The most important application of activated carbon adsorption where large
amounts of activated carbons are being consumed and where the consumption is ever
increasing is the purification of domestic and industrial waste water. More than 800
specific organic and inorganic chemical compounds have been identified in ground and
surface waters. Many of these compounds are carcinogenic and cause many other
ailments. Several methods such as coagulation, aeration, oxidation and activated carbon
adsorption have been used for the treatment of water but the activated carbon adsorption
has been found to be the best broad spectrum technology available at the present
moment. The more important parameters that influence and determine the adsorption of
inorganics from aqueous solutions are the acidic carbon-oxygen surface groups present
on the carbon surface and the pH of the solutions. These two parameters determine the
nature and concentration of the ionic and molecular species in the solutions.
Electrokinetic studies have shown that the nature and the extent of the carbon surface
charge can be modified by changing the pH of the carbon-solution system. The
adsorption of metal ions, therefore, mainly involves electrostatic attractive interactions
between the metal ionic species in the solution and the negative sites on the carbon
surface. The adsorption of organics, however, is quite different. The organic compounds
present in water can be polar or non-polar so that not only electrostatic interactions but
also dispersive interactions will play an important role. In addition the porous structure
of the carbon surface which includes the existence of mesopores shall also be an
important factor for the adsorption of essentially non-polar organic molecules.
Keywords: Adsorption, Activated carbon, pH, Adsorption capacity, Surface
groups, Cationic pollutants, (In)organic pollutants, Adsorption isotherms, Column
adsorption, Effluent concentration.
