Nitric acid aqueous-phase equilibrium

In the system nitric acid-nitroglycerine-water, a labile equilibrium is established, determined by the coefficient of phase separation. Thus under certain conditions as much as 8% nitric acid passes into the water phase whereas the nitroglycerine does not contain more than 0.01% HNO3. A thorough study of the partition of HNO3 and dinitroglycerine between nitroglycerine and aqueous solutions was made by Oehman [108]. 

Suresh et al. investigated the extraction of uranium and thorium by TsBP and TiBP (isomers of TBP with branched carbon chain) as an alternative choice for TBP (47). Higher homologues of TBP, for example, THP and TEHP, were reported to have higher extraction ability with reduced tendency toward third-phase formation (50, 51). The esters with bulkier substituents in place of the butyl group were proposed to be of practical value for the process applications in uranium and thorium separation (54). The LOC of thorium in equilibrium with aqueous nitric acid-thorium nitrate was reported to decrease in the order THP > TAP > TBP. Pathak et al. showed that TEHP can be a better choice for U/Th separation compared to TBP and TsBP (55). 

N03 is generated with difficulty in aqueous solution, the primary technique being radiolysis of concentrated nitric acid or nitrate-containing solutions. Its chemistry has recently been reviewed by Neta and Huie (227). Berdnikov and Bazhin gave the first estimate of E° for the N03/N03- couple as 2.3 + 0.1 V (45). This was obtained from gas-phase data and estimated hydration energies. A recent direct measurement of the equilibrium constant for the N02 + N03 N203 reaction... 

Dibutyl phosphoric acid (HDBP) also dimerizes in nonpolar solvents and solutions of HDBP in kerosene contacting aqueous nitric acid equilibrate to produce (HDBP)2, HDBP-H2 0 and HDBP-HNOs in both phases. In addition, the organic phase contains (HDBP)2-H20 and the aqueous phase (Bu"0)2P02 (DBP ) in equilibrium with HOBR " Such equilibria complicate the stoichiometry of extraction from aqueous sulfuric acid solutions. Thus the extraction of... 

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. 

The Acid-Thorex process has been used in recent years to recover 233U from neutron irradiated thoria targets. (] M This process uses n-tributyl-phosphate (TBP) in normal paraffin hydrocarbon (NPH) as the extractant and the relative uranium and thorium solubilities in each phase are adjusted by control of the nitric acid concentration. The Acid-Thorex process is the primary candidate for use in proposed aqueous thorium fuel cycles. In this process, uranium is separated from thorium through exploitation of the difference in equilibrium distributions since no usable valence change is available to aid in this separation. 

W. Davis, Jr., J. Mrochek, and C. J. Hardy. 1966. The system tri- -butyl phosphate (TBP)-nitric acid-water I activities of TBP in equilibrium with aqueous nitric acid and partial molar volumes of the three components in the TBP phase. J. Inorg. Nucl. Chem. 28 2001-2014. 

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. 

FIGURE 7.11 Equilibrium fraction of total nitric acid in the aqueous phase as a function of pH and cloud liquid water content at 298 K assuming ideal solution. 

As the (NH4)2S04 in the particles increases compared to the ammonium nitrate, the parameter Y decreases and the equilibrium product of ammonia and nitric acid decreases. The additional ammonium and sulfate ions make the aqueous solution a more favorable environment for ammonium nitrate, shifting its partitioning toward the particulate phase. Therefore, addition of ammonium sulfate to aqueous aerosol particles will tend to increase the concentration of ammonium nitrate in the particulate phase, and, vice versa, reductions of ammonium sulfate can lead to decreases of ammonium nitrate for aqueous aerosol. 

Competition between sulfate and nitrate for the available ammonia results in rather complicated system behavior. Addition of ammonium sulfate to solutions containing aqueous ammonium nitrate lowers the ammonia-nitric acid vapor pressure product in equilibrium with the aerosol phase (Figure 9.21). In Figure 9.21, Y is the ionic strength fraction of ammonium sulfate and is calculated as... 

Carbon Dioxide/Water Equilibrium 345 Sulfur Dioxide 348 Ammonia/Water Equilibrium 353 Nitric Acid/Water Equilibrium 355 Equilibrium of Other Important Atmospheric Gases Aqueous-Phase Reaction Rates 361 S(IV) to S(VI) Transformation and Sulfur Chemistry 363... 

AU equilibrium extractions were carried out at room temperature with 1 1 ionic liquid to aqueous phase ratio. The ionic hquid in its pure state absorbs a small amount of water depending on the initial nitric acid concentration that can vary from 17000 to 25000 ppm for 0.01 to 3 M nitric acid concentration, respectively. In the experiments a solution of 30 % (v/v) TBP in ionic liquids was prepared and equilibrated with the nitric acid solution at the required concentration by mechanical shaking at various time lengths. Saturation was confirmed by measuring the viscosity for both pure and saturated ionic liquid with a digital Rheometer DV-III Ultra (Brookfield). It was found that the ionic liquid was saturated after about 45 min shaking. Then, the two phases were separated and the pre-equihbrated... 

The extraction of Pu(IV) from nitric acid solutions was investigated by Cunninghame and Miles using CCl and benzene as solvents primarily, although other chlorinated hydrocarbons were used also. They find that, by neglecting aqueous phase nitrate complexing of the Pu, the equilibrium can be expressed by the equation... 

Fig. 21.9 Extraction of neptunium(vi) by 0.4 m methyldioctylamine in chloroform from aqueous solutions of hydrochloric, nitric, and sulphuric acids, at 20°C [178]. Initial concentration of neptunium 0.45 mu. The curves give the distribution ratio Das a function of the equilibrium acid concentration in the aqueous phase, Cg.

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