Effect of pH Adjustment Upon
Activated Carbon Adsorption of Dissolved Organics
From Industrial Effluents
LAWRENCE K-P. WANG,
RICHARD P. LEONARD
Cornell Aeronautical Laboratory
Cornell University, New York
DENNIS W. GOUPIL
University of Cincinnati
Cincinnati, Ohio
MU-HAO SUNG WANG
Rutgers University, New Jersey
INTRODUCTION
Highly porous carbon, activated by either thermal or chemical means, is by far the
most important of the adsorbents in current use in the field of environmental pollution
control.
The adsorption of a dissolved component by activated carbon can be divided into three
steps (1). The first step is the transport of the adsorbate to the exterior surface of the
adsorbent. The second step, with the exception of a small amount of adsorption that occurs
on the exterior surface, is the diffusion of the adsorbate into the carbon pores. The third step
is the adsorption of solute on the interior surfaces of the adsorbent.
Carbon adsorption processes can be of three types: physical adsorption, chemical
adsorption, and electrostatic adsorption (2). Physical adsorption results from molecular
condensation in the micropores of the activated carbon by so-called inner Van Der Waalsor
dispersion forces. Chemical adsorption results in the formation of a chemically-bound
monomolecular layer of the adsorbate on the surface through residual valence forces of the
surface molecules. Electrostatic adsorption describes the influence of electrical attractive
forces responsible for adsorbing solutes on activated carbon. Further, electrical attraction
between negatively charged carbon particles and positively charged adsorbate molecules or
ions reduces barriers to diffusion, and, thus, increases the adsorption efficiency.
Factors affecting adsorption include carbon dosage, type of carbon, time of contact,
concentration of the solution, temperature of treatment, pH of the solution, and type of
solvent. The purpose of this study was to review, organize, and further explore the pH effect
upon carbon adsorption of organics from single and multicomponent aqueous systems.
The influence of pH on activated carbon adsorption of organic compounds from
aqueous solution depends, of course, on the physico-chemical properties of individual
organic species. This paper suggests explanations for changes in measured adsorption of
various types of organic compounds effected by lowering or raising hydrogen ion
concentration. Types of organic compounds included in this study were anionic and
cationic surfactants, ionic low molecular weight organics and nonionic solutes. Industrial
effluents included in this study were paper mill waste and glue factory waste.
EXPERIMENTAL PROCEDURES
The powdered activated carbon used in confirmatory experiments was Aqua Nuchar
A, supplied by Westvaco Chemical Division. It had been finely ground to pass a 325 mesh
sieve and had a minimum carbon content of 93 percent and was used as received. Organic
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