Americium from nitric acid solutions

The nitratocomplexes MIAm02(N03)3 (M1 = Rb or Cs424) are precipitated from nitric acid solutions of americium(VI). The IR spectrum of RbAm02(N03)3 has been reported.249 Hydrated phosphato, arsenato and sulfato complex salts are included under Aqua species in the preceding section. 

Tachimori, S. 1979. Synergistic extraction of americium with MEHPA-DEHPA mixed solvent from nitric acid solution. J. Radioanal. Chem. 49(1) 31-35. 

Leonard, R. A., G. F. Vandegrift, D. G. Kalina, et al. 1985. The Extraction and Recovery of Plutonium and Americium from Nitric Acid Waste Solutions by the TRUEX Process— Continuing Development Studies. Argonne National Laboratory Report ANL-85-45, Argonne, IL. 

Americium extraction from nitric acid solutions by 0.1 M chloroform solution of reagent I... 

Carbamoyl methyl Phosphine Oxide Derivatives The physicochemical properties of various aryl derivatives of CMPO have been investigated at the Vernadsky Institute of Geochemistry and Analytical Chemistry. Extraction of americium and lanthanides from nitric acid with solutions of diphenyl- and dibutyl-(diethylcarbamoylmethyl) phosphine oxides (Ph2Et2-CMPO and Bu2Et2-CMPO) in dichloroethane have been investigated as a function of the concentrations of the extractants and nitric acid (110, 111). The observed dependences are characterized... 

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. 

Co-extraction of Np and Pu The waste from the uranium extraction battery is adjusted to 5 M LiNO and then passed through an IRA-400 column at a high flow rate (30 L/h). The americium is not sorbed. Neptunium and plutonium are stripped by a dilute nitric acid solution and precipitated as a hydroxide, and calcined to yield mixture of oxides. 

The ferric hydroxide precipitate obtained is dissolved with nitric acid and is made to about 7 M nitric acid solution. This is poured on an an ion-exchange resin column (3 (j> x 40 cm) in order to adsorb plutonium. The effluent from the column is almost neutralized and americium is extracted with 30 % dibutylphosphate-dodecane solution keeping the volume ratio of organic to aqueous phases 1 2. Americium is back-extracted with 1 M nitric acid. About 15 g of plutonium and 160 mg americium were recovered from about 200 1 of the aqueous waste from the plutonium laboratory. 

The equilibrium constant, = [Am(N03)3-3TBP]/[Am ] [NO3 ] [TBP] has the value of 0-4 at zero ionic strength [41]. While TBP, even undiluted, extracts americium only weakly from strong nitric acid solutions, americium is extracted by TBP quite strongly from neutral (or low-acid), highly salted nitrate solutions. 

Treatment of waste solution. The objective of the treatment of wastes of the type described in Table II is twofold first, the elimination of alpha-emitters from the waste, and secondly the recovery of americium 241 which can be utilized directly. Since all the waste solutions contain nitric acid, the only parameters which can conveniently be defined are ... 

A nearly white precipitate of Am and Ca oxalates was obtained while most of the metallic contaminants (e.g., Fe, Cr, Al) remained in solution as stable oxalato complexes. The precipitate was filtered off, dissoved in boiling concentrated nitric acid to destroy the oxalate, neutralized with ammonia to pH = 2.5 to 3, and the Am was extracted from the strongly salted aqueous ammonium nitrate solution by 0.5 M TCMAN/Solvesso. The loaded organic solvent was scrubbed with concentrated ammonium nitrate solution, and the americium was back-extracted with dilute nitric acid, precipitated as the oxalate, and converted into An by calcination at 800°C. Multi-gram amounts of 241 have been prepared with this procedure, with Am purities > 99%. 

Before the americium can be precipitated as the oxalate, the acidity of the solution must be lowered. This cannot be done by the addition of NaOH or KOH as these cations are carried down with the americium oxalate. The acidity adjustment can be made with NH40H with no product contamination, but processing problems resulting from ammonia vapors mixing with nitric acid fumes have to be avoided. Even with the use of efficient traps, some ammonia vapors escape to form solid ammonium nitrate which plugs glovebox exhaust filters plus, ammonium nitrate also slowly sublimes through the entire exhaust system. 

The usual effect of increasing the acid concentration is reported to be an increase in the (due to increased amounts of the extractable MA3 in the aqueous phase) followed by a decrease in the (due to formation of the extractant-HNC adduct), resulting in a maximum extraction at an acid concentration between 2 and 6 M. However, one study has noted an increase in americium extraction at nitric acid concentrations from 12 to 16 M. These data are not consistent with the usual view of americium distribution dependence on nitric acid and nitrate concentration, and the authors hypothesize that a TBP HN03 adduct, which is a stronger extractant for americium than TBP alone, is formed above 8 M HNO3 and an organic-phase complex of Am(N03)3 (TBP mHNC ) is formed rather than Am(N03)3 nTBP (26). While one may not absolutely discount this possibility, additional factors such as the extraction of HAm(N03) and deviations from ideal activities in such concentrated acid solutions should definitely be considered. 

Dissolution, described in Sec. 4.4, produces an aqueous solution of uranyl nitrate, plutonium(IV) nitrate, nitric acid, small concentrations of neptunium, americium, and curium nitrates, and almost all of the nonvolatile fission products in the fuel. With fuel cooled 150 days after bumup of 33,000 MWd/MT, the fission-product concentration is around 1700 Ci/liter. The fint step in the solvent extraction portion of the Purex process is primary decontamination, in which from 99 to 99.9 percent of these fission products are separated from the uranium and plutonium. Early removal of the fission products reduces the amount of required shielding, simplifies maintenance, and facilitates later process operations by reducing solvent degradation from radiolysis. 

Effect of Nitric Acid. Preliminary experiments showed Incomplete transfer of americium from 7.0M nitric acid through a membrane of undiluted DHDECMP to 0.25M oxalic acid. Danesl et al. ( ) have shown that such membranes also transport nitric acid. Consequently, the nitric acid concentration of the strip solution Increases with time and the driving force of the transfer, the nitrate concentration gradient. Is neutralized. When this occurs, equilibrium Is reached and no further net changes In americium concentration are observed. See Horwltz al. ( ) for the equations describing the chemistry of the extraction. 

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... 

Alyapyshev, M.Yu., Babain, V.A., Smirnov, I.V., Shadrin, A.Yu. 2006. Separation of americium and europium from solutions of nitric and perchloric acid using dipicolinic acid diamides. Czech. J. Phys. 56, Suppl. D D469-D475. 

---