Task-Specific Tailored Cationic Polymeric Network with High Base-Resistance for Unprecedented ⁹⁹TcO₄^– Cleanup from Alkaline Nuclear Waste

Abstract

Direct removal of 99 TcO 4 – from alkaline nuclear waste is desirable because of the nuclear waste management and environmental protection relevant to nuclear energy but is yet to be achieved given that combined features of decent base-resistance and high uptake selectivity toward anions with low charge density have not been integrated into a single anion-exchange material. Herein, we proposed a strategy overcoming these challenges by rationally modifying the imidazolium unit of a cationic polymeric network (SCU-CPN-4) with bulky alkyl groups avoiding its ring-opening reaction induced by OH – because of the steric hindrance effect. This significantly improves not only the base-resistance but also the affinity toward TcO 4 – as a result of enhanced hydrophobicity, compared to other existing anion-exchange materials. More importantly, SCU-CPN-4 exhibits record high uptake selectivity, fast sorption kinetics, sufficient robustness, and promising reusability for removing 99 TcO 4 – from the simulated high-level waste stream at the U.S. Savannah River Site, a typical alkaline nuclear waste, in both batch experiment and dynamic column separation test for the first time.

Porous Cationic Electrospun Fibers with Sufficient Adsorption Sites for Effective and Continuous 99TcO4− Uptake

“…The hydrophobic environment makes that PCE fibers favor the less hydrophilic and larger anions such as 99 TcO 4 − /ReO 4 − rather than NO 3 − and SO 4 2− , following the anti-Hofmeister bias. [5,7,15] The results confirm that PCE fibers have strong affinity and high selectivity toward ReO 4 − . The removal of ReO 4 − under different pH values were tested to show the fibers' adsorption ability in acidic and alkaline conditions (Figure S18, Supporting Information).…”

“…[ 7 ] Considering the high radioactivity and limited availability of 99 TcO 4 − , ReO 4 − having identical charge density with 99 TcO 4 − was applied as a nonradioactive surrogate in the following adsorption experiments, which have been proved to be feasible. [ 4–6 ] The adsorption kinetics of PCE fibers toward ReO 4 − had similar tendency as 99 TcO 4 − (Figure 3a). Additionally, the adsorption of ReO 4 − by PCE fibers was carried out at a high concentration (25 ppm) and two commercial anion exchange resins (A520E and IRA‐401) were also tested to adsorb ReO 4 − for comparison.…”

“…The removal of ReO 4 − under different pH values were tested to show the fibers' adsorption ability in acidic and alkaline conditions (Figure S18, Supporting Information). At selected pH range (2)(3)(4)(5)(6)(7)(8)(9)(10)(11), the removal efficiencies were high up to 90%. In certain types of nuclear waste streams, the pH values are either highly acidic or alkaline.…”

“…[3,4] Among the radioisotope contaminations, technetium-99 ( 99 Tc) is a β-emitting radionuclide produced from the nuclear fission of uranium-235 and plutonium-239 with a high fission yield of ≈6.1%. [5] Due to its long half-life (2.1 × 10 5 years), high water solubility (existed in the form of pertechnetate anions, 99 TcO 4 − ), and almost noncomplexing nature, 99 Tc has a fast migration in the environment and easily enters into local ecological systems, resulting in a serious environmental concern. Moreover, 99 Tc also disturbs the extraction of uranium, neptunium, and plutonium through its catalytic redox activity, and the volatile tendency of 99 TcO 4 − to 99 Tc 2 O 7 during nuclear waste vitrification process leads to a risk of leakage.…”

Trap Inlaid Cationic Hybrid Composite Material for Efficient Segregation of Toxic Chemicals from Water

“…Therefore, to address these issues, tremendous development of effective regenerable materials with substantially improved segregation properties has received special attention. That being said, pioneering endeavors have been employed to identify efficient adsorbents for the removal of specific oxoanions from contaminated water [14–16] . However, as a long‐term battle, improvement in terms of high selectivity, fast kinetics and capacities towards a group of toxic oxoanions at trace concentration, from natural groundwater sources to point‐of‐use are still needed for practical application, which is unexplored due to the lack of rational synthetic strategies.…”