Acid‐Base Characteristics of Powdered‐Activated‐Carbon Surfaces

Adsorption of heavy metals onto activated carbon has been described using the surface‐complex‐formation (SCF) model, a chemical equilibrium model. The SCF model requires a knowledge of the amphoteric nature of activated carbon prior to metal adsorption modeling. In the past, a single‐diprotic‐acid‐site model had been employed to describe the amphoteric nature of activated‐carbon surfaces. During this study, the amphoteric nature of two powdered activated carbons were investigated, and a three‐monoprotic site surface model was found to be a plausible alternative. The single‐diprotic‐acid‐site and two‐monoprotic‐site models did not describe the acid‐base behavior of the two carbons studied adequately. The two‐diprotic site was acceptable for only one of the study carbons. The acid‐base behavior of activated carbon surfaces seem to be best modeled as a series of weak monoprotic acids.