Abstract
D.Sc.
The ion exchange properties of a number of synthetic inorganic
ion exchangers and the natural zeolite, clinoptilolite, were
evaluated with respect to the elements Na, Cs, Sr, Ba, Ce(III),
Eu, Zr, U(VI), Np(V), PU(IV) and Am(III). The role of the
structure of crystalline exchangers in determining the
selectivity thereof, especially in the case of clinoptilolite,
was also investigated.
Hydrated antimony pentoxide and antimonic acid showed high
sorption of a number of ions over a wide pH range (2 - 10). The
selectivity order of hydrous oxides for the actinides was as
follows: PU(IV) > Am(III) > U(VI) > Np(V). Titanium phosphate,
zirconium phosphosilicate and sodium titanate, however, preferred
U to Am. To predict the selectivity order of crystalline
inorganic ion exchangers, the Eisenman theory could be used, but
other factors such as ion sieve effects had to be taken into
account. In such cases the parameters contributing to the change
in free energy during ion exchange plays a major role.
Samples containing clinootilolite from two deposits in South
Africa were evaluated with respect to chemical composition,
conversion to the sodium, calcium and cesium forms, as well as
the sorption of Cs and Sr from various media. Similar trends to
those:reported for clinoptilolite from other parts of the world
were found.
Rietveld refinement of the structure of Cs-exchanged clinoptilolite
was carried out using powder diffraction data and the
computer program WYRIET. The zeolite was not isolated from the
natural matrix, which meant that a number of phases had to be
included in the refinement process. The refinement confirmed the...