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Activated
Charcoal Or Carbon
Learn About Activated Charcoal or Carbon
by Anne Marie Helmenstine. Ph.D.
Activated
charcoal (also known as activated carbon) consists of small, black beads or a
solid black porous sponge.
It
is used in water filters, medicines that selectively remove toxins, and
chemical purification processes.
Activated
charcoal is carbon that has been treated with oxygen. The treatment
results in a highly porous charcoal.
These
tiny holes give the charcoal a surface area of 300-2,000 m2/g,
allowing liquids or gases to pass through the charcoal and interact with the
exposed carbon.
The
carbon adsorbs a wide range of impurities and contaminants, including
chlorine, odors, and pigments.
Other
substances, like sodium, fluoride, and nitrates, are not as attracted to the
carbon and are not filtered out.
Because
adsorption works by chemically binding the impurities to the carbon, the active
sites in the charcoal eventually become filled.
Activated
charcoal filters become less effective with use and have to be recharged or
replaced.
List of What Activated Charcoal Will and Won't Filter
The
most common everyday use of activated charcoal is to filter water. It improves
water clarity, diminishes unpleasant odors, and removes chlorine.
It's
not effective for removing certain toxic organic compounds, significant levels
of metals, fluoride, or pathogens.
Despite
persistent urban legend, activated charcoal only weakly adsorbs alcohol and it
not an effective means of removal.
It will filter:
· Chlorine
· Chloramine
· Tannins
· Phenol
· Some drugs
· Hydrogen sulfide and some other
volatile compounds that cause odors
· mall amounts of metals, such
as iron, mercury, and chelated copper
It won't remove:
· Ammonia
· Nitrates
· Nitrites
· Fluoride
· Sodium and most other cations
· Significant amounts of heavy
metals, iron, or copper
· Significant amounts of
hydrocarbons or petroleum distillates
What Determines Activated Charcoal Effectiveness?
Several
factors influence the effectiveness of activated charcoal.
The
pore size and distribution varies depending on the source of the carbon and the
manufacturing process.
Large
organic molecules are absorbed better than smaller ones. Adsorption tends to
increase as pH and temperature decrease.
Contaminants
are also removed more effectively if they are in contact with the activated
charcoal for a longer time, so flow rate through the charcoal affects
filtration.
Does Activated Charcoal De-Adsorb?
Some
people worry that activated charcoal will de-adsorb when the pores become full.
While
the contaminants on a full filter aren't released back into the gas or water,
used activated charcoal is not effective for further filtration.
It
is true that some compounds associated with certain types of activated charcoal
may leach into the water.
For
example, some charcoal used in an aquarium might start to release phosphates
into the water over time.
How Can Activated Charcoal Be Recharged?
Whether
or not you can or should recharge activated charcoal depends on its purpose.
It's
possible to extend the life of an activated charcoal sponge by cutting or
sanding off the outer surface to expose the interior, which might not have
fully lost its ability to filter media.
Also,
you can heat activated charcoal beads to 200 C for 30 minutes. This will
degrade the organic matter in the charcoal, which can then be rinsed away, but
it won't remove heavy metals.
For
this reason, it's generally best to just replace the charcoal.
Also,
you can't always heat a soft material that has been coated with activated
charcoal because it might melt or release toxic chemicals of its own, basically
contaminating the liquid or gas you want to purify.
The
bottom line here is that you possibly could extend the life of activated
charcoal for an aquarium, but it's inadvisable to try to recharge a filter used
for drinking water.
Anne Marie Helmenstine, Ph.D.
· Ph.D.
in biomedical sciences from the University of Tennessee at Knoxville - Oak
Ridge National Laboratory.
· Science
educator with experience teaching chemistry, biology, astronomy, and
physics at the high school, college, and graduate levels.
· ThoughtCo
and About Education chemistry expert since 2001.
· Widely-published
graphic artist, responsible for printable periodic tables and other
illustrations used in science.
Experience
Anne
Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education
since 2001, and other sciences since 2013. She taught chemistry, biology,
astronomy, and physics at the high school, college, and graduate levels.
She has worked as a research scientist and also abstracting and indexing
diverse scientific literature for the Department of Energy.
In
addition to her work as a science writer, Dr. Helmenstine currently serves as a
scientific consultant, specializing in problems requiring an interdisciplinary
approach. Previously, she worked as a research scientist and college
professor.
Education
Dr.
Helmenstine holds a Ph.D. in biomedical sciences from the University of
Tennessee at Knoxville and a B.A. in physics and mathematics with a minor
in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine
developed ultra-sensitive chemical detection and medical diagnostic tests.
Anne
Marie Helmenstine, Ph.D.
ThoughtCo
and Dotdash
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