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Ion exchange equilibrium and structural changes in clinoptilolite irradiated with β- and γ-radiation: Monovalent cations

Christidis Georgios, Daniel Moraetis , Vassilis Perdikatsis

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Summary

Thermodynamic calculations of ion-exchange reactions were applied for clinoptilolite in a naturalstate and after irradiation with three doses of β-radiation (1012, 1015, 3 × 1016 e/cm2) and γ-radiation(70 Mrad). Samples were equilibrated with binary systems of K+ ↔ Na+ and Cs+ ↔ Na+ at 25° and atotal normality of 0.025 N. Selectivity for K was not affected after β-radiation with doses of 1012 and1015 e/cm2 (ΔG° = –6.37 kJ/equiv, lnKα = 2.58 for the original clinoptilolite), whereas it increasedconsiderably after 70 Mrad of γ-radiation (ΔG° = –7.88 kJ/equiv, lnKα = 3.18). Selectivity for Cs+increased for the clinoptilolite irradiated with β-radiation (1012, 1015, 3 × 1016 e/cm2) and γ-radiation(70 Mrad). ΔG° and lnKα for original sample and Cs+ ↔ Na+ were –7.33 kJ/equiv and 2.96,respectively. Irradiated samples with β-radiation 1012, 1015, 3 × 1016 e/cm2 and 70 Mrad γ-radiationyielded ΔG° 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 highestdose of β-radiation (3 × 1016 e/cm2) with a concomitant decrease in cation-exchange capacity (CEC).Crystallographic parameters and especially exchangeable cation site coordinates were refi ned for allsamples with the Rietveld method. Cesium-saturated samples exhibited changes in the cation sitesCs2 and Cs3, which are next to clinoptilolite channel walls with lower Al3+ for Si4+ substitution. Theobserved changes include a shift in cation sites Cs2 and Cs3 toward channel walls and occupancydecrease in site Cs2.

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