Separation and Remediation of 99TcO4- from Aqueous Solutions

Technetium-99 (Tc-99) is one of the most-problematic radioisotopes in used nuclear fuel owing to its intrinsic features of a high fission yield, long half-life, high environmental mobility, volatile nature during waste vitrification, and its redox interface capability with actinides during used fuel repossessing. The selective separation of pertechnetate (TcO4-) from legacy nuclear waste and contaminated natural water is therefore highly desirable but still a significant challenge, because the conditions of a strong radiation field, high ionic strength, high acidity/alkalinity, and large amounts of competing anions are often involved in these systems. Until now, there are a handful of functional materials that can efficiently remove TcO4- from nuclear waste solutions with high uptake capacities, fast kinetics, and good selectivity, but room still remains to further improve our capabilities for controlling the contamination/separation of TcO4-. In this Perspective, we discuss the current state of the art TcO4- separation materials including precipitation agents, reducing materials, ion-exchange resins, inorganic cationic frameworks, cationic metal-organic frameworks (MOFs), and cationic polymeric networks (CPNs) materials. The intriguing separation mechanisms of these materials for TcO4- are also disclosed, which may hopefully shed light on further development in this field.