Hexavalent Oxidation State Research Articles

Electron injection in Te-doped derivatives ofTl2Mn2O7pyrochlore

A series of Te-substituted pyrochlores of stoichiometry ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2\ensuremath{-}x}{\mathrm{Te}}_{x}{\mathrm{O}}_{7}$ $(x<~0.2)$ has been prepared under high-pressure conditions, at 20 kbar. A neutron-diffraction study demonstrates that Te atoms partially replace Mn cations, adopting a hexavalent oxidation state. The samples are ferromagnetic (FM), showing a maximum ${T}_{C}$ of 193 K for the $x=0.1$ member, considerably higher that that of undoped compound ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7},$ with ${T}_{C}=120$ K. This trend implies the reinforcement of an extra FM superexchange interaction mediated by the conduction band. Hall effect shows a dramatic increase in the number of carriers upon Te doping, implying an electronic injection associated with the replacement of ${\mathrm{Mn}}^{4+}$ by the aliovalent ${\mathrm{Te}}^{\mathrm{VI}}.$ The magnetoresistance (MR) is lower than that observed for the undoped pyrochlore, as expected for a higher number of carriers. The high temperature resistivity can be modeled by a thermally activated behavior, via magnetic polaron hopping. The activation energy decreases upon Te doping, which also suggests an overall enhancement of the FM interactions in the conduction matrix.

DIPHONIX-CS : A NOVEL COMBINED CESIUM AND STRONTIUM SELECTIVE ION EXCHANGE RESIN*

ABSTRACT The recently developed Diphonix® resin contains the geminally substituted diphosphonic acid ligand chemically bonded to a styrene-divinylbenzene copolymer. The resin exhibits an extraordinarily strong affinity for actinides, especially in the terra- and hexavalent oxidation states. Therefore the resin has potential for application in TRU removal from nuclear wastes. The Diphonix-CS resin is a Diphonix-type resin that contains also phenolic groups chemically attached to the polymeric matrix. The phenolic groups exhibit high affinity for Cs+ ions from highly alkaline media. Thanks to the combined action of the diphosphonic acid and the phenolic groups, the Diphonix-CS resin can simultaneously remove actinide species, Cs and Sr from alkaline media. In this paper the results obtained in the characterization of the new resin are reported, with regard to the uptake equilibrium and kinetics of Cs+ and Sr+2 removal from NaOH solutions and from synthetic alkaline wastes. The chemical and radiolytic stability of the resin has been investigated. The results have indicated that the Diphonix-CS resin is remarkably stable under the experimental conditions of this work (up to 35 days in I to 4 M NaOH, and up to 200 MRad gamma ray absorbed dose). The possibility of stripping the Cs+ and Sr+2 from the resin has been investigated in column experiments by using 1 M HNO3 as the stripping agent. Some problems encountered in the stripping of Sr+2 and possible ways to improve the stripping performance are discussed.

DIPEX: A new extraction chromatographic material for the separation and preconcentration of actinides from aqueous solution

A novel extraction chromatographic resin consisting of a liquid diphosphonic acid supported on an inert polymeric substrate for the sorption of actinides from strongly acidic chloride media is described. The resin is shown to exhibit stronger affinity for actinides in the tri-, tetra- and hexavalent oxidation states and superior selectivity for americium(III) over aluminum(III) or iron(III) than an analogous chelating ion-exchange resin containing chemically bonded geminally substituted diphosphonic acid functionalities. These properties, along with the comparative ease of recovery of sorbed actinides, make the resin readily applicable to the separation and preconcentration of actinides, as a group, from complex matrices such as soils and bioassay samples.

Diphonix® Resin: A Review of Its Properties and Applications*

The recently developed Diphonix® resin is a new multifunctional chelating ion exchange resin containing geminally substituted diphosphonic acid ligands chemically bonded to a styrene-based polymeric matrix. Diphonix can be regarded as a dual mechanism polymer, with a sulfonic acid cation exchange group allowing for rapid access, mostly non-specific, of ions into the polymeric network, and the diphosphonic acid group responsible for specificity (recognition) for a number of metal cations. The Diphonix resin exhibits an extraordinarily strong affinity for actinides, especially in the tetra- and hexavalent oxidation states. Therefore the resin has potential for applications in TRU and mixed waste treatment and characterization, and in the development of new procedures for rapid actinide preconcentration and separation from environmental samples. Metal uptake studies have been extended to alkaline earth cations, to transition and post-transition metal species, and to metal sorption from neutral or near neutral solutions. Also the kinetic behavior of the resin has been investigated in detail. In view of the above applications the influence of the most commonly occurring matrix constituents (Na, Ca, Al, Fe, hydrofluoric, sulfuric, oxalic and phosphoric acids) on the uptake of actinide ions has been measured. This review paper summarizes the most important results obtained in the studies on the properties of the Diphonix resin and gives an overview of the applications already in existence or under development in the fields of mixed waste treatment, actinide separation procedures, treatment of radwaste from nuclear power and fuel processing plants, and removal of iron from copper electrowinning solutions. *Work performed under the auspices of the Office of Basic Energy Sciences, Divisions of Chemical Sciences and Advanced Energy Projects, U.S. Department of Energy, under contract W-31-109-ENG-38.

UPTAKE OF METAL IONS BY A NEW CHELATING ION-EXCHANGE RESIN. PART 5 : THE EFFECT OF SOLUTION MATRIX ON ACTINIDES

ABSTRACT The influence of commonly occurring matrix constituents on the uptake of representative actinides in the tri-, tetra-, and hexavalent oxidation states by a new chelating ion exchange resin, called Diphonix™, has been investigated. The effect of increasing concentrations of HF at three fixed HC1 concentrations on the retention of U(VI), Np(IV), and Am(III) was measured. All three actinides showed strong retention in HF even up to a concentration of 1 M The effect of sulfuric, oxalic and phosphoric acids at three fixed HNO3 concentrations on the retention of Th(IV), U(VI), and Am(III) was also measured. Only when the concentration of the complexing acids was above 0.1 M was the retention of the actinides decreased significantly at 0.1 M HNO3 The effect was much less pronounced at higher HNO3 concentrations. Sodium, calcium, aluminum and iron were selected to study the influence of cationic matrix constituents on the uptake of actinide ions by Diphonix. In the case of tetra- and hexavalent actinides (represented by Th and U, respectively) only the very highest concentrations of Fe(III) and Al(III) caused a significant decrease in the retention of the two higher valent actinides. On the other hand, Am(III) retention was significantly lowered by Al and Fe(III) concentrations above 10−2 M The influence of Al and Fe(III) on the uptake of Am(III) may be minimized by use of fluoride ion to complex Al and by reducing Fe(III) to Fe(II). Macroconcentrations of sodium and calcium had only minimal influence on the uptake of actinides in all three oxidation states.

Afterchrome dyeing of wool. Part B — characterisation of chromium‐treated wool by secondary particle mass spectrometry

Secondary particle mass spectrometry has been used for the first time to determine the oxidation state and depth distribution of chromium on and in wool fibres. Wool tops were dyed with 4% o.w.f. CI Mordant Black 11 and aftertreated with 1% o.w.f. potassium dichromate, and wool samples treated in a blank dyebath aftertreated with 6% o.w.f. potassium dichromate were analysed. It could be shown that the absolute concentration of chromium in a surface layer 50 nm thick became enriched with chromium by a factor of two, compared with the bulk fibre. Chromium in the hexavalent oxidation state was found to be mainly present in the outermost part of the fibres, while trivalent chromium was dominant inside the fibres.

Accumulation of chromium in Chinese hamster V79-cells and nuclei

The bioavailability of carcinogenic compounds plays an important role in the process of oncogenesis. Chromium in its hexavalent oxidation state is classified as carcinogen to humans. Therefore we studied the uptake of chromate(VI) into Chinese hamster V79 cells and nuclei isolated after the incubation of the whole cells with chromate. The chromium content of cells and nuclei was determined by atomic absorption spectroscopy. Chromate is taken up in a concentration dependent manner and accumulates to about 30 fold over the extracellular concentration of 0.1 mmol/l. Incubating whole cells with the same concentration results in an intranuclear concentration of up to 6 mmol/l after 3 h. The kinetic parameters (KM = 0.34 mmol/l, Vmax = 0.12 fmol per cell and minute) are in the same order of magnitude as previously published data. The consequences of the high intracellular and intranuclear concentrations are discussed in terms of the genotoxic effects.

The chemistry and kinetic behavior of Cu‐Cr‐As/B wood preservatives. I. Fixation of chromium on wood

AbstractThe kinetic behavior of CrO3 in its reaction with wood has been elucidated. Various reactions take place between CrO3 and the lignin and cellulose in wood. CrO3 reacts with cellulose in a two‐step reaction: the first step is an adsorption of CrVI onto the cellulose to form CrVI/cellulose activated complexes. The second step is a CrVI → CrIII reduction taking place on the cellulose surface. The CrIII formed is only physically adsorbed to the cellulose or very weakly bound as small amounts of CrIII can be released into the reaction medium. The CrVI adsorbed by cellulose appears mainly to be reduced to CrIII. The reaction of CrVI with lignin has been shown to be the composition of the three successive reaction of Cr2O72−, HCrO4−, and CrO42− with the guaiacyl units of lignin. Insoluble and stable CrVI/lignin complexes in which chromium maintains its hexavalent oxidation state are formed. Rate constants and energies of activation for all the reactions have been determined. The fixation of CrO3‐derived compounds on wood has been explained as the combination of the various reactions investigated. The results indicate that 60% of Cr is fixed irreversibly to the lignin of wood as CrVI and 40% is weakly bound, probably just precipitated, on the cellulose surface as CrIII of which small amounts can be released in a water medium. The complex CrVI and CrIII species forming complexes with the guaiacyl units have been identified.

On the reaction between molten lithium perchlorate and chromium(III) oxide

The reaction at 300°C between molten lithium perchlorate and chromium(III) oxide gave lithium dichromate. When lithium perchlorate and chromium(III) oxide were in the formula weight ratio of 2:1 respectively, the chromium was oxidized completely into the hexavalent oxidation state, and only a negligible chloride percentage of 0·1 remained in the resulting lithium dichromate. Different formula weight ratios were taken for the reaction at 300°C. In the runs where the formula weight ratios of the perchlorate and oxide were lower than 2:1, the amount of chromium oxidized was higher than expected by the proposed route, and an explanation is given. Reactions with 51Cr 2O 3 showed that a very small amount of chromium volatilized. Results obtained from experiments both in vacuum and air were in very good agreement. A reaction mechanism is proposed.

Phase Relations in the System UO2‐UO3– Y2O3

The phase relations in the system U02‐U03‐Yz03, particularly in the Y203‐rich region, were examined by X‐ray and chemical analyses of reacted powders heated at temperatures up to 1700°C in H2, CO2‐CO2 and air. Four phases were identified in the system at temperatures between 1000° and 1700°C: U308, face‐centered cubic solid solution, body‐centered cubic solid solution, and a rhombohedral phase of composition (U,Y)7O2 ranging from 52.5 to 75 mole % Y2O3. The rhombohedral phase oxidized to a second rhombohedral phase with a nominal composition (U,Y), at temperatures below 1000°C. This phase transformed to a face‐centered cubic phase after heating in air above 1000° C. The solubility of UO, in the body‐centered cubic phase is about 14 mole % between 1000° and 1700°C but decreases to zero as the uranium approaches the hexavalent oxidation state. The solubility of Yz03 in the face‐centered cubic solid solution ranges from 0 to 50 mole % Y2O3 under reducing conditions and from 33 to 60 mole % Y2O3 under oxidizing conditions at 1000°C. At temperatures above 1000° C, the face‐centered cubic solid solution is limited by a filled fluorite lattice of composition (U,Y)O2. For low‐yttria content, oxidation at low temperatures (<300°C) permits additional oxygen to be retained in the structure to a composition approaching (U,Y)O2.25 A tentative ternary phase diagram for the system UO2‐UO3‐Y2O3 is presented and the change in lattice parameter and in cell volume for the solid‐solution phases is correlated with the composition.

The origin of thucholite

The origin of the organic material, and the mechanism of formation of the organo-U complex, in thucholite from the Besner Mine, Parry Sound District, Ontario, have been investigated. Results indicate that thucholite was formed by the action of aqueous solutions containing organic material, possibly as an oil-in-water emulsion. U, Pb, and other relatively soluble oxides were leached from uraninite while Al, Fe, Mg, and silica were deposited in the thucholite. The separation of U from Th and the rare earths is believed to have occurred by oxidation of tetravalent U to the more soluble hexavalent oxidation state. Oxidation of U and the organic fraction of thucholite in an otherwise reducing environment is assumed to be due to the action of radiation decomposition products of water, the hydroxyl radical and/or hydrogen peroxide. Oxidation of the organic material may also be due to subsequent reaction with hexavalent U. The liquid and solid hydrocarbons, by virtue of their optical activity, are shown to be of plant or animal origin, rather than polymerization products of methane and other low molecular weight gases. The hydrocarbons are probably not contemporaneous with the organic fraction of thucholite.