Ferrate treatment for removing chromium from high-level radioactive tank waste.

A method has been developed for removing chromium from alkaline high-level radioactive tank waste. Removing chromium from these wastes is critical in reducing the volume of waste requiring expensive immobilization and deep geologic disposition. The method developed is based on the oxidation of insoluble chromium(III) compounds to soluble chromate using ferrate. This method could be generally applicable to removing chromium from chromium-contaminated solids, when coupled with a subsequent reduction of the separated chromate back to chromium(III). The tests conducted with a simulated Hanford tank sludge indicate that the chromium removal with ferrate is more efficient at 5 M NaOH than at 3 M NaOH. Chromium removal increases with increasing Fe(VI)/Cr(II) molar ratio, but the chromium removal tends to level out for Fe(VI)/ Cr(III) greaterthan 10. Increasingtemperature leadsto better chromium removal, but higher temperatures also led to more rapid ferrate decomposition. Tests with radioactive Hanford tank waste generally confirmed the simulant results. In all cases examined, ferrate enhanced the chromium removal, with a typical removal of around 60-70% of the total chromium present in the washed sludge solids. The ferrate leachate solutions did not contain significant concentrations of transuranic elements, so these solutions could be disposed as low-activity waste.

Coordination of lanthanide triflates and perchlorates with N,N,N',N'-tetramethylsuccinamide.

Compounds formed from the reaction of N,N,N',N'-tetramethylsuccinamide (TMSA) with trivalent lanthanide salts possessing the poorly coordinating counteranions triflate (CF3SO3-) and perchlorate (ClO4-) have been prepared and examined. Structural features of these Ln-TMSA compounds have been studied in the solid phase by thermogravimetric analysis, infrared spectroscopy, and, in selected cases, by single-crystal X-ray diffraction and in solution by infrared spectroscopy. Eight-coordinate compounds, [Ln(TMSA)4]3+, derived from coordination of four succinamide ligands to the metal ion could be formed with all lanthanides examined (Ln = La, Pr, Nd, Eu, Yb, Lu). Structural analyses by single-crystal X-ray diffraction were performed for the lanthanide triflate salts Ln(C8H16N2O2)4(CF3SO3)3: Ln = La, compound 1, monoclinic, P2(1)/n, a = 11.0952(2) A, b = 19.2672(2) A, c = 24.9759(3) A, beta = 90.637(1) degrees, Z = 4, Dcalcd = 1.586 g cm-3; Ln = Nd, compound 2, monoclinic, C2/c, a = 24.6586(10) A, b = 19.3078(7) A, c = 11.1429(4) A, beta = 90.450(1) degrees, Z = 4, Dcalcd = 1.603 g cm-3; Ln = Eu, compound 3, monoclinic, C2/c, a = 24.4934(2) A, b = 19.3702(1) A, c = 11.1542(1) A, beta = 90.229(1) degrees, Z = 4, Dcalcd = 1.617 g cm-3; Ln = Lu, compound 5, monoclinic, C2/c, a = 24.2435(4) A, b = 19.6141(2) A, c = 11.2635(1) A, beta = 90.049(1) degrees, Z = 4, Dcalcd = 1.626 g cm-3. X-ray analysis was also carried out for the perchlorate salt: Ln = Eu, compound 4, triclinic, P1, a = 10.9611(2) A, b = 14.6144(3) A, c = 15.7992(2) A, alpha = 106.594(1) degrees, beta = 91.538(1) degrees, gamma = 90.311(1) degrees, Z = 2, Dcalcd = 1.561 g cm-3. In the presence of significant amounts of water, 7-coordinate compounds with mixed aquo-TMSA cation structures [Ln(TMSA)3(H2O)]3+ (Ln = Yb) and [Ln(TMSA)2(H2O)3]3+ (Ln = La, Pr, Nd, Eu, Yb) have been isolated with structural determinations by single-crystal X-ray diffraction obtained for the following species: Yb(C8H16N2O2)3(H2O)(CF3SO3)3, compound 6, monoclinic, P2(1)/n, a = 8.9443(3) A, b = 11.1924(4) A, c = 44.2517(13) A, beta = 93.264(1) degrees, Z = 4, Dcalcd = 1.735 g cm-3; Yb(C8H16N2O2)3(H2O)(ClO4)3, compound 7, monoclinic, Cc, a = 19.2312(6) A, b = 11.1552(3) A, c = 19.8016(4) A, beta = 111.4260(1) degrees, Z = 4, Dcalcd = 1.690 g cm-3; Yb(C8H16N2O2)2(H2O)3(CF3SO3)3, compound 8, triclinic, P1, a = 8.6719(1) A, b = 12.2683(2) A, c = 19.8094(3) A, alpha = 75.815(1) degrees, beta = 86.805(1) degrees, gamma = 72.607(1) degrees, Z = 2, Dcalcd = 1.736 g cm-3. Unlike in the analogous nitrate salts, only bidentate binding of the succinamide ligand to the lanthanide metal is observed. IR spectroscopy studies in anhydrous acetonitrile suggest that the solid-state structures of these Ln-TMSA compounds are maintained in solution.

The synthesis and characterization of N-substituted iminodiacetato cis-, trans-R, R- and trans-S, S-1, 2-diaminocyclohexane platinum(II) complexes: steric effects on the diastereomeric ratios.

A series of platinum(II) complexes of the type [Pt(N-R-IDA)(DACH)], where DACH was either cis-1,2-diaminocyclohexane, trans-R, R-1, 2-diaminocyclohexane, or trans-S, S-1, 2-diaminocyclohexane, and N-R-IDA was either the iminodiacetate, N-methyliminodiacetate, N-n-propyliminodiacetate, or N-t-butyliminodiacetate ion, has been prepared and characterized. A detailed NMR investigation shows that the N-R-IDA ions bind to the platinum (II) ion through one of the acetate oxygens and the imino nitrogen, forming a five-membered ring. The second acetate ion does not bind to the platinum. By virtue of the prochiral N-atom of N-R-IDA and the absence of a horizontal plane of symmetry of the Pt(DACH) moiety, two diastereomers are observed corresponding to the two different orientations of the unbound acetate and the R-group with respect to the platinum coordination plane. The ratio of the two geometric isomers is controlled by steric factors depending upon both the isomeric form of 1,2-diaminocyclohexane and the nature of the R group bound to the imino nitrogen of N-R-IDA.