16    SORPTION PROCESSES OF BENTONITE WITH
LIQUID ORGANICS
A. Mahendra Rodrigo, Graduate Student
Paul C. Chan, Professor
Department of Civil and Environmental Engineering
New Jersey Institute of Technology
Newark, New Jersey 07102
INTRODUCTION
The contamination of surface and subsurface environment due to toxic and hazardous pollutants
has become a serious problem as it threatens the human lives. Various standards regarding the
drinking water, industrial effluents and waste disposal have been set up by regulatory agencies in
order to minimize the health hazards. For example, the U.S. Environmental Protection Agency has
published a priority list of pollutants consisting of 129 organic contaminants1 in conjunction with
stipulated stringent regulations.
Studies have been performed extensively on the migration of toxic and hazardous wastes in soils
and ground water systems in order to identify the factors affecting the movement of these substances.
The transport and fate of these contaminants in ground water systems are found to be dependent
upon the chemical and biological reactions including binding rate, capacity and strength of pollutants
to soil particulates. The binding of contaminants may be through the ion exchange reactions, adsorption or precipitation of them onto soil particles. The sorption characteristics of contaminants are
governed by the material properties as well as the environmental factors. The influence of these
variables on the binding of toxic pollutants onto clays are not well established. In fact, various
investigators have attempted to study the kinetics and strength of sorption of chemicals onto clay
soils. However, very few studies have been performed on the reversibility of the sorption processes,
which is useful in examining the leachability of sorbed compounds. So far, it was identified (e.g.,
Means and Wood,2 La Poe,3 Greenland and Laby4) that the organic carbon content of soil, the
solubility and octanol-water partition coefficient of the solute to be the most crucial solid and solute
parameters with regard to the sorption characteristics.
In ground water modeling, it is of utmost importance if one can predict the equilibrium sorption
capacities and reaction kinetics of pollutants in conjunction with their leachability. One of the prevailing problems in contaminated sites is the leaching out of the sorbed components from the soil matrix.
Furthermore, it has been found that the sorption of pollutants onto the hydraulic barriers could result
in deterioration of them leading to an ultimate failure, which may be due to the increase in permeability, excessive cracking or consolidation.
The overall objective of this research is to study the sorption characteristics of hazardous and toxic
liquid organics and their effects on the geotechnical properties of clay soils.
BACKGROUND
In this chapter the sorption processes between solutes (i.e., liquid organic pollutants) and solids
(i.e., soils) were considered. The sorption of liquid-solid systems has been studied by various investigators. They have correlated the sorption characteristics with physical properties of soils and solutes.
A study by Greenland et al.4 on the adsorption of glycine and its di-, tri- and tetra-peptides on Ca-
montmorillonite shows linear isotherms, suggesting a partition between solution and the stern layer of
the adsorbent. This type of an isotherm is characterized by constant partition of adsorbate between
solution and adsorbent. Linearity of the curve indicates that the number of sites for adsorption
remains constant (i.e., as more solute is adsorbed more sites become available).
Singhal and Singh5 concluded, on the basis of adsorption isotherms and X-ray analysis that the
physical adsorption was the primary mechanism of adsorption of Nemagon onto bentonite. Physical
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
115