Denise Bauer

ENHANCEMENT OF THE EXTRACTION RATE OF GALLIUM BY THE 7-)1-VINYL-3,3,5,5 TETRAMETHYLHEXYL(-8-QUIN0LIH0L USING A MICROEMULSION AS ORGANIC PHASE

ABSTRACT The extraction rate of gallium from aqueous NaOH solutions vith the 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol into kerosene is increased when a vater-in-oil microemulsion is used as organic phase. This microemulsion is formed by adding a surfactant and an alcohol to the extraction system. The efficiencies of sodium salts of long chain carboxylic acids and a fev other anionic surfactants have been compared. The effects of the alcohol and surfactant concentrations and of the length of the alcohol and carboxylate hydrocarbon chains have been studied. An extraction mechanism has been proposed vhich is in good agreement vith experimental results. The rate limiting step is the complexation reaction vhich takes place at the macroscopic interface between the aqueous phase and the microemulsion. It emphasizes the role of extractant molecules adsorbed on the water droplets solubilized in the microemulsion.

Comportement electrochimique de la galene (PbS) dans les conditions de pH proches de celles de la flottation

Abstract The electrochemical behaviour of lead sulphide mineral (galena) has been investigated by cyclic voltammetry and controlled potential electrolyses. In the pH range 5–9, the oxidation leads—at + 0.5 V vs sce—to the formation of elemental sulphur and lead species: Pb2+, Pb(OH)2 or Pb(OH)Cl depending on the pH, and on the nature of the electrolyte. The reactions involved in the overall anodic/cathodic cycle have been interpreted; at pH 9, galena is reduced at − 1.3 V, to lead metal and HS− ions.

Electrochemical study of some palladium compounds at a carbon paste electrode—application to the determination of palladium in oxidation automotive catalysts

The carbon paste electrode has been used for studying the electrochemical behaviour of Pd(II), Pd(0) and palladium black. Some of our results are consistent with the already existing literature values except the reduction of PdO into Pd metal which was found to occur at about −20 mV/sce in 0.5 M HClO4. The freshly deposited palladium metal was relatively easier to oxidize compared with the commercial one. We have also applied this method to the quantitative determination of palladium in oxidation automative catalysts. Palladium was present in the form of Pd(0) in the new catalyst examined, while a substantial fraction of it was converted into PdO in the corresponding spent catalyst.

Determination of fixation of alkyldithiocarbonate isotherms on galena by a dynamic method: Chromatographic saturation front analysis

Abstract The isotherms of adsorption of alkylxanthate on galena are determined by a new method: the analysis of the chromatographic saturation front. A chromatographic column is filled with grounded galena (20–50 μm). The galena surface state is controlled by percolation of suitable solutions: a cleaning treatment (EDTA and ether alternatively) and an oxidative treatment (aqueous solution at controlled pH, in equilibrium with oxygen at a given partial pressure). The alkylxanthate solution is then percolated and the saturation front is recorded. The amount of fixed product may be calculated from the value of the retention volume. For a non-oxidized galena, the galena (20–50 μm) adsorbs 2 × 10−7 mol g−1 of ethylxanthate (5 × 10−5 to 10−4M; pH 8.5). The fixed quantities increase with the oxidation duration. Amylxanthate is twice much fixed as ethylxanthate. The effect of pH on the fixation rate has been studied between pH 7.5 and 9.5.

A STUDY OF THE ELECTROCHEMICAL BEHAVIOUR OF SOME PLATINUM COMPOUNDS AT A CARBON PASTE ELECTRODE WITH ELECTROLYTIC BINDER

The carbon paste electrode has been used for studying the stoichiometry of the electrochemical reduction of Pt(IV) and Pt(II) and of the electrochemical oxidation of Pt(II) and platinum black in acidic media. The electrochemical reduction of PtO2 in 2 M H2SO4 and in HCl (2 M and 6 M) was also reported. The reduction of Pt(II) to Pt(0) and the evolution of H2 was found to occur at about the same potential of −200 mV in HCl. We have been able to verify the effect of chloride concentration on the oxido-reduction potential of some of these reactions. The potential range values obtained agree with those predicted from thermodynamic data for some reactions. Pt(II) in solid PtCl2 was found to behave differently from Pt(II) in the solution of PtCl2.

ELECTROCHEMICAL BEHAVIOUR OF SOME AUTOMOTIVE CATALYSTS AT A CARBON PASTE ELECTRODE AND WITH ELECTROLYTIC BINDER

The electrochemical behaviour of some automotive catalysts has been investigated. We have also looked into the possibility of using this technique to determine the quantity of platinum, palladium, iron and lead that could be present in these catalysts. In most of the cases, the values obtained with this technique agree fairly well with those obtained from the analysis by atomic absorption technique. The oxidation states in which some of these elements are present in the studied catalysts were also reported.

Equilibrium and kinetic studies of copper extraction from chloride solutions with pyridine carboxylates

Equilibrium studies carried out at constant and non-constant water activity in chloride media demonstrate the superiority of the commercially available and well-tailored extractant ACORGA CLX-50 over studied pyridine carboxylate models, especially in respect of the selectivity of copper(II) extraction versus iron(III), zinc(II), lead(II) and hydrochloric acid. The ability of pyridine monocarboxylates for extracting copper(II) increases as follows: decyl picolinate < decyl nicotinate < decyl isonicotinate,whereas that of pyridine dicarboxylates ranges in the following order: dioctyl pyridine-3, 5-dicarboxylate < dioctyl pyridine-2, 4-dicarboxylate = dioctyl pyridine-2, 5-dicarboxylate. Model pyridine monocarboxylates are much less selective for copper(II) than ACORGA CLX-50, especially with respect to iron(III). Among studied pyridine monocarboxylates, only decyl nicotinate shows a strong tendency to extract zinc(II). Pyridine monocarboxylates strongly extract HC1 and can be ranged in the following order as far as their affinity for HC1 is concerned: decyl picolinate < decyl nicotinate < decyl isonicotinate. On the other hand, ACORGA C.L.X-50 can extract only very small amounts of HC1. The rate of copper(II) extraction depends upon the ionic strength of the aqueous phase, concentration of reagents, extractant hydrophobicity and position of the esterified carboxylic group(s). For instance, decyl nicotinate extracts copper(II) much more rapidly than decyl isonicotinate. The flux of copper(II) decreases as the length of the alkyl group is increased in the homologous series of alkyl nicotinates, i.e. when the hydrophobicity of the extractant is increased.

Electrochemical study of some rhodium compounds at a carbon paste electrode with electrolytic binder

We have used the carbon paste electrode to study some rhodium compounds in various media. The oxidation of Rh(0) led to the formation of two different types of the Rh(III) complex in 6 M HCl, while the reduction of RhCl. 3H2O was found to take place at about the same potential that the reduction of H+ occurs. The reduction of Rh(III) in 1 M KCl and in 1 M KCl plus 20% ethanol led to Rh(0) and it took place, respectively, at −285 and −330 mV. On the contrary, the reduction of Rh(III) was found to lead to Rh(I) in the presence of triphenylphosphine and in 1 M KCl with 20% ethanol. The reduction of Rh(III) in a mixture of 1 M KCl and 1 M pyridine would most probably lead to a mixture of Rh(I) and Rh(II) and the reaction was reversible.

DETERMINATION OF ACID-BASE CONSTANTS AND OF AKIII) and Ga(III) COMPLEXES FORMATION CONSTANTS FOR THREE 5-SUBSTITUTED 8-HYDROXYQUINOLINES

ABSTRACT The acid-base constants and the formation constants of the extracted complexes as sell as the formulas of the involved species have been obtained by computer simulation of extraction curves. Three newly synthetized extractants are considered. The values obtained for the chemical constants compare favorably Mith those that can be deduced from an HAHHETT evaluation.

Some Properties of New Ion Exchangers with Organopolysiloxane Structure

New ion exchangers have been recently synthesized at DEGUSSA by the polycondensation of suitable bifunctional silane monomers. Such ion exchangers can be obtained as spherical or egg-shaped particles with a grain size of about 0.1 to 1.5 mm and surface areas up to 700 m2/g. They are composed of a siliceous core and contain a high concentration of functional groups so that their exchange capacity is comparable to that of conventional organic systems. The functional groups are bound to the matrix via carbon-silicon bonds which are fairly stable towards hydrolysis (up to pH = 11 or 12). The main advantages of the new exchangers lie in the absence of swelling or shrinking during ion exchange operations, in their high thermal stability (up to 200 °C) and in the great variety of functional groups now available. The ion exchange properties of these exchangers have been investigated by studying the fixation of Ag(I) and Cu(I), As(III) and Sb(IIl), Bi(III), Cu(II) and Ni(II), Ga(III), Pd(II) and Pt(IV).