CA1138361A - Treatment of oil sands slimes and modified bitumen recovery process - Google Patents
Treatment of oil sands slimes and modified bitumen recovery processInfo
- Publication number
- CA1138361A CA1138361A CA000353509A CA353509A CA1138361A CA 1138361 A CA1138361 A CA 1138361A CA 000353509 A CA000353509 A CA 000353509A CA 353509 A CA353509 A CA 353509A CA 1138361 A CA1138361 A CA 1138361A
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- Canada
- Prior art keywords
- bitumen
- clay
- oil
- water
- slaked lime
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
Slimes from the slimes pond formed from the tailings stream of a hot water process for recovery of bitumen from oil sands is treated to effect separation of bitumen, clay and aqueous phases therefrom by a controlled two-stage addition of slaked lime thereto. The first slaked lime addition is used to form a water-in-oil emulsion from the bitumen and the second slaked lime addition is used to effect flocculation of the clay suspension following separation of the water-in-oil emulsion. The tailings' stream from a hot water process is treated in similar manner to avoid the formation of slimes.
In another modification of the hot water process, the middlings stream from the primary separation step is mixed with slaked lime prior to passage to the flotation scaven-ging operation in order to improve the separation of bitumen from the aqueous phase. The bitumen-free tailings stream which results is readily dewatered using further slaked lime addition settling.
Slimes from the slimes pond formed from the tailings stream of a hot water process for recovery of bitumen from oil sands is treated to effect separation of bitumen, clay and aqueous phases therefrom by a controlled two-stage addition of slaked lime thereto. The first slaked lime addition is used to form a water-in-oil emulsion from the bitumen and the second slaked lime addition is used to effect flocculation of the clay suspension following separation of the water-in-oil emulsion. The tailings' stream from a hot water process is treated in similar manner to avoid the formation of slimes.
In another modification of the hot water process, the middlings stream from the primary separation step is mixed with slaked lime prior to passage to the flotation scaven-ging operation in order to improve the separation of bitumen from the aqueous phase. The bitumen-free tailings stream which results is readily dewatered using further slaked lime addition settling.
Description
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TREATMENT OF OIL SANDS SLIMES
AND MODIFIED BITUMEN RECOVERY PROCESS
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The present invention relates to improvements in tha recovery of bitumen from oil sands.
There are major accumulations of oil sands at a number of global locations. Oil sands are basically a mixture of bitumen, mineral and water, of variable bitumen content. Only those surficial deposits in the Athabasca region of Alberta, Canada are being exploited on a commercial scale at this time. In the deposits, the bitumen content varies up to 18 wt% and averages about 12 wt%, water is usually about 3 to about 6 wt% and the mineral content, predominantly quartz, ranges from about 84 to about 86 wt%.
At the present time there is one commercial procedure for the recovery of bitumen from these deposits/ known as the "hot water" process. The procedure involves intercon-nected steps o feed conditioning, bitumen separation, waste disposal and bitumen concentrate cleaning and recoveryO
The hot water process has a major disadvantage 20 which involves the discharge of a ~ailings stream which, ' after removal of sand, settles in ponds to an upper aqueous layer contain_ng less than 5% clay solids which is reusable in the plant and a lower slimes layer cont~ining 5 to 30%
clay solids which has proved to be extremely difficult to separate heretofore into its solids and wa-ter compon~nts and is not reusable as such.
The net volume of tailings produced b~ the hot water process in the form of sand and slimes amounts to about 40%
greater in volume than the mined tar sand, thus representing a serious backfill problem, and a large lake of slimes has accumulated in the 10 or so years of commercial operation.
The present invention, in one aspect, is directed to a clean~up procedur~ for the slimes pond, effecting efficient separation of solid and ~queous phases, recovery 3~ of residual bitumen contained in the slimes which is typically present in a concentration of abouk 4 wt~, and recovery of alkali in the aqueous phase~
Accordingly, in one aspect, the present invention provides a method of treatment of slimes from a tailings pond of a hot water process for the recovery of bitumen from oil ... . .. .
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sands, the slimes comprising a suspension of clay and bitumen in water, which method comprises: mixing sufficient slaked lime with the slimes to form a water-in-oil emulsion from the bitumen; separating the water-in-oil emulsion from the resulting clay suspension, and dewatering the resulting clay suspension.
The present invention, in another aspect is directed to modifications to the hot water process to prevent slimes formation and eliminate the necessity for a slimes pond of the current type which provides little water recycle and con-tinues to grow in size as commercial operations continue.
Accordingly, in one embodiment of a second aspect of the invention, there is provided a method o~ treating a tailings stream from a hot water process for the recovery of bitumen from oil sands, the tailings stream comprising an aqueous suspension of clay and bitumen~ which comprises:
mixiny sufficient slaked lime with the tailings stream to form a water-in-oil emulsion from the bitumen; separating the water-in-oil emulsion from the resulting clay suspension;
and dewatering the resulting clay suspensionO
Further, in a second embodiment of the second aspect of the invention, there is provided in a method for the recovery of bitumensfrom oil sands by slurrying the oil sands with an aqueous medium at an elevated temperature~
sepaxating the slurry into an oil froth phase containing most of the bitumen from the oil sands, an aqueous phase containing clay minerals and some bitumen and a sand phase, recycling part of the aqueous phase to slurry formation, effecting additional bitumen recovery from the remainder of the aqueous phase in the form of an oil froth, dewatering the oil froths to recover bitumen and provide an aqueous stream, and discharging a tailings stream comprising an aqueous clay suspension resulting from the additional bitumen recovery and the aqueous stream, the improvement which comprises:
mixing sufficient slaked lime with the remainder of the aqueous phase to form a water-in-oil emulsion from the bitumen therein; and dewatering the tailings stream.
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In the procedure according to the first aspect of the invention, a controlled two-step addition of slaked lime to the ponds slime is effected. In the first step, su~ficient lime is added to and rapidly mixed with the slim~
S to cause more complete formation of a water-in-oil emulsion from the bitumen present in the slime. The water-in-oil emulsion is separated by air flotation and may be passed sub-sequently to the dewatering procedure within the hot water process plant. Further improvea bitumen separation may be possible by diluting the remaining slimes with water and subjecting the diluted slimes to air flotation.
Alternatively, the water~in-oil emulsion may be dewatered separately, such as, by the addition o~ an organic solvent for the bitumen, such as, hexane or naphtha, to the 15 emulsion to dissolve out the bitumen and form a bitumen~
solvent solution and an aqueous clay suspension~
Separation of the bitumen-solvent solution may be enhanced by centrifugation. The solvent may be removed for recycle and the bitumen forwarded to upgrading.~
Depending on the level of the pond from which the slime is taken, the initial addition of lime may cause a decrease in gel strength and viscosity of the slime. These effec~s are more pronounced for slime from greater depths of the pond than at lesser depthsO
Continued addition of lime beyond the quantity re~uired to form the water-in oil emulsion and to decrease the gel strength and viscosity, causes a sharp increase in the gel strenyth and viscosity since flocculation of the clay starts to occur. The quantity of lime added in the first stage is at least sufficient to effect the more complete formation of the water-in-oil emulsion but insuf-ficient to result in any significant increase in gel strength and viscosity.
It has been found that about 0.2 to about ~.Og~
preferably about 0.5 to about 1.25g, of slaked lime per litre of slime gives satisfactory results~ the optimum amount depending on the depth of the pond from which the slime is taken.
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The clay suspension resulting from the separation of the water-in-oil emulsion is subjected to dewatering.
This is preferably effected by rapidly mixing the suspension with additional quantities of slaked lime sufficient to cause flocculation of the clay. It has been found that the addition of lime to these clay suspensions in increasing incremental quantities above a minimum level leads to a rapidly-increasing dewatering ability until a maximum dewatering ability is reached above which further lime additions do not significantly improve dewatering.
The quantity of lime required to be added to achieve maximum dewatering ability varies, depending on the depth o~
the ~lime ~ond being treatedO For example, for a 15 ft sample, maximum dewatering may be effected at an amount of lime of about 1 to about 2 g/lO
The flocculated clay may be separated from the aqueous phase in any convenient manner, such as/ by simple gravity se~tling, centrifugation, filtration, by free~e-thaw techniques, or b~ a combination of such techniques.
Compact clay of high solids content is obtained in a form suitable for disposalO The clear aqueous phase, which contains sodium hydroxide recovered from the slimes~ may be used to provide water requirements in the hot water process , after some softening as necessary, or may be disposed of.
An alternative manner of effecting the procedure noted above is to mix all the lime at once lnto the slime, add organic solvent to the mixture and centrifuge to separate an upper bitumen-solvent solution layer, f.rom which the bitumen may be xecovered, and a lower dense clay layer from an intermediate clear aqueous layer. This proceduret however, is much less preferred than that described above since large volumes of solvent are required, solvent losses occur in the aqueous phase and the clay, centrifuge equipment is required and separa~ion has been rendered more :~
3s difficult by an increase in viscosity brought about by excessive lime addition.
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Other calcium salts may be used, for ~locculation of the clay in this and later~described aspects of the invention, such as, calcium chloride7 but alkali recovery i5 not effected in this case, since the sodium ions form sodium chloride.
S The slimes treatment procedure of this invention, therefore, achieves separation of the previously intractable slimes pond material into a bitumen fraction, suitable for upgrading, a compact clay fraction suitable for disposal, and-a clear aqueous layer containing recovered alkali suitable for reuse in the hot water process or for disposalO
The present invention, therefore, provides a procedure which is able to clean up the existing slimes pond to recover additional bitumen and alkali and to recover reusable water, thereby alleviating the existing major environmental problem of the hot water process.
As mentioned previously, another aspect of the present invention involves modifications to the hot water process to prevent slimes formation, so as to ~ecrease the -need for the large accumulating pond area once it has been cleaned up in accordance with the first aspect of the invention~
In the hot water process, the oil sand is conditioned with sodium hydroxide solution in a rotating drum at 180F at a pH of about 8.0 to 8~5O The conditioned pulp at about 70% solids is discharged to a feed sump to which mi~dlings recycle and ~ater are added to provide the required consistency of material for pumping to separation cells.
In the separation cells, sand settles to tha bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlingslayer containing predominantly clay minerals and some bitumen is formed between these layers. Some of this middlings layer is used for recycle to the feed sump and the major part thereof is passed througha scavenging step to recover additional amounts of bitumen by air flotation.
The oil froths from the primary separation step and the middlings scavenging step are combined, diluted with sol-, :; . .
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vent to dissolve the bitumen, the bitumen~solvent solution is separated :Erom the aqueous phase usually by centrifugation, and removed. The solvent is removed from the bitumen for recycle and the bitumen forwarded to the upgrading plant.
The sand tailings from the separation cell, the middlings tailings from the scavenging step and the tailinys from the centrifuge step are usually con~ined in the conventional procedure and pumped to a settling pond.
In accordance with one embodiment of this aspect of the invention, this combined tailings stream is treated directly to effect separation of residual bitumen, separate clay particles as a compact mass for easy disposal and recover most of the aqueous phase of the tailings stream and the sodium hydroxide contained therein for recycle.
The combined tailings stream is allowed to stand to separate out sand therefromO The resultant clay suspen sion is mixed with slaked lime to cause the formation of a water-in-oil emulsion of residual bitumen in the suspension.
The quantity of slaked lime used should be insufficient to cause flocculation of clay particlesO The bitumen emulsion is separated by air flotation~ removed from the remaining clay suspension and returned to the oil froth treatment pro-cedure for dewatering the emulsion and the recovery of the bitumen therein. Alternatively, the emulsion may be de-~5 watered separately to effect bitumen recoveryO
Thereafter, the clay suspension is dewatered by~urther slaked lime addition followed by settling, such as, by prolonged standing, or by centrifugation, filtrakion, or a freeze~thaw operation, or ~y a combination of such operations, and a compact clay mass is formed, suitable for disposal. The suh-stantially clear aqueous phase containing recovered alkali is suitable for recycle as water make-up within the hot water process, after softening toremove residual calcium ions, if required~
The clay settling step may be effected in a large pond area. This pond is substantially different in size from the slimes pond now used in the hok water process~ The se-ttling pond produces clear water for recycle and forms a compact clay mass for disposal, in contrast with the existing slimes pond wherein less water recovery can be effected in a reasonable period of time.
The procedure used in accordance with -this one feature of this aspect of the invention, the~refore, is analogous in certain respects to that employed in the slimes treatment procedure described in detail ahove~
The considerations governing the quantity of lime employed in the two separate lime additionc with respect to that procedure also apply with respect to the procedure of this aspect of the invention.
A modification of this embodiment of the invention is to omit combination of the sand tailings stream with the other tailings streams and treat the clay tailings streams in accordance with the procedure described above~
In accordance with another embodiment of this second aspect of the invention, the major portion of the middlings stream from the primary separation step, instead of passing directly to the flotation scavenging operation first is rapidly mixed with slaked lime prior to passage to the flotation scavenging operation in order to improve the separation of bitumen from the aqueous phase as a water-in oil emulsion. The quantit~ of slaked lime used should be insufficient to cause the flocculation of clay particles at this stage. The bitumen separation procedure may be urther enhanced by subjecting the middlings stream to an aeration-oxidation step prior to the slaked lime addition.
The tailings stream from the flotation step is sub-stantially bitumen-free and, after combining with the clay suspension from the separation o bit~men-solvent solution, and optionally after combination with the sand tailings from the primary separator, is subjected to dewatering and separa-tion using slaked lime, as described above with respect to other bitumen-free clay suspensions.
The invention is described further, by way of illustration, with reference to the accompanying drawings, in whicho Figure 1 is a schematic flow sheet of slimes separ-ation and bitumen recovery procedure according to one embodiment of the invention;
Figure 2 is a schem~tic flow sheet of one modifica-tion to the hot water process for preventing slimes . - , . ..
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., iormation; and Figure 3 is a schematic flow sheet of a second modification to the hot water process for preventing slimes formation O
Refexring first to Figure 1, which illuskrates a slimes treatment procedure, slime from the slimes pond is passed by line 10 to a mixing tank 12 wherein sufficient slaked lime fed by line 14 is rapidly mixed therewIth to form a water-in-oil emulsion from the bitumen contained in the slime and additionally aften to decrease the gel strength and viscosity of the slime.
The lime-treated slime is passed by line 16 to a flotation tank 18 wherein the water-in-oil emulsion is caused to separate as an upper layer by dispersed airO
Any other convenient separation technique may be employed.
The water-in~oil emulsion~ or "~itumen ~roth~' or "oil froth"
as it is somètimes called when formed in the hot water process,after separation from the aqueous phase, may hé
forwarded to the bitumen froth clean-up operation in the hot water process plant, or may be dewatered separately, as illustratedO
The bitumen froth is forwarded by line 20 to a mixing tank 22 wherein a water-immiscible solvent for the bitumen, such as~ naphtha, fed by line 24, i5 mixed therewith to dissolve the bitumen. This mixture is forwarded by line 26 -to a centrifuge 28 wherein the bitumen-solvent solution is separated ~rom the aqueous phase. The need Eor centrifugation may be decreased by the addition of clear water to the bitumen froth prior to addition of the solvent thereto~
The bitumen-solvent solution is forwarded by line 30 to solvent recovery 32. The solvent may be recovered by any convenient tec~mi~ue, such as, distillation, and the recovered solvent is recycled by line 34 to the solvent inlet line 24 along with any make-up solvent fed by line 36.
The bitumen which is recovered following solvent separation is removed by line 38 for passage to the bitumen upgrading procedure of the oil sands treatment plant.
The clay suspension resultin~ from the flotation separation of the water-in-oil emulsion in flotation tank :~ :
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g 18 is passed by line 40 to a mixing tank 42. The small volume of clay suspension resulting from the centrifuge 28 after separation of the bitumen-solvent solution also may be forwarded by line 44 to the mixing tank 42 or to the 5 flotation tank 18.
In the mixing tank 42, the clay suspensions are rapidly mixed with sufficient slaked lime fed by line 46 to 10cculate the clay particles and permit dewatering of the suspension. The limed suspension is then forwarded by line 10 48 to a dewatering and settling pond 50~ wherein the limed suspension is subjected to any convenient dewatering and ;
settling procedure, such as, simple gravity settling by per mitting the limed suspension to stand for a prolonged period, or the limed suspension may be dewatered by subjecting the 15 same to centrifugationr to ~reezing and thawing, or to filtra-tion. A o~ination of such dewatering techniques also may be usedO
A compact clay mass 52 results from the dewatering suitable for disposal. The clear aqueous phase remaining contains recovered sodium hydroxide and is suitable for re-20 use, after softening to remove residual calcium ions, ifnecessary, for example, using sodium carbonate, and/or for disposal, as desiredt and is removed from pond 50 by line 54.
The procedure described with respect to Figure 1, therefore, achieves substantially complete separation of the 25 previously~substantially inseparable slime into its component constituents of bitumen, clay and water by a controlled two-stage addition of slaked lime ~ombined with sim le and inex-pensive separation techni~uesO
Turning now to Figure 2, wherein there is illus-30 trated a modification of the hot water process to preventthe formation of slimes and the accumulation of a slimes pond, oil sand and water along with sodium hydroxide are fed respectively by lines 110 and 112 to a conventional hot water process plant 114 producing bikumen in line 116 35 ~rom the oil sand suitable for upgrading and an aqueous tailings stream in line 118 .
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The tailings st.ream 118 consists of an aqueous sus-pension of clay and sand particles and is normally discharged to the slimes pond, the sand separating out to form pond dykes. In the illustrated inventive process, the tailings stream 118 first is forwarded to a sand se.parator 120 wherPin sand and other readily separable solids rapidly gravity settle from the tailings and are removed clS a compact mass by line 122 for dlsposal as landfill or ot:herwise.
The remainder of tailings stream consisting of a relatively stable suspension of clay and emulsified bitumen particles in water is forwarded by line 124 to a mixing tank 126 wherein the suspension is rapidly mixed with sufficient slaked lime fed b~ line 123 to cause the bitumen to form a water-in-oil emulsion bu~ .~nsufficient to çause flocculation of the claysn The limed suspension is forwarded by line 130 to a flotation tank 132 wherein the water-in-oil emulsion is separated by dispersed air flotation~ or any other convenient technique.
The water-in-oil emulsion~ or "bitumen froth" as equivalent emulsions ~ormed.in the hot water process are sometimes called, is removed from the remaining relatively bitumen-free cla~ suspension and is forwarded by line 134 to the bitumen froth dewatering procedure of the hot water process plant 114 or to a separate dewatering procedure for the recovery of bitumen, ~or example, that illustrated in Figure 1 in connection with the bitumen froth in line 200 The clay suspension remaining following bitumen froth removal is forwarded by line 136 to a mixing tank 138 wherein the clay suspension is rapidly mixed with sufficient slaked lime ~ed by line 140 to flocculate the clay particles.
If desired, the clay suspension in line 136 may first be subjected to a settling step to remove kaolinite therefrom.
The limed suspension is passed by line 142 to a dewatering and clay settling pond 144 wherein any convenient clay de-watering technique may be adopted, such as, simple gravitysettling by allowing the limed suspension to stand for a prolonged period. Any other convenient dewatering technique may be employed, such as, centrifugation, freezing and thaw-ing, or filtration of the limed suspension, or by a combina-.. ~ . ~ . :
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11tion of these procedures.
The separatea clay is obtained as a compact mass 146 which may remain in the settling pond :L44, or may be removed for disposal. The clear aqueous phase containing 5 recovered alkali is recycled by line 148 t:o the water inlet line 112 for reuse in the hot water process plant 114. Any make-up water and alkali required are added to the water inlet line 112 by line 150.
The pxocedure of Figure 2, thereforel directly 10 treats ~he tailings stream of a hot water process plant by a controlled two-stage slaked lime addition thereto combined with simple and inexpensive separation technique to recover additional bitumen, produces compact sand and clay effluents which are suitable for simple disposal and recovers 15 a substantial proportion of the water and sodium species o$
the tailinys stream or reuseO `
Figure 3 illustrates a further modification to the hot water process which results in a more readily separable tailings stream than is normally the case and avoids the 20 necessity for separate separation of residual ~itumen, such as occurs in the procedure of Figure 2.
In Figure 3, oil sands and water and steam are ~ed respectively by lines 210 and 212 to a conditioning - tank 214. The pulp so formed is forwarded by line 216 to 25 a feed sump 218 wherein it is mixed with water and sodium hydroxide fed by line 220 and recycle middlings stream 222 to the desired consistency and then passed by lme 224 to a primary separator 226. In the primary separ~tor 226, the mixture is separated into a lower sand layer which is removed by 30 ~ine 228 for disposal, an upper oil fxoth layer which is removed by line 230 for bitumen recovery and an intermediate middlings layer which is partly recycled by line 222 to the feed sump 218 and partly removed by line 232 for froth processing.
The oil froth in line 230 enters a mixing tank 234 to which a water-immiscible solvent fo~ the bitumen, such as9 naphtha or hexane, is also fed by line 236 for mixing there-with to form a solution of the bitumen in the solvent~ If desired, clear water may be added to the oil froth prior to ~3~3~
solvent addition. The resulting mixture is passed by line 238 to a centri~uge 240 to separa-te the bitumen solvent solution from the aqueous phase.
The bitumen-solvent solution is removed from the centrifuge 240 and f~rwarded by line 242 to solvent recovery 244 wherein -the solvent is removed, such as, by distillation, and recycled by line 246 to the mixing tank feed line 236, make-up quantities o solvent being fed by line 248. The bitumen remaining after solvent removal is passe~ by ~ine 250 ~o an upgrading plant.
The aqueous phase remaining ~rom centrifugation, consisting of a relatively bitumen-free suspension of clay particles in water~ is removed fxom the centrifuge by line The procedures so far described with respect to Figure 3 are the we~l-known conventional ones of a hot water process plant for the separation of bitumen from oil sands and require no ~urther explanation.
In accordance with thi~ modi~ication to the hot water process, the middlings stream in line 232, consisting of bitumen, clay and water, is fed into a mixing tank 254 wherein it is rapidly mixed with slaked lime fed by line 256. The lime addition may be preceded ~y an aeration-oxidation treatment to improve later separation of the bitumen.
The lime is used in a quantity su~ficient to effect formation of a water-in~oil emulsion of the ~itumen contained in the middlings stream but insufficient to cause floc¢ula-tion of clay particles. The limed middlings stream is passed by line 2S8 to a ~lotation tank 260 w~erein the emulsion is separated from the remainder o~ the aqueous phase by dispersed air flotation~ Any other convenient separation technique may ~e employed.
The separated water-in-oil emulsion, or "oil froth"
is passed by line 262 to the solvent mixing tank 234 for emulsion dewatering along with the oil froth in line 230.
In the conventional hot water process, the middlings stream 232 is fed directly to the flotation tank 260. The liming . .
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treatmeni: and optional pre-oxidation treatment ensure more complete separation of bitumen from the aqueous phase and eliminates the necessi.ty to process the aqueous phase separately to effect such bitumen separation, such as is 5 described above with respect to Figure 2.
The aqueous phase remaining a~ter separation of the oil froth formed in the flotation step, consisting of a suspension of clay particles, is forwarcled by line 264 to a mixing tank 266, along with the clay suspension in I0 line 252. To the mixing tank 266 is rapidly added sufficient slaked lime by line 268 to effect flocculation and dewatering of the clay suspension. If desired, the clay suspension in line 264 may first be subjected to a settling step to remove kaolinite therefromO
The limed suspension is forwarded by line 270 to a settling pond 272 wherein the suspension is subjected to any desired clay dewatering procedure, such as, simple gravity settling. Any other convenient dewatering techni~ue may be.
used, such as, centrifugation, a freeze-thaw technique, fil-20 tration or a combination~ :
The clay settles from the aqueous phase and forms a compact mass 274 w~ich can remain in the pond 272~ or may be disposed of. The remaining clear aqueous phase containing sodium hydroxide is removed from the pond 272 by line 276 and 25 is recycled to the water inlet line 220 as reusable water~
Any make-up water and alkali requirements are fed by line 278.
As in the case of the procedure of Figure 2, the pro-cedure of Figure 3 eliminates the necessity for an extensive slimes pond, since the waste effluent from the procedure is in 30the form of compact solids which are readily disposed of, and effects economic use of alkali.
While the various operat~ons described above in~
connection with Figurés 1 to 3 have been indicated to occur in separate reaction vessels, khis is for convenience and 35ease of illustration and description~ In certain cases, combinations of two or more of the individual operations may he effected in the same reaction vessel r if convenient.
The invention is illustrated further by the following Examples:
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Example 1 This Example shows the effect of the addition of slaked lime on the yel strength of slimes.
Samples of slimes from the 15-foot and 30-foot 5 depths of the slimes pond at the Suncor Ltd. facility at Fort Mc~urray, Alberta were treated with varying quantities of lime and the gel strength of the resulting slimes was measured on a Fann Viscometer. The results are reproduced in the following Table I:
TABLE I
Lime10 min. gel str~ngth Addition(lb./100 sq.ftO) (g/l) 15 foot 30 fo~t o.oO 23 32 0~50 - 19 0~66 6 6 1.00 4 5 1.66 8 7 ,
TREATMENT OF OIL SANDS SLIMES
AND MODIFIED BITUMEN RECOVERY PROCESS
. ~ , . _ . . .
The present invention relates to improvements in tha recovery of bitumen from oil sands.
There are major accumulations of oil sands at a number of global locations. Oil sands are basically a mixture of bitumen, mineral and water, of variable bitumen content. Only those surficial deposits in the Athabasca region of Alberta, Canada are being exploited on a commercial scale at this time. In the deposits, the bitumen content varies up to 18 wt% and averages about 12 wt%, water is usually about 3 to about 6 wt% and the mineral content, predominantly quartz, ranges from about 84 to about 86 wt%.
At the present time there is one commercial procedure for the recovery of bitumen from these deposits/ known as the "hot water" process. The procedure involves intercon-nected steps o feed conditioning, bitumen separation, waste disposal and bitumen concentrate cleaning and recoveryO
The hot water process has a major disadvantage 20 which involves the discharge of a ~ailings stream which, ' after removal of sand, settles in ponds to an upper aqueous layer contain_ng less than 5% clay solids which is reusable in the plant and a lower slimes layer cont~ining 5 to 30%
clay solids which has proved to be extremely difficult to separate heretofore into its solids and wa-ter compon~nts and is not reusable as such.
The net volume of tailings produced b~ the hot water process in the form of sand and slimes amounts to about 40%
greater in volume than the mined tar sand, thus representing a serious backfill problem, and a large lake of slimes has accumulated in the 10 or so years of commercial operation.
The present invention, in one aspect, is directed to a clean~up procedur~ for the slimes pond, effecting efficient separation of solid and ~queous phases, recovery 3~ of residual bitumen contained in the slimes which is typically present in a concentration of abouk 4 wt~, and recovery of alkali in the aqueous phase~
Accordingly, in one aspect, the present invention provides a method of treatment of slimes from a tailings pond of a hot water process for the recovery of bitumen from oil ... . .. .
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sands, the slimes comprising a suspension of clay and bitumen in water, which method comprises: mixing sufficient slaked lime with the slimes to form a water-in-oil emulsion from the bitumen; separating the water-in-oil emulsion from the resulting clay suspension, and dewatering the resulting clay suspension.
The present invention, in another aspect is directed to modifications to the hot water process to prevent slimes formation and eliminate the necessity for a slimes pond of the current type which provides little water recycle and con-tinues to grow in size as commercial operations continue.
Accordingly, in one embodiment of a second aspect of the invention, there is provided a method o~ treating a tailings stream from a hot water process for the recovery of bitumen from oil sands, the tailings stream comprising an aqueous suspension of clay and bitumen~ which comprises:
mixiny sufficient slaked lime with the tailings stream to form a water-in-oil emulsion from the bitumen; separating the water-in-oil emulsion from the resulting clay suspension;
and dewatering the resulting clay suspensionO
Further, in a second embodiment of the second aspect of the invention, there is provided in a method for the recovery of bitumensfrom oil sands by slurrying the oil sands with an aqueous medium at an elevated temperature~
sepaxating the slurry into an oil froth phase containing most of the bitumen from the oil sands, an aqueous phase containing clay minerals and some bitumen and a sand phase, recycling part of the aqueous phase to slurry formation, effecting additional bitumen recovery from the remainder of the aqueous phase in the form of an oil froth, dewatering the oil froths to recover bitumen and provide an aqueous stream, and discharging a tailings stream comprising an aqueous clay suspension resulting from the additional bitumen recovery and the aqueous stream, the improvement which comprises:
mixing sufficient slaked lime with the remainder of the aqueous phase to form a water-in-oil emulsion from the bitumen therein; and dewatering the tailings stream.
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In the procedure according to the first aspect of the invention, a controlled two-step addition of slaked lime to the ponds slime is effected. In the first step, su~ficient lime is added to and rapidly mixed with the slim~
S to cause more complete formation of a water-in-oil emulsion from the bitumen present in the slime. The water-in-oil emulsion is separated by air flotation and may be passed sub-sequently to the dewatering procedure within the hot water process plant. Further improvea bitumen separation may be possible by diluting the remaining slimes with water and subjecting the diluted slimes to air flotation.
Alternatively, the water~in-oil emulsion may be dewatered separately, such as, by the addition o~ an organic solvent for the bitumen, such as, hexane or naphtha, to the 15 emulsion to dissolve out the bitumen and form a bitumen~
solvent solution and an aqueous clay suspension~
Separation of the bitumen-solvent solution may be enhanced by centrifugation. The solvent may be removed for recycle and the bitumen forwarded to upgrading.~
Depending on the level of the pond from which the slime is taken, the initial addition of lime may cause a decrease in gel strength and viscosity of the slime. These effec~s are more pronounced for slime from greater depths of the pond than at lesser depthsO
Continued addition of lime beyond the quantity re~uired to form the water-in oil emulsion and to decrease the gel strength and viscosity, causes a sharp increase in the gel strenyth and viscosity since flocculation of the clay starts to occur. The quantity of lime added in the first stage is at least sufficient to effect the more complete formation of the water-in-oil emulsion but insuf-ficient to result in any significant increase in gel strength and viscosity.
It has been found that about 0.2 to about ~.Og~
preferably about 0.5 to about 1.25g, of slaked lime per litre of slime gives satisfactory results~ the optimum amount depending on the depth of the pond from which the slime is taken.
.
:, ~13~33~
The clay suspension resulting from the separation of the water-in-oil emulsion is subjected to dewatering.
This is preferably effected by rapidly mixing the suspension with additional quantities of slaked lime sufficient to cause flocculation of the clay. It has been found that the addition of lime to these clay suspensions in increasing incremental quantities above a minimum level leads to a rapidly-increasing dewatering ability until a maximum dewatering ability is reached above which further lime additions do not significantly improve dewatering.
The quantity of lime required to be added to achieve maximum dewatering ability varies, depending on the depth o~
the ~lime ~ond being treatedO For example, for a 15 ft sample, maximum dewatering may be effected at an amount of lime of about 1 to about 2 g/lO
The flocculated clay may be separated from the aqueous phase in any convenient manner, such as/ by simple gravity se~tling, centrifugation, filtration, by free~e-thaw techniques, or b~ a combination of such techniques.
Compact clay of high solids content is obtained in a form suitable for disposalO The clear aqueous phase, which contains sodium hydroxide recovered from the slimes~ may be used to provide water requirements in the hot water process , after some softening as necessary, or may be disposed of.
An alternative manner of effecting the procedure noted above is to mix all the lime at once lnto the slime, add organic solvent to the mixture and centrifuge to separate an upper bitumen-solvent solution layer, f.rom which the bitumen may be xecovered, and a lower dense clay layer from an intermediate clear aqueous layer. This proceduret however, is much less preferred than that described above since large volumes of solvent are required, solvent losses occur in the aqueous phase and the clay, centrifuge equipment is required and separa~ion has been rendered more :~
3s difficult by an increase in viscosity brought about by excessive lime addition.
. .
: .
i-: ; .
~L~3~33eEi~iL
Other calcium salts may be used, for ~locculation of the clay in this and later~described aspects of the invention, such as, calcium chloride7 but alkali recovery i5 not effected in this case, since the sodium ions form sodium chloride.
S The slimes treatment procedure of this invention, therefore, achieves separation of the previously intractable slimes pond material into a bitumen fraction, suitable for upgrading, a compact clay fraction suitable for disposal, and-a clear aqueous layer containing recovered alkali suitable for reuse in the hot water process or for disposalO
The present invention, therefore, provides a procedure which is able to clean up the existing slimes pond to recover additional bitumen and alkali and to recover reusable water, thereby alleviating the existing major environmental problem of the hot water process.
As mentioned previously, another aspect of the present invention involves modifications to the hot water process to prevent slimes formation, so as to ~ecrease the -need for the large accumulating pond area once it has been cleaned up in accordance with the first aspect of the invention~
In the hot water process, the oil sand is conditioned with sodium hydroxide solution in a rotating drum at 180F at a pH of about 8.0 to 8~5O The conditioned pulp at about 70% solids is discharged to a feed sump to which mi~dlings recycle and ~ater are added to provide the required consistency of material for pumping to separation cells.
In the separation cells, sand settles to tha bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlingslayer containing predominantly clay minerals and some bitumen is formed between these layers. Some of this middlings layer is used for recycle to the feed sump and the major part thereof is passed througha scavenging step to recover additional amounts of bitumen by air flotation.
The oil froths from the primary separation step and the middlings scavenging step are combined, diluted with sol-, :; . .
.. . . .
: -.
.: : ,. . ~. :
~3~
vent to dissolve the bitumen, the bitumen~solvent solution is separated :Erom the aqueous phase usually by centrifugation, and removed. The solvent is removed from the bitumen for recycle and the bitumen forwarded to the upgrading plant.
The sand tailings from the separation cell, the middlings tailings from the scavenging step and the tailinys from the centrifuge step are usually con~ined in the conventional procedure and pumped to a settling pond.
In accordance with one embodiment of this aspect of the invention, this combined tailings stream is treated directly to effect separation of residual bitumen, separate clay particles as a compact mass for easy disposal and recover most of the aqueous phase of the tailings stream and the sodium hydroxide contained therein for recycle.
The combined tailings stream is allowed to stand to separate out sand therefromO The resultant clay suspen sion is mixed with slaked lime to cause the formation of a water-in-oil emulsion of residual bitumen in the suspension.
The quantity of slaked lime used should be insufficient to cause flocculation of clay particlesO The bitumen emulsion is separated by air flotation~ removed from the remaining clay suspension and returned to the oil froth treatment pro-cedure for dewatering the emulsion and the recovery of the bitumen therein. Alternatively, the emulsion may be de-~5 watered separately to effect bitumen recoveryO
Thereafter, the clay suspension is dewatered by~urther slaked lime addition followed by settling, such as, by prolonged standing, or by centrifugation, filtrakion, or a freeze~thaw operation, or ~y a combination of such operations, and a compact clay mass is formed, suitable for disposal. The suh-stantially clear aqueous phase containing recovered alkali is suitable for recycle as water make-up within the hot water process, after softening toremove residual calcium ions, if required~
The clay settling step may be effected in a large pond area. This pond is substantially different in size from the slimes pond now used in the hok water process~ The se-ttling pond produces clear water for recycle and forms a compact clay mass for disposal, in contrast with the existing slimes pond wherein less water recovery can be effected in a reasonable period of time.
The procedure used in accordance with -this one feature of this aspect of the invention, the~refore, is analogous in certain respects to that employed in the slimes treatment procedure described in detail ahove~
The considerations governing the quantity of lime employed in the two separate lime additionc with respect to that procedure also apply with respect to the procedure of this aspect of the invention.
A modification of this embodiment of the invention is to omit combination of the sand tailings stream with the other tailings streams and treat the clay tailings streams in accordance with the procedure described above~
In accordance with another embodiment of this second aspect of the invention, the major portion of the middlings stream from the primary separation step, instead of passing directly to the flotation scavenging operation first is rapidly mixed with slaked lime prior to passage to the flotation scavenging operation in order to improve the separation of bitumen from the aqueous phase as a water-in oil emulsion. The quantit~ of slaked lime used should be insufficient to cause the flocculation of clay particles at this stage. The bitumen separation procedure may be urther enhanced by subjecting the middlings stream to an aeration-oxidation step prior to the slaked lime addition.
The tailings stream from the flotation step is sub-stantially bitumen-free and, after combining with the clay suspension from the separation o bit~men-solvent solution, and optionally after combination with the sand tailings from the primary separator, is subjected to dewatering and separa-tion using slaked lime, as described above with respect to other bitumen-free clay suspensions.
The invention is described further, by way of illustration, with reference to the accompanying drawings, in whicho Figure 1 is a schematic flow sheet of slimes separ-ation and bitumen recovery procedure according to one embodiment of the invention;
Figure 2 is a schem~tic flow sheet of one modifica-tion to the hot water process for preventing slimes . - , . ..
- i ~: :
: . ~
:: , : : , :, :~:: ~ :;
., iormation; and Figure 3 is a schematic flow sheet of a second modification to the hot water process for preventing slimes formation O
Refexring first to Figure 1, which illuskrates a slimes treatment procedure, slime from the slimes pond is passed by line 10 to a mixing tank 12 wherein sufficient slaked lime fed by line 14 is rapidly mixed therewIth to form a water-in-oil emulsion from the bitumen contained in the slime and additionally aften to decrease the gel strength and viscosity of the slime.
The lime-treated slime is passed by line 16 to a flotation tank 18 wherein the water-in-oil emulsion is caused to separate as an upper layer by dispersed airO
Any other convenient separation technique may be employed.
The water-in~oil emulsion~ or "~itumen ~roth~' or "oil froth"
as it is somètimes called when formed in the hot water process,after separation from the aqueous phase, may hé
forwarded to the bitumen froth clean-up operation in the hot water process plant, or may be dewatered separately, as illustratedO
The bitumen froth is forwarded by line 20 to a mixing tank 22 wherein a water-immiscible solvent for the bitumen, such as~ naphtha, fed by line 24, i5 mixed therewith to dissolve the bitumen. This mixture is forwarded by line 26 -to a centrifuge 28 wherein the bitumen-solvent solution is separated ~rom the aqueous phase. The need Eor centrifugation may be decreased by the addition of clear water to the bitumen froth prior to addition of the solvent thereto~
The bitumen-solvent solution is forwarded by line 30 to solvent recovery 32. The solvent may be recovered by any convenient tec~mi~ue, such as, distillation, and the recovered solvent is recycled by line 34 to the solvent inlet line 24 along with any make-up solvent fed by line 36.
The bitumen which is recovered following solvent separation is removed by line 38 for passage to the bitumen upgrading procedure of the oil sands treatment plant.
The clay suspension resultin~ from the flotation separation of the water-in-oil emulsion in flotation tank :~ :
, - '' . .
.
~3L3~6~L
g 18 is passed by line 40 to a mixing tank 42. The small volume of clay suspension resulting from the centrifuge 28 after separation of the bitumen-solvent solution also may be forwarded by line 44 to the mixing tank 42 or to the 5 flotation tank 18.
In the mixing tank 42, the clay suspensions are rapidly mixed with sufficient slaked lime fed by line 46 to 10cculate the clay particles and permit dewatering of the suspension. The limed suspension is then forwarded by line 10 48 to a dewatering and settling pond 50~ wherein the limed suspension is subjected to any convenient dewatering and ;
settling procedure, such as, simple gravity settling by per mitting the limed suspension to stand for a prolonged period, or the limed suspension may be dewatered by subjecting the 15 same to centrifugationr to ~reezing and thawing, or to filtra-tion. A o~ination of such dewatering techniques also may be usedO
A compact clay mass 52 results from the dewatering suitable for disposal. The clear aqueous phase remaining contains recovered sodium hydroxide and is suitable for re-20 use, after softening to remove residual calcium ions, ifnecessary, for example, using sodium carbonate, and/or for disposal, as desiredt and is removed from pond 50 by line 54.
The procedure described with respect to Figure 1, therefore, achieves substantially complete separation of the 25 previously~substantially inseparable slime into its component constituents of bitumen, clay and water by a controlled two-stage addition of slaked lime ~ombined with sim le and inex-pensive separation techni~uesO
Turning now to Figure 2, wherein there is illus-30 trated a modification of the hot water process to preventthe formation of slimes and the accumulation of a slimes pond, oil sand and water along with sodium hydroxide are fed respectively by lines 110 and 112 to a conventional hot water process plant 114 producing bikumen in line 116 35 ~rom the oil sand suitable for upgrading and an aqueous tailings stream in line 118 .
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~383~`~
The tailings st.ream 118 consists of an aqueous sus-pension of clay and sand particles and is normally discharged to the slimes pond, the sand separating out to form pond dykes. In the illustrated inventive process, the tailings stream 118 first is forwarded to a sand se.parator 120 wherPin sand and other readily separable solids rapidly gravity settle from the tailings and are removed clS a compact mass by line 122 for dlsposal as landfill or ot:herwise.
The remainder of tailings stream consisting of a relatively stable suspension of clay and emulsified bitumen particles in water is forwarded by line 124 to a mixing tank 126 wherein the suspension is rapidly mixed with sufficient slaked lime fed b~ line 123 to cause the bitumen to form a water-in-oil emulsion bu~ .~nsufficient to çause flocculation of the claysn The limed suspension is forwarded by line 130 to a flotation tank 132 wherein the water-in-oil emulsion is separated by dispersed air flotation~ or any other convenient technique.
The water-in-oil emulsion~ or "bitumen froth" as equivalent emulsions ~ormed.in the hot water process are sometimes called, is removed from the remaining relatively bitumen-free cla~ suspension and is forwarded by line 134 to the bitumen froth dewatering procedure of the hot water process plant 114 or to a separate dewatering procedure for the recovery of bitumen, ~or example, that illustrated in Figure 1 in connection with the bitumen froth in line 200 The clay suspension remaining following bitumen froth removal is forwarded by line 136 to a mixing tank 138 wherein the clay suspension is rapidly mixed with sufficient slaked lime ~ed by line 140 to flocculate the clay particles.
If desired, the clay suspension in line 136 may first be subjected to a settling step to remove kaolinite therefrom.
The limed suspension is passed by line 142 to a dewatering and clay settling pond 144 wherein any convenient clay de-watering technique may be adopted, such as, simple gravitysettling by allowing the limed suspension to stand for a prolonged period. Any other convenient dewatering technique may be employed, such as, centrifugation, freezing and thaw-ing, or filtration of the limed suspension, or by a combina-.. ~ . ~ . :
, ., ' . '' ~' ' ' :
. :
: . :
~13836~
11tion of these procedures.
The separatea clay is obtained as a compact mass 146 which may remain in the settling pond :L44, or may be removed for disposal. The clear aqueous phase containing 5 recovered alkali is recycled by line 148 t:o the water inlet line 112 for reuse in the hot water process plant 114. Any make-up water and alkali required are added to the water inlet line 112 by line 150.
The pxocedure of Figure 2, thereforel directly 10 treats ~he tailings stream of a hot water process plant by a controlled two-stage slaked lime addition thereto combined with simple and inexpensive separation technique to recover additional bitumen, produces compact sand and clay effluents which are suitable for simple disposal and recovers 15 a substantial proportion of the water and sodium species o$
the tailinys stream or reuseO `
Figure 3 illustrates a further modification to the hot water process which results in a more readily separable tailings stream than is normally the case and avoids the 20 necessity for separate separation of residual ~itumen, such as occurs in the procedure of Figure 2.
In Figure 3, oil sands and water and steam are ~ed respectively by lines 210 and 212 to a conditioning - tank 214. The pulp so formed is forwarded by line 216 to 25 a feed sump 218 wherein it is mixed with water and sodium hydroxide fed by line 220 and recycle middlings stream 222 to the desired consistency and then passed by lme 224 to a primary separator 226. In the primary separ~tor 226, the mixture is separated into a lower sand layer which is removed by 30 ~ine 228 for disposal, an upper oil fxoth layer which is removed by line 230 for bitumen recovery and an intermediate middlings layer which is partly recycled by line 222 to the feed sump 218 and partly removed by line 232 for froth processing.
The oil froth in line 230 enters a mixing tank 234 to which a water-immiscible solvent fo~ the bitumen, such as9 naphtha or hexane, is also fed by line 236 for mixing there-with to form a solution of the bitumen in the solvent~ If desired, clear water may be added to the oil froth prior to ~3~3~
solvent addition. The resulting mixture is passed by line 238 to a centri~uge 240 to separa-te the bitumen solvent solution from the aqueous phase.
The bitumen-solvent solution is removed from the centrifuge 240 and f~rwarded by line 242 to solvent recovery 244 wherein -the solvent is removed, such as, by distillation, and recycled by line 246 to the mixing tank feed line 236, make-up quantities o solvent being fed by line 248. The bitumen remaining after solvent removal is passe~ by ~ine 250 ~o an upgrading plant.
The aqueous phase remaining ~rom centrifugation, consisting of a relatively bitumen-free suspension of clay particles in water~ is removed fxom the centrifuge by line The procedures so far described with respect to Figure 3 are the we~l-known conventional ones of a hot water process plant for the separation of bitumen from oil sands and require no ~urther explanation.
In accordance with thi~ modi~ication to the hot water process, the middlings stream in line 232, consisting of bitumen, clay and water, is fed into a mixing tank 254 wherein it is rapidly mixed with slaked lime fed by line 256. The lime addition may be preceded ~y an aeration-oxidation treatment to improve later separation of the bitumen.
The lime is used in a quantity su~ficient to effect formation of a water-in~oil emulsion of the ~itumen contained in the middlings stream but insufficient to cause floc¢ula-tion of clay particles. The limed middlings stream is passed by line 2S8 to a ~lotation tank 260 w~erein the emulsion is separated from the remainder o~ the aqueous phase by dispersed air flotation~ Any other convenient separation technique may ~e employed.
The separated water-in-oil emulsion, or "oil froth"
is passed by line 262 to the solvent mixing tank 234 for emulsion dewatering along with the oil froth in line 230.
In the conventional hot water process, the middlings stream 232 is fed directly to the flotation tank 260. The liming . .
~3836~
treatmeni: and optional pre-oxidation treatment ensure more complete separation of bitumen from the aqueous phase and eliminates the necessi.ty to process the aqueous phase separately to effect such bitumen separation, such as is 5 described above with respect to Figure 2.
The aqueous phase remaining a~ter separation of the oil froth formed in the flotation step, consisting of a suspension of clay particles, is forwarcled by line 264 to a mixing tank 266, along with the clay suspension in I0 line 252. To the mixing tank 266 is rapidly added sufficient slaked lime by line 268 to effect flocculation and dewatering of the clay suspension. If desired, the clay suspension in line 264 may first be subjected to a settling step to remove kaolinite therefromO
The limed suspension is forwarded by line 270 to a settling pond 272 wherein the suspension is subjected to any desired clay dewatering procedure, such as, simple gravity settling. Any other convenient dewatering techni~ue may be.
used, such as, centrifugation, a freeze-thaw technique, fil-20 tration or a combination~ :
The clay settles from the aqueous phase and forms a compact mass 274 w~ich can remain in the pond 272~ or may be disposed of. The remaining clear aqueous phase containing sodium hydroxide is removed from the pond 272 by line 276 and 25 is recycled to the water inlet line 220 as reusable water~
Any make-up water and alkali requirements are fed by line 278.
As in the case of the procedure of Figure 2, the pro-cedure of Figure 3 eliminates the necessity for an extensive slimes pond, since the waste effluent from the procedure is in 30the form of compact solids which are readily disposed of, and effects economic use of alkali.
While the various operat~ons described above in~
connection with Figurés 1 to 3 have been indicated to occur in separate reaction vessels, khis is for convenience and 35ease of illustration and description~ In certain cases, combinations of two or more of the individual operations may he effected in the same reaction vessel r if convenient.
The invention is illustrated further by the following Examples:
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~1383~L
Example 1 This Example shows the effect of the addition of slaked lime on the yel strength of slimes.
Samples of slimes from the 15-foot and 30-foot 5 depths of the slimes pond at the Suncor Ltd. facility at Fort Mc~urray, Alberta were treated with varying quantities of lime and the gel strength of the resulting slimes was measured on a Fann Viscometer. The results are reproduced in the following Table I:
TABLE I
Lime10 min. gel str~ngth Addition(lb./100 sq.ftO) (g/l) 15 foot 30 fo~t o.oO 23 32 0~50 - 19 0~66 6 6 1.00 4 5 1.66 8 7 ,
2.0~ 8 10 2.33 9 8 2.66 63 22
3.00 41 It will be seen from the results of the above Table that the addition of slaked lime initially caused a decrease in the gel strength of the slimes, the effect being more pro-nounced for the 30-foot sampleO Continued addition of slaked lime caused a sharp increase in the gel strengkhO
~
Based on a series of laboratory experiments, a mass balance for the slimes treatment procedure illustrated in Figure 1 was arrived atO
750 ml ~795 g~ of slime from the 15 ft, level of a hok water process slimes pond containiny about 22 wt%
solids and about 13 wt~ bitumen on a dry basis is rapidly mixed for about 3a seconds with 0.3 y of slaked lime per 400 ml of slimeO The mixture is subjected to air ~lotation with dispersed air to separate 85 ml of drained hitumen froth and .: ;. . .. . . .
: . . -:
, ~ . ., . ~ . .. .
. , . :: , . , ~ . . i :, .
: ,: :,:
11383~
leave 690 ml o~ clay suspension.
The bitumen froth is separated from the clay suspension, mixed with "VARSOL" (Trademark) 3139 in a 2 to l volume ratio and centrifuged at a rate of 1600 x g to separate a bitumen-solvent solution from a clay suspension.
18 g of bitumen are separated from the slimes by this procedure, representing R0% of the bitumen contained therein.
The clay suspension from the air flotation step is rapidly mixed for 10 seconds with 1.38 g o~ slaked 7ime and 10 the limed suspension subjected to freezing and thawiny whereupon the clay settles from the aqueous medium. 235 g o clay of 57 wt% solids consistency and containing 3.4 wt%
bitumen on a dry basis is recovered along with 456 ml of clear water.
15 Example 3 Slimes from the 30-foot level of a hot water process slimes pond containing 25.6 wt.% solids and about 4.7 wt.%
bitumen on a dry basis was rapidly mixed with 2 gpl of slaked lime. The mixture was subjected to air flotation with dis-2~ persed air for 12 minutes to separate a bitumen froth. Thebitumen froth was separated from the resulting clay suspen-sion and was found to contain about 22,7 wt.~ bitumen~
representing 68.6 wt.% of the bitumen in the slimes The remaining clay suspension was separated into two batches. To both batches was rapidly mixed 2 gpl of slaked lime. One batch was allowed to settle by gravity for 201 days at room temperature while the other batch was centri-fuged for 90 minsO at 2000 rpm. In each case the clay suspen-sion separated into a compact lower clay layer and an upper clear water layer~ The solids content of the clay layer and the percent water recovery in the clear water layer were determined. The results appear in the following Table IIo TABLE I I
Clay Layer Clear Layer 3S wt.% solids wt.~ recovery Centrifugation48~9 63.9 Gravity Settling 34.2 33.9 The results shown in the above Table II indicate . : :
:~ :
L3~33~ii31 that centrifugation was superior to gravity settling in terms of water recovery, as determined under the conditions of the experimentO
In summary of this disclosure, the present invention provides a slimes pond clean-up procedure which enables residual bitumen and reusable water to be recovered from the slimes and a dense clay mass to be formed for ready disposal. The present invention also inc]udes modi.~ications to the hot water process to eliminate slimes production and the necessity for a slimes pond, Modifications are possible within the scope of the inventionO
.~ ,
~
Based on a series of laboratory experiments, a mass balance for the slimes treatment procedure illustrated in Figure 1 was arrived atO
750 ml ~795 g~ of slime from the 15 ft, level of a hok water process slimes pond containiny about 22 wt%
solids and about 13 wt~ bitumen on a dry basis is rapidly mixed for about 3a seconds with 0.3 y of slaked lime per 400 ml of slimeO The mixture is subjected to air ~lotation with dispersed air to separate 85 ml of drained hitumen froth and .: ;. . .. . . .
: . . -:
, ~ . ., . ~ . .. .
. , . :: , . , ~ . . i :, .
: ,: :,:
11383~
leave 690 ml o~ clay suspension.
The bitumen froth is separated from the clay suspension, mixed with "VARSOL" (Trademark) 3139 in a 2 to l volume ratio and centrifuged at a rate of 1600 x g to separate a bitumen-solvent solution from a clay suspension.
18 g of bitumen are separated from the slimes by this procedure, representing R0% of the bitumen contained therein.
The clay suspension from the air flotation step is rapidly mixed for 10 seconds with 1.38 g o~ slaked 7ime and 10 the limed suspension subjected to freezing and thawiny whereupon the clay settles from the aqueous medium. 235 g o clay of 57 wt% solids consistency and containing 3.4 wt%
bitumen on a dry basis is recovered along with 456 ml of clear water.
15 Example 3 Slimes from the 30-foot level of a hot water process slimes pond containing 25.6 wt.% solids and about 4.7 wt.%
bitumen on a dry basis was rapidly mixed with 2 gpl of slaked lime. The mixture was subjected to air flotation with dis-2~ persed air for 12 minutes to separate a bitumen froth. Thebitumen froth was separated from the resulting clay suspen-sion and was found to contain about 22,7 wt.~ bitumen~
representing 68.6 wt.% of the bitumen in the slimes The remaining clay suspension was separated into two batches. To both batches was rapidly mixed 2 gpl of slaked lime. One batch was allowed to settle by gravity for 201 days at room temperature while the other batch was centri-fuged for 90 minsO at 2000 rpm. In each case the clay suspen-sion separated into a compact lower clay layer and an upper clear water layer~ The solids content of the clay layer and the percent water recovery in the clear water layer were determined. The results appear in the following Table IIo TABLE I I
Clay Layer Clear Layer 3S wt.% solids wt.~ recovery Centrifugation48~9 63.9 Gravity Settling 34.2 33.9 The results shown in the above Table II indicate . : :
:~ :
L3~33~ii31 that centrifugation was superior to gravity settling in terms of water recovery, as determined under the conditions of the experimentO
In summary of this disclosure, the present invention provides a slimes pond clean-up procedure which enables residual bitumen and reusable water to be recovered from the slimes and a dense clay mass to be formed for ready disposal. The present invention also inc]udes modi.~ications to the hot water process to eliminate slimes production and the necessity for a slimes pond, Modifications are possible within the scope of the inventionO
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Claims (20)
1. A method of treatment of slimes from a tailings pond of a hot water process for the recovery of bitumen from oil sands, said slimes comprising a suspension of clay and bitumen in water, which method comprises:
mixing sufficient slaked lime with said slimes to form a water-in-oil emulsion from said bitumen, separating said water-in-oil emulsion from the resulting clay suspension, and dewatering said resulting clay suspension.
mixing sufficient slaked lime with said slimes to form a water-in-oil emulsion from said bitumen, separating said water-in-oil emulsion from the resulting clay suspension, and dewatering said resulting clay suspension.
2. The method of claim 1 wherein about 0.2 to about 2.0 g of slaked lime is mixed per litre of slimes.
3. The method of claim 2 wherein the quantity of slaked lime is about 0.5 to about 1.25 gpl of slimes.
4. The method of claim 1, 2 or 3 wherein said oil-in-water emulsion is separated from said clay suspension by air flotation.
5. The method of claim 1, 2 or 3 wherein said water-in-oil emulsion is separated from said clay suspension by air flotation and said water-in-oil emulsion is dewatered to recover bitumen therefrom.
6. The method of claim 1 wherein said clay suspension is dewatered by mixing a calcium salt with the suspension in an amount sufficient to flocculate the same and effecting separation of solid and aqueous phases.
7. The method of claim 6 wherein the calcium salt is slaked lime and said latter slaked lime is used in an amount of about 1 to about 2 gpl of suspension.
8. The method of claim 7 wherein the slaked lime used in said emulsion formation step is mixed with said slimes in an amount of about 0.2 to about 2.0 gpl of slimes.
9. A method of treating a tailings stream from a hot water process for the recovery of bitumen from oil sands, said tailings stream comprising an aqueous suspension of clay and bitumen, which comprises mixing sufficient slaked lime with said tailings stream to form a water-in-oil emulsion from said bitumen, separating said water-in-oil emulsion from the resulting clay suspension, and dewatering said resulting clay suspension.
10. The method of claim 9 wherein said water-in-oil emulsion is separated from the clay suspension by air flotation.
11. The method of claim 9 wherein said water-in oil emulsion is separated from the clay suspension by air flotation and said water-in-oil emulsion is dewatered to recover bitumen therefrom.
12. The method of claim 11 wherein said dewatering of said water-in-oil emulsion is effected in an oil froth dewatering operation in said hot water process.
13. The method of claim 9 wherein said tailings stream also contains sand and said sand is separated therefrom prior to said mixing with said slaked lime.
14. The method of claim 9, 11 or 13 wherein said clay suspension dewatering is effected by mixing at least sufficient slaked lime with the same to effect flocculation of the clay particles and to form sodium hydroxide solution therefrom and effecting separation of solid and aqueous phases.
15. The method of claim 91 11 or 13 wherein said clay suspension dewatering is effected by mixing at least sufficient slaked lime with the same to effect flocculation of the clay particles and to form sodium hydroxide solution therefrom and effecting separation of solid and aqueous phases, and the aqueous phase resulting from said latter separation is recycled to said hot water process for use therein.
16. In a method for the recovery of bitumen from oil sands by slurrying said oil sands with an aqueous medium at an elevated temperature, separating the slurry into an oil froth phase containing most of the bitumen from the oil sands, an aqueous phase containing clay minerals and some bitumen and a sand phase, recycling part of the aqueous phase to slurry formation, effecting additional bitumen recovery from the remainder of said aqueous phase in the form of an oil froth, dewatering the oil froths to recover bitumen and provide an aqueous stream, and dischar-ging a tailings stream comprising an aqueous clay suspension resulting from said additional bitumen recovery and said aqueous stream, the improvement which comprises:
mixing sufficient slaked lime with said remainder of said aqueous phase to form a water-in-oil emulsion from the bitumen therein, and dewatering said tailings stream.
mixing sufficient slaked lime with said remainder of said aqueous phase to form a water-in-oil emulsion from the bitumen therein, and dewatering said tailings stream.
17. The method of claim 16 wherein said tailings stream is dewatered by mixing at least sufficient slaked lime with the same to effect flocculation of clay particles therein and to form sodium hydroxide solution therefrom and effecting separation of solid and aqueous phases.
18. The method of claim 17 wherein said aqueous phase is recycled to said slurrying step.
19. The method of claim 16 wherein said oil froths are dewatered by adding at least sufficient water-immiscible solvent for bitumen to said oil froths to form a bitumen-solvent solution and separating the bitumen-solvent solution from the remaining aqueous phase.
20. The method of claim 19 wherein said remaining aqueous phase is recycled to said slurrying step.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7920002 | 1979-06-08 | ||
| GB7920002 | 1979-06-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1138361A true CA1138361A (en) | 1982-12-28 |
Family
ID=10505724
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000353509A Expired CA1138361A (en) | 1979-06-08 | 1980-06-06 | Treatment of oil sands slimes and modified bitumen recovery process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1138361A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8354020B2 (en) | 2008-06-27 | 2013-01-15 | Exxonmobil Upstream Research Company | Fouling reduction in a paraffinic froth treatment process by solubility control |
| US10647606B2 (en) | 2017-08-18 | 2020-05-12 | Graymont Western Canada Inc. | Treatment of oil sands tailings with lime at elevated pH levels |
| US10894730B2 (en) | 2018-09-11 | 2021-01-19 | Graymont (Pa) Inc. | Geotechnical characteristics of tailings via lime addition |
| US11027995B2 (en) | 2017-11-08 | 2021-06-08 | Graymont Western Canada Inc | Treatment of tailings streams with one or more dosages of lime, and associated systems and methods |
-
1980
- 1980-06-06 CA CA000353509A patent/CA1138361A/en not_active Expired
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8354020B2 (en) | 2008-06-27 | 2013-01-15 | Exxonmobil Upstream Research Company | Fouling reduction in a paraffinic froth treatment process by solubility control |
| US10647606B2 (en) | 2017-08-18 | 2020-05-12 | Graymont Western Canada Inc. | Treatment of oil sands tailings with lime at elevated pH levels |
| US11390550B2 (en) | 2017-08-18 | 2022-07-19 | Graymont Western Canada Inc. | Treatment of oil sands tailings with lime at elevated PH levels |
| US11613485B2 (en) | 2017-08-18 | 2023-03-28 | Graymont Western Canada Inc. | Treatment of tailings with lime at elevated PH levels |
| US11027995B2 (en) | 2017-11-08 | 2021-06-08 | Graymont Western Canada Inc | Treatment of tailings streams with one or more dosages of lime, and associated systems and methods |
| US11618697B2 (en) | 2017-11-08 | 2023-04-04 | Graymont Western Canada Inc. | Treatment of tailings streams with one or more dosages of lime, and associated systems and methods |
| US10894730B2 (en) | 2018-09-11 | 2021-01-19 | Graymont (Pa) Inc. | Geotechnical characteristics of tailings via lime addition |
| US11718543B2 (en) | 2018-09-11 | 2023-08-08 | Graymont Western Canada Inc. | Geotechnical characteristics of tailings via lime addition |
| US11724946B2 (en) | 2018-09-11 | 2023-08-15 | Graymont Western Canada Inc. | Geotechnical characteristics of tailings via lime addition |
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