CA1273888A

CA1273888A - Flocculant for bitumen tailings

Info

Publication number: CA1273888A
Application number: CA000519513A
Authority: CA
Inventors: Amar J. Sethi
Original assignee: Suncor Inc
Current assignee: Suncor Energy Inc
Priority date: 1986-10-01
Filing date: 1986-10-01
Publication date: 1990-09-11

Abstract

ABSTRACT

An improved method for the flocculation of aqueous tailings obtained from the processing of bitumen from tar sands comprising the addition to the tailings as a flocculant, a 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.

Description

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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 ~73888 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 ~Z738~38 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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~3~8 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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~X~3~8 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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the flocculation of aqueous bitumen-containing tailings from a tar sands processing operation to obtain three distinct layers comprising an upper bitumen layer, a middle aqueous layer and a bottom mineral layer which comprises adding to said tailings a flocculation-effective amount of a 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.

2. The process of claim 1 wherein the amount of flocculant is from about 5 to about 25 ppm.

3. The process of claim 2 wherein the molecular weight of the polyacrylamide is from about 4 to about 6 million.

4. The process of claim 3 wherein the upper bitumen layer is recovered and recycled to the tar sands processing operation.

5. The process of claim 3 wherein the middle aqueous layer is recycled as process water.