Have you ever seen news coverage or other pictures of an oil spill in the ocean? Oil spills can devastate wildlife and damage our precious water resources. So it is important to try to clean spilled oil (which can come from shipping tankers or offshore oil drilling rigs) quickly and thoroughly. But cleaning spills can be challenging. And scientists are often looking for new and different substances to help them. In this science activity you can test the absorptivity of different materials (called sorbents) to discover which ones are best at removing oil from water.
Oil isn't just for fueling cars. Are you wearing shoes right now? Chances are good that some parts of those shoes are made from petroleum oil. Now look at the fabric of your clothes, chair cushion, bedspread, carpet and drapes. If they aren't entirely cotton or another natural fiber, many of these fabrics were made at least in part from oil. In the kitchen you may find fruits and vegetables grown with the help of fertilizers and pesticides, which are also oil-containing products. If you head to the bathroom, you might find medicines, lotions, toothpaste, shampoos and bandages made in part from oil. Oil products are everywhere, including outdoors: car tires, roads and, yes, the fuel that powers most motor vehicles.
Because oil is used in so many ways, great amounts of it are carried long distances to factories that turn it into the products that we have become accustomed to having. Every day, millions of barrels of oil are moved around, mostly on tankers—which can carry more than 200,000 tons each. Occasionally these tankers have accidents, or offshore drilling rigs are damaged, and oil spills into the ocean. One way environmental engineers try to clean spills is with sorbents—materials good at absorbing liquids. If you’ve used a sponge, paper towel or kitty litter, you’ve already used a sorbent. Now we will explore specifically which sorbents are good for removing oil from water.
- Large plastic garbage bag
- Four-cup liquid measuring cup (A smaller measuring cup can be used if the other quantities in the activity are relatively scaled down, but the results will not be quite as impressive.)
- One-cup measuring cups
- Three or more sorbents that you want to test, with one cup of each sorbent (Examples include: cotton, such as cotton balls; fur; coconut husks; shop towels; feathers. Shop towels are often found in the automotive section of many stores. If you want to test coconut husks, you will also need gloves; eye protection, such as goggles; a hammer; and a large towel or burlap bag.)
- Vegetable oil (at least three cups)
- Reusable mesh coffee filter (It should be able to easily fit inside the four-cup liquid measuring cup.)
- Stopwatch, timer or clock that shows seconds
- Liquid soap
- Spread newspaper onto your work surface to make cleanup easier. Also open your garbage bag and put it close to the liquid measuring cup.
- Prepare each of your sorbents one at a time. Cut (or break) large sorbents into small, thumb-size pieces so that they can easily fill the measuring cup. Prepare one cup of each sorbent this way.
- If you want to test coconut husks, while wearing eye protection and gloves, cover the coconut with a large towel or place it in a burlap bag and then smash it with a hammer. Be sure to only smash it on a surface that you have permission to hammer on.
- When you are done preparing your sorbents, take a look at each of them. How do your different sorbents look and feel? How well do you think each one will absorb oil?
- Pour three cups of water into the liquid measuring cup. Then slowly add one cup of vegetable oil. Do the oil and water separate or mix? If many bubbles form between the water and oil layers, wait a couple minutes until the bubbles mostly disappear.
- Put one cup of one of your sorbents into the reusable mesh coffee filter. Lower it slowly into the water–oil mixture and gently move the filter from side to side for a few seconds until the sorbent is completely submerged. You may need to slowly lower the filter below the surface of the liquid in the measuring cup for the liquid to easily get into the filter.
- After the sorbent has been submerged in the liquid, start your stopwatch or timer (or note what time it is on your clock). After 30 seconds lift the filter (with the sorbent inside) and hold it just above the surface of the water–oil mixture for a few seconds to drain. Does it look like the sorbent has soaked up much of the liquid?
- Dump the contents of the mesh coffee filter into the plastic garbage bag.
- Get down to eye level with the liquid measuring cup and read the total water and oil level. (Note that this level should have been four cups originally because you added three cups of water and one cup of oil into the measuring cup.) What is the level of all of the liquid in the measuring cup now?
- Now read the level of the water only in the measuring cup, looking for where the water and oil layers meet. (Note that this should have been three cups originally, because you added three cups of water.) What is the level of the water in the measuring cup now?
- Calculate how much oil is left by subtracting the amount of water from the total amount of liquid in the measuring cup. How much oil is left?
- Now divide the amount of remaining water by the amount of remaining oil. What is the ratio of remaining water to remaining oil? Based on this, how effective do you think this sorbent is at removing oil from water?
- Wash out the mesh coffee filter and measuring cup with soap and water.
- Repeat this entire process with the other sorbents you want to test, first refilling the measuring cup with three cups of water and one cup of oil, and then submerging one cup of a new sorbent in the mesh filter for the same amount of time. (Be sure to wash the mesh coffee filter and measuring cup after testing each sorbent.) What is the ratio of remaining water to remaining oil for the other sorbents you test?
- The higher the ratio, the better the sorbent was at removing oil from water. Based on your results, which sorbent that you tested do you think is most effective at removing oil from water? Which is the least effective?
- Extra: This science activity let you investigate which sorbent was the best based on the volume of oil and water it absorbed. Figure out a way to instead investigate how well the different sorbents work based on the mass of the water and oil they can absorb. Which sorbent is the best by mass?
- Extra: Investigate how well the different sorbents work over shorter and longer periods of time. Which sorbent is the best by time?
Observations and results
If you tested them, did cotton balls and fur absorb oil better than coconut husks and feathers?
In this activity you tested some common household materials for their ability to act as good sorbents for vegetable oil. The original ratio of water to vegetable oil in the measuring cup was 3 to 1, as three cups of water and one cup of vegetable oil were used (and three divided by one equals three). Consequently, sorbents that absorbed more oil than water (“good” sorbents) would have a ratio greater than 3 to 1, whereas sorbents that absorbed more water than oil (poorer oil sorbents) would have a ratio smaller than 3 to 1. If you tested cotton balls and dog fur, you may have found they were relatively good sorbents, with a ratio of remaining water to remaining oil being approximately 5 to 1 or above. On the other hand, if you tested coconut husks and feathers, you may have found that they were poorer sorbents, with a ratio of 3 to 1 or lower. To selectively absorb oil from oil spills in the ocean a sorbent would need a relatively high ratio.
If you made any oily messes, try cleaning them with warm water and soap. Much of the “waste” from this activity can be composted (such as vegetable oil, most newspaper, coconut husks, fur, feathers, etcetera); if you compost, look into whether you can compost the waste you have left over from doing the activity and then dispose of it properly.
More to explore
Petroleum Oils, from the U.S. Environmental Protection Agency
Goo-Be-Gone: Cleaning Up Oil Spills, from Science Buddies
Oil Spill Basics, from AbsorbentsOnline.com
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies