Lanthanide americium separation from

Americium and other actinide elements may be separated from lanthanides by solvent extraction. Lithium chloride solution and an eight to nine carbon tertiary amine are used in the process. Americium is then separated from curium by the above methods. 

Studies (1, 2, 3, 4) on the separation of americium-curium from lanthanide elements indicate that both cation exchange chromatography (8, 9) and the Talspeak solvent extraction process (U), 11) are promising methods. Only the most recent work at Oak Ridge National Laboratory is reported in this paper. Potential chemical processes for americium-curium removal and evaluations of their feasibility have been reported previously (U 2, 3, 4). The most recent experimental work carried out includes the following ... 

The formation of thiocyanate complexes of actinide(iii) ions (Section 21.4.6) has also been successfully utilized for the separation of actinides from lanthanides by means of anion exchange [188,201]. From a 5 m ammonium thiocyanate solution, americium (iii) is strongly sorbed on an anion-exchange column while the lanthanides pass through [201]. In this way, americium (iii) can be almost completely separated from lanthanides present even in very large amounts. 

Americium may be separated from other elements, particularly from the lanthanides or other actinide elements, by techniques involving oxidation, ion exchange and solvent extraction. One oxidation method involves precipitation of the metal in its trivalent state as oxalate (controlled precipitation). Alternatively, it may be separated by precipitating out lanthanide elements as fluorosilicates leaving americium in the solution. Americium may also he oxidized from trivalent to pentavalent state by hypochlorite in potassium carbonate solution. The product potassium americium (V) carbonate precipitates out. Curium and rare earth metals remain in the solution. An alternative approach is to oxidize Am3+ to Am022+ in dilute acid using peroxydisulfate. Am02 is soluble in fluoride solution, while trivalent curium and lanthanides are insoluble. 

Weaver, B.S., Kappelmann, F.A. 1964. Talspeak A new method of separating americium and curium from lanthanides by extraction from an aqueous solution of aminopo-lyacetic acid complex with a monoacidic phosphate or phosphonate. ORNL-3559. 

Under the same conditions, in contrast to what is observed for calix[4]arene-bearing CMPO moieties, with CPil2, distribution ratios of lanthanides increase from the lightest lanthanide, lanthanum, to europium. Americium can be easily separated from the lightest lanthanides (separation factor DAm/La > 20, DAm/Ce =15, /lAlll,Nd = 10, UAi /si = 7.5, DAm/Eu = 6), which are the most abundant lanthanides in fission-product solution. Cavitands bearing picolinamide (Cv5) or thiopicolin-amide (Cv6) residues seems much less selective than their calixarene counterparts, giving SAm/Eu < 2.18... 

A mixture of well-known extractants, di-(2-ethylhexyl)phosphoric acid (HDEHP) and CMPO, in n-paraffin was used for the study of combined extraction of different actinides (americium, plutonium, and uranium) and lanthanides (cerium and europium) and their separation from fission products (cesium, strontium, ruthenium, and zirconium).54 Combined extraction of MAs and lanthanides was studied together with group separation of MAs from lanthanides by selective stripping with a solution of diethylenetriaminepentaacetic acid (DTPA), formic acid, and hydrazine hydrate. This solution strips only MAs, leaving lanthanides in the organic phase. Subsequently, the lanthanides are stripped using a mixture of DTPA and sodium carbonate. 

Cyanex 301 One of the solvent extraction processes, used together with UREX, for separating the components of used nuclear fuel. This process uses a complex phosphinic acid, [bis(2,4,4-trimethylpentyl)dithiophosphinic acid], made by Cytec Industries, Canada. Its purpose is to separate americium, curium, and lanthanide fission products from the other components. 

Many of the classic partitioning processes rely on the formation of Am" to facilitate separation from trivalent lanthanides or heavier trivalent actinides. Americium(VI) can be prepared in basic aqueous solutions from Am using powerful oxidants, such as peroxydisulfate, and from Am using weaker oxidants, such as Ce. It can be precipitated from solution as a carbonate by electrolytic or ozone oxidation of concentrated carbonate solutions of Am or Am, or solubilized by dissolution of sodium americyl(VI) acetate. These oxidations and the resulting coordination compounds have been used for relatively large scale processing. For examples, Stephanou et found that Cm could be separated from Am by oxidizing the latter to Am with... 

Plutonium Purification. The same purification approach is used for plutonium separated from sediments or seawater. In case reduction may have occurred, the plutonium is oxidized to the quadrivalent state with either hydrogen peroxide or sodium nitrite and adsorbed on an anion exchange resin from 8M nitric acid as the nitrate complex. Americium, curium, transcurium elements, and lanthanides pass through this column unadsorbed and are collected for subsequent radiochemical purification. Thorium is also adsorbed on this column and is eluted with 12M hydrochloric acid. Plutonium is then eluted from the column with 12M hydrochloric acid containing ammonium iodide to reduce plutonium to the non-adsorbed tervalent state. For seawater samples, adequate cleanup from natural-series isotopes is obtained with this single column step so the plutonium fraction is electroplated on a stainless steel plate and stored for a-spectrometry measurement. Further purification, especially from thorium, is usually needed for sediment samples. Two additional column cycles of this type using fresh resin are usually required to reduce the thorium content of the separated plutonium fraction to insignificant levels. 

First, the trivalent actinide and lanthanide elements are separated from the other elements in the waste. In the second step, americium and curium are then separated from the lanthanide elements. Experimental studies have largely been laboratory-scale in which synthetic waste solutions and tracer levels of radioactivity were utilized. A few laboratory-scale experiments were made in hot cells on the coextraction of trivalent actinides and lanthanides. The two most promising methods investigated for co-removal of trivalent actinides and lanthanides are ... 

Trivalent americium forms relatively unstable complexes with Cl and NOs and more stable complexes with the thiocyanate ion CNS. These americium complexes are more stable than those of the corresponding lanthanide compounds, so that americium can be separated from trivalent lanthanides by anion exchange with concentrated solutions of liQ, liNOs, or NH4CNS. Trivalent americium can be extracted with TBP from a concentrated nitrate solution. It can also be extracted with TBP from a molten LINO3 -KNOs eutectic at 150°C, with much higher distribution coefficients than in extraction from aqueous solutions. Americium is more readily extracted by this process than is trivalent curium [K2]. 

Modolo, G., P. Kluxen, and A. Geist. 2009. Selective separation of americium (III) from curium (El), californium (111) and lanthanides (IE) by the LUCA process. Proceedings of Global 2009, Paris, France, Sept. 6-11, Pap>er 9336. 

Publications on the analysis of soil samples by Smith et al. [78] and Crain et al. [79] summarized two possible routes for the analysis of aqueous samples in chromatography extraction columns, with detection by conventional radiometric techniques such as ICP-MS. In this procedure, TRU-Spec SPS columns were used for group separation of actinides and TEVA-Spec columns were used to isolate the trivalent actinides from the lanthanide elements. A reduced solution (with ascorbic acid) was passed through a 1 mL TRU-Spec column equilibrated with 2 M nitric acid and 0.5 M aluminum nitrate. The trivalent actinides including americium and the lanthanide elements were eluted from the column with 12 mL of 4 M HCl. Plutonium and thorium were removed with 30 mL of... 

Bhattacharyya, A., Mohapatra, P. K., Roy, A., Gadly, T., Ghosh, V. K., and Manchanda, V. K. 2009. Ethyl-bis-triazinylpyridine (Et-BTP) for the separation of Americium(lll) from trivalent lanthanides using solvent extraction and supported liquid membrane methods. Hydrometallurgy 99 18-24. 

Am(iii) is sorbed much more strongly onto anion-exchange resins from concentrated lithium chloride solutions than are the lanthanides [61], Americium distribution ratios increase with increased lithium chloride concentration (Fig. 8.1), whereas increased temperature enhances the separation of americium from rare earths. A lithium-chloride-based anion-exchange process for separating multigram amounts of americium and curium from lanthanide fission products and to isolate an Am-Cm fraction free of heavier actinides is routinely operated at the Oak Ridge facility [14]. 

Zhu, Y. 1995. The separation of americium from light lanthanides by Cyanex 301 extraction. Radiochim. Acta 68 (1) 95-98. 

Chen, J., Tian, G., Jiao, R., Zhu, Y. 2001. A hot test for separating americium from fission product lanthanides by purified Cyanex 301 extraction in centrifugal contactors. Actinides 2001, Hayama, Japan, November 4—9. 

Treatment of irradiated targets. The chemical operations relative to the production of transplutonium elements (americium 243, curium 244) are all performed using a nitric acid medium. The highly corrosive nature of the solutions concentrated with Cl" ions, which were used in the USA for the development of the Tramex process (JO, and the instability of SCN" ions to radiation (12), led us to select nitric acid solution to perform the chemical separations. Once the medium was selected, it was necessary to find an adequate additive which, in combination with a suitable extractant, would allow solution of the main problem namely separation of the trivalent actinides from triva-lent lanthanides. 

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