PARTITIONING BEHAVIOR OF TC-99 AND I-129 FROM SIMULATED HANFORD TANK WASTES USING POLYETHYLENE-GLYCOL BASED AQUEOUS BIPHASIC SYSTEMS

Three simulated Hanford tank wastes, SY-101, NCAW, and SST, were prepa red and contacted with aqueous solutions of 20-60% (w/w) polyethylene glycol (PEG)-2000. The combined salting out action of OH-, CO32-, SO42 -, PO43- , and possibly other minor constituents in the waste simulant s, results in the formation of aqueous biphasic systems (ABS). Investi gation of the partitioning behavior of Tc-99 (as (TcO4-)-Tc-99) and I- 129 (as I-129(-)) from the waste simulant phase to the upper PEG-rich phase at 25 and 50 degrees C revealed distribution ratios as high as 1 90 for (TcO4-)-Tc-99 and 7.5 for I-125(-). The partitioning of several of the other major species in these solutions (Na+, PO43-, CO32- SO42 -, PEG), as well as the general physical characteristics of the ABS we re also Investigated. In general, the observed distribution ratios are affected (increased if they prefer the PEG-rich phase, decreased if t hey prefer the salt-rich phase) by increasing the concentration of PEG -2000 used to form the ABS which increases the difference in actual PE G concentration in each phase. Stripping of the (TcO4-)-Tc-99 from the loaded PEG-rich phase has been accomplished by reduction of pertechne tate and contact with a fresh salt ((NH4)(3)(citrate)) solution. Other possible stripping or disposal options are also discussed.