Nitric Acid System Research Articles

Dissolution rates of uranium dioxide sintered pellets in nitric acid systems

AbstractThe dissolution process for sintered uranium dioxide into nitric acid falls into two regimes of behaviour which depend on the overall transfer rate. The critical dissolution rate is approximately 8 mg. cm.−2 min−1, its precise value depending upon the solvent composition. Below this critical value there is a large degree of chemical kinetic control, the dissolution rate being proportional to the cube of nitric acid concentration, the experimental activation energy being 15 kcal. mole−1. Above the critical value the process appears to be controlled by the diffusion of a nitric acid species as the transfer rate is directly proportional to acid concentration with an activation energy of about 4 kcal. mole−1.In addition, the reaction is autocatalysed by the nitrite product so that forced convection can reduce rates by a factor of four times, and nitrite neutralisers can reduce them by a factor of one hundred times.To a first approximation the dissolution rate depends simply on the total nitrate concentration although polyvalent nitrates and, in particular, ferric nitrate, tend to accelerate the reaction.

Dissolution rates of uranium dioxide sintered pellets in nitric acid systems

Dissolution rates of uranium dioxide sintered pellets in nitric acid systems

Hydrochloric acid promoted hydrolysis of tri-n-butyl phosphate

This study, an extension of a previous note, (6) revealed that the fundamental reaction in the hydrolysis of tri-butyl phosphate accelerated by hydrochloric acid is the cleavage of the OC linkage, and it has been shown that the dealkylation reaction in the organic phase yields butyl chloride and acid esters. First-order rate constants were calculated and compared with those for a similar nitric acid system. A mechanism for the acidolytic degradation, based on the new data, is proposed. Previous observations of a greatly increased rate of hydrolysis of the organic phase as its water content increases have been confirmed, and the differences in rate in parallel nitric and hydrochloric acid systems explained accordingly.

Nonmonotonic ordering of lanthanides in tributyl phosphate-nitric acid extraction systems

The partition of tracer-level lanthanides, yttrium, and americium between various tri- n-butyl phosphate (TBP) phases and aqueous nitric acid phases has been studied radiometrically as a function of solvent concentration, nitric acid concentration, and Z. In undiluted TBP systems, a plot of log K vs. Z approximates two straight lines joining at Z = 64). The line for the high- Z region has a positive slope somewhat less than that of the line for the low- Z region at 18·5 M HNO 3. This difference in slope becomes intesified as the concentration of nitric acid is lowered, the high- Z line ultimately acquiring a negative slope. The slope of the low- Z line remains positive throughout the region studied. This general half-filled shell effect is also noted for systems involving diluted TBP. It is postulated that the extracting species is [M(TBP) α(H 2O) (χ−α)](NO 3) 3, in which α is a function of the nitric acid concentration and of Z. In all of the systems studied, for plotting purposes yttrium may be assigned an “apparent Z” of 65–68. In the dilute nitric acid systems, the americium plot is nearly coincident with that for praseodymium.

The significance of the "mercurinium ion" in oxymercuration.

The complex formed by mercuric nitrate with cyclohexene seems not to resemble similar argentous, cuprous, and platinous salt complexes, since it is stabilized by nitric acid while they are decomposed by acidic media. Furthermore, the cyclohexene – mercuric nitrate – nitric acid system is not stable as are the others in absence of air but decomposes to yield two equivalents of mercurous salt and one equivalent of formylcyclopentane. One or both of these products are presumed to be the material which earlier workers by implication defined as 1-hydroxy-2-nitratomercuricylohexane. It has now been found that this product could not have been formed under the reaction conditions used by these earlier workers. Finally the solubilization of cyclohexene in aqueous mercuric nitrate, on which the earlier workers based their concept of an alkene-mercurinium ion, does not have its counterpart in the solubilization of cyclohexene in aqueous mercuric acetate, since the rate of solution in the latter case is not faster than the rate of hydroxymercuration. In consequence there is no present evidence that such an ion is involved in oxymercuration of alkenes.