Separation and Remediation of ⁹⁹TcO₄^– from Aqueous Solutions

Abstract

Technetium-99 (99Tc) 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.

Sb-doped zirconium dioxide submicron fibers for separation of pertechnetate (TcO4–) from aqueous solutions

“…[2] For research, Tc is only available as radioactive tracers that is preventing its use in experimental facilities without license for radioactive work. Therefore, many researchers have used rhenium as a comparable surrogate for Tc because also Re prevails as heptavalent ReO 4 and can undergo redox reactions. However, the slight differences between TcO 4 and ReO 4 can have a significant impact on separation.…”

“…[4,5] However, performances of ion exchange resins and adsorbents often suffer from the presence of other ions, and organic resins are prone to radiation damage. [6] For that reason, several inorganic materials have been developed for more selective removal of TcO 4 and ReO 4 such as mesoporous alumina, [7] metalorganic frameworks, [8,9,10,11] zero valent iron (ZVI), [12,13] Fe 2 O 3 and Fe 3 O 4 [12] and zirconium dioxide nanoparticles anchored onto reduced graphene oxide (ZrO 2 @rGO). [14] In addition, universal nonselective sorbent materials including activated carbon have been utilized in TcO 4 removal.…”

“…[6] For that reason, several inorganic materials have been developed for more selective removal of TcO 4 and ReO 4 such as mesoporous alumina, [7] metalorganic frameworks, [8,9,10,11] zero valent iron (ZVI), [12,13] Fe 2 O 3 and Fe 3 O 4 [12] and zirconium dioxide nanoparticles anchored onto reduced graphene oxide (ZrO 2 @rGO). [14] In addition, universal nonselective sorbent materials including activated carbon have been utilized in TcO 4 removal. [15,16,17] Li et al [18] observed that after TcO 4 was remediated by porous iron, Tc(VII) was mainly reduced to Tc(IV) and co-precipitated with FeO(OH) and Fe 3 O 4 or incorporated into their structure.…”

“…[15,16,17] Li et al [18] observed that after TcO 4 was remediated by porous iron, Tc(VII) was mainly reduced to Tc(IV) and co-precipitated with FeO(OH) and Fe 3 O 4 or incorporated into their structure. Even though the ZVI materials show good potential for TcO 4 uptake, these materials have their limitations such as low surface area and susceptibility for leaching. [18,19,20] In addition to ZVI, also other materials have shown potential for reductive separation.…”

“…[18,19,20] In addition to ZVI, also other materials have shown potential for reductive separation. Koivula et al [21] observed that Sb-doped SnO 2 was able to efficiently separate TcO 4 from water solutions. The Tc uptake was suggested to be a combination of reduction and anion exchange as the sorption behavior could not be explained only with one mechanism.…”