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Ion exchange equilibrium and structural changes in clinoptilolite irradiated with β- and -radiation. Part II: divalent cations

Department of Mineral Resources Engineering, Technical University of Crete, 73100, Chania, Greece

^* Corresponding author, e-mail: moraetis{at}mred.tuc.gr

Thermodynamic calculations of ion exchange for divalent cations were made for clinoptilolite in natural state and after irradiation with three different doses of β-radiation (10¹², 10¹⁵ and 3 x 10¹⁶ e/cm²) and -radiation (70 Mrad). The samples were equilibrated with binary systems of divalent cations, namely Sr²⁺ 2Na⁺, Ca²⁺ 2Na⁺ and Mg²⁺ 2Na⁺ at 25 °C and total solution normality of 0.025 N. The selectivity order Sr²⁺ > Ca²⁺ > Mg²⁺ was observed in non-irradiated clinoptilolite. After irradiation with -radiation the affinity of clinoptilolite for Sr²⁺ increased and that for Mg²⁺ decreased, whereas the affinity for Ca²⁺ remained unchanged. Irradiation with β-radiation influences selectivity order and clinoptilolite affinity decreases for Sr²⁺, whereas it increases for Ca²⁺. For the sample irradiated with maximum dose of β-radiation the selectivity was almost identical for Ca²⁺ and Sr²⁺. The crystallographic parameters and exchangeable cation site coordinates were refined for all samples with the Rietveld method. The structure refinement of Sr²⁺-saturated samples yielded changes both in exchangeable sites and site occupancy in channels A and B after irradiation with β-and -radiation. The cation sites Sr1 and Sr3 exhibit major changes both in site coordinates and site occupancy after irradiation with β-radiation. In addition, irradiation with -radiation yielded major changes in Sr1 occupancy, whereas coordinates changed only slightly. These structural modifications control the observed changes in thermodynamic parameters after irradiation.

Key-words: clinoptilolite, ion exchange, β-radiation, -radiation, thermodynamics, Rietveld refinement.