Effects of additives on nickel electrowinning from sulfate system

In order to eliminate the pitting and improve the surface morphology of cathode nickel,the influence of additives of boric acid and dodecyl sodium sulfate(SDS)on the process of nickel electrowinning from sulfate system was studied by cathode polarization tests and nickel electrodeposition experiments.The experimental results show that the addition of boric acid can increase the cathode polarization while SDS can decrease the cathode polarization.Both boric acid and SDS are useful to eliminate the pitting on nickel deposits and improve the morphology of surface.Good deposit morphology with rare pitting and high current efficiency is favored by adding 10 g/L boric acid and 40 mg/L SDS in the electrolyte under the condition of nickel ion concentration of 80 g/L, sodium ion concentration of 10 g/L,pH of 3,current density of 220 A/m 2 and temperature of 70℃.

Microstructure and electrolysis behavior of self-healing Cu-Ni-Fe composite inert anodes for aluminum electrowinning

The microstructure evolution and electrolysis behavior of(Cu_(52)Ni_(30)Fe_(18))–x Ni Fe_2O_4(x=40wt%,50wt%,60wt%,and 70wt%)composite inert anodes for aluminum electrowinning were studied.Ni Fe_2O_4 was synthesized by solid-state reaction at 950°C.The dense anode blocks were prepared by ball-milling followed by sintering under a N_2 atmosphere.The phase evolution of the anodes after sintering was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy.The results indicate that a substitution reaction between Fe in the alloy phase and Ni in the oxide phase occurs during the sintering process.The samples were also examined as inert anodes for aluminum electrowinning in the low-temperature KF–NaF–AlF_3 molten electrolyte for 24 h.The cell voltage during electrolysis and the corrosion scale on the anodes were analyzed.The results confirm that the scale has a self-repairing function because of the synergistic reaction between the alloy phase with Fe added and the oxide phase.The estimated wear rate of the(Cu_(52)Ni_(30)Fe_(18))–50Ni Fe_2O_4 composite anode is 2.02 cm·a^(-1).

Effect of added cobalt ion on copper electrowinning from sulfate bath using doped polyaniline and Pb-Ag anodes

Effect of added Co2 +(aq)on copper electrowinning was studied using doped polyaniline(Pani)and Pb-Ag(1%)anodes and a stainless steel cathode.The presence of added Co2+ (aq)in the electrolyte solution was found to decrease the anode potentials.The optimum level of Co2 +(aq)concentration in the electrolyte,with respect to the maximum saving of power consumption was established.Linear sweep voltammetry(LSV)was used to study the influence of added Co2 +(aq)on the anodic processes in a copper sulfate-sulfuric acid electrolyte.The oxygen-evolution potential for Pani anode is depolarised at lower current densities(≤0.01 A/cm2)and attains saturation atρ(Co 2+ )o≈0.789 g/L;whilst the oxygen-evolution potential for Pb-Ag(1%)anode is depolarised at higher current densities(≤0.02 A/cm2)and attains saturation atρ(Co 2+ )o≈1.315 g/L.The preferred orientations of the copper deposits change from(220)to(111)with the addition of 0.394?0.789 g/L Co 2+ but higher concentrations favor(220)orientation again.

Effect of rolling technologies on the properties of Pb?0.06wt%Ca?1.2wt%Sn alloy anodes during copper electrowinning

The objective of this work was to study the effect of different rolling technologies on the properties of Pb-0.06wt%Ca-1.2wt%Sn anodes during copper electrowinning and to determine the relationship between the properties of the anodes and rolling techniques during copper electrowinning. The anode process was investigated via anodic polarization curves, cyclic voltammetry curves, electrochemical impedance spectra, and corrosion tests. The microscopic morphology and phase composition of the anodic oxide layers were observed by scanning electron microscopy and X-ray diffraction, respectively. Observable variations in the electrocatalytic activity and reaction kinetics of anodes during electrowinning indicated that the electrochemical behavior of the anodes was strongly affected by the rolling technology. An increase in the rolling number tended to decrease the oxygen evolution overpotential and the corrosion rate of the anodes. These trends are contrary to that of the apparent exchange current density. Furthermore, the intensities of diffraction peaks associated with PbO, PbOx, and α-PbO2 tended to increase with increasing rolling number. In addition, the rolled anodes exhibited a more uniform microstructure. Compared with one-way rolled anodes, the eight-time cross rolled anodes exhibited better electrocatalytic activity and improved corrosion resistance.

Properties of Al/Conductive Coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 Composite Anode for Zinc Electrowinning

The properties of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 composite anode for zinc electrowinning were investigated. The electrochemical performance was studied by Tafel polarization curves（Tafel）, electrochemical impedance spectroscopy（EIS） and corrosion rate obtained in an acidic zinc sulfate electrolyte solution. Scanning electron microscopy（SEM）, X-ray diffraction（XRD）, and energy dispersive X-ray spectroscopy（EDXS） were used to observe the microstructural features of coating. Anodes of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-ZrO2, and Pb-1%Ag anodes were also researched. The results indicated that the Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 showed the best catalytic activity and corrosion resistant performance; the intensity of diffraction peak exhibited the highest value as well as a new PbWO4 phase; the content of WC and ZrO2 in coating showed the highest value as well as the finest grain size.

Comparison of effective parameters for copper powder production via electrorefining and electrowinning cells and improvement using DOE methods

The influences of cupric ion concentration （5-35 g/L）,current density （500-2000 A/m2）,circulation rate of the electrolyte solution （15-120 mL/min）,and temperature （25-60℃） on the physical and chemical properties of copper powders obtained in electrolysis cells were investigated.Two industrial processes,electrorefining （ER） cells with a synthetic electrolyte and electrowinning （EW） cells with an original solution of coppermineral leaching,were utilized to produce copper powders.Finally,the statistical full factorial method of design of experiments （DOE） was employed to investigate the interaction or the main effects of processes.The results show that increasing the copper concentration and temperature can increase the grain size,apparent density,and electrical energy consumption.On the other hand,increasing the current density and circulation rate of the electrolyte can decrease them.This production process is optimized via DOE to control the interactive and main effects to produce copper powders with favorable properties.

Electrowinning of Copper Using Rotating Cylinder Electrode Utilizing Lead Anode

The effect of lead anode, rotating cylinder electrode (RCE), amount of 1,2-dihydroxypropane (12-DHP), temperature and rotation on the electrowinning of copper from low concentration acidified copper sulphate solution has been investigated. Copper powder was electrodeposited onto RCE that made of pure copper. From cyclic voltammetry experiments, an empirical parameter called the departure percent, S, was obtained which may represent the stability of the organic additive in the given medium and under the experimental conditions. The inhibition percentage, P, was 0.00 - 89.91% depending on the experimental variables. P was affected by temperature and mole fraction of 12-DHP, while rotation did not show any influence on it. Values of activation energy of electrodeposition process, Ea, were found to be less than 28 kJ mol-1 indicating diffusion controlled process. The overall mass transfer correlations under the present conditions have been computed using the dimensional analysis method. The data were valid for 90 < Sh < 1098, 737 < Sc < 59284 and 271 < Re < 7046 and the results agreed with the previous studies of mass transfer to rotating cylinders in turbulent flow regimes. The effect of time, content of 12-DHP, temperature and the speed of rotation on the morphological changes of the electrodeposited copper powder as well as deposits composition and crystallite size have been studied. Various crystallite sizes ranged 7.1 nm - 250.6 nm were obtained and characterized by EDS and XRD. Different topographs proved that the rate of copper electrodeposition increased by increasing deposition time, temperature and the speed of rotation. Also, they proved that the deposition rate decreased by adding 12-DHP to the solution. Therefore, the results obtained by SEM supported those achieved by measuring the limiting current density and follow the normal manner when organic solvents were added to the electrodeposition bath.

BEHAVIORS OF Sb,Sn AND As IN LEACHING AND ELECTROWINNING FROM JAMESONITE CONCENTRATE

The separating efficiency of Sb from As and Sn in jamesonite concentrate could be improved by changing the composition of leaching solution and other conditions.The related kinetic parameters of electrode reaction were evaluated under discussion on the form of complex ion AsS_3^(3-)in extract and the reduction at amalgam electrode.It was also discussed about the ef- fect of eoncentration of Na_2S and SbS_3^(3-)in solution on the current efficiency of SnS_4^(4-) reduction.

Behavior of arsenic in zinc electrowinning

The effects of arsenic on the cathode polarization process in zinc electrowinning,its kinetics equation,parameters and polarization mechanism were studied by multiple electrochemistry approaches.The experimental results show that,if[As 3+]≥3 mg/L,electrowinning first enters into stationary passivation range,and then enters into precipitation range,which indicates that the depolarization function of impurity arsenic is zinc electrowinning.

Polyaniline anode for zinc electrowinning from sulfate electrolytes

Polyaniline(Pani)anode is tested to highlight the feasibility of reduction of both energy consumption and capital costs in zinc electrowinning from sulfate solution without any modification to the existing plant.Current density,electrolyte temperature, added gelatin,added Mn 2+ ,oxygen-evolution potential,cell potential and long duration tests were investigated.The zinc deposits were also studied by means of scanning electron microscope(SEM)and X-ray diffraction(XRD).The results show that current density and added gelatin change the preferred crystal orientations of the zinc deposits.Compared with Pb-Ag(1%)anode used in industry,the cell voltage decreases by 0.15-0.30 V,energy consumption of Zn is 2.46-2.70 kW·h/kg which results in 20%energy savings.Long duration tests show that Pani anode can represent a good alterative ability for zinc electrowinning.Zinc deposits obtained have no Pb pollution.The additions of Mn2 +ions and gelatin also change the surface morphology and deposit quality of the electrodeposited zinc,affecting the crystal orientation.These researches demonstrate that Pani anode has distinct advantages over acidic electrowinning process.

Electrochemical Properties and Microstructure of Al/Pb–Ag and Al/Pb–Ag–Co Anodes for Zinc Electrowinning

The Al/Pb-0.8%Ag and Al/Pb-0.75%Ag-0.03%Co （in mass fraction） anodes used in zinc electrowinning are prepared through the electrodeposition of lead methanesulfonate electrolyte onto an aluminum matrix. The results of anode polarization curves, Tafel curves, and EIS characterizations indicated that the Al/Pb-0.75%Ag-0.03%Co anode has higher electrocatalytic activity and corrosion resistance than the Al/Pb-0.8%Ag anode. SEM observations on the fruit surfaces demonstrated the crystals on the Al/Pb-0.8%Ag anode are larger than on the Al/Pb-0.75%Ag-0.03%Co anode. After 24 h of anodic polarization, SEM observations and XRD analysis showed that the MnO2-PbO2 layer on the Al/Pb-0.75%Ag- 0.03%Co anode surface is characterized by dendritic crystals, and the PbSO4-PbO2 layer under the MnO2-PbO2 layer is characterized by uniform and chaotic orientation tetragonal symmetry crystallites of PbSO4. However, the MnO2-PbO2 layer on the Al/Pb-0.8%Ag anode surface is characterized by granular crystals, and the PbSO4-PbO2 layer under the MnO2 PbO2 layer is characterized by well-organized orientation crystallites of PbSO4, which are concentrated in certain zones.

Influence of arsenic,antimony and cobalt impurities on the cathodic process in zinc electrowinning

By means of an electrochemical study,the influence of arsenic,antimony and cobalt on cathodic polarization in the zinc electrowinning process,the associated kinetic equations and parameters,and the polarization mechanism have been studied.The results show that the experimental values of the kinetic parameters are in accord with the theoretical values in the ZnSO4/H2SO4 solution with a single impurity is added.In contrast,the charge transfer coefficient α is smaller than the theoretical value in the ZnSO4/H2SO4 solution when the three impurities are added together.

Deep cleaning of a metallurgical zinc leaching residue and recovery of valuable metals

Huge quantities of zinc leaching residues(ZLRs) generated from zinc production are dumped continuously around the world and pose a potential environmental threat because of their considerable amounts of entrained heavy metals(mainly lead). Most ZLRs have not been properly treated and the valuable metals in them have not yet been effectively recovered. Herein, the deep cleaning of a ZLR and recovery of valuable metals via a hydrometallurgical route were investigated. The cleaning process consists of two essential stages: acid leaching followed by calcium chloride leaching. The optimum conditions for extracting zinc, copper, and indium by acid leaching were a sulfuric acid concentration of 200 g·L^(-1), a liquid/solid ratio of 4:1(m L/g), a leaching time of 2 h, and a temperature of 90°C. For lead and silver extractions, the optimum conditions were a calcium chloride concentration of 400 g·L^(-1), a pH value of 1.0, a leaching time of 1 h, and a temperature of 30°C. After calcium chloride leaching, silver and lead were extracted out and the lead was finally recovered as electrolytic lead by electrowinning. The anglesite phase, which poses the greatest potential environmental hazard, was removed from the ZLR after deep cleaning, thus reducing the cost of environmental management of ZLRs. The treatment of chlorine and spent electrolyte generated in the process was discussed.

Preparation of Al_3Sc Intermetallic Compound by FFC Method

The FFC Cambridge process is a direct electrodeoxidation process used to reduce metal oxides for metals or alloys in molten salts. Al-Sc compound oxides are used as a precursor which formed upon blending and sintering Al2O3, Sc2O3 and AI powders and are successfully reduced by using the FFC Cambridge process at 973 K with a constant cell voltage of -3.2 V. This method is applied to the preparation of fine Al3Sc particles, which can give another new view for aluminum industry.

BASIC ELECTROLYTIC METHOD FOR RECOVERY OF LEAD FROM SCRAP BATTERIES

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Effects of Zr content on electrochemical performance of Ti/Sn-Ru-Co-ZrO_(x)electrodes

The low cell voltage during electrolytic Mn from the MnCl_(2) system can effectively reduce the power consumption.In this work,the Ti/Sn−Ru−Co−Zr modified anodes were obtained by using thermal decomposition oxidation.The physical parameters of coatings were observed by SEM(scanning electron microscope).Based on the electrochemical performance and SEM/XRD(X-ray diffraction)of the coatings,the influence of Zr on electrode performance was studied and analyzed.When the mole ratio of Sn−Ru−Co−Zr is 6:1:0.8:0.3,the cracks on the surface of coatings were the smallest,and the compactness was the best due to the excellent filling effect of ZrO_(2)nanoparticles.Moreover,the electrode prepared under this condition had the lowest mass transfer resistance and high chloride evolution activity in the 1mol%NH_(4)Cl and 1.5mol%HCl system.The service life of 3102 h was achieved according to the empirical formula of accelerated-life-test of the new type anode.

Electrochemical investigation of the anode processes in LiF-NdF3 melt with low oxygen content

The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper.Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF-NdF_(3)melt after a lengthy period of pre-electrolysis purification at 1000℃(during which the oxygen content reduced from 413 to 150 mg/kg).The oxidation process of oxygen ions was found to have two stages:oxidation product adsorption and CO/CO_(2)gas evolution.The adsorption stage was controlled by diffusion,whereas the gas evolution was controlled by the electrochemical reaction.In comparison with oxygen content of 413 mg/kg,the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred.Fluorine-ion oxidation peaks that occurred at about 4.2 V vs.Li/Li+could be clearly observed in the reverse scanning processes,in which fluorine ions were oxidized and perfluorocarbons were produced,which resulted in an anode effect.

Bio-leaching of low-grade large porphyry chalcopyrite-containing ore

In order to economically recover the copper from the low grade copper ores, a bioleaching solvent extraction electrowinning plant with a design capacity of 2 000 t cathode copper per year in Dexing Copper Mine was operated in September, 1997. The results during the 10 month period of the industrial copper dump leaching have been obtained and the approaches have been carried out to enhance the copper dissolution from the waste rocks. The overall operation flowsheet is depicted. The problems confronted in the process and possible way for improving are discussed.

Preparation of Sintered Titanium Anode and Its Electrochemical Properties

In this paper, the sintered Ti anodes (STA) with Ti suboxide intermediate layers and β-MnO_2 active layers were investigated in detail. At usual industrial current densities, the oxygen evolution overpotential on STA is reduced by 350 mV compared with lead anodes. According to the equation obtained experimentally, the service life of STA may be expected to be more than 3 years. After los- ing activity, STA may be recoated with β-MnO_2 active layers and used again. The electrocatalytic activity and the service life of the reused anodes remained almost unchanged. The possible reasons for losing activity of STA during the anodic evolution of oxygen were investigated by means of elec- tron probe microanalysis, electron scanning microscope and X-ray diffraction.

Cobalt Recovery from Waste Catalysts (Petroleum Refining Industry from Gujarat)

A hydrometallurgical process has been developed for cobalt recovery from a waste catalyst (petroleum refining industry). This waste catalyst containing about 2.18 weight % of Co, is highly contaminated by Mg, Al, Si, Ca, Fe, Ni, Cu, Zn, Mo. The major steps are: (I) The spent catalyst is roasted with flux material in an electrical furnace at very high temperature (700?C) for a specific duration. (II) The roasted sample is leached with sulphuric acid to bring the metal contents into solution form. (III) For separating cobalt values from the leach solution, the solution pH is raised by NaOH addition, where all cobalt content is precipitated at a pH of about 12. (IV) This cobalt hydroxide precipitate is filtered and dissolved in minimum amount of sulphuric acid to get cobalt sulphate solution which is used as the electrolyte for the electrolytic recovery of cobalt. For optimizing various parameters like (1) H2SO4 concentration;(2) Duration;(3) Cobalt concentration;(4) Current density;(5) Temperature;(6) Stirring etc., The particle surface morphology and deposited layers have been characterized by scanning electron microscopy (SEM). A compact metallic deposit containing 70% cobalt was obtained.