Oxidation of cerium(III) to cerium(IV) using a mixture of hot concentrated perchloric and sulfuric acids

The oxidation of cerium(III) to cerium(IV) using a hot concentrated mixture of perchloric and sulfuric acids is shown to be quantitative Optimum conditions for the oxidation are described Complete removal of chlorine, an interfering decomposition product of boiling perchloric acid, is achieved by purging the concentrated acid solution with nitrogen before dilution with water The presence of sulfuric acid is essentral, the chief role of sulfuric acid apparently being to stabihze the cerium(IV) as a sulfatocerate complex.     

Synthesis and stability of bis(acetato)(5,10,15,20-tetraphenylporphyrinato)zirconium(IV)

The results of studying a unique synthesis method, the kinetics and mechanism of dissociation in acid media, and the stability of a new octacoordinated zirconium complex with two bidentate acetate ligands and one 5,10,15,20-tetraphenylporphine ligand, (AcO)₂ZrTPP, are presented. The method of synthesis is distinguished by the use of stable ZrOCl₂ in the complex formation reaction, instead of readily hydrolyzed zirconium tetrachloride, in boiling phenol, which exhibits the reduction properties. The UV, visible, IR, and ¹H NMR spectral parameters and the values of chromatographic mobility and stability of the complex are obtained. A protolytic dissociation scheme, which is universal for mixed porphyrin-containing zirconium complexes, is substantiated using data on the dissociation rates of an (Cl)₂ZrTPP analogue, depending on the temperature and acidity of the medium. The scheme includes a trimolecular rate-determining step (the complex ionized at one or both noncyclic ligands and two nonionized sulfuric acid molecules) and kinetically significant equilibria of dissociation of the noncyclic acido ligands and sulfuric acid.     

Spectrophotometric determination of cerium(IV), arsenic(III), and nitrite with promazine hydrochloride

Promazine hydrochloride is proposed as a new reagent for the spectrophotometric determination of cerium(IV), arsenic(III), and nitrite. The reagent forms a red-colored radical with cerium(IV) instantaneously in 0.5?2 M sulfuric acid or 0.5?2.5 M phosphoric acid solution. The red radical exhibits maximum absorbance at 505 nm. An 11-fold molar excess of the reagent is necessary for the full development of the color intensity. Beer's law is valid over the concentration range 0.5–15 ppm in sulfuric acid and 0.5–21 ppm in phosphoric acid. The sensitivities of the reaction in sulfuric and phosphoric acid media are 0.022 and 0.019 μg/cm², respectively. The effects of acidity, time, order of addition of reagents, temperature, reagent concentration, and diverse ions are reported. The proposed method offers the advantages of good sensitivity, simplicity, rapidity, selectivity, and a wider range of determination without the need for extraction. Arsenic(III) and nitrite are indirectly determined.     

Extractive separation of Th(IV), U(VI), Ti(IV), La(III) and Fe(III) from Zarigan ore

In this study, the effects of various extraction parameters such as extractant types (Cyanex302, Cyanex272, TBP), acid type (nitric, sulfuric, hydrochloric) and their concentrations were studied on the thorium separation efficiency from uranium(VI), titanium(IV), lanthanum(III), iron(III) using Taguchi^??s method. Results showed that, all these variables had significant effects on the selective thorium separation. The optimum separations of thorium from uranium, titanium and iron were achieved by Cyanex302. The aqueous solutions of 0.01 and 1 M nitric acid were found as the best aqueous conditions for separating of thorium from titanium (or iron) and uranium, respectively. The combination of 0.01 M nitric acid and Cyanex272 were found that to be the optimum conditions for the selective separation of thorium from lanthanum. The results also showed that TBP could selectively extract all studied elements into organic phase leaving thorium behind in the aqueous phase. Detailed experiments showed that 0.5 M HNO₃ is the optimum acid concentration for separating of thorium from other elements with acidic extractants such as Cyanex272 and Cyanex302. The two-stage process containing TBP-Cyanex302 was proposed for separation thorium and uranium from Zarigan ore leachate.     

Extraction of Vanadium (IV) with DI-2-Ethylhexylphosphoric Acid

Abstract

It was established with the use of electron and ESR spectroscopic methods that in the presence of sodium sulfate, the extraction of vanadium (IV) with di-2-ethylhexylphosphoric acid takes place by a cation-exchange mechanism giving rise to two complex compounds of vanadium (IV) oxocation with sulfuric and di-2-ethylhexylphosphoric acid anions. The vanadium (IV) oxocation sulfate complex extracted in the solid state was examined with X-ray structural analysis. It was shown that the vanadium (IV) oxocation sulfate complex trihydrate crystallizes in the centrosymmetrical space group to form dimers with bridging sulfate groups.     

Experimental Study of Zirconium(IV) Extraction from Fluoride-Containing Acid Solutions

Zirconium(IV) extraction from acid solutions was studied, and the optimal parameters of the process were found. Extractants for zirconium(IV) recovery from nitric and sulfuric acid solutions in the presence of fluoride ions were selected. The distribution coefficients of zirconium(IV) and fluoride ion were determined.     

Electrochemical behavior of Ti(IV)/Ti(III) redox couple on dropping mercury electrode in sulfuric acid aqueous and aqueous-organic media

The processes of electrochemical reduction of Ti(IV) and oxidation of Ti(III) in aqueous solutions of H₂SO₄ not containing and containing AcOH or MeCN are studied by the methods of classical and commutation polarography. It is shown that in the absence of organic solvents the heterogenous electron transfer is irreversible in the media with the sulfuric acid concentration up to 9 M, while in aqueous-organic solution the same occurs at the concentration up to 7 M. Organic solvents are involved into the process of complex formation and like H₂SO₄, influence the step of heterogenous electron transfer; this effects weakens with the increase in the concentration of sulfuric acid.     

Reactions of (Hydroxo)(tetrakis(3,5-dicarboxy)-and (Hydroxo)(tetrakis(4,5-dicarboxy)phthalocyaninato)aluminum(III) with Sulfuric Acid: Simulation and Kinetic Experiments

The interaction of the octacarboxy-substituted aluminum(III) phthalocyanines (hydroxo)(tetrakis(3,5-dicarboxy)- and (hydroxo)(tetrakis(4,5-dicarboxy)phthalocyaninato)aluminum(III) with sulfuric acid is reported. It has been demonstrated by computer simulation (PM3 method) and by studying the dependence of the electronic absorption spectra of the complexes in sulfuric acid on the acidity of the medium that ((OH)AlPc(4-COOH)₄(5-COOH)₄ has three protonated forms (mono-, di-, and trication) both in the gas phase and in concentrated sulfuric acid and (OH)AlPc(3-COOH)₄(5-COOH)₄ has three protonated forms in the gas phase and two ones in concentrated sulfuric acid. The destruction kinetics of the aluminum(III) phthalocyanines in hot sulfuric acid is investigated. A destruction mechanism is suggested in which the rate-limiting step is the dissociation of an Al-N bond and the transition state consists of one aluminum(III) phthalocyanine molecule and one hydronium ion. A stability series is established for a set of differently carboxy-substituted aluminum(III) phthalocyanines. The major factors in the stability of the complexes are the negative inductive effect and the number of carboxyl groups.     

间接荧光检测离子色谱法分析维生素C、亚硫酸根和硫代硫酸根

报道了一种用离子色谱分析维生素Ｃ、亚硫酸根和硫代硫酸根离子的新方法。在这种方法中采用了四价铈柱后氧化还原反应和三价铈荧光检测法。同时也给出了使用这种方法的一些最佳的实验条件。     

Simultaneous determination of uranium(VI) and thorium(IV) ions with carminic acid by bivariate calibration

A bivariate calibration method, has been applied to the simultaneous determination of U(VI) and Th(IV) ions as complexes with carminic acid by visible absorption spectrophotometry. The bivariate calibration method was applied satisfactorily to the determination of these ions in synthetic solutions simulating sulfuric acid leach solution obtained from uranium-thorium ores and the results were compared with those given by first derivative spectrophotometry. No significant advantages of any method were found.     

Isomerization of Maleic Acid to Fumaric Acid Catalyzed by Cerium(IV) and N-Bromo Compounds

Maleic acid (MA) in aqueous sulfuric acid undergoes catalytic isomerization in the presence of small amounts of Cerium(IV) ion and N-bromosuccinimide (NBS) or N-bromoacetamide (NBA). The rate of isomerization is very fast even at room temperature and the yield is quite acceptable. The rate of isomerization depends on the relative amounts of MA, Ce(IV), NBS, NBA, and H₂SO₄. However, maleic acid has greater effect on the final yield. Sulfuric acid exhibits more chemical effect than physical effects. The competitive redox reactions of Ce(IV), NBS, and NBA with MA limit the yield of isomerization to about 85%. In the vicinity of room temperature, a raise of five degrees in temperature nearly doubles the rate of isomerization. Acrylamide shows inhibitive effect on the isomerization. The rate of hydrolysis of NBS or NBA in aqueous acidic solution depends on the concentrations of hydrogen ion, and NBS or NBA itself. The rate of hydrolysis of NBA is much faster than that of NBS. Mechanism involving bromine atom as catalyst is proposed to explain experimental results.     

Solvent extraction of Hf(IV) from mixed electrolyte solutions into di-2-ethylhexylphosphoric acid (HDEHP)

Extraction of hafnium(IV) from aqueous sulfuric and sulfuric-nitric acid solutions into di-2-ethylhexylphosphoric acid (HDEHP) in xylene has been investigated. The Hf(IV) species extracted from 5M sulfuric acid was found to be HfY₂(HY₂)₂ where Y and HY₂ represent the anions of monomeric HY and dimeric H₂Y₂ forms of HDEHP, respectively. In the presence of nitrate ion the species extracted are found to be Hf(NO₃)Y(HY₂)₂ and Hf(NO₃)₂)(HY₂)₂. But when the aqueous phase is 3.0M HNO₃+2.5M H₂SO₄ only one species, Hf(NO₃)₂(HY₂)₂ was extrated. No synergism was observed from 5M H₂SO₄ by HDEHP with the addition of thenoyltrifluoracetone (HTTA).     

Catalytic Titrations of Silver(I) Using an Iodide-Catalyzed Mn(IV)-As(III) Indicator Reaction in the Presence of Sulfuric Acid with Detecting the End-Point by Methods with Two Polarized Electrodes

Catalytic bipotentiometric and biamperometric methods for determining silver(I) with the use of the new manganese(IV)-arsenic(III) indicator reaction catalyzed by iodide ions in the presence of sulfuric acid have been developed. The effects of the sulfuric acid concentration of some ionic species, of the mole ratio of manganese(IV) to arsenic(III) in the solution titrated, and of the titrand temperature, as well as of the current and potential difference, respectively, used for polarization of the indicator electrodes on the conditions for determinations of silver(I) of various concentrations were investigated. The error in the determination of 1.0 g/cm³ silver(I) do not exceed 2%, and the precision of the results is high for both methods.     

Kinetics and mechanism of naringenin reaction with Ce(IV) in different aqueous solutions of dimethylsulfoxide

The reaction of naringenin with Ce(IV) was studied in different aqueous solutions of DMSO (50–80% v/v) and various sulfuric acid concentrations using a spectrophotometric method. The reaction was arranged to be under pseudo‐first‐order condition with respect to Ce(IV). It was found that 1 mol of Ce(IV)sulfate on average has consumed by about 2 mol of naringenin to complete the reaction. To determine the stoichiometric ratios of metal ion and the ligand in the formed complex species, the continuous variation method has been used. The results showed that pseudo‐first‐order rate constants increase with increasing naringenin concentration and decrease by increasing the amount of DMSO and sulfuric acid in solution. The rate constant (k₁) was measured at different conditions. Finally, a mechanism consistent with the observed results has been proposed and discussed at various aqueous DMSO solutions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 715–724, 2011     

Simultaneous determination of uranium(IV) and thorium(IV) ions with Arsenazo III by partial least squares method

A multivariate calibration method, Partial Least Squares Type 1 (PLS-1), is proposed for simultaneous spectrophotometric determination of uranium and thorium ions as their complexes with arsenazo III in hydrochloric acid medium. Several data characteristics are taking into account in order to minimize the optimum number of factors required for the construction of calibration model, while using various statistical criterions of selection. Finally, the evaluated calibration model is satisfactorily applied to determination of these ions in samples that resemble sulfuric acid leach solution obtained from a uranium ore.     

Recovery of Thorium(IV) in Utilization of Solutions Formed in Sulfuric Acid Breakdown of Perovskite

Extraction of thorium(IV) with di-2-ethylhexyl hydrogen phosphate, octanol, and tributyl phosphate in sulfuric acid processing of perovskite was studied. The main stages of utilization of waste hydrochloric acid solutions were considered.     

Fluorimetric estimation of U(VI) in the presence of a large excess of Th(IV)

A fluorescence based method has been developed for the determination of trace amounts of uranium in thorium matrix using a mixture of phosphoric acid (H₃PO₄) and sulfuric acid (H₂SO₄), as fluorescence enhancing reagent for uranyl (UO₂ ²⁺) ion fluorescence. Synthetic samples mimicking the composition of ThO₂ fuel were prepared and the concentration of U(VI) was estimated. Satisfactory results are obtained when uranium is present at a concentration of 10 ppm in solid thorium samples with good precision.     

Chemiluminescence behavior based on oxidation reaction of rhodamine B with cerium(IV) in sulfuric acid medium

The chemiluminescence (CL) of the rhodamine B (RhB)-cerium(IV) system was investigated by flow-injection. Rhodamine B was suggested to be a suitable chemiluminescent reagent in acidic conditions. When the concentration of rhodamine B was 100 mg l⁻¹ and cerium sulfate was 1.6 mmol l⁻¹ in sulfuric acid, the chemiluminescent intensity was found to be highest by using 0.3 mol l⁻¹ sulfuric acid as a carrier solution. The particular chemiluminescent system could tolerate such distinct acidic environments that it was utilized for detecting many compounds that are stable in acidic solutions. Furthermore, by virtue of IR, UV-Vis and luminescence spectroscopic measurements, the chemiluminescent behavior of rhodamine B was studied and a possible mechanism for this chemiluminescent reaction was proposed. The emitter was affirmed to be a radical species due to one of the oxidation products of RhB; the chemiluminescent emissive wavelength was about 425 nm.     

Joint Electrodeposition of Tellurium(IV) and Cadmium(II) from Acid Solutions in the Presence of 2,2'-Dipyridyl

Cyclic voltammetry was applied to study the effect of addition of 2,2'-dipyridyl on joint electroreduction of Te(IV) and Cd(II) from sulfuric acid solutions on glassy carbon and titanium electrodes. The optimal potentials of electrodeposition of CdTe films were determined and the structure of these films was studied by means of X-ray phase analysis.     

Studies on the solvent extraction behaviour of Pu(IV) from sulfuric acid medium into di-2-ethylhexyl phosphoric acid (HDEHP)

Extraction of plutonium(IV) from aqueous sulfuric and sulfuric-nitric acid into di-2-ethylhexyl phosphoric acid (HY) in the diluents n-dodecane, toluene or chloroform has been investigated. The composition of the Pu(IV) species extracted from H₂SO₄ was found to be PuH₂Y₆, which changed to Pu(NO₃)H₂Y₅ and Pu(NO₃)₂H₂Y₄ with increasing concentration of nitrate ion in the aqueous medium. These three species can be represented as PuY₂(HY₂)₂, Pu(NO₃)Y(HY₂)₂ and Pu(NO₃)₂(HY₂)₂, respectively, where Y represents the anion of monomeric HY, and HY₂ the anion of dimeric H₂Y₂. Synergism in the extraction of Pu(IV) by the addition of thenoyltrifluoroacetone (HTTA) to HY was also investigated and attributed to extraction of the additional species, Pu(TTA)Y(HY₂)₂ and Pu(TTA)₂(HY₂)₂. The addition of the neutral extractant tri-n-octylphosphine oxide (TOPO) to HY did not result in synergism in the extraction of Pu(IV) from aqueous sulfuric acid. With aqueous nitric acid under similar conditions, however, synergism was observed. The possible equilibria in these systems were identified and the corresponding equilibrium constants were determined.