Ethyl-bis-triazinylpyridine (Et-BTP) for the separation of americium(III) from trivalent lanthanides using solvent extraction and supported liquid membrane methods

The present paper deals with the solvent extraction and supported liquid membrane studies on Ln(III)/An(III) separation using ethyl-bis-triazinylpyridine (Et-BTP) as the extractant. The solvent extraction studies involved evaluation of a) diluents, b) phase modifiers, c) stripping agents and d) role of feed acidity. Though reasonably high separation factor values were obtained when Et-BTP was used along with α-bromo carboxylic acids, the mixtures could not be used for liquid membrane studies due to unsatisfactory stripping. On the other hand, a combination of Et-BTP with chlorinated cobalt dicarbollide (CCD) in nitrobenzene resulted in significant Am(III) mass transfer when used in the solvent extraction as well as SLM studies. Improved transport, membrane stability, and decontamination from lanthanides were observed when the organic phase diluent composition was 60% nitrobenzene + 40% n-dodecane. Using 0.02 M Et-BTP along with 0.005 M CCD in 60% nitrobenzene + 40% n-dodecane, the SLM studies on a mixture of ²⁴¹Am, ¹⁵²Eu and ¹⁴⁷Nd in a feed containing 0.1 M HNO₃, indicated quantitative Am³⁺ transport in 3.5 h with co-transport of about 8% Nd³⁺ and 22% Eu³⁺.     

The cyanidation of silver metal: Review of kinetics and reaction mechanism

Published rate data are analysed for the chemical and electrochemical dissolution of silver metal from rotating discs in aerated/oxygenated cyanide solutions at ≈25 °C, pH 11 and different partial pressures of oxygen. The current status of the reaction mechanism is also reviewed. Speciation analysis of 0.01 mM silver(I) in 1–100 mM cyanide solutions shows that Ag(CN)₂⁻ is the predominant complex (50%) at cyanide concentrations < 20 mM. However, at higher cyanide concentrations, Ag(CN)₃²⁻ (up to 60%) and Ag(CN)₄³⁻ (up to 10%) can be formed. Thus, it is important to consider a silver(I) : cyanide ion ratio of 2 or 3 in the Levich equation to calculate the diffusion coefficient of cyanide ion. Likewise, it is important to consider a silver(I) : oxygen ratio of 1 : 0.5 to calculate the diffusion coefficient of oxygen. This indicates the reduction of oxygen to hydrogen peroxide in the surface reaction. Analysis of exchange current density data for silver oxidation as a function of cyanide concentration shows the involvement of between 1 and 2 cyanide ions in the surface reaction. The limiting rate of silver dissolution at high cyanide concentrations (2.5 × 10^− 5 mol m^− 2 s^− 1 at ≈21 kPa oxygen pressure) represents the maximum surface coverage by cyanide. This value is in close agreement with the rate constant of the surface reaction 4 × 10^− 5 mol m^− 2 s^− 1 based on the pure kinetic current of the mixed “charge transfer plus diffusion” model proposed by Li and Wadsworth [Li, J., Wadsworth, M.E., 1993. Electrochemical study of silver dissolution in cyanide solutions. J. Electrochem. Soc. 140, 1921–1927].     

Studies of sorption and separation processes of rare earth element complexes on the anion-exchanger Wofatit SBW in the CH3OH–HNO3 system

For the 90% v/v CH₃OH–10% v/v 7 M HNO₃ system the affinity series of nitrate complexes of rare earth elements(III) for the strongly basic anion-exchanger Wofatit SBW×4% DVB was determined. The effect of ammonium nitrate and polar organic solvent addition on the effectiveness of separation of the ion-exchanging pair Y(III)–Nd(III) on Wofatit SBW×4% DVB as well as that of macrocomponent (yttrium) concentration on the yield of the purification process on Wofatit SBW×6% DVB were investigated. The weight and bed distribution coefficients for individual rare earth elements(III) were determined. It was shown that the neodymium content in the purified yttrium(III) can be decreased from 1% to 10⁻³% under controlled conditions.     

Leaching of gold and palladium with aqueous ozone in dilute chloride media

The recycling of gold and palladium from metallic scraps can be carried out by ozone-leaching at ambient temperature and low (∼0.1 M) H⁺ and Cl⁻ concentrations. Rh and Pt remain un-reacted, whereas metals such as Cu, Ni, Ag, can be previously eliminated through O₂/H⁺ and O₂/O₃/H⁺ leaching pretreatments. Gold and palladium are dissolved in O₃/Cl⁻/H⁺ with formation of AuCl₄⁻ and PdCl₄²⁻. Leaching studies showed a passive region, basically located at < 0.01 and < 0.05 M Cl⁻ for Au and Pd, respectively. In the non-passive region, rates were only slightly dependent on either H⁺ and Cl⁻. Secondary formation of chlorine or hypochlorous acid was negligible at ≤ 0.1 M Cl⁻. Kinetics appeared to be controlled by mass transfer of O_3(aq) to the solid–liquid interface, showing first order dependency with respect to [O₃]_aq. Rates increased with temperature up to about 40 °C, but decreased at higher temperatures due to the fall in the O₃ solubility. The ozone mass transfer coefficients showed an activation energy < 20 kJ/mol. Gold leaching rate gradually diminished for pH > 2, as consequence of the influence of the [H⁺] on transfer control. The electric power consumption associated with O₃ generation was in the range 4–8 kWh/kg metal leached.     

A review of effects of silver,lead, sulfide and carbonaceous matter on gold cyanidation and mechanistic interpretation

Despite the wealth of published data on the beneficial or detrimental effects of silver, lead, sulfide, and carbonaceous matter on the rate of gold cyanidation at an anode or by dissolved oxygen, the lack of comparative studies on relative effects has hampered rationalisation of the role of these activators or passivators of gold. In the present study, the published rate data per unit surface area of gold, silver, and gold–silver alloys based on electrochemical or chemical dissolution of rotating discs or foils of constant surface area in aerated cyanide solutions at ambient temperatures are analysed on the basis of the Levich equation. The current status of the reaction mechanism is also reviewed and updated on the basis of species distribution and potential–pH diagrams, stoichiometric factors, and interim chemical species of gold(I), silver(I), and lead(II). The anodic peak potentials of reported voltammograms closely follow the potential–pH lines of Au(I)/Au(0) and Pb(II)/Pb(0) couples. Despite the formation of stable complexes between lead(II), nitrate, and hydroxide ions, the total calculated soluble lead(II) in alkaline solutions of pH range 10–11 saturated with lead hydroxide is shown to be < 0.1 g/m³. A comparison of the reported diffusion coefficients of cyanide ions and dissolved oxygen with the values based on the Levich plots of reported rates reveals the rate-controlling stoichiometric M/CN or M/O₂ molar ratios. The difference between some of these ratios and the generally accepted ratios of M/CN = 1/2 and M/O₂ = 1/0.5 or 1/0.25 based on the formation of M(CN)₂⁻, H₂O₂ or OH⁻ in the overall cyanidation reaction is attributed to the oxidation of cyanide to cyanate and passivation due to the formation of gold hydroxides/oxides. The alloyed or dissolved silver and lead eliminate passivation due to the involvement of mixed hydroxo–cyano complexes of silver and lead ions in the surface reaction. Gold dissolution by oxygen in cyanide-rich solutions is limited by oxygen diffusion, but enhanced by the presence of a low concentration of sodium sulfide due to the involvement of hydrosulfide ion in the surface reaction. However, excess lead or sulfide retards gold cyanidation due to surface blockage by metallic lead, lead hydroxide, or due to passivation by Au₂S/S. Even low concentrations of hydrosulfide passivate gold–silver alloys due to the formation of Ag₂S. This can be eliminated by adding stoichiometric quantities of lead(II) to precipitate sulfide as PbS. Large stoichiometric ratios of O₂/M for the cyanidation of graphite coated gold appears to be a result of the enhanced oxidation of cyanide by oxygen or hydrogen peroxide, leading to a cyanide deficiency at the surface and passivation of gold by hydroxide/oxide. The presence of excess cyanide or lead(II) does not override this effect.     

Extraction of gold(III) in hydrochloric acid solution using monoamide compounds

The extraction and separation properties of Au(III) using two monoamide compounds, N,N-di-n-octylacetamide (DOAA) and N,N-di-n-octyllauramide (DOLA), which have different side chain lengths attached to the carbonyl carbon (CH₃ for DOAA and n-C₁₁H₂₃ for DOLA), were investigated. The solvent extraction of some precious and base metals (Au(III), Pd(II), Pt(IV), Rh(III), Fe(III), Cu(II), Ni(II) and Zn(II)) in HCl solutions was carried out using DOAA and DOLA diluted with n-dodecane and 2-ethylhexanol. A good selectivity for Au(III) extraction with 0.5 M extractant is obtained at lower HCl concentrations (< 3.0 M) in both systems. The extractability of Au(III) with DOAA is greater than that with DOLA. In the 0.5 M DOAA–3.0 M HCl system, a third phase is formed when the Au(III) concentration in the initial aqueous phase is over 39 g/L. In contrast, third phase formation is not found in the 0.5 M DOLA–3.0 M HCl system, and its loading capacity of Au(III) is about 79 g/L. The Au(III) extracted in the organic phase is effectively back-extracted by 1.0 M thiourea in 1.0 M HCl solution in both systems, while some thiourea is precipitated using the organic phase containing 20 g/L of Au(III). The back extraction of Au(III) using water is poor in the DOAA system, but possible in the DOLA system.     

Leaching and kinetic modelling of low-grade calcareous sphalerite in acidic ferric chloride solution

The leaching kinetics of a low grade-calcareous sphalerite concentrate containing 38% ankerite and assaying 32% Zn, 7% Pb and 2.2% Fe was studied in HCl–FeCl₃ solution. An L₁₆ (five factors in four levels) standard orthogonal array was employed to evaluate the effect of Fe(III) and HCl concentration, reaction temperature, solid-to-liquid ratio and particle size on the reaction rate of sphalerite. Statistical techniques were used to determine that pulp density and Fe(III) concentration were the most significant factors affecting the leaching kinetics and to determine the optimum conditions for dissolution. The kinetic data were analyzed with the shrinking particle and shrinking core models. A new variant of the shrinking core model (SCM) best fitted the kinetic data in which both the interfacial transfer and diffusion across the product layer affect the reaction rate. The orders of reaction with respect to (C_Fe³⁺), (C_HCl), and (S/L) were 0.86, 0.21 and − 1.54, respectively. The activation energy for the dissolution was found to be 49.2 kJ/mol and a semi-empirical rate equation was derived to describe the process. Similar kinetic behavior was observed during sphalerite dissolution in acidic ferric sulphate and ferric chloride solutions, but the reaction rate constants obtained by leaching in chloride solutions were about tenfold higher than those in sulphate solutions.     

200, 020, and 002 X-ray peaks in tempered Fe-18 Ni-C martensites

Separate 200, 020, and 002 X-ray peaks were recorded for 0.0, 0.4, and 0.8 wt pct carbon (18 pct Ni) martensites after tempering between 25 and 500°C. The carbon bearing martensites studied here have been tempered initially enough to eliminate the “high tetragonality” 002 peak usually recorded for as-quenched martensite and the present results apply to tempered martensite only. The peak maximum is taken to determine the lattice parameter and the peak shape is recorded. At all carbon levels and after all tempering treatments, the “crd parameter is larger than or equal to the “a” or “b”. The relative enlargement is very small (0.08 pct) for the lowest carbon level and for any carbon level after severe tempering (500°C for 15 min). For the two higher carbon alloys tempered at temperatures below 400°C (for 15 min) the “c” parameter is significantly larger than the “a” and “b” and for the 0.4 wt pct C alloy the “b” is significantly smaller than the“a” whereas in the 0.8 pct C alloy the “b” is slightly larger than the “a”. Within experimental error the mean volume of the unit cell does not change during the tempering studied here and is nearly unaffected by the initial carbon content. This indicates that little (at most 0.1 wt pct) carbon is dissolved in tempered martensite. In the low carbon alloy the peaks are symmetric and sharpen symmetrically during tempering. In the higher carbon alloys the peaks are nearly symmetric and sharp after severe tempering. After less severe tempering the 002 peak is asymmetrically broadened toward lower9 values (higher lattice parameters) whereas the 200 and 020 peaks are asymmetrically broadened toward higher 0 values corresponding to lower lattice parameters. This collection of results is tentatively interpreted as being due to strains in martensite due to transformation induced substructure and precipitated carbides.     

Separation of Eu（III） with supported dispersion liquid membrane system containing D2EHPA as carrier and HNO3 solution as stripping solution

The Eu(III) separation in supported dispersion liquid membrane (SDLM),with polyvinylidene fluoride membrane (PVDF) as the support and dispersion solution containing HNO3 solution as the stripping solution and Di(2-ethylhexyl) phosphoric acid (D2EHPA) dis-solved in kerosene as the membrane solution,was studied.The effects of pH value,initial concentration of Eu(III) and different ionic strengths in the feed phase,volume ratio of membrane solution and stripping solution,concentration of HNO3 solution,concentration of carrier,different stripping agents in the dispersion phase on the separation of Eu(III) were also investigated,respectively.As a result,the optimum separation conditions of Eu(III) were obtained as the concentration of HNO3 solution was 4.00 mol/L,concentration of D2EHPA was 0.160 mol/L,and volume ratio of membrane solution to stripping solution was 30:30 in the dispersion phase,and pH value was 5.00 in the feed phase.Ionic strength had no obvious effect on the separation of Eu(III).Under the optimum conditions studied,when initial concentration of Eu(III) was 1.00×10–4 mol/L,the separation rate of Eu(III) was up to 94.2% during the separation period of 35 min.The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry.The results were in good agreement with the literature data.     

Intracellular recovery of gold by microbial reduction of AuCl4 ions using the anaerobic bacterium Shewanella algae

Microbial reduction and intracellular precipitation of gold was achieved at 25 °C and pH 7 by using the mesophilic anaerobic bacterium Shewanella algae with H₂ as the electron donor. The reductive precipitation of gold by S. algae was a fast process: 0.1–1 mol/m³ AuCl₄⁻ ions were completely reduced to insoluble gold within 30 min. The biogenic precipitates were crystalline gold nanoparticles of 10–20 nm present in the periplasmic space. The reducing power of S. algae at 3.2 × 10¹⁵ cells/m³ and 25 °C was comparable to that of aqueous citric acid solution (chemical reductant) at 20 mol/m³ and 50 °C. The intracellular recovery of gold is potentially attractive as an environmentally friendly alternative to conventional methods.     

Kinetics of aluminum can dissolution in sec-butyl alcohol for aluminum sec-butoxide

A kinetic study of dissolution reaction of Al can was conducted for the synthesis of aluminum sec-butoxide (ASB). With the Al can scraps and sec-butyl alcohol (SBA) as reactants, the reaction was examined at the condition of 3 mol SBA/mol Al of stoichiometric ratio, adding 10^− 3 mol HgI₂/mol Al for catalyst and no agitation at the reaction temperature ranging from 80 to 100 °C. After the dissolution of 24 h at 100 ^oC, the reaction gave a 75% yield. A two-stage dissolution mechanism was proposed in which the dissolution rate is determined first by a chemical reaction and then by ash layer diffusion as the previous dissolution kinetics for the synthesis of AIP (Aluminum iso-propoxide) (Yoo, S.-J.,Yoon,H.-S., Jang, H.D., Lee,M.-J., Lee, S.-I.,Hong, S.-T., Park,H.S., 2007a. Dissolution kinetics of aluminum can in isopropyl alcohol for aluminum isopropoxide. Chem. Eng. J. 133, 79–84.). On the basis of the shrinking core model with the shape of flat plate, the first dissolution rate of Al can was controlled by chemical reaction. The concentration of SBA was largely changed during the dissolution reaction because it was added the stoichiometric ratio to the reactor. Therefore it was included as an integral term of the reaction time. By using the Arrhenius expression, the apparent activation energy of the first chemical reaction step was determined to be 200.5 kJ mol^− 1. In the second stage, the dissolution rate is controlled by diffusion control through the ash layer. The apparent activation energy of the second step was determined to be 101.8 kJ mol^− 1.     

Study on transport of Dy（III） by dispersion supported liquid membrane

The transport of Dy(III) through a dispersion supported liquid membrane (DSLM) consisting of polyvinylidene fluoride membrane (PVDF) as the liquid membrane support and dispersion solution including HCl solution as the stripping solution and 2-ethyl hexyl phosphonic acid-mono-2-ethyl hexyl ester (PC-88A) dissolved in kerosene as the membrane solution, was studied. The effects of pH value, initial concentration of Dy(III) and different ionic strength in the feed phase, volume ratio of membrane solution and stripping solution, concentration of HCl solution, concentration of carrier, different stripping agents in the dispersion phase on transport of Dy(III) were also investigated, respectively. As a result, when the concentration of HCl solution was 4.0 mol/L, concentration of PC-88A was 0.10 mol/L, and volume ratio of membrane solution and stripping solution was 40:20 in the dispersion phase, and pH value was 5.0 in the feed phase, the transport effect of Dy(III) was the best. Ionic strength had no obvious effect on transport of Dy(III). Under the optimum condition studied, when initial concentration of Dy(III) was 0.8 × 10^?4 mol/L, the transport rate of Dy(III) was up to 96.2% during the transport time of 95 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The diffusion coefficient of Dy(III) in the membrane and the thickness of diffusion layer between feed phase and membrane phase were obtained and the values were 1.99 × 10^?7 m²/s and 15.97 μm, respectively. The results were in good agreement with experimental results.     

Electrochemistry of samarium in lithium-beryllium fluoride salt mixture

The electrochemical behaviour of samarium was investigated in LiF-BeF2 system on an inert (Mo) electrode by cyclic voltammetry and chronopotentiometry at 804, 833, 847 and 872 K. Redox process Sm3++e-→Sm2+ was recognized and analysed. Cyclic voltammetry data suggested that at potential sweep rates lower than 0.25 V/s, the reduction was limited by the diffusion of Sm3+ ions. It was not possible to observe reduction process of Sm2++2e-→Sm0 due to insufficient electrochemical stability of LiF-BeF2. Diffusion coefficients of Sm3+ ions in LiF-BeF2 were calculated from voltammetric and chronopotentiometric data in the temperature range 804-872 K. Diffusion coefficient values obeyed Arrhenius law. Activation energy was calculated to be 102.5 kJ/mol.     

Extraction and permeation of cadmium ions through supported liquid membrane impregnated with mixtures of D2EHPA and M2EHPA

Abstract

The use of an organic carrier consisting of di-(2-ethylhexyl) phosphoric acid (D2EHPA) and mono-(2-ethylhexyl) phosphoric acid (M2EHPA), diluted in kerosene, for separation of cadmium through a supported liquid membrane (SLM) was investigated. The extraction percentage of cadmium and permeability coefficients rose by increasing M2EHPA and feed phase concentration. By increasing the volume percentage of M2EHPA, the permeability coefficient of cadmium increased to a maximum value of 8 cm s^?1 at 1·5 vol.-% declining at higher volume percentages. The permeability of cadmium ions through the SLM decreased with time. The permeation coefficient increased as the initial cadmium concentration increased.

On a étudié l’utilisation d’un support organique consistant d’acide phosphorique di-(2-éthylhexyle) (D2EHPA) et mono-(2-éthylhexyle) (M2EHPA), dilué dans du kérosène, pour la séparation du cadmium à travers une membrane liquide supportée (SLM). Le pourcentage d’extraction du cadmium et les coefficients de perméabilité s’élevaient avec l’augmentation du M2EHPA et de la concentration de la phase d’alimentation. En augmentant le % de volume de M2EHPA, le coefficient de perméabilité du cadmium augmentait à une valeur maximale de 8 cm s^?1 à un volume de 1·5% et déclinait à des % plus élevés du volume. La perméabilité des ions de cadmium à travers la SLM diminuait avec le temps. Le coefficient de perméation augmentait avec l’augmentation de la concentration initiale de cadmium.     

Thermal expansion anomaly and spontaneous magnetostriction of Gd2Fe17 compound

Materials with negative thermal expansion have many practical applications. However, these materials are known in only several oxide systems, and when the negative thermal expansion occurs, the contraction is usually small and limited to a narrow temperature range beyond room temperature. For obtaining a compound with negative thermal expansion in broad temperature range, the structural and magnetic properties of Gd2Fe17 compound were investigated by means of X-ray diffraction and magnetization measurements. The Gd2Fe17 compound annealed at 1050 oC had a Th2Zn17-type structure. There existed an anisotropic strong spontaneous magnetostriction and a negative thermal expansion in Gd2Fe17 compound. The average thermal expansion coefficients was =-7.40×10-6/K in the temperature range of 294-453 K and =-1.80×10-5/K in 453-534 K, respectively. The spontaneous magnetostrictive deformation ωS decreased from 4.34×10-3 to near zero with temperature increasing from 294 to 572 K. The spontaneous linear deformation λc was much larger than λa at the same temperature below about 500 K.     

Kinetics of reduction of gold(III) complexes using H2O2

In this article, the effect of different kinetic parameters, namely, temperature, pH, and reductant concentration, on the rate of Au(III) reduction from aqueous chloride solutions by H₂O₂ was investigated. The possible mechanism of complex [Au(OH)₄]⁻ ion reduction by hydrogen dioxide is also discussed and the model mechanism based on experimental data is postulated. On the basis of the suggested mechanism, the rate equation for Au precipitation is given in the form , in which respective rate constants k ₁, k ₃, and k ₅ were determined experimentally and are given in the text.     

Solvent extraction of some base and precious metals using 1,3,4-thiadiazole-2-nonylmercapto-5-thiol

This investigation is one of a series of studies in which the fundamental chemistry which underlies the extraction and separation of precious metals is considered. The title compound (TNSTH) was used as a solvent extraction reagent and shows some promise for extracting and separating the chloro-anions of Au(III) and Pd(II) from strong hydrochloric acid solutions (ca. 5 M). The distribution coefficients from such media were in the order of 10⁴. The title reagent may be used to separate the precious metals from each other. For example, the separation coefficients (i.e., ratios of distribution coefficients) for mixed solutions are 10⁶ for Au(III)/Rh(III) and Pd(II)/Rh(III); 145 for Au(III)/Pd(II); 180 for Pd(II)/Cu(I or II); 10⁶ for Pd(II)/Pt(IV). The time for half of the Pd(II) to be extracted is approximately 6 min, which is acceptable for a commercial process. The title reagent provides a means of separating precious metals from base metals as the latter, with the exception of copper, are not extracted. In the case of copper, the extraction is as Cu(I) rather than Cu(II). The stoichiometry of the Pd(II) extraction is Pd:TNSTH is 1:1.5. Some additional information concerning the nature of the complexes formed by the title compound and chloro-anions in alcoholic solution indicates that Cu(TNST), Ag(TNST), Pd(TNST)₂, and RhCl₃(TNST)₂ are formed. Most of the metals, with the notable exception of rhodium(III) and iridium(IV), can be stripped using a thiourea/HCl solution. The reagent TNSTH appears to be a chelating agent with donor N and S atoms.     

The solvent extraction separation of bismuth and molybdenum from a low grade bismuth glance flotation concentrate

The main purpose of this study was to characterize and to extract bismuth and molybdenum from a low grade bismuth glance concentrate. Selective leaching of bismuth could be obtained at a temperature range 60 to 85 °C for a leaching duration of 2 h with hydrochloric acid concentration of 150 gpl, lignin calcium concentration of 0.02 gpl and using a solid–liquid ratio 1/4 g/cc. Treatment of leach liquor for the solvent extraction of bismuth with N235 showed that 8.0 × 10^− 2 M N235 in kerosene, a 3 min period of equilibration and a pH 0.2 were sufficient for the extraction of Bi(III). This bismuth-loaded organic phase was almost completely stripped using 0.5 M EDTA solution. Treatment of leached residue was dealt with by roasting in the presence of slaked lime, and followed by hydrometallurgical treatment of the roasted products. In the lime roasting process, molybdenum recoveries of around 99% were achieved when an excess of 50% lime over stoichiometric requirement was roasted at 700 °C for 2 h and the calcine was leached with 4 M HCl, at 70–80 °C for 2 h. Molybdenum then was effectively extracted from the leached residual solution with N235. An optimum pH of 0.5 was determined for molybdenum extraction. From loaded solvent, this metal was easily stripped with ammonia solutions to give a pregnant solution suitable for final recovery of metal by salt precipitation. Under the optimized conditions, the ultimate recovery rate of bismuth and molybdenum was more than 99% and 98% respectively.     

Hydrogen permeation through oxide and passive films on iron

Hydrogen permeation through thin films of Fe_I–Y O on iron and through chemically polished iron were investigated by the sensitive electrochemical technique. The oxide was formed on the exit side of the sample membrane. The hydrogen arriving at the iron/oxide interface is in an atomic or protonic state which renders the hydrogen uptake by the oxide possible. The wustite films were formed by oxidation in a H₂O-H₂-atmosphere. The dependence of the hydrogen permeation current on temperature and film thickness and different degrees of nonstoichiometry in Fe_I–Y O was studied. Hydrogen permeation through these oxides is possible, but very low permeation coefficients have been found, of the magnitude of at 25°C. The diffusion coefficient of diffusible hydrogen was determined to be about 4 · 10^?10 cm²/s. Measurements of the potential dependence of permeation across the film indicate that hydrogen migrates in the oxide as a charged particle (proton). In the case of the passive surface film on iron formed by chemical polishing, the dependence of the permeation current on temperature and anodic potential was measured. The electrochemical behaviour of the film was studied by cyclic voltametry. Electron transfer reactions were investigated by means of the hexacyanoferrate (II/III) redox system. Further information on the film composition were obtained by Auger electron spectroscopy. On the one hand, electron transfer across the film can occur, but on the other hand, the film is nearly impermeable for hydrogen, even if the hydrogen is in the atomic or protonic state. Cyclic voltamograms show the formation of an oxygen adsorption layer on the film in a range of anodic potential.