In situ AFM and XPS Investigation of U~(6+) Reduction by Fe~(2+) on Hematite and Pyrite

摘要

Uranyl adsorption/reduction by Fe~(2+) on hematite and pyrite has been studied at neutral pH under anoxic and CCVfree conditions. XPS results confirm that more U_3O_8 precipitates on hematite than on pyrite reacted for 24 h in 160 μM uranyl nitrate and 160 μM Fe~(2+) solution at initial pH 7.3. These results are explained in terms of co-adsorption energy and U atom Mulliken charge transfer by quantum mechanical calculations. Moreover, in situ fluid tapping-mode AFM experiments on hematite indicate a deceleration of the U reduction rate within 24 h due to the passivation of the surface caused by the formation of orthorhombic U_3O_8 crystals. In addition, crystals observed using AFM show morphologies of orthorhombic schoepite appearing on hematite after 5 h.