How Activated Charcoal Works

If you look on the label of a water filter, you'll often see the filter contains activated charcoal -- but what exactly is this stuff? Tune in as Marshall Brain explains the nature of activated charcoal in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
Welcome to Brainstuff from how Stuff works dot com where
smart happens. This podcast is brought to you by Audible
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com slash brain Stuff today for details. I am Marshall

(00:24):
brain with today's question. What is activated charcoal and why
is it used in filters? Charcoal is carbon. Activated charcoal
is charcoal that has been treated with oxygen to open
up millions of tiny pores between the carbon atoms. These
pores give the charcoal amazing surface area, maybe a thousand

(00:44):
square meters or more per gram of charcoal. The word
ads orb is important here. When a material adds orbs something,
it attaches to it by chemical attraction. The huge surface
aery of activated charcoal gives it countless bonding sites. When
certain chemicals pass next to the carbon surface, they attached

(01:05):
to the surface and they get trapped. Activated charcoal is
good at trapping other carbon based impurities organic chemicals in
other words, as well as things like chlorine, many other
chemicals are not attracted to carbon at all. Sodium nitrates,
things like that so they pass right through. This means
that an activated charcoal filter will remove certain impurities while

(01:29):
ignoring others. It also means that once all the bonding
sites are filled and activated charcoal filter stops working. At
that point, you have to replace the filter. Do you
have any ideas or suggestions for this podcast? If so,
please send me an email at podcast at how stuff
works dot com. For more on this and thousands of

(01:49):
other topics, go to how stuff works dot com