Adsorption of Humic Substances in the Presence of Sodium Salts

Inorganic sodium salts were found to enhance the adsorptive capacity of activated carbon for humic substances. The interactions between the salts and the surface of the carbon were investigated as a function of salt type and concentration by zeta potential measurements. At a constant pH, increasing the concentration of humic substances markedly increased the magnitude of the negative value of the zeta potential, whereas increasing salt concentration neutralized the zeta potential. The anion of the salts had little effect on adsorptive capacity or on the change in the zeta potential. Sodium ion concentration is thus the primary factor responsible for the increased adsorption of humic substances, probably via the neutralization of negative charges on both humate molecules and carbon surface functional groups.