Remediation of $^{137}$Cs-contaminated concrete gravels by supercritical CO$_2$ extraction

A. Leybros (1, 2) , N. Segond (3) , Agnès Grandjean (1, 2)

1 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)
2 DPME - Département de recherche sur les Procédés et Matériaux pour les Environnements complexes
3 ORANO

The removal of cesium contamination is a critical issue for the recycling of concrete gravel in most decommissioning sites . The high solvent strength and diffusivity of supercritical CO$_2$ make it an attractive choice as vector for extractant system in this context. Experimental extraction runs have been carried out in a radioactive environment on gravels contaminated with $^{137}$Cs. The best extraction system was found to be CalixOctyl (25,27-Bis(1-octyloxy)calix(4)arene-crown-6, 1,3-alternate) with pentadecafluorooctanoic acid as a modifier. The effects of various operating parameters were investigated, namely the coarseness of the gravel, the temperature of SC-CO$_2$, the residual water and initial cesium concentrations, and the amounts of extractant and modifier used. The yields from direct extraction were low (< 30percent), because of the virtually irreversible sorption of Cs in concrete. The best extraction yield of $\sim$55percent was achieved by leaching the concrete gravel with nitric acid prior to supercritical CO$_2$ extraction.

Keywords: supercritical CO$_2$; metal extraction; calixarene; concrete gravel

Domains: Nuclear Experiment [nucl-ex]; Nuclear Theory [nucl-th]

A. Leybros, N. Segond, Agnès Grandjean. Remediation of $^{137}$Cs-contaminated concrete gravels by supercritical CO$_2$ extraction. Chemosphere, 2018, 208, pp.838-845. ⟨cea-02339847⟩