IDENTIFICATION OF REMOVAL MECHANISMS FOR LEAD IN GRANULAR ACTIVATED CARBON (GAC) COLUMNS

In an earlier study the removal of lead by a granular activated carbon (GAC) column was increased by over 600% when the carbon ]Hydrodarco 4000 (HD4000), Norit Americas, Inc.] was contacted with a 0.1 N HNO3-0.1 N NaOH rinse. Hypothesized removal mechanisms were adsorption, surface preceipitation, and pore precipitation. In this work a series of experiments were conducted on samples of the virgin and acid-base rinsed carbon to determine their acid-base behavior, pH(zpc), and Pb removal ability. If adsorption was a dominant removal mechanism, then significant differences in these parameters for the virgin and acid-base rinsed carbons would be expected. The strong acid-base rinse did not significantly alter the acid-base behavior, pH(zpc), or the Pb removal ability compared to virgin HD4000. Thus, it appears that the dramatic increase in metal removal by the regenerated GAC columns was not caused by an increase in the number or type of adsorption sites but was due to the precipitation of Pb on the carbon surface or in the carbon pore liquid. Future research efforts will focus on the modeling of Pb removal in GAC columns using precipitation as the primary removal mechanism.