PARTITIONING BEHAVIOR OF99Tc AND,129I FROM SIMULATED HANFORD TANK WASTES USING POLYETHYLENE-GLYCOL BASED AQUEOUS BIPHASIC SYSTEMS

Abstract

Three simulated Hanford tank wastes, SY-101, NCAW, and SST, were prepared and contacted with aqueous solutions of 20-60% (w/w) polyethylene glycol (PEG)-2000. The combined salting out action of OH^-, C0₃ ²’, SO₄ ²rsquo;, PO₄ ³\ and possibly other minor constituents in the waste simulants, results in the formation of aqueous biphasic systems (ABS). Investigation of the partitioning behavior of ⁹⁹Tc (as ⁹⁹Tc0₄) and ₁₂₉I (as ⁹⁹T) from the waste simulant phase to the upper PEG-rich phase at 25 and 50°C revealed distribution ratios as high as 190 for ⁹⁹Tc0₄ and 7.5 for ¹²⁹I. The partitioning of several of the other major species in these solutions (Na⁺, P0₄ ³, C0₃ ²’, S0₄ ²\ PEG), as well as the general physical characteristics of the ABS were also investigated. In general, the observed distribution ratios are affected (increased if they prefer the PEG-rich phase, decreased if they prefer the salt-rich phase) by increasing the concentration of PEG-2000 used to form the ABS which increases the difference in actual PEG concentration in each phase. Stripping of the ⁹⁹Tc0₄ from the loaded PEG-rich phase has been accomplished by reduction of pertechnetate and contact with a fresh salt ((NH₄)₃ (citrate)) solution. Other possible stripping or disposal options are also discussed.