77    BINDING CHARACTERISTICS OF HAZARDOUS ORGANIC
SUBSTANCES TO CLAY SOILS
G.A. Selvakumar, Graduate Assistant
A.M. Rodrigo, Graduate Research Assistant
P. Chan, Professor
Civil and Environmental Engineering Department
New Jersey Institute of Technology
Newark, New Jersey 07102
INTRODUCTION
Hazardous and toxic pollutants have been found in groundwater as a result of accidental spills,
leaks, and intentional disposal from industrial and municipal waste disposal systems. As a result, the
ground water contamination is at an alarming state and poses a health hazard. The U.S. Environmental Protection Agency has published the priority pollutant list,1 consisting of organic contaminants in
conjunction with stipulated stringent regulations.
The disposed liquid organic contaminants may percolate through the vadose zone and reach the
water bearing aquifers. During the migration of contaminants towards the water bearing aquifers, the
contaminants are constantly in contact with the soil. However, the fate of these contaminants is
dependent upon chemical and biological reactions, including sorption kinetics. Certain chemicals that
are hydrophobic and non-reactive in nature cause more affinity to solid particles than that of water.
In the case of clay soils, the negative surface charges tend to bind dipolar organic compounds to form
a diffuse electrical double layer. Hence, the degree to which the liquid organic contaminants are
bound to the clay particles is one of the key factors which controls the contaminant transport. Thus,
the rate, capacity and strength of sorption must be included in determining the fate of the contaminants in the groundwater system.
A research project to identify and quantify the important factors influencing the binding of toxic
and hazardous organic compounds to clay soils has been initiated at New Jersey Institute of Technology. Results of the batch study on illite with phenol, chlorophenol and chlorobenzene are presented in
this paper.
LITERATURE REVIEW
The sorption of chlorinated hydrocarbon pesticides onto clay minerals was studied by Huang and
Cheng.2 They found that there are varying amounts of sorption capacity in clay minerals, which
depend upon the type of clay and pesticides. They also pointed out that desorption could occur if the
pesticides coated soil particles are subjected to washing. This can act as a source of supply of toxic
compounds into the groundwater system. Because of the sorption capacity of clays, a number of
investigators have attempted to use clays and clay mixtures in attenuating heavy metals and other
pollutants from the waste effluents before their ultimate disposal.3
Weber4 identifies two primary driving forces for adsorption. The first involves the degree of
solubility of the dissolved substance, while the second involves the affinity of the solute for the solids.
In the first case, a hydrophobic substance is literally driven from the liquid phase to the solid phase
where adsorption occurs. Then a process of exchange adsorption occurs, in which ions of a substance
accumulate at the surface of the solid due to electrostatic attraction. Therefore, the smaller the
particles, the greater the specific surface area and hence the greater the sorption capacity.
Hurle and Freed5 predicted that adsorption decreases and mobility increases as the solubility of
solute in the solvent increases, i.e., the hydrophobic nature of sorbants results in more adsorption by
clay soils.
Recently, Uchrin and Katz6 studied the sorption characteristics of Lindane to New Jersey coastal
plain aquifer soils which is predominantly sand. They identified two components of adsorption as
reversible and resistant. A considerable discussion on the sorption process, including reversibility and
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