Abstract
A solid phase of natural zeolite was transformed to Na-zeolite P (NaP zeolite) by a “top-down approach” hydrothermal reaction using 3 M of NaOH solution in a 96 °C oven. Time-dependent X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), XRF, and scanning electron microscopy (SEM) analysis as well as kinetic, isotherm, and cation exchange capacity experiments were performed to understand the mechanism of mineral transition from natural zeolite to NaP zeolite. The XRD crystal peaks of the natural zeolite decreased (decrystallization phase) first, and then the NaP zeolite XRD crystal peaks increased gradually (recrystallization phase). From the XRF results, the dissolution rate of Si was slow in the recrystallization phase, while it was rapid in the decrystallization phase. The specific surface area measured by BET analysis was higher in NaP zeolite (95.95 m2/g) compared to that of natural zeolite (31.35 m2/g). Furthermore, pore structure analysis confirmed that NaP zeolites have more micropores than natural zeolite. In the kinetic experiment, the results showed that the natural zeolite and NaP zeolite were well matched with a pseudo-second-order kinetic model, and reached equilibrium within 24 h. The isotherm experiment results confirmed that both zeolites were well matched with the Langmuir isotherm, and the maximum removal capacity (Qmax) values of Sr and Ni were highly increased in NaP zeolite. In addition, the cation exchange capacity (CEC) experiment showed that NaP zeolite has an enhanced CEC of 310.89 cmol/kg compared to natural zeolite (CEC = 119.19 cmol/kg). In the actual batch sorption test, NaP zeolite (35.3 mg/g) still showed high Cs removal efficiency though it was slightly lower than the natural zeolite (39.0 mg/g). However, in case of Sr and Ni, NaP zeolite (27.9 and 27.8 mg/g, respectively) showed a much higher removal efficiency than natural zeolite (4.9 and 5.5 mg/g for Sr and Ni, respectively). This suggests that NaP zeolite, synthesized by a top-down desilication method, is more practical to remove mixed radionuclides from a waste solution.
Highlights
Over the past few decades, low- and intermediate-level radioactive wastes composed of long-lived radionuclides such as 137 Cs, 90 Sr, and 63 Ni have been generated extensively during nuclear power plant (NPP) operations
The results showed that the natural zeolite and NaP zeolite were well matched with a pseudosecond-order kinetic model, and reached equilibrium within 24 h
This was due to the NaP zeolite being more Al rich as opposed to natural zeolite
Summary
Over the past few decades, low- and intermediate-level radioactive wastes composed of long-lived radionuclides such as 137 Cs, 90 Sr, and 63 Ni have been generated extensively during nuclear power plant (NPP) operations. 137 Cs and 90 Sr have long-term radio-biological risks, because 137 Cs can transfer to human muscles through the K+ channel [2], and ingested 90 Sr can be deposited on the surface of bone in which Ca can be replaced with 90 Sr [3]. Both 137 Cs and 90 Sr are the most common fission products produced by nuclear fission in nuclear reactors or nuclear weapons. The biological risk of 63Ni is not high compared
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
