Speaker
Description
Methods for the determination of all actinides including thorium, uranium, neptunium, plutonium, americium and curium are of major importance for nuclear chemical technology, radiation protection and environmental control. Combined separation procedures, whatever measurement technique is joined to them, make the analysis time shorter, allow the complex analysis from single sample aliquot and assure an inherent selectivity for each actinide over other possible interfering ones.
Extraction chromatography (EC) for the separation of actinides has got a wide-spread application after actinide-specific resins became commercially available (e.g., EiChrom, Triskem). Our laboratories have been involved in in-house method development for decades. In the presentation, we will show our approaches for the development of procedures for all actinides using single resin columns or a combination of two (stacked) resin columns.
An a priori selection of the appropriate resin for the analytical purpose is based on the equilibrium distribution coefficients (Dw) of the actinides. For retaining the actinides on a resin from complex matrices high Dw values are desirable. For stripping the actinides, low Dw values are advantageous, and differences in the Dw values among actinides have to be maximized. These contradictory goals can often be achieved by strict control of actinide oxidation states, formation of specific complexes, and influencing the kinetics of the process, e.g., by changing the separation temperature, mostly under on-column conditions.
We developed two separation schemes for all actinides using a single chromatographic column. The 1st resin that had acceptable high Dw values for the tri-, tetra- and hexavalent actinides was TRU resin containing carbamoylmethylphosphine oxide (CMPO). The weak link of the procedure was the limited retention of Am-Cm. Therefore, only a “rapid” procedure was developed for small samples (soil up to 1 g). DGA resin containing diglycolamide proved to be a much stronger extractant for trivalent actinides while retaining tetravalent, and to lesser extent, hexavalent ones as well. The method developed can be used for the simultaneous separation of all actinides from bigger samples (up to 100 mL liquid waste, 5 g soil), but the interfering Ca has to be removed before the chromatography. This procedure is sensitive to changes in conditions [1].
To obtain more robust separation, two-column procedures were developed for the analysis of all actinides from about 1 liter of water (tap, sea). In the TEVA-TK221 method, the TEVA resin (containing quaternary amine) of high Dw values for tetravalent actinides, sequentially separated Th, Pu(IV) and Np(IV). For the separation of hexavalent U and trivalent Am-Cm, the TK221 resin containing CMPO and DGA extractants is used [2]. Finally, it will be discussed how the latter separation scheme had to be modified when TEVA resin was replaced by TK201 resin containing a similar organic amine extractant.
[1] Vajda N, Zagyvai M, Groska J, Bokori E, Molnár Zs, Braun M (2020) Determination of uranium, plutonium and americium in soil and sediment by a sequential separation procedure using a single DGA column, J. Radioanal. Nuclear Chem., 326(1); p. 695-710.
[2] Papp, I, Vajda, N, Happel, S (2022) An Improved Rapid Method for the Determination of Actinides in Water, J. Radioanal. Nuclear Chem. https://doi.org/10.1007/s10967-022-08389-9.