CA1109408A - Destabilization and improvement in permeability and shear strength of sludge treated with hydrolyzed starch flocculant and portland cement - Google Patents
Destabilization and improvement in permeability and shear strength of sludge treated with hydrolyzed starch flocculant and portland cementInfo
- Publication number
- CA1109408A CA1109408A CA295,881A CA295881A CA1109408A CA 1109408 A CA1109408 A CA 1109408A CA 295881 A CA295881 A CA 295881A CA 1109408 A CA1109408 A CA 1109408A
- Authority
- CA
- Canada
- Prior art keywords
- sludge
- layer
- pond
- normalized
- pounds per
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/01—Separation of suspended solid particles from liquids by sedimentation using flocculating agents
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/5263—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using natural chemical compounds
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Treatment Of Sludge (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A treatment for a tar sands tailing pond is disclosed whereby an increase in shear strength and permeability of a sludge layer within the pond is attained. The treatment comprises the combined application of potato starch flocculant and Portland cement.
A treatment for a tar sands tailing pond is disclosed whereby an increase in shear strength and permeability of a sludge layer within the pond is attained. The treatment comprises the combined application of potato starch flocculant and Portland cement.
Description
DESTABILIZATION AND IMPROVEMENT IM
PERMEABILITY AND SYEAR STRRNGTH IN SLUDGE TREATED
WIT~ HYDROLYZED STA2CH FLOCCULANT AND PORTLAND CE~ENT
~AC~GROUND OF THE INVENTION
This invention relates to the hot water process for treating bituminous sands, such as Athabasca tar sands, and more particularly, to the treatment of the water and fines-containing effluent discharged from the process.
Tar sands (which are also known as oil sands and bitu-minous sands) are sand deposits which are impregnated with dense, viscous petroleum. Tar sands are found throughout the world, often in the same geographical areas as conventional petroleum. The largest deposit, and the only one of present commercial importance is in the Athabasca area in the northeast of the Province of Alberta, Canada. This deposit is believed to contain perhaps 700 billion - 1 trillion barrels of bitumen.
For comparison, 700 billion barrels is just about equal to the world-wide reserves of conventional oil, 60~ of which is found in the Middle East.
~f~
Athabasca tar sand is a three-component mixture of bitumen, mineral and water. Bitumen is the value for the extraction of which tar sands are mined and processed.
The bitumen content is variable, averaging 12 wt.% of the deposit, but ranging from 0 to 18 wt.%. Water typically runs 3 to 6 wt.% of the mixture, increasing as bitumen content decreases. The mineral content is relatively constant ranging from 84 to 86 wt.%.
Several basic extraction methods have been known for many years for separating the bitumen from the sands. In the so-called "cold water" method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in water. The combined mass is then subjected to a pressure or gravity separation.
The hot water process for primary extraction of bitumen from tar sands consists of three major process steps (a fourth step, final extraction, is used to clean up the recovered bitumen for downstream processing.) In the first step, called conditioning, tar sand is mixed with water and heated with open steam to form a pulp of 70 to 85 wt.%
solids. Sodium hydroxide or other reagents are added as required to maintain pH in the range 8.0 - 8.5. In the second step, called separation, the conditioned pulp is diluted further so that settling can take place. The bulk of the sand-size mineral rapidly settles and is withdrawn as sand tailings. Most of the bitumen rapidly floats (settles upward) to form a coherent mass known as froth which ~ L$~ 3 is recovered by skimming the settling vessel. A third stream may be withdrawn from the settling vessel. This stream, called the middlings drag stream, may be subjected to a third processing step, scavenging. This step provides incremental recovery of suspended bitumen and can be ac-complished by conventional froth flotation.
The mineral particle size distribution is particularly significant to operation of the hot water process and to sludge accumulation. The terms sand, silt, clay, and fines are used in this specification as particle size designations wherein sand is siliceous material which will not pass a 325 mesh screen. Silt will pass 325 mesh, but is larger than
PERMEABILITY AND SYEAR STRRNGTH IN SLUDGE TREATED
WIT~ HYDROLYZED STA2CH FLOCCULANT AND PORTLAND CE~ENT
~AC~GROUND OF THE INVENTION
This invention relates to the hot water process for treating bituminous sands, such as Athabasca tar sands, and more particularly, to the treatment of the water and fines-containing effluent discharged from the process.
Tar sands (which are also known as oil sands and bitu-minous sands) are sand deposits which are impregnated with dense, viscous petroleum. Tar sands are found throughout the world, often in the same geographical areas as conventional petroleum. The largest deposit, and the only one of present commercial importance is in the Athabasca area in the northeast of the Province of Alberta, Canada. This deposit is believed to contain perhaps 700 billion - 1 trillion barrels of bitumen.
For comparison, 700 billion barrels is just about equal to the world-wide reserves of conventional oil, 60~ of which is found in the Middle East.
~f~
Athabasca tar sand is a three-component mixture of bitumen, mineral and water. Bitumen is the value for the extraction of which tar sands are mined and processed.
The bitumen content is variable, averaging 12 wt.% of the deposit, but ranging from 0 to 18 wt.%. Water typically runs 3 to 6 wt.% of the mixture, increasing as bitumen content decreases. The mineral content is relatively constant ranging from 84 to 86 wt.%.
Several basic extraction methods have been known for many years for separating the bitumen from the sands. In the so-called "cold water" method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in water. The combined mass is then subjected to a pressure or gravity separation.
The hot water process for primary extraction of bitumen from tar sands consists of three major process steps (a fourth step, final extraction, is used to clean up the recovered bitumen for downstream processing.) In the first step, called conditioning, tar sand is mixed with water and heated with open steam to form a pulp of 70 to 85 wt.%
solids. Sodium hydroxide or other reagents are added as required to maintain pH in the range 8.0 - 8.5. In the second step, called separation, the conditioned pulp is diluted further so that settling can take place. The bulk of the sand-size mineral rapidly settles and is withdrawn as sand tailings. Most of the bitumen rapidly floats (settles upward) to form a coherent mass known as froth which ~ L$~ 3 is recovered by skimming the settling vessel. A third stream may be withdrawn from the settling vessel. This stream, called the middlings drag stream, may be subjected to a third processing step, scavenging. This step provides incremental recovery of suspended bitumen and can be ac-complished by conventional froth flotation.
The mineral particle size distribution is particularly significant to operation of the hot water process and to sludge accumulation. The terms sand, silt, clay, and fines are used in this specification as particle size designations wherein sand is siliceous material which will not pass a 325 mesh screen. Silt will pass 325 mesh, but is larger than
2 microns, and clay is material smaller than two microns in-cluding some siliceious material of that size.
Conditioning tar sands for the recovery of bitumen ; consists of heating the tar sand/water feed mixture to pro-cess temperature (180-200F), physical mixing of the pulp to uniform composition and consistency, and the consumption (by chemical reaction) of the caustic or other reagents added.
Under these conditions, bitumen is stripped from the indiv-idual sand grains and mixed into the pulp in the form of dis-crete droplets of a particle size on the same order of that of the sand grains. The same process conditions, it turns out, are also ideal for accomplishing deflocculation of the clays which occur naturally in the tar sand feed. Defloccu-lation, or dispersion, means breaking down the naturally occurring aggregates of clay particles to produce a slurry of individual particles. Thus, during conditioning, a large fraction of the clay particles become well dispersed and mixed thoroughout the pulp.
v ~
Those skil]ed in the art wlll therefore understand that the conditioning process, which prepares the resources (bitumen) for efficient recovery during the following process steps also prepares the clays to be the most clifficult to deal with in the tailings disposal operations.
The second process step, called separation, is actually the bitumen recovery step, (the separation having already occurred during conditioning). The conditioned tar sand pulp is screened to remove rocks ancd unconditionable lumps of tar sands and clay. The reject material, "screen oversize", is discarded. The screened pulp is further diluted with water to promote two settling processes: globules of bitumen, essentially mineral-free, settle (float) upward to form a coherent mass of froth on the surface of the separation cells;
and, at the same time, mineral particles, particularly the sand size mineral, settle down and are removed from the bottom of the separation cell as tailings. The medium through whieh these two settling processes take place is ealled the middlings. The middlings eonsists primarily of water, with suspended fine material and bitumen partieles.
The partiele sizes and densities of the sand and of the bitumen partieles are relatively fixed. The parameter whieh influenees the settling proeesses most is the viseosity of the middlings and viseosity is directly related to fines eontent. Charae~eristieally, as the fines content rises above a eertain thresholcl (whieh varies aeeording to the eomposition of the fines), middlings viscosity rapidly reacnes high values with the effect that the settling processes essentially stop.
In this operating condition, the separation cell is said to be "upset". Little or no oil is recovered, and all streams exiting the eell have about the same composition as the feed.
As feed fines content increases, more water must be used in the process to maintain middlings viscosity within the operable range.
The third step of the hot water process is scavenging.
The feed fines content sets the process water requirement through the need to control middlings viscosity which, as noted above, is governed by the clay/water ratio. It is usually necessary to withdraw a drag stream of middlings to maintain the separation cell material balance, and this stream of middlings can be scavenged for recovery of in-cremental amounts of bitumen. Air flotation is an effec-tive scavenging method for this middlings stream.
Final extraction or froth clean-up is typically ac-complished by centrifugation. Froth from primary extrac-tion is diluted with naptha, and the diluted froth is then subjected to a two stage centrifugation. This process yields an oil product of an essentailly pure (diluted) bitumen. Water and mineral removed from the froth, during this step constitute an additional tailing stream which must be disposed of.
In the terminology of extractive processing, tailings is the throwaway material generated in the course of ex-tracting the valuable material from an ore. In tar sands processing, tailings consist of the whole tar sand ore body plus net additions of process water less only the recovered bitumen product. Tar sand tailings can be sub-divided into three categories; viz: (1) screen oversize, (2) sand tailings (the fraction that settles rapidly), and (3) tailings sludge (the fraction that settles slowly).
Screen oversize is typically collected and handled as a separate stream.
, " ~
~$~
Tailings dlsposal is all the operations required to place the t~.ilings in a final resting place. One obvious long-range goal of tailings disposal is to replace the tailings in the mined out area in a satisfactory form. Thus, in tar sands processing, there are two main operating modes for tailings disposal: (1) "dike building" which is hydraulic conveying of tailings followed by mechanical compaction of the sand tailings fraction; and (2) "overboarding" which is hydraulic transport with no mechanical compaction.
~ecently, in view of the high level of ecological consciousness in Canada and the United States, technical interest in tar sands operation has begun to focus on tailings disposal. The concept of tar sands tailings disposal is straightforward. Visualize mining one cubic foot of tar sands. Thisleaves a one cubic foot hole in the ground.
The ore is processed to recover the resource (bitumen) and the remainder, including both process material and the gangue, constitutes the tailings; tailings that are not valuable and are to be disposed of. In tar sands processing, the main process material is water, and the gangue is mostly sand with some silt and clay. Physically, the tailings consists of a solid part (sand tailings) and a more or less fluid part (sludge). The most satisfactory place to dispose of these tailings is, of course, the existing one cubic foot hole in the ground. It turns Ollt, however, that the sand tailings from the one cubic foot of ore occupy just about one cubic foot.
The amount of sludge is a variable, depending on ore quality and process conditions, but may run up to 0.3 cubic feet.
4~
The tailings simply will no~ fit into the hole in the ground.
The historical literature covering the hot water process for the recovery of bitumen from tar sands contains little in the way of a recognition that a net accumulation of liquid tailings or sludge would occur. Based on analysis of field test unit operations which led to the Great Canadian Oil Sands plant design near Ft. McMurray, Alberta, the existence of sludge accumulation was predicted. This accumulation came to be called the "pond water problem".
Observations during start-up and early commercial operations at Ft. McMurray (1967-1969) were of insufficient precision to confirm the prediction. Since 1969, commercial operating data have confirmed the accumulation in GCOS' tailings disposal area of a layer of fine material and water (sludge) which settles and compacts only very slowly, if at all after a few years.
At the GCOS plant, for dike building, tailings are conveyed hydraulically to the disposal area and discharged onto the top of a sand dilce which is constructed to serve as an impoundment for a pool of liquid contained inside.
On the dike, the sand settles rapidly, and a slurry of fines, water, and minor amounts of bitumen flows into the pond interior. The settled sand is mechanically compacted to build the dike to a higher level. The slurry which drains into the pond interior commences stratification in settling over a time scale of months to years. As a result of this long-term settling, two layers form. The top 5 to 10 feet of the pool are a layer of relatively clear water containing 0 to 5 wt. % solids. Below this clarified water layer is a discontinuity in solids content. Over a matter of a few feet, solids content increases to 10-15 wt.%, and thereaf-ter, solids content increases regularly toward the pond bottom. In the deepest parts of the pond, solid contents of over 50 wt.% have been recorded. This second layer is called the sludge layer. The solids content of the sludge layer increases regularly from top to bottom by a factor of 4-5. The clay-water ratio in this layer increases also, but by a lower factor of 1.5 -2.5. The clays, dispersed during processing, apparently have partially reflocculated into a very fragile get network. Through this gel, fines of lar-ger-than-clay sizes are slowly settling.
Overboarding is the operation in which tailings are discharged over the top of the sand dike directly into the liquid pool. A rapid and slow settling process occurs but their distinction is not as sharp as in dike building and no mechanical compaction is carried out. The sand portion of the tailings settles rapidly to form a gently sloping beach extending from the discharge point toward the pond interior. As the sand settles, fines and water drain into the pool and commence long-term settling.
In summary: (1) tar sands contain clay minerals, (2) in the hot water extraction process, most of the clays be-come dispersed in the process streams and traverse the cir-cuit, exiting in the tailings, (3) the amount of process water input is fixed by the clay content of the feed and the need to control viscosity of the middlings stream, (4) the amount of water required for middlings viscosity control represents a large volume relative to the volume of the ore itself, and (5) upon disposal, clays settle only very very ~' .
slowly; thus, the process water component of tailings is only partially available for reuse via recycle. That which can't be recycled represents a net accumulation of tailings sludge.
The pond water problem is then: to devise long-term economically and ecologically aeceptable means to eliminate minimize, or permanently dispose of, the accumulation of liquid tailings or sludge.
Flocculation of the drag stream in order to improve the settling characteristics thereto has been proposed and practiced in the prior art. In flocculation, individual particles (in this case clay particles) are united into rather lossely bound agglomerates or flocs. The degree of flocculation is controlled by the probability of collisions between the clay particles and their tendeney toward adhesion after collision. Agitation inereases the probability of eollision and adhesion tendeney is inereased by the addition of floeeulants.
Reagents aet as floeeulants through one or more of three general meehanisms: (1) neutralization of the elee-trieal repulsive forees surrounding the small partieles whieh enables the van der Waals eohesive foree to hold the partieles together onee they have eollided: (2) preeipita-tion of voluminous floes, sueh as metal hydroxides, that en-trap fine partieles; and (3) bridging of partieles by natural or synthetie, long-ehain, high-moleeular-weight polymers.
These polyeleetrolytes are believed to aet by absorption (by ester formation or hydrogen bonding) of hydroxyl or amide groups on solid surfaees, eaeh polymer ehain bridging be-tween more than one solid partiele in the suspension.
Among the various reagents which have been found useful for flocculating clay are: aluminum chloride, polyalkylene oxides, such as polyethylene oxide, compounds of calcium such as calcium hydroxide, calcium oxide, calcium chloride, calcium nitrate, calcium acid phosphate, calcium sulfate, calcium tartrate, calcium citrate, calcium sulfonate, calcium lactate, the calcium salt of ethylene diamine tetraacetate and similar organic sequestering agents. Also useful are quar flour or a high molecular weight acrylamide polymer such as polyacrylamide or a copolymer of acylamide and a copolymerizable carboxylic acid such as acrylic acid. Additional flocculants which have been considered include the polymers of acrylic or methacrylic acid derivitives, for example, acrylic acid, methacrylic acid, the alkali metal and ammonium salts of acrylic acid or methacrylic acid, acrylamide methacrylamide, the aminoakyly acrylates, the aminoalkyl acrylamides, the aminoakyl methacrylamides and the N-alkyl substituted aminoakyly esters of either acrylic or methacrylic acids.
Those skilled in the art will understand that a satis-factory solution to the "pond water problem" must be economically, as well as ecologically, acceptable, and the above listed flocculants fail to meet this fundamental criteria when employed in the treatment of tailings from the tar sands hot water extraction process. However, a distinct step forward in the art was achieved by the use of hydrolyzed starch flocculants as set forth in copending Canadian patent application Serial Number 275,214, filed March 31, 1977~ and entitled Destabilization of Sludge with Eydrolyzed Starch Flocculants.
As discussed in detail therein, starches are polysaccharides containing many monosaccharides joined together in long chains.
Upon complete hydrolysis by chemical or enzymatic means, starch yields monosaccharides. Hydrolyzed corn and potato starches are effective as folcculants in destabilizin~ dilute as well as thick sludge suspensions. Potato starch flocculants are generally superior to corn starch f]occulants, and the potato starch flocculants are equally effective on oil-removed and no-oil removed-sludge suspensions.
It has been found that the use of starch flocculants is very effective in accelerating the rate at which clay and clay-like silt settles. However, the ultimate extent to which the sludge layer may be compacted does not appear to be significantly superior to the compaction observed to take place over a longer period of time without treatment by a flocculant.
Restated, the solids concentration, shear strength and permeability of the sludge layer, given sufficient settling time, is substantially the same whether or not a flocculant, including starch flocculant, is employed. Thus, those skilled in the art will appreciate that it would be highly desirable to provide means by which clays and clay-like silt fines in - a tailings pond may be rapidly settled to obtain a sludge layer characterized by increased shear strength and increased permeability beyond that heretofore obtained.
O~JECTS OF THE INVENTION
It is therefore a broad object of this invention to provide an effective flocculating agent for treating tar sands tailings streams which carry suspended clay particles.
It is another object of this invention to provide such a flocculating agent which is economical to prepare and employ in the treatment of tar sands tailings streams.
In another aspect, it is an object of this invention to provide such a flocculating agent which is safe and easy to handle and which itself offers no ecologically undesirable side effects.
It is a more specific object of this invention to provide a flocculating agent combination comprising starch flocculant and cement, the use of which is prescribed portions results in a rapidly settled sludge layer having improved shear strength and permeability characteristics.
Briefly, these and other objects of the invention are achieved by adding Portland cement, preferably in the form of a dilute slurry, in a concentration on the order of 3.6 pounds per hundred Imperial gallons of normalized sludge in conjunction with the addition of starch flocculant within the range of 0.1 lbs. 0.5 lbs. per hundred Imperial gallons.
Now, and in accordance with the present teachings, in a tar sands tailings pond system for receiving affluent from an industrial process, a method is provided of obtaining a sludge layer in the tailings pond which had improved shear strength and permeability characteristics and which includes the steps of adding a potato starch flocculant to the effluent and adding Portland cement to the effluent at a dosage rate of at least
Conditioning tar sands for the recovery of bitumen ; consists of heating the tar sand/water feed mixture to pro-cess temperature (180-200F), physical mixing of the pulp to uniform composition and consistency, and the consumption (by chemical reaction) of the caustic or other reagents added.
Under these conditions, bitumen is stripped from the indiv-idual sand grains and mixed into the pulp in the form of dis-crete droplets of a particle size on the same order of that of the sand grains. The same process conditions, it turns out, are also ideal for accomplishing deflocculation of the clays which occur naturally in the tar sand feed. Defloccu-lation, or dispersion, means breaking down the naturally occurring aggregates of clay particles to produce a slurry of individual particles. Thus, during conditioning, a large fraction of the clay particles become well dispersed and mixed thoroughout the pulp.
v ~
Those skil]ed in the art wlll therefore understand that the conditioning process, which prepares the resources (bitumen) for efficient recovery during the following process steps also prepares the clays to be the most clifficult to deal with in the tailings disposal operations.
The second process step, called separation, is actually the bitumen recovery step, (the separation having already occurred during conditioning). The conditioned tar sand pulp is screened to remove rocks ancd unconditionable lumps of tar sands and clay. The reject material, "screen oversize", is discarded. The screened pulp is further diluted with water to promote two settling processes: globules of bitumen, essentially mineral-free, settle (float) upward to form a coherent mass of froth on the surface of the separation cells;
and, at the same time, mineral particles, particularly the sand size mineral, settle down and are removed from the bottom of the separation cell as tailings. The medium through whieh these two settling processes take place is ealled the middlings. The middlings eonsists primarily of water, with suspended fine material and bitumen partieles.
The partiele sizes and densities of the sand and of the bitumen partieles are relatively fixed. The parameter whieh influenees the settling proeesses most is the viseosity of the middlings and viseosity is directly related to fines eontent. Charae~eristieally, as the fines content rises above a eertain thresholcl (whieh varies aeeording to the eomposition of the fines), middlings viscosity rapidly reacnes high values with the effect that the settling processes essentially stop.
In this operating condition, the separation cell is said to be "upset". Little or no oil is recovered, and all streams exiting the eell have about the same composition as the feed.
As feed fines content increases, more water must be used in the process to maintain middlings viscosity within the operable range.
The third step of the hot water process is scavenging.
The feed fines content sets the process water requirement through the need to control middlings viscosity which, as noted above, is governed by the clay/water ratio. It is usually necessary to withdraw a drag stream of middlings to maintain the separation cell material balance, and this stream of middlings can be scavenged for recovery of in-cremental amounts of bitumen. Air flotation is an effec-tive scavenging method for this middlings stream.
Final extraction or froth clean-up is typically ac-complished by centrifugation. Froth from primary extrac-tion is diluted with naptha, and the diluted froth is then subjected to a two stage centrifugation. This process yields an oil product of an essentailly pure (diluted) bitumen. Water and mineral removed from the froth, during this step constitute an additional tailing stream which must be disposed of.
In the terminology of extractive processing, tailings is the throwaway material generated in the course of ex-tracting the valuable material from an ore. In tar sands processing, tailings consist of the whole tar sand ore body plus net additions of process water less only the recovered bitumen product. Tar sand tailings can be sub-divided into three categories; viz: (1) screen oversize, (2) sand tailings (the fraction that settles rapidly), and (3) tailings sludge (the fraction that settles slowly).
Screen oversize is typically collected and handled as a separate stream.
, " ~
~$~
Tailings dlsposal is all the operations required to place the t~.ilings in a final resting place. One obvious long-range goal of tailings disposal is to replace the tailings in the mined out area in a satisfactory form. Thus, in tar sands processing, there are two main operating modes for tailings disposal: (1) "dike building" which is hydraulic conveying of tailings followed by mechanical compaction of the sand tailings fraction; and (2) "overboarding" which is hydraulic transport with no mechanical compaction.
~ecently, in view of the high level of ecological consciousness in Canada and the United States, technical interest in tar sands operation has begun to focus on tailings disposal. The concept of tar sands tailings disposal is straightforward. Visualize mining one cubic foot of tar sands. Thisleaves a one cubic foot hole in the ground.
The ore is processed to recover the resource (bitumen) and the remainder, including both process material and the gangue, constitutes the tailings; tailings that are not valuable and are to be disposed of. In tar sands processing, the main process material is water, and the gangue is mostly sand with some silt and clay. Physically, the tailings consists of a solid part (sand tailings) and a more or less fluid part (sludge). The most satisfactory place to dispose of these tailings is, of course, the existing one cubic foot hole in the ground. It turns Ollt, however, that the sand tailings from the one cubic foot of ore occupy just about one cubic foot.
The amount of sludge is a variable, depending on ore quality and process conditions, but may run up to 0.3 cubic feet.
4~
The tailings simply will no~ fit into the hole in the ground.
The historical literature covering the hot water process for the recovery of bitumen from tar sands contains little in the way of a recognition that a net accumulation of liquid tailings or sludge would occur. Based on analysis of field test unit operations which led to the Great Canadian Oil Sands plant design near Ft. McMurray, Alberta, the existence of sludge accumulation was predicted. This accumulation came to be called the "pond water problem".
Observations during start-up and early commercial operations at Ft. McMurray (1967-1969) were of insufficient precision to confirm the prediction. Since 1969, commercial operating data have confirmed the accumulation in GCOS' tailings disposal area of a layer of fine material and water (sludge) which settles and compacts only very slowly, if at all after a few years.
At the GCOS plant, for dike building, tailings are conveyed hydraulically to the disposal area and discharged onto the top of a sand dilce which is constructed to serve as an impoundment for a pool of liquid contained inside.
On the dike, the sand settles rapidly, and a slurry of fines, water, and minor amounts of bitumen flows into the pond interior. The settled sand is mechanically compacted to build the dike to a higher level. The slurry which drains into the pond interior commences stratification in settling over a time scale of months to years. As a result of this long-term settling, two layers form. The top 5 to 10 feet of the pool are a layer of relatively clear water containing 0 to 5 wt. % solids. Below this clarified water layer is a discontinuity in solids content. Over a matter of a few feet, solids content increases to 10-15 wt.%, and thereaf-ter, solids content increases regularly toward the pond bottom. In the deepest parts of the pond, solid contents of over 50 wt.% have been recorded. This second layer is called the sludge layer. The solids content of the sludge layer increases regularly from top to bottom by a factor of 4-5. The clay-water ratio in this layer increases also, but by a lower factor of 1.5 -2.5. The clays, dispersed during processing, apparently have partially reflocculated into a very fragile get network. Through this gel, fines of lar-ger-than-clay sizes are slowly settling.
Overboarding is the operation in which tailings are discharged over the top of the sand dike directly into the liquid pool. A rapid and slow settling process occurs but their distinction is not as sharp as in dike building and no mechanical compaction is carried out. The sand portion of the tailings settles rapidly to form a gently sloping beach extending from the discharge point toward the pond interior. As the sand settles, fines and water drain into the pool and commence long-term settling.
In summary: (1) tar sands contain clay minerals, (2) in the hot water extraction process, most of the clays be-come dispersed in the process streams and traverse the cir-cuit, exiting in the tailings, (3) the amount of process water input is fixed by the clay content of the feed and the need to control viscosity of the middlings stream, (4) the amount of water required for middlings viscosity control represents a large volume relative to the volume of the ore itself, and (5) upon disposal, clays settle only very very ~' .
slowly; thus, the process water component of tailings is only partially available for reuse via recycle. That which can't be recycled represents a net accumulation of tailings sludge.
The pond water problem is then: to devise long-term economically and ecologically aeceptable means to eliminate minimize, or permanently dispose of, the accumulation of liquid tailings or sludge.
Flocculation of the drag stream in order to improve the settling characteristics thereto has been proposed and practiced in the prior art. In flocculation, individual particles (in this case clay particles) are united into rather lossely bound agglomerates or flocs. The degree of flocculation is controlled by the probability of collisions between the clay particles and their tendeney toward adhesion after collision. Agitation inereases the probability of eollision and adhesion tendeney is inereased by the addition of floeeulants.
Reagents aet as floeeulants through one or more of three general meehanisms: (1) neutralization of the elee-trieal repulsive forees surrounding the small partieles whieh enables the van der Waals eohesive foree to hold the partieles together onee they have eollided: (2) preeipita-tion of voluminous floes, sueh as metal hydroxides, that en-trap fine partieles; and (3) bridging of partieles by natural or synthetie, long-ehain, high-moleeular-weight polymers.
These polyeleetrolytes are believed to aet by absorption (by ester formation or hydrogen bonding) of hydroxyl or amide groups on solid surfaees, eaeh polymer ehain bridging be-tween more than one solid partiele in the suspension.
Among the various reagents which have been found useful for flocculating clay are: aluminum chloride, polyalkylene oxides, such as polyethylene oxide, compounds of calcium such as calcium hydroxide, calcium oxide, calcium chloride, calcium nitrate, calcium acid phosphate, calcium sulfate, calcium tartrate, calcium citrate, calcium sulfonate, calcium lactate, the calcium salt of ethylene diamine tetraacetate and similar organic sequestering agents. Also useful are quar flour or a high molecular weight acrylamide polymer such as polyacrylamide or a copolymer of acylamide and a copolymerizable carboxylic acid such as acrylic acid. Additional flocculants which have been considered include the polymers of acrylic or methacrylic acid derivitives, for example, acrylic acid, methacrylic acid, the alkali metal and ammonium salts of acrylic acid or methacrylic acid, acrylamide methacrylamide, the aminoakyly acrylates, the aminoalkyl acrylamides, the aminoakyl methacrylamides and the N-alkyl substituted aminoakyly esters of either acrylic or methacrylic acids.
Those skilled in the art will understand that a satis-factory solution to the "pond water problem" must be economically, as well as ecologically, acceptable, and the above listed flocculants fail to meet this fundamental criteria when employed in the treatment of tailings from the tar sands hot water extraction process. However, a distinct step forward in the art was achieved by the use of hydrolyzed starch flocculants as set forth in copending Canadian patent application Serial Number 275,214, filed March 31, 1977~ and entitled Destabilization of Sludge with Eydrolyzed Starch Flocculants.
As discussed in detail therein, starches are polysaccharides containing many monosaccharides joined together in long chains.
Upon complete hydrolysis by chemical or enzymatic means, starch yields monosaccharides. Hydrolyzed corn and potato starches are effective as folcculants in destabilizin~ dilute as well as thick sludge suspensions. Potato starch flocculants are generally superior to corn starch f]occulants, and the potato starch flocculants are equally effective on oil-removed and no-oil removed-sludge suspensions.
It has been found that the use of starch flocculants is very effective in accelerating the rate at which clay and clay-like silt settles. However, the ultimate extent to which the sludge layer may be compacted does not appear to be significantly superior to the compaction observed to take place over a longer period of time without treatment by a flocculant.
Restated, the solids concentration, shear strength and permeability of the sludge layer, given sufficient settling time, is substantially the same whether or not a flocculant, including starch flocculant, is employed. Thus, those skilled in the art will appreciate that it would be highly desirable to provide means by which clays and clay-like silt fines in - a tailings pond may be rapidly settled to obtain a sludge layer characterized by increased shear strength and increased permeability beyond that heretofore obtained.
O~JECTS OF THE INVENTION
It is therefore a broad object of this invention to provide an effective flocculating agent for treating tar sands tailings streams which carry suspended clay particles.
It is another object of this invention to provide such a flocculating agent which is economical to prepare and employ in the treatment of tar sands tailings streams.
In another aspect, it is an object of this invention to provide such a flocculating agent which is safe and easy to handle and which itself offers no ecologically undesirable side effects.
It is a more specific object of this invention to provide a flocculating agent combination comprising starch flocculant and cement, the use of which is prescribed portions results in a rapidly settled sludge layer having improved shear strength and permeability characteristics.
Briefly, these and other objects of the invention are achieved by adding Portland cement, preferably in the form of a dilute slurry, in a concentration on the order of 3.6 pounds per hundred Imperial gallons of normalized sludge in conjunction with the addition of starch flocculant within the range of 0.1 lbs. 0.5 lbs. per hundred Imperial gallons.
Now, and in accordance with the present teachings, in a tar sands tailings pond system for receiving affluent from an industrial process, a method is provided of obtaining a sludge layer in the tailings pond which had improved shear strength and permeability characteristics and which includes the steps of adding a potato starch flocculant to the effluent and adding Portland cement to the effluent at a dosage rate of at least
3.0 pounds per lO0 Imperial gallons of normalized sludge dis-charged into the tailings pond, which normalized sludge is de-fined as a fluid which has approximately an average of 20%
(w/v) solids content after settling into the sludge layer.
In accordance with a further embodiment, an improve-ment is provided in an aqueous process for separating oil from bituminous sands which includes the steps of forming a mixture of bituminous sand and water; passing the mixture into a separa-tion zone; settling the mixture in the separation zone to form an upper oil froth layer, a middlings layer comprising oil, ',~
t~3 water and clay, and a lower sand tailings layer; withdrawing separate streams from the oil froth layer, the sand tailings layer and a middlings layer; collecting an effluent discharge comprising the effluent from the sand and tailings layer and the effluent from the middlings layer; and adding a flocculating agent to the effluent discharge whereby finely divided minerals including clay settle into a lower sludge layer within the storage zone for the effluent discharge. The improvement which is pro-vided in accordance with the present teachings is the flocculating agent employed comprises a combination of potato starch flocculant and a Portland cement in which the dosage of Portland cement is at ]east 3.0 pounds per 100 Imperial gallons of normalized sludge, which normalized sludge is defined as fluid having approximately an average solids content of 20~ (w/v) after settIing into the sludge layer.
DESCRIPTION OF THE DR~WINGS
The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to the manner in which the flocculating combination is prepared and the method of employing it, may best be understood by reference to the following description taken in connection with the drawing of which:
Figure 1 is a somewhat simplified schematic representa-tlon of a hot water extraction process wherein the invention finds particular use; and Figure 2 is a graph illustrating the results of tests employing various combinations of starch and cement on normalized sludge as observed in the laboratory.
-12a-DETAILED DESCRIPTInN OF TIIE INVENTION
Re-Eerring now to Figure 1, bituminous tar sands are fed into the system through a line 1 and pass to a conditioning drum or muller 18. Water and steam are introduced to the muller through another line 2. The total water so introduced in liquid and vapor form is a minor amount based on the weight o:E the tar sands processed. The tar sands, heated and conditioned with steam and water, pass through a line 3 to the -feed sump 19 which serves as a zone for diluting the pulp with additional water before passage to the separation zone 20.
The pulp tar sands are continuously flushed from the feed sump 19 through a line 4 into a separator 20. The settling zone within the separator 20 is relatively quiescent so that bituminous froth rises to the top and is withdrawn via line 5 while the bulk of the sand settles to the bottom as a tailings layer which is withdrawn through line 6.
A relatively bitumen rich middlings stream is withdrawn ;;
through line 8 and transferred to a flotation scavenger zone 21. In this scavenger zone, an air flotation operation is conducted to cause the formation of additional bituminous froth which passes from the scavenger zone through line 9 in mixture with the primary froth from the separation 20 to a froth settler 22. A bitumen-lean water stream is removed from the bottom of the scavenger zone 21 through line 10 to be further processed as described below. In the settler zone 22, some further bitumen-lean water is withdrawn from the froth and removed through line 11 to be mixed with the bitumen-lean water stream from the flotation scavenger zone and the sand tailings stream from the separation zone. The bitumen from the settler .
is removed through line 12 for further treatment, typically upgrading to synthetic crude oil.
Bitumen-lean water from the froth settler 22, the scavenger zone 21,and the separation zone 20, all of which make up an effluent discharge stream carried by line 7, are discharged into a settling pond 15 having a clarified water layer 26 and a sludge layer 27. The sand included in the tailings stream quickly settles in the region 14, and the fines-containing water flows into the body of the pond 15 where settling takes place.
In accordance with the present invention, potato starch flocculant and cement are mixed with the effluent stream, preferably as separate or combined slurrys injected, through individual lines 23 and 24 or combined line 25, into line 7. The quantity of cement injected should be at least 3.0 pounds (and preferably 3.6 pounds or more) of cement per hundred Imperial ~allons of sludge which may be expected to accumulate when the liquid fraction of the tailing stream is discharged into the pond 15 and settled. The concentration of starch flocculants injected typically falls within the range 0.1 to 0.5 pounds per hundred Imperial gallons of sludge.
As represented by the dashed lines in Figure 1, initialization of an existing pond may require broadcas~ing of the necessary quantities of cement and/or starch flocculant over the surface of the pond (or by such other means as recirculation with injection into the recirculates stream) in order to bring the concentration of cement in the pond to at least 3.0 pounds per hundred Imperial gallons of sludge. As set forth in more detail below, "sludge", for the purposes only of defining the concentrations of cement and starch flocculant required, may be more particularly defined as "normalized" sludge containing about 20% w/v solids. As previously noted, in an
(w/v) solids content after settling into the sludge layer.
In accordance with a further embodiment, an improve-ment is provided in an aqueous process for separating oil from bituminous sands which includes the steps of forming a mixture of bituminous sand and water; passing the mixture into a separa-tion zone; settling the mixture in the separation zone to form an upper oil froth layer, a middlings layer comprising oil, ',~
t~3 water and clay, and a lower sand tailings layer; withdrawing separate streams from the oil froth layer, the sand tailings layer and a middlings layer; collecting an effluent discharge comprising the effluent from the sand and tailings layer and the effluent from the middlings layer; and adding a flocculating agent to the effluent discharge whereby finely divided minerals including clay settle into a lower sludge layer within the storage zone for the effluent discharge. The improvement which is pro-vided in accordance with the present teachings is the flocculating agent employed comprises a combination of potato starch flocculant and a Portland cement in which the dosage of Portland cement is at ]east 3.0 pounds per 100 Imperial gallons of normalized sludge, which normalized sludge is defined as fluid having approximately an average solids content of 20~ (w/v) after settIing into the sludge layer.
DESCRIPTION OF THE DR~WINGS
The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to the manner in which the flocculating combination is prepared and the method of employing it, may best be understood by reference to the following description taken in connection with the drawing of which:
Figure 1 is a somewhat simplified schematic representa-tlon of a hot water extraction process wherein the invention finds particular use; and Figure 2 is a graph illustrating the results of tests employing various combinations of starch and cement on normalized sludge as observed in the laboratory.
-12a-DETAILED DESCRIPTInN OF TIIE INVENTION
Re-Eerring now to Figure 1, bituminous tar sands are fed into the system through a line 1 and pass to a conditioning drum or muller 18. Water and steam are introduced to the muller through another line 2. The total water so introduced in liquid and vapor form is a minor amount based on the weight o:E the tar sands processed. The tar sands, heated and conditioned with steam and water, pass through a line 3 to the -feed sump 19 which serves as a zone for diluting the pulp with additional water before passage to the separation zone 20.
The pulp tar sands are continuously flushed from the feed sump 19 through a line 4 into a separator 20. The settling zone within the separator 20 is relatively quiescent so that bituminous froth rises to the top and is withdrawn via line 5 while the bulk of the sand settles to the bottom as a tailings layer which is withdrawn through line 6.
A relatively bitumen rich middlings stream is withdrawn ;;
through line 8 and transferred to a flotation scavenger zone 21. In this scavenger zone, an air flotation operation is conducted to cause the formation of additional bituminous froth which passes from the scavenger zone through line 9 in mixture with the primary froth from the separation 20 to a froth settler 22. A bitumen-lean water stream is removed from the bottom of the scavenger zone 21 through line 10 to be further processed as described below. In the settler zone 22, some further bitumen-lean water is withdrawn from the froth and removed through line 11 to be mixed with the bitumen-lean water stream from the flotation scavenger zone and the sand tailings stream from the separation zone. The bitumen from the settler .
is removed through line 12 for further treatment, typically upgrading to synthetic crude oil.
Bitumen-lean water from the froth settler 22, the scavenger zone 21,and the separation zone 20, all of which make up an effluent discharge stream carried by line 7, are discharged into a settling pond 15 having a clarified water layer 26 and a sludge layer 27. The sand included in the tailings stream quickly settles in the region 14, and the fines-containing water flows into the body of the pond 15 where settling takes place.
In accordance with the present invention, potato starch flocculant and cement are mixed with the effluent stream, preferably as separate or combined slurrys injected, through individual lines 23 and 24 or combined line 25, into line 7. The quantity of cement injected should be at least 3.0 pounds (and preferably 3.6 pounds or more) of cement per hundred Imperial ~allons of sludge which may be expected to accumulate when the liquid fraction of the tailing stream is discharged into the pond 15 and settled. The concentration of starch flocculants injected typically falls within the range 0.1 to 0.5 pounds per hundred Imperial gallons of sludge.
As represented by the dashed lines in Figure 1, initialization of an existing pond may require broadcas~ing of the necessary quantities of cement and/or starch flocculant over the surface of the pond (or by such other means as recirculation with injection into the recirculates stream) in order to bring the concentration of cement in the pond to at least 3.0 pounds per hundred Imperial gallons of sludge. As set forth in more detail below, "sludge", for the purposes only of defining the concentrations of cement and starch flocculant required, may be more particularly defined as "normalized" sludge containing about 20% w/v solids. As previously noted, in an
4~
actual settling pond, the demarcation between a clarified water layer 26 and a sludge layer 27 is ill-defined and variable, and the characteristics of the sludge layer 27 change from top to bottom such that it is necessary to calculate an "average normalized" sludge from samples from a pond to determine the minimum dosage of cement and starch flocculant.
Water from the clarified water layer 26 may be withdrawn by a pump 28 for recycle by a line 17 to be mixed with Eresh water and charged into the hot water process.
In order to substantiate the beneficial effect of employing cement in conjunction with starch flocculant in the tailings pond, controlled laboratory tests were undertaken in which different amounts of Portland Cement, type III, were added along or in combination with starch flocculant to natural sludge from the Tar Island Pond at the GCOS mine. The cement was added in the form of a dilute slurry (5%) and the solids concentration in the treated sludge samples was adjusted to 14.9% (w/w) prior to centrifugation. The treatment dosages referred to hereinafter are expressed in pounds per hundred Imperial gallons of sludge containing 20% (w/v) solids.
A sample of the treated sludge was centrifuged for 320 minutes for the purpose of determining the amounts of solids present in the supernatent and sedimented cake. The floc volume after different periods of centrifugation was also recorded to provide information on the settling rate.
In the remaining treated sludge samples, the amounts of soluble Ca and SiO2 in the pore fluid after 1, 7, and 21 days of aging were determined. In the case of the sludge sample treated with cement alone, the amounts of amorphous Ca and SiO2 were determined in the sludge solids after 1, 7, and 2 days of aging.
In order to test consolidation, permeability, and shear strength, natural sludge samples with 22.4 to 34.5 (w/w) initial solids concentration from different depths of the Tar Island Pond were treated with different dosages of starch flocculants and cement. In each case, the solids and treated sludge were concentrated with the aid of a bucket centrifuge.
To accomplish this, sludge was fed into a bucket centrifuge in batches of about 120 ml, and each sample was centrifuged for one hour at 3,000 rpm. The resultant concentrated sludge obtained from bucket centrifugation (with solids content of 50 to 60% (w/w), was consolidated using Farnell consolidometers, and changes in volume with time at different loads were recorded manually. The coefficient of consolidation and the permeability of each sample were calculated from this data at each equilibrium load. The shear strength of the consolidated sample was determined by the vane shear method at the conclusion of the experiment.
As to stabilization, the solids content observed in both the supernatent and sedimented cake, after centrifuging the treated sludge for 320 minutes at 1370 RPM, are presented in Figure 2. The addition of cement with a dosage of less than 3.6 pounds per hundred Imperial gallons, in the presence of the starch flocculant, significantly increases the stability of the sludge as may be seen by the high solids content in the supernatent. This is, of course, a counterproductive condition.
Influ nc~ of starch flocculant ~t t~o dosages of ccmcnt on th~ solublo Slû2 (pprl) pr~sent In th~ por~ f~uld _ 5'2 (ppm) concrntratlon In por~ fluld Ag ing Tlna C men~ dos~ge 1 2 Ib Crmcnt dosag~ I ô Ib (dly5) tio flocculant 0 12 Ib Starch 0 24 Ib Starch ~Jo Flocculant 0 12 Ib Starch ¦ 0 24 Ib Starch Flocculan~ Flocculant Flocculant ¦ Flocculant ., l 10 99 14 2 16 ~2 12 04 23 31 21 2 2 8 29 21 62 '5 3' lo 65 15 68 16 0 3 ~ 34 21 20 15 68 '~ 65 17 21 18 38 Cement and floccul~nt dos~g~ 3r~ In Ib/lûOgallonso~ sludge contdlnlng 2û~ (W/V) solids The minimum amount oE cement required to flocculate the sludge, even in the presence of starch flocculant, is still obscrved to be 3.6 pounds per hundred Imperial gallons.
The additional benefits of flocculant addition to this dosage of cement is that it further reduces the interparticle distances and increases the solids concentration in the sediment. For example, when starch flocculant is added at the rate of 0.48 pounds per hundred gallons along with 3.6 pounds of cement per hundred gallons of sludge, the final solids content in the sedimented cake obtained is about the same as with five pounds of cemellt alone per hundred gallons of sludge. If the amount of soluble SiO2 present in the pore fluid is any indication of a higher degree of hydration reaction oE cement, and if there is a minimum amount of cement required to destabilize the sludge, it is then apparent from Table 1 that the addition of staTch flocculant does increase the hydration reaction of cement. lhis decreases the amount of cement re~uired to destabilize the sludge as seen by the increase in the amount of soluble silica present in the pore fluid.
~,'3~2~
It is clear that, ir' one on]y considers the pond water ol~lelll in tcrms Or soli(ls contcnt:, the beneficial effect of f] occu1ant when used in combination with cement is marginal .
It is essent;al to recognize that the final solids content rcflects only tl-e compressabi1ity of- the sedimented mass and not rates o-f compression, nor such important properties as permeability and shear strength.
The influence o-E starch flocculant in combination with different dosa~es of cement on physico-mechanica1 prol,ertics Or s1ud~e is summarizecl in Table 2. The two sets of consolidation data obtained on sludge Wit}l different initial solids content (34 . 5 and 22 . 4% w/w) are also given in Table 2. It is eviclent from a study of the results that the use of cement in combination with starch flocculant is beneficial in increasing consolidation, permeability and shear strength significantly only when the amount of cement added is greater than about 3 . 6 pounds per hundred Imperial gallons of "normalized" sludge as best shown in Fi~ure 2.
.tm~nt ~nd con,ol~datlon dat~
¦ Natur~ and Dosage of Coeff~clent oF Permeabillty Shear No. conc. I per ioo ra i ions ( l~p ) Consoi idat i ion. cv K (10 5 cm s~c ' ) Strength tW/W) ¦ with 2û~6 (W/V) Solids c~ sec (p.s.i.) __ I . 34.5 No treatment 0.06 0.22 3.0 2 34.5 0.18 starch fir~ccuiant 0.36 1.0 3.8 3 34.5 0,18 s~Drch flocculAnt 1.3 1.7 16.4 3 0 i 52 alcohoi 4 22.4 No ~reatmen~ o os o.os 6 22.4 o.lB starch flocculant o.o8 0.04 5.2 ~ 1.54 ~Icohol 6 22.4 0.16 starch flocculant 0.21 0.37 6.5 t 1.6 alcohol + 3.1 Portland cem~nt 7 2 2 4 + i . 5 4 a i coho i 0 . 2 5 0 . 4 2 8 . 2 ~ 3.RS Portland Cem~nt 4 0 8 2 2, 4 t i . 5 4 a i c oho I o . I s o . 6 7 7 . 5 ~ 4.63 Portl~nd cr~nt Th~ v~lu~s f Cv and K glven h~re ar~ at ~ vold rat~o of 1.25.
~.
4 ~
The observed and demonstrated increase in consolidation, permeability, and shear strength of the sludge obtained by practicing the present invention is believed to occur for the following reasons: The fines contained in the sludge suspension consist of primary, as well as secondary, minerals.
Primary minerals, which are most quartz and some feldspars, have very low specific sur-face area and little of any kind of charge. In contrast, the secondary minerals, which are mostly kaolinite and illite with some montmorillonite and intergrade mixed-layer minerals, have high specific surface area and a substantial amount of negative charge. There are some positive charges, usually at the edges of the crystal of some clay minerals. The addition of starch flocculant destabilizes the sludge through the formation of tactoids and the additional treatment of flocculated sludge with Portlan~
Cement causes an increase in shear strength and permeability of the flocculated mass through creation of inter and intra floc bonding.
While the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in the art many modifications of structure, arrangements, proportions, the elements, materials, and components, used in the practice of the invention which are particularly adapted for specific environments, and operating requirements without departing from those principles.
actual settling pond, the demarcation between a clarified water layer 26 and a sludge layer 27 is ill-defined and variable, and the characteristics of the sludge layer 27 change from top to bottom such that it is necessary to calculate an "average normalized" sludge from samples from a pond to determine the minimum dosage of cement and starch flocculant.
Water from the clarified water layer 26 may be withdrawn by a pump 28 for recycle by a line 17 to be mixed with Eresh water and charged into the hot water process.
In order to substantiate the beneficial effect of employing cement in conjunction with starch flocculant in the tailings pond, controlled laboratory tests were undertaken in which different amounts of Portland Cement, type III, were added along or in combination with starch flocculant to natural sludge from the Tar Island Pond at the GCOS mine. The cement was added in the form of a dilute slurry (5%) and the solids concentration in the treated sludge samples was adjusted to 14.9% (w/w) prior to centrifugation. The treatment dosages referred to hereinafter are expressed in pounds per hundred Imperial gallons of sludge containing 20% (w/v) solids.
A sample of the treated sludge was centrifuged for 320 minutes for the purpose of determining the amounts of solids present in the supernatent and sedimented cake. The floc volume after different periods of centrifugation was also recorded to provide information on the settling rate.
In the remaining treated sludge samples, the amounts of soluble Ca and SiO2 in the pore fluid after 1, 7, and 21 days of aging were determined. In the case of the sludge sample treated with cement alone, the amounts of amorphous Ca and SiO2 were determined in the sludge solids after 1, 7, and 2 days of aging.
In order to test consolidation, permeability, and shear strength, natural sludge samples with 22.4 to 34.5 (w/w) initial solids concentration from different depths of the Tar Island Pond were treated with different dosages of starch flocculants and cement. In each case, the solids and treated sludge were concentrated with the aid of a bucket centrifuge.
To accomplish this, sludge was fed into a bucket centrifuge in batches of about 120 ml, and each sample was centrifuged for one hour at 3,000 rpm. The resultant concentrated sludge obtained from bucket centrifugation (with solids content of 50 to 60% (w/w), was consolidated using Farnell consolidometers, and changes in volume with time at different loads were recorded manually. The coefficient of consolidation and the permeability of each sample were calculated from this data at each equilibrium load. The shear strength of the consolidated sample was determined by the vane shear method at the conclusion of the experiment.
As to stabilization, the solids content observed in both the supernatent and sedimented cake, after centrifuging the treated sludge for 320 minutes at 1370 RPM, are presented in Figure 2. The addition of cement with a dosage of less than 3.6 pounds per hundred Imperial gallons, in the presence of the starch flocculant, significantly increases the stability of the sludge as may be seen by the high solids content in the supernatent. This is, of course, a counterproductive condition.
Influ nc~ of starch flocculant ~t t~o dosages of ccmcnt on th~ solublo Slû2 (pprl) pr~sent In th~ por~ f~uld _ 5'2 (ppm) concrntratlon In por~ fluld Ag ing Tlna C men~ dos~ge 1 2 Ib Crmcnt dosag~ I ô Ib (dly5) tio flocculant 0 12 Ib Starch 0 24 Ib Starch ~Jo Flocculant 0 12 Ib Starch ¦ 0 24 Ib Starch Flocculan~ Flocculant Flocculant ¦ Flocculant ., l 10 99 14 2 16 ~2 12 04 23 31 21 2 2 8 29 21 62 '5 3' lo 65 15 68 16 0 3 ~ 34 21 20 15 68 '~ 65 17 21 18 38 Cement and floccul~nt dos~g~ 3r~ In Ib/lûOgallonso~ sludge contdlnlng 2û~ (W/V) solids The minimum amount oE cement required to flocculate the sludge, even in the presence of starch flocculant, is still obscrved to be 3.6 pounds per hundred Imperial gallons.
The additional benefits of flocculant addition to this dosage of cement is that it further reduces the interparticle distances and increases the solids concentration in the sediment. For example, when starch flocculant is added at the rate of 0.48 pounds per hundred gallons along with 3.6 pounds of cement per hundred gallons of sludge, the final solids content in the sedimented cake obtained is about the same as with five pounds of cemellt alone per hundred gallons of sludge. If the amount of soluble SiO2 present in the pore fluid is any indication of a higher degree of hydration reaction oE cement, and if there is a minimum amount of cement required to destabilize the sludge, it is then apparent from Table 1 that the addition of staTch flocculant does increase the hydration reaction of cement. lhis decreases the amount of cement re~uired to destabilize the sludge as seen by the increase in the amount of soluble silica present in the pore fluid.
~,'3~2~
It is clear that, ir' one on]y considers the pond water ol~lelll in tcrms Or soli(ls contcnt:, the beneficial effect of f] occu1ant when used in combination with cement is marginal .
It is essent;al to recognize that the final solids content rcflects only tl-e compressabi1ity of- the sedimented mass and not rates o-f compression, nor such important properties as permeability and shear strength.
The influence o-E starch flocculant in combination with different dosa~es of cement on physico-mechanica1 prol,ertics Or s1ud~e is summarizecl in Table 2. The two sets of consolidation data obtained on sludge Wit}l different initial solids content (34 . 5 and 22 . 4% w/w) are also given in Table 2. It is eviclent from a study of the results that the use of cement in combination with starch flocculant is beneficial in increasing consolidation, permeability and shear strength significantly only when the amount of cement added is greater than about 3 . 6 pounds per hundred Imperial gallons of "normalized" sludge as best shown in Fi~ure 2.
.tm~nt ~nd con,ol~datlon dat~
¦ Natur~ and Dosage of Coeff~clent oF Permeabillty Shear No. conc. I per ioo ra i ions ( l~p ) Consoi idat i ion. cv K (10 5 cm s~c ' ) Strength tW/W) ¦ with 2û~6 (W/V) Solids c~ sec (p.s.i.) __ I . 34.5 No treatment 0.06 0.22 3.0 2 34.5 0.18 starch fir~ccuiant 0.36 1.0 3.8 3 34.5 0,18 s~Drch flocculAnt 1.3 1.7 16.4 3 0 i 52 alcohoi 4 22.4 No ~reatmen~ o os o.os 6 22.4 o.lB starch flocculant o.o8 0.04 5.2 ~ 1.54 ~Icohol 6 22.4 0.16 starch flocculant 0.21 0.37 6.5 t 1.6 alcohol + 3.1 Portland cem~nt 7 2 2 4 + i . 5 4 a i coho i 0 . 2 5 0 . 4 2 8 . 2 ~ 3.RS Portland Cem~nt 4 0 8 2 2, 4 t i . 5 4 a i c oho I o . I s o . 6 7 7 . 5 ~ 4.63 Portl~nd cr~nt Th~ v~lu~s f Cv and K glven h~re ar~ at ~ vold rat~o of 1.25.
~.
4 ~
The observed and demonstrated increase in consolidation, permeability, and shear strength of the sludge obtained by practicing the present invention is believed to occur for the following reasons: The fines contained in the sludge suspension consist of primary, as well as secondary, minerals.
Primary minerals, which are most quartz and some feldspars, have very low specific sur-face area and little of any kind of charge. In contrast, the secondary minerals, which are mostly kaolinite and illite with some montmorillonite and intergrade mixed-layer minerals, have high specific surface area and a substantial amount of negative charge. There are some positive charges, usually at the edges of the crystal of some clay minerals. The addition of starch flocculant destabilizes the sludge through the formation of tactoids and the additional treatment of flocculated sludge with Portlan~
Cement causes an increase in shear strength and permeability of the flocculated mass through creation of inter and intra floc bonding.
While the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in the art many modifications of structure, arrangements, proportions, the elements, materials, and components, used in the practice of the invention which are particularly adapted for specific environments, and operating requirements without departing from those principles.
Claims (12)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a tar sands tailings pond system for receiving effluent from an industrial process, the method of obtaining a sludge layer in the tailings pond having improved shear strength and permeability characteristics which includes the steps of:
A) adding a potato starch flocculant to the effluent; and B) adding Portland cement to the effluent at a dos-age of at least 3.0 pounds per 100 Imperial gallons of normalized sludge discharged into the tailings pond, which normalized sludge is defined as fluid having approximately an average of 20% (w/v) solids content after settling into the sludge layer.
A) adding a potato starch flocculant to the effluent; and B) adding Portland cement to the effluent at a dos-age of at least 3.0 pounds per 100 Imperial gallons of normalized sludge discharged into the tailings pond, which normalized sludge is defined as fluid having approximately an average of 20% (w/v) solids content after settling into the sludge layer.
2. The method of Claim 1 in which the dosage of Portland cement approximates 3.6 pounds per 100 Imperial gallons of nor-malized sludge discharged into the tailings pond.
3. The method of Claim 1 in which starch flocculant in the range 0.1 to 0.5 pounds per 100 Imperial gallons of normal-ized sludge is added to the effluent discharge.
4. The method of Claim 2 in which starch flocculant in the range 0.1 to 0.5 pounds per 100 Imperial gallons of normal-ized sludge is added to the affluent discharge.
5. In an aqueous process for separating oil from bitu-minous sands comprising the steps of:
A) forming a mixture of bituminous sand and water;
B) passing the mixture into a separation zone;
C) settling the mixture in the separation zone to form an upper oil froth layer; a middlings layer comprising oil, water, and clay; and a lower sand tailings layer;
D) withdrawing separate streams from the oil froth layer; the sand tailings layer; and the middlings layer;
E) collecting an effluent discharge comprising the effluent from the sand tailings layer and the effluent from the middlings layer; and F) adding a flocculating agent to the effluent dis-charge; whereby finely divided minerals includ-ing clay settle into a lower sludge layer within a storage zone for the effluent discharge;
the improvement wherein:
G) the flocculating agent employed comprises a com-bination of potato starch flocculent and Portland cement and in which the dosage of Portland cem-ent is at least 3.0 pounds per 100 Imperial gallons of normalized sludge, which normalized sludge is defined as fluid having approximately an average solids content of 20% (w/v) after settling into the sludge layer.
A) forming a mixture of bituminous sand and water;
B) passing the mixture into a separation zone;
C) settling the mixture in the separation zone to form an upper oil froth layer; a middlings layer comprising oil, water, and clay; and a lower sand tailings layer;
D) withdrawing separate streams from the oil froth layer; the sand tailings layer; and the middlings layer;
E) collecting an effluent discharge comprising the effluent from the sand tailings layer and the effluent from the middlings layer; and F) adding a flocculating agent to the effluent dis-charge; whereby finely divided minerals includ-ing clay settle into a lower sludge layer within a storage zone for the effluent discharge;
the improvement wherein:
G) the flocculating agent employed comprises a com-bination of potato starch flocculent and Portland cement and in which the dosage of Portland cem-ent is at least 3.0 pounds per 100 Imperial gallons of normalized sludge, which normalized sludge is defined as fluid having approximately an average solids content of 20% (w/v) after settling into the sludge layer.
6. The process of Claim 5 in which approximately 3.6 pounds of Portland cement per 100 Imperial gallons of normalized sludge is added to the effluent discharge.
7. The process of Claim 5 in which starch flocculant in the range of 0.1 to 0.5 pounds per 100 Imperial gallons of normalized sludge is added to the effluent discharge.
8. The process of Claim 6 on which starch flocculant in the range 0.1 to 0.5 pounds per 100 Imperial gallons of normalized sludge is added to the effluent discharge.
9. A treatment for a tar sands tailings pond, applied to increase the shear strength and permeability of a sludge layer within the pond, comprising the combined application of potato starch flocculant and Portland cement and in which sufficient Portland cement is added to the pond to obtain a concentration of at least 3.0 pounds per 100 Imperial gallons of normlized sludge, which normalized sludge is defined as sludge having approximately an average of 20% (w/v) solids content.
10. The treatment of Claim 9 in which sufficient Port-land cement is added to the pond to obtain a concentration of approximately 3.6 pounds per 100 Imperial gallons of normalized sludge.
11. The treatment of Claim 9 in which sufficient starch flocculant is added to the pond to obtain a concentration in the range 0.1 to 0.5 pounds per 100 Imperial gallons of normal-ized sludge.
12. The treatment of Claim 10 in which sufficient starch flocculant is added to the pond to obtain a concentration in the range 0.1 to 0.5 pounds per 100 Imperial gallons of normalized sludge.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA295,881A CA1109408A (en) | 1978-01-30 | 1978-01-30 | Destabilization and improvement in permeability and shear strength of sludge treated with hydrolyzed starch flocculant and portland cement |
| US05/934,560 US4289540A (en) | 1978-01-30 | 1978-08-17 | Hydrolyzed starch-containing compositions |
| US06/145,296 US4330409A (en) | 1978-01-30 | 1980-05-01 | Destabilization of sludge with hydrolyzed starch flocculants |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA295,881A CA1109408A (en) | 1978-01-30 | 1978-01-30 | Destabilization and improvement in permeability and shear strength of sludge treated with hydrolyzed starch flocculant and portland cement |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1109408A true CA1109408A (en) | 1981-09-22 |
Family
ID=4110653
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA295,881A Expired CA1109408A (en) | 1978-01-30 | 1978-01-30 | Destabilization and improvement in permeability and shear strength of sludge treated with hydrolyzed starch flocculant and portland cement |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1109408A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9068776B2 (en) | 2009-10-30 | 2015-06-30 | Suncor Energy Inc. | Depositing and farming methods for drying oil sand mature fine tailings |
| US9404686B2 (en) | 2009-09-15 | 2016-08-02 | Suncor Energy Inc. | Process for dying oil sand mature fine tailings |
| US9909070B2 (en) | 2009-09-15 | 2018-03-06 | Suncor Energy Inc. | Process for flocculating and dewatering oil sand mature fine tailings |
| WO2022133600A1 (en) * | 2020-12-21 | 2022-06-30 | Envicore Inc. | Process for tailings stream sedimentation and segregation |
| US11639303B2 (en) | 2018-06-21 | 2023-05-02 | Envicore Inc. | Enhanced flocculation of intractable slurries using silicate ions |
-
1978
- 1978-01-30 CA CA295,881A patent/CA1109408A/en not_active Expired
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9404686B2 (en) | 2009-09-15 | 2016-08-02 | Suncor Energy Inc. | Process for dying oil sand mature fine tailings |
| US9909070B2 (en) | 2009-09-15 | 2018-03-06 | Suncor Energy Inc. | Process for flocculating and dewatering oil sand mature fine tailings |
| US10590347B2 (en) | 2009-09-15 | 2020-03-17 | Suncor Energy Inc. | Process for flocculating and dewatering oil sand mature fine tailings |
| US9068776B2 (en) | 2009-10-30 | 2015-06-30 | Suncor Energy Inc. | Depositing and farming methods for drying oil sand mature fine tailings |
| US11639303B2 (en) | 2018-06-21 | 2023-05-02 | Envicore Inc. | Enhanced flocculation of intractable slurries using silicate ions |
| US11912593B2 (en) | 2018-06-21 | 2024-02-27 | Envicore Inc. | Enhanced flocculation of intractable slurries using silicate ions |
| WO2022133600A1 (en) * | 2020-12-21 | 2022-06-30 | Envicore Inc. | Process for tailings stream sedimentation and segregation |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4289540A (en) | Hydrolyzed starch-containing compositions | |
| US4414117A (en) | Decarbonation of tailings sludge to improve settling | |
| US5626743A (en) | Tar sands extraction process | |
| US3487003A (en) | Removal of clay from the water streams of the hot water process by flocculation | |
| US4399039A (en) | Treatment of tailings pond sludge | |
| CA2667933C (en) | Method for dispersing and aggregating components of mineral slurries | |
| US5985138A (en) | Tar sands extraction process | |
| US11027993B2 (en) | Oil sands tailings treatment | |
| US4437998A (en) | Method for treating oil sands extraction plant tailings | |
| CA1146898A (en) | Recovery of bitumen from tar sands sludge using additional water | |
| US5846314A (en) | Process for treating a waste material resulting from an oil recovery from tar sands process | |
| US3931006A (en) | Method of reducing sludge accumulation from tar sands hot water process | |
| CA2168808C (en) | Tar sands extraction process | |
| US3751358A (en) | Freeze-thaw separation of solids from tar sands extraction effluents | |
| US4456533A (en) | Recovery of bitumen from bituminous oil-in-water emulsions | |
| CA1109408A (en) | Destabilization and improvement in permeability and shear strength of sludge treated with hydrolyzed starch flocculant and portland cement | |
| CA1085762A (en) | Grinding as a means of reducing flocculant requirements for destabilizing sludge (tailings) | |
| US3953318A (en) | Method of reducing sludge accumulation from tar sands hot water process | |
| US20120018383A1 (en) | Method for dispersing and aggregating components of mineral slurries | |
| CA1121555A (en) | Destabilization of sludge with hydrolyzed starch flocculants | |
| CN104066686B (en) | Dispersion and the method for coagulation ore pulp composition | |
| US5492628A (en) | Process for reducing sludge accumulation in the hot water extraction process for oil sands | |
| US4401552A (en) | Beneficiation of froth obtained from tar sands sludge | |
| WO2003004831A1 (en) | Oil sands separation process | |
| CA1110950A (en) | Destabilization of sludge with hydrolyzed starch flocculants |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |