Uranyl peroxide ((UO2)(O2)·4H2O; UO4) precipitation for uranium sequestering: formation and physicochemical characterization

Journal of Radioanalytical and Nuclear Chemistry - Applicability of uranium peroxide ((UO2)(O2)·4H2O; UO4) precipitation to remove uranium from secondary wastewaters, generated as part of a...     

Selective removal of Cs and Re by precipitation in a Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O<Subscript>2</Subscript> solution

The removal of Cs and Re (as a surrogate for Tc) by selective precipitation from the simulated fission products which were co-dissolved with uranium during the oxidative dissolution of spent fuel in a Na₂CO₃–H₂O₂ solution was investigated in this study. The precipitations of Cs and Re were examined by introducing sodium tetraphenylborate (NaTPB) and tetraphenylohosponium chloride (TPPCl), respectively. The precipitation of Cs by NaTPB and that of Re by TPPCl each took place within 5 min, and an increase in temperature up to 50 °C and a stirring speed up to 1000 rpm hardly affected their precipitation rates. The most important factor in the precipitation with NaTPB and TPPCl was found to be a pH of the solution after precipitation. Since Mo tends to co-precipitate with Cs or Re at a lower pH, an effective precipitation with NaTPB and TPPCl was done at pH of above 9 without the co-precipitation of Mo. More than 99% of Cs and Re were precipitated when the initial concentration ratio of NaTPB to Cs was above 1 and when that of TPPCl to Re was above 1. The precipitation of Cs and Re was never affected by the concentration of Na₂CO₃ and H₂O₂, even though they were raised up to 1.5 and 1.0 M, respectively. Precipitation yields of Cs and Re in a Na₂CO₃–H₂O₂ solution were found to be dependent on the concentration ratios of [NaTBP]/[Cs] and [TPPCl]/[Re].     

Complexation of U(VI), Ce(III) and Nd(III) with acetohydroxamic acid in perchlorate aqueous solution

Complexes of UO₂ ²⁺, Ce³⁺ and Nd³⁺ (M) with acetohydroxamic acid (AHA or L) in an aqueous solution have been investigated by the pH-spectral titration method at 25 °C in an aqueous medium of 1.0 M NaClO₄ ionic strength. Cerium(III) and neodymium(III) form [ML]²⁺, [ML₂]⁺, [ML₃] complexes with acetohydroxamic acid, while in case of UO₂ ²⁺ form [UO₂L]⁺, [UO₂L₂] complexes with acetohydroxamic acid. Data processing with SQUAD program calculates the best values for the stability constants from pH-spectrophotometric titration data. The protonation constant obtained was pK₁ = 9.15 ± 0.04 at 25 °C. The stability constants for acetohydroxamic acid with UO₂ ²⁺, Ce³⁺ and Nd³⁺ were β₁ = 7.22 ± 0.011, β₂ = 14.89 ± 0.018 for UO₂ ²⁺ and β₁ = 5.05 ± 0.062, β₂ = 10.60 ± 0.076, β₃ = 16.23 ± 0.088 for Ce³⁺ and β₁ = 5.90 ± 0.028, β₂ = 12.22 ± 0.038, β₃ = 18.58 ± 0.042 for Nd³⁺, respectively.     

Electrolysis of Nitric Acid by Using a Glassy Carbon Fiber Column Electrode System

The electrochemical redox behavior of nitric acid was studied using a glassy carbon fiber column electrode system, and its reaction mechanism was suggested and confirmed in several ways. Electrochemical reactions in less than 2.0M nitric acid was not observed. However, in more than 2.0M nitric acid, the reduction of nitric acid to nitrous acid occurred and the reduction rate was slow so that the nitric acid solution had to be in contact with an electrode for a period of time long enough for an apparent reduction current of nitric acid to nitrous acid to be observed. The nitrous acid generated in more than 2.0M nitric acid was rapidly and easily reduced to nitric oxide by an autocatalytic reaction. Sulfamic acid was confirmed to be effective to destroy the nitrous acid. At least 0.05M sulfamic acid was necessary to scavenge the nitrous acid generated in 3.5M nitric acid.     

Uranyl phosphate (MUO2PO4, M = Na+, K+, NH4+) precipitation for uranium sequestering: formation and physicochemical characterisation

Journal of Radioanalytical and Nuclear Chemistry - Uranyl phosphate synthesis (MUO2PO4, M = Na+, K+, NH4+) by diffusion method, direct and pH-controlled precipitation has been performed...     

Accelerated denitration by formic acid accompanied with residual acid-electrolytic trimming

The fruit bodies of wild-growing higher fungi (macromycetes), commonly called mushrooms, of various genera and species collected in localities with different geochemical features and man-made burden in the Czech Republic were analyzed by different modes of activation analysis. The elements Na, Mg, Al, S, Cl, K, Ti, V, Mn, Cu, Br, Ba and Dy were determined by short-term instrumental neutron activation analysis (INAA). Short-term epithermal INAA (ENAA) was used for determination of I and other elements, such as Rb, Ag, and U. The elements Na, K, Sc, Cr, Fe, Co, Cu, Zn, As, Se, Br, Rb, Ag, Cd, Sb, Cs, Ba, La, Ce, Sm, Eu, Hf, Au, Hg and Th were determined by long-term INAA, whereas long-term ENAA enabled determination of several other elements, such as Ni, Ta, W and U. The analytical possibilities of instrumental photon activation analysis (IPAA) using a microtron were also explored and found useful for determination of several additional elements, namely Sr, Y, Zr, Nb, and Pb. High concentrations of several essential and toxic trace elements found (up to hundreds of mg^.g^-1, dry mass) should be of concern in nutritional studies, because mushrooms form non-negligible part of diet in many countries, especially in Middle and East Europe.     

Oxidation State and Extraction of Neptunium with TBP

The change of Np oxidation state in nitric acid and the effect of nitrous acid on the oxidation state were analyzed by spectrophotometry, solvent extraction, and electrochemical methods. The Np extraction with 30 vol.% TBP was enhanced by the adjustment of the Np oxidation state using a glassy carbon fiber column electrode system. The knowledge of electrolytic behavior of nitric acid was important because the nitrous acid affecting the Np redox reaction was generated during the adjustment of the Np oxidation state. The Np solution used in this work consisted of Np(V) and Np(VI) but no Np(IV). The ratio of Np(V) in the range of 0.5M5.5 M nitric acid was 32%19%. The electrolytic oxidation of Np(V) to Np(VI) in the solution enhanced the Np extraction efficiency about five times higher than without electrolytic oxidation. It was confirmed that the nitrous acid in a concentration of less than about 10^–5 M acted as a catalyst to accelerate the chemical oxidation reaction of Np(V) to Np(VI).     

Targeting efficiency of a-1,3-galactosyl transferase gene in pig fetal fibroblast cells

Animal cloning technology with somatic cells provides an alternative tool to conventional methods for producing transgenic animals. Gene targeting in animals is made feasible using somatic cells with homologous recombination procedure that is a major technique in embryonic stem cells for knocking-out genes. Homologous recombination events in somatic cells are relatively inefficient as compared to those in ES cells, suggesting the need for establishment of efficient gene targeting system in somatic cells. To investigate the efficiency of positive and negative selection for gene targeting in pig fetal fibroblast cells, pig alpha-1,3-galactosyl transferase (13-GT) gene was used for gene targeting. The neomycin phosphotransferase (Neo(r)) and herpes simplex virus-thymidine kinase (HSV-tk) genes were used as positive and negative selection markers in this experiment. Following transfection with targeting DNA construct, the pig fetal fibroblast cells were selected against resistance of G418 and gancyclovir. In DMEM medium containing 5 to 10% serum, Pig fetal fibroblast cells failed to proliferate during drug selection. Increasing serum concentration to 15% of medium yielded less senescent colonies of pig fetal fibroblast cells following drug selection that allowed enough cell colonies to screen genomic DNA. The frequency of gene targeting in pig fetal fibroblast cells with double drug selection was more than 10-fold efficient compared to that with G418 single selection. Double selection method with Neo' and HSV-tk genes could be useful for gene targeting in somatic cells for production of cloned animals carrying targeted endogenous genes.     

Electrochemical de-chlorination/transformation of metal chloride for the preparation of NZP structure product

A new two-step process was investigated to treat LiCl molten salt waste containing volatile radionuclides generated from an electro-metallurgical processing (pyro-processing) of spent oxide fuels. First, the chemical form of the soluble LiCl waste was transformed into a chloride-free and less soluble hydroxide compound by an electrochemical method, where an electrolytic de-chlorination was performed without adding any chemical salt. Then, a gelation process of the chemical form-changed Li compound, named gel-route stabilization/solidification (GRSS) system aimed to reduce the volatility of the radionuclides greatly, was introduced to stabilize/solidify the hydroxide salt wastes. The application of the electrochemical dechlorination/transformation process and the subsequent gel-route stabilization process to treat the soluble LiCl salt wastes was found to be effective.     

A liquid-liquid static contactor using capillary phenomena induced by a highly packed fiber bundle

A new static contactor was developed for solvent extraction using capillary phenomena induced among clearances formed within a highly packed fiber bundle. Feeding two immiscible phases cocurrently into the fiber bundle generated a very large liquid-liquid contact area for mass transfer within the fiber bundle without any flow turbulence or drop phenomena. In order to test the characteristics and stability of the fiber bundle contactor, continuous extraction experiments were carried out using the fiber bundle contactor with a TBP-uranyl ion-nitric acid system. The fiber bundle contactor had the same extraction performance as that of an ideal batch extractor with good reproducibility due to the sufficient liquidliquid contact area generated by the packed fiber bundle. A minimum residence time of the aqueous phase within the fiber bundle contactor was required for the extraction system to reach an extraction equilibrium state. In the TBP-uranyl ion-nitric acid system, the residence time was about 1.9 minutes. This contactor was confirmed to be effective enough to perform solvent extraction and to study the extraction kinetics because of the stable and large static liquid-liquid contact area.