Competitive Adsorption of p-Hydroxybenzoic Acid and Phenol on Activated Carbon: Experimental Study and Modeling

The competitive adsorption of phenol and p-hydroxybenzoic acid (4HBA) has been investigated on activated carbon (AC) for a wide range of concentrations under unbuffered conditions. The results show a preferential adsorption of 4HBA, which can be explained by the lower solubility of 4HBA and the electrostatic interactions between the AC and the ionic form of the molecule in this range of pH. The Langmuir isotherm was found suitable to describe the single-component adsorptions, indicating a monolayer adsorption in accordance with the microporous nature of the AC. Then the empirical extended Langmuir model and the predictive ideal adsorption solution theory model have been compared for competitive adsorption. When using parameter values optimized for single pollutants, both models show rather poor agreement with mixture data. However, after fitting the extended Langmuir parameters with the whole data set, better results can be obtained, showing that there is some peculiar behavior of the mixture under oxic conditions, probably tied to the effect of 4HBA on the irreversible adsorption of phenol. DOI: 10.1061/(ASCE)EE.1943-7870.0000600. (C) 2013 American Society of Civil Engineers.