ADSORPTION EQUILIBRIUM IN THE SYSTEM 'Cr (III) - ACTIVATED CARBON'

摘要

It is well known, that the net surface charge is important in controlling the adsorption, so far as the metal cations sorption is encouraged on the negative species. Therefore, it would be expected that Cr (III) uptakes should increase as initial pH increases due to the deprotonation of the carbon activated sites. However, close inspection of the obtained kinetics data for the studied systems has revealed that the situation is not entirely straightforward. The adsorption has been found to be maximal at pH 2 and pH 3.2 when complete equilibrium in the studied systems "Cr (III) - activated carbons" has been reached. The adsorption equilibrium studies have revealed the dynamic character of the Cr (III) - carbon interaction as a function of the pH and have confirmed the slow kinetics for the studied system to accomplish the equilibrium. Therefore, we have considered that an important factor for the kinetics and equilibrium state in the studied systems is the affinity of each Cr III species for each of the surface sites at different pH media. Thus, at the pH range of the maximum adsorption, i.e. 2H>3.5 the adsorption mechanism has been suggested to be the superposition of the different operating mechanisms with the ion-exchange and adsorption-complexation as a prevalent ones, This hypothesis is currently being explored and our on-going research will address the modelling work of the Cr (III) adsorption on activated carbon.