The compositional flexibility of the sodium zirconium phosphate
(NaZr2(PO4)3) structure has been
exploited in the design of monophasic radiophases capable of immobilizing
the most common cations associated with reprocessed high-level commercial
waste streams. Highly crystalline, monophasic members of the
NaZr2(PO4)3 structural family ([NZP])
have been prepared with conventional processing methods and equipment. These
radiophases were tailored to accommodate 10–20 wt % modified PW-4b simulated
calcine as single phases isostructural with
NaZr2(PO4)3. To meet the challenge of
designing monophasic materials capable of accommodating the chemical
complexity of PW-4b, an ionic substitution scheme based on crystal chemical
principles was developed. The radiophases were prepared with inexpensive,
inorganic precursors and a solution sol-gel method; these materials were
heat treated and/or sintered under a variety of conditions to determine the
optimum conditions for single phase [NZP] formation. X-ray powder
diffraction provided valuable information that was used to assess the
suitability of the ionic substitution model developed in this investigation.
The results of this investigation suggest that monophasic [NZP] radiophases
capable of accommodating 10–20 wt % modified PW-4b simulated calcine may be
continuously processed with conventional ceramic processing methods and
equipment. Moreover, the relatively low temperatures involved and the
reproducibility of the process make [NZP] radiophases economically
attractive hosts for radioactive and heavy metal industrial wastes.