A preliminary batch study of sorption kinetics of Cr(VI) ions from aqueous solutions by a magnetic ion exchange (MIEX®) resin and determination of film/pore diffusivity

A magnetic ion exchange resin was tested for the removal of Cr(VI) ions from aqueous solutions in a batch reactor at different resin dosages (0.5-1.5 g L− 1), pH values (2 − 10), temperatures (25 °C-55 °C) and initial concentrations of Cr(VI) (0.11-2.12 mmol L− 1 or 5.7-110 mg L− 1). The experimental data were evaluated using kinetic models based on the rate controlling steps relevant to pseudo-first order or pseudo-second order reactions or diffusion through fluid film or pores of the MIEX resin beads. Fast uptake of Cr(VI) ions by MIEX resin facilitates the attainment of equilibrium within 60 min. The sorption process is strongly dependent on the initial pH of the solution with maximum occurring at pH 4-6. The sorption of Cr(VI) at equilibrium increases with the increase in initial concentration according to the Langmuir isotherm, with a maximum sorption capacity of 93 mg g− 1 on MIEX resin. Relatively low activation energy of 43 kJ mol− 1 at a high initial concentration of 1 mmol L− 1 Cr(VI) suggests a mixed chemical-diffusion controlled process, supported by the agreement of the sorption results with the homogeneous particle diffusion model with a film diffusivity of Df = 1 × 10− 9 m2 s− 1 and a pore diffusivity of Dp = 8 × 10− 13 m2 s− 1.