Sorption of Neptunium(V) on Various Iron Oxides and Hydrous Iron Oxides

Abstract

In order to see the effect of crystallinity and surface conditions of various oxides and hydrous oxides on the sorption of metal ions, the sorption of tracer concentration (~10" 12 M) of neptunium(V) on naturally-occurring iron minerals (goethite, hematite, magnetite), synthetic iron oxide powders (a-Fe 2 0 3 and Fe 3 0 4 ) and laboratory-prepared hydrous iron oxides (a-FeOOH and amorphous hydrous iron oxide) was studied as a function of pH. The sorption was found to strongly depend on the crystal structure as a-FeOOH > amorphous > a-Fe 2 0 3 , Fe 3 0 4 . Hydrous oxides heat-treated at various temperatures were also examined to see the effect of structural changes. The hydrous oxides retained their original α-FeOOH and amorphous structure below 200°C, while both gradually changed into a-Fe 2 0 3 above 300°C. For the hydrous oxides heat-treated at above 300°C, the sorption was qualitatively correlated with their crystallinities. Intense crushing and grinding of the natural hematite and magnetite resulted in higher sorption of Np(V) than the synthetic powders at lower pH, presumably owing to freshly exposed surface conditions.

Sorption coefficients and molecular mechanisms of Pu, U, Np, Am and Tc to Fe (hydr)oxides: A review

“…The sorption behavior of Np(V) to hematite under aerobic and anaerobic conditions was not noticeably different, because the Np(V) species onto hematite was not reduced [110]. The sorption was found to strongly depend on the type of FHOs: goethite > ferrihydrite > hematite, magnetite [114]. More recently, Tinnacher et al [115] investigated kinetics of Np(V) sorption and desorption on goethite using experimental and modeling methods.…”

An X-ray Absorption Spectroscopy Study of Neptunium(V) Reactions with Mackinawite (FeS)

“…A number of studies of neptunium sorption on geological phases have been carried out, in particular on iron oxides and hydrous oxide materials (12)(13)(14). Using XAS, Combes et al (13) showed that sorption of Np(V) onto goethite involved inner-sphere complexation of the NpO2 + unit to the surface.…”

Spent fuel canister for geological repository: Inner material requirements and candidates evaluation

“…It possesses high sorption capabilities for heavy elements, like uranium [116][117][118][119][120][121], plutonium [122,123], neptunium [123,124], americium [125] or strontium [126,127]. Additionally, under reducing conditions, it can fix hydrogen while transforming to magnetite (Fe 3 O 4 ).…”