Iodate Ions Research Articles

New insight into the potential oscillations during iodate reduction in alkaline solution

Potential oscillations during the reduction of iodate ions in alkaline solution under galvanostatic conditions have been re-investigated without adding iodide. The oscillations can take place only when the applied current is larger than the limiting current, and the oscillation amplitudes are within the plateau region of the limiting current. The bistability, i.e., iodate reduction and hydrogen evolution at different potentials, coupled with convection feedback, induced by hydrogen evolution, accounts for the oscillations. The mechanism was supported by the experimental results of current sweep and cyclic voltammetry. Our study shows that physical processes, i.e., alternately predominant mass transfer of the iodate by diffusion and by convection, play an important role in the oscillations.

Spectrophotometric determination of periodate or iodate ions by liquid-liquid extraction as an ion-pair using tetramethylammonium iodide

A simple and accurate extractive Spectrophotometric procedure was developed for the microdetermination of periodate and iodate in aqueous media. The determination of periodate was based upon the extraction of the ion-pair formed between the periodate and tetramethylammonium iodide at pH 4 in chloroform followed by direct Spectrophotometric measurements at 509, 358 and 288 nm. The optimum concentration range evaluated by Ringbom's plot, the molar absorptivity, the Sandell's sensitivity and the stoichiometry of the formed ion-pair were critically determined. Iodate could be determined quantitively by the proposed procedure after oxidation to periodate with potassium persulphate. The effect of the diverse ions on the determination of the periodate and/or iodate by the proposed procedures was also investigated. The application of the method for the analysis of iodate or periodate in the artificial fresh water was successfully carried out.

Improved iodine-125 removal in anionic form of iodate by column method using laterite soil

Soil column experiments have been conducted to treat liquid wastes from hospitals containing125I. Three sorbent samples of laterite clay materials with different contents of iron oxides (goethite, α-FeOOH) and hydroxides were used to sorb anionic iodate. Post-treatment on effluent wastes with sodium hypochlorite (redox reagent) oxidized the iodide to the desirable iodate ion. Effluent pH after treatment ranges between 4.8 to 5.8, which does not vary much from the initial effluent pH of 4.5 before treatment. Results show that 90 to 97% sorption of iodine radionuclides with a decontamination factor ranges between 10–32 was obtained after the first two hours of experiments. Concentration has decreased from the initial 10 Bq/ml to concentration ranges of 0.3 to 0.9 Bq/ml. Batch experiments conducted using different sorbent masses of soils, show that there was a drop in sorption as the mass of soils fell below approximately 0 to 0.25 g. The sorption remains constant with the soil mass above 0.25 g. Another batch experiment using a different concentration shows that the adsorption capacity of the laterite soil was 1.1 μCi/g. The adsorption is about 96% with a distribution coefficient of 1170.

Neutron and X-ray single-crystal structure determination of Be(IO3)2 · 4H2O

Abstract The crystal structure of Be(IO3)2 · 4H2O has been determined by both neutron and X-ray single-crystal studies (Pccn, Z = 4, a = 1581.0(6) pm, b = 650.66(10) pm and c = 877.5(2) pm, R = 4.20% and 2.50%) on the basis of 402 and 1063 reflections, respectively, and synchrotron X-ray powder diffraction. The layered structure is built up of tetrahedral Be(H2O)4 2+ units linked to adjacent iodate ions by hydrogen bonds. The shortest interionic I…I and I…O distances are with 360.1 pm and 276.8 pm unusually small, the intraionic bond lengths resemble those of other iodate hydrates. The four crystallographically different hydrogen bonds (rH…o: 159.6 pm, 166.0 pm, 167.0 pm and 178.4 pm), which are the strongest bonds known so far of salt hydrates, as also established by the wavenumbers of the uncoupled OD stretching modes, are discussed in connection with the bond valences of the intramolecular OH bonds and the great synergetic effect of Be2+ ions.

Oxidation of tris(1, 10-phenanthroline)iron(II) ion by iodate and periodate ions in neutral medium

The reactions of iodate and periodate with Fe(phen)32+ have been studied in neutral medium iodate ion is unreactive with ferroin in aqueous solution. The reaction is autocatalytic in the case of IO4−. The autocatalysis disappears in an excess of IO3−. The rate constants of both processes were determined and a reaction mechanism has been proposed. © 1996 John Wiley & Sons, Inc.

Oxidation of tris(1, 10‐phenanthroline)iron(II) ion by iodate and periodate ions in neutral medium

Oxidation of tris(1, 10‐phenanthroline)iron(II) ion by iodate and periodate ions in neutral medium

Influence of the reduction of iodate ion by hydrogen peroxide on the model of the Bray-Liebhafsky reaction

The reduction of iodate ion by hydrogen peroxide, originally postulated by Liebhafsky, is considered as a possible step in the kinetic model proposed by Kolar-Anic and G. Schmitz for the overall Bray-Liebhafsky oscillatory process.

Behaviour of periodate ion in isotachophoresis using cyclodextrins

The effects of α-,β - and γ-cyclodextrins on the migration behaviour of periodate ion in capillary isotachophoresis were investigated. The qualitative index R E for periodate ion increased linearly with increasing cyclodextrin concentration in the leading electrolyte. The magnitude of the increase was in the order β- > α- > γ- cyclodextrin. During migration, periodate ion was decomposed to iodate ion in the presence of cyclodextrins. The decomposition rate was in the order γ- > β- > α-cyclodextrin. For the simultaneous determination of iodate and periodate ions, β-alanine was better than histidine as the buffer added to the leading electrolyte. Triton X-100 was also better than poly(vinyl alcohol) as the additive to the leading electrolyte.

Neutronenbeugungs-Untersuchung von Mg(IO3)2·4H2O -Einkristallen / Neutron Diffraction Studies on Mg(IO3)2 · 4H2O Single Crystals

Abstract The crystal structure of Mg(IO3)2·4H2O has been determined by neutron single crystal diffraction (P21/c, Z = 2, R = 2,2% on the basis of 1107 observed reflections). Mg(IO3)2·4H2O forms a layered structure built up of octahedral Mg(H2O)4(IO3)2 units linked by hydrogen bonds. The two crystallographically different water molecules are in­ volved in asymmetric, nearly linear hydrogen bonds to adjacent iodate ions (νOD of matrix isolated HDO: 2480, 2475, 2425 und 2412 cm-1, IR spectroscopic data, 90 K). The strength of the hydrogen bonds as well as that of other iodate hydrates is discussed in terms of both the synergetic effect and Brown’s bond valences.

A symptotic analysis of canards in the EOE equations and the role of the inflection line

The Edblom–Orbán–Epstein (EOE) reaction, involving iodate, sulphite and ferrocyanide ions may have oscillations in a continuous stirred tank reactor. A simplification of a 10-variable model, including two state variables, was analysed numerically by Peng et al. ( Phil. Trans. R. Soc. Lond . A337, 275 (1991)). They found that within a very small range of the inflow concentration, the amplitude of of the oscillations varied drastically. Such behaviour is well understood in singular perturbations systems, where it is known as a canard explosion . Apparently, the EOE equations do not belong to this class. We show that the two-dimensional EOE equations can be recast as a singular perturbation problem. An asymptotic expansion of the the canard point is obtained, with very good agreement with the numerical results of Peng et al . To deal with the canard explosion in systems which are not of singular perturbation type, Peng et al . introduce a new definition of the canard point, based on change of curvature of the limit cycle. We discuss the new definition, and show that it may essentially agree with the definition based on a singular perturbation approach, but is much less fit for analytical computations. We show that the discontinuous canard transition suggested by Peng et al . violates a continuity theorem in the theory of ordinary differential equations.

Differential Determination of Iodate and Iodide by a Kinetic-Catalytic Method

An analytical method for the determination of Iodate and iodide ions at the μg 1−1 level in mixtures was investigated. Iodide in samples was first oxidized with sodium nitrite; the free iodine liberated was then released from the solution by heating. Excess nitrite was destroyed with amidosulfuric acid (sulfamic acid). The iodate remaining in the solution was determined by a kinetic-photometric method based on the catalytic effect of iodine on the oxidation of chlorpromazine by hydrogen peroxide in a sulfuric acid solution. The total iodine was also determined by a similar analytical procedure without carrying out operations for the removal of iodide; the iodide was found from the difference between the two results. Mixtures of iodate and iodide in the 0.2–5 μg 1−1 range of total iodine could be determined within an error of 10%. The proposed method has been successfully applied to a differential determination of iodate and iodide in natural fresh-water samples.

Determination of nitrite ions in well water by biamperometric standard addition

AbstractA new modified biamperometric method of analysis is proposed which has the advantage of producing straight lines as plots. Nitrite ions in well water have been determined by biamperometry and standard addition of solutions containing nitrite or iodate ions. Two platinum foils are immersed in the solution and 100 mV potential is applied between the electrodes; the resulting current is measured. The standard nitrite or iodate ions react with excess of iodide ions, producing triiodide. The reversible redox pair I/I− is responsible for a change in current, allowing the biamperometric measurement. The concentration of triiodide formed depends on the nitrite concentration. Twenty ppb of nitrite ions have been determined with good accuracy and precision. EDTA was added to eliminate interference from Fe(III), Cu(II), and other metal ions.

Study of iodine-iodate isotopic exchange reaction in neutral aqueous solutions by radiotracer technique

The isotopic exchange of iodine atom in neutral aqueous solutions of iodate ions and iodine (in KI) is found to obey the rate law R = k[IO 3 −] 0.4[I 2] 1.2 at 175°C. The addition of neutral ionic salts, e.g. KCl and KNO 3, in the reaction mixture showed a slight catalytic effect on the exchange rate. Further, the kinetic salt effect indicated the involvement of at least one neutral species in the rate-determining step. The activation energy in neutral aqueous solutions of iodate ions and iodine is found to be 86 ± 3 kJ mol −1, which decreases in the presence of KCl (79 ± 3 kJ mol −1) and KNO 3 (82 ± 3 kJ mol −1). The activation parameters, viz. free energy of activation, enthalpy of activation and entropy of activation, were also calculated. Based on these results, an association-dissociation type of reaction mechanism is proposed for this exchange reaction in neutral aqueous medium, similar to that proposed earlier for iodide-iodate isotopic exchange reaction in neutral aqueous solutions, nitrate eutectic melts and iodide-iodate melts.

Oxidative dissolution of chromium(III) oxides by metaperiodate ions in perchloric acid

The kinetics of oxidative dissolution of a number of different samples of chromium(III) oxide by periodate ions in 1 mol dm–3 HClO4 solution have been studied and the results interpreted using the inverse-cubic rate law. The metaperiodate acts as a two-electron oxidant and the overall reaction stoichiometry involves the reaction of 3 mol of periodate with 1 mol of CrIII oxide. From a detailed study of the kinetics of dissolution the rate-determining step appears to be the reaction between an adsorbed periodate ion and its associated CrIII oxide surface site, with inhibition by one of the reaction products, iodate, through competitive adsorption. Analysis of the kinetic data generates values for the Langmuir adsorption coefficients for periodate and iodate ions on highly hydrated CrIII oxide of 84 ± 8 and 2600 ± 370 dm3 mol–1, respectively. The CrIII oxide–periodate reaction has a high overall activation energy, 82 ± 6 kJ mol–1. The kinetics of dissolution of highly hydrated CrIII oxide under conditions in which the simple inverse-cubic rate law function does not apply can be successfully predicted using a simple kinetic model.

Ion-exchange Equilibrium Studies with Iodate Ion in Mixed Aqueous Alcohols

Ion-exchange Equilibrium Studies with Iodate Ion in Mixed Aqueous Alcohols

亜硝酸によるヨウ素酸イオンの還元反応速度

As a part of the fundamental research work for radioactive iodine removal in the reprocessing of spent fuel from a nuclear reactor, the reduction reaction of iodate ion by nitrous acid was experimentally examined in an aqueous acidic solution with a spectrophotometer. The overall reaction is as follows: 2IO3-+5HNO2+2H+→I2+5HNO3+H2O. In this reaction, there exists an induction period when production of iodine is very slow. The reaction is accelerated by the produced iodine, and finally the whole iodate ion is converted into iodine, though the rate is fairly small. The overall auto-catalytic production rate of iodine was formulated and the temperature dependency of the reaction rate constant was determined. The resulting activation energy was 61.6kJ·mol-1.

Complexes of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with chloride, nitrate, iodate, and sulfate ions in aqueous media: I. Formation constants, thermodynamic properties, and bonding mechanisms

Complexation stoichiometries and formation constants of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with NO 3 − , Cl−, IO 3 − and SO 4 2− ions are determined by pH potentiometric and13C NMR spectrometric measurements. Estimates of ΔH and ΔS are obtained from the values of the temperature dependent formation constants and acid dissociation constants. All four anions form only 1 : 1 complexes with the triprotonated amine species. NO 3 − and Cl− form 1 : 1 complexes only with the tetraprotonated amine, while IO 3 − and SO 4 2− form both 1 : 1 and 2 : 1 complexes. The complexation behavior is interpreted in terms of solvation and internal hydrogen bonding interactions.

Complexes of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with chloride, nitrate, iodate, and sulfate ions in aqueous media: II. Analysis of the underlying experimental and theoretical assumptions

In a previous paper [1] the complexation behavior of 1,4,8,12-tetraazacyclopentadecane with various anions was studied. This analysis depended on various assumptions involving the accuracy and the interpretation of the experimental data. In this paper these assumptions are examined using pH potentiometry,13C NMR, and conductometric techniques. The validity of each of the assumptions was confirmed.

Study of iodide-iodate isotopic exchange reaction in a few eutectic melts by radiotracer technique

The isotopic exchange of iodine between iodide and iodate ions was investigated in molten NaNO 3-KNO 3 eutectic and iodide-iodate melts using 131I as radiotracer. This exchange reaction obeys the rate law R = k[I −][10 3 −] 0.8 at 340°C in eutectic molten nitrate. The activation energy is found to be 145±5 kJ mol −1. The activation parameters, i.e. free energy of activation, enthalpy of activation and entropy of activation, were also calculated. The exchange in homogeneous melts of NaINaIO 3 and KIKIO 3 systems is found to be very fast, probably instantaneous at 5°C above the melting temperature. No noticeable exchange is observed even after heating the samples for 30 min at a temperature 20°C below the corresponding melting point. These results support an association-dissociation type reaction mechanism similar to that proposed earlier for this exchange reaction in neutral aqueous medium.

Kinetics and mechanism of indigo carmine‐acidic iodate reaction. An indicator reaction for catalytic determination of Ru(III) ion

AbstractA kinetic study of uncatalyzed and Ru(III) catalyzed oxidation of indigo carmine(IC) (disodium 3,3′‐dioxobi‐indolin‐2,2′‐ylidene‐5,5′‐disulphonate) by iodate ion in aqueous sulphuric acid solution is reported. The uncatalyzed reaction order was found to be four; one each with respect to IC and iodate ion and second order with H+ ion. The Ru(III) catalyzed reaction was of fifth order, second order with respect to H+ and first order with respect to reductant, oxidant, and catalyst. Stoichiometric ratios of both reactions were the same with a 3:2 reductant‐oxidant ratio. In both uncatalyzed and catalyzed reactions isatin‐5‐monosulphonic acid (2,3‐dioxoindoline‐5‐sulphonic acid) was observed as the oxidation product. Rate constants for both the reactions are reported. Reaction mechanisms consistent with the experimental data are suggested.Further, a fixed time method is described for the determination of Ru(III), based on its ability to catalyze the oxidation of IC by acidic iodate. Using [H+] 2.25M, [iodate] 1.00 × 10−3M and [IC] 5.0 × 10−5M, in presence of Ru(III), the reaction followed first order kinetics with respect to IC. The interference of various cations, neutral salts, and potassium iodide on the determination of Ru(III) was studied using synthetic mixtures. The selectivity of the method and the recommended procedure are described.