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Re: Activated carbon

Hello Dave, Bob,

> > Obviously, AC made from animal bones will contain a lot of          > > phosphorus, that from wood will have substantially less and AC      > > made from once-distilled petroleum tar -- only traces of            > > phosphorus, if that
.
> George, this is not at all obvious to me.   Can you explain how       > you reached this conclusion?

My fault for not explaining more fully: Bone is porous and the pores are
filled with all kinds of cells -- each containing phosphorus. After bone
is burned, the organic material converts (partially) to carbon, but the
phosphorus (and other materials) convert to their inorganic salts that
are soluble in water.
 
On top of that, the inorganic structural material of bone is calcium
phosphate. It is quite insoluble, but a few ppm of it will dissolve. 

Thus bone carbon is not an ideal choice for aquaria, however it has good
adsorption properties and is used where a few ppm of phosphorus don't
matter.

> > Not all AC is made from the same starting materials. The most       > > common materials used to make granulated AC are probably wood,       > > bone, coal, petroleum tar. Actually, any carbon-containing          > > material can be converted to AC.
 
> What if we put some sugar in a jar, poured the appropriate acid 
> over it, and harvested the carbon (I saw this done in 7th grade       > science - it was impressive, but I can't remember which acid it 
> was).  There would be no phosphorus at all.  what do you do to  
> make it "activated"?

YES! Sugar (sucrose) can produce a nice, foamy carbon, with a large
surface area. However, I would not use the acid method for
carbonization, but use just plain heat: Heat sugar to about 200+ deg. C
and it starts to decompose -- carmelizes. The escaping gases foam the
sugar, forming a porous structure. After carbonization is complete, the
mess "sets" and forms a block of charcoal.

There are many processes for "activating" carbon. Many of them are trade
secrets suitable to a particular carbon and particular end use. Most of
them one would not try without a properly equipped laboratory.

The two best known methods are superheated steam treatment and heating
in absence of oxygen. While I would NOT come near superheated steam,
heating carbon in absence of oxygen is relatively easy. All one needs is
a tube furnace and a purging gas -- nitrogen, CO2, etc.
 
Hope that this explains it more fully.

Best,

George