Actinide complexes oxalates

The actinides have a high degree of specificity for neutral and anionic oxygen-containing organic molecules. The actinide complexes with O -donor ligands that are most widely studied include alkoxides, aryloxides amide, carboxylates, and oxalates. Complexes with alcohols, ethers, esters, ketones, aldehydes, ketoenolates, and carbamates have also been reported. 

Oxalate. A large number of actinide(VI) oxalate and mixed ligand oxalate complexes have been reported (see Table 46). Different coordination modes of uranyl by the oxalate group have... 

Conceptual Flowsheet for the Extraction of Actinides from HLLW. Figure 5 shows a conceptual flowsheet for the extraction of all the actinides (U, Np, Pu, Am, and Cm) from HLLW using 0.4 M 0< >D[IB]CMP0 in DEB. The CMPO compound was selected for this process because of the high D m values attainable with a small concentration of extractant and because of the absence of macro-concentrations of uranyl ion. Distribution ratios relevant to the flowsheet are shown in previous tables, IV, V, VI, and VII and figures 1 and 2. One of the key features of the flowsheet is that plutonium is extracted from the feed solution and stripped from the organic phase without the addition of any nitric acid or use of ferrous sulfamate. However, oxalic acid is added to complex Zr and Mo (see Table IV). The presence of oxalic acid reduces any Np(VI) to Np(IV) (15). The presence of ferrous ion, which is... 

The measurement of stability constants of complexes of yttrium, lanthanide, and actinide ions with oxalate, citrate, edta, and 1,2-diaminocyclohexanetetra-acetate ligands has revealed that there is a slight increase in the stability of complexes of the /-electron elements, relative to the others. A series of citric acid (H cit) complexes of the lanthanides have been investigated by ion-exchange methods and the species [Ln(H2cit)]", [Ln(H2cit)2] , [Ln-(Hcit)], and [Ln(Hcit))2] were detected. Simple and mixed complexes of dl- and jeso-tartaric acid have been obtained with La " and Nd ions, and the stability constants of lactate, pyruvate, and x-alaninate complexes of Eu and Am " in water have been determined. 

Table 31 Actinide(IV) Mixed Oxalates and Oxalato Complexes...

When ammonium oxalate or potassium oxalate is slowly added to a solution containing actinides, actinide(IV) and (VI) ions form soluble complex ions, whereas actinide(III) ions precipitate as oxalates. Actinide(IV) and (VI) ions present in ammonium or potassium oxalate solutions precipitate by addition of cobalt (III) or chromium(III) complex salts. 

Hexamminecobalt(III) salt cannot be used as a precipitant in the oxalato complex precipitation system because it precipitates as hexamminecobalt(III) oxalate. Besides the hexaureachro-mium(III) salt, hexamminechromium(III), tris(ethylenediamine)cobalt (III) or tris(trimethylenediamine)cobalt(III) salts can be used as precipitants. Hexamminechromium(III) and tris(ethylenediamine) cobalt (III) salts form precipitates with actinide(IV) or (VI) oxalato complex ions, whereas tris(trimethylenediamine)co-balt(III) salt forms precipitates with Th(IV) or U(VI) oxalato complex ions leaving Pu(IV) ion in the supernatant solution.Therefore, this reagent plays the role of both a separating agent and a precipitant and is applicable for the separation of Pu(IV) ion from Th(IV) or U(VI) ion. 

The solution reactions of Cm3+ closely resemble those of the lanthanide and actinide +3 ions, and the fluoride, oxalate, phosphate, iodate, and hydroxide are insoluble. Complexes appear to be weaker than those of preceding elements. 

Salts of 0x0 anions, snch as nitrate, snlfate, perchlorate, iodate, hydroxide, carbonate, phosphate, oxalate, and so on, are important for the separation and reprocessing of technologically important actinides, while hydroxide, carbonate, and phosphate ions are important for the chemical behavior of the actinides in the enviromnent. The general trends of complexes formed in aqneons solntions are as follows ... 

The predicted waste inventory for the repository indicates that potentially significant quantities of the organic ligands—acetate, citrate, oxalate, and EDTA—will be present (US DOE, 1996). Actinide interactions with these compounds were not considered in the speciation and solubility modeling, as calculations suggested that they would be mostly complexed by transition metal ions (Fe, Ni " ", Cr, and Mn " ") released by corrosion of the steel waste containers and waste components. A thermodynamic model of actinide-ligand interactions appropriate to brines will be included in solubility calculations for WIPP recertification. 

Amines, hydrazines, and hydroxylamines. Amine complexes are known for tetravalent complexes of the earliest actinides (Th, U), particularly for the halides, nitrates, and oxalates. The complexes are generated either in neat amine, or by addition of amine to the parent compound in a nonaqueous solvent. Some of the known simple amine compounds are presented in Table 6. The molecular structure of ThCl4(NMe3)3 has been determined. The coordination environment about the metal is a chloride capped octahedron. A very limited number of adducts exist in which a tetravalent actinide is coordinated by a hydrazine or hydroxylamine ligand the parent compound is generally a halide or sulfate complex. Cationic metal hydrates coordinated with primary, secondary, or tertiary amines have also been isolated with acetylacetonate, nitrate, or oxalate as counterions. 

Table 26 Actinide(IV) mixed oxalate and oxalato complexes.

To prevent during the denitration step the formation of precipitates on which Pu and Am were partially and irreversibly adsorbed, denitration and oxalate precipitation were carried out in a single step by addition of the waste solution to the formic and oxalic acid mixture, the latter acid acting as a metal complexant during the denitration step. By experimental tests performed on simulated HAW according to this modified process scheme, separation yields of about 99.5% for Pu and 99.8% for Am were measured. A further reduction of the actinide content was reached by flowing the clarified HAW solution through a Dowex 50 resin column. The oxalate precipitation experiments on fully active HAW solutions have practically been completed. The results obtained from five runs (Table IV) confirmed the previous results obtained on simulated solutions. 

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