Characterization of UOP IONSIV IE-911

As a participating national lab in the inter-institutional effort to resolve performance issues of the non-elutable ion exchange technology for Cs extraction, we have carried out a series of characterization studies of UOP IONSIV IE-911 and its component parts. IE-911 is a bound form (zirconium hydroxide-binder) of crystalline silicotitanate (CST) ion exchanger. The crystalline silicotitanate removes Cs from solutions by selective ion exchange. The performance issues of primary concern are: 1) excessive Nb leaching and subsequent precipitation of column-plugging Nb-oxide material, and 2) precipitation of aluminosilicate on IE-911 pellet surfaces, which may be initiated by dissolution of Si from the IE-911, thus creating a supersaturated solution with respect to silica. In this work, we have identified and characterized Siand Nboxide based impurity phases in IE-911, which are the most likely sources of leachable Si and Nb, respectively. Furthermore, we have determined the criteria and mechanism for removal from IE-911 of the Nb-based impurity phase that is responsible for the Nb-oxide column plugging incidents. In parallel, UOP has revised the manufacturing process to eliminate or minimize these impurity materials, which are the sources of column plugging oxides. The primary alteration in the manufacturing process is the addition of a NaOH wash of the IE-911 at the factory in a batch mode. A major thrust of the studies described here was to characterize these new materials (baseline—acid and leached—NaOH treated), specifically to determine if the leachable components had been minimized or removed. Primary results include: • The leachable Nb in the UOP-leached IE-911 was reduced by a factor of 20, compared to the original IE-911, acid-form materials (UOP batches 98-5, 99-7, 99-9). • By TEM inspection, the soluble, Nb-based impurity phase is almost completely removed from the UOP-leached IE-911. • There are single crystals of niobium oxide, several microns in diameter, abundant in both the baseline and leached IE-911 (which is regarded to be largely insoluble in NaOH, see first bullet). This impurity phase makes up less than a total of 1 % by volume of the IE-911. • The leachable Si is determined to arise from trace impurities of silicate and aluminosilicate, incorporated into the IE-910 and IE-911 batches during the manufacturing process. • These Si-containing impurities are not controllable, and vary in an unpredictable manner in composition, morphology, leachability and concentration between batches. Finally, one additional sidelight study presented in this report is characterization of the binder, particularly its behavior in caustic solutions. The results of this study provided a better overall understanding of behavior and spectroscopic characterizations of IE-911.