U(VI) removal by nanoscale zero-valent iron (nZVI) supported on raw and modified montmorillonite

ROCÍO VALIENTE; JOSÉ LUIS MARCO BROWN; ROSA TORRES SANCHEZ; ROBERTO CANDAL

Ciudad Obregón

Simposio; 6th International Simposium on Environmental Biotechnology and Engineering; 2018

ITSON

Water contamination by uranium is a problem of particular concern for people living near mining areas or nuclear fuel production plants. Immobilization of soluble U(VI) to suitable sorbents and reduction to less soluble U(IV) are ways to remove or diminish U(VI) mobility. In this work, the removal efficiency of U(VI) from water by a combination of adsorption and reduction/precipitation processes using nanoscale zero valent iron (nZVI) and nZVI supported on raw and Fe/Al pillared montmorillonite (MMT) was evaluated. It is expected that nZVI immobilization on support materials enhance the stability of nZVI compared with non-supported nZVI.Fe/Al pillared clays were prepared following a previously reported method1, with Fe/(Fe+Al) molar ratio of 0.33 (FeMMT0.33) or 0.5 (FeMMT0.5). nZVI were synthesized via Fe(III) reduction with NaBH4 and obtained as it or supported on raw MMT (nZVIMMT) or FeMMT0.33 (nZVIFeMMT0.33). Additionally, the Fe(III) present in FeMMT0.5 sample was reduced with NaBH4 to Fe(0) (ZVIFeMMT0.5). Samples were characterized by XRD and Mössbauer spectroscopy and by N2 adsorption-desorption isothermal analysis. Removal kinetics of U(VI) by the different materials were studied in anoxic batch systems at pH 4 and 6; U(VI) concentration, pH and oxidation-reduction potential (ORP) were measured during kinetics. Fe(0) presence was determined by Mössbauer in materials containing Fe(0) (ZVI materials). U(VI) removal was higher at pH 6 than at pH 4. U(VI) removal from solutions with initial U(VI) concentration: [U(VI)]0 = 50 mgL-1 and pH 6 varied according to the material. Total U(VI) removal was achieved by nZVIMMT and ZVIFeMMT0.5 in about 10 and 25 min respectively. After 60 minutes, a complete removal of U(VI) was not achieved neither using nZVI, nor nZVIFeMMT0.33. The occurrence of reduction process of U(VI) was proven when ZVI materials were used by the analysis of ORP vs time plots. Raw MMT, FeMMT0.33, FeMMT0.5 removed less than 30% of U(VI) after 60 min by adsorption process.U(VI) removal using of nZVI supported on raw or pillared MMT proved to be more efficient than using non-supported nZVI. Supported nZVI are projected into the future as a suitable material for the development of U(VI) removal technologies.