ADSORPTION PROPERTY OF AROMATIC SULFONATE IONS BY HEAT-TREATED LAYERED DOUBLE HYDROXIDES

The adsorption of 2-naphthol-3,6-disulfonate (NDS) and m-benzenedisulfonate (BDS) ions with the oxide solid solutions prepared by the thermal decomposition of synthetic Mg-Al and Zn-Al carbonated layered double hydroxides was investigated at 25-degrees-C. Both of the oxides were found to adsorb these anions to reconstruct the layered double hydroxide structure. In the case of the Mg-Al system, the Freundlich adsorption isotherms bent at about 0.2 mmol.dm-3 of the equilibrium concentration were obtained. This is due to the fact that the higher equilibrium pH of 11-12 causes a preferential adsorption of OH- in the low concentration region of the sulfonate ions. On the other hand, the Freundlich adorption isotherms obtained in the Zn-Al system became straight line because of the lower equilibrium pH of 9-10 (Fig.2). In both systems, the adsorbed amount of NDS was larger than that of BDS, and the interlayer distance of the solid products varied with the size and adsorbed amount of the guest anions (Fig.3).