Americium distilled metal

PUCI3, and MgCl2 to form a 50/50 mole % NaCl-CaCl salt phase and a molten Am-Pu-Mg-Ca alloy which is immiscible in the above salt(lO). After cooling, the metal phase is cleaved away from the salt phase and the salt phase is analyzed. Little, if any, Am or Pu remains in the salt phase and the salt residues can be discarded to waste. Metal recovery begins by evaporating magnesium and calcium from the residual metal button at about 800°C in vacuum. The americium can then be distilled away from the plutonium in a vacuum still operated at 1200°C, using yttria ceramic vessels to contain the molten metal fraction. The bottoms fraction contains the plutonium which is recycled back into the main plutonium stream. 

Vacuum distillation of the americium away from the plutonium has been demonstrated by Berry and Knighton.12 In this work the goal was to recover pure americium metal. They demonstrated the ability to recover >50 g batches of americium (>99% pure) in a two-stage distillation. 

Americium and curium can be obtained from the aqueous waste of the Purex process. This americium is a mixture of Am and " Am. Isotopically pure Am, the decay product of " Pu, can be obtained from aged plutonium. Solvent extraction and ion-exchange procedures are used to recover americium from waste streams. Americium metal is produced by lanthanum reduction of the oxide, followed by vacuum distillation of the americium at 1400°C. 

Traditionally, the recovery and purification of americium has utilized primarily aqueous ion-exchange, solvent extraction, and precipitation processes. Departures are represented by the pyrochemical process and distillation of americium metal in high vacuum used at the Rocky Flats plant (Colorado) [333]. 

Americium metal has been prepared by the following methods (1) reduction of AmF3 with barium (or lithium) metal (2) reduction of Am02 with lanthanum metal (3) bomb reduction of AmF4 with calcium metal (4) thermal decomposition of Pts Am. Lanthanum reduction of Am02 in tantalum equipment and subsequent distillation of the americium metal from the reaction mixture yields americium of very high (>99.9%) purity. There is about 10 -fold difference in americium-lanthanum volatility. Extensive application of this technique by the Euratom group has led to important new measurements of the physical properties and thermodynamic properties of americium metal [81,342], Rocky Flats workers have reported similar success with vacuum distillation [333]. 

Preparation of americium metal by thermal decomposition of the intermetallic compound PtsAm is a recent development. Muller, Reul, and Spirlet [343] produced high-purity americium metal by thermal decomposition of 4 g of PtsAm at 1550 C and 10 torr, followed by further distillation. 

The heats of solution of americium metal in aqueous hydrochloric add solutions at 298.15 0.05 K were redetermined in 1972 by Fuger, Spirlet, and Muller [241] with pure ameridum metal prepared by distillation. Combined with earlier results, the standard enthalpy of formation of Am (aq) at 198 K of — 616.7 1.3kJmol was calculated [242]. For hydration enthalpy and entropy, see Choppin [359]. 

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