REGENERATION OF ACTIVATED CARBON
FOR THE ADSORPTION OF CHROMIUM
Min-Hwang Wu, Graduate Student
Deh Yuan Hsu, Assistant Professor
Department of Civil Engineering
Wayne State University
Detroit, Michigan 48202
Chin-Pao Huang, Assistant Professor
Department of Civil Engineering
University of Delaware
Newark, Delaware 19711
INTRODUCTION
Recent studies have shown that chromium can be effectively removed by the carbon
adsorption process [1-7], but the practical application of this technique to the treatment
of industrial wastewater depends not only upon the adsorption capacity but also on the
feasibility of regenerating the spent carbon.
Work done on the regeneration of chromium-loaded activated carbon is scant.   Smith-
son [2] demonstrated that by caustic regeneration of Pittsburgh OL carbon, about 76%
of the adsorbed chromium could be stripped off.   Landrigan and Hallowell [7] modified
the caustic regeneration process by first aerating the carbon particles, which had been
wetted by 20% NaOH-500 mg/1 EDTA solution, and then desorbing the chromium attached
by 20% NaOH solution.   The regeneration efficiency was found to be unstable, ranging
from 51.4% to 99.75% in eight identical cycles of operation.
The major objective of this research was to study some physical and chemical techniques for the regeneration of chromium-loaded activated carbon.   Three regeneration
methods were investigated:   caustic desorption, thermal activation, and a combined
caustic-thermal process.   Calgon filtrasorb 400 activated carbon was used as the adsorbent.
The technique for the preparation of the chromium-loaded carbon, i.e., carbon adsorption process, was also studied.
MATERIALS AND PROCEDURE
A commercial activated carbon, Calgon filtrasorb 400, was used.   According to the
manufacturer, the carbon had a total surface area of 1050-1200 m5/g (Nj, BET method)
and a size distribution of #12-40, 96% minimum.   The source of chromium was prepared by dissolving sodium chromate (Na2CrO« ■ 4H20) in distilled water.
In order to prepare chromium-loaded carbon for regeneration, and to evaluate the
regeneration efficiency through the readsorption process, experiments including adsorption equilibrium and adsorption kinetics were first conducted to establish the optimum
pH Cr (VI)/C ratio, and contact time for chromium removal.
Adsorption Equilibrium
The adsorption experiment was prepared by adding 10 g/1 carbon to a total of 50 ml
solution containing chromium from 25.3 to 453.7 mg Cr(VI)/l and a constant ionic
strength of 0.1 M NaCl.   The pH of each solution was adjusted to various initial values
with 1 M HC1 and 1 M NaOH in order to give an equilibrium pH ranging from 2 to 10
after the adsorption process.   The samples were then shaken constantly at a frequency
of 200/min with a gyrotatory machine for 24 hr at room temperature (23+ 1 C).   At
the end of the reaction period the equilibrium pH was recorded; the carbon particles
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