Americium chemistry

Lambertin, D., Sanchev, S., Picard, G.S., and Lacquement, J. (2003) Temperature dependence and effect of oxide anion on the americium chemistry in the molten LiCl-KCl eutectic, Radiochim. Acta, 91, 449-452. 

In post-war work at Chicago, Cunningham isolated Am(OH)3 and measured the absorption spectrum of the Am aquo ion [2]. By the 1950s, the major center for americium chemistry research in the world was at Los Alamos. In the 1970s, the bulk of publications on americium came from the USSR and West Germany. 

Complexation and stability of americium ions in various media, including solids used for waste storage, are of increasing importance because of americium occurrence in nuclear process waste. Solutions to the problems of long-term, safe storage of americium must be found. To answer such questions, an increase in the study of americium chemistry is to be anticipated. 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Molten salt extraction residues are processed to recover plutonium by an aqueous precipitation process. The residues are dissolved in dilute HC1, the actinides are precipitated with potassium carbonate, and the precipitate redissolved in nitric acid (7M) to convert from a chloride to a nitrate system. The plutonium is then recovered from the 7M HNO3 by anion exchange and the effluent sent to waste or americium recovery. We are studying actinide (III) carbonate chemistry and looking at new... 

The following pages will describe several examples of pyrochemical processing as applied to the recycle of plutonium, and will briefly review the fundamental chemistry of these processes. We shall review the conversion of plutonium oxide to plutonium metal by the direct oxide reduction process (DOR),the removal of americium from metallic plutonium by molten salt extraction (MSE), and the purification of metallic... 

A production process has evolved from this original work, and is presently used for extracting americium from kilogram amounts of plutonium metal. This process is based upon equilibrium partitioning (by oxidation-reduction reactions) of americium and plutonium between the molten chloride salt and the molten plutonium phase. The chemistry of this process is indicated by the following reactions ... 

Ide HM. 1986. Americium and plutonium in fecal samples a screening procedure. In Health and environmental chemistry Analytical techniques, data management, and quality assurance. Gautier MA, Gladney ES, eds. Los Alamos, NM Los Alamos National Laboratory. Report LA-10300-M. 

Uranium, Neptunium, Plutonium and Americium. Zit. bei G. N. Yakovlev and V. N. Kosyakov, The Chemistry of Americium. Report A/Conf. 15/P/2127. Proceedings, 2nd Intemat. Conference on the Peaceful Uses of Atomic Energy, Geneva 1958, Vol. 28, S. 383. 

The Chemistry of Americium Compounds. Report AECD-1930 (Marz 1948). 

A Review of Americium and Curium Chemistry. Report A/Conf. 8/P/838. 

At Los Alamos National Laboratory in New Mexico the Analytical Chemistry Group (C-AAC) supports the Pu-238 Heat Source Project that fabricates heat sources for use in the space industry. These heat sources have been used on NASA s deep-space probes and on instruments exploring the surface of Mars. The chemical and isotopic purity of the heat sources are critically controlled to ensure dependable service. The Radiochemistry Task Area performs analyses of the heat source material for four radioisotopes americium-241, plutonium-238, neptunium-237, and uranium-235. 

Table 3. Formal reduction potentials (in volts) of uranium, neptunium, plutonium and americium for 1 M perchloric add solutions at 25 °C. (F. A. Cotton and G. Wilkinson Advanced Inorganic Chemistry. Interscience Publishers 1972)...

An examination of the chemistry of americium indicates that it is intermediate between that of plutonium and that of curium. The chemistry of curium bears a strong resemblance to that of the lanthanides in solution curium exists in the + 3 oxi dation state, although the tetravalent state has been observed as Cm F4 in a solid matrix. 

As trivalent americium has a smaller ionic potential than the ions of plutonium it hydrolyses to a much lesser extent than the various plutonium ions. However, like Pu3+, hydrolytic reactions and complex formation are still an important feature of the aqueous chemistry of Am3+. Starik and Ginzberg (25) have shown that Am(III) exists in its ionic form from pH 1.0 to pH 4.5 but above pH 4.5 hydrolysis commences and at pH 7.0 colloidal species are formed. The hydrolytic behaviour of Cm(III) resembles that of Am(III). 

Schulz, W. W. The Chemistry of Americium, U.S. Department of Energy Technical Information Center Oak Ridge, Tennessee, 1976 p. 203. 

Y. Shiokawa, S. Suzuki, in Americium and Curium Chemistry and Technology, (Eds. ... 

Matyunin, Yu. I. 1995. Investigation of plutonium and americium behavior at vitrification of simulated HLW with production of phosphate glass-like materials with various macrocompositions. Radio-chemistry, 37, 557-562 (in Russian). 

The Pu-enriched region also contained Am, REE, Zr, and Ru however, americium and the REE were present at lower than expected levels. The depletion of REE and Am in the precipitated Pu-layer is interesting as these elements are usually considered to be good analogues for Pu chemistry. The chemistry of Pu has been recently complicated by the discovery of Pu02+JC (Haschke et al. 2000 Conradson et al. 

In 1951 along with Edwin McMillan he received the Nobel prize in chemistry for the creation of the first transuranium elements. He created plutonium, americium, curium, berkelium, and californium at Berkeley. 

---