Experimental measurement and modeling of ion exchange equilibrium and kinetics of cadmium(II) solutions over microporous stannosilicate AV-6

Abstract

Microporous stannosilicate AV-6 was investigated for cadmium(II) removal from aqueous solutions in batch experiments. Ion exchange equilibrium of the Cd2+/K+/AV-6 system was modeled using the mass action law combined with activity coefficient models for the solution (ideal, Debye–Hückel and Pitzer equations) and for the solid (Wilson equation) with absolute average relative deviations (AARDs) between 6.56% and 6.75%. It was concluded that the system embodies strong intraparticle non-idealities, namely solid activity coefficients between 0.2602 and 0.7180 for Cd2+. The kinetics of cadmium(II) sorption was analyzed measuring removal curves and modeling the data with pseudo-first and pseudo-second order expressions, commonly adopted in the literature, and with Maxwell–Stefan (MS) and Nernst–Plank (NP) based models. The best results were achieved by MS and NP approaches, for which AARD was 3.74% and 3.71%, respectively. The kinetic performance of the ion exchange was also discussed taking into account structural aspects of the AV-6 material.