Americium phosphate

Following this principle, some authors [74] have S3mthesized first europium phosphate Eui/3Zr2(P04)3 and then americium phosphate Ami/3Zr2(P04)3 [75] and classified them as members of the NZP family. The IR spectra and structure refinement of the Eu phosphate were carried out by the Rietveld method which... 

The metabolism of americium consists of binding interactions with proteins and probably complex formation with various inorganic anions such as carbonate and phosphate, and carboxylic acids such as citrate and lactate (Durbin 1973 Taylor 1973 Webb et al. 1998). These types of interactions would be expected for all routes of exposure. 

Guilmette RA, Bay AS. 1981. Radio assays of americium or curium in biological material by isoctyl acid phosphate solvent extraction and a liquid scintillation counting. Anal Chem 53 2351-2354. 

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). 

In its precipitation reactions ameiicium(IIl) is very similar to the other tripositive actinide elements and to the rare earth elements. Thus the fluonde and the oxalate are insoluble and the phosphate and iodate are only moderately soluble in acid solution, whereas the nitrates, halides, sulfates, sulfides, and perchlorates are all soluble. Americium(VI) can be precipitated with sodium acetate giving crystals isostructural with sodium uranyl acetate,... 

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. 

Srinivasan, T.G., Vasudeva Rao, P.R., Sood, D.D. 1998. Diluent and extractant effects on the enthalpy of extraction of uranium(VI) and americium(in) nitrates by trialkyl phosphates. Solvent Extraction and Ion Exchange 16(6) 1369-1387. 

Solvent Extraction. Plutonium and americium were separated in a single pass through a set of mixer-settlers using 30% tri-n-butyl phosphate (TBP) in a n-paraffin hydrocarbon (NPH). 

The process operated successfully in the plant. More than 98% of the americium was recovered from the cation exchange column as an acidic nitrate solution. Substantial quantities of sodium, iron, nickel, sulfate, and phosphate were removed. Decontamination from these impurities was satisfactory, but almost all the chromium and small amounts of nickel, iron, and lead remained. 

Solvent extraction [tributyl phosphate (TBP)] operations to recover plutonium from unirradiated scrap have been performed at the Hanford Site since 1955. The aqueous raffinate (CAW stream) from the TBP plutonium extraction process contains, typically, <10 mg/L plutonium and 2-10 mg/L 2 1Am. This latter isotope is present in the plutonium scrap as the result of beta decay of Pu (t]/2 = 14.4 y) tri valent americium does not accompany plutonium from the HNO3-HF feed solution into the TBP solvent. 

Moskvin, A. I. Investigation of the complex formation of trivalent plutonium, americium, and curium in phosphate solutions, Soviet Radiochem., 13, 688 (1971). 

Ri/M 2(P04)3. a double americium zirconium phosphate Ami/3Zr2(P04)3 (M = Zr) was synthesized and characterized by X-ray diffraction methods [74,75], This phosphate belongs to the NZP structure type. The NH4H2PO4 solution was added to the starting solution of americium nitrate and ZrOCU thermal treatment of the precipitates was carried out stage-by-stage up to 800°C. 

In addition, the ARALEX process can be used to scrub residual TBP from various product streams such as americium and curium nitrate solutions, thus preventing the eventual precipitation of phosphates. The D s for TBP from dilute (0.17 to) to concentrated (8 M) HNO3 solutions using 2-EHOH are in the range of 8 x 103 to 5 x 103, respectively, at 25°C and 50°C. 

Large-scale purification of americium, curium, and californium with pressurized cation exchange has been planned at SRP for many years (1). Initial work involved SRP batch extractions to isolate a crude actinide-lanthanide fraction followed by solvent extraction and ion exchange in the SRL high level caves (1J. For large-scale purification, a single step was substituted for batch extraction and solvent extraction. Plant Purex solvent (30 vol % tri-n-butyl phosphate in n-paraffin) was used to minimize flush time and cross-contamination of solvent. 

In aqueous solution americium exists in the four oxidation states Am(III), Am(IV), Am(V), and Am(VI). In the absence of complexing agents trivalent, pentavalent, and hexavalent americium exist as Am , Am02, and Am02, usually in hydrated form. In aqueous solution tetravalent americium rapidly disproportionates, except in concentrated fluoride and phosphate solutions. 

The remaining elements, from Cf onward, have only the +3 state. The great similarity between the +3 ions of Am and the trans-americium elements has meant that the more conventional chemical operations successful for the separation of the previous actinide elements are inadequate and most of the separations require the highly selective procedures of ion-exchange discussed below solvent-extraction of the M3+ ions from 10-16M nitric acid by tributyl phosphate also gives reasonable separations. 

Supercritical Fluid Extraction of Plutonium and Americium from Soil Using p-Diketone and Tributyl Phosphate Complexants... 

When 3.5 mo % of the acidic beta-diketone hexafluoroacetylacetone was used in combination with 2.7 mol% tributyl phosphate, 76% 2 of the plutonium and 93% 1 of the americium could be extracted in a single 45 minute extraction at 65 °C. When the ligand concentrations were increased to 6.8 mol% hexafluoroacetylacetone and 5.3 mol% tributyl phosphate, and the extraction temperature was increased to 95 °C, a maximum of 83% 5 plutonium and 95% 3 americium were extracted. The SFE results for the TBP - HFA system are given in Table II. 

The effect of solvent structure on the enthalpy of extraction of americium (III) nitrate was studied using various trialkyl phosphates such as tri-n-butyl phosphate (TBP), tri-isobutyl phosphate, tri-n-amyl phosphate (TAP), tri-isoamyl phosphate and tri-n-hexyl phosphate. The results indicated that the enthalpy of extraction decreased in the order TBP>TsBP>TAP>TiAP THP. This behaviour was in contrast to the variation of the enthalpy of extraction of uranium (VI) with the alkyl carbon stmcture of the trialkyl phosphates reported in literature. 

The Lanthaniden Und Curium Americium (LUCA) process is developed in Germany for the selective separation of Am(III) from the solution issued either from the DIAMEX-SANEX processes or the GANEX process. It uses a mixture of bis(chlorophenyl)dithip-hosphinic acid ((ClPh)2PSSH) and tris(2-ethylhexyl)phosphate (TEHP) as the extractant. 

Fig. Z Americium and europium distriburion ratios for extraction by 5% tributyl phosphate (hexane) as a function of NaSCN concentration (pH 4-5) in the presence and absence of Naa04 as supporting electrolyte. Open symbols are for variable concentrations of NaSCN. Closed symbols represent NaSCN/NaC104 mixtures at 5.0 M total ionic strength. Data from Sekine(1965).

Complicating the development of ISEs for higher actinide ions is their inherent radioactivity. They also have chemistry tiiat often differs from that of the uranyl cation. Actinides from americium to lawrencium display solution-phase chemical features that resemble those of the trivalent lanthanides. Conversely, in certain oxidation states, the early actinides (thorium through neptunium) often mimic transition metals. Also, as mentioned above, many of the actinides can exist in a large number of oxidation states. For instance, in the case of plutonium, four oxidation states can exist simultaneously in aqueous solution. Finally, as true for the lanthanides, complex salts with hydroxide, halogens, perchlorates, sulfates, carbonates, and phosphates are well known for most of the actinides. 

Precipitation of /-element phosphates from molten salts was previously studied for NaCl-, KC1-, NaCl-KCl- and LiCl-KCl-based melts. The elements studied included uranium [1,2], plutonium [3,4], americium and curium [5] and lanthanides [1, 6-12]. A range of phosphates (sodium, potassium, lithium and ammonium) were employed as precipitants. Depending on the experimental conditions (melt composition, temperature, nature of the phosphate preeursor) the reactions resulted in the formation of single (LnP04) or double [M3Lu2(P04)3, M3Ln(P04)2l phosphates. 

Foos and Guillaumont [32] measured the partition of americium at 150-160°C between molten L1N03-KN03 phases and tri-n-butyl phosphate (TBP) and other extractants. 

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