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Fly ash: From toxic by-product to nearly-free metal replacement

Fly ash: From toxic by-product to nearly-free metal replacement

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Swapping out the expensive metals in car parts and lamp posts for a nearly-free coal burning by-product could save the environment and save money.

Swapping out the expensive metals in car parts and lamp posts for a nearly-free coal burning by-product could save the environment and save money, according to researchers from the Polytechnic Institute of New York University.

I spoke this week with Nikhil Gupta, associate professor of mechanical and aerospace engineering, about the unrealized benefits of fly ash. Here are excerpts of our discussion:

What is fly ash and where does it come from?

In power plants, when they burn coal in large quantities it generates ash. Some of the ash consists of hollow particles. These are the useful components. They're lightweight. They're a by-product of coal burning, so their price is very low. The only cost is in extracting the useful part and cleaning it.

How much fly ash is produced each year and what happens to it?

In the U.S., it's produced in about 70 million tons per year. Worldwide, the production is more than 300 million tons per year. In the U.S. about half of it is used in some applications. It's mixed with cement. But 35 million tons is still a lot of quantity. It is dumped in landfills. The big problem is that the particles, which are very low density, can fly with wind gusts. There are some toxins inside these particles, so it's not a good idea to just leave them in landfills. We need to find some applications for them where you can contain them in confined spaces.

You found that fly ash could be used to replace aluminum and magnesium in some products?

The main idea is to fill them into certain metals. Aluminum and magnesium are examples. We are also working with steel-based forms, where you'd put hollow fly ash inside steel. It can be beneficial in terms of reducing the weight of the total structure. Also, when you're replacing a metal, it's expensive. It's about $1 per pound. When you replace it with something that is almost free, the overall cost becomes lower.

What specific products could use fly ash?

Several of these components can be made in cars. We can start with some non-load bearing components like an engine cover. It doesn't take any load, so you don't have to worry about weakening the strength of the metal. With millions of cars sold every year, we can reduce some weight and we can reduce primary metal with these more environmentally unfriendly materials. This could be beneficial.

I also give the examples of lamp posts or park benches, where you put only a limited amount of load. Instead of making them solid with primary metals, we could make them with these other forms. They'll be lightweight and will use less aluminum or steel. Pollution associated with generating that much aluminum and steel is also saved.

What experiments did you do to determine that fly ash could be used in this way?

I worked with my collaborator at the University of Wisconsin - Milwaukee. His name is Pradeep Rohatgi. He runs a foundry and makes these materials in his lab. I have machines here that can test these materials in tension, compression and also on the conditions that are similar to high-speed car accidents. Once you put fly ash in aluminum or magnesium under compression, their energy absorption capabilities are very good. That means you don't compromise on the safety you get from primary metals, even by having this low cost environmentally unfriendly metal inside. That's an important part of the finding.

What are the downsides or challenges to using fly ash in this way?

These particles are hollow. Their walls are not perfectly made. We're trying to find only the component that's important for us. Having a process control is important. It's very important to understand the kind of product that will provide you the same level of strength. Without that it's difficult to understand how they would provide benefit.

What's the next step for this work?

We are working with some foundries in Wisconsin. We're trying to see if we can make some parts and put them into use with automakers so they feel more comfortable using them regularly. This would also help industry in the U.S. in becoming more competitive because the price can be pretty low. The whole cost of the part would be lower in this case.

Photo, top: Aluminum foundry

Photo, bottom: Nikhil Gupta

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Christina Hernandez Sherwood

Contributing Writer

Contributing Writer Christina Hernandez Sherwood has written for the Los Angeles Times, Newsday, the Philadelphia Inquirer, Diverse: Issues in Higher Education and Columbia Journalism Review. She holds degrees from the University of Delaware and Columbia University's Graduate School of Journalism. She is based in New Jersey. Follow her on Twitter. Disclosure