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ocean engineering

“Magic Sand” Cleans up floating oil

Article: Daria Boglaienko, Berrin Tansel. Instantaneous stabilization of floating oils by surface application of natural granular materials (beach sand and limestone)Marine Pollution Bulletin. 91(2015)107-112. http://dx.doi.org/10.1016/j.marpolbul.2014.12.020

 

Introduction

This may be the first time that you have heard the phrase “granular material”, but you are undoubtedly familiar with sand, snow, nuts, rice, coffee and corn flakes. They are all granular materials and are ubiquitous in our daily lives.

What is special about the members of this group? One important feature is that they have the properties of both solids and liquids. Take sand as an example. Sand castles at the beach have certain frames and shape. This is a special character that only solids have. However, when you fill a container with sand, it takes the shape of the container as liquids do. Therefore, granular materials are suggested to be an additional state of matter on top of solid, liquid and gas.

Adding small amount of water to sand significantly changes its properties. The reason is that water adds bridges between the sand particles and therefore wet sands hold better than dry ones. Imagining how hard it will be building a sand arch by dry sand (fig 1)?  Reversely, if we add granular material into liquid, what would happen?

Figure 1. Sand arch

Figure 1. Sand arch

(More on granular materials, check on http://www.physicscentral.com/explore/action/granular.cfm)

 

Experiment

Scientists found that granular material introduced into hydrophobic liquid (e.g. oil) significantly changes the characteristic of the liquid. Liquid adhere to particles and forms a “raft”, which sinks once it gets too dense (too many particles). This mechanism can be extremely useful in separating floating oil layer after oil spills. A group of scientists were interested in seeing how efficient this approach works.

Granular material used in this study consisted of limestone sand and quartz sand. Three sizes were chosen to study the effect from particle size on removal efficiency of oil. For every one-gram of particulate, there are 2900 particles of the largest group of sand and 1,700,000 particles of the finest sand (fig 2 top). 1 mL of crude oil was added into 100 mL saltwater in 125 mL Erlenmeyer flask. 0.5~3.5 g of sands were added in while the flasks began to shake. Once the oil-particle aggregates formed, they were filtering through fiberglass filter to calculate the capture efficiency of granular materials (fig 2 bottom). Because the aggregates were captured by the filter, the weight difference between before and after the experiment indicates the weight of sand plus oil. This weight difference was subtracted of the weight of particles to get the weight of oil.

1-s2.0-S0025326X14008212-gr3

Figure 2. Top: (a) medium limestone, (b) fine limestone, and (c) fine quartz.

Figure 2. Bottom: Formation of oil-sand aggregates: (a) floating oil, (b) formation and separation of particle–oil aggregates, (c) particle–oil aggregates separated by coarse filtration (crude oil-fine quartz aggregates).

Figure 2. Bottom: Formation of oil-sand aggregates: (a) floating oil, (b) formation and separation of particle–oil aggregates, (c) particle–oil aggregates separated by coarse filtration (crude oil-fine quartz aggregates).

Results and Implications

Results show significant reduction of floating oil with more sand added (fig 3). The oil capture efficiency increases most dramatically between 1g and 2g of sand per gram of floating oil (fig 4). As to the difference between granular particle sizes, it was found that smallest particles showed largest oil content.

Figure 3. Comparison of oil–particle aggregate formation with different granular particles with increasing particle/oil ratios. Top row: medium limestone, middle row: fine limestone, bottom row: fine quartz.

Figure 3. Comparison of oil–particle aggregate formation with different granular particles with increasing particle/oil ratios. Top row: medium limestone, middle row: fine limestone, bottom row: fine quartz.

 

This experiment demonstrated strong evidence of using natural granular material (lime sand and quartz sand) to aggregate floating crude oil. The aggregation settled very quickly and was stable. This reveals the potential of using natural granular materials to control the transport of floating oil. Because particle-oil aggregates sink, less oil will be spread by surface currents as well as entering the atmosphere by air-sea exchange.

Currently, spreading dispersants is the most common way to stabilize surface oil after oil spill. These dispersants divide oil into small droplets which are more available to bacteria. However, this application of dispersants is not applicable near the coast and the toxicity of dispersants remains to be studied. Natural granular material could be a more eco-friendly tool in fixing coastal floating oil.

Figure 5. Plane spreading oil dispersants over floating oil. (From http://www.cnn.com/2010/US/07/02/gulf.oil.dispersants/)

 

 

Interested in how the experiment was set up? Watch this video clip:

http://www.sciencedirect.com/science/MiamiMultiMediaURL/1-s2.0-S0025326X14008212/1-s2.0-S0025326X14008212-mmc1.mp4/271825/FULL/S0025326X14008212/49fc8658ba9f9d9e03835fc31b97a295/mmc1.mp4

Caoxin Sun
Caoxin is a graduate student in the Graduate School of Oceanography at the University of Rhode Island. Her research interest lies in persistent organic pollutants in the environment. When she is not doing research she likes to create new cuisines.

Discussion

3 Responses to ““Magic Sand” Cleans up floating oil”

  1. I found this article to be very well researched and of great help to me for learning more about the topic. I do have a question, and it is what are the effects of the aggregated oil once it is on the ocean floor before it goes into the natural cycle of air-sea exchange? I previously knew of some green solutions such as peat moss and bacteria to clean up oil spills, but I had never heard of this combination of sand or rock material (limestone and quartz) being used as a solution. I would never have suspected that sand or granular material could be used as a way to clean up oil, though after being presented with the information that sand possesses the ability to be both a liquid and a solid I realize what a valid solution it is. It was also a great comfort to me to hear about the experiments done to prove that it would both work and that it was a green solution. Many times (the dispersants) are used with knowledge of how they will work to get rid of the problem yet little research is done to find out how it affects the surrounding environment. I was also left with the question though beyond the effects of the aggregated oil, how does the material affect refined oil. In the article it was only mentioned that it could be used on crude oil, but there was no information on how it would affect refined oil. But all in all I found your introduction something that got my attention and helped me relate what granular material was and the properties it possesses.

    Posted by Chloe | March 5, 2017, 11:13 pm
  2. I believe that we should use the “Magic Sand” to clean up floating oil. Even though we have oil dispersants to clean up the oil, we do not know the long term effects of them. If we end up destroying the environment, our efforts to clean the ocean would be futile. I agree that we should switch to a more natural solution. However, we should have furthur testing and research to make sure the lime and quartz sand don’t hurt the animals. My first question is, how do you suggest we implement this idea into a working product? My second question is, if the oil dispersants end up being harmless, should we still switch to using lime and quartz sand? Overall, your article provides some great insight on possible solutions to the oil spills in our ocean.

    Posted by Dhruv Ahuja | March 3, 2017, 2:45 pm

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  1. […] driving point of the event is to encourage visitors to think of how these things can be used.  The hydrophobic sand coated in silicon was actually created to clean up oil spills in the ocean. The sand can coat the oil in the water and bind to it while never mixing with the water so it can […]

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