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FROTH FLOTATION METHOD FOX Recovery OF BITUMEN
FROM AUDI SUSPENSION OF TAR WANDS
This invention relate to a froth flotation method or the recovery of bitumen prom aqueous suspensions of tar sand.
The invention it particularly useful in conjunction with the Hot Water Process for the extraction of bitumen prom tar sands, because in this process a number of flotation operations are or can be performed.
Tar sands deposits, also known as oil sands and bituminous sands, have been identified in many areas ox the world including four major deposits in Alberta, Canada.
The Alberta tar sands typically contain between 70 and 90 percent by weight ox mineral solids, 5 and 20 per cent of viscous petroleum having a 6 to 10 APT gravity and specific gravity ox about 1~0 commonly referred to as Bohemian and Prom aye 1 Jo 10 percent of water. The mineral solids usually referred to a "coarse" are mostly quartz sand over 45 micron in particle size, whereas those referred to as phonies" are mostly clay, silts and wine sand having particle size lest than 45 microns. The content ox fines has been generally wound to increase with the decrease in bitumen content in the tar sands. The usually accepted physical arrangement ox the sand-bitumen-:
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-2-water mixture that constitute the tar sands depicts an aqueous phase which anvelop3 the hydrophilic sand grains and separates them prom the bitumen phase. queue key requirement for the production of bitumen is a fast and complete separation of the bitumen from the mineral solids. Various techniques or separating the bitumen prom mined tar sand have been developed to die rent degrees in thy last several decades. These include: direct coking, vent extraction, cold water separation, lo spherical agglomeration and a sand reduction process just to mention a few. These method are not being used on commercial scale due to a variety of reasons, such as material handling problems, low bitumen recoveries, high energy retirement solvent losses, etc.
The present commercial plant, Succor and Sync rude, are based on the Hot Water Process which war initiated in the 1920'~ by the Research Council of Alberta led by K. A.
Clark.
An excellent write-up on tar sands and on bitumen recovery technology is presented by Donald Tyson in Kirk-Other Encyclopedia of Chemical Technology, Third Edition, pages 602-6Q7.
It the Hot Water Process, the mined tar sands are treated in a tumbler with hot water, steam and additives, usually caustic, to break down the lumps and produce a slurry at approximately 80C-90C. The slurry is diluted
-3-with hot water to approximately 50% old, then pumped into a gravity separation cell where entrained air causes the bitumen to float. The flotation process produces the primary froth, middlings and an under flow, which constitutes the primary tailings.
The secondary froth, which is produced from the middlings by air flotation, contains approximately twice the amount ox solids and water as compared to the primary Roth. Tailings from the secondary circuit join the primary tailings to form the extraction plant tailings.
Following duration and heating, the combined Roth stream is further treated by dilution and centrifuging to remove the solids and water prom the bitumen in preparation for the upgrading or coking process. The solids and water removed together with residual hydrocarbons constitute the froth treatment plant tailings.
Since the early stages of development of the Hot Neater Process, it has been recognized that lower grad ore, with its higher percentage of fines and lower bitumen content, results in lower bitumen recovery in the primary separation stage and increased load total middlings flow and solids content) in the secondary air flotation circuit. Since the secondary separation produces Roth with high, mainly fine solids content, the total solids and water content may surpass the handling capability of do ~6~39 I
the Roth treatment plant. Con equently, large amounts of bitumen are lost in the traction plant tailings. A more efficient separation of bitumen from the middlings stream it highly desirable it a high level of bitumen recovery it to by achieved This may also allow for reduced cutoff grade of tar sands ore at the mine and increase the total tar sand resource available for processing.
Many improvements of the Hot Water Process have been proposed which could be classified under two headings:
lo l. Improved control to increase bitumen recovery and separation efficiency of the existing plants;
2. Development of methods for the recovery of the residual hydrocarbons prom the tailings and for improving the settling characteristics ox the sludge.
Some of these proposals seem to be more effective than other; however, most are not C08t effective because they require major modifications to the existing plants.
It is, therefore, the object ox the present invention to provide a novel flotation method whereby a high quality froth with high bitumen recoveries is obtained, and this without requiring major modifications to the existing installations. This object is achieved by carrying out flotation with COY in the presence of a dispersing/sequestering agent.
C2 gas flotation is already known and is disclosed in I
I;
Canadian Patent Nos. 949,910 and l,023,677. Carbon dioxide flotation reduces the pulp pi and enhances destruction of the mineral hydrocarbon bond thus increasing froth grade t~Bitumen/(Bitumen solids water) over that with air flotation. However, bitumen recovery to the concentrate remains about the same or lower compare to air flotation.
It it also known to perform C02 flotation with acid addition to the pulp to initially reduce the pi to about phi a it disclosed in Canadian Patent No. 1,022,098. This way wound to increase bitumen recovery over C02 flotation but the froth grade is drastically reduced.
On the other hand, it is also known to perform air flotation with addition of dispersing agents such as sodium phosphate compounds or soda ash to the pulp as disclosed in Canadian Patents 775,088 and 914,093 and US.
Patent 3l846,276 and 4,425,227. Although the addition of a do pursing agent generally increases froth grade, it has been found to have a devastating eject on thy overall Bitumen recovery.
Applicant has surprisingly found in accordance with thy present invention, that the addition of a disappearing sequestering agent in the tar sand pulp during C02 gas flotation not only results in a significant improvement in froth quality (i.e. lower solids content) but also increases bitumen recovery. It is believed that the prime function ox the dispersing/sequestering agent during C02 ~3'7~
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flotation it to sequester or syllable complexes) or precipitate undesirable cations, such a calcium, which contribute to the mineral-bitumen bond and enhance mineral flotation. Once this bond it destructed the mineral flotation is depressed while the bitumen and the surfactants present in the pulp are readily attached to the C02 gay bubble and form the froth. The dispersing/sequestering or precipitating agent may, o'er example, be a phosphate compound, such a sodium tripolyphosphate or soda ash. The amount of dispersiny/sequestering agent to be added may vary depending on the agent used and on the actual process or treatment in which it is employed. When using sodium tripolyphosphate and soda ash, it ha been found that disper~ant additions of up to 0.7 kg/t ox pulp are sufficient to improve recovery to the point that no further addition is beneficial. The dispersing/
sequestering gent may be added prior to or during flotation or in stages during flotation, The invention will now be further described with reverence to a non-limltative example, and with reference to the appended drawing in which Figure 1 shows comparative value ox bitumen recovery versus froth grade using various flotation methods.
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ampule: E
Tests were conducted on primary separation vessel middlings containing 1.1% bitumen and 33~ solids. The flotation tests were conducted with air, with Coy, with C2 and HO with air and a dispersing/sequestering agent and finally with COY and a dispersing/sequestering agent. The dispersing/sequestering agent dosages were varied. The froth was collected after 6 and 12 minutes of flotation. The results of the tests are presented in Figure 1 and in the following Table.
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TABLE
6 MINUTE O~NeE~TR~lE 12 MINUTE oCNCE~lRArE
METHOD Grow ~XIUMEN Recovery GRACE gENCVTRY
Betty web Betty web (wit basis) (jet basis) I 1~.7 73.3 11.3 81.0 CX~2 ~2S44~ 71.8 4.5 84.0 AIR 12.5 76.8 9.1 81.
AIR ARTS*
STOP 0.08424.~ 72.8 16.1 78,1 STOP 0.1~830.7 ~6.9 21.4 73.8 STOP ~.67240.9 57.5 31.~ 65.9 soda ash 0.16R 15.4 72.9 15.4 78.6 Soda ash 0.336 21.0 70.9 13.8 78.2 soda ash 0.705 18.9 69.g 18.9 76.1 2 Hyannis*
SIP 0.16~19.4 8~,2 15.6 84.3 Soda Ash 0.336 16.4 77.5 12.7 84.2 STOP 0~504 - - 19.5 ~2.3 osseous are in Xg/ton meddlings Eye Thy above Table and Figure 1 depict the bitumen recovery and concentrate grad after 6 and 12 minutes of flotation lima at 80C using COY, COY + H2SO4, Air, Air + dispersing/sequestering event and finally C02 +
disper~ing/se~uestering agent. From the above results, the following operations can be mad:
a) the application of sodium tripol~phosphate or soda ash with air or carbon dioxide as flotation gas substantially improves thy concentrate bitumen grade over lo the standard air flotation.
by all levels of sodium tripolyphosphate and soda ash when used with air had the effect of reducing the rate of bitumen recovery. This phenomenon was not observed with carbon dioxide where the rate of bitumen recovery was increased by about 3% over the standard air flotation.
Applicant ha alto found that the addition of a dispel ing/~e~uestering agent during C02 flotation raises the initial pulp pi from 8.3 to 8.5 while flotation with C2 alone as disclosed in Canadian Patents 949,910 and 1,023,677, or with COY H2SO4 as disclosed in Canadian Patent l,022,098 reduces the initial phi The invention is not limited to the specific embodiments described above and any modifications obvious to those skilled in the art are also included therein. The novel method can be used in any system that utilizes induced or forced COY gas flotation but it is particularly 3~3'~
useful in con; unctioll with the Hot Water Process where it can be employed, with advantage, at various stages such as, middlings streams, tailings streams tailings ponds and any combine lions of the above .