锌电积用节能阳极的研究现状

综述了新型铅合金阳极、钛基尺寸稳定阳极(DSA)、铝基阳极、复合阳极等锌电积用节能阳极材料的研究现状,展望了其发展趋势。     

Gas-diffusion electrodes catalysed with tungsten carbide as anodes for nickel electrowinning

The characteristics of gas-diffusion electrodes catalysed with tungsten carbide have been investigated under the conditions of nickel electrowinning. It is shown that their use as anodes in this process leads to a considerable decrease of the energy consumption and the nickel produced is free of heavy metal impurities.     

Electrochemical noise studies of the corrosion behaviour of lead anodes during zinc electrowinning maintenance

Following anodic polarisation of lead anodes with different silver contents (0.5-0.7%) during Zn electrowinning, the discharge and corrosion of lead anode during the decay period at open circuit potential in sulphuric acid bath have been studied by electrochemical noise analysis (ENA) method. Potential and current decay behaviour over 16 h shows 4 and 2 main characteristic regions, respectively. The wavelet transform has been employed to analyse the ENA data. The results of wavelets have demonstrated that energy distribution plot “EDP” was a powerful tool to provide useful information about the dominant process for different discharge and corrosion stages and mechanisms. The discharge is predominant than corrosion for all anodes for the regions I, II and III, and ENA feature of events changes from large timescale to low timescale, diffusion control or exfoliation to metastable pitting and pit growth, respectively. Region IV, only observed for 0.6% and 0.7%Ag, corresponds to general and metastable pitting corrosion under diffusion control. It has been found that anode containing lower silver content have more corrosion products even after 16 h of decay (discharge and attack dominated by pitting corrosion type with the highest corrosion due to the longest period of pitting during the 16 h).     

锌电积用PbO_2复合惰性阳极材料制备及性能研究

以3Cr13不锈钢为基体,在由PbO45g/L和NaOH160g/L组成的镀液中加入20g/LCeO2(平均粒径30nm)或/和20g/LB4C(平均粒径6μm),采用阳极电沉积的方法制备了α-PbO2–B4C、α-PbO2–CeO2、α-PbO2–CeO2–B4C等3种复合惰性阳极材料,观察了其表面微观组织特征,测试了其电沉积时的阳极极化曲线以及在ZnSO4–H2SO4溶液中的循环伏安曲线和塔菲尔曲线,并与纯α-PbO2电极进行了对比。结果表明,CeO2、B4C或其两者与α-PbO2的共沉积改变了阳极沉积电位和α-PbO2的电结晶形貌,使晶粒尺寸减小,并导致α-PbO2在ZnSO4–H2SO4溶液中的阴极还原峰电位正移,及有助于提高α-PbO2的耐蚀性。α-PbO2–CeO2和α-PbO2–CeO2–B4C复合惰性阳极材料分别在低电位区和高电位区具有良好的析氧电催化活性。     

Utilization of gas-diffusion electrodes catalysed with tungsten carbide as anodes for zinc electrowinning

Gas-diffusion electrodes with varying amounts of tungsten carbide catalyst are studied, and their feasibility as suitable anodes for zinc electrowinning is demonstrated. The energy savings achievable with the use of such anodes are evaluated.     

Corrosion rates of lead based anodes for zinc electrowinning at high current densities

The corrosion rates of anodes made from various lead/silver alloys have been determined during electrolysis in sulphuric acid solution, pure and containing additives, using current densities in the range 2500 to 10 000 A m^–2. An increase in acid concentration, and in some cases temperature, caused an increase in the corrosion rate. In the absence of manganese in the bath, the corrosion rate was effectively independent of current density in the range studied, whereas in the presence of manganese, the corrosion rate decreased with decreasing current density. The corrosion rates of various calcium, tin and thallium alloys of lead were also determined. The presence of chloride ions in the electrolyte increases the corrosion rate, whereas potassium ions and strontium carbonate have a negligible effect. Pre-treating silver/lead anodes with a solution of acidic potassium fluoride at 500 A m^–2 prior to testing markedly decreased the corrosion rate in the presence of manganese, but increased the corrosion rate with manganese absent. The effect of zinc on the corrosion rate in synthetic electrolyte solutions, with and without manganese present, has also been determined for silver/lead alloys at 10 000 A m^–2. At zinc levels over 1 M, the corrosion rate increased with and without added manganese. As the work has been undertaken in an attempt to improve the electrowinning of zinc, an electrolyte based on acidified industrial solution has also been tested. The rates observed were similar to those obtained for synthetic zinc-containing solutions.     

Performance of a catalytically activated ceramic hot gas filter for catalytic tar removal from biomass gasification gas

Silicon carbide-based filter elements were catalytically activated to provide filter elements for catalytic tar removal from biomass-derived syngas. The filter element support was coated with CeO₂, CaO–Al₂O₃ and MgO with a specific surface of 7.4, 15.9 and 21.9 m²/g synthesized by exo-templating with activated carbon. Doping of a MgO coated filter element with 60 wt% NiO has led to an increase of the specific surface from 0.15 to 0.21 m²/g, whereas in case of a MgO–Al₂O₃ coated filter element a decrease from 1.18 to 0.91 m²/g was found. An increase of the NiO loading from 6 to 60 wt% on a MgO coated filter element resulted in an increase of the naphthalene conversion from 91 to 100% at 800 °C and a face velocity of 2.5 cm/s at a naphthalene concentration of 5 g/Nm³ in model biomass gasification gas. In case of a MgO–Al₂O₃ coated filter element with 60 wt% NiO in addition to complete naphthalene conversion in the absence of H₂S, a higher conversion of 66% was found in the presence of 100 ppmv H₂S compared to 49% of the MgO–NiO coated filter element. After scaling up of the catalytic activation procedure to a 1520 mm long filter candle, which shows an acceptable differential pressure of 54.9 mbar, 58 and 97% naphthalene conversion was achieved in the presence and absence of H₂S, respectively. The calculated WHSV value of 209.6 Nm³ h⁻¹ kg⁻¹ indicates the technical feasibility of a further increase of the catalytic performance by an increase of the NiO loading.     

Activated basket anodes from nickel powder Part III: Electrochemical behaviour of sulphur activated anodes

The characteristics of anodic dissolution of nickel electroplating anodes produced from compacted nickel powder by a liquid phase sintering process have been determined. Sulphur incorporated in the sintered product was found to increase the electrodissolution activity and inhibit passivation. The activity of the anodes increased with increase in sulphur content and approached that of commerical sulphur-depolarized anodes produced by electroforming. Sintering temperature and rate of cooling during preparation of the anodes had little influence on the dissolution activity and resistance to passivation. No direct relationship was found between activity and the generation of anode fines. The rate of anodic dissolution of sulphur-containing anodes has been found to be comparable to that for synthetic heazlewoodite (Ni₃S₂ electrodes). The influence of the presence of sulphur on the kinetics of nickel dissolution is interpreted in terms of the development on the metal surface of Ni₃S₂ from which nickel is extracted to leave a sulphide of lower nickel content; the latter sulphide then reacts with underlying elemental nickel to reform Ni₃S₂.     

Influence of Co2+ and Mn2+ ions on the kinetics of lead anodes for zinc electrowinning

The influence of Co²⁺ and Mn²⁺ ions on the kinetics of lead and lead–silver alloy anodes is analysed using impedance spectroscopy and steady-state polarisation curves. With lead–silver anodes, increasing the Mn²⁺ concentration catalyses the oxygen evolution current by stimulating the reaction rate. Impedance data reveal a transient inhibition of the reaction, ascribed to the adsorption of a silver-salt containing manganese. The addition of Co²⁺ catalyses oxygen evolution, mainly on the pure lead anode. For lead–silver anodes, the small catalytic effect of Co²⁺ ions implies an increase in the Tafel coefficient for the oxygen reaction. The transient inhibiting process suggests the formation of a cobalt-containing adsorbate on the pure lead anode.     

Structure of the catalytically active compound in caprolactam polyamidation activated by the phosphoric acid-polyethylene glycol system

Conclusions Direct experimental proofs have been given for the formation of bis-(polyethylene glycol) phosphate — a catalytically active compound in the cationic polyamidation of caprolactam which is activated by the phosphoric acid-polyethylene glycol system.Translated from Khimicheskie Volokna, No. 4, pp. 14–16, July–August, 1988.     

A preliminary investigation of some anodes for use in fluidized-bed electrodeposition of metals

The development of fluidized-bed electrowinning for copper and other metals appears to be impeded by the high electrical energy consumption associated with the anodes used in such electrowinning. This paper describes preliminary work aimed at seeking anodes which consume less energy and are suitable for scale-up. Using laboratory-scale cells in which copper was electrowon from strong (25 g dm^–3 Cu), acidified (100 g dm^–3 H₂SO₄) sulphate solutions on to fluidized cathodes, the following anodes were tested: fluidized-bed anodes of catalyst-coated titanium particles, packed-bed anodes of lead shot and graphite, single and double layers of catalyst-coated titanium mesh, and cloth-covered anodes placed directly in the fluidized cathode. In addition, the possibility of using alternative anode reactions, namely oxidation of sulphur dioxide, ferrous ions or cuprous ions, as well as fluidized-bed electrowinning from a cuprous-ion catholyte, were examined. Except for the fluidized anode and the lead packed-bed anode, all the above systems yielded energy savings. The investigation was not sufficiently detailed to define which of the above was best, although, at 2.0 kW h kg^–1 Cu, electrowinning from cuprous solutions with cuprous oxidation on a graphite packed-bed anode offered an energy consumption better than that of the conventional electrowinning plants.     

Formation of corrosion-resistant layers by electrodeposition of refractory metals or by alloy electrowinning in molten fluorides

The electrolytic treatment of less resistant metals such as iron, copper and nickel with tantalum or niobium has been carried out in K₂TaF₇-LiF-NaF or K₂NbF₇-LiF-NaF solutions in the 550 to 1050°C temperature range. Two kinds of experiments have been used.

1. At lower temperatures, electroplating with pure tantalum and niobium on inert cathodes was performed. The electrodeposition mechanism of each metal was studied and coherent electroplates were prepared which were tested in electrocatalytic applications.
2. At higher temperatures (850–1050°C), using nickel cathodes, intermetallic compounds were obtained at more positive potentials than that for pure electrodeposition (Ta₂Ni, TaNi, TaNi₂, TaNi₃, NbNi, NbNi₃). The electrowinning of stable TaNi₃ and NbNi₃ layers was carried out by the metalliding process which makes these materials resistant to corrosion in various media. Further, a study of the kinetics of growth of the diffusion layer allowed a diffusion parameter to be determined which was in agreement with other results obtained by conventional methods.

     

Development of novel catalytically active polymer-metal-nanocomposites based on activated foams and textile fibers

In this paper, we report the intermatrix synthesis of Ag nanoparticles in different polymeric matrices such as polyurethane foams and polyacrylonitrile or polyamide fibers. To apply this technique, the polymer must bear functional groups able to bind and retain the nanoparticle ion precursors while ions should diffuse through the matrix. Taking into account the nature of some of the chosen matrices, it was essential to try to activate the support material to obtain an acceptable value of ion exchange capacity. To evaluate the catalytic activity of the developed nanocomposites, a model catalytic reaction was carried out in batch experiments: the reduction of p-nitrophenol by sodium borohydride.     

New oxygen evolution anodes for metal electrowinning: MnO<Subscript>2</Subscript> composite electrodes

Several modifications of manganese dioxide (MnO₂) were investigated for use in composite electrode materials for oxygen evolution, the target application being anodes for the industrial electrowinning of metals. It is demonstrated that the performance of this material depends strongly on the modifications of MnO₂. All modifications investigated were found to be more active than the usual anode of lead alloyed with silver (PbAg) used in zinc electrowinning. A composite sample containing chemical manganese dioxide (CMD) was found to give an oxygen evolution overpotential 0.25 V lower than the standard PbAg anode material. In the second part of the article, we investigate the effect of varying several parameters of the composite electrode assembly, including the size of the catalyst particles and percentage of the catalyst material used. A model is proposed where the performance of the material is proportional to the total length of the boundaries between the lead matrix material and the MnO₂ catalyst particles. Physicochemical processes contributing to the observed data are discussed.     

Performance of non-porous graphite and titanium-based anodes in microbial fuel cells

Four non-porous materials were compared for their suitability as bio-anode in microbial fuel cells (MFCs). These materials were flat graphite, roughened graphite, Pt-coated titanium, and uncoated titanium. The materials were placed in four identical MFCs, of which the anode compartments were hydraulically connected in series, as well as the cathode compartments. The MFCs were operated with four resistors. The anode kinetics at these electrode materials were studied by means of dc-voltammetry and electrochemical impedance spectroscopy (EIS). Both techniques were compared and showed that the bio-anode performance decreased in the order roughened graphite > Pt-coated titanium > flat graphite > uncoated titanium. Uncoated titanium was unsuitable as anode material. For the other three materials, specific surface area was not the single variable explaining the differences in current density for the different materials. All polarization curves showed a clear limiting current. This limit could not be attributed to mass transfer of the substrate and reflected the maximum biomass activity. The current density of the non-porous bio-anodes, except for the uncoated titanium anode, was comparable to the reported current densities of porous materials when normalized to the projected surface area. The high current densities that were recorded by dc-voltammetry, however, could not be maintained in a stable way for a longer period. This shows that polarization curves of MFCs should be evaluated critically.     

Graphitized boron-doped carbon foams: Performance as anodes in lithium-ion batteries

The electrochemical performance as potential anodes in lithium-ion batteries of several boron-doped and non-doped graphitic foams with different degree of structural order was investigated by galvanostatic cycling. The boron-doped foams were prepared by the co-pyrolysis of a coal and two boron sources (boron oxide and a borane–pyridine complex), followed by heat treatment in the 2400–2800 °C temperature interval. The extent of the graphitization process of the carbon foams depends on boron concentration and source. Because of the catalytic effect of boron, lightweight graphite-like foams were prepared. Boron in the foams was found to be present as carbide (B₄C), in substitutional positions in the carbon lattice (B–C), bonded to nitrogen (B–N) and forming clusters. Larger reversible lithium storage capacities with values up to ∼310 mA h g⁻¹ were achieved by using the boron oxide-based carbon foams. Moreover, since the electrochemical anodic performance of these boron-doped foams with different degree of structural order is similar, the beneficial effect of the presence of the B–C boron phase was inferred. However, the bonding of boron with nitrogen in the pyridine borane-based has a negative effect on lithium intercalation.     

Electrochemical behaviour of metals in micellar medium and in water—tributylphosphate emulsions. Application to electrowinning of metals in waste water—I. Micellar medium

The inhibition of copper(II), nickel(II), cadmium(II), lead(II), cobalt(II), zinc(II) reduction by a non-ionic surfactant is studied in NaClO₄ as a non-complexing medium and in KSCN as a complexing medium. The magnitude of inhibition of these reactions appears very different according to pH in the perchlorate medium. In the thiocyanate medium, it seems that the stability of the complex has a very significant role in the inhibition process.     

Comparison of the behaviour of glassy carbon and some metals for use as nonconsumable anodes in alumina-cryolite melts

Current interest exists in development of nonconsumable anodes for the Hall-Heroult process of aluminium production and also in situ analytical probes for determination of Al₂O₃ content in the cryolite melts used in this process. A comparison of the behaviour of glassy carbon and metals such as tungsten, tungsten carbide, nickel and stainless steel (SS-316) used as anodes in alumina-cryolite melts is investigated by means of electrochemical transient techniques (cyclic voltammetry and chronoamperometry) and Tafel anodic polarization experiments. The results show that only glassy carbon could be used as a successful sensor electrode for an in situ determination of Al₂0₃ in alumina-cryolite melts and that the metals investigated are unresistant to anodic attack in such melts. Consequently, the metals investigated cannot be used as sensor electrodes for in situ electro-analytical determination of alumina in alumina-cryolite melts, nor as anodes in the production of aluminium by the Hall-Heroult process.     

Energy efficiency in metal electrowinning

The components of the electrical energy requirements for metal electrowinning are reviewed. Various energy saving measures are assessed, including the use of dimensionally stable anodes (DSA) having low oxygen overvoltages. The current-density distribution on parallel electrodes is computed as a function of the electrochemical parameters of the electrode reactions, the ionic resistivity of the electrolyte, and the internal electronic resistivity of the electrodes. The validity of the mathematical model has been experimentally verified using DSA anodes in a copper electrowinning circuit. The energy savings achievable using dimensionally stable anodes are shown to be affected greatly by the internal resistance of the anode substrate. The effects of variation of the kinetic parameters are secondary.