Application of layered double hydroxides for ~(99)Tc remediation

摘要

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 degrees 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 Tc-O 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 Mg-0.67/Al-0.33-LDH and Mg-0.75/Fe-0.25-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 Mg-0.67/Al-0.33-LDH and Mg-0.75/Fe-0.25-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-.