KINETIC INVESTIGATION AND SURFACE COMPLEXATION MODELING OF Cd(II) ADSORPTION ONTO FELDSPAR

Abstract

The aim of this study is to determine the feldspar adsorption kinetics and isotherm of Cd(II) and to model the adsorption data with the aid of a metal-surface binary complexation approach. The adsorption of Cd(II) ion onto feldspar was approximated using a triple-site model by the aid of the FITEQL 3.2 computer program calculating the relative distribution of surface species. Experiments were carried out at I=0.1 ionic strength using an inert electrolyte (NaClO4). Of the three metal-binding surface sites of feldspar, it was assumed that (K,Na,Ca,Mg)X represents ion exchangable negative-charged sites, -S1OH silanol groups, and -S2OH pH-dependent aluminol groups. Metal hydrolysis was neglected under the experimental conditions employed, and Cd(II) was assumed to bind to the clay surface as the sole Cd2+ cation. The equilibrium constants of the reactions between Cd(II) ion and the surface sites were calculated using FITEQL 3.2. Cd(II) adsorption on feldspar showed Langmuiran character and pseudo-first order kinetics. The maximum adsorption capacity of feldspar for Cd(II) ions was found as 1.29 mg metal ion/g adsorbent. The results of this study are believed to facilitate the solution of environmental problems like metal ion migration and adsorptive treatment by clay minerals.