Removal of Co2+ ions from aqueous solutions using iron-functionalized sepiolite

The efficiency of iron-functionalized sepiolite for the removal of Co2+ ions from aqueous solutions was determined under different experimental conditions, using the batch method. The ionization constants of the surface functional groups of the sepiolite–iron system, determined from potentiometric titration data, were p K a 1 int = 6.7 ± 0.1 and p K a 2 int = 10.2 ± 0.1 . The sorption experiments were performed as a function of initial metal concentration, initial pH value, and the equilibration time. The equilibrium process was well described by the Langmuir isotherm model. The pseudo-second order kinetic model provides the best correlation of the experimental kinetic data. The iron–sepiolite system had a noticeably higher Co2+ sorption capacity than the natural sepiolite sample as a result of higher specific sorption and a higher ion exchange capacity.