Hydrothermal-based synthesis of iodosodalite waste forms to immobilize iodine eluent

Iodine eluent is a type of secondary waste that adsorbs radioactive iodine during the reprocessing of used nuclear fuel. To better deal with it, Na₂SiO₃ and NaAlO₂ were used to immobilize iodine eluents by synthesizing iodosodalite via a hydrothermal method. Orthogonal experiments were designed to investigate the effects of four factors: mass ratio of iodine eluent, Al/Si ratio, temperature, and aging time. Powder X-ray diffraction with Rietveld refinements was performed to characterize the structures and phases of the samples, of which iodosodalite and hydrosodalite are the primary phases that immobilize iodine effluents. Fourier-transform infrared spectroscopy and scanning electron microscopy results demonstrated a cage-like sample structure. Energy-dispersive X-ray spectroscopy revealed a homogeneous distribution of Na, Al, Si, O, and I on the sample surfaces. X-ray photoelectron spectroscopy indicated the presence of both iodide and iodate in the synthesized products. The optimal synthesis process is a reaction temperature of 190 ℃, NaI + NaIO₃:Na₂SiO₃+ NaAlO₂ ratio of 1:5, Si/Al ratio of 1:1, and aging time of 7 d. The leaching rate of iodine (including I⁻ and IO₃⁻) indicates considerable chemical durability of the optimized sample.