ADSORPTION OF HUMIC SUBSTANCES ON ACTIVATED CARBON FROM AQUEOUS-SOLUTIONS AND THEIR EFFECT ON THE REMOVAL OF CR(III) IONS

The adsorption of different compounds such as gallic, tannic, and humi c acids on an activated carbon at 298 K has been studied. The capacity of this carbon to adsorb gallic acid is much higher than for the othe r two acids, which has been explained on the basis of both their molec ular size and ionization degree. The influence of dissolved Cr(NO3)(3) On the adsorption of these acids has been investigated. The capacity of the carbon to adsorb gallic and tannic acids in the presence of Cr( III) is slightly higher than in the absence of this metal. The variati on of the surface properties of the carbon, both porous texture and ch arge, with the adsorption of these humic substances also has been test ed. The porous texture changes have been studied from the N-2 adsorpti on isotherms and the changes in the carbon surface charge from the pH drift tests. The results indicate that the adsorption of these acids o n the activated carbon brings about, to a greater or lesser extent, bo th pore blockage and an increase in the negative surface charge of the carbon. Finally, changes in the amount of Cr(III) adsorbed on the car bon as a function of the concentration of each of these three acids ha ve been studied. A large decrease in the Cr(III) uptake is observed wh en these acids are present at low concentrations due to the pore block age effect of the acid adsorbed on the carbon surface. When the acid c oncentration increases, the Cr(III) uptake also increases due to inter actions of the Cr(III) cations with the negatively charged unbound fun ctional groups of the adsorbed acid.