Effect of OH-/Al3+ and Al3+/clay ratios on the adsorption properties of Al-pillared bentonites

In this work, the adsorption properties of Al-pillared bentonites were investigated by using phenol and 2-chlorophenol as model pollutants. The Al-pillared bentonites were prepared by the conventional method of pillaring involving the mixing of a dilute clay suspension with a dilute pillaring solution. To study the effect of textural changes on the adsorption properties, the adsorbents were prepared by using different OH-/Al3+ and Al3+/Clay ratios. It was determined that the adsorbed amounts of phenol decrease with increasing OH-/Al3+ and Al3+/clay ratios. Adsorption of 2-chlorophenol on the adsorbent adsorbing the highest amount of phenol was studied. It was found that the amounts adsorbed are nearly same for both of the adsorbates at low equilibrium concentrations and a slight difference is observed at concentrations exceeding 60 mg/L. The adsorbed amounts were compared with the amounts adsorbed by hexadecyltrimethylammonium bromide (HDTMA)-bentonite. It was obtained through the modification of bentonite with hexadecyltrimethyl ammonium bromide, in an amount equivalent to 100% of cation exchange capacity of the clay. It was observed that the adsorbed amounts of phenol are approximately three times higher in the case of Al-pillared bentonite having 1.44 and 1.8 OH-/Al3+ and Al3+/Clay ratios, respectively. This behavior is attributed to the high surface area. Although the adsorbed amounts of 2-chlorophenol on the Al-pillared bentonite are same with that of phenol, they are lower than the amounts adsorbed on HDTMA-bentonite and it was concluded that the existence of pseudo-organic layer is of importance in the case of the adsorbates having low water solubility and the form of the sample I modified with HDTMA will be more efficient. (C) 2006 Elsevier B.V. All rights reserved.