Adsorption and desorption of heavy metals on α-alumina

Abstract

Adsorption of Mn, Zn, Co, Ba and Ra from solutions in the range 10^-5-10^-10 mol^-1 was measured in varying degrees of detail on α-alumina. It was found that (i) below a limiting concentration of about 1 × 10^-1 moll^-1, the logarithmic adsorption isotherm was linear whereas, above this limit, the logarithmic adsorption isotherm was curvilinear for Ba, Ra, Mn, and Co but linear for Zn with a slope of 0.51 ; (ii) below this limiting concentration, the pH at 50% adsorption was independent of solution concentration; and (iii) this limiting concentration was independent of the adsorbing metals studied. An adsorption model for the concentration-independent regime was developed based on adsorption at high energy, negatively charged adsorption sites by M(OH)ⁿ⁺ ions without accompanying proton release from either the surface or the adsorber.