Adsorption of Cr(VI), a non-radioactive surrogate for Tc(VII), by reduced carbon Microspheres@Hydrochar from lactic acid modification

Abstract

During reprocessing of spent nuclear fuel, technetium mainly exists as pertechnetate (TcO4-), whose high solubility and environmental mobility pose long-term risks. The migration and hazards of pertechnetate will decrease when it is reduced to TcO2 by reducing materials. Therefore, developing efficient reduction materials to convert TcO4- to TcO2 is crucial for safe disposal of spent fuel reprocessing wastewater. In this study, a reduced carbon microsphere@hydrochar from lactic acid modification (LAHC) was prepared. Lactic acid was involved in the construction of reductive carbon microspheres on the surface of LAHC while simultaneously enriching reducing oxygen-containing functional groups in LAHC. The reducing capacity of LAHC on Tc(VII) was evaluated by investigating the adsorption of Cr(VI) as a non-radioactive surrogate for radioactive Tc(VII). Electrochemical analysis showed that LAHC exhibited a good reducing capacity, owing to its reduced carbon microspheres and surface oxygen-containing functional groups. The Cr(VI) adsorption on LAHC proceeded through heterogeneous chemisorption. Furthermore, the calculated maximum Langmuir adsorption capacity of Cr(VI) by LAHC reached 383.68 mg·g−1. The removal process of Cr(VI) by LAHC involved an adsorption-coupled interfacial redox mechanism. These findings suggested that lactic acid modification effectively enhanced the reducing capacity of hydrochar, with LAHC offering potential for Cr(VI)/Tc(VII) removal in nuclear effluents.