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1.
The sorption of uranyl ions in mesoporous MCM-41 and MCM-48 was accomplished with the help of a direct-template-exchange route, and the progress was monitored as a function of pH of the precursor uranyl nitrate solution. Under identical conditions of synthesis, around one and a half times larger amount of uranium was found to be sorbed in MCM-48 (∼12.5 wt.%) as compared to MCM-41 (∼9.5 wt.%). Further, the powder X-ray diffraction (XRD) data revealed that the expansion of unit cell parameters and broadening of reflections of the uranium containing samples depended on the pH of the precursor uranyl solution. Likewise, the Fourier transform infrared spectroscopy (FT-IR) studies showed a progressive decrease in the frequency of the axial OUO asymmetric stretching vibrational band, νa(UO) of the anchored uranyl groups with the increase of pH of the exchanging uranyl solution. The presence of two bands at ∼920 and 879 cm−1 for uranyl exchanged samples prepared at pH > 5 indicated the presence of trinuclear (UO2)3+5(OH) species. The occlusion of uranium thus depends upon the pore structure of the host material and the nature and dimension of the hydrolysis species formed at a particular pH of uranyl solution. Furthermore, the template-exchange of hexavalent uranium in MCM-41 and MCM-48 not only results in the formation of bulky hydrolysis species in the mesovoids, but also substitutes (isomorphously) in the silicate matrix resulting in the formation of UMCM-41 and UMCM-48.  相似文献   

2.
Decomposition of aqueous suspensions of uranium(IV) oxalate under the action of an ozone–oxygen mixture was studied. The process occurs in two steps. In the first step, the U(IV) oxidation with the formation of oxalic acid uranyl solutions prevails. The second step involves decomposition of oxalate ions and hydrolysis of uranyl ions. An increase in temperature accelerates the transformation of uranium(IV) oxalate into uranium(VI) hydroxide compounds. In solutions containing KBr or UO2Br2, the following reaction occurs: O3 + Br → O2 + BrO. The arising hypobromite ions and hypobromous acid oxidize uranium(IV) oxalate extremely efficiently. The possible mechanism of ozonation of aqueous uranium(IV) oxalate suspensions is discussed.  相似文献   

3.
针对某矿区含碳硅岩和碳质灰岩样品的铀分析应用标准方法分析过程复杂、分析结果不够准确的状况,采用激光荧光法,实验一种快速准确的分析方法。通过马弗炉灼烧和硝酸-氢氟酸-高氯酸冷浸湿法预处理,在一定的硝酸介质中铀酰离子与荧光增强剂生成稳定络合物,在激光激发下产生荧光。使用MUA型微量铀分析仪可直接用标准加入法测定样品中铀的含量。探讨了样品分解、酸度、灵敏度对不同铀含量样品的测定条件的影响。初步形成一种广含量的铀的可靠分析方法,从而提高了分析效率和准确度,并降低了分析成本。  相似文献   

4.
The structure of the glass obtained by incorporation of the residue from reprocessing of the spent extractant, tributyl phosphate, into sodium aluminophosphate glass and the structural state of uranium in this glass were studied by vibration (IR, Raman) and X-ray absorption (XAFS) spectroscopy. An IR and Raman spectroscopic study shows that the structural network of the glasses is formed by ortho- and pyrophosphate groups linked by tetrahedral AlO4 units. As follows from the XAFS data, uranium is present in the glass in the form of uranyl ions and of separate UO2+x particles. The glass has high hydrolytic durability: The uranium leach rate determined in accordance with GOST (State Standard) R 52 126–2003 is of the order of 10–8 g cm–2 day–1.  相似文献   

5.
The presence of uranium and other elements in high concentrations in acid mine drainage at Poços de Caldas Uranium Mine (Brazil) is a matter of concern. The acid water pH is around 2.7, the uranium concentration is in the range of 6–14 mg L−1, sulfate concentration near 1400 mg L−1, fluoride 140 mg L−1 and iron 180 mg L−1. In this solution, where sulfate is present in elevated concentrations, uranium is basically in the form of UO2(SO4)34−. This study investigated the separation of uranium from the other anions present in the acid water under batch and column mode using ion exchange technique. The pH studied was 2.7 and 3.9. Two strong base anionic resins were tested. The influence of ions, commonly found in acid waters like sulfate and fluoride, on ion exchange process was also assessed. Equilibrium studies were carried out to determine the maximum adsorption capacities of the resins. The resins showed a significant capacity for uranium uptake which varied from 66 to 108 mg g−1 for IRA 910U and 53 to 79 mg g−1 for Dowex A. The results also showed that SO42− is the most interfering ion and it had a deleterious effect on the recovery in the pH range studied. Fluoride did not affect uranium removal.  相似文献   

6.
Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO2(2+)aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.  相似文献   

7.
Uranium-containing samples of magnesium potassium phosphate (MPP) compound were synthesized using a nitric acid uranium solution. Uranium is incorporated in the MPP compound in the form of potassium uranyl phosphate with the structure of metaankoleite natural mineral, K(UO2)PO4·3H2O. The differential and integral uranium leach rates, determined in accordance with GOST (State Standard) R 52 126–2003 on the 28th day of contact of the compound with water, are 1.7 × 10–6 and 2.7 × 10–6 g cm–2 day–1, respectively, and the degree of leaching is 0.014%. High hydrolytic durability of the compound with respect to uranium leaching reduces the risk of release of uranium isotopes from radioactive waste into the environment.  相似文献   

8.
Isotope composition of U in minerals of two mineral associations based on aeschynite and pyrochlore was studied. Although the ratio of U isotopes in the mineral associations as a whole is equilibrium (or close to equilibrium), the distribution of the radiogenic 234U isotope between separate parts of these associations is essentially nonuniform. Two models of the disturbance of the radioactive equilibrium are discussed: dependence of the 234U/238U ratio on the U concentration in the mineral (Adloff-Roessler model) and transfer of 234Th recoil atoms from one phase to another (Sheng-Kuroda model). It is impossible within the framework of any of the models to consistently account for the observed distribution of the radiogenic U between different mineral phases. For the quasi-closed mineral system based on aeschynite, a model of the redistribution of the radiogenic U under the action of natural solutions mainly within the mineral association is suggested; for the open system involving pyrochlore, the effects of natural leaching are explained taking into account the valence and chemical state of uranium in the minerals.  相似文献   

9.
Biosorption equilibrium, kinetics and thermodynamics of binding of uranium ions to Cystoseria indica were studied in a batch system with respect to temperature and initial metal ion concentration. Algae biomass exhibited the highest uranium uptake capacity at 15 °C at an initial uranium ion concentration of 500 mg l−1 and an initial pH of 4. Biosorption capacity increased from 198 to 233 mg g−1 with an decrease in temperature from 45 to 15 °C at this initial uranium concentration. The Langmuir isotherm model were applied to experimental equilibrium data of uranium biosorption depending on temperature. Equilibrium data fitted very well to the Langmuir model C. indica algae in the studied concentration range of Uranium ions at all the temperatures studied. The saturation type kinetic model was applied to experimental data at different temperatures changing from 15 to 45 °C to describe the batch biosorption kinetics assuming that the external mass transfer limitations in the system can be neglected and biosorption is chemical sorption controlled. The activation energy of biosorption (EA) was determined as −6.15 using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (ΔG°, ΔH° and ΔS°) were also evaluated.  相似文献   

10.
To properly design a final cover for uranium mill tailings impoundments the designer must attempt to find an effective geotechnical solution which addresses the radiological and non-radiological potential impact and prevents geochemical processes from occurring within the tailings. This paper presents a computer-based method for evaluating the performance of engineered final covers for the remediation of uranium mill tailings impoundments. Three hypothetical final covers were taken from scientific literature to investigate the proposed method: (i) a compacted clay liner (CCL); (ii) a composite liner (CL) and (iii) a capillary barrier (CB). The processes investigated: (i) the saturated hydraulic flux; (ii) the unsaturated hydraulic flux (exclusively for the capillary barrier) and (iii) the radon exhalation to the atmosphere. The computer programs utilised for the analyses are: (i) Hydrologic Evaluation of Landfill Performance (HELP); (ii) SEEP/W and (iii) RADON. The site considered for the development of the research presented herein was the uranium mill tailings impoundment located at the Brazilian city of Poços de Caldas, in the Minas Gerais State.  相似文献   

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