| Abstract: |
The sorption behaviour of niobium on kaolinite and illite minerals in sodium and calcium perchlorate solutions was evaluated with use
of the mass distribution coefficient, Rd, obtained in batch sorption experiments. Very high distribution coefficient
values, about 100 m3/kg, were obtained for both minerals in the neutral pH range between 6 and 8. Values were somewhat
lower at pH 5. In NaClO4 solution, the sorption of niobium starts to decrease at pH higher than 8. This is in agreement with
the increase, with pH, in the proportion of anionic niobate species, which are presumed to be low or non-sorbing. A similar decrease
was not observed in Ca(ClO4)2 solution, probably owing to the influence of Ca on niobium solution speciation and surface
species. The surface complexation model was applied to model the Rd values. The model fitted well for the NaClO4
solution but only at pH below 9 for the Ca(ClO4)2 solution. The discrepancy between the strong sorption of niobium in
calcium-bearing solution at high pH and the calculated speciation is due in part to the non-inclusion of calcium niobate solution
species and Ca-Nb compounds in the present NEA and other similar thermodynamic databases. |
