ABSTRACTIE-911 is a bound form of cystalline silicotitanate (CST) that was extensively tested for removing 137Cs from the Savannah River Site (SRS) tank wastes. In some simulant tests, column plugging incidents were observed, which led to thorough investigations to determine the causes and to develop protocols to avoid future plugging incidents. A related problem was the apparent decrease in Cs scavenging capability in some long-term tests. Our studies revealed that the interaction of IE-911 with the highly basic, high ionic strength, SRS average salt simulant could result in precipitation of; 1) poorly crystalline Nb-oxide, or 2) aluminosilicate zeolitic phases. The source for the Nb-oxide precipitate was determined to be a minor impurity phase that is a byproduct of CST manufacturing. The mechanisms of dissolution and re-precipitation of this phase in column pretreatment solution were investigated, and a protocol to rid IE-911 of this impurity was devised. The source material for the aluminosilicate zeolite precipitate was determined to be predominantly from the waste solution rather than the IE-911. Solubility experiments coupled with a thermodynamic analysis provided a protocol to predict when aluminosilicate precipitation will and will not occur. Finally, it was also established that aluminosilicate precipitation on the surfaces of the IE-911 granules could also account for an apparent decrease in equilibrium Kd and decrease in kinetics of Cs sorption.
Modeling Long-Term Plutonium Transport in the Savannah River Site Vadose Zone