Adsorption of Acid Dyes on Hydrotalcite-Like Anionic Clays

Abstract

Hydrotalcite-like anionic clays have attracted considerable attention in last few decades for their capacity to remove wide range of pollutants from aqueous systems. In this chapter, we discuss our recent studies on synthesis of anionic clays with various compositions (Mg/Al, Zn/Al and Ni/Al) and concentrations and their application for the removal of acid dyes from water. Adsorption efficiencies of the synthesized clays were investigated for the dyes, Acid Blue 113 and Orange II, in aqueous medium. Very high dye uptake capacities were recorded for both the above dyes by using Mg/Al clay (M2+: M3+molar ratios 2 and 3) having NO3-interstitial ion. Adsorption equilibria data were explained using Langmuir and Freundlich isotherm models, however, Langmuir model fitted better than the Freundlich model. Lagergren first order and pseudo-second order kinetic models were used to explain the dye adsorption kinetics of the pristine clay materials. X-ray diffraction studies of the pristine clays and dye loaded clays indicate both anion exchange and physical adsorption were involved in the Orange II uptake process however, uptake of Acid Blue 113 was solely due to physical adsorption. Influence of solution pH on dye uptake by the clay adsorbents and on equilibrium pH of the solution after adsorption was investigated.