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.     

Limiting current density and specific energy consumption in electrochemical cells with inert turbulence promoters

Electrochemical cells with inert turbulence promoters (ITP) and plain cells of the same geometry have been compared with respect to their productivity and specific energy consumption. As cathode reaction the diffusion controlled copper ion deposition process has been used, while the anode reactions were either metal dissolution or oxygen evolution on a stable anode. It has been found that in the ITP cells with an insoluble anode the contribution of ITP to the mass transfer enhancement is higher. The relationship between pumping energy and process energy has also been analysed as a function of hydrodynamic conditions for each cell separately. The application of ITP cells has significant advantages in electrowinning and plating processes, while they are not suitable, from an energy perspective, in galvanising processes, in which soluble anodes are used. In the case of electrowinning the minimum energy consumption is found to be in the region of 0.1–1 g dm⁻³ of reacting ions, depending on the kind of cell used.     

Sulphurous acid as anodic depolarizer in copper electrowinning Part II

The growing interest in the electrowinning of copper has lead to several modifications including anodic reactions proposed to reduce the high energy requirement. The addition of sulphurous acid to a copper sulphate electrolyte has been studied to avoid oxygen evolution at the anode which requires a potential in excess of 2V. In particular, the effect of different anode materials, concentration of sulphurous acid, current density, copper and sulphuric acid concentrations in the electrolyte have been investigated. Measurements of anode potential, cell voltage, current efficiency and energy consumption during the electrowinning of copper have been made using a diaphragm cell. It was found that graphite and lead coated with Ir–O₂ are better electrode materials than lead and DSA anodes and sulphurous acid can be used as anodic depolarizer.     

Computerized scaled cells to study the effect of additive ratios and concentrations on nodulation during copper electrorefining

Scaled copper electrorefining cells were designed, built and computerized to simulate as closely as possible industrial conditions at three Canadian copper refineries. The industrial dimensions of Falconbridge, Kidd Metallurgical Division, were considered while designing scaled cells. Anode width to cell width ratio, anode width to cathode width ratio, anodic surface to cathodic surface ratio, as well as electrolyte volume to cathodic surface ratio, which was about 60 L m^–2, were consistent with Kidd's industrial ratios. However, the cell design also allowed simulation of INCO's Copper Cliff Copper Refinery (CCCR) or Noranda's Canadian Copper Refinery (CCR). Electrorefining cells were 135.0 cm deep by 14.7 cm wide. Electrolyte flow rate was parallel to the electrodes. Electrolyte was circulated from the lower part of the electrorefining cells to the top where there was an overflow going to the electrowinning circuit. The equipment was computer controlled using Labview software. Experiments were conducted using this scaled electrorefining set-up to evaluate the effect of various ratios and concentrations of additives on nodulation during copper electrorefining under high current densities. Cathodic polarization curves, SEM micrographs, porosity analyses and copper grain analyses were used to characterize the cathodes produced.     

An investigation of sulphite ion oxidation as an alternative anodic reaction in fluidized bed electrowinning or other high rate electrolysis cells

The oxidation of sulphite ion to sulphate ion appears to offer attractions as an anodic reaction for cells operated at high current density such as those used in the fluidized bed electrodeposition of metals. In the present investigation several anodes were tried in a cell where the anolyte was aqueous ammonium sulphite solution and copper was electrowon from acidified aqueous cupric sulphate solution onto a fluidized cathode. The cell voltage was determined as a function of current density and a porous anode consisting of reticulated vitreous carbon with a lead coating was found to yield low cell voltages as did a DSA anode. The former anode did not evolve oxygen in the current density range up to 5500 A m^–2 whereas the latter showed the onset of oxygen evolution as the current density was raised. Some effects of anolyte flow rate and extent of conversion of sulphite to sulphate, as well as the distribution of potential drops in the cell were determined. Below 3500 Am^–2, sulphite ion oxidation using the reticulated vitreous carbon anode resulted in cell voltages below those of conventional commercial cells for copper electrowinning.     

Electrochemical and physical characterisation of lead-based anodes in comparison to Ti–(70%) IrO2/(30%) Ta2O5 dimensionally stable anodes for use in copper electrowinning

The suitability of various dimensionally stable anodes (DSAs^?) was investigated in comparison to the conventional lead alloy anodes in the electrowinning of copper. DSA^? plate and mesh specimens of composition Ti–(70%) IrO₂/(30%) Ta₂O₅ and lead–(6%) antimony were evaluated. The electrochemical behaviour of these anodes was studied by carrying out open circuit potential measurements, galvanostatic chronopotentiometry, cyclic voltammetry and chronoamperometry. Physical characterisation was done using a scanning electron microscope. It was observed that the DSA^? plate anode exhibited the highest corrosion resistance followed by the DSA^? mesh and lead anodes, respectively. The results also showed that during copper electrowinning using lead anodes, dissolution of the anode occurs while for both DSAs^? marginal loss of coating was observed. The lead anode had the highest anode potential followed by the DSA^? plate and mesh anodes, respectively. Overall, it was demonstrated that the DSA^? plate anode is the most suitable anode for copper electrowinning.     

The effect of anodic bubble formation on cathodic mass transfer under natural convection conditions

The enhancing effect of gas bubbles generated at an anode, on the ionic mass transport rate at the associated cathode is analysed by means of an experimental laboratory-scale copper electrowinning cell in which the bubbles were (a) permitted to rise freely in the entire cell and (b) restricted in their motion by a copper baffle-plate placed between the two electrodes. The improvement in mass transfer observed in the unrestricted case has been correlated via statistical regression analysis to the intensity of bubble motion and pertinent cell parameters.     

铜镉渣酸浸液旋流电积提铜对比分析

针对湿法炼锌副产物铜镉渣氧化酸浸液成分特点,采用旋流电积工艺回收其中的金属铜。研究了不同旋流电积工艺对电积过程中相关技术参数及杂质离子迁移规律的影响,并对不同电积工艺的优缺点进行了对比分析。结果表明：一段旋流电积可使溶液中铜离子浓度从44.14g/L降低到1.42g/L,而分段旋流电积可使溶液中终点铜离子浓度从1.42g/L继续降低至0.5g/L以下,溶液中铜离子在阴极上的电沉积率可从96.78%提高到99.20%,阴极电流效率可从90.52%提高到98.49%。当溶液中铜离子浓度降低到10g/L左右及以下时,杂质离子在阴极与铜发生共沉积现象逐渐明显,分段旋流电积得到的阴极铜产品光泽度及形貌质量较一段电积更好。与一段旋流电积工艺相比,分段旋流电积工艺具有电流效率高、能耗低、产品质量好等优点。     

从高铜氰溶液中电积铜和锌

用电积-部分酸化法从溶剂萃取法处理金矿贫液产出的高浓度铜氰溶液中电积铜和锌,研究了电积工艺条件如阴极电流密度、电积液中游离CN-浓度、铜浓度、电积液的温度、pH值和电积时间等对阴极电流效率和合金中铜含量的影响规律,确定了电积黄铜或粗铜的最佳工艺条件,获得了含Cu71%的黄铜(Cu-Zn合金)或含Cu98.6%的粗铜,每电积5～6h需将电积液部分酸化脱去游离CN-,电积和部分酸化交替进行可使平均阴极电流效率维持在63%以上.     

Hydrometallurgical process for the recycling of copper using anodic oxidation of cuprous ammine complexes and flow-through electrolysis

Flow-through electrolysis for copper electrowinning from cuprous ammine complex was studied in order to develop a hydrometallurgical copper recycling process using an ammoniacal chloride solution, focusing on the anodic oxidation of cuprous to cupric ammine complexes. The current efficiency of this anodic oxidation was 96% at a current density of 200 A m⁻² under a batch condition. In a flow-through electrolysis using a sub-liter cell and a carbon felt anode, the anodic current efficiency increased with the flow rate and was typically higher than 97%. This tendency was explained by the backward flow of the cupric ammine complex, which was formed on the anode, through the diaphragm. The anodic overpotential was lower than 0.3 V even at an apparent current density of 1500 A m⁻². A similar current efficiency and overpotential were also achieved in a liter scale cell, which indicates the scale flexibility of this electrolysis. The power consumption requirements for copper electrowinning in this cell were 460 and 770 kWh t⁻¹ at the current densities of 250 and 500 A m⁻², respectively, which were much lower than that of the conventional copper electrowinning despite the longer interpolar distance.     

Recovery of Nickel and Cobalt from Spent NiMH Batteries by Electrowinning

For nickel and cobalt recovery from spent NiMH batteries by electrowinning, the effect of different electrowinning parameters as boric acid concentration, temperature, current density, and pH were studied using different synthetic solutions. The optimized operational parameters were applied in an electrowinning test with a solution achieved by leaching the electrodes of NiMH batteries. The electrowinning tests were performed galvanostatically in a two‐compartment cell separated by an anionic membrane. A platinum/iridium‐coated titanium anode and a stainless‐steel cathode were used. A sodium sulfate solution served as anolyte. The results demonstrate the technical viability of nickel and cobalt recovery. The chemical composition of the obtained deposit presented high nickel and cobalt concentrations.     

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.     

铜电积用惰性阳极材料的研究现状

根据基体材料的不同,综述了国内外铜电积用惰性阳极材料的研究现状,重点阐述了铅及铅合金阳极、铅基涂层阳极、钛基涂层阳极等的制备、电化学性能及优缺点。     

Performance of catalytically activated anodes in the electrowinning of metals

The performance of titanium anodes coated with oxides of Ir–Co or Ir–Ta has been compared using long term polarization techniques under simulated electrowinning conditions. Possible reasons for anode failure are explained from SEM and XRD. Potentiodynamic studies in 2m H2SO4 indicate that approximately 450mV reduction in anode potential can be achieved with Ti/(Ir–Co) as against lead. This anode is also suitable in chloride contaminated sulfate electrolyte. The anode potential measurements in different electrowinning electrolytes indicate that a potential saving up to 370– 420mV can be achieved. It is interesting to note that mixed electrolyte containing sulfate and chloride behaves similarly to pure chloride electrolyte with respect to anode potential.     

锌电积过程中聚苯胺/碳化钨阳极的结构变化及失效行为

研究了锌电积过程中聚苯胺/碳化钨(PANI/WC)阳极的结构变化和失效行为,采用加速电解寿命测试和仪器分析考察了PANI/WC阳极在锌电积过程中表面形貌和结构的变化. 结果表明,整个电解过程中槽电压从3.71 V降到3.57 V后急剧升高到10 V,即经历活化、稳定、迅速升高阶段. 随锌电积进行,阳极表面出现脱落、开裂,迅速进入失效阶段,而微观结构无明显变化. PANI/WC阳极失效主要是由包覆WC的PANI大量剥蚀而使WC裸露和阳极开裂导致的.     

Methanol and formic acid oxidation in zinc electrowinning under process conditions

The possibility of using methanol or formic acid oxidation as the anode process in zinc electrowinning was examined. The activity for methanol and formic acid oxidation on Pt coated high surface area electrodes was investigated over 36 h, at a current density used in industry. The activity could be maintained at a constant potential level in a synthetic electrowinning electrolyte if the current was reversed for short periods. During the tests, the anode potential was, more than 1.2 V below the potential for the oxygen evolving lead anodes used in modern zinc electrowinning. The lowered anode potential would lead to a significant energy reduction. However, tests in industrial electrolyte resulted in a very low activity for both methanol and formic acid oxidation. The low activity was shown to be caused mainly by chloride impurities. A reduction of the chloride content below 10⁻⁵ M is needed in order to obtain sufficient activity for methanol oxidation on Pt for use in zinc electrowinning. Pt and PtRu electrodes were compared regarding their activity for methanol oxidation and the latter was shown to be more affected by chloride impurities. However, at a potential of 0.7 V vs NHE, with a chloride content of 10⁻⁴ M, formic acid oxidation on PtRu gives the highest current density.     

Preparation of high-purity antimony by electrodeposition

Detailed studies were carried out on the electrowinning of antimony from SbCl₃–HCl–H₂SO₄ and SbCl₃–HCl baths using a graphite anode and a tantalum cathode, the anode being enclosed in a cylindrical glass compartment provided with a sintered disc. Disintegration of the graphite anode increased with increase in anode current density and duration of electrolysis. Analysis of gas evolved at the anode indicated that the presence of sulphuric acid increased the production of CO₂. The anodic disintegration was reduced to a negligibly low value by circulation of 6m HCl through the anode compartment. Optimum conditions were determined for electrowinning of antimony from a SbCl₃–HCl bath. The tantalum content in the metal was 0.1–0.2 p.p.m.     

High speed zinc electrowinning system using a hydrogen anode and a rotating aluminium disc cathode

The performance of a novel high speed zinc electrowinning system using a hydrogen anode and an aluminium rotating disc cathode (1 m diam.) was investigated under various experimental conditions. This new type of zinc electrowinning system was continuously operated at a current density of 70 A dm^–2, which is twelve times higher than that usually employed. Current efficiency is 90% at 50 A dm^–2 in an electrolyte containing 60 g dm^–3 Zn + 160 g dm^–3 H₂SO₄, the zinc purity being at least 99.999%. The energy usage of the system is 1650 kWh per tonne of zinc, 380 m³ of H₂ gas being required.     

Bio-hydrometallurgical processing of low grade chalcopyrite for the recovery of copper metal

A process flowsheet was developed to recover copper metal from the lean sulfide ore of copper available at Malanjkhand, Hindustan Copper Limited (HCL), India. Copper pregnant leach solution (PLS) obtained from bio-heap leaching of chalcopyrite containing 0.3% copper was purified through solvent extraction (SX) and the copper recovered by electrowinning (EW). The copper-free raffinate obtained from SX stripping unit was returned back to the bioleaching circuit. The purity of the electrolytic copper produced at pilot scale was found to be 99.96%. During electrowinning, the effect of flow rate of electrolyte on current efficiency and energy consumption was also studied.     

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.