Zeolites Photo Credit: Seaterror [CC-BY-SA-3.0], via Wikimedia Commons

Of all the toxic waste sites around the country, perhaps the most difficult to handle are those with radioactive nuclear waste. Since the waste remains toxic for hundreds or even thousands of years, it must be removed from the environment essentially forever. In this Science Update, you’ll hear about a new way to trap and seal up the toxins.


Netting out nuclear waste. I'm Bob Hirshon and this is Science Update.

Tanks of radioactive waste fester at toxic dumps around the country. At the University of New York at Stony Brook, a team lead by John Parise is looking into ways to filter out and lock up the worst of the chemicals.

So, take 8 tanks that might have very different chemistries, how do you separate out just those elements that are nasty, and sepulchrate them. Sepulchration means not just remove them from the environment, but entomb them.

The answer may lie in a family of cage-like molecules called zeolites. Parise says that different zeolites have different sized holes that allow molecules to enter the cage. Recently, scientists at Sandia National Laboratory developed a zeolite with just the right dimensions to trap radioactive strontium. Better yet, heating the material makes the holes clamp shut, sealing the toxin inside. Parise and his colleagues at Stony Brook's Center for High Pressure Research are studying the zeolite's behavior.

And once we've discovered why it behaves that way, the next question we ask is how can we improve it?

Eventually, it's hoped that these tiny filters will be able to clean up a variety of toxins, and lock them up for good.

For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Zeolites are basically molecular sieves: solid materials with holes that are just the right size to let some molecules pass through, while blocking larger molecules out. They're not a new invention. In fact, they've been used since the 1970's to help refine gasoline. They're also used on missions to outer space, in the soil of experimental plants. The zeolites release and absorb nutrients in the soil, which cuts down on the need for liquid water.

Now, Parise and his colleagues want to use zeolites to help separate toxic waste and isolate dangerous chemicals from the environment. When you've got huge tanks of toxic waste sitting around in storage, there are a couple of potential problems. One is that some kinds of radioactive waste take an incredibly long time to break down. So no matter how tightly sealed your tanks look today, five hundred years from now they'll probably be leaking toxic waste into the ground.

Another problem is that toxic waste is basically a stew of all sorts of radioactive chemicals mixed together. Because they're all mixed up, that presents an opportunity for other chemical reactions to take place, which in turn could produce even more toxic chemicals. The result is a ticking time bomb of any number of poisonous chemicals just waiting for an opportunity to escape—and they've got all the time in the world to do it.

Using zeolites, researchers may be able to stop this process. Instead of letting the waste sit around all mixed together, they could separate out each chemical component one at a time. For example, they could make a zeolite for radioactive strontium (a particularly dangerous chemical), run the waste through it, and thereby take the strontium out of the mixture. This process could be repeated with every radioactive chemical, until only harmless chemicals, like potassium and sodium, remained. It's almost like taking a glass of lemonade and separating it back out into water, sugar, and lemon juice.

Of course, now you've just got a whole bunch of canisters of individual radioactive chemicals, and it's easy for those chemicals to flow back out of the zeolites just the way they came in. That's why the Sandia researchers are trying to develop zeolite materials that seal up when they're heated. That's what they mean by sepulchration—the radioactive chemicals are locked up forever in a kind of molecular sepulchre, or tomb.

Now try and answer tthese questions:

  1. What are some of the problems with storing toxic waste?
  2. What are zeolites? How do they trap and isolate chemicals?
  3. How might zeolites help with toxic waste cleanup?
  4. Why are the currently available forms of zeolites insufficient to solve the problem?
  5. Can you think of other forms of waste and pollution that are left in the environment for a long time, even after they're "cleaned up"? What kind of a threat might they pose a hundred or a thousand years from now?

For Educators

Explore these websites for more information on zeolites:

Play the Toxic Waste River Rafting Game! on the National Institute of Environmental Health Sciences (NIEHS) website. This game demonstrates the importance of keeping our waters clean and pure, and challenges you to take a tube ride down a "toxic waste" river and see how long you can avoid the hazards.

Go to the Toxic Waste Site in Microbe Zoo's Dirtland to learn about the role microbes play in eliminating or neutralizing toxic compounds in the environment.

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