Oxidation Of Sulfide Ions Research Articles

Sulfur speciation: Methodology and application to sulfide oxidation studies at the sediment-water interface

A single column ion chromatographic method for the determination of sulfide, sulfite, sulfate and thiosulfate was developed. It uses an anion exchange column (Waters, IC-Pak A) and a borate-gluconate buffer at pH 8.5 that contains EDTA and ascorbic acid to prevent sulfite oxidation. This eluent has relatively low background values for both conductivity and ultraviolet absorption, which allows determination of the above sulfur anions with high sensitivity. The mean percent recovery of the investigated anions in synthetic mixtures were 98.6, 100.0, 99.6 and 100.2 % for sulfide, sulfite, thiosulfate and sulfate, respectively. The method was applied to study sulfide ion oxidation at the water-sediment interface using six aquifer samples collected within the continental United States. Results indicated that sulfide ion disappearance follows a pseudo first-order profile and that the rate of disappearance correlates with the total organic carbon and clay content of the sediment.

Anodic Oxidation of Sulfide Ions in Molten Lithium Fluoride

Cyclic voltammetry experiments have been performed on lithium sulfide in a lithium fluoride electrolyte at 1161 K using a graphite working electrode and a platinum quasi‐reference electrode. Two distinct oxidation mechanisms are observed for the sulfide ions. The first oxidation produces sulfur and at a higher potential a disulfide species is proposed to have formed. Both oxidations appear to be reversible and diffusion controlled.

Catalytic oxidation of sulfide ions over NiPS 3

Sulfide ion oxidation to elementary sulfur over NiPS 3, which is an efficient Catalyst for that process, has been studied by means of electrochemical measurements, electron spin resonance spectroscopy and X-ray photoelectron spectroscopy. Based on the results obtained by these physical methods and on reaction kinetics, a mechanism of the process is suggested. Reduction and oxidation steps of the Catalytic cycle are modelled by the topotactic redox reaction of intercalation-deintercalation of hydrated alkali ions.

Effect of hydrophobized active carbon on the catalytic activity and adsorptivity of supported cobalt(II)-phthalocyanine

The catalytic activity of cobalt(II)-phthalocyanine [Co(II)Pc] supported on active carbon the oxidation of sulfide ions to elemental sulfur by dioxygen in aqueous solution has been studied. Hydrophobization of the carbon surface facilitates activation of dioxygen by adsorption. The sulfide ion is activated mainly on the supported Co(II)Pc.

Polyselenide formation in borosilicate glasses

Several mechanisms are presented for the formation of polyselenide ions (Se x 2−) in a reference alkali borosilicate melt. Such ions exist in selenium-containing melts as intermediates in the redox equilibrium between elemental selenium and selenide ions under relatively reducing conditions. Molecular selenium can also be reduced to polyselenide ions by iron (Fe 2+) or uranium (U 5+) under somewhat more oxidizing conditions in the melt. Even though polyselenides exist in low concentration in the melt, they greatly affect the resulting optical properties by imposing an amber coloration. The redox mechanism for the formation of polyselenides by the reduction of elemental selenium in glass melts is in opposition to that for the formation of polysulfides which relies on the oxidation of sulfide ions by iron, vanadium, or uranium redox couples.

Which material for which medium: a survey: Schornagel, A.J. Roestvast Staal Dec. 1989 (6), 39–43 (in Dutch)

Electrochemical methods were investigated to assess the tarnish resistance of typical gold alloys used mainly for decorative purposes. Three mechanically clad alloys (14 and 18 carats (ct) Au-Ag-Cu and 14 ct Au-Ag-Cu-Zn) and three electroplated coatings (18 ct Au-Cu-Cd, 22 ct Au-Ni and 22 ct Au-Ni plus a flash layer for colour matching) were studied. Potentiostatic, cyclic constant-current chronopotentiometric and coulometric measurements were carried out in 1 N NaOH containing between 10-5 and 0.26 M Na2S. The electrochemical data were compared with the results obtained from liquid-based and vapour-phase chemical tests by means of colorimetric measurements and the data were expressed in the Commission Internationale de l'Eclairage (CIE) 1976 L∗a∗b∗ colour space. The electrochemical measurements showed that the sulphidation of non-noble metals of the gold alloys occurred in parallel with the oxidation of sulphide ions. Only the first reactions contributed to tarnish by producing insoluble, adherent and coloured sulphide films, while the oxidation of sulphide led to mainly colourless and non-adherent species. The current density measured at a properly chosen potential of the potentiostatic scan correlated with the non-noble metal content of the alloy. The cathodic charge determined by chronopotentiometry provided an excellent indication of the extent of sulphidation of a given alloy. The results of these electrochemical techniques were in good agreement with the data obtained from chemical tests. The thickness of the tarnished films as determined by cathodic reduction in 1 N NaOH was smaller than 100 Å assuming a silver sulphide coverage of unity. The potential value and length of the arrest in the potential vs. time curve gave interesting qualitative and quantitative information on the chemical composition of the tarnished films.

Mechanical properties of superplastically formed titanium and aluminium alloys: Partridge, P.G., Mcdarmaid, D.S., Bottomley, I. and Common, D.

Electrochemical methods were investigated to assess the tarnish resistance of typical gold alloys used mainly for decorative purposes. Three mechanically clad alloys (14 and 18 carats (ct) Au-Ag-Cu and 14 ct Au-Ag-Cu-Zn) and three electroplated coatings (18 ct Au-Cu-Cd, 22 ct Au-Ni and 22 ct Au-Ni plus a flash layer for colour matching) were studied. Potentiostatic, cyclic constant-current chronopotentiometric and coulometric measurements were carried out in 1 N NaOH containing between 10-5 and 0.26 M Na2S. The electrochemical data were compared with the results obtained from liquid-based and vapour-phase chemical tests by means of colorimetric measurements and the data were expressed in the Commission Internationale de l'Eclairage (CIE) 1976 L∗a∗b∗ colour space. The electrochemical measurements showed that the sulphidation of non-noble metals of the gold alloys occurred in parallel with the oxidation of sulphide ions. Only the first reactions contributed to tarnish by producing insoluble, adherent and coloured sulphide films, while the oxidation of sulphide led to mainly colourless and non-adherent species. The current density measured at a properly chosen potential of the potentiostatic scan correlated with the non-noble metal content of the alloy. The cathodic charge determined by chronopotentiometry provided an excellent indication of the extent of sulphidation of a given alloy. The results of these electrochemical techniques were in good agreement with the data obtained from chemical tests. The thickness of the tarnished films as determined by cathodic reduction in 1 N NaOH was smaller than 100 Å assuming a silver sulphide coverage of unity. The potential value and length of the arrest in the potential vs. time curve gave interesting qualitative and quantitative information on the chemical composition of the tarnished films.

Corrosion and compatibility: Berry, W.E. CAB Curr. Aware. Bull. Dec. 1989 196, 4

Electrochemical methods were investigated to assess the tarnish resistance of typical gold alloys used mainly for decorative purposes. Three mechanically clad alloys (14 and 18 carats (ct) Au-Ag-Cu and 14 ct Au-Ag-Cu-Zn) and three electroplated coatings (18 ct Au-Cu-Cd, 22 ct Au-Ni and 22 ct Au-Ni plus a flash layer for colour matching) were studied. Potentiostatic, cyclic constant-current chronopotentiometric and coulometric measurements were carried out in 1 N NaOH containing between 10-5 and 0.26 M Na2S. The electrochemical data were compared with the results obtained from liquid-based and vapour-phase chemical tests by means of colorimetric measurements and the data were expressed in the Commission Internationale de l'Eclairage (CIE) 1976 L∗a∗b∗ colour space. The electrochemical measurements showed that the sulphidation of non-noble metals of the gold alloys occurred in parallel with the oxidation of sulphide ions. Only the first reactions contributed to tarnish by producing insoluble, adherent and coloured sulphide films, while the oxidation of sulphide led to mainly colourless and non-adherent species. The current density measured at a properly chosen potential of the potentiostatic scan correlated with the non-noble metal content of the alloy. The cathodic charge determined by chronopotentiometry provided an excellent indication of the extent of sulphidation of a given alloy. The results of these electrochemical techniques were in good agreement with the data obtained from chemical tests. The thickness of the tarnished films as determined by cathodic reduction in 1 N NaOH was smaller than 100 Å assuming a silver sulphide coverage of unity. The potential value and length of the arrest in the potential vs. time curve gave interesting qualitative and quantitative information on the chemical composition of the tarnished films.

Oxidation of hydrosulphide ions on gold Part I: A cyclic voltammetry study

The results of an investigation to determine the mechanism(s) of oxidation of sulphide ions on a gold electrode are discussed. The cyclic voltammetry results are presented in Part I and characterization results after various electrochemical pretreatments are to follow in Part II. The cyclic voltammetry studies show that several stages are involved in oxidation of sulphide ions to form elemental sulphur. Initially, sulphide ions undergo underpotential deposition to form chemisorbed sulphur as isolated atoms. As oxidation proceeds, a monolayer of chemisorbed atoms is formed which reacts with sulphide ions in solution to form polysulphides at higher potentials. As the potential for oxidation is further increased elemental sulphur is produced. The reduction of polysulphide to hydrosulphide ions occurs by a 2-electron transfer process whereas the reduction of elemental sulphur occurs by a l-electron transfer process. The latter reaction involves the formation of an activated complex which is a relatively slow process.

はっ水性触媒存在下における硫化物イオンの酸素酸化

表面が揆水性を有する触媒を用いて, 酸素により水溶液中の硫化物イオンを酸化した。PTFE (ポリ(テトラフルオロエチレン)) で処理した活性炭を硫化ナトリウムの水溶液に懸濁させながら空気ガスを通気したところ, 硫化物イオンはポリ硫化物イオンを経てチオ硫酸イオンへ変化した。硫化物イオンの酸化速度は PTFE 量 3wt% のとき最大となり, 触媒不存時および PTFE 処理しない活性炭存在時の 10 倍以上であった。アルミナおよびチタニアは PTFE 処理しても触媒活性を示さなかった。

Electrochemical assessment of the tarnish resistance of decorative gold alloys

Electrochemical methods were investigated to assess the tarnish resistance of typical gold alloys used mainly for decorative purposes. Three mechanically clad alloys (14 and 18 carats (ct) Au-Ag-Cu and 14 ct Au-Ag-Cu-Zn) and three electroplated coatings (18 ct Au-Cu-Cd, 22 ct Au-Ni and 22 ct Au-Ni plus a flash layer for colour matching) were studied. Potentiostatic, cyclic constant-current chronopotentiometric and coulometric measurements were carried out in 1 N NaOH containing between 10 -5 and 0.26 M Na 2S. The electrochemical data were compared with the results obtained from liquid-based and vapour-phase chemical tests by means of colorimetric measurements and the data were expressed in the Commission Internationale de l'Eclairage (CIE) 1976 L ∗ a ∗ b ∗ colour space. The electrochemical measurements showed that the sulphidation of non-noble metals of the gold alloys occurred in parallel with the oxidation of sulphide ions. Only the first reactions contributed to tarnish by producing insoluble, adherent and coloured sulphide films, while the oxidation of sulphide led to mainly colourless and non-adherent species. The current density measured at a properly chosen potential of the potentiostatic scan correlated with the non-noble metal content of the alloy. The cathodic charge determined by chronopotentiometry provided an excellent indication of the extent of sulphidation of a given alloy. The results of these electrochemical techniques were in good agreement with the data obtained from chemical tests. The thickness of the tarnished films as determined by cathodic reduction in 1 N NaOH was smaller than 100 Å assuming a silver sulphide coverage of unity. The potential value and length of the arrest in the potential vs. time curve gave interesting qualitative and quantitative information on the chemical composition of the tarnished films.

The Electrochemical Behavior of Sulfide Ions in Molten Cryolite

The electrochemical behavior of sulfide ions in molten cryolite (Na/sub 3/AlF/sub 6/) has been studied by cyclic voltammetry using graphite electrodes at 1323 K. The oxidation of sulfide ions is found to proceed via a quasi-reversible mechanism, i.e., one in which the current is controlled by both diffusion and charge-transfer kinetics, S/sup 2 -/ reversible S + 2e/sup -/. The transfer coefficient ..beta.. and the standard rate constant k/sub s/ are estimated to be 0.5 and 0.0042 cm/s, respectively. The apparent diffusion coefficient for sulfide ions in cryolite at 1323 K is about 3.93 x 10/sup -5/ cm/sup 2//s.

ChemInform Abstract: Voltammetric Study of the Anodic Oxidation of Sulfide Ions in Molten Fluorides.

Information regarding the electrochemical behavior of sulfide ions in molten salts is important for questions of battery technology in the case of high-temperature secondary batteries, and for metallurgical molten-salt processes. The present investigation is concerned with the electrochemical behavior of sulfide in molten LiF-NaF. The investigation has the objective to evaluate the feasibility of the LiF-NaF melt as solvent for the electrolysis of Al2S3. The results are presented of a voltammetric study of the electrochemical oxidation of sulfide in LiF-NaF eutectic at 1023 K. It is found that the anodic oxidation of sulfide ions in LiF-NaF eutectic is reversible and diffusion controlled. The obtained experimental data correspond to the reaction mechanism 2S(2-) yields reversibly S2(2-) + 2e(-).

Voltammetric Study of the Anodic Oxidation of Sulfide Ions in Molten Fluorides

The electrochemical oxidation of sulfide ions has been studied in eutectic by linear sweep voltammetry using graphite electrodes at 1023 K. The oxidation is found to be reversible and diffusion controlled. A detailed analysis of the experimental results suggests the following mechanism for the oxidation of sulfide ions . The average apparent diffusion coefficient for sulfide ions is calculated to be at 1023 K.

Electrochemical Behavior of Li2 S in Fused LiCl ‐ KCl Electrolytes

Cyclic voltammetric studies of lithium sulfide in electrolytes have shown that the voltammograms obtained in a large range of potentials with an inert, glassy carbon electrode were dependent on concentration, temperature, and electrolyte composition. Voltammograms suggest three successive sulfide ion oxidation stages and a complex reduction electrochemistry. A detailed analysis of the results allows postulation of different possible redox mechanisms, but because numerous ionic sulfur species can exist in molten salts, an overall definitive mechanism, based solely on these electrochemical measurements, cannot be proposed. The diffusion coefficient of S2− and the solubility of have also been investigated as a function of electrolyte composition at temperatures between 400° and 450°C. The diffusion coefficient of S2− is in the electrolytes used; the solubility of is at 454°C in the eutectic electrolyte and increases with increasing concentration.

The electrochemical behavior of Al 2S 3 in molten MgCl 2 + NaCl + KCl eutectic

The electrochemical behavior of Al 2S 3 in MgCl 2 + NaCl + KCl eutectic has been studied at graphite electrodes at 1023 K using the technique of linear sweep voltammetry. The electrolytic decomposition of Al 2S 3 in the eutectic involves the cathodic reduction of aluminum ions (or aluminum-ion-containing species) and the anodic oxidation of sulfide ions (or sulfide-ion-containing species). The reduction has been found to proceed by a reversible, three-eletron transfer that forms an insoluble product. The average apparent diffusion coefficient for aluminum ions during deposition is 1.03 × 10 −5 cm 2 s −1. The oxidation involves the two-electron discharge of sulfide ions (S 2− ⇌ S + 2 e), followed by the dimerization of sulfur atoms to S 2 (S + S ⇌ S 2), which is very fast and very much displaced towards S 2. The average apparent diffusion coefficient for sulfide ions is calculated to be 2.73 × 10 −5 cm 2 s −1.

ChemInform Abstract: THE EFFECT OF IRON(III) ON THE CADMIUM ION‐SELECTIVE ELECTRODE

AbstractFe(III) stört den Betrieb von Cd‐, Pb‐ oder Cu‐Ionen‐selektiven Elektroden.

The Effect of Iron(III) on the Cadmium Ion-selective Electrode

Abstract Iron(III) interferes with the operation of a cadmium, lead and copper ion-selective electrode. The cadmium ion-selective electrode (CdS/Ag2S) showed a potential shift to the positive direction of more than 100 mV for a decade change of iron(III) concentration. However, the exact mechanism for this interference is not known, though it is expected to be the oxidation of sulfide ion by Fe(III). The mechanism of interference by iron(III) was studied by using the cadmium ion-selective electrode, flow-through cell, pH buffer solutions, potentiometric titrations, and atomic absorption spectrophotometry measurements. It was found that iron(III) promotes dissolution reaction of cadmium ions from the solid cadmium sulfide electrode and that flow conditions of samples have no effect on the iron(III) interference.

Anodic Corrosion Rate Measurements in LiCl ‐ KCl Eutectic: I . Electrochemical Considerations

Electrochemical apparatus and techniques are described for determining the nature and degree of anodic corrosion of candidate current collector metals for the lithium‐iron sulfide molten salt battery. Sufficiently low background currents were achieved to permit measurement of fractional mil‐per‐year average dissolution rates directly in pure eutectic at ∼450°C, corresponding to a nearly charged battery, and indirectly in eutectic, corresponding to the nearly discharged state. Voltammetric studies in eutectic with inert electrodes indicate successive sulfide ion oxidation to and S, and a complex reduction chemistry. Voltammetry on the iron‐iron sulfide couple indicates that graphite, platinum, and molybdenum may all be employed as inert indicating electrodes in eutectic. The latter melt was observed to attack Pyrex, forming a soluble silicon species capable of reacting with metal surfaces.

Improvement of the trapping solution for atmospheric hydrogen sulfide by addition of EDTA

The fluorometric method using the aqueous sodium hydroxide solution as the trapping solution possesses a sufficient sensitivity to determine hydrogen sulfide of background levels in the atmosphere. But the sulfide ion collected in the trapping solution is unstable, so the samples must be analyzed soon after sampling. The authors modified the trapping solution by adding a small amount of EDTA for better stability of the sulfide ion in the solution. The EDTA added into the solution masks the metallic ions such as ferrous, ferric and manganse ions, and it lowers the rate of oxidation of sulfide ion as a result of decrease of these ions in the solution which are considered to work as catalysts of oxidation. In case of 1.0×10-5 M of sodium sulfide in 0.1 N NaOH, the concentration decreased at a rate of about 20% in a day at room temperature, but it became more stable by the presence of 0.01 M EDTA and the sulfide solution was stable at least for one week if the solution was kept in a dark room. The sulfide solution containing EDTA was also quite stable to aeration; 5×10-6 M of sodium sulfide in 0.1 N NaOH in the presence of 0.01 M EDTA was stable even after passing air through the solution at a flow rate of 0.5 1/min for 2 hours. The modified trapping solution containing EDTA enables the fluorometric method to be more practical in the determination of hydrogen sulfide of background levels in the atmosphere.