The reason any charcoal "absorbs" - or in reality adsorbs - stuff is due to the presence of pockets of small crevices and high porosity. It is the presence of those tiny regions of large surface area that permit molecules to adsorb. The size of the molecule and the size of the porosity are the primary controlling factors as to what sticks and what doesn't.
In truly activated charcoal, the percentage of such porosity is very high, making the accompanying surface area huge - in the neighborhood of 500 to 1000 square meters per gram - so it can adsorb large volumes. In horticultural charcoal, only small portions of the pieces are truly "activated," so adsorption is far less. Graphite, tending to be plate-like in structure, with the flat surfaces stacked against each other, has little surface area by comparison. Interestingly enough though, if I recall correctly, in activated carbon, the surfaces are very much like graphite, but again, it's a surface area per unit volume thing. Ray Barkalow - First Rays Orchids - www.firstrays.com Plants, Supplies, Books, Artwork, and Lots of Free Info! . . . . . . . .
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