Americium complexes carbonates

Aluminum(III) hydroxyfluorides minerals, 846 Alzheimer s disease aluminum removal, 770 Amberlite LA 2 solvent extraction palladium and platinum, 809 Americium breeder reactor fuels Purex process, 955 reprocessing, 954 Purex process, 946,950 sequestering agents, 962 Americium(III) complexes carbonates... 

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. 

The principal abiotic processes affecting americium in water is the precipitation and complex formation. In natural waters, americium solubility is limited by the formation of hydroxyl-carbonate (AmOHC03) precipitates. Solubility is unaffected by redox condition. Increased solubility at higher temperatures may be relevant in the environment of radionuclide repositories. In environmental waters, americium occurs in the +3 oxidation state oxidation-reduction reactions are not significant (Toran 1994). 

The corresponding chloride and bromide are made by heating the dioxide with carbon tetrachloride and aluminium bromide respectively. The only tetrahalide of plutonium yet isolated is the fluoride, PUF4, although the tetrachloride appears to exist in solution. Americium forms a tetrafluoride and also a complex fluoride, KAmFg. 

In addition to the aqueous raffinates from the solvent extraction cycles of the Purex process, an actinide bearing waste stream will arise from the washing of the TBP/OK solvent prior to its recycle to the first cycle. These wastes will typically contain actinides in a mixed NajCOs/NaNOs solution which also contains HjMBP and HDBP. The uranium present will form soluble U complexes with carbonate, as discussed in Section 65.2.2.l(i). Carbonate complexation of Pu also leads to solubility in alkaline solutions and in Na2C03 media precipitation did not occur below pH 11.4, although precipitates did form on reduction to Pu One Pu" species precipitated from carbonate media has been identified as Pu(0H)3-Pu2(C03)3 H20. In 2M Na2C03 media, Np is oxidized by air to Np above pH 11.7 while Np either precipitates or is reduced above pH 13. The potential of the Am /Am " couple, in common with those of other actinides, becomes more cathodic with increasing carbonate concentration. In the total bicarbonate plus carbonate concentration range 1.2-2.3 M all the americium oxidation states from (III) to (VI)... 

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. 

From experimentation with supercritical fluid extraction it is known that neither plutonium nitrate or oxides nor americium nitrate or oxides are soluble in carbon dioxide without the aid of soluble complexing agents. Even with the aid of selected complexing agents plutonium extraction efficiency from spiked... 

On the other hand, Dyrssen and Liem (1960) report (table 7) greater variation in both distribution ratios [for americium and europium extraction by dibutyl phosphoric acid (HDBP)] and in separation factors as a function of diluent. The separation factors and distribution coefficients are correlated (more or less consistently) inversely with the distribution ratio of the extractant between the phases. In this system, the largest separation factors are observed in n-hexane, chloroform, and carbon tetrachloride. Diluents capable of direct coordination (i.e., those possessing potential oxygen-donor atoms) are correlated with reduced distribution ratios and separation factors. The observations of greater separation factors in non-complexing diluents suggest that more effective separation is observed when the inner-coordination sphere of the hydrophobic complex is not disturbed. 

Bemkopf, M.F., and J.I. Kim, 1984, Hydrolysis Reactions and Carbonate Complexation of Trivalent Americium in Natural Aquatic Systems, Inst, for Radiochem., Report No. RCM-02884 (Technical University of Munich, Munich). In German. 

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. 

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