首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
The kinetics and mechanism of uranium(VI) extraction from nitric acid solution by bis(octylsulfinyl)methane (BOSM) are studied with the method of stationary interface cell. The effects of temperature, extractant and nitric acid concentrations are discussed. The results showed that the extraction process is controlled by the following reaction: UO2(NO3)2 + BOSM(i)k1 k-1UO2(NO3)2BOSM(i). The variation of enthalpy associated with the extraction is -22.1±2.1 kJ/mol. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
For the quantitative generation of uranous from uranyl ions in the presence of hydrazine in nitric acid medium, electrochemical reduction was carried out in divided and undivided cells. The influence of process conditions, viz. current density, concentration of nitric acid and hydrazine was studied for 50, 100 and 150 g/l of U(VI) solutions. The performance of the cathodes (titanium and platinum) was evaluated by calculating the conversion efficiencies in the reduction process using these electrodes for the reduction of 100 g/l U(VI) at 6 mA/cm2 as the cathodic current density. Batch mode experiments using Ti cathode revealed the reduction reaction of U(VI) to follow zero order kinetics and the simultaneous reduction of nitric acid to follow first order kinetics. From the temperature dependence, the activation energy for the reduction of U(VI) was determined to be 4.05 kJ/mol. The chemical stability of U(IV) in nitric acid–hydrazine medium, under ambient conditions of temperature and pressure was established from the amount of U(VI) produced from U(IV) by aerial oxidation over a period of 16 weeks.  相似文献   

3.
Microwave-assisted dissolution of ceramic uranium dioxide in tri-n-butyl phosphate (TBP)–HNO3 complex was investigated. The research on dissolution of ceramic uranium dioxide in TBP–HNO3 inclusion complex under microwave heating showed the efficiency of the use of this method. Nitric acid present in the inclusion complex participates both dissolution of UO2, and oxidation of U(IV)–U(VI), the resulting UO2(NO3)2 extracted with tri-n-butyl phosphate. Dissolution rate depends on both temperature of microwave dissolution process, and concentration of nitric acid present in the inclusion complex. The most intensive dissolution process is when the concentration of nitric acid ≥2 mol/L and the temperature of 120 °C. From the experimental data obtained by two kinetic models activation energies were calculated. At the average activation energy of UO2 dissolution in TBP–HNO3 complex equal 70 kJ/mol, and reaction order is close to one, i.e. the reaction takes place in an area close to kinetic.  相似文献   

4.
The extraction of uranium(VI) with bis(hexylsulfinyl)methane (BHxSM) from nitric acid aqueous solution has been investigated. It was found that the extraction increased with increasing nitric acid concentration up 8.5 mol/l and then decreased. Extraction distribution ratio also increased with the bis(hexylsulfinyl)methane concentration. The extraction species appear to be UO2(NO3)2 .2BHxSM. The influences of temperature, salting-out concentration and oxalate concentration on the extraction equilibrium were also investigated, and the enthalpy of the extraction reaction was obtained. The result shows that the reaction of uranium(VI) extraction with BHxSM is an exothermic one.  相似文献   

5.
Extraction behavior of U(VI) and Th(IV) from nitric acid medium is investigated using organo-phosphorous extractant, tri(butoxyethyl) phosphate in n-paraffin at room temperature (27 ± 1 °C). The effect of diluents, nitric acid concentration as well as extractant concentration on extraction of U(VI) and Th(IV) are evaluated. Extraction of U(VI) and Th(IV) from nitric acid medium proceeds via solvation mechanism. Slope analysis technique showed the formation of neutral complexes of the type of UO2(NO3)2·2TBEP and Th(NO3)4·3TBEP with U(VI) and Th(IV) respectively in the organic phase. The FTIR data showed shifting of P=O stretching frequency from 1,282 to 1,217 cm−1 indicating the strong complexation of P=O group with UO2 2+ ions in the organic phase. Effect of stripping agents, other metal ions and their separation with respect to U(VI) extraction has also been investigated.  相似文献   

6.
2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) forms a 1:1 complex with the uranyl ion in the presence of sulphosalicylic acid, which acts as stabilizer for this complex in the triethanol amine/perchloric acid buffer system. A change in the stoichiometry of the complex was seen at pH<5. Kinetic measurements were carried out using stopped-flow spectrophotometer in the presence of an excess concentration of U(VI) in the pH range 6.5 to 8. The dependence of the pseudo-first-order rate constant, k(obs), on the concentrations of U(VI), ligand and hydrogen ion showed that Br-PADAP reacts with UO2(OH)+ to form an intermediate species (equilibrium constant = 1.28×104mol.dm−3) that then rearranges (rate constant = 5.6×10−2s−1) to form the product species. UO2(OH)+ is present in equilibrium with the unreactive species UO2(OH)2, as well as with the unreactive sulfosalicylic acid complex.  相似文献   

7.
The reaction kinetics between acetic acid and Ag2+ in nitric acid medium is studied by spectrophotometry. The effects of concentrations of acetic acid (HAc), H+, NO?3, and temperature on the reaction are investigated. The rate equation has been determined to be –dc(Ag2+)/dt = kc(Ag2+)c(HAc)c?1(H+), where k = (610 ± 15) (mol/L)?1 min?1 with an activation energy of about (48. 8 ± 3.5) kJ mol?1 when the reaction temperature is 25°C and the ionic strength is 4.0 mol L?1. The reduction rate of Ag2+ increases with the increase in HAc concentration and/or temperature and the decrease in HNO3 concentration. However, the effect of NO?3 concentrations within 0.5–2.5 mol L?1 on the reaction rate is negligible. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 47–51, 2013  相似文献   

8.
The complexation of the uranyl ion with humic acid is investigated. The humic acid ligand concentration is described as the concentration of reactive humic acid molecules based on the number of humic acid molecules, taking protonation of functional groups into account. Excess amounts of U(VI) are used and the concentration of the humic acid complex is determined by the solubility enhancement over the solid phase. pH is varied between 7.5 to 7.9 in 0.1M NaClO4 under normal atmosphere and room temperature. The solubility of U(VI) in absence of humic acid is determined over amorphous solid phase between pH 4.45 and 8.62. With humic acid, only a limited range of data can be used for the determination of the complexation constant because of flocculation or sorption of the humic acid upon progressive complexation. Analysis of the complex formation dependency with pH shows that the dominant uranyl species in the concerned pH range are UO2(OH)+ and (UO2)3(OH)5 +. The complexation constant is evaluated for the humate interaction with the to UO2(OH)+ ion. The stability constant is found to be logβ = 6.94±0.3 l/mol. The humate complexation constant of the uranyl mono-hydroxo species thus is significantly higher than that of the nonhydrolyzed uranyl ion (6.2 l/mol). Published data on the Cm3+, CmOH2+ and Cm(OH)2 + humate complexation are reevaluated by the present approach. The higher stability of the hydrolysis complex is also found for Cm(III) humate complexation.  相似文献   

9.
Electrochemical reduction of U(VI) in nitric acid-hydrazine solution is greatly influenced by the concentration of nitric acid. In low acidity nitric acid solution such as 0.1M (M=mol/dm3) HNO3, U(VI) was firstly reduced to U(V) and then partially reduced to U(IV). In high acidity nitric acid solution, e.g., 3-6M HNO3, an electrode process of two-electron transfer was involved in the reduction of U(VI). A higher U(IV) yield could be achieved in nitric acid solution with higher concentration. Hydrazine was very effective in suppressing the reduction of concentrated nitric acid, and the optimal concentration of hydrazine added was 0.075 to 0.15M in 6M HNO3 This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
The thermodynamic extraction of uranium(VI) with hexyloctylsulfoxide (HxOSO) has been studied. It was found that the distribution ratio increases with increasing nitric acid concentration up to 2.3 mol/l and then decreases. The distribution ratio also increases with increasing extractant concentration. The extracted species appears to be UO2(NO3)2 .2HxOSO. The influences of temperature, sodium nitrate and oxalate concentrations on the extraction were also investigated, and the thermodynamic functions of the extraction reaction were obtained.  相似文献   

11.
Summary The synergistic extraction of uranium(VI) from aqueous nitric acid solution with a mixture of tri-n-butyl phosphate (TBP) and i-butyldodecylsulfoxide (BDSO) in toluene was investigated. The effects of the concentrations of extractant, nitric acid, sodium nitrate and sodium oxalate on the distribution ratios of uranium(VI) have been studied. The values of enthalpy change for the extraction reactions with BDSO, TBP and a mixture of TBP and BDSO in toluene were -23.2±0.8 kJ/mol, -29.2±1.4 kJ/mol and -30.6±0.6 kJ/mol, respectively. It has been found that the maximum synergistic extraction effect occurs when the molar ratio of TBP to BDSO is close to 1. The composition of the complex of the synergistic extraction is UO2(NO3)2 . BDSO . TBP.  相似文献   

12.
The liquid-liquid extraction behavior of 2-ethylhexyltolylsulfoxide (EHTSO) towards uranium(VI) contained in nitric acid aqueous solution has been investigated. It was found that the extraction increases with increasing nitric acid concentration up to 5.0 mol/l and then decreases. Extraction also increases with increasing extractant concentration. The extracted species appears to be UO2(NO3)2 .2EHTSO. The influences of temperature, NH4NO3 and Na2C2O4 concentrations on the extraction equilibrium were also investigated and the thermodynamic functions of the extraction reaction were obtained.  相似文献   

13.
A new extractant, N-octanoyl-2-methylpiperidine (OMPPD) has been synthesized. The extraction of U(VI) with N-octanoyl-2-methylpiperidine (OMPPD) in nitric acid has been studied. The dependence of the partition reaction of U(VI) on the concentrations of nitric acid, extractant, salting-out agent LiNO3, and temperature has been studied. In the light of the results, the extraction mechanism is discussed. The synergistic extracted complexes may be presented as UO2(NO3)2(OMPPD)2 . The related thermodynamic functions were calculated.  相似文献   

14.
Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous uranyl ion (UO2 2+) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized by SEM, NMR, SAXS, and N2 sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of pH, contact time, initial U(VI) concentration, ionic strength and solid–liquid ratio. The results show that the sorption of U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid–liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g at pH 5.3 ± 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.  相似文献   

15.
The liquid-liquid extraction behavior of uranium(VI) from aqueous nitric acid with bis(octylsulfinyl)ethane (BOSE) in 1,1,2,2-tetrachloroethane has been studied over a wide range of conditions. The extracted species appears to be UO2(NO3)2·2BOSE. It was found that the extraction increases with increasing nitric acid concentration up to 7 mol/l and then decreased. Extraction also increases with increasing extractant concentration. The influence of temperature and salting-out agent concentration on the extraction equilibrium and stripping of uranium(VI) was also investigated and the enthalpy of the extraction reaction was obtained.  相似文献   

16.
The extractive properties of tri-isoamyl-phosphate (TAP), an indigenously prepared extractant, and the loading capacity of extraction solvent containing TAP for U(VI) and Pu(IV) ions in nitric solution have been investigated. The dependence of the distribution ratio on the concentration of nitric acid showed that TAP has an ability to extract these actinides, while the fission product contaminants are poorly extracted. The distribution data revealed a quantitative extraction of both U(VI) and Pu(IV) from moderate nitric acidities in the range 2–7 mol · dm–3. Slope analysis proved predominant formation of the disolvated organic phase complex of the type UO2(NO3). 2TAP and Pu(NO3)4·2TAP with U(VI) and PU(IV), respectively. On the contrary, the extraction of fission product contaminants such as144Ce,137Cs,9Nb.,147Pr,106Ru,95Zr was almost negligible even at very high nitric acid concentrations in the aqueous phase indicating its potential application in actinide partitioning. The recovery of TAP from the loaded actinides could be easily accomplished by using a dilute sodium carbonate solution or acidified distiled water (0.01 mol · dm–3 HNO3) as the strippant for U(VI) and using uranous nitrate or ferrous sulphamate as that for Pu(IV). Radiation stability of TAP was adequate for most of the process applications.  相似文献   

17.
The liquid-liquid extraction of uranium(VI) from aqueous nitric acid with bis(octylsulfinyl)methane (BOSM) has been studied over a wide range of conditions. The extracted species appear to be UO2(NO3)2·2BOSM. It was found that the extraction increased with increasing nitric acid concentration up to 8.5 mol/l and then descreased. Extraction also increased with increasing extractant concentration. The influence of temperature and salting-out agent concentration on the extraction equilibrium has also been investigated, and the enthalpy of the extraction reaction was estimated.  相似文献   

18.
The liquid-liquid extraction of uranium(VI) from aqueous nitric acid with n-octyldecylsulfoxide (ODSO) in toluene has been studied over a wide range of conditions. The extracted species appears to be UO2(NO3)2·2ODSO. The extraction increased with increasing nitric acid concentration up to 2.0 mol/l and then decreased. Extraction also increased with increasing extractant concentration. The influence of temperature, salting-out agent concentration and complex anion concentration on the extraction equilibrium were also investigated, and the enthalpy of the extraction reaction was calculated.  相似文献   

19.
Uranyl–sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO2(NO3)2 + Na2SO4 solutions of different Φ S = [SO42−]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO2(NO3)2 + NaNO3 solutions with different Φ N = [NO3]/[U(VI)] ratio at pH = 2 were also measured. The effects of Φ S and Φ N ratios value were most pronounced in wavelength interval 380–500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO2SO4, UO2(SO4)22−, UO2NO3 + and UO2(NO3)2 coincided well with published data, but those for UO2(SO4)34− and UO2(NO3)3 were significantly lower.  相似文献   

20.
A study was carried out to understand the sorption of uranium (U) onto soil surface and identify the species of U on soil surface using X-Ray Photoelectron Spectroscopy (XPS). For the study soil was amended with uranyl nitrate and surface speciation study was carried out by investigating the energy region for U in spectrum. Analysis of spectrum revealed that U is present in U(VI) state. Deconvolution of XPS spectrum of U(VI) sorbed on soil surface revealed that U(VI) species such as, UO2 2+ and (UO2)x(OH) y (2x?y)+ form complex with silanol, aluminol and goethite sites. The possible surface complexation is: ≡Al(OH)2UO2 2+, ≡SiO2UO2, ≡SiO2(UO2)3(OH)5 and ≡Fe(OH)2UO2.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号