INFLUENCE OF SURFACE-IONIZATION ON THE ADSORPTION OF AQUEOUS ZINC SPECIES BY ACTIVATED CARBONS

A surface ionization and adsorption model is used to simulate the adso rption of zinc species From aqueous solutions of varying pH on a numbe r of different activated carbons and the results compared with experim ental data. In all cases good agreement is obtained between theory and experiment. It is shown that for most of the carbons the uptake of zi nc is due to adsorption of Zn2+ ions on ionized acid sites, the calcul ated equilibrium constants being of the order of 10(6)-10(7). On the o ther hand, one of the carbons used (NORIT AZO) contains virtually no a cid sites, but a high concentration of strong basic sites, and the upt ake of zinc in this case appears to be due to adsorption of a negative ly charged hydroxy complex on protonated basic sites, the estimated eq uilibrium constant being 10(8). (C) 1997 Elsevier Science Ltd.