Vermiculite as efficient sorbent of Ce-III and Ce-IV

Abstract

This study focussed on the mechanism of CeIII and CeIV uptake on vermiculite (Ver), which has been studied sporadically. Chemical equilibrium and leaching experiments in acid solutions were evaluated using batch experiments and changes of mineral composition were monitored by X-ray powder diffraction analysis. The concentrations of Ce, Na, K, Ca, Mg, Al and Si were determined by atomic emission spectroscopy coupled with inductively coupled plasma (AES-ICP). The data for CeIII uptake on Ver in neutral aqueous solution were fitted both with adsorption and ion-exchange models. The latter, with a calculated selectivity constant EN16112_IE1.gif = 14.30 (L mmol–1)k–1, showed a better fit with experimental data than adsorption models. The uptake of CeIII on Ver at pH 2 was also controlled by intensive leaching of cations from 2 : 1 layers and therefore these data were not fitted. A much higher uptake of CeIV on Ver (~6 mequiv. g–1, i.e. ~210 mg g–1) at pH 2 and 6 in comparison with the cation-exchange capacity of original vermiculite (1.28 mequiv. g–1) was found and explained. With regard to the different rate of CeIV species fixation on Ver, their different CeIV solubility in NaCl solution, aqueous acid solution (pH 2), and 3 M H2SO4, three species of CeIV bonded on vermiculite are proposed. They are ion-exchanged CeIV, CeIV–complex 1 and CeIV–complex 2. The CeIV species uptake on Ver was quantitatively determined both for pH 2 and 6. The new findings show a very effective method of cerium uptake, especially from acidic aqueous solutions.