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 mechanismof Ce(III) and Ce(IV) uptake onmontmorillonite 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 onMt surface by scanning electron microscopy (SEM). The concentrations of Ce, Na, K, Ca,Mg, Al, and Siwere determined fromaqueous solutions using atomic emission spectroscopy with Inductively Coupled Plasma (AES-ICP). The isothermfor Ce(III) uptake onMtwere fitted both by adsorption and ion exchange models. The exchange model with the calculated selectivity constant K = 15.2 L/mmolk−1 showed a better fitwith experimental data than adsorptionmodels. The uptake of Ce(III) onMt at pH 2was controlled by ion exchange, accompanied by increasing leaching of cations from 2:1 montmorillonite layers. A high uptake of Ce(IV) on Mt (~ 6 meq/g, i.e. ~ 210 mg/g) at pH 2 and 6 in excess of the cation exchange capacity (0.76 meq/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 3 M H2SO4 but insoluble in acid aqueous solution at pH 2. A small amount of ion exchanged Ce (IV) (~ 0.27 meq/g) was also determined in samples of Ce(IV)-Mt prepared at pH 2. The Ce(III) and Ce(IV) uptake on Mt at pH 6 reached equilibrium in b30 min, while the uptake of Ce (IV) at pH 2 needed at least 24 h. The new findings show a very effective way for cerium uptake, especially from acidic aqueous solutions.