Americium (z = 95) is a manmade radioactive element generated by the bombardment of uranium or plutonium by neutrons in a nuclear reactor. In terms of inventory at the Waste Isolation Pilot Plant (WIPP) (i.e., the world’s only currently-operating deep geologic repository for the disposal of defense-related transuranic waste), the radioactivity of Am-241 is of comparable concern to that of plutonium (&gt; 1,000,000 Ci) and, with a half-life of 432 years, poses a radiological risk for thousands of years. Ethylenediamenetetraacetic acid (EDTA) is an organic complexant commonly used to produce, process, and separate actinide elements or decontaminate items contaminated with actinides, and is thus co-disposed with Am at the WIPP. In this work, we used UV-vis-NIR spectrophotometry to study the effect of elevated temperature on Am-EDTA complexation. Samples were prepared in an anoxic glovebox with 10–5 M Am-243 and H-Na-EDTA salt (with H and Na ranging from 0–4, depending on the desired pH) in 0.1 m NaClO4 as a function of pH (1–13), temperature (25–90°C), and time (0–60 days). At each time point, the pH of the sample was measured and spectra were acquired using a Varian Cary 5000 UV-Vis-NIR spectrophotometer equipped with a temperature controller. Samples were then filtered through 10 kDa filters and measured by ICP-MS to determine concentration, so as to check for precipitation and normalize spectral measurements. The resulting stability constants contribute to a growing actinide thermodynamic database and can be used to determine the extent and likelihood of Am mobility in the environment.

Spectrophotometric determination of americium-EDTA complexation in perchlorate media at elevated temperature

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