Hydrotalcite-like layered bismuth–iodine–oxides as waste forms

The effective capture and storage of radiological I (129I) remains a significant concern for safe nuclear waste storage and safe nuclear energy. Due to its long half-life (1.6 × 107 a) and concerns for involvement in human metabolic processes, durable waste forms are of great interest and research focus. Long term durability is mimicked in geological analogs. As a result, the authors have utilizing a facile, in situ   process of synthesizing mineral analogs of layered (hydrotalcite-like) bismuth–iodine–oxide waste forms that does not require advanced separation and isolation of the I species from the aqueous solution. Specifically, the phases are crystallized and precipitated out of the waste stream at room temperature by the simple titration of an acidified Bi nitrate solution which precipitates layered oxide phases; phase composition and I weight loading is determined by the Bi:I ratio in solution. Products are designed to combine high I loading levels with chemical durability. Several characterization techniques were employed to better understand the relationship between waste forms, their abilities to encapsulate I, and their stability under possible repository conditions. They include solubility leach testing with elevated levels of common ground water anions Cl-,HCO3-,SO42-, thermal stability testing, elemental analysis, X-ray diffraction and microscopy studies.

Research highlights
► Hydrotalcite-like Bi–O–I phases are viable low-solubility radioiodine waste forms.
► Bi–O–I phases are a low cost alternative to radioiodine capture with Ag-zeolites.
► Bi–O–I radioiodine waste forms fabricated easily at room temperature.