共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Nava-Galve G. Pacheco G. Fetter P. Bosch S. Bulbulian 《Journal of Radioanalytical and Nuclear Chemistry》1996,207(2):263-274
A Mexican montmorillonite clay was intercalated on the one hand with aluminium or zirconium polyhydroxications, and on the other with two organic compounds. Radioactive cobalt was used to study the Co2+ sorption curves in the original and pillared clays. It was found that pillaring in general does not favour the diffusion of cobalt between the layers specially the organic pillared clays. In equilibrium, the cobalt retention reached the highest level, around 0.7 meq/g in the Zr pillared clay. 相似文献
2.
Madhuri A. Patel Aishwarya S. Kar Dimple Garg Sumit Kumar B. S. Tomar R. K. Bajpai 《Journal of Radioanalytical and Nuclear Chemistry》2017,313(3):555-563
Worldwide argillaceous clays are being studied as promising host rock for nuclear high level waste disposal. Cuddapah argillite is under evaluation for Indian clay rock based repository. Herein characterization of this clay and evaluation for its sorption characteristics towards Cs(I) and Eu(III) has been studied. Surface complexation modeling of Cs(I) sorption on argillaceous clay revealed that Cs(I) is sorbed on high as well as low affinity ion exchange sites. In modeling of Eu(III) sorption data, surface complexes of Eu(III) and europium carbonate species, along with ion exchange reaction, reproduced the sorption profile with ankerite dissolution influencing distribution of various surface complexes. 相似文献
3.
The sorption and desorption isotherms of untreated calcareous soil and three treated soils to remove CaCO3, organic matter (OM) and both CaCO3 and OM were determined and analyzed with the Freundlich equation at pH 7.8, moderate concentrations of NpO2
+ (~10-5mol/l), in the presence of 0.01 mol/l CaCl2 and under ambient aerobic conditions. The relative contribution of CaCO3 and OM to the neptunium(V) sorption on calcareous soil and the sorption/desorption hysteresis is discussed. The effects of adding fulvic acid (FA) and carbonate in to the solution on the sorption of neptunium(V) on the soils were also studied. The sorption and desorption characteristics of NpO2
+, Zn2+, Sr2+ and Cs+ on the soils are compared. 相似文献
4.
Cheknane B Zermane F Baudu M Bouras O Basly JP 《Journal of colloid and interface science》2012,381(1):158-163
Effect of the granulation process onto the thermodynamic and kinetic sorption parameters of two basic dyes (Basic Yellow 28-BY 28 and Basic Green 4-BG 4) was evaluated in the present work. The charge surface properties of the surfactant-modified aluminium-pillared clay (CTAB-Al-Mont-PILC) particles were not modified, and the isoelectric point remains constant after high shear wet granulation. The Gibbs free energy of both BY 28 and BG 4 sorption was negative and decreased with the granulation; the endothermic nature of the sorption process was confirmed by the positive values of ΔH°. Adsorption kinetics of the two dyes, studied at pH 6 and 150 mg L(-1), follow the pseudo-first order kinetic model with observed rate constants of 2.5-4.2×10(-2) min(-1). The intraparticle diffusion model, proposed by Weber and Morris, was applied, and the intraparticle plots revealed three distinct sections representing external mass transfer, intraparticle diffusion and adsorption/desorption equilibrium. Diffusion coefficients, calculated from the Boyd kinetic equation, increased with the granulation and the particle size. Pseudo-first order kinetic constants, intraparticle diffusion rate constants and diffusion coefficients were determined for two other initial concentrations (50 and 100 mg L(-1)) and include in a statistical study to evaluate the impact of granulation and initial concentration on the kinetic parameters. Kruskal-Wallis tests, Spearman's rank order correlation and factor analysis revealed a correlation between (i) the diffusion coefficients and granulation, and between (ii) the intraparticle diffusion rate constants and initial concentration. 相似文献
5.
A. I. Karelin E. N. Semenov N. A. Mikhailova 《Journal of Radioanalytical and Nuclear Chemistry》1991,147(1):33-40
A coulometric titration method with controlled current and amperometric end-point detection with two indicator electrodes was worked out to determine neptunium in solutions which were obtained while treating the spent nuclear fuel. This method allows to determine in presence of 1000-fold quantities and more of Pu, Ce, Cr, Fe, Mn, 1000-fold quantities and more of U. The error of determination is 0.2% for pure Np solutions and increases up to some precent in presence of large amounts of impurity. 相似文献
6.
P. Cauchetier 《Analytica chimica acta》1981,124(2):443-448
(Spectrophotometric determination of neptunium.) Use of the absorption peak of the NpO+2 ion at 981 nm is discussed. Quantitative conversion to Np(V) requires oxidation of Np(IV) by Ce(IV), reduction of Np(VI) and excess of Ce(IV) with hydrazinium nitrate, and destruction of excess of hydrazine by nitrite. The measurable concentration range in the cuvette is 2–1000 mg l-1 and the precision is± 1% in the higher range. Uranium and plutonium at ratios Me/Np ? 10-3 do not interfere. 相似文献
7.
8.
N. Xu L. Tandon D. Gallimore E. Lujan D. R. Porterfield L. Colletti K. Kuhn 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(1):245-249
A case study for dissolution and assay of neptunium oxide is presented in this paper. A simple analytical method for completely dissolving neptunium oxide is described. Addition of 12 M HNO3 is sufficient to dissolve neptunium oxide without precipitate formation. Various analytical chemistry methods were evaluated for neptunium assay including controlled potential coulometry, gas proportional counting/alpha spectrometry, gamma spectrometry using a high purity germanium detector, inductively coupled plasma-mass spectrometry, and isotope dilution-inductively coupled plasma-mass spectrometry. The precision and uncertainty of each analytical method is discussed. 相似文献
9.
10.
P. K. Kalsi L. R. Sawant R. C. Sharma S. Vaidyanathan 《Journal of Radioanalytical and Nuclear Chemistry》1994,187(4):265-275
A narrow span (E
o
±0.1 V) controlled potential coulometric method has been developed for the determination of neptunium in 1M H2SO4 with a RSD of 0.2%. The main advantage of this method over the existing coulometric methods is that it can tolerate up to a 5-fold excess of plutonium. The method involves carrying out the electrolysis to about 97% and calculating by an iterative computation the formal electrode potential in situ, which is used to calculate the total amount present in the sample. The method consists in oxidation of all the neptunium to Np (VI) by Ce(IV), destruction of excess Ce(IV) and reduction of Np(VI) to Np(V) by NaNO2, destruction of excess nitrite by sulfamic acid followed by coulometric titration of Np(V) to Np(VI). 相似文献
11.
A simple and quick method for the potentiometric determination of neptunium on the 2-5 mg scale has been developed. It consists of oxidation to Np(VI) by AgO or fuming with HClO(4), destruction of excess of AgO by sulphamic acid, reduction of Np(VI) to Np(IV) with a slight excess of standard Fe(II) in 2M H(2)SO(4) and potentiometric titration of the excess of Fe(II) with standard Ce(IV). The precision is +/-0.5%. 相似文献
12.
《Journal of the Less Common Metals》1982,83(2):263-267
Single crystals of neptunium arsenides (Np3As4 and NpAs2) were prepared by chemical transport using iodine as the transporting agent. The neptunium arsenides were transported from 720 to 760 °C and from 800 to 850 °C for Np3As4 and NpAs2 respectively. The single-crystal size is in the millimetre range. 相似文献
13.
John E. Crooks Hosny El-Daly Mohammed Y. El-Sheikh Abdul-Fatah M. Habib Ahmed B. Zaki 《国际化学动力学杂志》1993,25(3):161-168
The kinetics for the exchange of Li+, K+, Rb+, and Cs+ for Na+ as the exchangeable cation on bentonite and montmorillonite K10 and KSF have been studied using conductimetric stoppedflow. Dilute aqueous suspensions of the clays, of particle sizes of a few micrometers, were used, so that diffusion was fast and the rate-determining step was the substitution of one cation by another on the lattice surface. The kinetics were treated in terms of relaxation from equilibrium. Relaxation times ranged from 100 to 250 ms, and forward rate constants from 30 to 500 M?1 s?1. The reactions had very low activation enthalpies (7–25 kJ mol?1) and were only slow enough to be studied by the stopped-flow technique because of the large negative entropies of activation (?120 to ?170 J K?1 mol?1). © 1993 John Wiley & Sons, Inc. 相似文献
14.
U. M. Kasar A. R. Joshi S. K. Patil 《Journal of Radioanalytical and Nuclear Chemistry》1991,150(2):369-376
A method for controlled potential coulometric determination of neptunium by titration with internally electrolytically generated iron(II) has been developed. The method involves oxidation of Np to Np(VI) by Ce(IV), destruction of excess of Ce(IV) by NaNO2 followed by determination of neptunium by reduction of Np(VI) to Np(IV) by internal generation of Fe(II). The method was employed for various neptunium solution samples and a precision of ±0.25% at 2–5 mg level of neptunium was obtained. 相似文献
15.
《Journal of Inorganic and Nuclear Chemistry》1976,28(3):495-500
The neptunium-oxygen system for 2·00 < O/Np < 2·7 was studied between room temperature and 900°C and under controlled oxygen pressure. Thermogravimetry, gas manometry and X-ray diffraction were applied to decomposition of Np(V) and Np(VI) hydroxides and Np(V) nitrate. The oxide region of apparent stoichiometry 2·50 < O/Np < 2·67 was emphasized, and evidence is presented showing that the only higher oxide in this region is monoclinic Np2O5,. Decomposition to the dioxide is achieved by heating to above 700°C, for which the O2 pressure dependence is given. Oxide having the Np(VI) hydroxide as a precursor is shown to decompose through an additional intermediate near Np4O9. 相似文献
16.
L. F. Bellido V. J. Robinson H. E. Sims 《Journal of Radioanalytical and Nuclear Chemistry》1993,172(1):107-115
A new chemical method based in two separation steps was developed to isolate235Np from uranium targets irradiated with charged particles. Neptunium and plutonium are separated from uranium and most of the fission products by ion exchange. Then, neptunium is isolated from plutonium and remaining contaminants by extraction chromatography with tributyl phosphate in hydrochloric acid solution. High decontamination was achieved. 相似文献
17.
In order to increase the adsorption capacities of bentonite, sepiolite, and illite for the removal of boron form aqueous solution, the clay samples were modified by nonylammonium chloride. Specific surface areas of the samples were determined as a result of N2 adsorption-desorption at 77 K using the BET method. X-ray powder diffraction analysis of the clays and modified clays was used to determine the effects of modifying agents on the layer structure of the clays. The surface characterization of clays and modified clay samples was conducted using the FTIR technique before and after the boron adsorption. For the optimization of the adsorption of boron on clays and modified clays, the effect of pH and ionic strength was examined. The results indicate that adsorption of boron can be achieved by regulating pH values in the range of 8-10 and high ionic strength. In order to find the adsorption characteristics, Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherms were applied to the adsorption data. The data were well described by Freundlich and Dubinin-Radushkevich adsorption isotherms while the fit of Langmuir equation to adsorption data was poor. It was reached that modification of bentonite and illite with nonylammonium chloride increased the adsorption capacity for boron sorption from aqueous solution. 相似文献
18.
A lamellar neptunium(IV) methylphosphonate, Np(CH3PO3)(CH3PO3H)(NO3)(H2O).H2O, has been prepared under hydrothermal conditions via the in situ reduction of NpVI to NpIV. The single crystal structure of this compound shows polar layers that are joined to one another via a hydrogen-bonding network involving interlayer water molecules. Magnetic susceptibility measurements demonstrate that the NpIV ions are magnetically isolated from one another. 相似文献
19.
N. Xu D. Gallimore A. Martinez L. Townsend 《Journal of Radioanalytical and Nuclear Chemistry》2013,297(1):127-132
An ICP-MS analytical method as an alternative to the current radiochemical method was developed to analyze trace level 237Np in bulk plutonium materials. In this method, 237Np is determined together with a suite of trace elements during a single analysis using one dissolution solution. Method validation was achieved through precision examination, spike recovery study, detection limit determination, comparison of results with the radiochemical method, and laboratory intercomparison studies on Pu metals. The ICP-MS method significantly reduced the analysis cost, the sample amount, consumption of chemicals and waste generation, as well as the sample turnaround time. 相似文献
20.
The feasibility of the reaction Np4++2Ni0Np0+2Ni2+ in organic liquids is reported. This reaction, which is impossible to carry out in water, has been achieved in acetonitrile, while it remained impossible in dimethylformamide. This behavior in the two liquids is determined by solvent effects on the ions (Np4+, Ni2+) and we demonstrate that the classical Bom equation, as modified by Tanaka, is capable to foresee these different behaviors. 相似文献