Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
The present invention relates generally to an improvement in the recovery
¦ of bitumen from tar sands. The invention further relates to an
! improvement in the recovery of bitumen in aqueous processes for
..
5 extracting bitumen from tar sands. Generally the invention involves the
beneficiation of froth obtained from tar sands sludge. The invention
particularly relates to the improved treatment of froth produced during
the treatment of sludge obtained from a retention pond used to store
; tailings obtained from water extraction of bitumen from tar sands. The
10 invention involves the beneficiation of sludge froth by dilution with
water and subjecting the resulting mixture to concurrent agitation and
S aeration.
Tar sands are also known as oil sands or bituminous sands. The sand
deposits are found in numerous locations throughout the world, e.g.,
Canada, United States, Venezuela, Albania, Rumania, Malagasy and U.S.S.R.
The largest deposit, and the only one of present commerical importance is
in the northeast of the Province of Alberta, Canada.
Tar sand is a three-component mixture of bitumen, mineral and water.
Bitumen is the component 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 about O to 18 wt.%, and as used herein bitumen
includes hydrocarbons. Water typically runs 3 to 6 wt.% of the mixture,
increasing as bitumen content decreases. The mineral content constitutes
the balance.
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¦ Several basic extraction methods have been known for many years for
I separating the bitumen from the sands. In the "cold-water" method, the¦ separation is accomplished by mixing the sands with a solvent capable of
¦ dissolving the bitumen. The resnlting mixture is then introduced into a
5 large volume of water, water w1th a surface active agent added, or a
solution of 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
consistg of three major process steps (a fourth step, final extraction,
I' 10 is used to clean up the recovered bitumen for further processing~. In
7 the first step, called conditioning, tar sand is mixed with water andheated with open steam to form a pulp of 70-85 wt.% solids. Sodium
hydroxide or other reagents are added as required to maintain the pH in
the range of about 8.0-8.5. In the second step, called separation, the
15 conditioned pulp i8 diluted further so that settling can take place. The
bulk of the sand-sized particles (greater than 325 mesh screenj rapidly
settles and is withdrawn 8S sand tailings. Most of the bitumen rapidly
floats (settles upwflrd) to form a coherent mass known as bitumen froth
which is recovered by skimming the settling vessel. An aqueous middlings
20 layer containing some mineral and bitumen is formed between these layers.
A scavenger step may be conducted in the middlings layer from the primary
separation step to recover ad~itional amounts of bitumen therefrom. This
step usually comprises aerating the middlings. The froths recovered from
the primary and scavenger step can be combined, diluted with naphtha and
25 centrifuged to remove more water and residual mineral. The naphtha is
then distilled off and the bitumen is coked to a high quality crude
suitable for further processing. Hot water processes are described in
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the prior art. Tailings can be collected from the aforementioned
processing steps and generally will contain solids as well as dissolved
chemicals. The tailings are collected in a retention pond in which
additional separation occurs. The tailings can also be considered as
processing water containing solids which are discharged from the
extraction process. The tailings comprise water, both the natural
occurring water and added water, bitumen and mineral.
The mineral particle si2e distribution is particularly significant to
operation of the hot water process and to sludge accumulation. The terms
"sand," "silt" and "clay" are used in this specification as particle size
designations. Sand is siliceous material which will not pass through a
325 mesh screen. Silt will pdS8 through a 325 mesh screen, but is larger
than two microns and can contain siliceous material. Clay is smaller
than 2 microns and also can contain siliceous material. The term "fines"
lS as used herein refers to a combination of silt and clay.
Conditioning tar sands for the recovery of bitumen compri~es the heating
of the tar eand/water feed mixture to process temperature (180-200F),
physical mixing of the pulp to uniform composition and consistency, and
the consumption (by chemical reaction) of the caustic or other added
reagents. Among the added reagents disclosed in the prior are are
phosphates, sodium hydroxide and sodium tripolyphosphate, alkali metal
bicarbonates, and the product resulting from the addition of ammonium
hydroxide to aqueous tannic acid. Also non-foaming wetting agents
including nonionic detergents are often added. Under these conditions,
bitumen is stripped from the individual sand grains and mixed into the
~.
' pulp in the form of discrete droplets of a particle size on the same
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order as 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 sand feed. Deflocculation, or dispersion, means
¦ breaking down the naturally occurring aggregates of clay particles to
¦ 5 produce a slurry of individual particles. Thus during conditioning, a
lar~e fraction of the clay particles becomes well dispersed and mixed
throughout the pulp. lhe conditioning process which prepares bitumen for
efficient recovery during the following process steps also causes the
clays to be the most difficult to deal with in the tailings operation.
The conditioned tar sand pulp is screened to remove rocks and
unconditionable lumps of tar sands and clay. The reject material.
"screen oversize," is discarded. The next process step, called
"separation," is the bitumen recovery step. The screened pulp is further
diluted with water to promote two settling processes. Globules of
bitumen, essentially mineral-free, float upward to form a coherent mass
of froth on the surface of the separation units; at the same time,
mineral psrticles, particularly the sand size material, settle down and
are removed from the bottom of the separation unit as sand tailings.
These two settling processes take place through a medium called the
middlings. The middlings consists primarily of water, bitumen particles
and suspended fines.
The particular sizes and densities of the sand and of the bitumen
particules are relatively fixed. The parameter which influences the
settling processes most is the viscosity of the middlings.
Characteristically, as the suspended material content rises above a
certain threshold, which varies according to the composition of the
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suspended fines, viscosity rapidly achieveæ high values with the effect
that the settling processes essentislly stop. Little or no bitumen i8
recovered and all streams exiting the unit have about the same
coMposition as the feed. As the feed suspended 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 ~eed
suspended fines content sets the process water requirement through the
need to control middlings viscosity which, as noted before, is governed
by the clay/water ratio. It is usually necessary to withdraw a drag
stream of middlings to maintain the separation unit material balance, and
this stream of middlings can be scavenged for recovery of incremental
amounts of bitumen. Air flotation is an effective scavenging method for
this middlings stream.
Final extraction or froth clean-up can be accomplished by centrifugation.
Froth from primary extraction can be diluted with`a naphtha, and the
diluted froth can be then subjected to a two-stage centrifugation. Such
methods and varations are described in in the prior art. These processes
yield a product of essentially pure, but diluted, bitumen. Water and
mineral and any unrecovered bitumen removed ~rom the froth constitutes an
additional tailing stream which must be disposed of. Methods for washing
secondary-separator froths are disclosed in U.S. Patents Nos. 3,784,464
and 3,738,930 both of which are discussed hereafter.
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Tailings are a throwaway material generated in th~ course of extracting
thc valuable material from the non-valuable material and in tar sands
processing consist of the whole tar sand plus net additions of process
wa~er le8s only the recovered bitumen product. Tar sand tailings can be
subdivided into three categoriës: (1) screen oversize; (2) sand
tailings - the fraction that settles rapidly, and (3) tailing sludge -
the fraction that settles slowly. Screen oversize is typically collected
and handled as a separate stream.
Tailings disposal in all the operations is required to place the tailings
in a final resting place. Because the tailings contain bitumen
emulsions, finely dispersed clay with poor settling characteristics and
other contaminants, water pollution considerations prohibit discarding
the tailings into rivers, lakes or other natural bodies. Currently, the
tailings are stored in retention ponds (also referred to as evaporation
ponds) which involve large space requirements and the construction of
expensive enclosure dikes. A portion of the water in the tailings can be
recycled back into the water extraction process as an economic measure to
cDnserve water. Currently two main operating modes for tailings disposal
are (1) dike building - hydraulic conveying of tailings followed by
mechanical compaction of the sand tailings fraction; and (2) overboarding
- hydraulic transport with no mechanical compaction.
At one commercial location, for dike building, tailings are conveyed
hydraulically to the disposal area and discharged onto the top of a sand
dike which is constructed to serve as an impoundment for a pool of liquid
contained inside. On the dike, sand settles rapidly and a slurry of
water, silt, clay and minor amount of bitumen, as well as any chemical
11746Z ~'
used during processing 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 layer, e,g,, about 5-10 feet of the
pool, is a layer of relatively clear water containing minor amounts of
¦ solids, e,g,, up to about 5 wt,% and any dissolved chemicals. ~his layer
, of pond water can be recycled to the water extraction process without
interfering with extraction of bitumen from tar sands, Below this clear
water layer is a discontinuity in solid contents, Over a few feet,
solids content increases to about 10-15 wt.% and thereafter, solids
contents increase regularly toward the pond bottom, In the deeper parts
of the pond, solid contents of over about 50 wt,% have been measured,
This second layer is commonly called the sludge layer. The solids
contents of the sludge layer increase regularly from toy to bottom by a
factor of about 4-5, Portions of the solids are clays. The clays,
dispersed during processing, apparently have partially reflocculated into
a fragile gel network. Through this gel, particles of larger-than-clay
sizes are slowly settling. Generally this æludge layer cannot be
recycled to the separation step because no additional bitumen is
extracted. A third layer formed of sand also exists.
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 again occurs, but this distinction is not as sharp as in
the previously described dike building and no mechanical compaction is
carried out. The sand portion of the tailings settles rapidly to form a
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gently sloping beach, extending from the discharge point toward the pond
interior. As the sand settles, a slurry drains into the pool and
commences long-term settling.
In general pond water containing more than about 10-15 wt.% mineral
matter can be referred to as sludge. Thus water in ponds prepared by
both dike building and overboarding can be included in the general
definition of sludge in the present description.
Methods for treating sludge formed in a retention pond used to store
I tailings from a hot water extraction of bitumen from tar sands are
J lo disclosed in Canadian Patents Nos. 975,696; 975,697; 975,698; 975,699 and
975,700 all issued October 7, 1975 to 1l. J. Davitt. Thc first mentioned
Csnadian Patent discloses removing sludge from a pond, placing the sludge
in an air scavenger treating zone wherein the sludge is aerated and
agitated concurrently to form an upper bitumen froth layer and a lower
tailings of water and mineral water. The lower tailings can be
discharged into a retention pond. The upper bitumen froth is sent to a
6ettling zone wherein two layers are formed, an upper bitumen layer
reduced in mineral matter and water and a lower layer comprised
substantially of mineral matter and water with minor amounts of bitumen.
The latter lower layer is recycled back to the air scavenger treatin8
zone while the upper bitumen layer is processed further to recover the
bitumen. This Canadian patent and the others also disclose that sodium
silicate can improve bitumen recovery when used in connection with
aeration and agitation. Canadian Patent No. 975,697 discloses a proce~s
similar to that described in the previous patent with an additional step
in that a portion of the lower layer, which otherwise would be recycled
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back to the air scavenger treatin8 zone, is returned to the retention
pond. Canadian Patent No. 975,698 discloses feeding the sludge from a
retention pond to an air pressure zone wherein the sludge is aerated at
superatmospheric pressure to aerate bitumen in the sludge. Canadian
Patcnt No. 975,6g9 discloses feeding sludge recovered from a retention
pond to a settling zone and permitting the sludge to form an upper froth
layer nnd a lower tailings layer. Canadian Patent No. 975,700 discloses
feeding sludge to an air scavenger treating zone wherein the sludge is
aerated and agitated concurrently and resulting froth is separated in the
scavenger treating zone, while the tailings are returned to the pond.
However, none of the previously discussed patents discloses or suggests
applicants' improved method of treating froth obtained by agitation and
aeration of pond sludge.
U.S. Patent 3,594,306, E W. Dobson, July 20, 1971, discloses upgrading
froth from a secondary recovery operation (generally a flotation
scavenger zone treatin8 the bitumen-rich middlings from a separation
zone) by allowing the froth to settle in a settling zone whereby an upper
layer is formed which is substantially upgraded in bitumen content
compared to the secondary froth. The lower layer formed in the settling
zone can be recycled. Again, nothing in the aforementioned U.S. patent
discloses or suggests applicants' improved method of treating froth
obtained by treatment of pond sludge.
U.S. Patent No. 3,738,930, V.P. Kaminsky, June 12, 1973, discloses
forming a froth from a middlings stream from a primary cell. The formed
froth is produced in a secondary cell and as it leaves the secondary cell
it is treated to a fresh hot water wash which deaerates the secondary
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formed froth. The combination of the hot water wash and deaerated froth
is subjected to intimate contacting in a froth washer cell and within a
quiescent settling zone a more concentrated (as to bitumen) froth is
formed. The temperature range of the hot water wash is 100-200F. U.S.
S Pàtent No. 3,784,464, V. P. Kaminsky, June 8, 1974, discloses apparatus
which can be used in the hot water washing of secondary froth.
U.S. Patent No. 3,296,117, S. ~OS8, etal, January 3, 1973, discloses
upgrading froth from a primary recovery operation (wherein fresh tar sand
and water are contacted) by water washing the froth. The washing
involves contacting incoming froth countercurrently with incoming water.
The water used contains an additive such as tetrasodium pyrophosphate and
the temperature of the water washing zone is maintained in the range of
140F to 200F. The water washed product, an emulsion, is separated from
solids (contained in the froth) and contacted with a selective
demulsifier mixture whereby a water-free oil phase and an oil-free water
phase are obtained and separated. U.S. Patent No. 3,331,765,
C. R. Canevari, et al, July 18, 1967, discloses a similar process using a
different demulsifier mixture. U.S. Patent No. 3,330,757, J. A. Bichard,
July 11, 1967, also discloses a similar process using a chelating agent
with the water wash for the froth produced in the primary tar sand-water
mixing step. However, nothing in the previously discussed U.S. patents
discloses or 6uggests applicants' improved method for treating pond
sludge, as distinguished, for example, from the middlings treated by
Raminsky.
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U.S. Patent No. 4,018,664, F. A. Bain et al., April 19, 1977, discloses a
method for treating sludge from a retention pond associated with hot
water extraction of bitumen from bitumen sands. The method involves
withdrawing sludge from a pond, diluting and mixing it with water, and
settling to obtain a froth layer, a middle layer containing less solids
than the original sludge, and a lower layer containing increased solids
over the original sludge. Agitation and/or aeration, for example,
aeration sufficient to mildly agitate the sludge, are disclosed as
beneficial and essential to the extent that proper mixing is achieved.
Proper mixing presumably means that the sludge and dilution water are in
such close association that samples taken anywhere in the mixture all
would contain essentially the same amount of water. However, nothing in
the aforementioned patent suggests applicants' method for treating froth
obtained from sludge.
SUMMARY OF T}E INVENTION
The present invention is an improved method for processing froth
containing bitumen, mineral and water. The froth is obtained from the
treatment of sludge obtained from a retention pond used to store tailings
from water extraction of bitumen from tar sands. The improved method
involves diluting the froth prepared from the treatment of pond sludge
w;th water, agitsting snd aerating concurrently the resulting mixture and
then separating sn upper layer of resulting froth in which most of the
bitumen is conceatrated. The improved method can be also eonsidered as
demineralizing froth or as the benefi.ciation of the froth.
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DESCRIPTlON OF THE DRAWING
The attached drawing is a schematic representation of a hot water tar
sands extraction process and how one embodiment of applicants' method
relates to the extraction process. The following discussion describes
generally the hot water tar sands extraction process and describes how
applicants' improvement could be incorporated therein.
DETAILED DESCRIPTION
Referring now to the single figure, tar sands are fed into the system
through a line 1 and pass to a conditioning drum (or muller) 30. Water
and stream are introduced to the drum 30 through another line 2. The
total water so introduced in liquid and vapor form is a minor amount
based on the weight of the tar sands processed. The tar sands
conditioned with water, pass through a line 3 to a feed sump 31 which
serves as a zone for diluting the pulp with additional water via line 20
beforc passage to the separation zone 32. The additional water 20 may be
clear pond water.
The pulp tar sands sre continuously flushed from the feed sump 31 through
a line 4 into separator zone 32. The settling zone within the separtor
32 is relatively quiescent so that bitumen 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. The froth withdrawn
via line S is sent to froth fiettling zone 34 where it is processed along
with froth from the flotation scavenger zone.
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A middlings stream i8 withdrawn through line 7 to be processed as
described below. Another middlings stream, which i~ relatively
bitumen-rich compared to the stream withdrawn through line 7, is
withdrawn from the separation zone 32 via line 8 to a flotation scavenger
zone 33. In this zone, an air flotation operation is conducted to cause
the formation of additional bitumen froth. The froth from zone 33 is
sent via line 9 to froth settling zone 34.
¦ Also a bitumen-lean water stream is removed from the bottom of the
scavenger zone 33 through line 10 to be further processed as described
below.
The combined froths from zones 32 and 33 can be sent to a froth settler
zone 34. In the settler zone 34 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 33, the sand
lS tailings stream from the separation zone 32 and a portion of the lower
middlings withdrawn via line 21 from the separation zone 32. The bitumen
froth from the settler 34 is removed through line 12 for further
treatment.
The bitumen-lean water from the froth settler zone 34, the scavenger zone
33 and the separator 32, all of which make up a tailing discharge stream,
which can be collected and handled via a dike building or a overboarding
operation both of which are previously described. The tailing discharge
stream via line 13 can be fed to distribution pipe 14. The distribution
piping provides for continuous and uniform delivery of the effluent lS to
the pond 35. The latter can be considered another separation zone; it is
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a zone of quietness. Both the dike building and overboarding operation
result in whst i6 commonly referred to as a pond, particularly a
retention pond. And as previously described three layers are formed in
the pond. They are (1) a top water layer relatively free of clay and
bitumen and which can be recycled; (2) a middle layer consisting of
bitumen and mineral (defined as not being soluble in toluene); and (3) a
bottom layer having a relatively hi8h concentration of sand. The middle
layer of the pond is often referred to as sludge.
The sludge is continuously being formed in a time span of many months and
even years. As a result, its charactistics are different from those of
the middlings layer drawn off from the separation zone 32 via lines 7 and
8. Some of the differences include a higher pH (e.g.l about 8.4) of the
middlings layer wheress the sludge has a lower pH (e.g., about 7.3). The
difference8 in pH reflect changes which are not fully understood but
~hich are occurring in the pond. Another difference between the sludge
and middlings streams (via lines 7 and 8) is the weight percent of
mineral, e.g., the middlings stream contains about a 8-12 wt.% whereas
the sludge contains a higher weight %, at least about 15 wt.%, e.g.,
G~/fS Y/~ about 15-3~ wt-%-
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Sludge iB withdrawn from the pond 35 and treated by adding an effective
amount of a bitumen release promoter, e.g., sodium silicate, to the
sludge. Then the resulting mixture is concurrently agitated and aerated
and as a result substantial quantities of bitumen are released from the
sludge. In particular, sludge from the pond 35 is withdrawn by known
means, for example, line 16 which is attached to suction pu~p 38.
Line 17 from the latter carries the sludge to treatin~ zone 36, wherein
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it is agitated and aerated to produce an upper froth layer of
bitumen-rich materi~al and a lower layer of bitumen-lean material. An
effective amount of the additive is admixed with the incoming sludge 17
or added to treating zone 36. The additive can be added to the treating
zone 36, e.g., via line 18. In any of the previously described methods
the resulting bitumen-rich froth can be separated and forwarded to
additional processing via l;ne 19 while the remaining bitumen-lean
material can be returned to the same pond or a different pond (not shown)
via line 24.
In one embodiment of applicants' improvement the resulting froth, with or
without additive, from treating zo~e 36 is sent to beneficiation zone 37
wherein the froth is mixed with additional water via line 25 and
¦ subjected to agitation and aeration concurrently, An upper layer of the
resulting froth is separated which layer contains most of the bitumen.
~he separated froth containing the concentrated bitumen is removed and
transferred via line 23 for further processing, while the bottoms layer
containing much of the mineral is also transferred via line 22 for
further suitable treatment.
.~._.
In applicants' improved method of treating froth an effective amount of
water is used to dilute the incoming froth to the beneficiation zone. An
effective amount is that amount which causes an increase in the
concentration of bitumen contained in the upper froth layer while at the
same time decreasing the amount of mineral and water. The water can be
pond water (clear upper layer) or fresh water or some other suitable
water. Generally the water does not contain an adverse amount of bitumen
and/or mineral or any other material which would interfere with the
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separation process, and does not contain a substantial amount of mineral
matter. Generally, the amount of water used i8 within the range of 0.5
to 2 volumes of added water per vo]ume of froth.
The resulting mixture of froth and effective amount of dilution water is
also concurrently agitated snd aerated vigorously. The amount and kind of
agitation and aeration i8 sufficient to cause the froth containing a
higher concentration of bitumen to form. The agitation and aeration is
obtained by use of a turbine or other means known to those skilled in the
art of mixing. The length of agitation and aeration can vary depending,
in part, on the particular mixing means used, the relative amounts of
: material being processed compared to the size of the equipment and other
variables known to those skilled in the art. Further, the a~ount of
vigorous agitation and seration used concurrently causes a turbulence of
the mixture which exceeds mere mixing wherein the object it to obtain a
uniform composition. Generally, the high-shear agitation used to
practice the invention can be at a suitable Reynolds Number for a
particular unit, howcver, preferably the Reynolds Number would be higher
than 10,000, more preferably higher than 100,000.
Contrary to the expectation that one would have, based on the discussed
prior art, applicants have found that in treatinB froth derived from
sludge an elevated temperature (e.g., 80-85C) is not desirable. In
fact, as demonstrated in the Examples, applicants have found that the
temperature o~ the water used to dilute the forth should be an ambient
temperature, e.g., 20C. As used herein ambient refers to a temperature
range of about 0C-37C.
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In the beneficiation zone the upper layer of the resulting formed froth
can be separated from the balance of froth by ~nown techniques, e.g.,
skimming, either while the agitation and aeration is occurring or after
both have stopped. Also the froth formed can be transferred to a foam
settler, and the separation performed in the settler. In any of the
foregoing descriptions the advantage of applicants' improved method is
that the bitumen is concentrated in the froth while the mineral and water
content are decreased. Thus further processing of applicants' froth is
greatly enhanced since a high mineral content causes high operating
costs. Also applicants' method has the advantage of decreasing the water
concentration of the separated froth.
Essentially then, applicants' improved method for separating bitumen from
tsr sands by a water extraction process wherein froth containing bitumen,
mineral and water is recovered and further treated to separate the
bitu~en from the froth, comprises (a) diluting the froth feed with an
effective amount of water such that after concurrent agitation and
aeration most of the bitumen is concentrated in an upper portion of
resulting froth, and the water used is at ambient temperature;
(b) vigorously agitating and aerating concurrently the resulting mixture
of feed froth and dilution water; and ~c) separating an upper layer of
resulting product froth in which most of the bitumcn is concentrated.
Further, applicants' improvement resides in obtaining the feed froth from
the processing of tailing pond sludge. Still further, applicants'
improvement is characterized by relatively low concentration of bitumen
in the feed froth and the upper resulting layer of product froth having a
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relatively high concentration of bitumen. And still further, applicants'
improvement is characterized by use of clear pond water as the dilution
water.
The following examples illustrate the invention. Comparative examples
are also given.
EXAMPLES
A froth was prepared in the following manner. Sludge and air were pumped
continuously into the bottom of a flotation cell similar to a Western
Machinery flotation cell (also referred to as a Wemco Cell) except that
the agitator was a shrouded turbine. The product overflowed into a
8hallow tank where the froth was removed and collected in a large
container. At the end, after thorough mixing, the f~ th analyzed 21% ~/fS
bitumen and 21% mineral, thè remainder being water.
The data shown in the accompanying Table were obtained using the
following procedure. The previously prepared froth, containing 21 wt.%
bitumen and 21 wt.% mineral or a ratio of 1/1, was charged to a vessel
along with an equal amount of pond water (clear, top layer). The
resulting mixture was a8itated by the use of a standard bladed turbine
(in a baffled vessel) turning at 2000 rpm for five minutes. "Standard"
is a word recognized by a person skilled in the art of mixing and refers
to the ratio of blades to baffles sizes. At 2000 rpm the turbine also
aerates the mixture. The upper layer of the froth was skimmed off and
,~ analyzed for content of bitumen and other components. The dilution and
high agitation and aeration of run 1 caused concentration of bitumen to
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occur. Compsred to the charged froth which had a hitumen/mineral ratio
of 1/1, the skimmed off froth had a bitumen/mineral ratio of about 8.6/1.
The wt.% of bitumen recovered was 95% of the amount charged, indicating
an efficient process.
Run 2 was conducted to determine if an elevated temperature causes
density differences which further increase recovery. Run 2 was conducted
in the same manner as Run 1 except that instead of being conducted at
20C it was conductéd at 85C. The data in the Table indicates that
increasing the temperature, even with dilution, causes the wt.% bitumen
recovered to decrease significantly, i.e., from 95 wt.% to 36 wt.%.
Run 3 was conducted in the same fashion as Run 2 except that the mixing
was gentle, using a spatula. Because of the gentle agitation and no
aeration the wt.% bitumen recovered greatly decreased compared to Run 1.
Runs 4 and 5 were conducted to demonstrate the effect of the lack of
dilution with water. Run 4 was performed at an elevated temperature
using the turbine. As shown in the Table the skimmed froth resulted in
substantially no separation as compared to 36 wt.% bitumen recovery from
Run 2. Run 5 shows that gentle mixing, without dilution and at an
elevated temperature, causes some concentration of bitumen compared to
Run 3.
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¦ Run 6 demonstrated that a low temperature, mild agitation treatment fails
to cause any separation of bitumen.
Treatment of other froths having different compositions also gives the
~ advantages of applicants' dilution method. Also, use of other dilution¦ S rstios gives similar beneficiation of the various froths.
,1
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