Electrowinning Process Research Articles

Microstructural modification of Ni electrodeposit in an acidic NiCl2 solution

Electrowinning is an important process to extract Ni from aqueous solutions. In this work, the characteristics of electro-deposited Ni were modified by employing magnetic agitation and flowing bubbles in an acidic chloride solution. The nucleation and growth of Ni grains were analyzed in the electro-crystallization. Phase compositions and morphologies of the modified deposits were characterized. As well, the positive effects of magnetic agitation and flowing bubbles on the electrowinning process were discussed. Mass transportation of Ni 2+ ions was efficiently accelerated by magnetic agitation and upwards flowing bubbles. The preferential growth of Ni deposit was also facilitated along the (111) orientation. The nucleation and growth of Ni crystals proceeded in the instantaneous nucleation mode and the lateral growth mode, respectively. The introduction of magnetic agitation and upwards flowing bubbles can promote the detachment of hydrogen gas and be available for the enhancement of current efficiency. • Microstructure of Ni deposit was modified by magnetic agitation and flowing bubbles. • Mass transfer of Ni 2+ ions during electrowinning was accelerated. • Nucleation mode of Ni was transformed from instantaneous to progressive. • Preferential growth of (111) plane orientationally was promoted. • Compact deposit consisting of bar grains was formed in the lateral growth mode.

A BP Neural Network Based on GA for Optimizing Energy Consumption of Copper Electrowinning

In this paper, achieving minimum energy consumption in the copper electrowinning process is taken as the research objective. In the traditional production process, sulfate ion concentration, copper ion concentration, and current density are carried out according to the empirical value, which cannot ensure the energy consumption reaching the optimal level. Therefore, this paper proposes a BP neural network model to optimize energy consumption according to the relationship between current density, sulfate ion concentration, copper ion concentration, electrolytic tank voltage, and current efficiency, and the established BP neural network model is trained by using real data from the enterprise. The simulation results show that there is a definite error between the predicted electrolytic tank voltage and current efficiency and corresponding to predict electrolytic tank voltage and current efficiency measured at the production site. The BP neural network improved by GA is proposed to further improve the prediction accuracy of the BP neural network. Simulation results indicate that the prediction error of electrolytic tank voltage and current efficiency is greatly reduced that meets the accuracy requirements, and then the minimum energy consumption can be calculated. On the premise of guaranteeing the quality of copper electrowinning, the current density, sulfate ion concentration, and copper ion concentration corresponding to the minimum energy consumption accurately predicted by this method can be respectively adjusted in real time, which realizes the optimization of energy consumption in the process of copper electrowinning under the background of low carbon and environmental protection.

Copper and Antimony Recovery from Electronic Waste by Hydrometallurgical and Electrochemical Techniques.

A strategy for the efficient recovery of highly pure copper and antimony metals from electronic waste (e-waste) was implemented by the combination of hydrometallurgical and electrochemical processes. The focus is on copper recovery as the main component in the leached solution, whereas the antimony recovery process was established as a purification step in order to achieve a highly pure copper deposit. The strategy includes mechanical methods to reduce the size of the wasted printed circuit boards to enhance the efficiency of antimony and copper lixiviation via ferric chloride in acidic media (0.5 M HCl) followed by an electrowinning process. In order to establish the best parameters for copper electrowinning, the leached solution was characterized by cyclic voltammetry and cathodic polarization. Then, an electrochemical reactor with a rotating cylinder electrode was used to evaluate the copper concentration decay, the cathodic current efficiency, the specific energy consumption, and mass-transfer coefficient. Furthermore, antimony was recovered via precipitation by a pH modification in accordance with the Pourbaix diagram. Under this methodology, two valuable products from the e-waste were recovered: a 96 wt % pure copper deposit and 81 wt % pure antimony precipitate. The strategy for recovery of other metal ions, such as lead, present in the e-waste at high concentrations will be reported in further works.

Lowering the Energy Consumption of Zinc Electrowinning By Electrocatalysis of Oxygen Evolution Reaction Using Manganese Oxides

Zinc has a wide range of commercial applications including but not limited to galvanizing iron and steel and production of various metal alloys such as brass and bronze. In hydrometallurgical processes, zinc electrowinning from sulfate-based electrolytes is the last step of zinc extraction in which high purity metallic zinc is electrodeposited from a highly acidic solution on an aluminum cathode. The electrowinning stage is very energy-intensive and responsible for approximately 80% of the power requirement of a zinc refinery (1). Thus, improving the energy efficiency and lowering the operating costs of zinc electrowinning are of primary significance. The oxygen evolution reaction (OER) overpotential on conventional lead-silver (Pb-Ag) anodes contributes to nearly 25% of the total electrowinning cell potential (2). Therefore, the high anodic OER overpotential places a heavy financial burden on zinc refining plants.The present study aims to evaluate novel anodic electrocatalysts incorporating MnO x in order to lower the anodic OER overpotential of the zinc electrowinning process. Anodically electrodeposited MnO x catalysts on Pb-Ag electrodes were prepared using galvanostatic and potentiodynamic polarizations. The OER catalytic activity and stability of MnOx electrodeposited Pb-Ag electrodes were evaluated in 160 g/L sulphuric acid solution with 3 g/L of manganese (II) and in the absence and presence of 0.3 g/L of chloride ion at 35°C, using a standard three-electrode setup. The electrolyte composition and operating conditions were selected such that to be directly applicable to the industrial zinc electrowinning process. The OER activity of the MnOx electrodeposited electrodes was investigated through potentiodynamic polarization and 72-hour galvanostatic electrolysis at 50 mA/cm2 superficial current density. Finally, the activity of MnOx electrodeposited Pb-Ag electrodes was explored in a full zinc electrowinning cell through 24-hour galvanostatic electrolysis at 50 mA/cm2 superficial current density.The OER potential variations of the bare Pb-Ag and MnO x electrodeposited Pb-Ag anodes during the 72-hour galvanostatic polarization are shown in Fig. 1. In the absence and presence of chloride ions, the three MnO x electrodeposited Pb-Ag electrodes are observed to reduce the anodic potential by maximum of 150 mV and 90 mV, respectively. Investigation of these novel electrodes in the full-cell zinc electrowinning operation corroborated the half-cell experiments, revealing a maximum of 80 mV reduction in cell potential at 50 mA/cm2 superficial current density and in the presence of 0.3 g/L of chloride ion. Thus, this work demonstrates that MnO x electrodeposited Pb-Ag anodes have great capacity to lower the power consumption of the zinc electrowinning process.Fig. 1. OER activity and stability comparison under galvanostatic polarization for four anodes: bare Pb-Ag (baseline) and three MnOx electrodeposited Pb-Ag anodes prepared via linear scan voltammetry (LSV), constant current density (CCD), and cyclic voltammetry (CV). Superficial current density: 50 mA/cm2. Electrolyte:160 g/L H2SO4 with 3 g/L Mn2+ and 0.3 g/L Cl- at 35°C.

Effect of aluminium on polarisation parameters and deposit characteristics in typical nickel sulfate electrolyte for electrowinning applications

Impurities present in the sulfate electrolyte during nickel electrodeposition influence the electrowinning process and morphology of deposited nickel metal in various ways. The presence of aluminium can be either detrimental or beneficial, depending on its concentration. Effects of the presence of aluminium in the electrolyte during nickel electrowinning were investigated by evaluation of the relationship between nucleation and plating overpotentials, nickel morphology, deposit contamination, internal stress development, and buffer characteristics of the electrolyte. Results showed that aluminium present at concentrations of lower than 1250 mg/L was unfavourable for the electrowinning process and highly strained nickel deposits of poor morphology were produced; at higher concentrations, the presence of aluminium was advantageous for the morphology and internal stress, and correlated with increased buffer characteristics of the electrolyte.

Improve the energy efficiency: Effects of additives on longtime zinc electrowinning

In this paper, the theoretical energy consumption required in the zinc electrowinning process was analyzed. The theoretical energy consumption is only a half of the energy consumption in industrial production. To save energy of the production process, we studied five kinds of additives with the industrial electrolyte in the longtime zinc electrowinning process. The results indicated that the presence of non-ionic compound (thiourea) or anionic surfactant (sodium dodecyl sulfonate or sodium dodecylbenzene sulfonate) adversely affected the energy consumption and current efficiency. However, an improvement in energy consumption was observed with the addition of cetyltrimethylammonium bromide. Our results should be helpful for the production of zinc electrowinning.

Process parameters affecting the efficiency of indium electrowinning results from sulfate baths

Since indiumisconsidereda strategic material, a study for developing and optimizing a recovery process by electrowinning has been performed. The possibility of using electrolytic baths based on sulfates instead of chlorides has also been evaluated. Nowadays, chlorides are widely used because they generally present greater current efficiencies;however, the dangers of chlorine gasrequireexpensive-sealed systems to avoid human health and environmental issues. The use of sulfatesdoes not present the same problems;therefore the electrowinning process optimization can represent a definite indium recovery improvement. For this purpose, the effects of electrolyte composition, temperature, current density and pH on the quality of the deposit, specific energy consumption (SEC) and current efficiency (CE) have been assessed. The sulfate electrolytic solutionhas been then appropriately modified with organic additives, mineral salts and complexing agents to optimize the indium recovery by electrowinning. ACE of about80% and SEC equal to 2.7 kWh/kg have been obtained, operating with a pH in the range 2.2–2.3 at 40 °C and using 25 A/m2 current density with an electrolytic solution containing 60 g/l of In3+, 30 g/l of Na2SO4, 20 g/l of Al2(SO4)3 and 20 g/l of H3BO3.

Extracting of copper from simulated leaching solution of copper-cadmium residues by cyclone electrowinning technology

Cyclone electrowinning technology has obvious technical advantages in treating polymetallic mixed solutions, and it has been widely used to separate and purify cu, au, ag, Ni, co and other metals. Simulated leaching solution of copper‑cadmium residues was prepared as electrolyte, the extraction of copper by three-stage cyclone electrowinning in sequence were investigated in this study, and the optimum conditions of each stage were determined. In the first stage, the purity of cathode copper can reach over 99.996%, and the current efficiency can reach to 98.75% when the current density was 300A/m2 and the electrolyte circulation flow was 400 L/h. in the second stage, the purity of cathode copper can achieve the standard of the cathode copper(>99.99%)，and the current efficiency can reach to 98.93% when the conditions are determined as the current density of 400A/m2 and the circulation flow of 700 L/h. in the third stage, the cathode copper with over 99.9% purity can be obtained and the current efficiency can reach to 93.37% when the current density was 200A/m2 and the circulation flow was 500 L/h. the concentration of copper ions in the electrolyte can be reduced to below 0.1 g/L and the removal efficiency of copper can reach over 99% in the study. Compared to the traditional electrowinning process，the cyclone electrowinning shows the advantages of high metals selectivity，high current efficiency, high purity of electrolytic products and low environmental pollution, which has good economic and social environmental benefits

Indium electrowinning study from sulfate aqueous solution using different metal cathodes

Electrowinning represents a promising methodology for recovery of strategical, scarce metals. In this study, an indium electrowinning process using a sulfate electrolyte on stainless steel, nickel, titanium, aluminum and copper (SS, Ni, Ti, Al and Cu) cathodes was investigated. Firstly, cyclic voltammetry carried out at 15 mV/s scanning rate and 25 °C temperature evaluated the suitability of electrolyte and the surface reactivity on different metal cathodes. Subsequently, indium was deposited using a current density of 25 A/m2 for 22 h at 40 °C and pH 2.3. After electrowinning process, analysis of specific energy consumption (SEC), current efficiency (CE) morphological (SEM/EDX), and crystallographic (XRD) tests on obtained deposits were performed. Cyclic voltammetry results revealed that the chemical reagents of solution stabilize the indium reduction reaction, while Ni cathode showed the highest current intensity for reduction reaction followed by SS, Ti, Cu, and Al. With a significant CE and SEC performance, Ni and SS cathodes reached around 93 % CE and 1.67 kW h/kg SEC, respectively. Referring to Ti cathode, other optimization tests should be performed to enhance obtained results. After deposition process, different surface morphologies and different crystallinity degree can be observed for each deposit, being common the presence of surface defects. The findings of this investigation allowed to determine the most suitable cathode for indium electrowinning from sulfate electrolyte.

A method of simultaneously electrodepositing α/β-PbO2 coating materials in methanesulfonic acid and its application in zinc electrowinning

In the present work, nucleation mechanism, preparation conditions, performance testing and application simulation of lead dioxide coating materials prepared by electrodeposition from methanesulfonic acid were studied to improve anodic process in zinc electrowinning process. Phase growth and transformation of lead dioxide were analyzed by anodic polarization curves, X-ray powder diffraction, scanning electron microscopy SEM, electrochemical impedance spectroscopy (EIS) and Tafel curves. The selection of temperature ranges was found to cause a quantitative difference in the formation of α/β-PbO2 phases, as it made interval effects on the overpotential that was the primary control condition to affect transfer process, while without changing the reaction mechanism apparently. In this way, the precise conditions of obtaining α- or β-PbO2 phases by varying temperatures was confirmed and samples were selected to be tested in long-period galvanostatic electrolysis, electrode (deposition time-α&β: 2 h&2 h) showed the best physicochemical properties and could effectively extend the lifetime (70.4 h) compared with the traditional lead dioxide electrodes (32.3 h) in zinc electrowinning.

Approach for the determination of maintenance strategies based on an empirical case study

The global demand for raw materials is increasing consistently in the modern world such that a resource efficient handling becomes more and more important in today’s manufacturing processes. A very challenging task is to optimize maintenance strategies for manufacturing processes to increase the efficiency of the process itself as well as the efficient and sustainable use of degrading tools in such manufacturing processes. This study provides an approach to derive different maintenance strategies based on an empirical failure study. Therefore, the failure behavior of a tool was analyzed considering different process conditions in a case study. The failure behavior was modeled using the three-parametric Weibull distribution. The determination of confidence intervals of the parameters of the Weibull distribution as well as the confidence band of the cumulative distribution function enables the determination of maintenance strategies with regard to a certain failure probability. The industrial application example of this case study is the electrowinning process of non-ferrous metals.

Power scheduling optimization under single-valued neutrosophic uncertainty

Optimization problems with improper expression of constraints exist widely in practical engineering. In order to achieve a reasonable degree of constraints satisfaction, this paper investigates a single-valued neutrosophic optimization method to deal with system uncertainty. Firstly, an equivalent model based on single-valued neutrosophic entropy is proposed to transform the original problem into a crisp multi-objective optimization problem. The Pareto-front of the optimization problem is then obtained by a multi-objective state transition algorithm. Finally, the best solution is determined by a multi-criteria decision making method. A practical example of a zinc electrowinning process is used to illustrate the effectiveness and advantage of the developed new optimization approach, which provides a more cost-effective solution to decrease the electricity utility charge and satisfy the daily output production requirements.

Optimizing zinc electrowinning processes with current switching via Deep Deterministic Policy Gradient learning

This paper proposes a model-free Deep Deterministic Policy Gradient (DDPG) learning controller for zinc electrowinning processes (ZEP) to save energy consumption during the current switching periods. To overcome the problems such as inaccurate modeling and various time delays, the proposed DDPG controller utilizes various control periods and parameters for different working conditions. Strategies such as action boundary setting, reward function definition, state normalization are applied to ensure its learning performance. Simulations and experiments show that the DDPG learning controller can significantly decrease energy consumption during the ZEP current switching periods. The optimal control policy will be learnt for different working conditions with only one group hyperparameters. Furthermore, the smoother control actions of the DDPG controller will improve the stability and reduce more energy consumption by comparing with traditional proportional-integral (PI) controller, model predictive control (MPC) and artificial experiences. The artificial intelligence-based optimal control framework brings both energy saving and intelligence to zinc manufacturing plants.

Recovery of Pb and Zn from a citrate leach liquor of a roasted EAF dust using precipitation and solvent extraction

Electric arc furnace (EAF) dust is globally one of the biggest metal-containing waste fractions, with a composition that challenges the recycling of dust back to the steel process due to the high Zn and Pb content, which also prevents it from being landfilled. The current study presents a process flowsheet with zinc and lead removal from EAF dust via citric acid leaching, lead removal by precipitation, and further solvent extraction (SX) of zinc for recovery. The process produces fractions that can be directly routed back to a steel plant (leach residue), a zinc electrowinning process (pregnant leach solution, PLS), and a lead smelter (lead sulfate, PbSO4 precipitate). Moreover, zinc separation by solvent extraction from citric acid leach solution originating from EAF was performed successfully with minimal impurity content in the final electrolyte, using di(2-ethylhexyl)phosphoric acid (D2EHPA). The total lead removal from PLS was achieved with an addition of only 0.012 M sulfate ion (from sulfuric acid) at room temperature. The optimization of zinc separation via SX was performed at a temperature range of 25–55 °C varying the D2EHPA concentration (10–25 vol-%) with different O/A ratios. With an optimized EAF SX process (pH = 5, t = 15 min, T = 25 °C, CD2EHPA = 20 vol-%, O/A = 1:1) and stripping process (t = 15 min, T = 25 °C, CH2SO4 = 1 M, O/A = 3:1), the zinc content in the electrolyte could be enriched up to 50 g/L, and the amount of impurities in the solution decreased down to a level where they have no adverse effect on the zinc electrowinning process and final zinc recovery. Moreover, the iron-rich leach residue was also shown to be chemically suitable as a raw material for the EAF process. With the proposed roasting-leaching-precipitation-SX-EW unit operation, EAF dust can be converted into three different secondary raw material streams, suitable for integration into state-of-the-art processes.

Electrowinning of Iron from Spent Leaching Solutions Using Novel Anion Exchange Membranes.

In the Pyror process, electrowinning (EW) is used to recover acid and iron from spent leaching solutions (SLS), where a porous Terylene membrane acts as a separator between the cathode and anode. In this study, a novel anion exchange membrane (AEM)-based EW process is benchmarked against a process without and with a porous Terylene membrane by comparing the current efficiency, specific energy consumption (SEC), and sulfuric acid generation using an in-house constructed EW flow cell. Using an FAP-PK-130 commercial AEM, it was shown that the AEM-based process was more efficient than the traditional processes. Subsequently, 11 novel polybenzimidazole (PBI)-based blend AEMs were compared with the commercial AEM. The best performing novel AEM (BM-5), yielded a current efficiency of 95% at an SEC of 3.53 kWh/kg Fe, which is a 10% increase in current efficiency and a 0.72 kWh/kg Fe decrease in SEC when compared to the existing Pyror process. Furthermore, the use of the novel BM-5 AEM resulted in a 0.22 kWh/kg Fe lower SEC than that obtained with the commercial AEM, also showing mechanical stability in the EW flow cell. Finally, it was shown that below 5 g/L Fe, side reactions at the cathode resulted in a decrease in process efficiency, while 40 g/L yielded the highest efficiency and lowest SECs.

Reducing the energy consumption and cell sludge of the zinc electrowinning process by using a pyramid-shaped 3D-Pb anode

In this work, the surface morphology, inner structure and phase composition of the oxide layers formed on Pb and pyramid-shaped 3D-Pb (Pyra-Pb) anodes after different periods of galvanostatic polarization were investigated. The results showed that in the preliminary stage, the lead compounds and MnO2 deposited at a higher rate on the Pyra-Pb anode. The deposited MnO2 layer on the Pyra-Pb anode was compact and well adhered, while that on the Pb anode exhibited a loose and porous structure. After a longer period of galvanostatic polarization, the oxide layer on the Pyra-Pb anode exhibited a higher stability due to its smaller thickness, denser surface structure and higher physical stability of the inner MnO2 layer. Consequently, the potential-time curve of the Pyra-Pb anode was smooth, while that of the Pb anode presented an oscillatory character with potential spikes and steps. Furthermore, the performance of the Pyra-Pb anode during 72 h of galvanostatic electrolysis was evaluated and compared with that of the Pb anode. The results showed that in the presence of 4 and 6 g L−1 Mn2+, the average anodic potentials of the Pyra-Pb anode were approximately 70 mV and 100 mV lower than those of the Pb anode, respectively. The lower potentials could be explained by the lower ohmic resistance of the MnO2 layer due to its denser structure and smaller thickness. It was also found that the Pyra-Pb anode significantly reduced the mass of the cell sludge, which could be attributed to the higher stability of the MnO2 layer and lower Mn3+ concentration in the electrolyte. In summary, it was demonstrated that the Pyra-Pb anode has a great potential to reduce the energy consumption and cell sludge of the zinc electrowinning process.

Recovery of metals from waste printed circuit boards by selective leaching combined with cyclone electrowinning process

This paper provides a benign process that realized the metals separation and recovery from wPCBs in an efficient and low cost way. The chemical active order and potential-pH diagram of the metals enlightened us to apply stepwise leaching to selective separation of the metals from the wPCBs. The results indicated that the selective separation of Fe, Al, Zn; Sn and Cu can be achieved by the dilute sulfuric acid leaching, displacement leaching using copper sulphate and sulfuric acid leaching with air-oxidization, respectively. Under the optimal conditions, the leaching efficiency of Fe, Al, Zn, Sn and Cu were 92.59%, 90.51%, 89.73%, 1.44% and 0.82%, respectively, in the dilute sulfuric acid leaching. In the displacement leaching, the displacement efficiency of Sn was as high as 95.20%, with little Cu leached. The data of sulfuric acid leaching with air-oxidization experiments shows that the leaching efficiency of Cu reached 95.72%. In order to recover the Sn and Cu in the solutions, the hydrolysis precipitation and cyclone electrowinning were introduced. With these techniques, 92.75% Sn was precipitated and the smooth cathode copper (purity 99.98%) was obtained with the current efficiency was 94.96%. Moreover, the analysis of the mass distribution about the process demonstrated that the H+ and Cu2+ were consumed, but also produced in different procedure, that means the process is a simple and eco-friendly technology, not only due to its high recovery efficiency, but also high reagents recyclable.

Failure investigation of stainless steel anodes used in gold electrowinning

Failure of austenitic stainless steel anodes in a gold electrowinning process (EW) was reported after a short period of service (3–6 weeks). Different analytical and characterization techniques were employed to conduct root cause failure analysis (RCFA) of the failed anodes. Electrochemical behaviour of the stainless steel alloy in the industrially supplied and synthesized electrowinning solutions were evaluated using different electrochemical test methods. The main failure mechanism of these anodes was found to be transpassive dissolution. Local solution acidification in the pores and crevices also contributed to the high corrosion rate of the stainless steel anodes as the transpassive dissolution rate increases when the pH of the electrowinning solution decreases. Gold and silver were found in the anodic layer along with typical stainless steel corrosion products (iron and chromium oxides), contributing to gold loss in the electrowinning process. Materials selection, design change, solution and process modifications are recommended to prevent similar failures or maximize the lifetime of the anodes.

Hydrometallurgical recovery of lead from spent lead-acid battery paste via leaching and electrowinning in chloride solution

Recycling spent lead-acid batteries has always been a research hotspot. Although traditional pyrometallurgical smelting is still the dominant process, it has serious environmental drawbacks, such as the emission of lead dust and SO2, and high energy consumption. This study presents a clean process for recycling spent lead-acid battery paste. The lead in paste was recovered via hydrometallurgical leaching and electrowinning in chloride solution. The leaching ratio of lead was >99% under optimum conditions: temperature of 90 °C, CaCl2 concentration of 400 g/L, Fe2+ concentration of 5 g/L, pH 1.0, and leaching time of 2 h. The appropriate minimum Pb concentration and optimum current density for electrowinning were determined to be 10 g/L and 200 A/m2, respectively. Cathode lead powders with a purity of 99.6% were obtained via electrowinning. The current efficiency and the power consumption at 200 A/m2 were 96.3% and 85.9 kWh per ton of lead produced, respectively. Due to the use of soluble anode (iron), the energy consumption of the electrowinning process was considerably reduced and the chlorine evolution was avoided. The electrowinning has obvious economic advantages over cementation, and the metallic lead with high purity can be obtained using this method. Furthermore, as the spent electrolyte containing ferrous ions is recyclable, the consumption of reagents and the liquid effluent are minimised. The final leaching residue is a mixture of harmless akaganeite and calcium sulphate. The experimental results show that the proposed process is promising for the recovery of lead from spent lead-acid battery paste.

Bubble-assisted densification of cobalt deposit during electrowinning in CoCl2 solution

Preparation of densified cobalt deposit during electrowinning can enhance the quality of cobalt products effectively for more application. Here we proposed a bubble-assisted electrowinning process in aqueous solution of CoCl2 to achieve the production of high-density cobalt deposit. Electrowinning processes with and without the assistance of a flow of gaseous bubbles was compared by characterizing the microstructure and phase composition of the cobalt deposits. Moreover, electrochemical behavior of cobalt ions was investigated. Upward flowing bubbles can eliminate unsatisfactory influence of dendritic growth and hydrogen evolution on the product, forming compact deposit consisting of fine cobalt crystals. The flowing bubbles are available for preferred growth of cobalt deposit. The current density used in this work and the concentration of CoCl2 can be elevated to an industrial level without the growth of dendritic product. This bubble-assisted method can be employed for the densification of various metals during electrowinning in aqueous solution.