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MIT engineers have come up with a method of extracting clean water and reusable oil from oil spills using nanoparticles that turn the oil into magnetic ferrofluids.

When oil spills occur, the polluted surface is usually skimmed and a centrifuge system then used to separate the oil and water, as Ocean Therapy Solutions' machines did following the 2010 BP disaster. According to the company, it can clean up to 790,000 litres of oily water per day. Turning the oil slick into a ferrofluid mix will, MIT is now suggesting, provide a faster and more efficient alternative. "After the BP oil disaster about two years ago, I got the idea that if the oil were magnetic we would be able to remove it with strong magnets and separate it from the water," says engineering professor Markus Zahn, who will be presenting a paper on the theory at the International Conference on Magnetic Fluids in January 2013.


Lead author on the paper and postdoctoral student Shahriar Khushrushahi explains, "The current oil technology like skimmers are very good in calm waters but in choppy waters their oil recovery efficiency is about 50 percent, so whatever they recover from the water would be half oil, half water. Our technology is supposed to improve that efficiency and act as an add on."

The engineering team tested their theory by adding magnetic ferrous nanoparticles to test samples of oily water and then using a series of cylindrical magnets to pull off the newly magnetically charged contaminate. The method differs from other experiments that separate oil from water in this way by partially submerging the magnets in the murky water and ensuring they are positioned perpendicularly to the flow. In past investigations the magnets were held above water, but by submerging it the engineers ensured the oil rushed to the top of the cylinder where it peaks out of the water (a magnet's field is strongest at its edges, and since the fluid could not reach the submerged bottom, it would inevitably rise to the surface). In the above video you can see the fluid spring to life and leap up and around the magnets after it is poured into the water bath.

Traditional methods of separating oil and water in this way rely on a system that pumps the mixture through a channel, with exterior magnets manipulating the flow of the ferrofluid away from the water. This, says Zahn, is not an entirely reliable method since it is dependant on having accurate readings on the concentration of the ferrofluid and in the context of an oil spill it is difficult to be able to predict and measure this. Rather than relying on a series of channels where pathways could potentially be infiltrated by trace amounts of water or oil, the MIT team overcame the challenge by using the cylindrical magnets, then removing the collected oil using a Halbach array -- an arrangement of magnets where one end has a field near zero and the other has nearly double its usual magnetic field.


MIT tested the theory in small confined containers, and would like to see oil companies doing the same -- skimming the surface and opting to carry out the rest of the water separation onboard a vessel on site, before shipping it off to a refinery to be reused.

It's hoped the economical approach and process will outdo centrifuging in terms of efficiency. "You could think of separating oil from water by centrifuging or something like that, but in a lot of cases, the fluids are pretty much equal in density: Some of the oil sinks, some of it floats, and a lot of it is in between," says former Exxon researcher and author of Ferrohydrodynamics Ronald Rosensweig. "The magnetic hook could, hopefully, make separation faster and better." "They often collect the oil and water in these big tanks and let it separate due to density differences -- but that takes a long time," says Khushrushahi. "[With our method] you can separate the two very quickly because the forces are so much stronger than density -- you can process this much faster and continuously, without any real power being expended."

The team is investigating the possibility that water molecules are becoming trapped in the ferrofluids, as a precautionary measure, but preliminary tests look good.