114 before discharging it to the inside of the dyke 73. Carbon dioxide (CO2) present in the injected flue gas reacts with water and produces carbonic acid. This reaction changes the pH of the sediment and allows fines clays, silts and sands to settle and the water to release. The low moisture materials taken from the outside of the dyke 73 help the dewatering, compaction and eventually consolidation of the low pH sediment. The low moisture materials can be loaded using loaders or transported using a conveyer 113 to the mixing mean 114. After mixing with the low pH sediment, the mixture is discharged to the inside of the dyke 73 using an auger or a conveyer 115.
The mixing ratio of low moisture material to the low pH sediment needs to be changed according to the water content in the sediment to achieve the best compaction.

[0049] Fig. 3 is a more detailed illustration of the mixed material placement for compaction (sectional view and bird view) and consolidation according to embedment 2 of the present invention. The dyke is formed from two discharging operations; one is from the line 44a where there is no pH modifier involved; another is from the auger or conveyer 115 where a pH modifier is involved. The dyke can be built in such a way that the discharges with (120 and 122) and without (73, 121 and 123) a pH modifier can be placed alternatively to achieve the best compaction and eventually consolidation.

[0050] Another benefit of flue gas injection to tailing sediment is that the CO2 can react with the minerals in the tailings to form mineral carbonates. Flue gas can be captured from utility or upgrading facilities and piped to the injection point. This process will reduce the footprint of the tailing ponds and the amount of fresh water needed to process bitumen.
At the same time, it can be expected that this process of sequestering CO2 into tailings will eliminate some of CO2 emission produced in oil sands operations.

[0051] Chloride acid should not be used as a pH modifier, because residual chloride stays in recycle water and can be taken into downstream and creates significant corrosion problems in upgrading.

[0052] Referring to Fig. 4, whereby a variation of embedment 2 of the present invention is employed in combination of a self contained flue gas generator to produce flue gas (CO2) and replacement of the low moisture material to improve tailing sediment compaction and eventually consolidation along the dyke of the thickening pond. The flue gas is generated using a co-combustion burner 123 that burns variety of inexpensive fuels 124, such as used oils, scrape tires, coal, petroleum coke and sludge's containing high level of oil. The heat contained in the hot flue gas is recovery by using a heat exchanger 120 that heats up the recycle water before its delivery to bitumen extraction plant via line 121.
After heat recovery, the flue gas is then injected to the sediment at the injection point 112 on sludge line 111. This self contained flue gas generator 123 combining with the heat exchanger 120 provides warm recycle water for bitumen extraction, which can reduce the load to utility.

[0053] Fig. 5 is a chart showing dependent carbonate equilibrium. Bitumen extraction is operated at approximately pH 8.5. To further dewatering by using CO2 in flue gas to produce sufficient carbonic acid, it is necessary to bring pH of the water in sludge from 8.5 to 4.5 as shown in Fig. 5.

[0054] Fig. 6 is a chart showing total CO2 concentration in water as a function of pH at different CO2 volume percentages. Based on lab tests, to achieve significant dewatering performance, total CO2 concentration in sludge needs to be higher than 50 mg/L
at pH 4.5, which requires that CO2 concentration in the flue gas injected should be higher than 5% by volume. This requirement can always be satisfied as any flue gas has more than 5% CO2, for example, CO2 volume concentration is 9.5% in flue gas produced by burning natural gas; and 14.4 % by burning bitumen.

[0055] Embedment 1 shown in Fig. 1 and embedment 2 shown in Fig. 2 as well as the variation of embedment 2 shown in Fig. 4 are deployed by using a dynamic thickening pond and a dynamic settling pond. Fines are captured partially, e.g. 50%, and the sand deposits on beach of the settling pond can be used for building dykes to expend the settling pond.

i

[0056] Referring to Fig. 7, whereby another embedment (embedment 3) of the present invention is employed by changing the dynamic thickening pond into a static thickener 130 and the dynamic setting pond into a static sand collector 140 and a static settling pond. Raw tailing in line 44 is split into two streams of branch line 44a to the thickener 130 and branch line 44b to the sand collector 140 where coarse sands settle at the bottom and the fines overflow into the settling pond via line 142. The sand collector works as if it collects sands from beach in the case of dynamic thickening pond and allows only fines to run off. All settled sands in the sand collector are collected and exit as underflow 141 and mixed with thickener underflow 131 using a blender 150 to make a stackable tailing deposit for disposal in a dedicated disposal area. Both the thickener underflow 131 and the sand collect underflow 141 are exited by using a screw or a spiral mechanism as they are not pumpable.

[0057] To capture all fines using coarse sands, sediment in the settling pond is withdrawn via line 93 and a high performance chemical is injected at the injection point 100 into the sediment. After combining the sediment in line 93 into line 44a and mixed using an inline mixer, the mixture is discharged into the thickener for flocculation and separation. To minimize adverse impacts of the residual high performance chemical remaining in thickener overflow, the thickener overflow 132 is mixed with raw tailing in the branch line 44b to consume the residual amount of the high performance chemical. A moderate performance chemical is added to the thickener overflow 132 at injection point 76 before mixing the overflow 132 with the raw tailing 44b to facilitate remaining fines to settle in the settling pond.

i

[0058] Referring to Fig. 8, whereby another embedment (embedment 4) of the present invention is employed in a similar way to embedment 3 by changing the dynamic thickening pond into a static thickener 130 and the dynamic setting pond into a static sand collector 140 and a static settling pond. However, raw tailing in line 44 is directly discharged to the sand collector and coarse sands contained in the raw tailing are settled and exited as underflow 141 from the sand collector to the blender 150; and only the fines in overflow 142 split into two streams: one stream 142a to the thickener 130 and another stream 142b to the settling pond.
The sand collector works as if it collects sands from beach in the case of dynamic thickening pond and allows only fines to run off. All settled sands in the sand collector are collected and mixed with thickener underflow 131 using the blender 150 to make a stackable tailing deposit for disposal in a dedicated disposal area. Both the thickener underflow 131 and the sand collect underflow 141 are exited by using a screw or a spiral mechanism.
However, the thickener underflow can also be exited by using a sludge pump as it is pumpable.

[0059] To capture all fines using coarse sands, sediment in the settling pond is withdrawn via line 93 and a high performance chemical is injected at the injection point 100 into the sediment. After combining the sediment in line 93 into line 142a and mixed using an inline mixer, the mixture is discharged into the thickener for flocculation and separation. To minimize adverse impacts of the residual high performance chemical remaining in thickener overflow, the thickener overflow 132 is mixed with fine tailing in the branch line 142b to consume the residual amount of the high performance chemical. A moderate performance chemical is added to the fine tailing in the branch 142b at injection point 76 before mixing the i fine tailing 142b with the thickener overflow 132 to facilitate remaining fines to settle in the settling pond.

[0060] Composition of the mixed tailing deposit after blending in the blender 150 can be adjusted by changing mixing volume ratio of the sand collector underflow 141 to the thickener underflow 131 to form loam soil (20-52% sands, 10-30% clays and 30-50% silts) for deep-rooted plants, such as alfalfa, to grow and remove water from the tailing deposit hydroponically. The loam soil having 25-52% sands formulated using tailing materials (sands, clays and silts) is spread on top of the tailing deposit as a top soil in the dedicated disposal area and the deep-rooted plants reclaim the surface of the tailing deposit to trafficable within three years. There are two ways of producing the make-up loam soil; one is to split the sand collector underflow into two streams 141 and 143, adjusting the volume ratio of the stream 141 and the stream 143 so that the mixture of streams 141 and 131 can produce a loam soil composition: 20-50% sands, 10-30% clays and 30-50% silts, leaving stream 143 and placing it at the bottom of the stack of the tailing deposit. Another way of producing the loam soil is to introduce sufficient inventory tailing and combine it with the thickener underflow and then use the mixture to consume all sand collector underflow.

[0061] The raw tailing split (embedment 3) shown in Fig. 7 and the fine tailing split (embedment 4) shown in Fig. 8 are deployed by moving mixed stackable tailing deposits to a dedicated disposal area, keeping the thickener, sand collector and settling pond unchanged.
All fines are captured and more recycle water is available for reuse, hence reducing fresh water import and land disturbance significantly.

[0062] Fig. 9 illustrates the performance of the raw tailing split (A) and the fine tailing split (B) at volume ratio of 1:1, respectively. Figs. 10 and 11 illustrate two different site plans of the present invention; one having settling pond in overburden dump area, another having the settling pond in an external area. The tailing deposit is stacked within an in-pit toe berm.

[0063] Fig. 12 is a schematic illustration of the mixed tailing deposit disposal with a layer (0.5 to 1 meter in thickness) of make-up loam soil spreading on top surface suitable for deep-rooted plants to grow. Deep-rooted plants, e.g. alfalfa, are used to remove water retained in the stable non-segregating tailing deposit hydroponically and to reclaim the tailing deposit to trafficable criteria of ERCB Directive 074 within 3 years. Alfalfa can produce 2-3 tonnes of dry matter per acre, and take approximately 500 tonnes of water for each tonne of dry matter.
Upon germination, a strong taproot develops rapidly and penetrates almost vertically downward. It often reaches a depth of 5 to 6 feet in the first season, 10 to 12 feet by the end of the second year, and may ultimately extend to depths of 20 feet or more.
Alfalfa can grow when temperature is above 3 C; and grow its roots at below 20 C and its stems and leaves above 20 C. Alfalfa can develop its roots in April, May, June and November; develop its stems and leaves during June - October at northern Alberta. These features make it perfect to remove water from the formed stable tailing deposit hydroponically, and turn the tailing deposit trafficable within 3 year.

[0064] Proper amount of fertilizer and a thin layer of garden or landscape soil (10-15 cm) are spread on top of the make-up loam soil before plant seeding. Optionally, shredded dry alfalfa can be mixed with the make up loam soil to improve soil quality and reduce fertilizer level.
Alfalfa needs to be cut twice every summer and shredded for recycle back to the newly formed loam soil. Alfalfa can take some pollutants from the contaminated process water and can not be used as forage or hey to avoid pollutant coming into food chain.

[00651 Using tailing pond materials (sands, clay and silt) to formulate desirable texture of loam soils (25-52 % sands, 10-30 % clays, 30-50 % silts) that can be spread on top surface of the tailing deposit for alfalfa initial growth can eliminate cost of transporting overburden as top soil and avoid its inhomogeneity problem. With global warming, the climate in northern Alberta will be more suitable for alfalfa and other deep-rooted plants to grow for a longer time period, taking more water out of the tailing deposits.

Claims (31)

Claims Embodiments of the present invention may be described as follows:

1. Processes for treating oil sands tailings, being capable of minimizing or eliminating potential adverse impacts of chemicals (flocculants/coagulants) application to tailing treatment on bitumen extraction within the area of tailing treatment regardless of the types of chemicals (flocculants/coagulants) used and significantly enhancing in both dewatering and consolidation of the sludge layer in a dynamic thickening pond or a static thickener, comprises any one of the following cases:

I. Base case: a dynamic thickening pond to receive tailings from bitumen extraction units and bitumen froth treatment unit via a tailing receiving line, a dynamic settling pond to receive and hold a mixture of the fines-containing water, transferred via a water transfer line from the thickening pond to the settling pond, and the tailing coming from the tailing receiving line for further solids/water separation, a recycle water line for withdrawing recycle water from the settling pond for water reuse in bitumen extraction from oil sands, and a sludge transfer line with a chemical injection point for transferring mature fine tailing (MFT) from the settling pond back to the tailing receiving line.
The chemical injection point can accept any kind of high performance chemicals (flocculants/coagulants), regardless of their potential adverse impacts on the bitumen extraction.

II. Base case with a pH modifier.
III. Raw tailing split.

IV. Fine tailing split.

2. The process of claim 1, in the base case, wherein the tailing receiving line is combined with sludge transfer line then reaches to the thickening pond for solids and water separation. This mixture is dispersed over a sand pile to form additional sand layers whereby a part of the clay, silt, and water in the stream is retained in the interstices of the sand layers.

3. The process of claims 1 & 2, wherein the sludge transfer line has a chemical injection point at which a high performance chemical (flocculants/coagulants) is added to the MFT withdrawn from the settling pond to improve solids settling in the thickening pond.

4. The process of claims 2 & 3, wherein the chemical injection point is located at a place along the sludge transfer line, but before the sludge transfer line merges into the tailing receiving line.

5. The process of claim 2, wherein the thickening pond comprises a clarified water layer and a sludge layer. The sands included in the tailing stream quickly settle at the edge of the pond and the fines-containing water flows into the body of the pond.

6. The process of claims 3 & 5, wherein the high performance chemical (flocculants/coagulants) can be slightly over dosage to achieve the best performance of solids/water separation, such as maximizing the clarified water layer, thickening the sludge layer and shorting the settling time.

7. The process of claim 6, wherein the chemical (flocculants/coagulants) dosage should be optimized in an ideal fashion. If little chemical is used, adequate thickening of the sludge may take longer than the desired time. If too much chemical is used, large, loose flocs tend to be generated, which do not thicken in an ideal fashion.
Different amounts of the high performance chemicals (flocculants/coagulants) may be required if different types of chemicals (flocculants/coagulants) are used.

8. The process of claim 5, wherein the clarified water in the thickening pond that may consist of a residual amount or an excess amount of the high performance chemicals (flocculants/coagulants) due to chemical equilibrium between the corresponding phases is withdrawn through a water transfer line and mixed with the tailing from the tailing receiving branch line then transferred to the settling pond at an inclined sand pile situated adjacent a dyke. The volume ratio of the clarified water to tailing is controlled in a range so that the excess amount of the high performance chemicals (flocculants/coagulants) in the clarified water can be consumed by the mixed excess amount of tailing. There is a moderate performance chemical injection point along the water transfer line at the location before the line joins the tailing receiving branch line. A moderate performance chemical (flocculants/coagulants) that has no significant adverse impacts on bitumen extraction can be injected to the water before it is mixed with the tailing.

9. The process of claim 8, wherein the mixture discharged at the inclined sand pile situated adjacent a dyke. The sands included in the mixture quickly settle at the edge of the pond and the fines-containing water flows into the body of the settling pond, which comprises a clarified water layer on the top and a sludge/suspension (known as MFT) layer at the bottom of the settling pond.

10. The process of claims 1 & 9, wherein the MFT layer at bottom of the settling pond is withdrawn via a sludge withdrawal mean and is transferred to the sludge transfer line by a sludge pump which is supported by a flotation mean on the surface of the settling pond.

11. The process of claims 9 & 10, wherein the MFT withdrawn from the bottom of the settling pond may be mixed with the clarified water withdrawn from the top via a branch water transfer line to archive a higher water to solids weight ratio for a better solids/water separation. Preferably, water to solids weight ratio is in a range of 0.5 to 5. The higher the water to solids ratio, the larger the size of the flocs can be formed, hence the quicker settling speed and the denser of the flocs.

12. The process of claim 9, wherein the clarified water layer in the settling pond only consists of residual amount of the high performance chemicals (flocculants/
coagulants) due to that significant excess amount of tailing can consume most of or all of the residual high performance chemicals (flocculants/ coagulants) in the clarified water layer withdrawn from the thickening pond, minimizing the potential negative impacts of recycling the clarified water withdrawn from the settling pond on bitumen extraction.

13. The process of claims 1 & 12, wherein the recycle water line for withdrawing recycle water via a water pump from the settling pond for water reuse in bitumen extraction from oil sands comprises three branch lines, one branch line combines with the sludge transfer line, another two branch lines for oil sands conditioning and diluting the conditioned oil sands, respectively.

14. The process of claim 1, in the base case, wherein the chemical injection point can accept any kind of high performance chemicals (flocculants/coagulants), regardless of their potential adverse impacts on the bitumen extraction, as the residual amount or excess amount of added high performance chemicals (flocculants/coagulants) can be consumed by the tailing mixed before transferring the water withdrawn from the thickening pond to the settling pond.

15. The process of claim 1, in the base case with a pH modifier, wherein a process for treating oil sands tailings, being capable of minimizing or eliminating potential adverse impacts of flocculants application to tailing treatment on bitumen extraction within the area of tailing treatment regardless of the types of chemicals (flocculants/coagulants) used and significantly enhancing in both dewatering and consolidation of the sludge layer in a dynamic thickening pond by using a pH
modifier, such as flue gas or acetic acid, comprises: a dynamic thickening pond to receive tailings from bitumen extraction units and bitumen froth treatment unit via a tailing receiving line, a settling pond to receive and hold a mixture of the fines-containing water, transferred via a water transfer line from the thickening pond to the settling pond, and the tailing coming from the tailing receiving line for further solids/water separation, a mixing mean to mix sediment withdrawn from the thickening pond and materials taken from outside of the dyke around the thickening pond to improve dewatering, compaction and consolidation eventually.

16. The process of claim 15, wherein the mixing mean receives 1) a lower pH
sediment via a sludge line and a sludge pump mounted on a floating mean in the thickening pond and 2) materials taken from outside of the dyke of the thickening pond via loaders or a conveyer, and discharges the mixture to the inside of the dyke of the thickening pond via a auger or a conveyer.

17. The process of claim 16, wherein the sludge line should be enough long and has a pH
modifier (flue gas or acetic acid) injection point located close to the sludge pump to ensure sufficient time for carbon dioxide (CO2) in the injected flue gas to dissolve in the sediment and reach a CO2 concentration not less than 50 mg/L if flue gas is injected. Flue gas can be captured from utility or upgrading plant and be injected into the sediment without purification.

18. The process of claim 17, wherein the flue gas can be generated using a self contained co-combustion burner hooked up with a heat exchanger for heat recovery and providing warm recycle water for bitumen extraction.

19. The process of claim 18, wherein the burner can burn variety of inexpensive fuels, such as used oils, scrape tires, coal, petroleum coke and sludge's containing high level of oil.

20. The process of claims 2 and 16, wherein the two discharge operations form a dyke around the thickening pond in such a way that the discharges with and without pH
modifier injection can be placed alternatively to achieve the best compaction and eventually consolidation.

21. The process of claim 1, in the case of raw tailing split, wherein a process for treating oil sands tailings, being capable of minimizing or eliminating potential adverse impacts of chemicals (flocculants/coagulants) application to tailing treatment on bitumen extraction within the area of tailing treatment regardless of the types of chemicals (flocculants/coagulants) used and significantly enhancing in both dewatering and consolidation of the sludge layer in a static thickener, comprises: a static thickener, a sand collector, a blender and a settling pond; a raw tailing receiving line to split the raw tailing into two streams: branch line A to the said thickener and branch line B to the said sand collector, a water transfer line, having a chemical injection point for injecting moderate performance chemicals, to transfer overflow of the said thickener to the said sand collector, a sludge transfer line, having a chemical injection point for injecting high performance chemicals, to transfer the sludge from the settling pond to the said thickener

22. The process of claim 1, in the case of fine tailing split, wherein a process for treating oil sands tailings, being capable of minimizing or eliminating potential adverse impacts of chemicals (flocculants/coagulants) application to tailing treatment on bitumen extraction within the area of tailing treatment regardless of the types of chemicals (flocculants/ coagulants) used and significantly enhancing in both dewatering and consolidation of the sludge layer in a static thickener, comprises: a static thickener, a sand collector, a blender and a settling pond; a sludge splitting line from the sand collector to split the sludge (overflow of the sand collector) into two streams: branch line A to the said thickener and branch line B to the said settling pond, a water transfer line and a sludge transfer line,

23. The process of claim 22, wherein the water transfer line transfers the overflow of the said thickener and merges into the sludge branch line B and discharge the mixture to the settling pond; and the sludge transfer line, having a chemical injection point for injecting high performance chemicals, transfers the sludge from the settling pond to the said thickener.

24. The process of claim 22, wherein the branch line B has a chemical injection point for injecting moderate performance chemicals before the line merges into the water transfer line; and the sludge transfer line has a chemical injection point for injecting high performance chemicals before the line merges into the branch line A.

25. The processes of claims 21 and 22, wherein the high performance chemicals can be any kind of flocculants/coagulants regardless of their adverse impacts on bitumen extraction, while the moderate performance chemicals should be the chemicals that have insignificant adverse impacts on bitumen extraction.

26. The processes of claims 21 and 22, wherein the static thickener, sand collector and settling pond mean that they are fixed in shapes and sizes, once constructed, in comparison with the dynamic thickening pond and dynamic settling pond that shapes and sizes are changed at all times in operations.

27. The processes of claims 21 and 22, wherein both the sand collector underflow and the thickener underflow are discharged to the blender by using a spiral or a screw mechanism. The mixed tailing deposit is then discharges into a conveyer that transports the discharge to a dedicated disposal area. In the case of fine tailing split, the thickener underflow can also be pumped into the blender as the sediment is pumpable.

28. The process of claim 22, wherein the sand collector has two underflow exits A to the blend and B to a loading area for loaders to move the coarse sand to a dedicated disposal area. The exit B is closed during regular operation and is open during make-up loam soil operation.

29. The process of claim 28, wherein the make-up loam soil is produced by adjusting the volume ratio of the sand collector underflow (exit A) to the thickener underflow to achieve a loam soil composition: 20-52% sands, 10-30% clays and 30-50% silts.
The make-up loam soil can be produced in two ways: one way is to use all underflow of the thickener and a portion underflow of the sand collector (exit A), leaving the remaining underflow of the sand collector (exit B) to the loading area and placing it at the bottom of the stack of the tailing deposit in a dedicated disposal area.
Another way of producing the loam soil is to introduce sufficient inventory tailing and combine it with the thickener underflow and then use the mixture to consume all sand collector underflow.

30. The process of claims 29, wherein the make-up loam soil is spread on top surface of tailing deposit. The make-up loam soil layer has a thickness of 0.5 to 1 meter for deep-rooted plants to grow. Deep-rooted plants, e.g. alfalfa, are used to remove water retained in the stable tailing deposit hydroponically and to reclaim the tailing deposit to trafficable criteria of ERCB Directive 074 within 3 years. Proper amount of fertilizer and a thin layer of garden or landscape soil (10-15 cm) are spread on top of the make up loam soil before plant seeding. Optionally, shredded dry alfalfa can be mixed with the make-up loam soil to improve soil quality and reduce fertilizer level.
Alfalfa needs to be cut more than once, preferably twice, every summer and shredded for recycle back to the newly formed loam soil. Alfalfa can take some pollutants from the contaminated process water and can not be used as forage or hey to avoid pollutant coming into food chain.

31. The processes of claim 1, in all cases, wherein a water transfer line for transferring solids-containing water from i. the thickening pond or ii. the thickener or iii. the sand collector to the settling pond and a sludge transfer line for transferring sludge from the settling pond to i. the thickening pond or ii. the thickener compromise inline mixers to mix the materials contained in the respective lines. The inline mixers are located after any chemical injection points and line merging points, and have a certain distance to the line ends to ensure sufficient mixing the said materials but avoid the said materials settling and plugging the lines.