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4.1 Basic Principles of Adsorption and Ion Exchange 245

nonaromatics (carbon tetrachloride, chloroalcyl ethers, and he utadiene), xachlorob
high molecular weight hydrocarbons (dyes, gasoline, amines, humics, and k erosene,
oil), and surfactants (alkyl benzene sulfonates).
y
,
(b) Inorganic compounds : chlorine, bromine, iodine, fluoride, antimon arsenic, bis-
,
,
muth, chromium, tin, solv mercury cobalt, and zirconium.
er
In contrast, organic compounds like alcohols, lo acids and -weight k w-molecular etones,
aldehydes, sugars and starches, very high molecular weight or colloidal or lo ganics, w-
molecular-weight aliphatics, and inorganic compounds such as nitrate, phosphate, chlo-
el,
anadium,
ride, bromide, iodide, lead, nick titanium, v iron, copper cadmium, zinc,
,
barium, selenium, molybdenum, manganese, tungsten, and radium are poorly absorbed on
activated carbons.
There are a number of cases where carbon adsorption is preferably used in water treatment:
• if compounds are not compliant for biode gradation,
• if the molecule contains branched chairs, has a large molecular weight, and lo w polar-
ity,
• in the case of removing solids for concentrations lower than 50 ppm,
• in the case of removing oil for concentrations is lower than 10 ppm,
• generally, in the case of removing organics and inorganic species, for concentrations
lower than 5000 and 1000 mg/L, respecti ely v .

Besides the applications of water treatment, acti ated carbon is called into action for the v
ents,
removal of volatile organic compounds such as solv toxic gases, and odors from
ide,
gaseous waste streams. Hydrogen sulf mercury and radon can also be remoed from v
,
gas streams by means of chemically impregnated carbons. In f among the adsorbents, act,
it is the most attractive material because it is the only common nonpolar adsorbent (Noble
and Terry, 2004). The polarity of the adsorbent’ace plays a major role in the type of s surf
the compounds that can be adsorbed. Polar adsorbents will preferentially adsorb moisture
in gaseous waste streams, and as a result their usage in such applications is limited. In con-
v
trast, actiated carbon is an appropriate material in such cases, where the goal is the con-
trol of emissions of organic solv odors, toxic gases, acid v phenols, and
ents,
apors,
hydrocarbon vapors.
Some basic rules for carbon adsorption are the follo wing:
• Larger molecules adsorb better than smaller molecules.
• Nonpolar molecules adsorb better than polar molecules.
• Nonsoluble or slightly soluble molecules adsorb better than highly soluble molecules.
• On the basis of the polarity or solubility or both, of the molecule being adsorbed, the
,
v pH may hae an influence on the extent of adsorption.
• Temperature increases the rate of diffusion through the liquid to the adsorption sites;
but since the adsorption process is exothermic, increases in temperature may reduce the
degree of adsorption. This temperature effect is negligible in w-treatment applica- ater
tions and ambient v apor -phase applications.