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

Thermodynamic calculations of ion-exchange reactions were applied for clinoptilolite in a natural state 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 a total normality of 0.025 N. Selectivity for K was not affected after β-radiation with doses of 10¹² and 10¹⁵ e/cm² (ΔG° = -6.37 kJ/equiv, lnKα = 2.58 for the original clinoptilolite), whereas it increased considerably 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-radiation yielded 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 highest dose 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 refined 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 Al³⁺ for Si⁴⁺ substitution. The observed changes include a shift in cation sites Cs2 and Cs3 toward channel walls and occupancy decrease in site Cs2.