Functional Carbon Capsules Supporting Ruthenium Nanoclusters for Efficient Electrocatalytic 99TcO4-/ReO4- Removal from Acidic and Alkaline Nuclear Wastes

The selective removal of the beta-emitting pertechnetate ion ((TcO4-)-Tc-99) from nuclear waste streams is technically challenging. Herein, a practical approach is proposed for the selective removal of (TcO4-)-Tc-99 (or its surrogate ReO4-) under extreme conditions of high acidity, alkalinity, ionic strength, and radiation field. Hollow porous N-doped carbon capsules loaded with ruthenium clusters (Ru@HNCC) are first prepared, then modified with a cationic polymeric network (R) containing imidazolium-N+ units (Ru@HNCC-R) for selective (TcO4-)-Tc-99 and ReO4- binding. The Ru@HNCC-R capsules offer high binding affinities for (TcO4-)-Tc-99/(TcO4-)-Tc-99 under wide-ranging conditions. An electrochemical redox process then transforms adsorbed (TcO4-)-Tc-99 to bulk ReO3, delivering record-high removal capacities, fast kinetics, and excellent long-term durability for removing ReO4- (as a proxy for 99TcO(4)(-)) in a 3 m HNO3, simulated nuclear waste-Hanford melter recycle stream and an alkaline high-level waste stream (HLW) at the U.S. Savannah River Site (SRS). In situ Raman and X-ray absorption spectroscopy (XAS) analyses showed that adsorbed Re(VII) is electrocatalytically reduced on Ru sites to a Re(IV)O-2 intermediate, which can then be re-oxidized to insoluble Re(VI)O-3 for facile collection. This approach overcomes many of the challenges associated with the selective separation and removal of 99TcO(4)(-)/ReO4- under extreme conditions, offering new vistas for nuclear waste management and environmental remediation.

Automated summary

This study proposes a practical approach for the selective removal of radioactive pertechnetate ions under extreme conditions. By modifying carbon capsules and utilizing an electrochemical redox process, the researchers achieved high removal capacities and excellent durability. This method offers new possibilities for nuclear waste management and environmental remediation.