Reductive capacity of iron-bearing soil minerals for U(VI)

Oxidation-reduction processes play a major role in the mobility, transport, and fate of uranium (U) in the geological system. Under reducing conditions, U mobility is much slower than in oxidizing conditions. Previous studies have reported that iron oxides, hydroxides, and oxyhydroxides are associated with U retention in the subsurface environment. Therefore, measuring reductive capacity of iron-bearing soil minerals is important for assessing the U mobility in geological systems where U can be easily disposed. In this study, magnetite (Fe3O4), greenrust (GR-SO4), nZVI, mackinawite (FeS), and pyrite (FeS2) were used to estimate and compare their reductive capacity for U(VI). nZVI showed the fastest U(VI) removal kinetic and highest reduction capacity among the iron-bearing soil minerals tested. We found that the iron-bearing soil mineral with higher content of reactive Fe(II) on its surface is more favorable for U(VI) sorption and reduction. This is because the U(VI) reduction capacity is attributed to surface Fe-O complexes and amount of surface Fe(II) reducing sorbed U(VI). The experimental results show that surface Fe(II) in iron-bearing soil minerals is an important factor that significantly stabilize and immobilize U(VI) in the geological system. This can be used as basic knowledge for the prediction of U fate in the natural environment and for the development of remediation technology to treat uranium-contaminated sites.