Stable nZVI-based nanocomposites for adsorption and reduction processes: The case of U(VI) removal

Abstract

Stable iron nanoparticles are proposed as a relatively low-cost material for the removal of U(VI) in water. Nanoscale zero valent iron (nZVI) and nZVI supported on raw or pillared montmorillonite (MMT) were synthesized by a classical methodology (using NaBH4 as reducing agent) and their stability after expositions to air was analyzed by Mössbauer spectroscopy. Moreover, the structural and textural properties of the synthesized materials were determined. Mössbauer spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the samples. Microscopic observations indicated that unsupported nZVI tends to form aggregates, while supported nZVI remains well dispersed on raw or pillared MMT. The removal efficiency of U(VI) from water by a combination of adsorption and reduction/precipitation processes using the synthesized materials was evaluated. U(VI) concentration, pH and oxidation-reduction potential (ORP) were measured during removal kinetics experiments. The removal of U(VI) turned out dependent on solution pH, being more favorable at acid pH. U(VI) removal using nZVI supported on raw or pillared MMT proved to be more efficient than using non-supported nZVI or than using other materials reported in literature. Supported nZVI is projected into the future as a suitable material for the development of U(VI) removal technologies.