scholarly journals Disproportionation and Polymerization of Plutonium(IV) in Dilute Aqueous Solutions

1983 ◽  
Vol 26 ◽  
Author(s):  
T. W. Newton ◽  
V. L. Rundberg
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Second Order ◽  
Disproportionation Reaction ◽  
Reaction Products ◽  
Constant Ph ◽  
Low Concentrations ◽  
Dilute Aqueous Solutions ◽  
Ph Range

ABSTRACTThe rates of polymerization and disproportionation of Pu(IV) have been studied using low concentrations: (1.7 − 10) × 10−6M Pu, (0.8 − 12) × 10−4M HCI and 0.01M ionic strength. Osmium(II) complexes such as the tris−4,41−2,21−bipyridine complex were found to react rapidly with Pu(IV) but very slowly, if at all, with Pu(IV) polymer, Pu(lll), or Pu(V). Thus, it is possible to determine unreacted Pu(IV) in the presence of reaction products by using Os(II) complexes. Disproportionation reaction products, Pu(IlI) and Pu(V), were determined using their reactions with Ce(IV) sulfate. We find −d[Pu(IV)]/dt = k'[Pu(IV)]2 at constant pH. Log k1 varies from about 4.25 at pH 3 to about 7.0 at pH 4.1 (units for k1 are M−1min−1). The [H+] dependence varies from about −2 to −3 over the pH range studied. The measured rate is the sum of those for polymerization and disproportionation; the latter reaction amounts to about 75% of the total at pH 3 and 20% at pH 4. The second-order rate constants for disproportionation are very much larger than expected on the basis of extrapolation from 0.2 to 1.OM HClO, solutions. The products of the reaction do not affect the rate, but U(VI), aged Pu(IV) polymer, and CO2 increase the rate.

Adsorption of U(VI) from dilute aqueous solutions onto peat moss

2007 ◽  
Vol 95 (1) ◽  
Author(s):  
H. A. Omar ◽  
M. Aziz ◽  
K. Shakir
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Uranium Concentration ◽  
Probable Mechanism ◽  
Peat Moss ◽  
Optimum Conditions ◽  
Low Concentrations ◽  
Equilibrium Data ◽  
Dilute Aqueous Solutions

The adsorption of U(VI) onto peat moss has been studied as a function of uranium concentration, pH, shaking time and ionic strength. The pH and ionic strength of the solution markedly affect the extent of removal. The attainment of equilibrium is fast and the equilibrium data fit well the Freundlich, Langmuir and Dubinin-Radushkevich equations. A probable mechanism of uptake is discussed. Further studies demonstrate that under optimum conditions peat moss can be used for the treatment of waste solutions containing low concentrations of uranium.

scholarly journals Ultrasonic irradiation of chemical compounds in aqueous solutions

1992 ◽  
Author(s):  
Αναστασία Κοτρωναρου
Keyword(s):  
Aqueous Solutions ◽  
Ultrasonic Irradiation ◽  
Energy Utilization ◽  
Oxidation Products ◽  
Utilization Efficiency ◽  
Interfacial Region ◽  
Reaction Products ◽  
Operation Conditions ◽  
Cavitation Bubbles ◽  
Ph Range

The ultrasonic irradiation of para-nitrophenol, S(-II), and parathion is studied in aqueous solutions at 20 kHz and ~ 75 W-cnT2. Para-nitrophenol was degraded primarily by denitration and secondarily by ΌΗ radical attack to yield N 02, NO3, benzoquinone, hydroquinone, 4-nitrocatechol, formate and oxalate. These reaction products and the kinetic observations are consistent with a model involving high-temperature reactions of p-nitrophenol in the interfa.cia.1 region of cavitation bubbles. The average effective temperature of the interfacial region surrounding the cavitation bubbles was estimated to be T ~ 800 K. Ultrasonic irradiation of S(-II) is studied in aqueous solutions over the pH range 7 - 12. The reaction of HS“ with OH is the principal pathway for theoxidation of S(-II) at pH > 10; the oxidation products are SO2“, SO2", and S20 Upon prolonged sonication, SO2" is the only observed product. At pH < 8.5, thermal decomposition of H2S within or near collapsing cavitation bubbles becomes the important pathway and elemental sulfur is found as an additional product of the sonolysis of S(-II). The sonolytic oxidation of H2S at pH > 10 was successfully modeled with an aqueous-phase free-radical chemistry mechanism and assumingcontinuous and uniform ΌΗ input into solution from the imploding cavitation bubbles. Parathion degradation occurred primarily by enhanced hydrolysis and secondarily by direct ΌΗ radical attack.The effect of various physical and chemical parameters on sonolytic yields is examined. The observed effects are in qualitative agreement with the sonolysis mechanisms proposed for the chemicals of interest and the existing hydrodynamic theories of acoustic cavitation. The formation of iodine upon ultrasonic irradiation of potassium iodide solutions and the sonolysis of S(-II) are used as probes to compare the sonochemical efficiency of different experimental set-ups. This work elucidates the mechanisms of the ultrasonic decomposition of typical organic and inorganic pollutants. It is shown that ultrasound has the potential to become a viable alternative for the destruction of chemical contaminants in water and wastewater. The current limitation of sonolysis is its low energy utilization efficiency, but there is room for improvement by optimizing reactor design and physical/chemical operation conditions. This work offers some recommendations and insight in that respect.

scholarly journals KINETICS OF OZONE REACTIONS WITH ADENINE AND CYTOSINE IN AQUEOUS SOLUTIONS

2020 ◽  
Vol 63 (10) ◽  
pp. 17-22
Author(s):  
Aigul A. Maksyutova ◽  
Elvina R. Khaynasova ◽  
Yuriy S. Zimin
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Correlation Coefficients ◽  
Activation Parameters ◽  
Second Order ◽  
Order Kinetic ◽  
Temperature Dependences ◽  
Ozone Reactivity ◽  
Kinetics Of ◽  
Ozone Reactions

The ultraviolet spectroscopy method has been applied to study the kinetics of the ozone reactions with nitrogenous bases (NB), namely adenine and cytosine in aqueous solutions. At the first research stage, the range of NB working concentrations has been determined. It was found that linear dependences between optical densities and concentrations of nitrogenous bases aqueous solutions are quite reliable, with correlation coefficients r ≥ 0.998, are satisfied up to [NB] = 2.3 ∙ 10–4 mol/l. According to the Bouguer-Lambert-Beer law, adenine and cytosine extinction coefficients in aqueous solutions were determined and subsequently used to calculate their residual concentrations. At the next stage, the kinetics of nitrogenous bases ozonized oxidation was studied with equal initial concentrations of the starting substances ([NB]0 = [О3]0). The results revealed that the kinetic consumption curves of the starting reagents are fairly well linearized (r ≥ 0.996) in the second-order reaction equation coordinates. As found with the bubbling installation, 1 mol of the absorbed ozone falls on 1 mol of the used NB. Thus, the reactions of ozone with adenine and cytosine explicitly proceed according to the second-order kinetic laws (the first – according to О3 and the first – according to NB). The rate constants were calculated by the integral reaction equations, the values of which indicate a higher ozone reactivity in relation to nitrogen bases. The temperature dependences of the second-order rate constants was studied ranging 285-309 K, and the activation parameters (pre-exponential factors and activation energies) of the ozone reactions with adenine and cytosine in aqueous solutions were determined.

Formation and Properties of Americium Colloids in Aqueous Systems

1981 ◽  
Vol 6 ◽  
Author(s):  
U. Olofsson ◽  
B. Allard ◽  
K. Andersson ◽  
B. Torstenfelt
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Storage Time ◽  
Large Fraction ◽  
Average Charge ◽  
Particle Sizes ◽  
Aqueous Systems ◽  
Ph Range ◽  
And Storage ◽  
Solution Changes

ABSTRACTThe formation and sorption properties of colloidal americium in aqueous solutions have been studied with variations of pH (2–12), ionic strength (0.01–1.0 M NaClO4), americium concentration (10−7 −10−11 M) and storage time (6 h–6 months). A large fraction of the americium is sorbed on the container walls or on Al2O3 in the pH-range 7–11. Around pH 5–8 and at pH above 12 centrifugable fractions (particle sizes greater than 100 nm) are obtained. The fraction formed at pH above 12, which seems to be a true hydroxide colloid, migrates through an A12O3-filled column with very little retention. The average charge of americium species in solution changes from positive values at pH below 7–8 to negative values at pH above 10–11, as indicated from electromigration studies.

KINETICS OF THE OXIDATION OF URANIUM (IV) BY IRON (III) IN AQUEOUS SOLUTIONS OF PERCHLORIC ACID

1955 ◽  
Vol 33 (12) ◽  
pp. 1780-1791 ◽  
Author(s):  
R. H. Betts
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Aqueous Solutions ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Kcal Mole ◽  
Kinetics Of Oxidation ◽  
Temperature Coefficients ◽  
Kinetics Of ◽  
Rate Controlling Step

The kinetics of oxidation of uranium (IV) by iron (III) in aqueous solutions of perchloric acid have been investigated at four temperatures between 3.1 °C. and 24.8 °C. The reaction was followed by measurement of the amount of ferrous ion formed. For the conditions (H+) = 0.1–1.0 M, ionic strength = 1.02, (FeIII) = 10−4–10−5 M, and (UIV) = 10−4–10−5 M, the observed rate law is d(Fe2+)/dt = −2d(UIV)/dt[Formula: see text]K1 and K2 are the first hydrolysis constants for Fe3+ and U4+, respectively, and K′ and K″ are pseudo rate constants. At 24.8 °C., K′ = 2.98 sec.−1, and K″ = 10.6 mole liter−1 sec−1. The corresponding temperature coefficients are ΔH′ = 22.5 kcal./mole and ΔH″ = 24.2 kcal./mole. The kinetics of the process are consistent with a mechanism which involves, as a rate-controlling step, electron transfer between hydrolyzed ions.

Kinetics and mechanism of disproportionation and ferricyanide oxidation of the 10-methylacridinium cation in aqueous base

1984 ◽  
Vol 62 (4) ◽  
pp. 729-735 ◽  
Author(s):  
John W. Bunting ◽  
Glenn M. Kauffman
Keyword(s):  
Ionic Strength ◽  
Second Order ◽  
Kinetics And Mechanism ◽  
Oxidation Pathway ◽  
First Order ◽  
Aqueous Base ◽  
Ph Range ◽  
Rate Profile ◽  
Kinetics Of ◽  
Major Oxidation

The kinetics of disproportionation and ferricyanide ion oxidation of the 10-methylacridinium cation have been measured spectrophotometrically over the pH range 9–14 in.20% CH3CN – 80% H2O (v/v) and ionic strength 1.0 at 25 °C. Disproportionation is kinetically second-order in total acridine species. The pH–rate profile is consistent with the rate-determining reaction of one acridinium cation with the pseudobase alkoxide anion derived from a second acridinium cation. Ferricyanide ion oxidation is kinetically first-order in each of ferricyanide ion and total acridine species. The pH–rate profile requires three distinct pathways for the ferricyanide ion oxidation of the 10-methylacridinium cation. For pH < 9.7, rate-determining attack of ferricyanide ion on the neutral pseudobase predominates, while for pH > 12.8 the predominant oxidation pathway involves reaction of ferricyanide ion with the pseudobase alkoxide ion. Between pH 9.7 and 12.8, the major oxidation pathway involves initial disproportionation of the acridinium cation followed by ferricyanide ion oxidation of the 9,10-dihydro-10-methylacridine product. This latter route accounts for a maximum of 69% of the total ferricyanide ion oxidation at pH 11.1.

Kinetics of oxidation of cis-bis(ethylenediamine)isothiocyanatonitrocobalt(III) ion with peroxodisulphate

1979 ◽  
Vol 44 (12) ◽  
pp. 3588-3594 ◽  
Author(s):  
Vladislav Holba ◽  
Olga Volárová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Oxidation Kinetics ◽  
Reaction Rate ◽  
Salt Effect ◽  
Activation Parameters ◽  
Reaction Products ◽  
Kinetics Of Oxidation ◽  
Thermodynamic Activation Parameters ◽  
Kinetics Of

The oxidation kinetics of cis-bis(ethylenediamine)isothiocyanonitrocobalt(III) ion with peroxodisulphate was investigated in the medium of 0.01 M-HClO4 in dependence on the ionic strength and temperature and the reaction products were identified. Extrapolated values of thermodynamic activation parameters were determined from the temperature dependence of the rate constants extrapolated to zero ionic strength. The distance of the closest approach was estimated for the reacting ions by evaluating the primary salt effect. To elucidate the mechanism, the influence of the cyclic polyether 18-crown-6 on the reaction rate was followed.

Kinetics and mechanism of covalent addition of S(IV) species to the acridinium cation

1996 ◽  
Vol 74 (3) ◽  
pp. 365-370 ◽  
Author(s):  
Maria P. Ros ◽  
Jesus Thomas ◽  
Guillermo Crovetto ◽  
Juan Llor
Keyword(s):  
Rate Constants ◽  
Carbonyl Compounds ◽  
Nonlinear Least Squares ◽  
Kinetics And Mechanism ◽  
Experimental Conditions ◽  
Ph Profile ◽  
First Order ◽  
Constant Ph ◽  
Ph Range ◽  
Experimental Values

The reaction of acridine with S(IV) species (SO2•H2O, HSO3−, and SO32−) to form the adduct acridine–S(IV) has been studied spectrophotometrically throughout the pH range 2.6–8 in aqueous solutions. The observed pseudo-first-order rate constants, kobs, were determined at 25 °C and ionic strength I = 0.11 M, and the pH profile of the rate reached a maximum at pH ≈ 6.1. At constant pH the kobs values were a linear function of the total S(IV) concentration with slopes that increased significantly with pH. These data are consistent with the rate-determining attack of SO3H− and SO32− upon the C-9 of the acridinium cation. A nonlinear least-squares fitting of the experimental values to the model equation, within the overall pH region studied, yields the pH-independent rate constants k1 = 3.7 ± 0.1 and k2 = (6.24 ± 0.04) × 104 M−1 s−1 for the attack of these two species, respectively. The experimental results agree very well with the kinetic model. Due to the experimental conditions used we did not detect any possible pseudobase formation in the pH range studied. The reactivity of the S(IV) species with acridine follows the order: [Formula: see text] The value obtained for the ratio k1/k2 is similar to the results given for other addition reactions of S(IV) species to the double bond of carbonyl compounds such as benzaldehyde and formaldehyde. Key words: covalent addition, acridine, acridine – S(IV) adducts, kinetics and mechanism.

Kinetik der Reaktion von Papain mit Bromacetamid / Kinetics of the reaction of papain with bromoacetamide

1971 ◽  
Vol 26 (1) ◽  
pp. 43-46 ◽  
Author(s):  
Hans-Gerhard Löffler ◽  
Friedhelm Schneider ◽  
Helmut Wenck
Keyword(s):  
Rate Constants ◽  
Turning Point ◽  
Ph Dependence ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Ph Range ◽  
Kinetics Of

The pH-dependence of the second order rate constants of the reaction of papain with bromoacetamide in the pH-range 5,5-8,5 is described by a curve with a turning point corresponding to a pK 7,3 ± 0,1 at 25°. This is the pK of a catalytically essential imidazole residue. The activation parameters of the reaction of papain with bromoacetamide were determined. The second order rate constants at pH 7 for the reaction is 200 times greater than for the reaction of bromoacetamide with simple SH-compounds.

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