Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3;?~ 3
1 FIELD OF THE INVENTION
2 The invention relates -to a process for treating the
3 sludge in a tailings pond of plant which uses the hot water
4 process for extractiny bitumen from oil sand.
S BACKGROUND OE' THE INVEN~ION
6 In the Athabasca region of Albe.rta, C~n~a, geological
7 depositions of oil sand occur. T~e:re are ln commercial
8 opera~ion, two plan~s which use the hot water extraction process
g for extracting bitumen from the oil sand. The hot water
extraction process has been well detailed in both publications
11 and patents.
12 Briefly, the first step of the hot water process
13 involves conditioning the oil sand by mixing the mined. oil sand
14 with hot water and sodium hydroxide in a rotating drum to form a
slurry~ The slurry is then screened and diluted with additional
16 hot water prior to being pumped into a flotation/settling vessel.
17 In this vessel, re~erred to as the PSVI most of the solids
18 (largely sand) sink to the base of the vessel, and are withdrawn
19 therefrom as an underflow stream termed primary tailings. A
major portion of the bitumen, present in the form of suspended
21/ globules, films over entrained air bubbles and rises to form
22 primary bitumen froth which is recovered.
23 A middlings stream comprising less floatable bitumen
24 together with clay particles forms between the settled solids and
floating froth layers. The middlings stream is withdrawn from
26 the PSV and subjected to secondary flotation in sub-aerated cells
27 to produce secondary bitumen froth and a tailings stream which
28 contains water, solids and a small amount of bitumen.
~13'0~ 13
l The fro~h streams are combined and subjected to
2 centrifugal ~eparation to yield pure bitumen and a tailings
3 stream. Again, this tailings stream comprises water, solids and
4 bitumen.
The three tailings streams are then combined and
6 discharged into a tailings pond.
7 The combin~d tailings stream thus comprises coarse sand
8 grains, fine clay particles (referred to as fines), water, and
g some bitumen. By fines is meant those particles having an
average size less than forty microns.
11 The tailings pond, typically, has a depth of
12 approximately 125-150 feet. Upon discharge of a combine~
13 tailings stream into ~he pond, a~er what is re~erred to as the
14 first sedimentation stage, the stream settles into an uppex layer
of clarified water oP about 15 fe0t in depth, a sludge layer of
16 about 60 feet in depth and a lower layer of dirty water.
17 Typically, the upper layer of clarified water is recycled to the
~8 plant. The lower sludge plus water layer is considered to be in,
19 what is termed, a steady~state pseudo-stabilized condition.
Hereinafter, the term 'sludge' will refer to these two layers in
21 the pseudo-stabilized state. Without being bound by same, it is
22 believed that it is the presence of fines which deletiorously
23 stabilizes the sludge layer thereby preventing normal settling of
24 the solids.
The properties of sludge are outlined in further detail
26 in a paper entitled ~Behaviour of Oil S~nd Tailings Sludge~ by J.
27 T. Scott et. al., published by the Petroleum Society of CIM in
28 Paper No. 82-33-85.
29 The prior art patents describe numerous se~i -ntation
~'~r~ 3
1proces~es~ exemplary patents being Canadian Patent 1,247,550,
2U~S. 4,783,268, and Canadian Patent 1,236,419.
3It is an objective of the present inven-tion to separate
4and remova the ~ines and residual bitumen from the sludge thereby
5permitting the r~ ~ining solids to settle and as a result recover
6improved yields of recycle water.
7SUMMARY OF THE IN~NllON
8The present invention is based on the discovery that a
9cationic surfactant is preferentially adsorbed by the fines in
10the sludge. When the sludge is aerated and diluted, the fines
11together with the residual bitumen are flocculated, and can be
12floatad off and removed. In the absence of a surfactant, the
13residual bikumen .- ~;n~ in the sludge.
1~In accordance with the present inven~ion there is
15provided a process for treating sludge in the tailings pond of a
16plant using the hot water extraction process to extract bitumen
17from oil sands. The process involves first adding a
18predetermined quantity of a cationic surfactant to said sludge.
19The mixture is agitated for a sufficient period of time for the
20surfactant to preferentially contact the fines.
21The cationic surfactant may be selected from alkyl
22amines or alkyl derivatives of ammonia and fatty acids.
23The quantity of surfactant would range between about
24100 g/tonne to about 1,000 g/tonne.
25The mixture is then aerated to flocculate and float
26said fines. A fraction of the flocculated fines is removed. As
27a result the rate of sedimentation of said sludge is accelerated.
28In a broad aspect, the invention relates to a process
1 -for treating a ~ines~con-taining sluclge in -the tailings pond of a
2 plant which uses the ho~ water process used for extracting
3 bitumen from oil sand which comprises:
4 adding a predetermined quantity of a cationic
surfactant to said sludge;
retAining said mixture under agitation for a suf~icient
7 period of time to permit said surfactant to contact said fines;
8 aerating said mixture to -flocculate and float said
g fines;
diluting said mixture; and
11 removing a fraction of said floccula~ed fines and
12 residual bitumen to thereby accelerate the rate of sedimentation
13 of said sludge.
14 DESCRIPTION OF THE DRAWINGS
Figure 1 is a plot of the rate of sedimentation of
16 fines versus time.
17 Figure 2 is an illustrative representation showing
18 settling of treated ~ludge with various quantities of surfackant
19 and untreated sludge.
Figure 3 is a schematic showing a plant process.
21 DESCRIPTION OF THE PREFERRED ENBODIMENT
22 Having reference ~o the accompanying figures, there is
23 provided a process for accelerating the rate of sedimentation of
24 a sludge found in the tailings pond of a plant using the hot
water process for the extraction of bitumen from oil sands.
26 The schematic for the process for a plant producing
27 20,700 b/d bitumen is illustrated in Figure 3.
~~3
ExpERIMENTAL
2 The following laboratory ~est work is included to
3 clemonstrate the operability of the present invention.
4 The measure o~ sedimentation rate of the sludge was
assessed using the standard sedimentation kest of Coe and
6 Clerenger wherein the position of the interface with settling
7 time is used as an indicia of settling rate.
8 A standard dressinq test appara~ls ~WEMCO Flotation
9 Cell) was used for processing the sludge prior to the ~atch-
settling test. A specimen of untreated sludge (A) was kept as a
11 control. No chan~e in the behaviour of the sludge or interface
12 separation was observed.
13 More speci;Eically, 500 cc of sludge was introciuced into
1~ the flotation cell. 3500 cc of tap water was added to dilute the
mixture. 0.065 g of d.iamine (supplied by AICZO Chemicals Ltd. CES
16 109), was added to the cell. The mixtuxe was mixed for about 5
17 minutes to allow time for the surfactant to contact the solids.
18 The pH was adjusted to about 8.2. The mixture was then aerated
19 in the flota-tion apparatus and the froth collected for 5 minutes.
3500 cc of tap water was added to dilute the mixture. The
21 flocculated fines were floated and the resultant froth was
22 removed from the mixture. 450 cc of the froth was ~ransferred to
23 a 500 cc glass, graduated cylinder. The evolution of the
24 interface i.e. settling was observed for approximately 1000
minutes. The results are illustrated in ~igure 2.
2~ B represents addition of 200 g of diamine/tonne of
27 solids contained in the sludge; C represents addition of 300 g of
28 diamine/tonne of solids contained in the sludge; D represents
29 addition of 475 g of diamine/tonne of solids contained in the
sludge and E shows the effec-t of addi-tion of 700 g of
2 diamine/tonne of solids con~ained in the sludge.
