Nitric acid americium extraction from

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

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... 

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... 

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. 

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. 

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%. 

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. 

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. 

A process for the recovery of Am (and Pu) from these concentrates, based on solvent extraction with tricapryl methyl ammonium nitrate, TCMAN (Aliquat-336, nitrate form), was developed (30), and was operated for some time in a small-scale facility equipped with pulsed glass columns at the Alkem company to produce multi-gram amounts of americium dioxide. In its final version (3JU the process worked as follows The concentrated effluents were made up to 6 to 7 moles/1 nitric acid, and the U and Pu were extracted in the first column by 0,5 moles/1 TCMAN dissolved in Solves-so-100, a high-boiling aromatic diluent. U and Pu... 

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. 

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. 

Metal-complexation/SFE using carbon dioxide has been successfully demonstrated for removal of lanthanides, actinides and various other fission products from solids and liquids (8-18), Direct dissolution of recalcitrant uranium oxides using nitric acid and metal-complexing agents in supercritical fluid carbon dioxide has also been reported (79-25). In this paper we explored supercritical fluid extraction of sorbed plutonium and americium from soil using common organophosphorus and beta-diketone complexants. We also qualitatively characterize actinide sorption to various soil fractions via use of sequential chemical extraction techniques. 

Muscatello et al. (117) discuss the use of hollow fiber ILMs containing blfunctlonal organophosphorus extractants to remove americium and plutcnlum from nltrate-nltrlc acid waste streams. A reduction In the actinide concentration In a waste stream would allow disposal of the stream as a low-level waste. Partial neutralization of the nitric acid In the waste stream was necessary to obtain high (>9M9) removal of the Am(III). 

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. 

We have Investigated the transfer of americium and, to some extent, plutonium from aqueous nitrate wastes using supported liquid membranes of the blfunctlonal organophosphorus extractants DHDECMP and 0()D(1B)CMP0 (+TBF). The results show good transfer and removal If the nitric acid In the feed Is first neutralized to O.IOM to minimize acid transfer and subsequent back transfer of the metal Ion. 

The microporous hollow-fiber membrane modules were employed for liquid-liquid extraction of neodymium as a surrogate for americium from 2 M nitric acid using dihexyl-A,A-diethylcarbamoylmethylphosphonate (DHDECMP) and CMPO extractants in diisopropylbenzene. These modules are applied for back extraction of neodymium from organic phase into 0.01 M nitric acid [149]. 

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... 

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. 

Some extraction systems are able to extract metals by both the solvation and ion exchange mechanisms an example of such a system is the americium (and lanthanide) extraction from nitric acid by a combination of 6,6 -Z>A-(5,6-dipentyl-l,2,4-triazin-3-yl)-2,2 -bipyridine and 2-bromohexanoic acid in tert-h xt benzene. At both high- and low-nitric acid concentrations, the metal distribution ratio is higher than it is for an intermidate nitric acid concentration. 

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