Evaluation of a rapid technique for measuring actinide oxidation states ina ground water simulant

A system using an ion chromatograph coupled to a now-cell scintillation det ector for rapidly measuring the oxidation states of actinides at low concen trations < 10(-6)M) in aqueous solutions was evaluated. The key components of the system are a cation-anion separation column (Dionex CS5) and a flow cell detector with scintillating cerium activated glass beads. The typical procedure was to introduce a 0.5 ml aliquot of sample spiked with actinides in the +III to +VI oxidation states into a 5 mi sample loop followed by 4 mi of synthetic groundwater simulant. Separation was achieved at a now rate of 1 ml/min using an isocratic elution with oxalic, diglycolic, and nitric acids followed by distilled water. Tests were first conducted to determine elution times and recoveries for an acidic solution (pH approximate to 2) and a ground water simulant (pH approximate to 8) containing Am(III)), Pu(I V), Th(IV), Pu(V), and U(VI). Then, an analysis was performed using a mixtu re of Pu(IV), Pu(V), and Pu(VI) in the ground water simulant and compared t o results using the DBM extraction technique. Approximate elution times wer e the same for both the acidic solution and the ground water simulant. Thes e were as follows: Pu(V) at 10 min, Am(III) at 15 min, Pu(IV) at 25 min, Th (IV) at 28 min and U(VI) at 36 min. Recoveries for the acidic solution wer e quantitative for U(VI) and Th(IV) and exceeded 80% for Am(III). Recoverie s for the ground water simulant were quantitative for U(VI), but they were generally not quantitative for Th(IV), Pu(IV), and Am(III). For Th(IV) and Pu(IV), less than quantitative recoveries were attributed to the formation of neutral hydroxides and colloids; for Am(m) they were attributed to insol uble carbonates and/or hydroxycarbonates. When applied to the measurement o f plutonium in the ground water simulant, the technique provided showed goo d agreement with the dibenzoylmethane (DBM) extraction technique, but it co uld not distinguish between Pu(V) and Pu(VT). This was likely due to the re duction of Pu(VI) to Pu(V) in the sample by the oxalic acid eluent. However , in spite of this limitation, the technique can be used to distinguish bet ween Pu(IV) and Pu(V) in aqueous environmental samples within a pH range of 4 to 8 and an E-H range of -0.2 to 0.6 V, the predominance region for Pu(I II), (IV), and (V). In addition, this technique can be used to corroborate oxidation state analysis from the dibenzoylmethane (DBM) extraction method for environmental samples.