Ion exchange equilibrium and structural changes in clinoptilolite irradiated with - and -radiation: Monovalent cations ARTICLE in AMERICAN MINERALOGIST · OCTOBER 2007 48 PUBLICATIONS 666 CITATIONS SEE PROFILE (original) (raw)

Thermodynamic calculations of ion-exchange reactions were applied for clinoptilolite in a natural state and after irradiation with three doses of β-radiation (10 12 , 10 15 , 3 × 10 16 e/cm 2 ) and γ-radiation (70 Mrad). Samples were equilibrated with binary systems of K + ↔ Na + and Cs + ↔ Na + at 25° and a total normality of 0.025 N. Selectivity for K was not affected after β-radiation with doses of 10 12 and 10 15 e/cm 2 (∆G° = -6.37 kJ/equiv, lnKα = 2.58 for the original clinoptilolite), whereas it increased considerably after 70 Mrad of γ-radiation (∆G° = -7.88 kJ/equiv, lnKα = 3.18). Selectivity for Cs + increased for the clinoptilolite irradiated with β-radiation (10 12 , 10 15 , 3 × 10 16 e/cm 2 ) and γ-radiation (70 Mrad). ∆G° and lnKα for original sample and Cs + ↔ Na + were -7.33 kJ/equiv and 2.96, respectively. Irradiated samples with β-radiation 10 12 , 10 15 , 3 × 10 16 e/cm 2 and 70 Mrad γ-radiation yielded ∆G° and lnKα -7.41, -8.83, -8.60, -8.25 kJ/equiv and 2.99, 3.57, 3.47, 3.33 for Cs + ↔ Na + , respectively. Remarkable amorphization of clinoptilolite was observed after exposure at the highest dose of β-radiation (3 × 10 16 e/cm 2 ) with a concomitant decrease in cation-exchange capacity (CEC). Crystallographic parameters and especially exchangeable cation site coordinates were refi ned for all samples with the Rietveld method. Cesium-saturated samples exhibited changes in the cation sites Cs2 and Cs3, which are next to clinoptilolite channel walls with lower Al 3+ for Si 4+ substitution. The observed changes include a shift in cation sites Cs2 and Cs3 toward channel walls and occupancy decrease in site Cs2.