Removal of Trace Organic Compounds Dissolved in Water. V.

Abstract

The adsorption equilibria of benzene derivatives (phenol, benzoic acid, nitrobenzene, and aniline), 1-hexanol, and heptanoic acid on activated carbon in aqueous solutions was studied. The activated carbon used as the adsorbent was Pittsburgh Activated Carbon (Calgon Co.). The adsorption isotherms were in good agreement with the Freundlich-type isotherm. The adsorbed amount of adsorbate increased with decreasing its solubility in water, except for phenol. The adsorbed amount of phenol was particularly large. To clarify the relationship between the surface-chemical structure of the activated carbon and the adsorption character of phenol, the activated carbon was treated with hydrochloric acid, hydrofluoric acid, and hydrogen-gas, and the adsorbed amounts of the above-mentioned adsorbates on the activated carbon were determined. The surface-modified activated carbon had the same pore structure as the surface-unmodified activated carbon, but surface-chemical structures differed. The adsorption isotherms were in good agreement with the Freundlich-type isotherm. All adsorbed amounts of adsorbates were larger for HCl·HF·H2 treatment than without modification. It thus seems that there is no specific interaction between the phenol molecule and the surface-chemical structure of the activated carbon. To investigate the influence of the ionization of phenol, the adsorbed amounts of phenol, benzoic acid, and aniline on an activated carbon treated with HCl·HF·H2 were measured over a wide pH range of their solutions. The adsorbed amounts of phenol and benzoic acid decreased with increasing pH. The adsorbed amount of aniline decreased with decreasing pH. Thus the adsorbed amount of phenol, benzoic acid, or aniline decreased with an increase in the amount of adsorbate ionized. The ionization constant of phenol was smaller than those of other adsorbates. Consequently, it is thought that phenol is adsorbed specifically owing to its small ionization constant.