A study was made of the electro-oxidation of several sulfides, selenides, and tellurides in cationic surfactant-aqueous sodium hydroxide suspensions in a slurry cell and a sandwich cell. Because the cationic surfactant increased the oxidation potential of water, it was possible to observe and study separate voltammetric waves for the oxidation of the sulfides to sulfur, sulfite, and sulfate; the selenides to selenium, selenites, and selenates; and the tellurides to tellurium, tellurite, and.tellurate. Superimposed, in some cases, on these oxidation waves were waves for the oxidation of the metal ions to higher oxidation states. Controlled potential coulometric studies of these oxidations showed that it was possible to perform each of these oxidations with essentially 100% current efficiency. The oxidation potentials of the sulfides to sulfur reflected differences which could be attributed to differences in crystallization energies. In cases where the oxidation of the metal ion did not interfere, the potentials for oxidation of sulfur to sulfite and sulfite to sulfate were independent of the metal ion because these reactions were the same. In a similar manner, the oxidation of the selenium to selenite, selenite to selenate, tellurium to tellurite, and tellurite to tellurate all showed potentials that were independent of the metal ion that was present. The oxidation of the selenides to selenium and tellurides to tellurium all occurred at the same potential and this potential was, within experimental error, equal to the first oxidation peak potential for the surfactant. This led to the conclusion that these oxidations all proceeded by a mechanism that involved electrochemical oxidation of the surfactant followed by chemical oxidation of the solid.Recently, as part of a series of studies on the uses of cationic surfactants in the electro-oxidation of insoluble, difficulty oxidizable compounds (1-8), it was reported that it was possible to electrolytically oxidize iron pyrite (9, 10) and galena (11) powders in a cationic surfactant-aqueous sodium hydroxide system. Previously, electrolytic oxidation studies of these sulfide minerals to obtain answers to questions in the field of mineral processing have primarily utilized crystalline electrodes or powders mounted in graphite paste or epoxy cements (12-26).This paper is a report on an extension of the previous studies (9-11) to electro-oxidation of several other sulfides and some selenides and tellurides suspended in surfactant systems. The purpose of these studies was to investigate the possible use of these surfactant systems in electroanalysis of insoluble powders and in areas of massive electrolysis such as electrolytic roasting of minerals.The previous studies (1-11) have shown that cationic surfactants affect these electro-oxidations in two ways. They solubilize the solids and form a hydrophobic film on the electrode, increasing the oxidation potential of water by 0.9V. Anionic and neutral surfactants solubilize insoluble solid powders but do not appreciably increa...
A study was made of the electro-oxidation of iron pyrite powders on polystyrene-surfactant filmed platinum electrodes using a suspension in a styrene-cationic surfactant-2N aqueous sodium hydroxide emulsion. In addition, a study was made in a thin layer cell in which the powder was trapped adjacent to the electrode. The film on the electrode allowed one to apply approximately an additional 1.7V before encountering interference from electrolysis of water. Without a film, one sees only one oxidation wave associated with a one electron oxidation of $2 = to $2-. In the filmed system, there are four oxidation reactions that can be studied $2(~ = --~ $2(~1-+ e [1] Fe(~+ + OH 1/2 Fe20.~,~ + e [2] S21si = ~ $2 ~ + 2e [3]and fourth, oxidation of organic compounds formed by the trapping of the $2-and $2 ~ free radicals.
ChemInform Abstract is studied using two types of cells, a slurry cell and a sandwich cell. Voltammetric and coulometric measurements show that a cationic surfactant such as Hyamine 2389 is useful in performing electrolytic oxidations of insoluble, difficultly oxidizable sulfides, selenides, and tellurides. The controlled potential coulometric studies show that it is possible to perform oxidations to produce X0, XO32-, and XO42-(X: S, Se, Te) with a current efficiency of 100%. The half-wave potentials for the oxidation of the sulfides of Pb(II), Mn(II), Ni(II), and Mo(IV) are close to each other and the oxidation potentials of the selenides studied are identical to each other but different from the corresponding sulfides. The fact that the oxidations to form Se0 and Te0 all occur at the same potential and that this potential agrees reasonably well with the potential for the oxidation of the surfactant indicates that the oxidation mechanism involves electrooxidation of the surfactant and subsequent chemical oxidation of the chalcogenide.
A study was made of the electro‐oxidation of galena in Hyamine 2389 surfactant systems. It was found that during the oxidation, one could observe four oxidation waves in voltammetric curves. These were concluded to be the oxidation of the galena to (i) normalPbO and S, (ii) normalPbO and SO3= , (iii) PbSO4 , and (iv) PbO2 and SO4= . A study of the effect of the relation between the amount of galena in a suspension and the height of the highest peak in the voltammetric curve showed a complex relationship. At low concentrations of galena, the height varied with a regular periodicity indicating the formation on the electrode of multilayers of the Hyamine‐galena micelle complex with the layers arranged in a manner similar to Langmuir‐Blodgett films, alternating in nature from hydrophobic to hydrophilic to hydrophobic, etc. At higher concentrations of galena, it behaves as if one has simple monolayer adsorption.
Copper(II) oxide and manganese(II) oxide were shown to be catalysts for the electro-oxidation of 2-chloroethyl ethyl sulfide, diethylsulfide, 2-hydroxyethyl ethyl sulfide, and l-ehlorobutane in aqueous suspensions containing cationic surfactants. These oxides were shown to act as catalysts by formation of eopper(III), manganese(III), and manganese(IV) oxides which chemically oxidized the organic compounds. Analysis of the product suspensions showed the production of only the sulfoxide by oxidation of the 2-chloroethyl ethyl sulfide and diethyl sulfide. Destruction of chlorobutane was catalyzed by both barium peroxide and eopper(II) oxide. Volatile product(s) was trapped in a liquid nitrogen trap during electrolysis. These products included butane and butene.
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