25    MODELING OF COPPER(H) REMOVAL BY IRON
OXIDE-COATED GRANULAR ACTIVATED CARBON
Tachung Wang, Graduate Student
Paul R. Anderson, Associate Professor
Pritzker Department of Environmental Engineering
Illinois Institute of Technology
Chicago, Illinois 60616
INTRODUCTION
Although Fe oxides (includes oxide, hydroxide, and oxyhydroxide Fe minerals) are recognized
as effective adsorbents for heavy metals, oxide adsorbent-based treatment processes have been
limited by their small particle size. When present as a discrete mineral phase in wastestreams, Fe
oxide particles are typically in a colloidal size range that is difficult to remove from aqueous solution. To overcome this limitation, some possible alternatives were described by Edwards and
Benjamin (1989), Huang and Vane (1989), and Theis et al. (1992, 1994), who used sand or activated carbon as the supporting medium for iron oxide precipitates, or cemented iron oxide with a
proprietary binding material.1^1 These adsorbents can solve the particle size problem associated
with iron oxide for use in a column process with promising abilities for both cationic and anionic
metals removal and recovery. For example, Edwards and Benjamin used iron oxide coated sand
as an adsorbent filter media to treat several cationic metals (Cd, Cr, Cu, Ni, and Pb) in a
column.1 Huang and Vane prepared an Fe2+ treated activated carbon to remove anionic As5+
from aqueous solution.2 Finally, Theis et al. produced a granular Fe oxide adsorbent for treating
cationic Cd and Pb, and anionic Cr metals in a mini-column process.3-4 Because the capacity of
these adsorbents for metals depends on the amount of iron oxide on the adsorbent surface, activated carbon would seem to have an advantage as a substrate because of its large surface area.
Therefore, we present some results of our work with a composite adsorbent made from Fe oxide
and granular activated carbon. A major objective of this work was to select an appropriate equilibrium model to describe the adsorption isotherm, and to show how a first or second order reaction or homogeneous surface diffusion models could be used to model the adsorption process in
the batch system.
BACKGROUND
Adsorption Isotherms
Common equilibrium models for describing adsorption include Freundlich and Langmuir
isotherm equations. The Langmuir isotherm (Equation 1) was developed on the assumption of a
monolayer adsorption, the same site energy on the adsorbent surface, and no adsorbate migration
after adsorbing on the adsorbent surface.
abC
q =  (i)
1 + bC
where q   ■   adsorbed metal concentration, M/M
C   =   soluble metal concentration, M/L3
a, b  =  model parameters
50th Purdue Industrial Waste Conference Proceedings. 1995, Ann Arbor Press, Inc., Chelsea. Michigan 48118.
Printed in U.S.A.
227