Synthesis, characterization, and ion exchange properties of a sodium nonatitanate, Na4Ti9O20.xH2O

Abstract

During the Cold War, the Hanford Weapons Site in Richland, Washington, produced weapons grade plutonium which first needed to be separated from the other products using the PUREX process (plutonium and uranium extraction). As a by product of this process, millions of cubic meters of highly acidic radioactive waste were produced which are now stored in million gallon tanks at the Hanford site. Over the years, some tanks have been known to leak and some are even in danger of exploding. Because of these problems, the waste needs to be removed from these tanks and given permanent, safe storage. The purpose of this research is to produce a more efficient ion exchanger to separate the highly radioactive isotopes (9oSr, 137 Cs and transuranics) from the large quantities of inert salts. The smaller volume of high level waste produced can then be vitrified in glass and stored, while the low level waste can be poured into less expensive cement and glass. In this work, different parameters of the synthesis of the sodium nonatitanate ion exchanger, Na4Ti9O2OoxH20, such as the Na and Ti reactants, the heating time, oven temperature, Na:Ti mole ratio, and heating method, were altered and their effects on Sr2' ion exchange selectivity were examined. For example, the heating time was varied from I day to 2, 3, 7, and 30 days. Although the crystallinity remained the same from the I day to the 2 day sample, as the heating time further increased, the crystallinity improved. The most Sr selective material was the 2 day sample with a Kd (distribution coefficient) of 1.22x 106 MI/g in O.lM Na/ O.OOIM Sr solution. The Kd's steadily decreased as the sample crystallinity increased with a maximum Kd of only 1.6OxlO5 in O.OIM Na/ O.OO I M Sr solution after a heating time of 30 days. However, in a simulated waste such as NCAW, the 2 day sample gave a Kd of only 1.44x 105 MI/g, while the I day sample gave a value of 2.50x 105 . This indicates that the nonatitanate synthesis needs to be uniquely designed to optimize Sr 2+ removal in each specific type of waste to be remediated.