Application of layered double hydroxides for 99Tc remediation

• Published in: Applied clay science 2019-08, Vol.176, p.1-10
• Main Authors: Daniels, N., Franzen, C., Murphy, G.L., Kvashnina, K., Petrov, V., Torapava, N., Bukaemskiy, A., Kowalski, P., Si, H., Ji, Y., Hölzer, A., Walther, C.
• Format: Article
• Language: English
• Subjects: Disposal; Layered double hydroxides; Technetium; Uptake
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2019.04.006

The present study investigates possible use of Layered Double Hydroxides (LDH) for Tc(VII) remediation. Mg/Al– and Mg/Fe–LDH were obtained by a hydrothermal route and thermally activated at 450 °C, which was shown to significantly improve the Tc(VII) removal efficiency. Based on XRD investigation of Tc–LDH phases, the uptake Tc(VII) from the solution follows the restoring of a LDH structure. X-ray absorption spectroscopy demonstrates that Tc ions interact solely via the TcO bond, leaving no evidences of farther atomic interactions with, e.g., layers of LDH. The presence of competing anions, like NO3−, or CO32– in the solution decreases Tc(VII) uptake by LDH. Maximum uptake capacity of thermally activated Mg0.67/Al0.33-LDH and Mg0.75/Fe0.25–LDH were derived from fitting the experimental data into the modified Langmuir equation and correspondingly comprise 0.227 mol/kg and 0.213 mol/kg. In agreement with these findings, theoretical simulations predicted incorporation energies for Mg0.67/Al0.33–LDH and Mg0.75/Fe0.25–LDH of −128 kJ/mol and − 110 kJ/mol, respectively. Investigation of stability of Tc–LDH in different aqueous solutions demonstrated a rather low release Tc(VII) in contact with diluted solutions containing Cl− and OH−, however, in a high saline solution, like Q-brine a rather fast release of TcO4− occurs due to anion exchange with Cl−. •Thermally “activated” at 450 °C Mg/Al– and Mg/Fe–LDH can efficiently remove soluble 99Tc(VII).•Theoretical prediction (DFT-simulation) of a higher stability of Tc(VII) incorporated in the Mg/Fe–LDH compared to Mg/Al–LDH.•99Tc–LDHs reveal rather high stability in diluted solutions containing Cl− and OH−, and on ambient conditions.•Fast release of 99Tc from LDHs in the highly saline solutions.