Adsorption Parameters and Superficial Species in the Nickel-Alumina System

Abstract

The equilibrium adsorption of nickel on γ-alumina was studied at 293 and 333 K. Nickel nitrate solutions in the range 0.1 - 2% (w/v, expressed as NiO) were used. Both the equilibrium constant and the number of adsorption sites increased with the adsorption temperature. Adsorption and desorption rate constants were estimated by fitting a theoretical model to the profiles obtained by impregnation of γ-alumina thin layers with nickel nitrate solutions. Representative solid samples differing in nickel contents were studied along both isotherms by X-ray diffraction, diffuse reflectance and X-ray photoelectron spectroscopy. It is concluded that, in the composition range studied, nickel forms a partially inverted spinel (NiAl2O4); the degree of inversion being greater in the samples prepared at 293 K than in those corresponding to 333 K. Also, the dispersion of nickel species is constant for each adsorption temperature.