Removal of radionuclides from acidic solution by activated carbon impregnated with methyl- and carboxy-benzotriazoles

Abstract

The removal efficiencies of metals commonly used to model the fate and transport of aqueous uranium and radioactive its daughter products, were observed on activated carbons impregnated with different benzotriazole derivatives. Acidic solutions containing U(VI), Sr(II), Eu(III), and Ce(III) were used to determine the immobilization potential of carboxybenzotriazole (CBT) and methylbenzotriazole (MeBT), where these derivatives were sorbed to different types of granular activated carbon (GAC). This sorption behavior can be predicted by Redlich-Peterson model. flow-through column tests showed that the immobilization of uranium and some of its daughter products, significantly improves in response to oxidized GACs saturated with carboxybenzotrzole (CBT), which reached a maximum elimination for U(VI) at 260 BV, Eu(III) at 114 BV, Ce(III) at 126 BV, and Sr(II) at 100. MeBT significantly desorbed from GAC under acidic conditions. Trace amounts of CBT were observed in some column effluents, but this did not appear to alter the effectiveness of metal removal, regardless of the model radionuclide studied. these results suggest that enhanced immobilization of selected metals on GAC, can be achieved by impregnating oxidized activated carbon with carboxylated benzotriazoles, and that metal removal efficiency on this media, is related to their valence and ionic radius in acidic environments. Significant sources of aqueous radioactive metals are associated with nuclear reactor operations, industrial radioisotope research, and health care applications 1. The treatment of wastewaters containing uranium and its radioactive daughter products continues to receive significant attention. Hooper and Kavanaugh 2 recognize the dominant regulatory principles governing radionuclide treatment that predominate today: as low as reasonably practicable (ALARP) and best available technology not entailing excessive cost (BATNEEC). A new generation of technology is needed for more effective immobilization of heavy radionuclides. The methods used to treat metal bearing radioactive wastewaters include chemical precipitation 3 , solvent extraction 4 , extraction chromatography (EXC) 5,6 ion exchange 7 , membranes 8,9 , and sorption processes 1,10-13. Because of costs and reliability, hydroxide precipitation remains one of the most common techniques for radioactive metal removal. However, where multiple metals are present, the efficiency of hydroxide addition can be compromised by solubility product and solute competition; thus, precipitating mixed metal wastes has significant treatment challenges, including the generation of low-density sludge 14. Sulfide precipitation is practiced in this sector, and has the following advantages over hydroxide precipitation: (i) better performance over broader pH ranges; and, (ii) better sludge dewatering characteristics 15. However, there are significant operational risks associated with sulfide precipitation, including H 2 S gas generation and colloid formation that poses sedimentation and membrane fouling challeng...

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