BREAKTHROUGH VOLUMES OF TcO~ ON REILLEXTM-HPQ ANION

ionic strength (It) of 6.22 M and a TcO~ of 5.00 x 10 -5 M and a 1:3 dilution of the DSS simulant, I.t = 2.07 M, with a TcO~ of 1.67 x 10 .5 M. The DSS flow rates {mL simulant/(cross section area of column.min)} through the column varied from 0.19 to 20.5 cm/min. The 1% breakthrough volumes varied from 50.0 to 1.3 bed volumes (BV), respectively. The 1:3 DSS flow rate varied from 0.95 t~ 11.9 cm]min and had 1% breakthrough volumes ranging from 94 to 20 BV, respectively. At a flow rate of 1.0 cm/min, the breakthrough bed volumes are 10.2 and 95.8 BV for the DSS and 1:3 DSS solutions, respectively. Obviously, there is an advantage in processing the 1:3 dilution of the feed stream. The United States Department of Energy (DOE) and its predecessor organizations have operated the Hanford Reservation in the state of Washington for 50 years. The site's mission was to produce plutonium for the U.S. weapons program by irradiating and dissolving uranium fuel. 1 Over the years the plutonium was recovered by various techniques, including bismuth phosphate precipitation, the REDOX process, and the PUREX process. Acidic raffinates from these processes were made causticand stored in 149 single-shell tanks (SST) and 28 larger, double-shell tanks (DST). In the last decade, reports of leaking tanks and potentially explosive gas generation in some tanks have raised concern about the safety and environment at the Hanford site. 2,3 In 1991 the DOE initiated the Tank Waste Remediation System (TWRS) program to store, treat, and immobilize the Tank waste. This program involves retrieving the tank waste and separating the material into high-level waste (HLW) and low-level waste (LLW) streams. 4 The HLW stream will be vitrified into borosilicate glass logs for disposal in a geologic repository, while the LLW will be vitrified and stored in vaults at the Hartford site. Approximately 1800 kg of technetium are stored in the Hanford waste tanks. 1 Technetium, as TcO~, is a mobile species in the environment. 5 This mobility, along with its long half-life (213,000 years) makes technetium a major contributor to the long-term hazard associated with storage of Hanford's LLW. These factors may require that technetium be removed from the waste and be disposed with the HLW. Anion exchange, using DowexrM-1 resin, was the baseline technology being considered for this separation. 6 A major concern in this process was the safety of eluting technetium from the resin with 8 M HNO3. ReillexTM-HpQ is a new resin which has shown superior radiation and chemical stability compared to DowexTM-I and other anion exchange resins. 7 This resin is a co-polymer of divinylbenzene and 4-vinylpyridine that has been methylated at the pyridine nitrogen to give pyridinium anionic sites. In a scoping study, Reillex~-HPQ had the highest technetium