Vermiculite as efficient sorbent of CeIII and CeIV

This study focussed on the mechanism of Ce-III and Ce-IV 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 Ce-III uptake on Ver in neutral aqueous solution were fitted both with adsorption and ion-exchange models. The latter, with a calculated selectivity constant (K-V) over bar = 14.30 (L mmol(-1))(k-1), showed a better fit with experimental data than adsorption models. The uptake of Ce-III 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 Ce-IV on Ver (similar to 6 mequiv. g(-1), i.e., similar to 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 Ce-IV species fixation on Ver, their different Ce-IV solubility in NaCl solution, aqueous acid solution (pH 2), and 3 M H2SO4, three species of Ce-IV bonded on vermiculite are proposed. They are ion-exchanged Ce-IV, Ce-IV-complex 1 and Ce-IV-complex 2. The Ce-IV 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.