Saturday, April 11, 1998

Magnetic Property of Steel Separates it from Other Recyclable Materials

What unique property does steel have that other recyclable materials don’t? Everyone with a motley assortment of magnets stuck to their refrigerator should know the answer to this question. Steel is attracted to a magnet.

Home refrigerators everywhere are plastered with mosaics of family photos, favorite recipes and important phone numbers, all clumped under a collection of magnets from a tacky tourist trap meant to commemorate last summer’s vacation. And before that invention of the sticky Post-it note, the refrigerator magnet was arguably the best way to hang a hastily scripted message to someone. We’re all inevitably drawn to the refrigerator by hunger, and so the message was sure to be seen and read.

But steel’s magnetic property comes in a little more handy in the world of solid waste management. You could even say it separates steel from all other types of recyclable materials.

One of the tricky parts of recycling is how to best separate the recyclables. Engineers have harnessed the natural power of magnetism to sort steel products from the solid waste stream. When commingled recyclables arrive at a material recovery facility, empty steel food, paint and aerosol cans are often the first products to be culled from the mix. At most facilities, the recyclables are loaded onto a conveyor belt and passed under a magnetic conveyor belt, which quickly and efficiently pulls steel containers out of the mix. The remaining materials continue along the original conveyor belt to undergo manual or mechanical sorting.

Steel’s magnetic attraction does more than just help steel cans to be cleanly and efficiently sorted at a material recovery facility. It also allows steel cans to be collected from the municipal solid waste stream in ways other materials can’t. For instance, there are 98 resource recovery facilities that recycle steel cans and combust municipal solid waste into energy or create refuse derived fuel. At these facilities steel cans are magnetically separated from the waste stream along with other iron and steel items, and shipped to a steel mill for recycling. Nearly half of the 40 million Americans facilities live in communities that do not offer curbside or drop-off recycling programs for steel cans. But thanks to steel’s magnetic property, the steel is automatically separated for recycling. Think about it, 20 million Americans are recycling virtually 100 percent of the steel cans that they use, simply by disposing of them, because the containers are efficiently separated with a magnet at the resource recovery facility.

And when it comes to appliances, those same magnetic properties that held your refrigerator magnets in place when it was in your kitchen, bring similar benefits when it is time to recycle the appliance. Appliances, when no longer operational, are dismantled and then torn apart in a shredder. This is done to break down the individual materials used to make the appliance. Steel again pulls away from the rest as the shredded appliance passes under the magnetic belts at the end of the shredder.

Steel’s magnetic property is also very useful when it comes to moving steel materials. Whether it’s a crushed automobile weighing up to a ton or a bale of steel cans weighing several hundred pounds, electromagnets make it easy to lift and move steel scrap.

So next time you hang your child’s report card or a clipping of your favorite cartoon on the refrigerator, remember that steel’s magnetic property comes in handy both during your appliance’s useful life-and especially after.

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