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

Abstract

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 (10 12 , 10 15 and 3 × 10 16 e/cm 2 ) and γ-radiation (70 Mrad). The samples were equilibrated with binary systems of divalent cations, namely Sr 2+ ↔ 2Na + , Ca 2+ ↔ 2Na + and Mg 2+ ↔ 2Na + at 25 °C and total solution normality of 0.025 N. The selectivity order Sr 2+ > Ca 2+ > Mg 2+ was observed in non-irradiated clinoptilolite. After irradiation with γ-radiation the affinity of clinoptilolite for Sr 2+ increased and that for Mg 2+ decreased, whereas the affinity for Ca 2+ remained unchanged. Irradiation with β-radiation influences selectivity order and clinoptilolite affinity decreases for Sr 2+ , whereas it increases for Ca 2+ . For the sample irradiated with maximum dose of β-radiation the selectivity was almost identical for Ca 2+ and Sr 2+ . The crystallographic parameters and exchangeable cation site coordinates were refined for all samples with the Rietveld method. The structure refinement of Sr 2+ -saturated samples yielded changes both in exchangeable sites and site occupancy in channels A and B after irradiation with β-and γ-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 γ-radiation yielded major changes in Sr1 occupancy, whereas coordinates changed only slightly. These structural modifications control the observed changes in thermodynamic parameters after irradiation.