Non-acidic Solutions Research Articles

New Approach to the Nuclear Fuel Reprocessing in Non-acidic Aqueous Solutions

A new nuclear fuel reprocessing method based on the anodic dissolution of spent fuels in aqueous alkaline solutions (Na2CO3-NaHCO3) has been proposed. Experiments of the anodic dissolution were performed by using a simulated spent fuel in a Na2CO3-NaHCO3 solution. Uranyl ions produced anodically were present in the solution as stable carbonato complexes, and at the same time, most of the simulated fission products (FP) were precipitated as hydroxo or carbonate compounds. Under this condition, Cs of an alkali metal group was dissolved in the solution and precipitated by adding sodium tetraphenylborate. Uranyl ion was recovered as hydroxo compounds by adding NaOH to the solution after removing precipitates of the simulated FP. In view of waste disposal, 99Tc having a long half-life should be removed. Precipitation behavior of Tc(VII) was examined by using Re(VII) as a simulant of Tc(VII). It was found that Re(VII) species are completely removed as a precipitate by adding tetraphenylphosphonium chloride. A large amount of Na used in the present method was recovered as NaHCO3 by blowing CO2 into alkaline solutions. As a result, it was clarified that the proposed method is fundamentally possible as a new reprocessing method.

Investigation of the interaction of molybdenum with a graphite surface by electrothermal atomization atomic-absorption spectroscopy and scanning tunnelling microscopy

The Mo memory effect usually observed during electrothermal atomization is explained in terms of a complex mechanism which involves both interaction with strong adsorption sites on the graphite substrate and a diffusion process. There is no correlation between the number of adsorption sites and the number of retained Mo atoms. The effect of HCl concentration on the Mo absorbance signal shows that Mo solutions containing 4–10% v v HCl give signals 1.4 times the average signals given by aqueous (non-acidic) solutions. Removal of Mo species occurs due to the presence of acid, and this in turn leads to a decrease in the observed memory effect. However, results indicate that there is a limiting acid concentration at which most Mo species are removed from the graphite. Results on the role of H + on the molybdenum electrothermal atomization lead to the conclusions: 1. 1. The presence of the acid does not permanently modify the graphite sites on which Mo will be adsorbed. 2. 2. There is no evidence that H + can compete with Mo for adsorption sites. 3. 3. The analyte and the acid (H +) must be combined in solution or on the surface in order to cause signal enhancement. 4. 4. The effect of the acid may favour the formation of aggregates by vacancy creation by protons in the liquid phase as well as at the liquid-solid interface. STM studies reveal that most adsorption in non-acidic solutions is on dislocations or rough areas, in which the analyte-surface interaction is stronger (a large retention effect). In acidic solutions the cluster distribution occurs on flat and rough areas of the graphite surface, in good agreement with the assumption that aggregates are formed in the liquid phase or at the liquid-surface interface.

Oxygen versus Nitrogen Bonding of Carboxamides to Pentaammineruthenium(II/III)

Reversible linkage isomerizations are identified for monodentate carboxamides on pentaammineruthenium(II) and -(III). The equilibrium between O-bonded and N-bonded amides is pH and oxidation-state dependent. When both O- and N-bound amides are neutral uncharged ligands (pH < 7, Ru(II); pH < 2, Ru(III)), the O-bonded isomers are thermodynamically more stable for both oxidation states. They are, however, inherently unstable, solvolyzing in coordinating solvents with loss of amide ligand (Ru(II), t(1/2) < 1 s; Ru(III), t(1/2) < 2 h; 25 degrees C, H(2)O) or isomerizing to deprotonated N-bonded isomers in nonacidic solutions. Cyclovoltammetry in base produces reversible Ru(III/II) couples for the substitution-inert deprotonated form, [(NH(3))(5)RuNHCOR](2+/+), which protonates for Ru(II) in acidic and neutral solutions (pK(a) approximately 7) and isomerizes to the O-bonded amide. Following oxidation to Ru(III), isomerization of the O-bonded amides (pK(a) >/= 10) back to the N-bonded amides (pK(a) </= 2) is driven by selective deprotonation to [(NH(3))(5)Ru(III)NHCOR](2+). In water (pH 6.2, 25 degrees C) the O-bonded amides on Ru(III) isomerize ( approximately 50%) in parallel with aquation (R = H, k(obs) = k(ON) + k(aq) = 8.1 x 10(-)(4) s(-)(1)), and both processes are catalyzed by base and Ru(II). In strong acid, Ru(III) complexes of uncharged N-bound amides are thermodynamically unstable but kinetically robust (t(1/2) > 6 days, 18 degrees C, H(2)O) as the stable iminol tautomer, [(NH(3))(5)RuNH=C(OH)R](3+). This has to tautomerize to [(NH(3))(5)RuNH(2)COR](3+) before N- to O-isomerization which is much slower than subsequent solvolysis of the O-bonded isomer and hence undetectable in coordinating solvents. The substitution lability of O-bonded amides in coordinating solvents, tautomerization of N-bonded amides on Ru(III), and catalysis by Ru(II) and base complicate measurements of the rates for linkage isomerizations.

Palladium clusters: Stoichiometric and catalytic reactions

The mechanistic aspects of organic reactions catalyzed with palladium clusters and stoichiometric reactions of carbonyl and carbene clusters are discussed. Palladium carbonyl carboxylates Pd 4(CO) 4 (OCOR) 4(RMe, CMe 3, Ph, CF 3, CCl 3) undergo thermolysis above 110–130°C, giving rise to CO 2, CO and diacyls. In solutions of aromatic compounds the insertion of carbon dioxide into the aromatic CH bond or activated CH bond of alkylaromatic compounds was observed in the course of the thermolysis. The decomposition of palladium carbene carboxylate cluster Pd 4(Ph 2C) 4(OAc) 4 at 80°C has been found to involve inner sphere carbene oxidation during which an oxygen atom is transferred from the carboxylate group to the carbene ligand. Analogously, the reaction of [Pd(OAc) 2PPh 3] 2 with formic acid, a reaction involving intermediate cluster formation, includes the transfer of an oxygen atom from the formate droup to the P atom of a phosphorus containing ligand, supposedly a diphenylphosphido bridging group. Positional and geometric α-alkene isomerization in aqueous PdCl 2− 2 solution has been found to be catalyzed by palladium (I) complexes of type Pd 2Cl 2− 4. Colloidal clusters containing more than 500 palladium atoms in the metal core, which are soluble in polar organic solvents, have been found to catalyze the oxidative reactions of alkenes, toluene, alcohols and formic acid. Alcohols bearing at least one hydrogen atom in α-position undergo dehydration under mild conditions in non-acidic solution containing a Pd, Mo octanuclear anionic cluster [Pd 4Mo 4(CO) 12Cp] 2−. The reaction of benzyl alcohol gives rise to trans-stilbene. All these catalytic reactions can be rationalized within a scheme including the oxidative addition of the substrates across cluster metal-metal bond as a key step.

The indirect anodic oxidation of 2-methylnaphthalene Part I. Ruthenium compounds as catalysts

The indirect anodic oxidation of 2-methylnaphthalene and naphthalene to 2-methylnaphthoquinone-1,4 and naphthoquinone, respectively, was carried out with RuCl 3·3H 2O, Ru(acac) 3 and Ru(NH 4) 2Cl 6 as catalysts, in an undivided cell using platinum electrodes. Current-potential analysis of the hydrocarbon shows two oxidation waves in solutions of acetonitrile-H 2SO 4 which collapse into a single wave in presence of water, implying an electrodic-chemical-electrodic (ECE) reaction sequence. RuCl 3·3H 2O or Ru(NH 4) 2-Cl 6 increases the selectivity for quinone formation, whereas Ru(acac) 3 has no such effect. Voltammetry shows that RuCl 3·3H 2O and Ru(acac) 3 oxidize water and not the hydrocarbon. It also identifies an activated complex in which RuCl 3·3H 2O, but not Ru(acac) 3, binds to the oxidised form of the hydrocarbon. This analysis explains the catalytic effect of RuCl 3·3H 2O and the inefficiency of the coordinatively saturated Ru(acac) 3. RuCl 3·3H 2O is also an efficient catalyst in non-acidic solutions containing high concentrations of diisobutylamine and diisopropylamine and in which oxidation of 2-methylnaphthalene to 2-methylnaphthoquinone-1,4 is possible at a very low potential.

Shapes of flow injection signals: effect of refractive index on spectrophotometric signals obtained for on-line formation of bromine from bromate, bromide and hydrogen ion in a single-channel manifold using large-volume time-based injections

The shapes of the spectrophotometric signals obtained with a single-channel manifold for large-volume (4 ml) time-based injections for the six possible combinations of the reagents bromate, bromide and nitric acid in the injectate and carrier stream, by which bromine can be formed on-line, have been determined. The injectate and carrier stream were 5.25 × 10–4M in bromate, 0.030 M in bromide and 1 M in nitric acid when these reagents were present. The signals consisted of two separate peaks caused by formation of bromine at the front and rear boundaries of the injected bolus. When both injectate and carrier stream were 1 M in nitric acid (i.e., for the reagent combination H+BrO3–-H+Br–) the two peaks were of equal height, and the signal was virtually the same whichever solution was used as the injectate. In reagent combinations where only one solution contained nitric acid the peaks were different in size, the smaller peak being that produced by the boundary in which the acidic solution was flowing behind the other solution. This difference in size between the front and rear peaks was shown to be caused by refractive index effects. When the refractive indices of the two solutions were matched either by increasing the potassium bromide concentration or by making the non-acidic solution 7% in sodium nitrate, the peaks became equal in size. When the potassium bromide concentration was increased there was an appreciable increase in peak size (about 4-fold): the changes in the amount of bromine formed must be due to kinetic or equilibrium effects. This increase in size did not occur when sodium nitrate was used to balance the refractive indices.

Well- and Formation-Damage Removal With Nonacid Fluids

Well damage, in the form of various impediments to fluid flow through the formation rock, can reduce or completely eliminate production or injection rates of the well. Prevention and/or removal of well damage have consequently become a major field of study and concentration within the petroleum industry. Although acid solutions have been used for well-damage removal since before the turn of the century, there are situations in which acid is not the best choice for damage removal. The most obvious condition under which acid is not applicable is where the damaging mechanism is not appreciably soluble in acid solutions. Use of acid here would be a waste of time and material.

Effect of Gamma Radiation on Glass Leaching

Significant increases in the leaching rate of PNL 76–68, a complex simulated nuclear waste glass, were observed to occur in the presence of gamma radiation. Some of the enhanced leaching is due to the generation of nitric acid from air radiolysis in the leach vessel. Nitric acid appears to preferentially attack zinc and lanthanides, both of which normally build up on the surface of the glass when leached in nonacidic solutions. Increased rates were also found for samples irradiated while leaching but with air excluded to eliminate nitric acid formation, indicating that water radiolysis products may also be important. Samples irradiated prior to leaching showed dissolution rates indistinguishable from those of unirradiated specimens.

Effects of radiation on the leaching behavior of nuclear waste forms

Radiation damage can induce significant structural changes in solid materials; these changes may be more extensive in crystalline materials than in glasses, due to amorphization of the crystalline phases. Leaching tests conducted on several simulated waste glasses doped with 244Cm show no significant change in leach rate as a function of increasing dose, even in the case of a partially devitrified waste glasses which exhibited both large volume changes (∼1%) and amorphization of a crystalline phase. Significant increases in the leaching rate of PNL 76-68, a complex simulated nuclear waste glass, were observed to occur in the presence of gamma radiation. Some of the enhanced leaching is due to the generation of nitric acid from air radiolysis in the leach vessel. Nitric acid appears to preferentially attack zinc and lanthanides, both of which normally build up on the surface of the glass when leached in nonacidic solutions. Increased rates were also found for samples irradiated while leaching, but with air excluded to eliminate nitric acid formation, indicating that water radiolysis products may also be important. Samples irradiated with gamma rays prior to leaching showed dissolution rates indistinguishable from that of unirradiated specimens.

Aquation of ?-cis-chloroaquoethylenediamine-N, N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

The displacement of chloride ligands from α-cis-chloro-aquoethylenediamine-N,N′-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10−5 s−1 in H2O, 2.71 × 10−5 s−1 in MeOH : H2O, 2.74 × 10−5 s−1 in EtOH: H2,O and 2.58 × 10−5 s−1 n in Me2CO : H2O. The corresponding ΔH* and ΔS* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's ET and Kosower's Z-values and, based on these correlations, a dissociative interchange (Id) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.

The photoinitiated substitution reactions of 2‐pyridinecarbonitrile with benzophenone in aqueous 2‐propanol

AbstractThe photoinitiated reaction of 2‐pyridinecarbonitrile and benzophenone in acidic 4:1 2‐propanol‐water yields substitution product 3 and bicyclic product 4. In nonacidic solution 3 is the principal product in addition to small amounts of a bipyridyl compound 5.

Rapid in vitro and in vivo conversion of hydroxymethyl-nitrofurantoin into nitrofurantoin as measured by HPLC

For the first time a method of separation between nitrofurantion and hydroxymethylnitrofurantoin is reported. Until now it has not been possible to separate these two substances because of a rapid degradation of hydroxymethyl-nitrofurantoin into nitrofurantion in, for instance, dimethylformamide and aqueous non-acid solutions. In vivo studies after administration of a commercially available formulation containing hydroxymethyl-nitrofurantoin, showed only nitrofurantoin to be present in urine. This formulation itself was also partly degraded. These results show that hydroxymethylnitrofurantoin acts as a pro-drug of nitrofurantoin.

Homolytic substitution of heteroaromatic compounds. Part I. Homolytic benzylation of pyridine, quinoline, and isoquinoline in acidic and non-acidic media

The effect of N-protonation on the homolytic benzylation of pyridine, quinoline, and isoquinoline has been studied. Pyridine is not benzylated in non-acidic solution, but 2- and 4-benzylpyridine are formed in acidic media. Benzylation of quinoline at positions 2 and 4, and isoquinoline at positions 1, 3, and 4, occurs to a small extent in nonacidic solution, and the reactivities of positions 2 and 4 in quinoline and position 1 in isoquinoline are enhanced in acidic media.

Takata-Aga reaction in the study of cerebrospinal fluid

The technique of this reaction, suggested by two Japanese authors, Takata and Aga, in 1926, consists in adding 1 drop of a 10% Na carbonici solution and 0.3 of a freshly prepared mixture of equal parts 0.5% sulfa solution and 0.02% fuchsin (non-acid) solution to 1 cc of liquid. The mixture is shaken well and left in a test tube, and examined now after shaking, after h, after h, and after 24 h. Having tested this reaction in 60 patients, D.K. Bogoroditsky found that it is a very subtle indicator of the state of the central nervous system.