Sorption of neptunium on iron-containing minerals
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The sorption of neptunium on magnetite, hematite and biotite in 0.05, 0.1 and 0.2 M NaNO3 was investigated at 25°C for pH values between 1 and 8. The pH dependence of the sorption was different for the three minerals. However, there were no or a little (biotite) dependence of the sorption on ionic strength. After the sorption experiment, desorption with water of which pH was adjusted to corresponding value, 1M KCl and 0.1M K2C2O4 was also carried out to investigate the Np sorption form. It was found that for magnetite 50% of sorbed Np were sorbed by ion exchange and 25% were sorbed on the crystalline part, and that for biotite 35% of Np were sorbed by ion exchange and 30% were sorbed on the crystalline part. The sorption on crystalline part was a dominant mechanism together with ion exchange in magnetite and biotite systems. For hematite system, the sorption mechanism changed from ion exchange to the sorption on noncrystalline and crystalline parts, especially on the crystalline part, around pH6. This phenomenon is considered because surface of hematite changed with increase of pH.
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