Interaction of UO22+ and Fe3+ ions with natural humic acid

The cation exchange in uranyl (UO22+) and iron (Fe3+) humates is studied. A t large Fe3+ concentrations, these ions are not exchanged for uranyl ions. However, even at large uranyl concentrations, Fe3+ ions can substitute for uranyl in its complexes with natural humic acid (NHA). X-ray photoelectron spectroscopy evidence shows that Fe3+ ions are more prone to complex format ion at the surface of NHA grains than uranyl ions. This prevents the diffus ion of uranyl ions into NHA grains and, hence, the formation of uranyl comp lexes with NHA.