Uptake of Ce(III) and Ce(IV) on montmorillonite

Abstract

Montmorillonite (Mt) doped by Ce(III) has good antimicrobial properties and doped by Ce(IV) has high permanent porosity, surface area and catalytic properties. The present study is focused on the mechanism of Ce(III) and Ce(IV) uptake on montmorillonite in neutral and acid aqueous solutions. Chemical equilibria and leaching experiments in acid solutions were evaluated using batch experiments, changes of mineral structure were monitored by X-ray diffraction (XRD), and Ce uptake on Mt surface by scanning electron microscopy (SEM). The concentrations of Ce, Na, K, Ca, Mg, Al, and Si were determined from aqueous solutions using atomic emission spectroscopy with Inductively Coupled Plasma (AES-ICP). The isotherm for Ce(III) uptake on Mt were fitted both by adsorption and ion exchange models. The exchange model with the calculated selectivity constant K=15.2L/mmolk−1 showed a better fit with experimental data than adsorption models. The uptake of Ce(III) on Mt at pH2 was controlled by ion exchange, accompanied by increasing leaching of cations from 2:1 montmorillonite layers. A high uptake of Ce(IV) on Mt (~ 6meq/g, i.e.~210mg/g) at pH2 and 6 in excess of the cation exchange capacity (0.76meq/g) was found and explained by the formation of a mixture of two Ce(IV) complexes fixed on Mt; the first was insoluble and the second soluble in 3M H2SO4 but insoluble in acid aqueous solution at pH2. A small amount of ion exchanged Ce (IV) (~ 0.27meq/g) was also determined in samples of Ce(IV)-Mt prepared at pH2. The Ce(III) and Ce(IV) uptake on Mt at pH6 reached equilibrium in <30min, while the uptake of Ce (IV) at pH2 needed at least 24h. The new findings show a very effective way for cerium uptake, especially from acidic aqueous solutions.