ADSORPTION OF PHENOL AND CHLOROPHENOLS FROM AQUEOUS-SOLUTION BY MODIFIED ELUTRILITHES

Modified elutrilithes were prepared by treating natural sample with calcium chloride or zinc chloride. Natural and treated products (Ca-Elut and Zn-Elut) were examined for their adsorptive properties towards phenol and several of its chlorinated congeners. The modified elutrilithes show, in contrary to the natural forms, a high adsorption capacity and high affinity for these organic compounds. The adsorption of the phenols from aqueous solution can be related to their hydrophobicities. Indeed the adsorption capacities and affinities can be related to the number of chlorine atoms on the phenol structure, phenol < chlorophenol < dichlorophenol < trichlorophenol. Hence, the adsorption capacity was not limited by the molecular size of the adsorbate. For the Zn-Elut adsorbent, the adsorption of phenols increases with increasing the pH of the aqueous solution. Maximal adsorption was observed at a pH close to the pK(a) of the adsorbate, and decreases sharply at larger pH values. The temperature, however, has a small influence on the phenols adsorption on Zn-Elut. In general, the adsorption of phenols increases with decreasing temperature. The strong bond between the phenols and the modified elutrilithes causes the high affinity (type-I adsorption isotherm according to the Langmuir model, indicating.a homogeneity of the adsorption sites on modified elutrilithes). Furthermore, the adsorption-desorption experiments demonstrated that the 3,5-dichlorophenol adsorption on Zn-Elut was a irreversible process. Between the two modified elutrilithes investigated, Zn-Elut exhibited larger adsorption capacities for phenols and was superior to modified clay materials.