Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: The role of Fe(II) and Fe(III)

Abstract

The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed that U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.9 to 9.0. For instance, at pH 6.9 the observed U(VI) reduction rates decreased by 81% and 82% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) possibly acted as an electron shuttle to ferry the electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 could facilitate U(VI) reductive immobilization in the contaminated groundwater.

Nanoenhanced Materials for Reclamation of Mine Lands and Other Degraded Soils: A Review

“…This literature confirmed that U 6+ was predominantly removed by nZVI via reductive precipitation of UO 2 2+ (U 4+ ) with minor precipitation of UO 3 •2H 2 O (U 6+ ) as confirmed by the Xray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses. Oxygen level, solution pH, and presences of bicarbonates and calcium ions all affect the reductive immobilization processes [84,85]. It has also been reported that nZVI was able to reduce higher valent Cr +6 to low valent Cr +3 in water or soil media.…”

“…These risks can be remediated by reducing it to insoluble U 4+ oxides by nZVI. Several related reports have shown that, compared to the other reductants such as metal iron filing, galena (PbS), and iron sulfide, nZVI is very efficient to reductively immobilize U 6+ from aqueous phase, which could be attributed to its nanosize, high reactivity, large surface area, and reactive Fe(II) produced by nZVI [84][85][86][87][88]. This literature confirmed that U 6+ was predominantly removed by nZVI via reductive precipitation of UO 2 2+ (U 4+ ) with minor precipitation of UO 3 •2H 2 O (U 6+ ) as confirmed by the Xray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses.…”

An overview of preparation and applications of stabilized zero-valent iron nanoparticles for soil and groundwater remediation

“…Based on these reactions, corrosion of the nZVI not only affects the surface and chemical properties of nZVI, but also impacts the aqueous chemistry, such as pH, ionic strength and coexisting ions. As a result, nZVI is typically present as a core-shell structure, i.e., the ZVI core wrapped in the iron (hydr)oxide (magnetite) shell (Nurmi et al, 2005;Yan et al, 2010b).…”

Nanoscale zero-valent iron particles for the remediation of plutonium and uranium contaminated solutions

“…Investigations for the remediation of radionuclides, however, remains less widely researched and includes: barium, [27], pertechnetate [21], [22] and uranium. [20], [28], [29], [30], [31], [32], [33], [34], [35] As demonstrated by [30], uranium uptake onto nZVI typically occurs via sorption and then surfacemediated chemical reduction. In comparison to the body of work reported for uranium, the uptake of plutonium by nZVI has not, as far as we are aware, been previously reported.…”