Selection of the Optimum Electrolysis Bath Composition for the Synthesis of Holmium–Iron Triad Metal Intermetallics

The results of high-temperature electrochemical synthesis of holmium–iron triad metal intermetallics in chloride melts are presented. The influence of the current density, the composition of an electrolysis bath, and the synthesis time on the electrolysis processes and the composition of the end product is studied. The electrolysis of the molten KCl–NaCl mixture containing 0.5–2.5 mol % holmium trichloride and 0.1–2.5 mol % nickel (cobalt) dichloride at a current density of 0.5–2.0 A/cm², a temperature of 973–1073 K, and an electrolysis time of 30–90 min is shown to cause the formation of a cathode deposit in the form of a “metal–salt pear” on a tungsten electrode. This pear consists of a mixture of metallic nickel (cobalt) and HoNi, HoNi₅, and HoNi₃ (HoCo₂, HoCo₃, HoCo₅, Ho₂Co₁₇) intermetallics. The intermetallic compound content in the cathode deposit is found to increase at a constant current density (1.2 A/cm²) and when the holmium chloride content in a melt or the ratio of the holmium chloride concentration to the nickel (cobalt) chloride concentration increases. Only a mixture of holmium–nickel (cobalt) intermetallics can exist in the cathode deposit if the electrolysis bath composition and the electrolysis parameters are controlled. The electrochemical synthesis of holmium–iron intermetallics was performed under galvanostatic conditions in molten KCl–NaCl–HoCl₃. Iron ions are introduced in a melt via the anodic dissolution of metallic iron. The results of X-ray diffraction analysis of the electrolysis products demonstrate the fundamental possibility of synthesizing holmium–iron intermetallics. The optimum conditions of electrosynthesis of holmium–iron triad metal intermetallics are determined.     

The effect of quality of anodes on the process of electrolytic of manganese dioxide

During the electrosynthesis of manganese dioxide, the anode material and anode current density (i _a) exert the largest influence on the characteristics of electrolysis and the quality of the obtained material. The activation of anodes, which consists of the deposition of the titanium-manganese alloy on the titanium base of the electrode by the thermal-diffusion method, prevents passivation at i _a = 100 and 200 A/m². The electrochemical characteristics of electrolysis for NTMA (a built-up titanium-manganese activated anode) and ATDP (an experimental activated anode with thermodiffusion coating) anodes at i _a = 100 and 200 A/m² have close values. The voltage across the bath does not exceed 2.2–3.0 V, the current efficiency is 95–98%, and electrical power consumption is 1.33–1.80 (kW h)/kg. The chemical composition and the crystalline modification of electrical manganese dioxide corresponds to the requirements of GOST (State Standard) 25823-83. The activated ATDP anodes behave similarly to the known HTMA anodes. After electrolysis, no variations in the surface layer are found on them.     

无硒氯化物体系电解金属锰消减氯气的实验研究

为了减少氯化物体系电解金属锰中氯气的溢出量,通过电化学测试及电解实验探究了阳极电流密度、锰离子以及氯化铵浓度对氯气溢出量的影响。阳极极化曲线测试表明,在氯化锰、氯化铵溶液中,阳极过程按电流密度分成两个区域:低电流区域,以Mn2+和Cl-的氧化为主要反应;高电流区域,以氧的析出反应为主要过程。电解实验证实上述结果,电流密度越高,氯气的溢出量越少;溶液中氯离子浓度越高,氯气的产生量也越多;纯氯化物体系电解金属锰在接近工业生产条件时,阳极过程难以完全抑制氯气的溢出,采用混合电解质为1 mol/L NH4Cl+0. 5 mol/L (NH4)2SO4时,氯气溢出量低于检出限,无硒电解条件下,Mn沉积效率可达到72. 81%。     

Electrodeposition of coatings of double carbides of tungsten and molybdenum from tungstate–molybdate–carbonate solutions

The electrochemical deposition of coatings of double tungsten and molybdenum carbides from tungstate–molybdate–carbonate melts is investigated. The composition of formed coatings is investigated by X-ray fluorescent and X-ray phase analyses. The crystal size and coating thickness are determined using scanning electron microscopy. Optimal deposition parameters of W₂C · Mo₂C coatings are as follows: the melt composition is Na₂WO₄–(1.0–4.0 mol %) Li₂WO₄–(1.0–4.0 mol %) Li₂MO₄–(1.0–5.0 mol %) Li₂CO₃, the cathode current density is 750–1500 A/m², the process temperature is 1123–1173 K, and the electrolysis duration is 4 h.     

温度对电解二氧化锰工艺影响的研究

电解Mn的影响因素多于电解MnO2,所以试图研究在低温下电解MnO2来解决同槽电解Mn和MnO2温度差异问题。通过对比试验,研究以钛板为阳极在MnCl2-HCl溶液中和在Mn-SO4-H2SO4溶液中、以钛钌板为阳极在MnCl2-HCl溶液中温度对电解二氧化锰的电流效率和槽电压的影响,结果表明以钛钌板为阳极在MnCl2-HCl溶液中电解MnO2,低温下(45℃时)就具有低且稳定的槽压(-2.7 V)和高的电流效率(45℃时,ηA70%;55℃时,ηA90%)。X衍射试验表明:以钛钌板为阳极在MnCl2-HCl溶液中45℃电解沉积的物质是γ型二氧化锰。     

Single cell extraction of zinc and manganese dioxide from zinc sulphide concentrate and manganese ores

The hydrometallurgical processing of zinc sulphide concentrates with sulphuric acid in the presence of manganese dioxide (manganese ore has been employed) and subsequent electrolytic co-deposition of cathodic zinc metal and anodic manganese dioxide is described.The influence of various parameters on the reaction

$\text{ZnS + MnO}{}_2\text{+ 2H}{}_2\text{SO}{}_4\text{= ZnSO}{}_4\text{+ MnSO}{}_4\text{+ S}{}^0\text{+ 2H}{}_2\text{O}$

has been studied. Optimum conditions for rapid and efficient reaction have been determined.The simultaneous electrowinning of zinc at the cathode and γ-MnO₂ at the anode from the leach liquor was studied. The effects of variation of current density, temperature, electrolyte composition etc. have been described in detail. During leaching 99% extraction of zinc, 98% of manganese, and 96% liberation of elemental sulphur was achieved. 80–90% anodic and cathodic current efficiencies can be obtained under optimum conditions with impurity levels of only a trace of manganese in the zinc deposit and vice-versa.The anodically deposited manganese dioxide was the γ-battery active variety and was found to be satisfactory.The results indicate the potential for the development of a technique for zinc and manganese dioxide production in a single cell.     

Study of the mechanism of anodic dissolution of Cu2S

The anodic dissolution of Cu₂S in sulfuric acid solutions was studied under galvanostatic and potentiostatic conditions. The anodic products were studied by mineralogical and X-ray diffraction methods. In every case, the formation of a digenite Cu_1-8S layer is observed at the surface of Cu₂S according to 5Cu₂S → 5Cu_1.8S + Cu⁺⁺ + 2e A copper concentration gradient appears through the digenite layer whose thickness remains constant as soon as a Cu_1.1S layer appears at its own surface according to 3Cu_1.8S → 4Cu_1.1S + Cu++ + 2e If the electrolysis conditions are such that the anodic potential remains low, the next reaction to occur is 10Cu_1.1S → HCu⁺⁺ + 10S + 22e But if under galvanostatic conditions, the current density is high enough at a given temperature to reach the sharp rise in anodic potential, or if under potentiostatic conditions the potential is kept high, two other reactions are possible: 10Cu_1.1S → 10CuS + Cu⁺⁺ + 2e followed by CuS → Cu⁺⁺ + S + 2e Moreover, at high anodic potential, the following reaction occurs also to some extent CuS + 4H₂O ? Cu⁺⁺ + SO₄ ⁼ + 8H⁺ +8e resulting in a decrease in anodic current efficiency for the copper dissolution. From a more practical point of view, it was shown that it is possible to deplete virtually completely the copper content of the anode (residue at less than 0.5 pct Cu)keepingthe electrode potential at a low value (less than +650 mV/ENH). Providing the temperature is high enough (75°C at least), the mean current density remains near to 2 A/dm², a suitable value to obtain good cathodic deposits.     

Electrochemical synthesis of powders of holmium and nickel intermetallic compounds in halogenide melts

The results of high-temperature electrochemical synthesis of powders of holmium and nickel intermetallic compounds are presented. Optimal synthesis conditions of these compounds are as follows: the electrolysis temperature (923–1073 K), cathodic current density (0.5–1.9 A/cm²), and composition of the electrolysis bath (mol %): KCl(48.25–49.5)–NaCl(48.25–49.5)–HoCl₃(0.5–3.0)–NiCl₂(0.5–2.5). The composition of formed powders is investigated by X-ray phase analysis and scanning electron microscopy.     

Electrodeposition of manganese metal: role of quaternary ammonium salts on current efficiency,morphology and polarisation behaviour

The electrodeposition of manganese metal from aqueous solutions is problematic due to its high electroreduction potential demanding unique process challenges. In the present work, electrolytic manganese metals (EMMs) of high quality are deposited from sulphate solutions in the presence of quaternary amines: tetra ethyl ammonium bromide (TEABr), tetra propyl ammonium bromide and tetra butyl ammonium bromide. The concentrations of these additives were varied over a relatively broad range to evaluate their effect on current efficiency (CE), specific energy consumption, polarisation behaviour of the cathode and deposit morphology of the electrodeposited manganese metal. A maximum CE of more than 68% was achieved in the presence of 100?mg.L^?1 TEABr in the electrolytic bath at a current density of 500?A.m^?2. X-ray diffraction studies revealed that (330, 411) planes were the most preferred planes of crystal growth during manganese electrodeposition resembling alpha-manganese regardless of the type of quaternary amines used. A smooth and compact deposit was obtained with TEABr that was also supported by the scanning electron micrographs showing uniform deposit morphologies. The presence of these quaternary amines in the electrolyte causes polarisation of the cathode during electrodeposition. The degree of polarisation increases with an increase in the bulkiness of the alkyl group on the quaternary nitrogen atom of the additive. The quaternary amine TEABr was found to be the most suitable additive for producing the desired quality of EMM with better current yield.     

二氧化锰电解工序研究

电解二氧化锰作为电池工业中非常重要的原料之一,其生产过程简单分为化合(制液)、净化(除杂)、电解、后处理(再加工)4个部分。在电解工序当中,锰在此工段以二氧化锰的形式电沉积在阳极板上并在剥离后送至后处理进一步加工。而电解作为整个电解二氧化锰的核心工序,其过程工艺对最终产品质量有很大的影响。主要介绍了电解工艺原理、电解生产时的参数控制以及简单作业流程。     

Electrode polarization in the DC electroslag melting of pure iron

It is evident from the known ionic properties of the slags used in electroslag melting, that the dc melting process must be accompanied by Faradaic reactions on the slag/ingot and slag/electrode interfaces. The present work has determined the magnitude of the overpotentials resulting from concentration polarization at these interfaces, in the case of pure iron/CaF₂+Al₂O₃, CaF₂+CaO slags using a galvanostatic pulsing technique in an electrolytic cell. The polarization overpotential existing on an electrode in an operating ESR unit has been measured by the same technique. It is found that the potentials observed on the ESR electrode agree well with the results from the electrolytic cell. The primary anodic process is postulated to be the corrosion of iron, leading to an Fe²⁺-saturated layer on the anode surface at sufficiently high current densities. The cathodic process is suggested to be the Faradaic reduction of Al³⁺ or Ca²⁺, to give a concentration of [Al]_Fe or (Ca)_slag in the cathode interface region. This observation is supported by the fact that the cathodic potentials with respect to a C/CO reference electrode are close to those predicted from the reactions: (Al₂O₃)+3C=3CO(g)+2Al(l) or (CaO)+C=CO(g)+Ca(g) At very high current densities both the anodic and cathodic processes may convert to arcs, leading to process instability. The chemical and thermal effects of the overpotentials are briefly discussed and compared with the present results on ESR ingots of pure iron.     

稀土6063变形铝合金阳极氧化与电解着色的研究

本文系在硫酸、硫酸亚锡溶液中对添加有稀土的6063变形铝合金进行了阳极氧化和电解着色。比较系统地研究了氧化电解液的浓度、温度、时间、电流密度对膜层厚度的影响;以及着色电流密度、电压、时间对膜层色度的影响。结果证实,稀土可以明显地提高6063变形铝合金氧化膜厚度和电解着色的色度,稀土含量以0.30％为好。     

Studies on the application of copper(I)-ammune sulphate electrolytes in copper electrorefining

The electrolysis of a copper(I)-ammine sulphate electrolyte between copper electrodes has been investigated. A sealed cell and a solution containing 30 g/kg Cu, 95 g/kg NH₃ and 95 g/kg SO₄ were used.Current efficiencies (cathodic and anodic), at current densities over 100 A/m², were higher than 95% and were practically independent of the electrolysis variables (25–55°, 100–500 A/m² and 70–130 g/kg of NH₃ solution).It was shown that at temperatures over 40°C the energy consumption for electrorefining is lower in the copper(I)-ammine electrolyte than in a typical acidic electrolyte.Contributions to the energy consumption from the electrode processes and the resistance of the electrolyte have been determined from the experimental data.     

电解二氧化锰用钛基钛锰合金全浸没板状阳极的研制

电解二氧化锰生产中采用铸铝横担钛基钛锰合金全浸没板状阳极代替传统阳极或条状钛基钛锰合金阳极，能显著地提高电解二氧化锰（ＥＭＤ）质量，有明显的节能效果。其设计合理，整体强度高，几何形状稳定，电解电流分配均匀，便于装卸和剥离产品，大大减轻了工人劳动强度，提高了设备利用率，有显著的经济效益和社会效益。     

Electro-extraction of molybdenum from Mo2C-type carbide

A process for the preparation of molybdenum from molybdenum carbide was investigated. It involved fused salt electrolysis of the carbide in an inert atmosphere electrolytic cell using a KCl-K₃MoCl₆ electrolyte. The preferred conditions for electrolysis carried out in a 0.075 m (3 in.) diam cell were: voltage 0.2 to 0.5 V; cathode current density 8000 A/m2 (720 amp/f²);bath temperature 1203 K; and electrolyte composition 7.5 pct molybdenum. Under these conditions, electrolysis in a 0.15 m (6 in.) diam cell charged with 1.5 kg of the carbide yielded a total metal recovery of 71 pct at an average current efficiency of 60 pct. The metal purity was better than 99.9 pct. The electron beam melt hardness for the electro-extracted molybdenum was in the range of 150 to 160 DPH. The paper presents a part of the thesis to be submitted by A. K. SURI to the University of Bombay (India).     

Electrochemical anodic dissolution of FeCuNiCoMn alloy in ammonium solutions containing clorine ions

The effect of chlorine ion concentration, temperature and current density on metal distribution among the electrolyte, cathode deposit and mud in the process of electrochemical dissolution of FeCuNiCoMn alloy in an ammonium medium is examined. High iron content (65.90%) compared to that of non-ferrous metals (12.07% Cu, 12.81% Ni, 1.30% Co) and Mn 5.33% is a specific feature of the alloy. The alloy was produced by means of high-temperature reduction smelting of manganese nodules from the Clarion Cliperrton area in the Pacific Ocean. It was found that electrochemical dissolution of the alloy is accompanied by formation of a CuNiCo-cathodic deposit and two types of mud: one tightly clinging to the anode surface, and another, finely suspended in the electrolyte. The highest-purity cathode deposit in mass %: 40.28 Cu, 50.27 Ni, 1.21 Co, 7.63 Fe and 0.61 Mn was obtained at ion ratio in the solution NH₄⁺: Cl⁻ = 2.5: 0.5, temperature 323 K, anodic current density 350 A/m², separation of the anode and cathode spaces by a shielding screen, continuous removal of the anodic mud and maintaining of a constant pH in the electrolyte (10 ± 0.2). In these conditions, >99% of Fe and Mn, 25% Cu, 54% Ni and 52% of Co is transferred into the mud.     

Continuous preparation of composition-controllable Y–Ni alloy in LiF–YF3–Y2O3 molten salt

The Y–Ni alloy is a primary precursor for the preparation of high-performance La–Y–Ni-based hydrogen storage materials. However, it cannot be produced continuously at low cost, which limits the wide popularization and application of La–Y–Ni-based materials. In this paper, this problem was solved perfectly using electrochemical reduction of Y₂O₃ in the LiF-YF₃ system. It is found that the reversible reduction from Y³⁺ to Y on the W electrode takes only one step, namely a significant soluble–soluble reaction controlled by Y³⁺ diffusion throughout the melt. Four typical signals of square wave voltammetry (SWV) corresponding to different kinds of Y–Ni intermetallic compounds are observed in LiF−YF₃ and LiF–YF₃–Y₂O₃ melts, and reduction potential can become positive with the addition of Y₂O₃, probably because of the formation of more complexes in the melts. Homogeneous Y–Ni alloy samples were produced continuously and prepared via galvanostatic electrolysis by using bargain-price raw material (Y₂O₃) and setting the current density at 10 A/cm² on the nickel electrode, before they were collected into a bottom receiver. A series of analyses including scanning electron microscopy-energy idspersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS), demonstrate that concentration of yttrium in Y–Ni alloy is adjustable within the wide range of 44 wt% to 72 wt% by fine-tuning the electrolysis temperature (875–1060 °C) in the LiF-YF₃ system to ensure the optimal hydrogen storage performance and economic efficiency of La–Y–Ni-based hydrogen-storage materials.     

Cathodic behavior of scandium(III) on reactive copper electrodes in LiF–CaF2 eutectic molten salt

The electrochemical formation of Sc–Cu alloy was investigated in LiF–CaF₂ eutectic molten salt employing various electrochemical methods. Cyclic voltammetry and square wave voltammetry indicate that the reduction of scandium(III) on the tungsten electrode is a one-step reduction process with three electrons transfer. And underpotential deposition of scandium on the copper electrode occurs owing to the depolarization effect, i.e., forming Sc–Cu intermetallic compounds. The thermodynamic properties of the Sc–Cu intermetallic compounds ScCu₄, ScCu₂, and ScCu in the temperature range of 1153–1223 K were estimated by open-circuit chronopotentiometry. Moreover, the Sc–Cu alloys were prepared by potentiostatic electrolysis and characterized by optical microscope, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results reveal that only Sc–Cu alloy composed of Cu-ScCu₄ can be synthesized at low cathodic current density and above eutectic temperature.     

超混沌电流对金属锰电解阳极电位振荡的调控

金属锰湿法电冶过程是一个典型的远离平衡态的非线性体系,直流作用下会出现电化学振荡、金属分形等非线性行为而引发体系额外的能耗。本文提出一种超混沌电流电解的新模式,通过引入超混沌电路代替原有直流电源来实现。超混沌电流作用下,采用恒电流极化曲线、阳极极化曲线、塔菲尔测试等分析方法和X射线衍射分析、扫描电子显微镜的表征方法,研究铅合金阳极电化学振荡行为与阳极沉积的锰氧化物之间的关联。研究结果表明,在电流密度为350 A·m?2恒电流极化30 min后,超混沌电流极化作用下电位振荡的平均振荡周期较直流极化提高5.6 s,平均振幅降低 38 mV;超混沌电流作用下阳极生成的MnO₂,其表面较为致密平整,在一定程度上可以提高铅合金阳极析氧反应活性和耐腐蚀性。综合分析可知,将超混沌电流运用于金属锰电解过程,可以实现对阳极电化学振荡的有效调控,为进一步降低电解过程能耗和污染排放提供新思路。      

利用钛白粉废酸、二氧化锰矿和硫铁矿制取电解金属锰的研究与开发

采用钛白粉废酸、二氧化锰矿和硫铁矿浸出、除铁、硫化法除重金属及电解金属锰的工艺流程、技术条件与试验结果。取得了较好的技术指标以及质量达到YB／T051-2003高纯级DJMnA电解金属锰产品。