Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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_CKGROUND OF THE INVENTION
This invention relates to an improved method for the
flocculation of aqueous tailings obtained in the
processing of bitumen from tar sands. More particularly,
the method of this invention rapidly converts tailings to
a three layer system comprised of a lower mineral layer,
a clear aqueous middle layer and an upper bitumen layer.
In general, these tailings are aqueous colloidal
suspensions containing either clay minerals or metal
oxides-hydroxides which are formed in large volume during
mining operations in the recovery of bitumen from tar
sands. In order to properly dispose of these voluminous
tailings, flocculants have conveniently been employed to
destabilize these suspensions and thus permit the
effective separation of water from the clay solids.
Among the various reagents which have been found
useful for flocculating clay are: aluminum chloride,
polyalkylene oxides, such as polyethylene oxide,
compounds or 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 quartz
flour or a high molecular weight acrylamide polymer such
as polyacrylamide or a copolymer or acrylamide and a
copolymerizable carboxylic acid such as acrylic acid.
Additional flocculants which have been considered include
the polymers of acrylic or methacrylic acid derivatives,
for example, acrylic acid, methacrylic acid, the alkali
metal and ammonium salts of acrylic acid or methacrylic
acid, acrylamide, methacrylamide, the aminoalkyl
acrylates, the aminoalkyl methacrylamides and the N-alkyl
substituted aminoalkyl esters of either acrylic or
methacrylic acids. More recently, improved clay
flocculants have been obtained from the starches corn,
wheat, potato, yam, cassava and dasheen which are
hydrolyzed in the presence of one or more insoluble salts
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formed ln situ.
While the above agents are effective with bitumen
tailings to various degrees, they do not provide the
benefits obtained by this invention.
OBJECTS OF THE INVENTION
It is an object of this invention to flocculate
tailings from the process of recovering bitumen from tar
sands so as to provide a three layer system comprised of
- a lower mineral layer, a clear aqueous middle layer and
an upper bituminous layer.
Another object is to provide a method for very high
recovery of bitumen from tar sands tailings.
A further object is to provide means to clarify the
water content of a tar sands tailings and recycle it for
reuse or discharge it to streams and rivers without
environmental problems.
Further objects will become clear from a discussion
of the invention.
BRIEF DESCRIPTION OF THE INVENTION
This invention employs a flocculant for aqueous tar
sands tailings a highly specific high-molecular weight,
water-soluble, anionic polyacrylamide having about 26% to
about 36~ of its amide groups hydrolyzed to carboxy
groups and converted to the sodium salt. This flocculant
is used at low concentrations (i.e., from about 5 to
about 25 ppm) to effect flocculation of the tailings into
- a lower, essentially all mineral layer, a middle, clear
aqueous layer and an upper layer of bitumen.
Furthermore, the process of the invention effectively
recovers essentially all of the bitumen that can be
recovered from the tailings.
DISCUSSION OF PRIOR ART
As indicated above, numerous agents, including high
molecular weight polyacrylamides have been used as
flocculants. For example, polyacrylamides of various
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molecular weights and degrees of hydrolysis have been
used in industrial water and waste water treatment. Such
agents, including those polyacrylamides used in this
invention, have also been recommended to give rapid
settlement of suspended solids and clear supernatents in
the treatment of iron ore, underground mine waters, steel
industry metals and coal fines. The bitumen recovery
process of subject process, however, is quite different
from a simple settlement of suspended solids. In the
recovery of bitumen it is desirable, as accomplished by
the present invention, not just to obtain a settlement of
suspended solids, but to obtain three layers, the bottom
containing the solids, the middle layer being an
essentially clear water layer, and the upper layer
comprising essentially all the bitumen that can be
recovered. Thus, the prior art actually teaches away from
subject invention in that it suggests only the separation
of solids without the three layer distribution system
required for subject bitumen recovery process.
It is also significant to note that of numerous
flocculants evaluated only the specific polyacrylamide
employed by the process of the invention was found to be
effective to give the high bitumen recovery in the
required three layer system.
DETAILED DESCRIPTION OF THE INVENTION
As pointed out above, the process of this invention
effectively recovers essentially all of the bitumen that
can be recovered from the tar sands tailings. Normally,
about 10% by weight of bitumen is bound to the clay in
the tailings and this amount of bitumen cannot be
separated from the tailings where it remains with the
sludge at the bottom of the pond. The remaining 90% of
bitumen in the tailings, however, are recoverable by the
process of the invention as will be seen in the examples.
In carrying out one embodiment of the invention, the
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specific polyacrylamide flocculant is added to the
tailings, preferably, by injection in~o the conduit
carrying the tailings to the pond. The flocculant is
added in an amount effective to cause flocculation in a
reasonable time and is usually used in an amount from
about 5 to about 25 parts per million (ppm), preferably
from about 7 to 15 ppm, most preferably about 10 ppm. As
indicated, the flocculant is a high molecular weight (4
to 6 million) water-soluble, anionic polyacrylamide which
has about 26% to about 36% of its amide groups hydrolyzed
to carboxy groups and, preferably, converted to the
sodium salt. This polyacrylamide has been characterized
by Chemical Abstracts under Registry No. 37224-28-5 and
is commercially available from Dow Chemical Company as
SEPARANTM AP 273 polymer. (See also Balakrishnan et al,
AICHE J. 21(6), 1225-7 and U.S. 3,965,708). -
After addition of the polymer, the tar sand tailings
separate into three distinct layers. The lower layer
contains the flocculated mineral material and the
approximately 10% of unrecoverable bitumen discussed
above. The middle layer is essentially clear water, and
the upper layer is the bitumen which may be recovered by
skimming or other means. The recovered bitumen is, of
course, added to that obtained by the primary processing
of the tar sands and thus the overall efficiency of the
tar sands operation is significantly increased.
-As indicated, however, another benefit of the
invention is the disposition of the clarified water
layer. This water layer is easily handled by pumping or
other means and may be recycled to the tar sands plant as
process water or, alternatively, it may be discharged to
-a river or stream without fear of environmental
endangerment.
The remaining bottom layer of clay minerals
resulting from the flocculation process of the invention
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is readily conveyed to the pond for dike building or for
eventual compaction.
The invention is further described by the following
examples.
Examples
Dow Chemical Company SeparanTM AP 273 was added to
the hot (75C.) tailings from a tar sands processing
operation in an amount of ten (10) ppm and thoroughly
mixed in a graduated cylinder. The level of the column
was about 45 cm. After thirty (30) minutes of settling
time samples from each 2.5 cm level of the column were
analyzed for bitumen by infra-red spectrophotometry using
a Freon fluorocarbon as solvent. The results obtained
are shown in Fig. 1 where the percent bitumen is shown
for each of the 2.5 cm samples evaluated.
For comparative purposes a similar experiment was
performed with a commercial flocculant available from
Allied Colloids as Percol 1017 whicn is a medium high
molecular weight anionic flocculant. This comparative
data is shown in Fig. 2.
As can be seen by Figure 1, about 70% of the bitumen
in the tailings is floating at the top of the column
(i.e., at the 36 to 45 cm level). No bitumen appears
between the 7 to 36 cm level in the column which was
observed to be clear water and only about 30% of the
bitumen is in the bottom level of minerals.
In contrast, Fig. 2 shows that with the commercial
- flocculant only about 12% (9 + 2 + 1) of the bitumen is
floating on the top of the column while about 88% (25 +
22 + 21 + 20) of the bitumen remains with the minerals at
the bottom. Thus, the process of the invention enables a
vastly improved recovery of bitumen from tailings to be
obtained and provides a clarified water level useful for
reuse in the processing plant or for safe discharge into
rivers or streams.
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