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Efficient separation of bitumen in oil sand extraction by using magnetic treated process water
Separation and Purification Technology 47 (2006) 126–134
Efficient separation of bitumen in oil sand extraction by using magnetic treated process water M.C. Amiri ∗ Department of Chemical Engineering, Isfahan University of Technology, Isfahan, Iran Received 22 December 2004; received in revised form 13 June 2005; accepted 27 June 2005
Abstract Extraction is a complex and also a key unit operation for separating and recovery of bitumen in oil sand industry. It has been reported that calcium and magnesium ions cause reduction in bitumen recovery. Experimental evidences showed that hardness ions in water act as a binder between montmorillonite clay particles and bitumen droplets (hetero-coagulation process), resulting in a coating layer of clay particles on the bitumen surface. This layer of clay particles on bitumen droplets causes a barrier for bitumen-air bubble attachment and results in poor bitumen recovery. Therefore, if it is possible to prevent Ca and Mg ions from taking part in hetero-coagulation process then recovery should increase. In this paper, the results of a theoretical and experimental approach to handle the hardness ions effect on bitumen extraction have been reported. For enhancing recovery of bitumen in oil sand extraction operation, for the first time magnetic treated process waters were used. The idea was checked firstly by using a novel technique for investigating the interaction among components of a suspension of bitumen, montmorillonite clay and hardness ions from the interaction measurement of zeta potential distributions. The idea was checked finally by running three sets of extraction experiments in batch scale using process waters. The experimental results show that the bitumen recovery in extraction operation can be enhanced by using magnetic treated process water. © 2005 Elsevier B.V. All rights reserved. Keywords: Bitumen recovery; Magnetic treated; Zeta potential distribution; Extraction operation
1. Introduction Although there are some reports that magnetic field has no significant effect on water treatment [1], most scientific investigations in last decade found positive effects and many of them have shown that magnetic treatment changes the mode of calcium carbonate precipitation in such that circular disc-shaped particles are formed rather than the branching or tree-like particles observed in non-treated water and this fact is the most accepted effect [2–6]. These studies do imply that magnetic water treatment has an effect on the formation of scale. However, various recent investigations show that magnetic field has much more effects than only changing the mode of calcium carbonate crystallization. Higashitani et al. [6–10] performed a systematic study to observe the effect of magnetic field on water treatment. ∗
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They reported a series of quantitative data on the effect of magnetic exposure on the rapid coagulation rate of colloids, the formation of CaCO3 crystal, the zeta potential and diffusivity of colloids in electrolyte solutions, and the emission intensity of fluorescent probes in solution. They also suggested a possible mechanism, “a conformational change of water molecules, ions or hydrated ions adsorbed on the solid surface”, to explain the phenomenon. Holysz et al. [11] studied both the effect of impurity ions (Mg2+ , Fe2+ or SO4 2− ) and time-dependent change of zeta potential and also other parameters of the freshly precipitated calcium carbonate due to magnetic field treatment. They found that both the exposure time and also the time after field removal had effects on zeta potential of freshly precipitated particles. In this study, we employed magnetic field for the first time to enhance the recovery of bitumen during extraction operation in oil sand industry. The study was inspired by some recent articles [12,13] indicating that bitumen recovery in extraction operation is depressed due to hetero-coagulation
M.C. Amiri / Separation and Purification Technology 47 (2006) 126–134
of montmorillonite clay on bitumen surface when the concentration of calcium and magnesium (hardness) ions increase above 40 ppm. Experimental evidence showed that a sharp depression of bitumen recovery was associated with preferential up-take of calcium/magnesium ions by certain clays. It is speculated that the hardness ions, in water up-taken by montmorillonite clay, can act as a binder between montmorillonite clay and bitumen and resulting in a coating layer of clay particles on the bitumen surface. This layer of clay particles on bitumen droplets causes a barrier for bitumen-air bubble attachment and results in a low attachment efficiency and finally poor bitumen recovery.
2. Theoretical analysis Kasongo et al. [12] found that the presence of montmorillonite clay together with high concentration of calcium hinders the bitumen-air attachment process. They experimentally validated the slime coating of montmorillonite clay on bitumen droplets in presence of 1 mM calcium or magnesium. They also suggested a mechanistic hypothesis for the observed inefficient flotation of bitumen by montmorillonite when calcium or magnesium ions were added. Based on their hypothesis, depressed bitumen recovery is caused by hetero-coagulation process of montmorillonite clay on bitumen surface promoted with Ca and Mg ions. Therefore, if it is possible to prevent Ca and Mg from taking part in hetero-coagulation process then recovery should increase. Any probable technique for removing the problem of Ca and Mg must satisfied the following serious constrains: • pH of pulp must be maintained about 8–9 (less than 8, the recovery is low but more than 9, bitumen droplets are unstable); • new impurities should not be introduced; • it must be economically feasible. Based on literature survey, we anticipated that applying a magnetic field might be a successful candidate for handling the problem. The three reported effects of magnetic field on water are: 1. Increase in water solubility [10]. 2. Increase in level of activity of agents due to removing or at least depressing the obstacle ions [9]. 3. Increase in mass transfer diffusivity [10]. At molecular level, one limiting factor that inhibits or diminishes chemical agent activity involves the interaction between the chemical agents and foreign molecules both in the water and in the ore, which reduces the ability of chemical molecules to perform completely. For example, bitumen with negative charge becomes attractively bonded to positively charged calcium and magnesium molecules commonly present in process water. This molecular association decreases the zeta potential of bitumen that finally results
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in depression of bitumen recovery in flotation process. Our new idea for handling the problem of hardness ions in oil sand extraction operation was investigated both electro-kinetically and also running oil sand extraction tests with process waters in batch scale. The idea was checked electro-kinetically by understanding a novel technique for investigating the interactions between bitumen, clay and hardness ions in an aqueous dispersion based on the measurement of zeta potential distributions [14]. For a single component suspension (i.e., clay or bitumen), a single curve of zeta potential distribution is obtained but in the case of a two-component (bitumen and clay mixture) system, the measured zeta potential shows either one or two distribution curves, depending on the chemical interaction in suspension. In the absence of hardness ions, a mixture of bitumen emulsion and montmorillonite clay suspension shows a two distinct zeta potential distribution curve, much similar to the curves measured individually for the bitumen and clay respectively. With the addition of 1 mM calcium/magnesium ion in a mixture of bitumen and montmorillonite, however, only one zeta potential distribution curve is obtained for the suspension. This result suggests theoretically (qualitatively) an interaction among bitumen, clay and hardness ions that causes the slime coating of montmorillonite clay on bitumen droplets. The position of the curve in this case shifts toward the curve either of montmorillonite clay or of bitumen suspension depending on the amount of clay to bitumen ratio. Therefore, if applying a magnetic field to a process water results in a two distinct zeta potential distribution curve for a suspension, similar to the curves measured individually, then we can expect the technique to be successful because it causes to modify adverse effect of calcium/magnesium ion on zeta potential distribution. However, although the electro-kinetic study provides a theoretical evidence for validity of this new idea, the proposed technique was also checked practically in extraction operation for final validation.
3. Principles of the experimental design The experimental works have been done in two stages. In the first stage, the idea was checked electro-kinetically by measuring the zeta potential distribution of bitumen emulsion and montmorillonite clay suspension individually and also mixtures of them in presence of hardness ions. We preferred to check the effect of hardness ions because the effect of calcium ion alone has already been checked easily by controlling the concentration of bicarbonate ion [13]. In the second stage, an able technician was invited to run three sets of extraction experiments in a batch scale. The tests were carried out on March 2 and 3, 9 and 10, and 16 and 17, 2004 using process waters. The operator was blind about tests March 9 and 10, and 16 and 17, 2004 and he was asked to do his best to keep similar conditions for each set of experimental tests. The extraction temperature was chosen 35(±0.5) ◦ C.
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3.1. Materials Ultrahigh purity KCl (>99.999%, Aldrich) was used as supporting electrolyte while deionized water had resistivity of 18.2 M cm, prepared with an Elix 5 followed by a Millipore ultra water purification system. Process water with 54 ppm Ca and 16 ppm Mg was used as a source of hardness ions in zeta potential measurement. A commercial magnetic conditioner (GMX model 400) was used to study the effect of magnetic field. It is composed of four permanent magnets of grade 8, strontium ferrite permanent ceramic. The size of each magnet is 2 in. × 1/2 in. × 1/2 in. with minimum strength of 3850 Gauss. 3.2. Methods Fig. 1 shows the experimental arrangement for the magnetic treatment of water and outline of applications. For measuring zeta potential distributions, the bitumen/water emulsion was prepared using a 550 Sonic dismembrator (Fisher). Coker feed bitumen was provided by Syncrude Canada Ltd. Water was magnetic treated as Fig. 1 shows. In the preparation of bitumen–clay mixture, the prepared bitumen emulsion (with or without magnetic treated water) and clay suspension (with or without magnetic treated water) were mixed to obtain a suspension containing about 0.05 wt.% and conditioned in an ultrasonic bath for about
Fig. 1. Experimental arrangement for the magnetic treatment of water and outline of applications.
20 min. Zeta potential, pH and conductivity measurements were carried out with Zetaphormeter III (SEPHY/CAD). It was equipped with a rectangular electrophoresis cell contacting a pair of Hydrogenated Palladium electrodes, a laser-illuminator, a digital video image capture and viewing system. The computerized operating system allowed an accurate positioning of the camera view field at a stationary layer to achieve accurate measurement of electrophoresis mobility. About 30 ml of sample was used to fill the electrophoresis cell. Through the laser-illuminating and video-viewing system, the movement of 50–100 particles in the stationary layer was traced, three times for each direction by alternating positive and negative electrode potentials. Oil sand flotation tests were carried out in a 1 l Denver flotation cell (adjusted agitator to 1500 rpm and air flow rate at 150 ml/min) by using about 300 g de-frosted D grade (poor) oil sand and 950 ml of process water with total hardness of either 165 or 235 ppm as calcium carbonate. The analysis of oil sand feed was 87.0% solids, 3.0% water and 10.0% bitumen. Before any froth collection and aeration, oil sand slurry conditioned for 5 min. During this time, the initial temperature was recorded. Each extraction test consisted of: 1. Flotation of poor grade feed (liberating and aerating of bitumen droplets to float and form a froth layer). 2. Preparing three froth samples in each run. They were collected from the froth floating at the top of the slurry surface for 3, 2 min (5 min total) and 5 min (10 min total from initial aeration). 3. Froth analysis. Each of three collected froth samples was transferred to the Watman filtration thimble (from Fisher Scientific) and separating into bitumen, solid and water contents. i. Froth analysis was done by refluxing with toluene in modified Dean Stark extractors. Co-distilled water and toluene were condensed into a trap whereby the water was collected in a graduated section while the toluene was allowed to reflux through the extraction thimble. The filtered solids were dried in the vacuum oven for an overnight. The resulting bitumen/solvent solution was centrifuged to separate non-filterable solids. ii. For measuring the bitumen content, 5 ml of aliquot of the centrifuge supernatant was pipetted onto filter paper placed on a watch glass. It was tried to evenly saturate the filter paper by applying a side-to-side motion. Evaporation to remove the solvent was done by hanging the saturated filter paper in the fume hood for 20 min. iii. The mass of the water, solids and bitumen were determined gravimetrically. It was reported that bitumen flotation kinetics obtained with this set up and analysis procedures are highly reproducible [14]. Table 1 shows a typical log sheet for an extrac-
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Table 1 Log sheet of extraction test March 2, 2004 Date Group # Oil sand grade Additive Wt. of oil sand (g) Initial temperature
March 2, 2004 – D (poor) Non-treated 300.98 35 ◦ C
Dean stark extraction Time (min) Initial: Thimble + Jar + 2Kimwipes (A) Final: Thimble + Jar + 2Kimwipes + froth (B) Extracted Thimble + Jar + 2Kimwipes (C) Total collected froth (B–A) Total solids in the froth (C–A) Initial: water bottle Final: water bottle Water in froth Initial: centrifuge tube (empty) Final: centrifuge tube + solids Suspended solids in 50 ml Initial: filter paper Final: filter paper + bitumen Bitumen in 5 ml Total bitumen in each step (250 ml) Cumulative recovery (%)
3 157.5802 257.4890 174.5253 99.9088 16.9451 22.0825 94.2703 91.8780 14.4464 14.5844 0.1380 1.1621 1.3555 0.1934 9.6700 32.13
Final temperature (◦ C) pH of tailings
35.5 8.4
tion test. Same procedure and similar log sheets were prepared for all tests. In each run, most desired findings in each stage are: total collected froth, total solids in the froth, water in froth, suspended solids, total bitumen in each step, cumulative recovery (%). Total collected froth was calculated by subtracting initial weight of (Thimble + Jar + 2Kimwipes) from final weight of (Thimble + Jar + 2Kimwipes + Froth). Kimwipes were paper tissues that used for cleaning. It should be noted that froth was composed of bitumen, solids, water and air. Total solids in the froth was calculated by subtracting initial weight of (Thimble + Jar + 2Kimwipes) from the weight of (extracted Thimble + Jar + 2Kimwipes). Weight of suspended solids was calculated by weighing the centrifuge tubes. Weight of bitumen in each step was calculated by weighing the filter paper. Cumulative recovery (%) was calculated by the following equation: Cumulative recovery (%) =
total weight of collected bitumen weight of bitumen in initial oil sand
Mass balance for each run showed that the accuracy of measurement was high. To check mass balance, the calculated total weights of bitumen, solids and water were compared to weight of froth. It was found that the calculated total weights
5 157.3768 179.4390 161.6666 22.0622 4.2898 22.4613 37.3666 14.9053 14.5251 14.6223 0.0972 1.1571 1.1976 0.0405 2.0250 38.85
10 157.3338 87.0900 161.9384 29.6662 4.6046 22.1920 44.1460 21.9540 14.5069 14.6196 0.1127 1.1506 1.1991 0.0485 2.4250 46.91
of bitumen, solids and water was not less than 97% froth weight when weight of air was ignored. Concentrations of hardness ions were measured by atomic absorption after centrifugation and reported in Table 3.
4. Results and discussion 4.1. Zeta potential distribution Fig. 2 (Right) shows the zeta potential distribution for montmorillonite clay distribution alone. It is a single curve and the zeta potential of clay particles are negative values in the range of −13 to −22 mV. But bitumen particles have negative zeta potential values in the range of −28 to −45 mV as Fig. 2 (left) shows. The measured zeta potential distribution of a mixture of bitumen emulsion and clay suspension in non-treated water has been shown in Fig. 3. The total hardness concentration was 235 ppm as calcium carbonate at pH 7.9 and T = 21.7 ◦ C. However, the zeta for the mixture exhibits a single distribution but different from of the individual components. The curve became more distributed and the zeta potential of particles is in the range of −13 to −37 mV. This broad distribution of zeta potential of particles indicates heterogeneous nature of mixture and as the minimum value (−37 mV) in the mixture is less than of bitumen droplets (−45 mV) it suggests that zeta potential of bitumen droplets have been depressed partially in this conditions.
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Fig. 2. Zeta potential distribution at pH 7.9 and T = 21.3 ◦ C for (left): bitumen emulsion; (right): montmorillonite clay suspension.
As we already discussed in theoretical section, the measured zeta potential shows either single or two distinct distributions curves, depending on the chemical interaction in the suspension. Zeta potential in Fig. 3 is a single distribution due to interaction in suspension. However, experimental results showed that chemical interaction in bitumen and clay suspension was modified if hard water had already been treated by magnetic field as Fig. 4 shows. There are two separate zeta potential distribution curves in Fig. 4 due to using magnetic treated process water. In this case, a slight shift of zeta distributions toward each other has occurred. This is a known effect due to hydrodynamic interaction of moving particles with different electrophoretic mobility in dispersion. This behavior is called electro-kinetic retardation (reduction in the speed of fast moving bitumen droplets) and electro-kinetic enhancement (increase in the speed of slow moving clay particles). These experimental results led us to accept the effect of magnetic treatment on hardness ions in process water and
encouraged us to do further study by carrying out some systematic bitumen extraction tests that are normally complex and also very tedious trials. 4.2. Bitumen extraction tests Table 1 shows the data log sheet for the extraction test March 2, 2004 that was a blank test for the next run, test March 3, 2004, full detailed outlined in Table 2. Each log sheet includes data on feed, experimental conditions and results. The measured experimental data (but not calculated data) are shown in bold print in each table. Similar log sheets have been prepared for all six tests. Concentration of Ca and Mg ions in various process waters and tailing samples in tests March 2 and 3, and 9 and 10 were recorded in Table 3. It is important to note that concentrations of hardness ions in tailing decreased sharply in untreated run because of consuming in binding of clay particles to bitumen droplets
Fig. 3. Zeta potential distribution for the mixture of bitumen emulsion and montmorillonite clay suspension in water with total hardness of 235 ppm at pH 7.9 and T = 21.7 ◦ C. There is a single distribution due to chemical interaction of hardness ions in suspension.
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Fig. 4. Zeta potential distribution for the mixture of bitumen emulsion and montmorillonite clay suspension in magnetic treated water with total hardness of 235 ppm at pH 7.8 and T = 21.5 ◦ C. There are two distinct distributions due to depressing of chemical interaction in suspension as a result of magnetic treatment.
Table 2 Log sheet of extraction test March 3, 2004 Date Group # Oil sand grade Additive Wt. of oil sand (g) Initial temperature (◦ C)
March 3, 2004 – D (poor) Magnetic treated 300.35 34.6
Dean stark extraction Time (min) Initial: Thimble + Jar + 2Kimwipes (A) Final: Thimble + Jar + 2Kimwipes + froth (B) Extracted Thimble + Jar + 2Kimwipes (C) Total collected froth (B–A) Total solids in the froth (C–A) Initial: water bottle Final: water bottle Water in froth Initial: centrifuge tube (empty) Final: centrifuge tube + solids Suspended solids in 50 ml Initial: filter paper Final: filter paper + bitumen Bitumen in 5 ml Total bitumen in each step (250 ml) Cumulative recovery (%)
3 157.0212 261.4550 175.6302 104.4338 18.609 22.4116 96.5426 74.1310 14.2345 14.3434 0.1089 1.1614 1.3596 0.1982 9.91 32.995
Final temperature (◦ C) pH of tailings
35 8.6
5 157.4537 198.5889 164.2553 41.1352 6.8016 22.5573 52.9250 29.8677 14.7901 14.929 0.1389 1.1467 1.2220 0.0753 3.756 45.53
10 157.6323 233.6836 169.5974 76.0513 11.9651 22.6675 78.7487 56.0812 14.6956 14.8089 0.1133 1.1494 1.2583 0.1089 5.445 63.66
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Table 3 Concentrations of hardness ions (ppm) in various samples in tests March 2 and 3, and 9 and 10 Sample
Process water
Tailing dispersion
Hardness
Ca
Mg
Ca
Mg
March 2 (untreated) March 3 (treated) March 9 (treated) March 10 (treated)
54.95 54.95 54.75 52.55
16.04 16.04 16.70 16.32
8.4 20.45 25.55 26.55
10.75 15.35 15.01 15.12
(hetero-coagulation process). This result confirms Fig. 3 where it shows zeta potential is single distribution due to chemical interaction of hardness ions in suspension. Magnesium ion concentration remained essentially constant during extraction operation in magnetic treated sample because of no tendency for it to take part in hetero-coagulation process. Calcium ion concentration in magnetic treated sample was decreased in tailing dispersion but not for taking part in hetero-coagulation process. The main reason for the decrease in calcium concentration in tailing is that it was consumed in calcium carbonate precipitation because in the operating pH 8.6 there is no chance for magnesium precipitation. Reduction in calcium ion concentration after magnetic treatment was also reported by other researchers [15]. This finding supports proposed theory of destabilization of fine nonmagnetic particle [16] as one of the possible mechanism of scale control. Lipus et al., used electrical double layer theory for the theoretical model of surface neutralization due to ion shifts from the bulk of the solution toward the particle surfaces to show the theoretical possibility of accelerated coagulation of scale-forming particles during and after MF treatment [16]. The results show that hardness ions, after magnetic treatment, have no tendency to take part in binding of clay particles to bitumen droplets (hetero-coagulation process) and therefore, the bitumen recovery improves. This result was confirmed in tests March 9 and 10 as Table 3 shows. Note that in both tests, magnetic treated process waters were used. Magnesium ion concentration here remained essentially constant. The concentration of calcium ion in test March 9 (25.55 ppm) is higher than of March 3 (20.45 ppm). This result confirms that there is a tendency for calcium ion to form calcium carbonate rather than to take part in binding process of clay on bitumen droplets. The main reason for the difference in calcium concentration of tests March 9, and of test March 3 is pH of tailing. As it is known, solubility of calcium carbonates at pH 7.5 is much more than of at pH 8.6, hence, the concentration of calcium ion in test March 9 (lower pH) is higher than of test March 3. Therefore, according on results of these three experimental tests, Ca and Mg ions have least tendency to take part in hetero-coagulation process after magnetic treatment.
pH Tailing
8.4 8.6 7.5 7.9
flotation process. It is known that higher recovery of bitumen and lower solid content in collected froth are both desirable in bitumen extraction. 4.3.1. Improvement in recovery Fig. 5 shows the cumulative recovery of bitumen in extraction operation in various tests with magnetic treated () and untreated () process waters. It illustrates that final accumulated recovery of treated sample is always higher than of untreated samples. However, this rule is not always correct for the froth samples colleted at 3 min (initial recovery). The trend in Fig. 5 indicates that enhancing the bitumen recovery due to magnetic treatment will be improved by increasing the flotation time. Behavior of cumulative recovery for run March 9 and 10 () in Fig. 5, both magnetic treated, shows an interesting finding of this work. It illustrates that effect of magnetic treatment of process water on bitumen extraction seems reproducible. These two tests were carried out in the same condition of using magnetic treated process waters although all conditions in these two tests were not the same exactly because of difficulty in extraction experiments. It suggests that a unique phenomenon must be occurred during using magnetic treated process water as recovery curves seem the same only with a fixed shift in y (recovery) axis. Although in both tests March 9 and 10 magnetic treated process waters were used, the initial temperature of the former was 35.6 ◦ C but the initial temperature of latter was 35 ◦ C in addition that process waters were not the same. At least a 10% difference was occurred for higher initial temperature, difference in total hardness of process water and pH.
4.3. Performance of flotation process Different approaches can be made to evaluate the effect of using magnetic treated process water on performance of
Fig. 5. Cumulative recovery of bitumen in extraction operation in various tests with magnetic treated (squares) and non-treated (triangles) process water.
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Fig. 6. Bitumen recovery vs. concentration of solid in collected froth for run March 3 (() magnetic treated) and March 2 (() non-treated).
Fig. 9. A typical change of mean grade of collected froth vs. time in bitumen extraction tests with magnetic treated () and non-treated () process water.
4.3.3. Mean grade of froth The performance of flotation process can also be evaluated [17] by defining a mean grade of froth (G): G= Fig. 7. Bitumen recovery vs. concentration of solid in collected froth for run March 17 (() magnetic treated) and March 16 (() non-treated).
4.3.2. Quality of collected froth Figs. 6–8 show the bitumen recovery versus concentration of solids in collected froth for various runs. These figures confirm that using magnetic treated water in flotation process results in better quality of collected froth (higher recovery with lower solid content). It is interesting to note that the slope of trend line always increased with using magnetic treated process water for all tests. The slope of trend line for treated samples is more than 4 but for non-treated samples is always less than 4.
f −F 1−F
where f and F are the mass fraction of bitumen in froth and feed, respectively. When G equals zero, no separation is taking place, hence, the value of G provides a qualitative estimation of the froth quality in extraction operation. Note that f and F are mass fractions in two different samples. F is equal to ratio of bitumen mass in feed to the summation of feed mass and mass of 950 ml of process water. F was 0.024 for all tests because we always used a poor oil sand in all tests, a fixed mass of feed about 300.5 ± 0.5 g and a fixed volume of water in each test. Fig. 9 shows a typical change of mean grade of froth versus time for both treated and non-treated samples. It shows that the quality of collected froth decays with time. This trend of decaying in froth grade was observed in all tests as can be expected.
5. Conclusions Bitumen recovery from poor oil sand is highly depending on the performance of extraction operation. Bitumen recovery is depressed when the concentrations of hardness ions are above 40 ppm. In this work, it was shown theoretically and experimentally that magnetic treatment of process water can result in handling the problem of hardness ions in bitumen extraction. It was found from this study that:
Fig. 8. Bitumen recovery vs. concentration of solid in collected froth for run March 9 and10 both magnetic treated.
1. The applied permanent magnetic force was sufficient to overcome whatever attraction might exist among the bitumen droplets, montmorillonite clay and the hardness ions.
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2. Zeta potential distribution of a suspension of montmorillonite clay, bitumen and hardness ions is modified by using magnetic field. 3. Ca and Mg ions have least tendency to take part in heterocoagulation process after magnetic treatment. 4. Magnetic treatment of process water is a promising physical technique to enhance recovery of bitumen during extraction operation. 5. Experimental results showed that magnetic treatment of process water has a unique phenomenon that is reproducible. 6. Magnetic treatment of process water always improves final performance of flotation process in bitumen extraction operation in every condition as Fig. 5 shows. Finally, it is important to note that this approach to oil sand industry should be followed by more detailed experimental and theoretical analysis by other independent investigators and also to extend it to include other aspects of possible applications such as water conservation, waste water minimization and more selective separation operations.
Department of Chemical and Materials Engineering, University of Alberta, Canada. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Acknowledgement The NSERC Chair Programme on Oil Sands Research, Profs. Masliyah and Xu are gratefully acknowledged for providing experimental facility during my sabbatical leave in
[14] [15] [16] [17]
J.S. Baker, S.J. Judd, Water Res. 30 (1996) 260. K.J. Kronenberg, IEEE Trans. Magn. 5 (1985) 2061. R.A. Barrett, S.A. Parsons, Water Res. 32 (1988) 612. A. Szkatula, M. Balanda, M. Kopec, Eur. Phys. J. AP 18 (2002) 41. J.M.D. Coey, S. Cass, J. Magn. Magn. Mater. 209 (2000) 74. K. Higashitani, A. Kage, S. Katamura, K. Imai, S. Hatade, J. Colloid Interface Sci. 152 (1992) 125. K. Higashitani, A. Kage, S. Katamura, K. Imai, S. Hatade, J. Colloid Interface Sci. 156 (1993) 90. K. Higashitani, H. Iseri, K. Okuhara, A. Kage, S. Hatade, J. Colloid Interface Sci. 172 (1995) 383. K. Higashitani, J. Oshitani, N. Ohmura, Colloids Surf. A 109 (1996) 167. K. Higashitani, J. Oshitani, Process safety and environmental protection, Trans. Ichem E 75-B 75 (1997) 115. L. Holysz, E. Chibowski, A. Szczes, Water Res. 37 (2003) 3360. T. Kasongo, Z. Zhou, Z. Xu, J. Masliyah, Can. J. Chem. Eng. 78 (2000) 674. J. Liu, Z. Zhou, Z. Xu, J. Masliyah, J. Colloid Interface Sci. 252 (2002) 418. J. Liu, Z. Zhou, Z. Xu, Ind. Eng. Chem. Res. 41 (2002) 52. C. Fan, Y.I. Cho, Heat Mass Transfer 24 (1997) 757. L.C. Lipus, J. Krope, L. Crepinsek, J. Colloid Interface Sci. 236 (2001) 60. M.C. Amiri, K.T. Valsaraj, Sep. Purif. Technol. 35 (2004) 161.
Efficient separation of bitumen in oil sand extraction by using magnetic treated process water M.C. Amiri ∗ Department of Chemical Engineering, Isfahan University of Technology, Isfahan, Iran Received 22 December 2004; received in revised form 13 June 2005; accepted 27 June 2005
Abstract Extraction is a complex and also a key unit operation for separating and recovery of bitumen in oil sand industry. It has been reported that calcium and magnesium ions cause reduction in bitumen recovery. Experimental evidences showed that hardness ions in water act as a binder between montmorillonite clay particles and bitumen droplets (hetero-coagulation process), resulting in a coating layer of clay particles on the bitumen surface. This layer of clay particles on bitumen droplets causes a barrier for bitumen-air bubble attachment and results in poor bitumen recovery. Therefore, if it is possible to prevent Ca and Mg ions from taking part in hetero-coagulation process then recovery should increase. In this paper, the results of a theoretical and experimental approach to handle the hardness ions effect on bitumen extraction have been reported. For enhancing recovery of bitumen in oil sand extraction operation, for the first time magnetic treated process waters were used. The idea was checked firstly by using a novel technique for investigating the interaction among components of a suspension of bitumen, montmorillonite clay and hardness ions from the interaction measurement of zeta potential distributions. The idea was checked finally by running three sets of extraction experiments in batch scale using process waters. The experimental results show that the bitumen recovery in extraction operation can be enhanced by using magnetic treated process water. © 2005 Elsevier B.V. All rights reserved. Keywords: Bitumen recovery; Magnetic treated; Zeta potential distribution; Extraction operation
1. Introduction Although there are some reports that magnetic field has no significant effect on water treatment [1], most scientific investigations in last decade found positive effects and many of them have shown that magnetic treatment changes the mode of calcium carbonate precipitation in such that circular disc-shaped particles are formed rather than the branching or tree-like particles observed in non-treated water and this fact is the most accepted effect [2–6]. These studies do imply that magnetic water treatment has an effect on the formation of scale. However, various recent investigations show that magnetic field has much more effects than only changing the mode of calcium carbonate crystallization. Higashitani et al. [6–10] performed a systematic study to observe the effect of magnetic field on water treatment. ∗
Tel.: +98 311 391 2675; fax: +98 311 391 2677. E-mail address: [email protected].
1383-5866/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2005.06.016
They reported a series of quantitative data on the effect of magnetic exposure on the rapid coagulation rate of colloids, the formation of CaCO3 crystal, the zeta potential and diffusivity of colloids in electrolyte solutions, and the emission intensity of fluorescent probes in solution. They also suggested a possible mechanism, “a conformational change of water molecules, ions or hydrated ions adsorbed on the solid surface”, to explain the phenomenon. Holysz et al. [11] studied both the effect of impurity ions (Mg2+ , Fe2+ or SO4 2− ) and time-dependent change of zeta potential and also other parameters of the freshly precipitated calcium carbonate due to magnetic field treatment. They found that both the exposure time and also the time after field removal had effects on zeta potential of freshly precipitated particles. In this study, we employed magnetic field for the first time to enhance the recovery of bitumen during extraction operation in oil sand industry. The study was inspired by some recent articles [12,13] indicating that bitumen recovery in extraction operation is depressed due to hetero-coagulation
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of montmorillonite clay on bitumen surface when the concentration of calcium and magnesium (hardness) ions increase above 40 ppm. Experimental evidence showed that a sharp depression of bitumen recovery was associated with preferential up-take of calcium/magnesium ions by certain clays. It is speculated that the hardness ions, in water up-taken by montmorillonite clay, can act as a binder between montmorillonite clay and bitumen and resulting in a coating layer of clay particles on the bitumen surface. This layer of clay particles on bitumen droplets causes a barrier for bitumen-air bubble attachment and results in a low attachment efficiency and finally poor bitumen recovery.
2. Theoretical analysis Kasongo et al. [12] found that the presence of montmorillonite clay together with high concentration of calcium hinders the bitumen-air attachment process. They experimentally validated the slime coating of montmorillonite clay on bitumen droplets in presence of 1 mM calcium or magnesium. They also suggested a mechanistic hypothesis for the observed inefficient flotation of bitumen by montmorillonite when calcium or magnesium ions were added. Based on their hypothesis, depressed bitumen recovery is caused by hetero-coagulation process of montmorillonite clay on bitumen surface promoted with Ca and Mg ions. Therefore, if it is possible to prevent Ca and Mg from taking part in hetero-coagulation process then recovery should increase. Any probable technique for removing the problem of Ca and Mg must satisfied the following serious constrains: • pH of pulp must be maintained about 8–9 (less than 8, the recovery is low but more than 9, bitumen droplets are unstable); • new impurities should not be introduced; • it must be economically feasible. Based on literature survey, we anticipated that applying a magnetic field might be a successful candidate for handling the problem. The three reported effects of magnetic field on water are: 1. Increase in water solubility [10]. 2. Increase in level of activity of agents due to removing or at least depressing the obstacle ions [9]. 3. Increase in mass transfer diffusivity [10]. At molecular level, one limiting factor that inhibits or diminishes chemical agent activity involves the interaction between the chemical agents and foreign molecules both in the water and in the ore, which reduces the ability of chemical molecules to perform completely. For example, bitumen with negative charge becomes attractively bonded to positively charged calcium and magnesium molecules commonly present in process water. This molecular association decreases the zeta potential of bitumen that finally results
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in depression of bitumen recovery in flotation process. Our new idea for handling the problem of hardness ions in oil sand extraction operation was investigated both electro-kinetically and also running oil sand extraction tests with process waters in batch scale. The idea was checked electro-kinetically by understanding a novel technique for investigating the interactions between bitumen, clay and hardness ions in an aqueous dispersion based on the measurement of zeta potential distributions [14]. For a single component suspension (i.e., clay or bitumen), a single curve of zeta potential distribution is obtained but in the case of a two-component (bitumen and clay mixture) system, the measured zeta potential shows either one or two distribution curves, depending on the chemical interaction in suspension. In the absence of hardness ions, a mixture of bitumen emulsion and montmorillonite clay suspension shows a two distinct zeta potential distribution curve, much similar to the curves measured individually for the bitumen and clay respectively. With the addition of 1 mM calcium/magnesium ion in a mixture of bitumen and montmorillonite, however, only one zeta potential distribution curve is obtained for the suspension. This result suggests theoretically (qualitatively) an interaction among bitumen, clay and hardness ions that causes the slime coating of montmorillonite clay on bitumen droplets. The position of the curve in this case shifts toward the curve either of montmorillonite clay or of bitumen suspension depending on the amount of clay to bitumen ratio. Therefore, if applying a magnetic field to a process water results in a two distinct zeta potential distribution curve for a suspension, similar to the curves measured individually, then we can expect the technique to be successful because it causes to modify adverse effect of calcium/magnesium ion on zeta potential distribution. However, although the electro-kinetic study provides a theoretical evidence for validity of this new idea, the proposed technique was also checked practically in extraction operation for final validation.
3. Principles of the experimental design The experimental works have been done in two stages. In the first stage, the idea was checked electro-kinetically by measuring the zeta potential distribution of bitumen emulsion and montmorillonite clay suspension individually and also mixtures of them in presence of hardness ions. We preferred to check the effect of hardness ions because the effect of calcium ion alone has already been checked easily by controlling the concentration of bicarbonate ion [13]. In the second stage, an able technician was invited to run three sets of extraction experiments in a batch scale. The tests were carried out on March 2 and 3, 9 and 10, and 16 and 17, 2004 using process waters. The operator was blind about tests March 9 and 10, and 16 and 17, 2004 and he was asked to do his best to keep similar conditions for each set of experimental tests. The extraction temperature was chosen 35(±0.5) ◦ C.
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3.1. Materials Ultrahigh purity KCl (>99.999%, Aldrich) was used as supporting electrolyte while deionized water had resistivity of 18.2 M cm, prepared with an Elix 5 followed by a Millipore ultra water purification system. Process water with 54 ppm Ca and 16 ppm Mg was used as a source of hardness ions in zeta potential measurement. A commercial magnetic conditioner (GMX model 400) was used to study the effect of magnetic field. It is composed of four permanent magnets of grade 8, strontium ferrite permanent ceramic. The size of each magnet is 2 in. × 1/2 in. × 1/2 in. with minimum strength of 3850 Gauss. 3.2. Methods Fig. 1 shows the experimental arrangement for the magnetic treatment of water and outline of applications. For measuring zeta potential distributions, the bitumen/water emulsion was prepared using a 550 Sonic dismembrator (Fisher). Coker feed bitumen was provided by Syncrude Canada Ltd. Water was magnetic treated as Fig. 1 shows. In the preparation of bitumen–clay mixture, the prepared bitumen emulsion (with or without magnetic treated water) and clay suspension (with or without magnetic treated water) were mixed to obtain a suspension containing about 0.05 wt.% and conditioned in an ultrasonic bath for about
Fig. 1. Experimental arrangement for the magnetic treatment of water and outline of applications.
20 min. Zeta potential, pH and conductivity measurements were carried out with Zetaphormeter III (SEPHY/CAD). It was equipped with a rectangular electrophoresis cell contacting a pair of Hydrogenated Palladium electrodes, a laser-illuminator, a digital video image capture and viewing system. The computerized operating system allowed an accurate positioning of the camera view field at a stationary layer to achieve accurate measurement of electrophoresis mobility. About 30 ml of sample was used to fill the electrophoresis cell. Through the laser-illuminating and video-viewing system, the movement of 50–100 particles in the stationary layer was traced, three times for each direction by alternating positive and negative electrode potentials. Oil sand flotation tests were carried out in a 1 l Denver flotation cell (adjusted agitator to 1500 rpm and air flow rate at 150 ml/min) by using about 300 g de-frosted D grade (poor) oil sand and 950 ml of process water with total hardness of either 165 or 235 ppm as calcium carbonate. The analysis of oil sand feed was 87.0% solids, 3.0% water and 10.0% bitumen. Before any froth collection and aeration, oil sand slurry conditioned for 5 min. During this time, the initial temperature was recorded. Each extraction test consisted of: 1. Flotation of poor grade feed (liberating and aerating of bitumen droplets to float and form a froth layer). 2. Preparing three froth samples in each run. They were collected from the froth floating at the top of the slurry surface for 3, 2 min (5 min total) and 5 min (10 min total from initial aeration). 3. Froth analysis. Each of three collected froth samples was transferred to the Watman filtration thimble (from Fisher Scientific) and separating into bitumen, solid and water contents. i. Froth analysis was done by refluxing with toluene in modified Dean Stark extractors. Co-distilled water and toluene were condensed into a trap whereby the water was collected in a graduated section while the toluene was allowed to reflux through the extraction thimble. The filtered solids were dried in the vacuum oven for an overnight. The resulting bitumen/solvent solution was centrifuged to separate non-filterable solids. ii. For measuring the bitumen content, 5 ml of aliquot of the centrifuge supernatant was pipetted onto filter paper placed on a watch glass. It was tried to evenly saturate the filter paper by applying a side-to-side motion. Evaporation to remove the solvent was done by hanging the saturated filter paper in the fume hood for 20 min. iii. The mass of the water, solids and bitumen were determined gravimetrically. It was reported that bitumen flotation kinetics obtained with this set up and analysis procedures are highly reproducible [14]. Table 1 shows a typical log sheet for an extrac-
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Table 1 Log sheet of extraction test March 2, 2004 Date Group # Oil sand grade Additive Wt. of oil sand (g) Initial temperature
March 2, 2004 – D (poor) Non-treated 300.98 35 ◦ C
Dean stark extraction Time (min) Initial: Thimble + Jar + 2Kimwipes (A) Final: Thimble + Jar + 2Kimwipes + froth (B) Extracted Thimble + Jar + 2Kimwipes (C) Total collected froth (B–A) Total solids in the froth (C–A) Initial: water bottle Final: water bottle Water in froth Initial: centrifuge tube (empty) Final: centrifuge tube + solids Suspended solids in 50 ml Initial: filter paper Final: filter paper + bitumen Bitumen in 5 ml Total bitumen in each step (250 ml) Cumulative recovery (%)
3 157.5802 257.4890 174.5253 99.9088 16.9451 22.0825 94.2703 91.8780 14.4464 14.5844 0.1380 1.1621 1.3555 0.1934 9.6700 32.13
Final temperature (◦ C) pH of tailings
35.5 8.4
tion test. Same procedure and similar log sheets were prepared for all tests. In each run, most desired findings in each stage are: total collected froth, total solids in the froth, water in froth, suspended solids, total bitumen in each step, cumulative recovery (%). Total collected froth was calculated by subtracting initial weight of (Thimble + Jar + 2Kimwipes) from final weight of (Thimble + Jar + 2Kimwipes + Froth). Kimwipes were paper tissues that used for cleaning. It should be noted that froth was composed of bitumen, solids, water and air. Total solids in the froth was calculated by subtracting initial weight of (Thimble + Jar + 2Kimwipes) from the weight of (extracted Thimble + Jar + 2Kimwipes). Weight of suspended solids was calculated by weighing the centrifuge tubes. Weight of bitumen in each step was calculated by weighing the filter paper. Cumulative recovery (%) was calculated by the following equation: Cumulative recovery (%) =
total weight of collected bitumen weight of bitumen in initial oil sand
Mass balance for each run showed that the accuracy of measurement was high. To check mass balance, the calculated total weights of bitumen, solids and water were compared to weight of froth. It was found that the calculated total weights
5 157.3768 179.4390 161.6666 22.0622 4.2898 22.4613 37.3666 14.9053 14.5251 14.6223 0.0972 1.1571 1.1976 0.0405 2.0250 38.85
10 157.3338 87.0900 161.9384 29.6662 4.6046 22.1920 44.1460 21.9540 14.5069 14.6196 0.1127 1.1506 1.1991 0.0485 2.4250 46.91
of bitumen, solids and water was not less than 97% froth weight when weight of air was ignored. Concentrations of hardness ions were measured by atomic absorption after centrifugation and reported in Table 3.
4. Results and discussion 4.1. Zeta potential distribution Fig. 2 (Right) shows the zeta potential distribution for montmorillonite clay distribution alone. It is a single curve and the zeta potential of clay particles are negative values in the range of −13 to −22 mV. But bitumen particles have negative zeta potential values in the range of −28 to −45 mV as Fig. 2 (left) shows. The measured zeta potential distribution of a mixture of bitumen emulsion and clay suspension in non-treated water has been shown in Fig. 3. The total hardness concentration was 235 ppm as calcium carbonate at pH 7.9 and T = 21.7 ◦ C. However, the zeta for the mixture exhibits a single distribution but different from of the individual components. The curve became more distributed and the zeta potential of particles is in the range of −13 to −37 mV. This broad distribution of zeta potential of particles indicates heterogeneous nature of mixture and as the minimum value (−37 mV) in the mixture is less than of bitumen droplets (−45 mV) it suggests that zeta potential of bitumen droplets have been depressed partially in this conditions.
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Fig. 2. Zeta potential distribution at pH 7.9 and T = 21.3 ◦ C for (left): bitumen emulsion; (right): montmorillonite clay suspension.
As we already discussed in theoretical section, the measured zeta potential shows either single or two distinct distributions curves, depending on the chemical interaction in the suspension. Zeta potential in Fig. 3 is a single distribution due to interaction in suspension. However, experimental results showed that chemical interaction in bitumen and clay suspension was modified if hard water had already been treated by magnetic field as Fig. 4 shows. There are two separate zeta potential distribution curves in Fig. 4 due to using magnetic treated process water. In this case, a slight shift of zeta distributions toward each other has occurred. This is a known effect due to hydrodynamic interaction of moving particles with different electrophoretic mobility in dispersion. This behavior is called electro-kinetic retardation (reduction in the speed of fast moving bitumen droplets) and electro-kinetic enhancement (increase in the speed of slow moving clay particles). These experimental results led us to accept the effect of magnetic treatment on hardness ions in process water and
encouraged us to do further study by carrying out some systematic bitumen extraction tests that are normally complex and also very tedious trials. 4.2. Bitumen extraction tests Table 1 shows the data log sheet for the extraction test March 2, 2004 that was a blank test for the next run, test March 3, 2004, full detailed outlined in Table 2. Each log sheet includes data on feed, experimental conditions and results. The measured experimental data (but not calculated data) are shown in bold print in each table. Similar log sheets have been prepared for all six tests. Concentration of Ca and Mg ions in various process waters and tailing samples in tests March 2 and 3, and 9 and 10 were recorded in Table 3. It is important to note that concentrations of hardness ions in tailing decreased sharply in untreated run because of consuming in binding of clay particles to bitumen droplets
Fig. 3. Zeta potential distribution for the mixture of bitumen emulsion and montmorillonite clay suspension in water with total hardness of 235 ppm at pH 7.9 and T = 21.7 ◦ C. There is a single distribution due to chemical interaction of hardness ions in suspension.
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Fig. 4. Zeta potential distribution for the mixture of bitumen emulsion and montmorillonite clay suspension in magnetic treated water with total hardness of 235 ppm at pH 7.8 and T = 21.5 ◦ C. There are two distinct distributions due to depressing of chemical interaction in suspension as a result of magnetic treatment.
Table 2 Log sheet of extraction test March 3, 2004 Date Group # Oil sand grade Additive Wt. of oil sand (g) Initial temperature (◦ C)
March 3, 2004 – D (poor) Magnetic treated 300.35 34.6
Dean stark extraction Time (min) Initial: Thimble + Jar + 2Kimwipes (A) Final: Thimble + Jar + 2Kimwipes + froth (B) Extracted Thimble + Jar + 2Kimwipes (C) Total collected froth (B–A) Total solids in the froth (C–A) Initial: water bottle Final: water bottle Water in froth Initial: centrifuge tube (empty) Final: centrifuge tube + solids Suspended solids in 50 ml Initial: filter paper Final: filter paper + bitumen Bitumen in 5 ml Total bitumen in each step (250 ml) Cumulative recovery (%)
3 157.0212 261.4550 175.6302 104.4338 18.609 22.4116 96.5426 74.1310 14.2345 14.3434 0.1089 1.1614 1.3596 0.1982 9.91 32.995
Final temperature (◦ C) pH of tailings
35 8.6
5 157.4537 198.5889 164.2553 41.1352 6.8016 22.5573 52.9250 29.8677 14.7901 14.929 0.1389 1.1467 1.2220 0.0753 3.756 45.53
10 157.6323 233.6836 169.5974 76.0513 11.9651 22.6675 78.7487 56.0812 14.6956 14.8089 0.1133 1.1494 1.2583 0.1089 5.445 63.66
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Table 3 Concentrations of hardness ions (ppm) in various samples in tests March 2 and 3, and 9 and 10 Sample
Process water
Tailing dispersion
Hardness
Ca
Mg
Ca
Mg
March 2 (untreated) March 3 (treated) March 9 (treated) March 10 (treated)
54.95 54.95 54.75 52.55
16.04 16.04 16.70 16.32
8.4 20.45 25.55 26.55
10.75 15.35 15.01 15.12
(hetero-coagulation process). This result confirms Fig. 3 where it shows zeta potential is single distribution due to chemical interaction of hardness ions in suspension. Magnesium ion concentration remained essentially constant during extraction operation in magnetic treated sample because of no tendency for it to take part in hetero-coagulation process. Calcium ion concentration in magnetic treated sample was decreased in tailing dispersion but not for taking part in hetero-coagulation process. The main reason for the decrease in calcium concentration in tailing is that it was consumed in calcium carbonate precipitation because in the operating pH 8.6 there is no chance for magnesium precipitation. Reduction in calcium ion concentration after magnetic treatment was also reported by other researchers [15]. This finding supports proposed theory of destabilization of fine nonmagnetic particle [16] as one of the possible mechanism of scale control. Lipus et al., used electrical double layer theory for the theoretical model of surface neutralization due to ion shifts from the bulk of the solution toward the particle surfaces to show the theoretical possibility of accelerated coagulation of scale-forming particles during and after MF treatment [16]. The results show that hardness ions, after magnetic treatment, have no tendency to take part in binding of clay particles to bitumen droplets (hetero-coagulation process) and therefore, the bitumen recovery improves. This result was confirmed in tests March 9 and 10 as Table 3 shows. Note that in both tests, magnetic treated process waters were used. Magnesium ion concentration here remained essentially constant. The concentration of calcium ion in test March 9 (25.55 ppm) is higher than of March 3 (20.45 ppm). This result confirms that there is a tendency for calcium ion to form calcium carbonate rather than to take part in binding process of clay on bitumen droplets. The main reason for the difference in calcium concentration of tests March 9, and of test March 3 is pH of tailing. As it is known, solubility of calcium carbonates at pH 7.5 is much more than of at pH 8.6, hence, the concentration of calcium ion in test March 9 (lower pH) is higher than of test March 3. Therefore, according on results of these three experimental tests, Ca and Mg ions have least tendency to take part in hetero-coagulation process after magnetic treatment.
pH Tailing
8.4 8.6 7.5 7.9
flotation process. It is known that higher recovery of bitumen and lower solid content in collected froth are both desirable in bitumen extraction. 4.3.1. Improvement in recovery Fig. 5 shows the cumulative recovery of bitumen in extraction operation in various tests with magnetic treated () and untreated () process waters. It illustrates that final accumulated recovery of treated sample is always higher than of untreated samples. However, this rule is not always correct for the froth samples colleted at 3 min (initial recovery). The trend in Fig. 5 indicates that enhancing the bitumen recovery due to magnetic treatment will be improved by increasing the flotation time. Behavior of cumulative recovery for run March 9 and 10 () in Fig. 5, both magnetic treated, shows an interesting finding of this work. It illustrates that effect of magnetic treatment of process water on bitumen extraction seems reproducible. These two tests were carried out in the same condition of using magnetic treated process waters although all conditions in these two tests were not the same exactly because of difficulty in extraction experiments. It suggests that a unique phenomenon must be occurred during using magnetic treated process water as recovery curves seem the same only with a fixed shift in y (recovery) axis. Although in both tests March 9 and 10 magnetic treated process waters were used, the initial temperature of the former was 35.6 ◦ C but the initial temperature of latter was 35 ◦ C in addition that process waters were not the same. At least a 10% difference was occurred for higher initial temperature, difference in total hardness of process water and pH.
4.3. Performance of flotation process Different approaches can be made to evaluate the effect of using magnetic treated process water on performance of
Fig. 5. Cumulative recovery of bitumen in extraction operation in various tests with magnetic treated (squares) and non-treated (triangles) process water.
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Fig. 6. Bitumen recovery vs. concentration of solid in collected froth for run March 3 (() magnetic treated) and March 2 (() non-treated).
Fig. 9. A typical change of mean grade of collected froth vs. time in bitumen extraction tests with magnetic treated () and non-treated () process water.
4.3.3. Mean grade of froth The performance of flotation process can also be evaluated [17] by defining a mean grade of froth (G): G= Fig. 7. Bitumen recovery vs. concentration of solid in collected froth for run March 17 (() magnetic treated) and March 16 (() non-treated).
4.3.2. Quality of collected froth Figs. 6–8 show the bitumen recovery versus concentration of solids in collected froth for various runs. These figures confirm that using magnetic treated water in flotation process results in better quality of collected froth (higher recovery with lower solid content). It is interesting to note that the slope of trend line always increased with using magnetic treated process water for all tests. The slope of trend line for treated samples is more than 4 but for non-treated samples is always less than 4.
f −F 1−F
where f and F are the mass fraction of bitumen in froth and feed, respectively. When G equals zero, no separation is taking place, hence, the value of G provides a qualitative estimation of the froth quality in extraction operation. Note that f and F are mass fractions in two different samples. F is equal to ratio of bitumen mass in feed to the summation of feed mass and mass of 950 ml of process water. F was 0.024 for all tests because we always used a poor oil sand in all tests, a fixed mass of feed about 300.5 ± 0.5 g and a fixed volume of water in each test. Fig. 9 shows a typical change of mean grade of froth versus time for both treated and non-treated samples. It shows that the quality of collected froth decays with time. This trend of decaying in froth grade was observed in all tests as can be expected.
5. Conclusions Bitumen recovery from poor oil sand is highly depending on the performance of extraction operation. Bitumen recovery is depressed when the concentrations of hardness ions are above 40 ppm. In this work, it was shown theoretically and experimentally that magnetic treatment of process water can result in handling the problem of hardness ions in bitumen extraction. It was found from this study that:
Fig. 8. Bitumen recovery vs. concentration of solid in collected froth for run March 9 and10 both magnetic treated.
1. The applied permanent magnetic force was sufficient to overcome whatever attraction might exist among the bitumen droplets, montmorillonite clay and the hardness ions.
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2. Zeta potential distribution of a suspension of montmorillonite clay, bitumen and hardness ions is modified by using magnetic field. 3. Ca and Mg ions have least tendency to take part in heterocoagulation process after magnetic treatment. 4. Magnetic treatment of process water is a promising physical technique to enhance recovery of bitumen during extraction operation. 5. Experimental results showed that magnetic treatment of process water has a unique phenomenon that is reproducible. 6. Magnetic treatment of process water always improves final performance of flotation process in bitumen extraction operation in every condition as Fig. 5 shows. Finally, it is important to note that this approach to oil sand industry should be followed by more detailed experimental and theoretical analysis by other independent investigators and also to extend it to include other aspects of possible applications such as water conservation, waste water minimization and more selective separation operations.
Department of Chemical and Materials Engineering, University of Alberta, Canada. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Acknowledgement The NSERC Chair Programme on Oil Sands Research, Profs. Masliyah and Xu are gratefully acknowledged for providing experimental facility during my sabbatical leave in
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