Removal of Cs+ and Sr2+ ions from simulated radioactive waste solutions using Zeolite-A synthesized from kaolin and their structural stability at high pressures

Zeolite-A was synthesized from kaolin activated at 500 °C at relatively lower temperature than the studies reported in the literature.The metakaolin formed at 500 °C was used to synthesise zeolite-A by treating with 1–5 M NaOH solutions at 80–100 °C for 3–24 h under hydrothermal reaction condition. The zeolite-A was characterized by XRD, FT-IR and SEM. The percentage of crystallinity and crystallite sizes of the zeolite-A were determined from XRD analysis; the crystal system of zeolite-A was found to be cubic with space group (Fm3‾c ). The ion-exchange property of zeolite-A for Cs+ and Sr+2 was explored at ambient temperature (25 °C). The adsorption efficiency of zeolite-A is higher for Sr+2 than that of Cs+; and adsorption capacities for Cs+ and Sr2+ ions were found to be 91.51% and 99.16% respectively. Strontium substituted zeolite has higher crystallinity and lattice strain than that of caesium substituted zeolite-A. Structural stability investigations were carried out on pristine zeolite-A and its Cs+ and Sr2+ substituted analogues by using high-pressure (0.1 MPa-11.4 GPa) X-ray diffractometry technique for the first time. The pristine zeolite-A shows comparatively lower bulk modulus than that of caesium and strontium loaded zeolite. It is also seen that the compressibility is least for the strontium loaded zeolite-A (SrZtA) followed by caesium loaded zeolite-A (CsZtA) and pristine zeolite-A (ZtA) (i.e compressibility of SrZtA < compressibility of CsZtA < compressibility of ZtA).