Sorption of 63Ni(II) to montmorillonite as a function of pH, ionic strength, foreign ions and humic substances

Different kinds of clay minerals have been studied extensively in the removal of radionuclides from large volumes of aqueous solutions because of their high sorption capacity. Herein, the Na-montmorillonite was characterized by using XRD and FTIR in detail. The sorption of 63Ni(II) from aqueous solution to montmorillonite as a function of pH, ionic strength, foreign ions, humic substances and temperature was studied by batch technique. The sorption of 63Ni(II) on montmorillonite achieved equilibration quickly. The sorption of 63Ni(II) to montmorillonite was strongly dependent on pH, and dependent on ionic strength at low pH and independent of ionic strength at high pH values. The sorption of 63Ni(II) on montmorillonite was enhanced at low pH in the presence of humic acid (HA), while a negative effect of HA on 63Ni(II) sorption was found at high pH values. At low pH values, the sorption of 63Ni(II) was attributed to outer-sphere surface complexation or ion exchange, whereas the sorption was dominated by inner-sphere surface complexation at high pH values. The montmorillonite sample is a suitable material in the preconcentration of radionuclides from large volumes and the material can be used as backfill material in nuclear waste repository.