In the Laboratory
Oil Spill Remediation Using Magnetic Particles An Experiment in Environmental Technology John D. Orbell,* Leroy Godhino, Stephen W. Bigger, Thi Man Nguyen, and Lawrence N. Ngeh Department of Chemical Sciences, Victoria University of Technology, P.O. Box 14428, Melbourne City Mail Centre, Melbourne, 8001, Australia New and innovative methods for dealing with environmental problems is an area that fires the imagination of chemistry students (1–3). Their enthusiasm may be further enhanced when an emphasis is placed on the importance of devising appropriate technologies for developing countries (4). The application of magnetic particle technology to environmental problems is one such method that has received considerable attention in recent years. For example, finely divided magnetite has been shown to be an effective way of clarifying sewage effluent through an accelerated coagulation process involving adsorption of contaminants onto the surface of the magnetite (5). As another example, specifically developed magnetic particles have been applied to the removal of radionuclides from milk. These particles consist of a magnetic core with a polymer coating and are targeted to specific contaminants by having either a functionalized resin as the coating or selective seed materials embedded in the coating (6). There is enormous scope for the further development of magnetic particle technology for application to a variety of environmental problems, including oil spill remediation. We describe herein a simple experiment in which commercially available steel “isoshot” pellets, used in shotblasting, are coated with an oil-adsorbing polymer such as polyethylene (PE) or poly(vinylchloride) (PVC). The potential of the resulting magnetic particles (or “beads”) to remediate an oil spill may be demonstrated. This experiment also demonstrates the possibility of recycling the beads and reclaiming the oil. For maximum didactic benefit to the student we recommend that the experiment be conducted in a three-hour period, although the concept is flexible enough to be condensed to a ten-minute lecture demonstration. The experiment is applicable to first-year students, although more advanced students may benefit from it as well. Experimental Procedure
Materials Required The following materials are required for the experiment:1 • Polyethylene (PE) powder (Courtney Polymers, Dandenong, Australia) and poly(vinylchloride) (PVC) powder (Plascoat Systems Ltd., Surrey, United Kingdom). In our experiments we have used grades 4612-05A and PC-80-ES of PE and PVC, respectively. • Steel “isoshot” pellets are produced commercially (Ervin Industries, Ann Arbor, MI) in a variety of grades that are characterized by different particle size distributions. To ensure physical integrity of the polymer coating and adequate surface coverage we have used grade S330 (0.84– 1.40 mm mesh size), which results in an average bead diameter of ca. 1 mm. *Corresponding author.
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Figure 1. Harvesting oil-laden beads using the “Laboratory Magnetic Tester” device.
• A muffle furnace for heating the steel pellets. • Magnetized tweezers and an electromagnet (one device per student is required). We have found that a most convenient device, which can be used as a cheap alternative to an electromagnet, is the “Laboratory Magnetic Tester” (Alpha Magnetics, Victoria, Australia). This device is shown in Figure 1. • Mechanical shaker for removing excess or unattached polymer from the coated pellets. • Low-power optical microscope for examination of the coated pellets. • Top-loading balance for gravimetric measurements. • Standard engine oil to be used as the “contaminant”. In our experiments we have used Mobil Super XHP, 20W-50 (1993 formulation). • Also required in varying quantities, depending on the class size, are beakers, conical flasks, glass stirring rods, porcelain crucibles, Petri dishes (7-cm), and paper towels.
Journal of Chemical Education • Vol. 74 No. 12 December 1997
In the Laboratory Manufacture of the Polymer-Coated Magnetic Particles heated steel "isoshot" pellets 10 cm
10 cm
cylindrical metal container (25 cm diameter) fluidized bed of polymer powder (2 kg charge) ceramic porous plate
5 cm
air inlet (5 mm diameter)
Figure 2. Schematic diagram of fluidized bed apparatus.
It is suggested that a stock of both PE- and PVC-coated beads be prepared prior to a laboratory session, allowing about 10 g of “isoshot” pellets per student. The method of preparation may be briefly demonstrated to the class by the instructor. To manufacture a stock of coated pellets, 5 g of the isoshot pellets is placed in a porcelain crucible and heated in a muffle furnace to ca. 650 °C. The heated steel pellets are then scattered into a fluidized bed of the powder (Fig. 2) using magnetized tweezers. This is achieved by striking the loaded tweezers on the rim of the container. It is important to carry out this procedure promptly to minimize heat loss from the pellets. The procedure is repeated with 5-g batches until the desired quantity of coated pellets is produced. After relaxing the fluidized bed (by turning off the air) the coated pellets (beads) may be harvested from the polymer powder magnetically. These are then placed in a conical flask and agitated for 5–10 min using a mechanical shaker. This removes loose flakes of polymer from the surface of the beads. The beads are harvested magnetically once again and put to one side for apportioning to the students. The students are invited to examine the beads microscopically, noting the surface texture and contrasting the difference between the PE and PVC coatings (Fig. 3). We recommend that one half of the class receive beads that are PE coated and the other half receive beads that are PVC coated. In this way, the effect on oil remediation of different coating materials can be examined.
Testing the Ability of the Beads to Remediate an Oil Spill Each student is supplied with approximately 12 g of coated beads. A fixed quantity of oil (ca. 0.5 g, top-loading balance) is charged into preweighed (w1) Petri dishes, which are then reweighed (w 2). A different weight of beads, in the range 0.1–1.75 g, is then applied to each dish and each dish is reweighed (w 3). Thus the bead-to-oil ratio, R, may be calculated according to eq 1: Figure 3. Electron micrographs of: (a) PE-coated pellet and (b) PVC-coated pellet.
Fluidized Bed Apparatus An apparatus for creating a fluidized bed of polymer powder is shown schematically in Figure 2. The apparatus is constructed from simple materials: a small, cylindrical metal bucket or container (25 cm diameter × 25 cm in height) and an air-porous ceramic or sintered glass plate, which is glued to the inside wall of the container 5 cm from the bottom. Air is admitted to the apparatus through a 5mm diameter gas nipple mounted to the wall of the container at the center of the cavity formed between the bottom of the container and the air-porous plate. No baffling is used in the cavity. A charge of ca. 2 kg of polymer powder is placed on top of the air-porous plate and the powder is fluidized by passing compressed air through a hose connected to the gas nipple. The flow rate of air is adjusted so that the top of the fluidized bed of polymer remains ca. 10 cm from the top of the container.
R = (w3 – w2) / (w2 – w1)
(1)
The beads are well mixed into the oil using a glass rod, taking care not to remove too much of the oil (although small losses will not affect the intended outcome of the experiment). The beads are left in the oil for five minutes, then are magnetically harvested (Fig. 2) and pooled into a beaker. The individual dishes are weighed (w4) to determine the amount of oil removed by the beads. This is expressed by the parameter P%, which is the percentage of the amount of oil originally present (eq 2). P% = [(w2 – w 4) / (w2 – w1)] × 100
(2)
A sample tabulation of data for PE-coated beads at R = 0.3 and R = 1.5 is given as follows:
w 1/g
w 2/g
w 3/g
w 4/g
R
P%
24.63
25.10
25.24
25.01
0.30
19
24.05
24.57
25.35
24.18
1.5
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Vol. 74 No. 12 December 1997 • Journal of Chemical Education
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In the Laboratory Conclusions 100 PE
P°(PE) = 87%
80 P°(PVC) = 73%
PVC
60 P% 40 R°(PE) = 1.78
20
R°(PVC) = 2.38
0 0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
R Figure 4. Percentage pick-up, P%, versus bead-to-oil ratio, R, for PE- and PVC-coated pellets.
Results A plot of P% versus R shows curves of a typical shape (Fig. 4), where an optimum percentage pickup, P°, is achieved for values of R greater than a critical value, R°. The percentage P° is characteristic of the polymer coating and the specific contaminant. The value of R° is controlled by the presented surface area of the beads, which, in turn, is determined by their average size and by the surface texture. For a given weight of beads, the rougher surface of the PE beads (Fig. 3a) presents more surface area to the oil than the smoother PVC beads (Fig. 3b); correspondingly, R°(PE) is less than R°(PVC) (Fig. 4). An explanation of the relative percentages P°(PE) and P°(PVC) (Fig. 4) requires consideration of the attractive forces involved. A remarkably high degree of reproducibility is achievable. For example, for both PE- and PVC-coated beads, 50 repeat measurements of P° by an experienced experimenter at a fixed value of R (where R > R°), resulted in a standard deviation of ca. 2.0% and a standard error of ca. 0.3%. It is an interesting exercise to compare the results of the whole class with respect to the two parameters, R° and P°. The used beads of the whole class may be pooled into a large beaker and allowed to stand for a few days, whereupon the oil is observed to drain to the bottom of the container. This suggests that a method such as centrifugation could be effective in recycling the beads and reclaiming the oil. If time permits the “recycled” beads from the draining experiment can be used to demonstrate the extent to which they still work.
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This simple yet versatile experiment introduces students to an innovative approach to a serious environmental problem and challenges their manipulative and organizational skills. That remediation of up to 90% is achievable with the PE-coated beads is an exciting finding for most students. The experiment highlights the fact that appropriate technology is not a poor relative of high technology and that effective innovation need not be expensive. The experimental design may be extended to include other coatings, different contaminants, or a variety of matrices such as oil/ water or oil/sand. Variations on the manufacturing of the beads could also be explored with a view to minimizing their size or altering their surface texture. Acknowledgments We are grateful to Ross Porz of Wiredex Wire Products Pty. Ltd., Clayton, Australia, for supply of materials and helpful advice. We also thank Chris O’Brien, Department of Botany, The University of Melbourne, and Philip Holgate, Department of Genetics, The University of Melbourne, for their assistance in obtaining the photographs. Note 1. Materials required for this experiment may also be obtained from the following North American suppliers: polyethylene, Dow Chemical, Freeport, TX; poly(vinylchloride), The Geon Company, Avon Lake, OH; magnetic tester, Bunting Magnetic Co., Newton, KS.
Literature Cited 1. Ibanez, J. G.; Takimoto, M. M.; Vasquez, R. C.; Basak, S.; Myung, N.; Rajeshwar, K. J. Chem. Educ. 1995, 72, 1050– 1052. 2. Emerging Technologies in Hazardous Waste Management, Vol. I–V; Tedder, D. W.; Pohland, F. G., Eds.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989–1995. 3. O’Brian and Gere Engineers, Inc. Innovative Engineering Technologies for Hazardous Waste Management; Van Nostrand Reinhold: New York, 1995. 4. Appropriate Waste Management Technologies for Developing Countries; Kanna, P.; Kaul, S. N., Eds.; Technical papers presented at the 3rd international conference held at NEERI, Nagpur, India, 25–26 February 1995; Industrial Consulting Internationa: Bombay. 5. Booker, N. A.; Keir, D.; Priestley, A. J.; Rithchie, C. D.; Sudarmana, D. L.; Woods, M. A. Water Sci. Technol. 1991, 123, 1703–1712. 6. Technology Profile; Ground Water Monitor 1994, 21(April), 60.
Journal of Chemical Education • Vol. 74 No. 12 December 1997
