Adsorption of phenol and chlorophenols on hexadecyltrimethylammonium-and tetramethylammonium-montmorillonite from aqueous solutions

Batch experiments were carried out at 25°C to obtain the adsorption isotherms of phenol, 2-cholorophenol, 4-chlorophenol and 2,4-dichlorophenol on hexadecyltrimethylammonium-exchanged-and tetramethylammonium-exchanged-montmorillonite (HDTMA-M and TMA-M) prepared from Wyoming bentonite SWy-2. The isotherms were interpreted principally using the Freundlich model. The reaction orders (n) and Freundlich constants (kF) for the adsorption of an adsorbate on HDTMA-M and TMA-M remain approximately constant against the variation of adsorbate to adsorbent ratios. Then value for most of the phenolic adsorbates on HDTMA-M is close to unity, indicating Langmuir-type adsorption but that on TMA-M is variable among different phenolic adsorbates. The degree of adsorption of phenolic compounds on HDTMA-M is primarily controlled by the hydrophobicity of the adsorbates but those on TMA governed by the complicated combinations of size, shape and hydrophobicities of the adsorbates. The estimated model parameters for the adsorption isotherms on HDTMA-M are in disagreement with those of earlier workers probably because of the differences in experimental conditions. This study also estimated the model parameters on TMA-M, which are not available in the literature.