Intensified ceria recovery from graphite substrate and cleanup of leachant using sonication

Abstract

There is a huge environmental concern for disposal of nuclear graphite. The current work demonstrates sonochemical decontamination of graphite using ceria coating as the simulated contamination. The ceria recovery in the leachant solution, demonstrated to drastically reduce by almost 50% beyond 30 min sonication, was attributed to the adsorption of cerium ions by the generated carbon residue due to exfoliation of graphite. The study of the carbon residue enabled to understand the anomaly in the observed kinetics and the role of the carbon residue in the removal of Ce3+ from the leach liquor. The recyclability of the graphite substrate has been studied by measuring its compressive strength and electrical conductivity before and after 7 h of sonication in nitric acid. The decontamination kinetics of graphite was found to follow the surface reaction controlled mechanism and cavitation was found to lower the activation energy from 102 to 80 kJ/mol. Overall, ultrasound was found to bring about a threefold increase in the ceria recovery over a silent process (in the absence of ultrasound). The decontamination and the recyclability of graphite demonstrated here will facilitate circular economy and serve as an important remediation technique.