Dynamics analysis of anion exchange in layered double hydroxides

Abstract

The anion exchange kinetics between NO 3 − and benzoate (BA) in layered double hydroxides (LDHs) have been studied. The experimental conditions were selected to favour a particle diffusion rate-controlling mechanism, subsequently confirmed by the variation of the exchange rate with temperature, resin bead size and stirring speed. Furthermore, the parallel diffusion model is successfully validated in this anion exchange process. Intraparticle effective diffusivities (D eff) of BA in these NO 3-LDHs macroparticles were determined from the homogeneous Fickian diffusion model at various temperatures. Crystallites diffusion is the rate-controlling step, in which the anion exchange in the interlayer is much slower than the anion diffusion in the pores between the crystallites. Keywords LDHs • Anion exchange • Parallel diffusion • Benzoate p = D p t∕r 2 0 c = D c t∕r 2 0 θ The apparent density, kg of wet NO 3-LDHs m −3