Behaviour of tungsten carbide hydrogen-diffusion electrodes in chloride etching solutions

Studies were performed of tungsten carbide hydrogen-diffusion electrodes operating as anodes in electrolytic baths for regeneration of etching solutions of CuCl₂ and FeCl₃. Under conditions of electrolytic regeneration of copper chloride solutions (i = 40 mA cm^–2, 40° C) after 1500 h operation the electrode polarization increased by about 200 mV. Maximum current efficiency of 60–65% was obtained at I _k = 80 mA cm^–2. It is demonstrated that the replacement of the standard carbon anodes with tungsten carbide hydrogen-diffusion electrodes and the elimination of the ion exchange membrane separating the anodic from the cathodic space leads to a 2–4 V decrease of the electrolytic bath voltage. The regenerated solutions of CuCl₂ and FeCl₃ can be reused as etching agents after adding 7–10 ml 30% solution of hydrogen peroxide per litre.     

In situ degradation of formaldehyde with electrogenerated hypochlorite ion

The oxidant ClO^– was generated on an SPR (SnO₂-PdO-RuO₂-TiO₂) anode and used to degrade formaldehyde in aqueous solution. The current efficiency of the production of hypochlorite ion was significantly affected by the concentration of chloride ion, pH and stirring rate. The effect of current density and temperature on the current efficiency for electrogeneration of hypochlorite ion was slight. The maximum anodic current efficiency was 99.3% when 100 C was charged. Increasing the concentration of chloride ion, pH, temperature, stirring rate and the concentration of formaldehyde in the solution and decreasing the current density and charge passed resulted in increased current efficiency of degradation of formaldehye with electrogenerated hypochlorite ion.     

Electrodeposition of Zn−Ni−Fe alloy in acidic chloride bath with separated anodes

The electrodeposition of ternary Zn–Ni–Fe alloy films was investigated in acidic chloride electrolyte. Electrodeposition was performed onto mild steel plates at pH 3 and 43°C. The influence of the chloride concentration (ZnCl₂, NiCl₂ and FeCl₂) on the surface appearance and deposit composition, as well as cathodic current efficiency, were investigated. Bright Zn–Ni–Fe alloy deposits were obtained in the electrolyte containing 0.4m of each of ZnCl₂ and NiCl₂ with 0.02 to 0.08m FeCl₂. The influence of current density, pH and temperature were also examined.     

The Mutual Effect of Iron(III) and Silver(I) Species in Concentrated Chloride Medium

Abstract

Earlier studies carried out to evaluate the selectivity of solvating extractants towards silver(I) in concentrated chloride media revealed that an intriguing situation occurs if a given excess of iron(III) concentration is present in the aqueous solution: the extraction of silver(I) becomes almost quantitative and independent of the initial chloride content. On the assumption that this effect may be due to a phenomenon occurring in the aqueous phase, a systematic study involving solutions containing different Ag(I), Fe(III), and HCl concentrations was carried out by solvent extraction and capillary electrophoresis. Capillary electrophoresis suggests that the AgCl₃ ^2? amount in solution decreases in the presence of Fe(III), whereas FeCl₃ seems to be partially converted onto FeCl₄ ^?. From the experiments performed, it can be concluded that the presence of Fe(III) seems to facilitate the formation of less anionic Ag(I) species, which are in turn more easily extracted by solvating extractants. Furthermore, the presence of FeCl₄ ^? has been detected in the organic phase of triisobutylphosphine sulfide (TIBPS) by UV‐Vis spectrophotometry, after equilibration with HCl solutions containing both Ag(I) and Fe(III), which was not identified during similar experiments carried out in the absence of Ag(I). Speciation of silver(I) and iron(III) in concentrated chloride medium has also been worked out by a numerical methodology.     

Nickel electrowinning using a Pt catalysed hydrogen-diffusion anode. Part I: Effect of chloride and sulfate ions and a magnetic field

The use of a Pt catalysed H₂-diffusion anode for Ni electrowinning has been studied from typical chloride, Watts and sulfate baths at 25 °C. Higher anodic current densities are found in a three-electrode cell when sulfate ions are gradually replaced by chloride ions. Adherent Ni deposits are obtained from the Watts and sulfate media, whereas in the chloride bath, Cl₂ is released at the anode and less adherent deposits are formed. Current efficiencies between 94 and 98 for anodic current densities ranging from 15 to 65 mA cm^-2 have been found. The energy costs for Ni electrowinning decrease with increasing chloride content in the bath, and their values are always much lower than those reported using conventional DSA, graphite or lead anodes. All deposits are composed of high-purity Ni, free of heavy metals and other impurities. The crystals have a face-centred cubic structure with a preferential orientation which mainly depends on the medium and current density. A superimposed magnetic field of 0.9 T orientated either parallel or perpendicular to electrodes in a two-electrode cell exerts only a small effect on the crystallographic orientation of Ni, although it has a certain influence on its morphology.     

Electrochemical decolourisation of dispersed indigo on boron-doped diamond anodes

In denim production the decolourisation of intensively coloured, indigo-particulate containing waste water is a factor of major environmental concern. Successful anodic decolourisation of solutions containing 0.29 mM dispersed indigo and 0.070 M Na₂SO₄ could be achieved on boron-doped diamond electrodes. Current densities were varied from 0.36 to 80 mA cm^− 2. Relative current efficiency decreases with increased current density from 43% to less than 1% at 80 mA cm^− 2. At higher concentration of dispersed indigo of 25.1 mM, increased relative current efficiency is observed.Diffusion limited current density for decolourisation of 0.292 M indigo dispersion can be calculated with 0.166 ± 0.007 mA cm^− 2. At the experimental conditions studied, peroxodisulfate, formed as by product of the electrolysis, was found to be ineffective for dyestuff destruction.Experiments in presence of small amounts of chloride proved, that the observed decolourisation of the dispersed indigo cannot be attributed to hypochlorite, formed by anodic oxidation of chloride. While anodic decolourisation of a soluble reactive dye proceeds rapidly, commercial vat dyes resist to oxidative anodic attack at the conditions chosen.Bleach experiments of dyed fabric failed, which supports the model of indigo oxidation in the diffusion layer of the anode.     

A study of mass transfer in electropolishing of copper

Limiting current was measured for the anodic polishing of vertical copper electrodes in o-H₃PO₄ acid using: (a) a cell with diaphragm where the effect of H₂ evolved at the cathode on the rate of mass transfer at the anode is eliminated. A general correlation of the data may be represented by the equation Nu = 0·72 (ScGr)^0.23, where Nu is the Nusselt number, Sc the Schmidt number and Gr the Grasshof number. The experimental range used in the correlation was 6·49 × 10¹¹ < ScGr š 2·9 × 10¹⁴; (b) a cell without diaphragm, where the effect of H₂ evolved at the cathode on the anodic limiting current and the rate of mass transfer was studied. It was found that H₂ evolved at the cathode increases the rate of mass transfer and the anodic limiting current by a value ranging from 2·8–28·4% depending on the operating conditions.     

FeCl3对污泥酸性发酵产物中丙酸比率的影响

采用半连续运行的序批式反应器进行污泥酸性发酵试验,研究了发酵液中FeCl₃浓度对污泥发酵产物中丙酸比率的影响。实验表明：在温度32℃、HRT 6.6 d、进泥VS浓度 20.43 g·L^-1、pH5.5～6.0的条件下,FeCl₃浓度由0增加到232 mg·L^-1时,发酵液中ORP逐渐提高,丙酸比率变化不大;FeCl₃相似文献   

Kinetics of armco iron dissolution in an anhydrous methanol and hydrochloric acid solution

The polarization behaviour of Armco iron in anhydrous solutions of CH₃OH+HCl and CH₃OH+HCl+LiCl was studied by the potentiostatic method. The following reaction orders were found for the anodic process: Z_a(Cl^?) = 1.7 –1.82 and Z_a(H⁺) = 0. The following mechanism of dissolution is proposed: Fe+Cl^? ? FeCl^?_ads, FeCl^?_ads+Cl^? → FeCl₂+2e (rate-determining step), FeCl₂?FeP²⁺ + 2Cl^?.     

Anodic dissolution phenomena accompanying supersaturation of copper sulfate along a vertical plane copper anode

Vertical plane copper anode was electrochemically dissolved in a stagnant CuSO₄ and CuSO₄-H₂SO₄ electrolyte solution. Measured anodic polarization curve showed three distinct stages: Stage I characterized by an increased current density with increasing in anodic overpotential, Stage II including a maximum peak current followed by an abrupt current decrease caused by CuSO₄ precipitates at higher overpotential and Stage III with much lower and virtually constant current density, that is, the existence of anodic limiting current density over a wide anodic overpotential range. The complete passivation phenomena were not encountered in the present experimental conditions. Supersaturation phenomena of Cu²⁺ near the anode surface in Stage II were in-situ measured by holographic interferometry. The degree of supersaturation more than 0.18 M CuSO₄ was recorded. It was followed by the nucleation phenomena of a kind of CuSO₄ crystal after a certain incubation period. With growth of precipitates on the anode, the degree of supersaturation of Cu²⁺ ion around them slightly decreased. A similar phenomenon was also observed in CuSO₄-H₂SO₄ solution. The measured anodic limiting current density in Stage III agreed well with the calculated one from the correlation equation:

     

Transport of cadmium and iron through a carboxylic membrane based on a poly(vinyl chloride)/poly(methyl methacrylate‐co‐divinyl benzene) system

The transport of cadmium and iron through a poly(vinyl chloride)/poly(methyl methacrylate‐co‐divinyl benzene) carboxylic ion‐exchange membrane was investigated with a system containing HCl as the receiver solution and CdCl₂ or FeCl₃ as the feed solution. Transport of the ions through the membrane depended on the H⁺ concentration in the receiver solution and the metal concentration in the feed solution. The rate of transfer for cadmium was about 35% higher than that for iron under the same conditions (0.5 mol/dm³ of HCl, 0.1 mol/dm³ of CdCl₂ or FeCl₃, and 5 h of dialysis). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 705–707, 2005     

Kinetics of the anodic oxidation of benzyl alcohol in dichloromethane in the presence of redox mediator and phase transfer catalyst

The kinetics of the anodic oxidation of benzyl alcohol in the two-phase system involving both, the redox mediator, OCl^?/Cl^?, and a phase transfer catalyst were investigated. The reaction order of the anodic oxidation of chloride ion in the aqueous phase was unity. The charge-transfer parameters, α,k ₂ ⁰ and the exchange current density,i ₀, of the anodic oxidation of chloride ion in the aqueous phase were obtained. The theoretical model calculations correlated well with experimental data. The fractions of anodic surface covered by the aqueous phase were evaluated to be 0.89, 0.61, and 0.23 when the organic-to-aqueous volume ratios were 0.5, 1.0, and 2.0, respectively.     

Transport of Iron and Cobalt Complex Ions through Liquid Membrane Mediated by Methyltrioctylammonium Ion with the Aid of Redox Reaction

Abstract

A new type of carrier-mediated metal transport through liquid membrane is presented. The system involves redox reactions rather than acid-base reactions which have often been utilized in metal transport systems. Iron ion was selectively transported and concentrated through the membrane via a chloride complex by use of a lipophilic quaternary ammonium ion, methyltrioctylammonium (MTOA, Q⁺), as a carrier. The two aqueous solutions of different redox potentials were separated by a polymer-supported liquid membrane in which MTOA · chloride (Q⁺·CI^?) was dissolved as the carrier. Iron(III) ion in hydrochloric acid media formed a FeCl₄ ^? type complex which was readily extracted to the organic membrane phase as an ion-pair complex Q⁺·FeCl₄ ^?. On contact with a reducing agent on the other side of the membrane, iron(III) was reduced to iron(II) and liberated into aqueous solution; the chloride complexes of iron(II) are too hydrophilic to stay in the membrane phase. On the other hand, cobalt ion was transported via nitrilotriacetic acid (NTA) complex by MTOA carrier in a similar manner to the iron transport. The nature of the transport reactions was studied under various operational conditions (redox agents, carrier and ligand concentration, pH, coexisting metals, etc.). The extension of these transport reactions to a water-in-oil-in-water type emulsion system as well as to a photoassisted transport system was studied.     

Electrochemical oscillations of the system Hg,HSO−4, BrO−3 and phenol

The electrochemical oscillations of the system Hg, HSO^?₄, BrO^?₃ and phenol are described. These oscillations arise at the dme in the range of potentials from +0.06 V to +0.01 V against a potential of a 1.5 mol dm^?3 Hg/Hg₂SO₄ electrode in a solution of sulphuric acid, sodium bromate and phenol. The temporal change of the limiting current and that of surface-tension of mercury oscillate in an anodic, anodic—cathodic or cathodic range depending on the concentration of phenol and on the value of the dme potential. The probable mechanism is also discussed. This is based on the simultaneous electroreduction of bromate ions and the electro-oxidation of mercury as the surface-tension changes, produced by the film of Hg₂SO₄ and Hg₂Br₂ formation and by the adsorption of phenol and/or its oxidation products.     

Comparative study of copper behaviour in bicarbonate and phosphate aqueous solutions and effect of chloride ions

Copper oxidation in aqueous solutions of pH 8 showed some differences in the presence of bicarbonate and phosphate ions. The bicarbonate ions did not interfere with Cu₂O film formation but the Cu²⁺ ions were stabilized by the complexing action of CO _2– ³ anions. In phosphate solutions, copper dissolved in the range of potentials associated with the Cu(I) oxidation state and the Cu(II) compound on the surface resulted in an extensive passivation region. In both solutions, a higher ion concentration caused an increase in the anodic current, suggesting that the copper ions were stabilized by the complexing action of the electrolyte. The copper oxidation current in a bicarbonate solution was higher than that observed in a phosphate solution of the same concentration. The thickness of the Cu(II) film rather than the Cu(I) layer appears to be the important factor related to the stability of the passive layer on the copper surface. The shift in the breakdown potential toward more positive values indicates that both bicarbonate and phosphate ions inhibit localized corrosion due to the presence of chloride ions. Their protective effect depends on the concentration of each anion, although the concentration of chloride ions necessary for pitting is larger in phosphate solutions than in bicarbonate solutions. In both solutions, long-term immersion of copper under anodic polarization results in the precipitation of a protective coating.     

Fe2+ and Fe3+ adsorption on 2‐vinylpyridine–divinylbenzene copolymers and acrylonitrile–methyl methacrylate–divinylbenzene terpolymers

The adsorption of Fe²⁺ and Fe³⁺ ions on 2‐vinylpyridine–divinylbenzene copolymer and acrylonitrile–methyl methacrylate–divinylbenzene terpolymer was investigated. In general, the adsorption of Fe²⁺ and Fe³⁺ in both resins increased with the enhancement of hydrochloric acid and metal concentration. The metal adsorption on the terpolymer increased sharply with the addition of small portions of ethanol, whereas the adsorption on the copolymer practically was not affected by the presence of the alcohol. An increase in temperature produced a small increase in iron adsorption for both resins. Fourier transform infrared spectra showed that nitrile and ester groups of the terpolymer did not suffer hydrolysis during metal adsorption, even for the highest HCl concentration and the highest temperature applied. A mechanism of iron adsorption through the ion exchange of chloride anions by tetrahedral [FeCl₄]^2? or [FeCl₄]^? anions is proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3905–3912, 2003     

Role of Cl in breakdown of Cu-Ag alloys passivity in aqueous carbonate solutions

The electrochemical behaviour of two Cu-Ag alloys was studied in 0.1 M Na₂CO₃ solution containing different concentrations of Cl⁻ ions using linear polarization and current/time transients under the effect of different variables of Cl⁻ ions concentration, scan rate and applied anodic potentials. In Cl⁻ free solutions, the anodic voltammogram consists of two potential regions I and II. The potential region I exhibits three anodic peaks A₁, A₂ and A₃ that correspond to the formation of Cu₂O, Cu(OH)₂ and CuO, respectively. The potential region II exhibited four anodic peaks A₄, A₅, A₆ and A₇ due to the formation of AgO⁻, Ag₂O, Ag₂CO₃ and Ag₂O₂. In the presence of Cl⁻ ions, the anodic voltammograms depends considerable on the concentration of Cl⁻ ions. Increasing the amounts of Cl⁻ ions up the 0.02 M (alloy I) or 0.006 M (alloy II) the heights of all the anodic peaks were decreased and their peak potentials were shifted to less negative values. The existence of pitting was confirmed by SEM micrograph. The pitting potential E_pit was shifted towards more active potential values as the concentration of Cl⁻ ions in the solution was increased. When the scan rate is high, initiation of the pitting can be noticed only at more positive potentials, corresponding to a sufficiently short pit incubation time. The potentiostatic current/time transients show that the incubation time decreases with increasing the applied anodic potential and the Cl⁻ ion concentration and the pitting corrosion can be described in terms of instantaneous three-dimensional growth under diffusion control.     

The polarographic reduction wave of magnesium ion(II) in a molten LiClKCl eutectic mixture

The polarographic reduction wave of magnesium ion was confirmed in the purified lithium chloride-potassium chloride eutectic + magnesium chloride (7.20 × 10^?2 mol/l) melt kept at 450°C. The half wave potential was ?2.53V vs the PtPt²⁺ reference electrode, which was very close to the equilibrium potential ?2.580V of MgMg²⁺ already reported. The limiting current increased proportionally with the increase of magnesium chloride concentration. The relation between the current and the potential in the reduction wave of magnesium cation was expressed by the Heyrovsky — Ilkovic equation. The residual current raised in two steps due to the reduction of water introduced in the purified lithium chloride-potassium chloride-magnesium chloride melt by the addition of unpurified magnesium chloride and hydrated magnesium chloride.     

Supersaturation of oxygen in acidic solution in the vicinity of an oxygen-evolving platinum anode

The concentration of O₂ in 1 M H₂SO₄ solution in the vicinity of the O₂-evolving smooth Pt anode was measured as a function of anodic cdi_a using the galvanostatic potential—transient method.The solution near the O₂-evolving anode was supersaturated with O₂. When the anodic current was interrupted, supersaturated concentration C^* decreased at a rate proportional to C^*  C₀, where C₀ is the solubility of O₂ in the electrolyte at 1 atm. The rate constant of the decay of the supersaturation under the open circuit condition was measured to be 0.069 sec^?1 at 25°C.At i_a < 40 mA/cm² there was a linear relation between log(C^*  C₀) and log i_a. At i_a > 200 mA/cm², however, the supersaturation exhibited a limiting value of 9.0 × 10^?2 mol/l.     

Corrosion properties of electrodeposited cobalt in sulfate solutions containing chloride ions

The corrosion properties of electrodeposited pure cobalt were investigated in deaerated 0.5 M Na₂SO₄ solutions at pH 5, 7, 10 and 13 by using polarization techniques. The effect of chloride concentration (0.01 and 0.1 M NaCl) was also studied. The results showed that increasing pH shifted the anodic polarization curves to more negative potentials. At pH 5 and 7, cobalt exhibited active dissolution without any distinctive transition to passivation. However, at pH 10, the metal surface was partially passivated and anodic current increased sharply at approximately −0.2 V_SCE and the corroded surface revealed several well-defined pits. On the other hand, at pH 13, a clear passivation region was observed within the potential range of −0.5 to 0.6 V_SCE. With increasing chloride concentrations of 0, 0.01, and 0.1 M at pH 10, both the anodic current and the number of pits on the cobalt surface were gradually increased. X-ray photoelectron spectroscopic investigations showed that the cobalt surface was covered mostly with cobalt hydroxide after anodic polarization at pH 10 in 0.1 M NaCl.