Magnetite and zero-valent iron nanoparticles for the remediation of uranium contaminated environmental water

The current work presents a comparative and site specific study for the application of zero-valent iron nanoparticles (nano-Fe0) and magnetite nanoparticles (nano-Fe3O4) for the removal of U from carbonate-rich environmental water taken from the Lişava valley, Banat, Romania.Nanoparticles were introduced to the Lişava water under surface and deep aquifer oxygen conditions, with a UVI-only solution studied as a simple system comparator. Thebatch systems were analysed over an 84 day reaction period, during which the liquid and nanoparticulate solids were periodically sampled to determine chemical evolution of the solutions and particulates.Results indicated that U was removed by all nano-Fe0 systems to <10 μg L−1 (>98% removal) within 2 h of reaction, below EPA and WHO specified drinking water regulations. Similar U concentrations were maintained until approximately 48 h. X-ray photoelectron spectroscopy analysis of the nanoparticulate solids confirmed partial chemical reduction of UVI to UIV concurrent with Fe oxidation. In contrast, nano-Fe3O4 failed to achieve >20% U removal from the Lişava water. Whilst the outer surface of both the nano-Fe0 and nano-Fe3O4 was initially near-stoichiometric magnetite, the greater performance exhibited by nano-Fe0 is attributed to the presence of a Fe0 core for enhanced aqueous reactivity, sufficient to achieve near-total removal of aqueous U despite any competing reactions within the carbonate-rich Lişava water.Over extended reaction periods (>1 week) the chemically simple UVI-only solution treated using nano-Fe0 exhibited near-complete and maintained U removal. In contrast, appreciable U re-release was recorded for the Lişava water solutions treated using nano-Fe0. This behaviour is attributed to the high stability of U in the presence of ligands (predominantly carbonate) within the Lişava water, inducing preferential re-release to the aqueous phase during nano-Fe0 corrosion.The current study therefore provides clear evidence for the removal and immobilisation of U from environmental waters using Fe-based nanoparticles. As a contrast to previous experimental studies reporting impressive figures for U removal and retention from simple aqueous systems, the present work demonstrates both nanomaterials as ineffective on timescales >1 week. Consequently further research is required to develop nanomaterials that exhibit greater reactivity and extended retention of inorganic contaminants in chemically complex environmental waters.

► Nano-Fe0 has been widely reported as a next generation solution to water treatment.
► World’s 1st study: nano-Fe0 for cleanup of U polluted water that is real in origin.
► Samples from abandoned U mine; results key in assessing effective cleanup strategy.
► Results crucial for determining viability of nano-Fe0 for real-world applications.
► Results conclude previous studies as largely overestimating nano-Fe0 performance.