Re: Inorganic Ion Binding by Activated Carbon, Why Some not Others

From our experience with a 50 million gallon/day plant, activated carbon 
does not remove chloride over a pH range of 7-8.  It does absorb 
chloramine, but the capacity at that pH range is not very high, perhaps as 
much as 0.2 mg monochloramine/lb carbon.  
I consulted Cheremisinoff, N.P., and Cheremisinoff, P.N., 1993, Carbon 
Adsorption for Pollution Control, PTR Prentice Hall, Englewood Cliffs, 
NJ.  ISBN 0-13-393331-8
"Carbon adsorption of a wide range of inorganic compounds, such as cyanide 
and chromium from electroplating wastes has been found to  be practical.  
However, adsorption may be quite variable from chemical to chemical, is 
likely to be highly pH dependent, and thermal or chemical regeneration may 
not be feasible.  As a rule, strong electrolytes will not be adsorbed on 
carbon."
"There are two methods of adsorption:  physiosorption and chemisorption.  
Physiosorption occurs when, as a result of energy differences and/or 
electrical attractive forces (weak van der Waals forces), the adsorbate 
molecules become physically fastened to the adsorbent molecules.  This 
type of adsorption is multilayered; that is, each molecular layer forms on 
top of the previous layer witht he number of layers being proportional to 
the contaminant concentration.  When a chemical compound is produced by 
the reaction between the adsorbed molecule and the adsorbent, 
chemisorption occurs.  Unlike physisorption, this process is one molecule 
thick and irreversible because energy is required to form the new chemical 
compound at the surface of the adsorbent, and energy would be necessary to 
reverse the process."
I'm sorry that I'm not more familiar with the theoretical mechanisms of 
carbon adsorption; maybe there isn't a better one yet.  Perhaps you'll be 
the one to work it out.