Equilibrium uranyl nitrate

As has been discussed, ordinary formamides have a barrier of about 21 kcal/ mol, which is a little less than that required for the isolation of atropisomers at room temperature. This means that, at a temperature slightly lower than ambient, it may be possible to obtain stable rotamers. This possibility was first realized by Gutowsky, Jonas, and Siddall (40). They used a uranyl nitrate complex of N-benzyl-N-methylformamide (4) crystallized from dichloromethane. When the crystals were washed with ice water to strip off the uranyl nitrate, a mixture of E and Z forms (Z/E = 1.6) was obtained. Since the equilibrium mixture gives a Z/E value of 0.8, it was possible to perform a kinetic study of equilibration... 

Siddall and his co-workers (46) have examined the barriers to rotation of a series of 2,6-disubstituted anilides. Af-Ethyl-A/-(2,6-xylyl)formamide (9) was recrystallized as a uranyl nitrate complex, and one isomer, which at equilibrium was favored by a factor of 3 1, was enriched up to a 30 1 ratio. The kinetics of rotation were examined at 0 to 29°C. The Arrhenius activation energy was 26 3 kcal/mol and log A was 18.5 2.4 hr-1. Siddall and Gamer (47) were able to obtain an almost pure isomer (which also predominated at equilibrium 1.3 1 for the ethyl compound and 1.1 1 for the methyl compound) of Ar-alkyl- V-(2-methyl-4,6-dibromophenyl)-l-naphthamide (10). The half-lives of... 

Moyer, B.A., Baes Jr. C.F., Case, F.I., Driver, J.L. 2001. Liquid-liquid equilibrium analysis in perspective II. Complete model of water, nitric acid, and uranyl nitrate extraction by di-2-ethylhexyl sulfoxide in dodecane. Solvent Extr. Ion Exch. 19 (5) 757-790. 

Uranyl Nitrate Influence on Polymer Growth. The effect of a solute such as uranyl nitrate on this polymer formation is so complex that the net effect on the polymer growth rate cannot be predicted. Experimentally, it is observed that the rates of growth at given initial HNO3 concentration are always slower in the presence of U02(N03)2 as indicated by the solid curve in Fig. 1. This occurs in spite of an observed back-shift in the Pu(IV) disproportionation equilibrium,... 

In particular, when a solvent extraction system of uranyl nitrate, aqueous nitric acid, and tri-n-butyl phosphate (TBP) in a hydrocarbon diluent was irradiated with a CO2 laser, a change was observed in the equilibrium distribution of uranyl nitrate between the phases (14). When the solution was irradiated at 944 cm 1, close to the uranyl asymmetric stretching frequency, the effect was observed. When a nonresonant frequency was used or the energy was absorbed in the solvent, no effect was observed. Little heating could be expected, and, in any case, heating effects should have been in the opposite direction from that observed. 

D.3 The flowsheet below is a liquid-liquid extraction process for uranyl nitrate (UN) extraction using tributyl phosphate (TBP). For this problem, the flowrates and equilibrium relation are in Ibm instead of moles. The quantities x and y are the mass... 

Even in mass-transfer-limiled processes, excursions in selectivity can be observed at finite contact times. This is predicted by rate models as simple as Eq. (8.4-1) for two metals with different equilibrium constant valoes, The phenomenon involves initially fast coextraction followed by crowding out of the less preferred metal during coijipetidon for extractant. This has been observed during simultaneous extraction of copper and zinc chlorides by TIOA in a growing-drop experiment"1 21 and in extraction or uranyl nitrate and nitric acid by TBP in a Lewis cell.2 as shown in Fig. 8.4-5. 

The principle of the Purex process, now commonly used for processing irradiated uranium by solvent extraction, is illustrated in Fig. 1.18. The solvent used in this process is a solution of tributyl phosphate (TBP) in a high-boiling hydrocarbon, frequently n-dodecane or a mixture of similar hydrocarbons. TBP forms complexes with uranyl nitrate [U0i(N03)2] and tetravalent plutonium nitrate [Pu(N03)4] whose concentration in the hydrocarbon phase is higher than in an aqueous solution of nitric acid in equilibrium with the hydrocarbon phase. On the other hand, TBP complexes of most fission products and trivalent plutonium nitrate have lower concentrations in the hydrocarbon phase than in the aqueous phase in equilibrium. 

The five solvents just discussed extract uranium in the form of neutral complexes of uranyl nitrate. With TBP the complex-forming equilibrium is... 

In an aqueous solution of uranyl nitrate there are present not only hydrated uranyl iotts UO2, but also a series of nitrate complexes UO2NO3, UO2 (NO3 )2, and U02(N03)3 . At room temperature there is rapid equilibrium between these complexed species. The formation of the hi -nitrate complexes is promoted by the presence of nitrate ions thus UO2NO3 may predominate in solutions 4 in nitrate concentrations, and U02(N03)2 in more concentrated nitrate solutions [F3]. 

Figure 10.31, calculated [G12] from Eq. (10.31), i Npobserved equilibrium ratios of Fig. 10.30, shows the dependence of Z>app on temperature and the concentrations of HNO2 and HNOa. Figure 10.31 is strictly valid only in the absence of nitrates other than nitric acid and traces of neptunium. When uranyl nitrate is present at appreciable molarity X j, Onp(vi) is given by Eq. (10.26), and the apparent equilibrium distribution coefficient for neptunium may be estimated from... 

Uranyl nitrate substantially increases the distribution coefficient Die- "Ihis was explained by the formation of a mixed nitrato-pertcchnetato-TBP complex of UOl" [121,122] according to the equilibrium ... 

A 20wt% solution of uranyl nitrate (UN) in water is to be treated with TBP to remove 90% of the uranyl nitrate. All operations are to be batchwise equilibrium contacts. Assuming that water and TBP are mutually insoluble, how much TBP is required for 100 g of solution if at equilibrium (g UN/gTBP) = 5.5(g UN/g HjO) and... 

The uranyl nitrate (UN) in 2 kg of a 20 wt % aqueous solution is to be extracted with 500g of tributyl phosphate. Using the equilibrium data in Problem 1.12, calculate and compare the percentage recoveries for the following alternative procedures. 

The MD simulations D - J focus on the demixing of completely mixed water/ C02/TBP/acid systems, which are "chaotic arrangements", also prepared by MD simulations (see methods). These systems, "perfectly mixed" at the microscopic level (probably more than they are in reality) are highly unstable. We want to investigate how they spontaneously evolve and relax, and in particular to which extent the aqueous and CO2 phases will separate, and how the acid and uranyl nitrate species will distribute once the equilibrium is reached. One critical issue, in relation with assisted extraction, is whether and under which conditions uranyl will be complexed by TBP and finally extracted to CO2. The pH-neutral D and E systems, described in more details in ref (28) are presented here for a purpose of comparison with the acidic ones F-J. 

An ejqslanatlon of the correlation can be offered by considering the solubility of uranyl nitrate to obey an equilibrium for which a constant may be written and related to the crystallization temperature. 

Equilibrium laws. The physical chemical principles Involved In the solvent extraction of uranyl nitrate have been summarized In references 308-312. Detailed methods of treating the various equilibria Involved have been devised.a more single approach, adapted from a paper by Carleson — Is herewith presented. 

Evidence considered In the section on non-aqueous solutions Indicates that uranium Is extracted from aqueous nitrate solutions as hydrated, solvated uranyl nitrate, U02(N02)2(H20)j. Under appropriate conditions, the hydrated, solvated trlnltrate-uranyl complex may be extracted. The relationship between partition coefficient and equilibrium constant for the extraction mechanism shows the extraction of the former species to be favored by large free nitrate and free solvent concentrations and by small water activity. 

The nitrate concentration plotted as the abscissa Includes that attributable to the equilibrium concentrations of uranyl nitrate In addition to that of the Initial concentration of saltlng-out agent. 

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