Electrochemical determination of thiourea and glue in the industrial copper electrolyte

An electrochemical method for determination of the thiourea and glue concentration in the industrial copper electrolyte has been developed. This method is based on changing of the copper cathode polarization potential. The amount of polarization potential change in the presence of glue and thiourea is not the sum of potential changes caused by the presence of each of those reagents separately. Thus, before determining the concentration of one component, the other component should be removed from the solution. Thiourea is removed by addition of H₂O₂ and glue—by hydrolysis at 60 °C for seven hours.     

Effect of thiourea on the copper cathode polarization behavior in acidic copper sulfate at 65 °C

The effects of different concentrations of thiourea (TU) on the copper cathode polarization behavior in an acidic copper sulfate solution was investigated at 65 °C using potentiodynamic and galvanostatic methods. The results showed that there was a transition current density for each concentration of the fresh TU, below which the TU exhibited a polarizing effect and above which the TU manifested a depolarizing effect on the copper cathode. The depolarizing effect increased with cathodic overpotential. The transition current density increased with TU concentration and decreased with time. Lowering of the electrolyte temperature resulted in diminution of the transition current density considerably. In the modern copper electrorefining conditions (65 °C, 150 to 350 A/m², and using approximately 1 to 4 mg/dm³ of TU), TU produces only a polarizing effect on the copper cathode.     

Collagen proteins in electrorefining: Rate constants for glue hydrolysis and effects of molar mass on glue activity

Animal glue (collagen proteins) degradation was studied in water and in a simulated copper electrolyte (150 g/L H₂SO₄, 46 g/L Cu²⁺ as CuSO₄) by size-exclusion chromatography. The rate of degradation was relatively slow in pure aqueous solutions, and depending on the temperature and glue concentration, some association to larger molar mass species was observed. For simulated electrolyte in a temperature range of 42 °C to 70 °C and a glue concentration range of 100 to 3000 mg/L, the degradation rate constant was described with the following relation:k′ = 1.5· 10⁷exp (-9951/T), min^-1 The degradation rate was zero order with respect to initial concentration of the protein and first order with respect to acid concentration. The results show that glue degradation under normal tankhouse operation should be rapid, with degradation to number-average molar mass (M _n ) < 10,000 units occurring in about 40 to 80 minutes depending on the mass transfer rate (or mixing) of the electrolyte solution. Samples of glue from three different sources showed almost no difference in degradation rates. Results calculated from the rate equation for glue degradation have been correlated with cathode polarization data from the literature, and the results suggest that critical glueM _n below which the glue loses most of its activity is 3700. Formerly Postdoctoral Fellow with the Department of Chemistry, University of Saskatchewan     

Glue analysis and behavior in copper electrolyte

Animal glue in combination with other chemicals is often used as a leveling agent in the copper electroplating industry. The control of the glue concentration in the electrolyte is critical to the quality of copper produced. A quantitative galvanostatic technique for glue analysis in copper electrolyte containing lignin sulfonate and Cl⁻ was developed. The kinetics of glue hydrolysis in industrial electrolytes was studied and found to follow first-order reaction kinetics, with sulfuric acid acting as a catalyst. The dependence of the glue hydrolysis rate constant on temperature follows the Arrhenius equation. By adding fresh glue to the electrolyte, the glue activity first rises and then falls. This effect can be explained by the presence of long-chain molecules in the glue which are less active but hydrolyze into the more active medium-sized molecules. A mathematical model of this process shows good agreement with experimental data. The bulk of the electrolyte flow in the INCO commercial electrolytic plating cell bypasses the electrodes, probably across the bottom of the cell. The electrolyte circulation between electrodes is not very intense. A simple equation for the glue concentration calculation in the cell inlet and outlet, depending on the glue addition rate, was derived. V.K. Blechta, formerly Section Leader of Process Technology, INCO Limited, is retired. Z.Z. Wang, formerly Research Scientist, INCO Limited, is Researcher, Laurentian University, Sudbury,Canada.     

The effect of electrolyte composition on the cathodic reduction of CuFeS2

The electrochemical reduction of CuFeS₂ mineral electrodes has been investigated by performing cathodic polarization curves, constant potential experiments, and cyclic polarization curves in various electrolytes. The effects of H₂SO₄, Fe²⁺ and Cu²⁺ concentrations have been examined as well as the effects of various dissolved gases, air, O₂, H₂S and N₂. Decreasing H₂SO₄ only shifts the curve to more negative potentials but initial concentrations of 0.36 M Fe²⁺ cause up to a ten-fold enhancement in the observed current. The presence of oxygen or Cu²⁺ also leads to an increase in the reduction current but in either case further increases in current are observed when Fe²⁺ is added to the electrolyte. Chalcocite (Cu₂S) or djurleite (Cu_1.96S) have been identified as products of reaction, although it is possible that a thin layer of a different copper-iron sulfide may form as an intermediate based on the color changes which appear after cathodic excursions. In addition, scanning Auger microprobe analyses of these surfaces show an increasing Cu:Fe ratio as the time at potential is increased. The results also indicate that the solid product layer is porous. A mechanism which accounts for the observed current increase in the presence of Fe²⁺ is proposed which involves a redox reaction between dissolved Fe²⁺ and cupric ion in the copper sulfide product layer.     

The effect of additives on the nucleation and growth of copper onto stainless steel cathodes

A potentiostatic technique has been used to study the effects of chloride ion, glue, and thiourea on the initial electrodeposition of copper. A stainless steel (AISI 304) rotating disc electrode (RDE) with an electrolyte containing 40 g/1 Cu²⁺ and 180 g/1 H₂SO₄ at 40 °C was employed. The current transients from the potential step measurements for the additive-free electrolyte could be fitted to a model that assumed progressive nucleation followed by growth of three-dimensional (3-D) centers under diffusion control. The growth mechanism and the type of nuclei were also confirmed by scanning electron microscopy (SEM) of the deposit. Chloride ions (40 ppm) affect the rate of the reaction, decrease the number of nuclei, and enhance the growth process. The particular glue (TPC 69, 5 ppm) used in this work is a polarizer and increases the number of nuclei formed on the surface. For the experimental parameters used in this research, the nucleation and growth mechanism is not changed by the presence of chloride ion or glue in the electrolyte. However, thiourea (0.5 ppm) additions caused the mechanism to change to instantaneous nucleation with 3-D growth under kinetic control, and a large number of equal sized nuclei are observed on the SEM micrographs, tending to verify the proposed mechanism.     

Effect of thiourea during nickel electrodeposition from acidic sulfate solutions

The effect of thiourea on the cathodic current efficiency (CE), deposit quality, crystallographic orientations, surface morphology, and polarization behavior of the cathode was investigated during nickel electrodeposition from acidic sulfate solutions for 2 hours at 60 °C. A slight decrease of 3 to 4 pct in the CE was observed, when the concentration of thiourea was increased from 2 to 40 mg dm⁻³. The nickel deposit quality deteriorated significantly at higher thiourea concentrations; the surface morphology deteriorated and the contamination of the nickel deposits increased. The presence of thiourea affected the peak intensities of the crystal planes. Cyclic voltammetric studies on nickel deposition at 25 °C revealed depolarization behavior of the cathode at lower thiourea concentrations, ≤10 mg dm⁻³; however, a mixed behavior is observed at higher thiourea concentrations. These changes were also observed in the exchange current density (i ₀) values.     

Effects of additives on zinc electrowinning from industrial waste products

An investigation of the effects of some additives on zinc electrowinning from a weak acidic sulphate electrolyte prepared from an industrial waste product has been carried out. Experiments were done in the presence of additives such as aluminium sulphate, animal glue and an extract of horse-chestnut nuts (HCE), used alone or in different mixtures.Using a rotating disc electrode (RDE) and cyclic voltammetry, the influence of the additives on the polarization curves and on the voltammograms was studied. SEM was used to determine the structure and the morphology of deposits.The results indicated that the additives tested exert a beneficial effect on the quality of the zinc deposits. They increase the cathodic polarization and promote levelling. Al₂(SO₄)₃ influences the reduction of zinc ions, increasing the nucleation overpotential and the deposition rate of zinc on the cathode. The conjoint use of Al₂(SO₄)₃, animal glue and HCE results in smooth, slightly bright deposits, showing a beneficial effect of the mixture on zinc electrodeposition. The analysis of deposit purity suggested that the additives inhibit the discharge rate of impurity metal ions, such as copper and lead, whose deposition is diffusion controlled.     

Effect of silicon on the rate of de-sulphurization of liquid Fe-S alloys by argon-hydrogen at 1550°C

Abstract

The passivation of copper anodes due to precipitation of copper sulfate on the anode surface was investigated as a function of electrolyte composition and temperature, and of anode composition. The slime layer present on the anode surface was shown to be the primary factor in causing passivation by inhibiting the diffusion of copper ions. Factors such as temperature, free acid level, Ni²⁺ and Cu²⁺ ion levels were also important in so far as they affected the mass transfer characteristics of Cu²⁺ ions and the solubility of copper sulfate.

Résumé

La passivation des anodes de cuivre due à la précipitation du sulfate de cuivre sur la surface de l'anode a été étudiée en fonction de la composition et la température de l'électrolyte et aussi en fonction de la composition de l'anode. Nous avons montré que la couche d'impuretés présente sur la surface de l'anode est la cause première de la passivation car elle empêche la diffusion des ions cuivre. D'autres facteurs tels que la température, le niveau d'acide libre, le niveau d'ions Ni²⁺ et Cu² sont également importants en ce qu'ils affectent les caractéristiques de transport de matière des ions Cu²⁺ et la solubilitédu sulfate de cuivre.     

Cathodic reactions of Cu2+ in cupric chloride solution

In this study we demonstrate the kinetics of Cu²⁺ reduction in concentrated cupric chloride solutions. Experiments were carried out near the boiling point of the solution ([NaCl] = 280 g/l and [Cu²⁺] = 1–40 g/l) at T = 90 °C, atmospheric pressure, pH = 2. Electrochemical methods such as cathodic polarization curves and cyclic voltammetry were used to investigate the cathodic reactions of copper complexes. To identify the nature and the rate-controlling steps of the reactions, rotating disk electrode (RDE) experiments were conducted. The chemical environment studied was similar to that of the Outokumpu HydroCopper^TM process, which uses a cupric chloride solution to leach copper from the mineral chalcopyrite.The results suggest that the cathodic reactions are the reduction of [CuCl]⁺ to the complex [CuCl₃]²⁻, the reduction of [CuCl₃]²⁻ to solid copper and hydrogen evolution. The diffusion coefficient and the unit rate constants for the solution species were calculated. The exchange current density and rate constant for electron transfer were also estimated. A simulation was made of the cathodic polarization curve and it was in good agreement with the experimental data.     

Lead and nickel distribution in the Cup-PbO-SiO2 and the Cup-NiO-SiO2 Systems equilibrated with liquid copper

The distribution of lead and of nickel between molten copper and a ternary cuprous oxide-metal oxide-silica saturated slag was measured at 1498 K. The results are correlated using ion fractions, calculated either according to Temkin’s method, or as electrically equivalent ion fractions. The simpler method suggested by Temkin correlates slightly better than the other giving the following relations between the ionic concentration quotients and impurity concentration in the metal: logN _Pb ⁺⁺/N ² _Cu ⁺ = logX _Pb + 2.40 ± 0.05, valid up toX _Pb = 0.003 logN _Ni ⁺⁺/N ² _Cu ⁺ = 0.44 logX _Pb + 0.15 ± 0.07, valid up toX _Ni = 0.004. In the nickel systems, an Ni rich phase, identified as NiO, separates from the metal at X_Ni = 0.04 (0.4 wt pct). A tentative phase diagram of the Cu₂O-NiO-SiO₂ system at 1498 K is presented. The data found in this investigation explain why the impurities Pb or Ni cannot be practically reduced to low levels by oxidation. This results from the large amounts of copper that are oxidized in going to low impurity levels. Use of a two-slag refining process is shown to cut slag losses of copper to less than half those encountered with a single slag operation.     

硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜

建立了硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜的新方法。探讨了硫氰酸铵溶液用量、十四烷基三甲基溴化铵（TTMAB）溶液用量和酸度等因素对Cu²⁺浮选率的影响,讨论了Cu²⁺的浮选分离机理。结果表明,在最佳条件下,由Cu²⁺,SCN^-和十四烷基三甲基溴化铵阳离子(TTMAB⁺)形成的不溶于水的三元缔合物(TTMAB)₂ ［Cu(SCN)₄］被定量吸附在TTMAB⁺与SCN^-作用产生的微晶物质TTMAB⁺·SCN^-表面,且被浮选至水相上形成界面清晰的液-固两相,而Fe³⁺、Co²⁺、Ni²⁺、Cd²⁺、Mn²⁺、Al³⁺等离子仍然留在水相中,实现了Cu²⁺与这些离子的定量分离。据此建立了硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜的新方法,进行了合成水样中Cu²⁺的定量浮选分离,浮选率为93.4%～103.6%。     

Stripping of copper from CYANEX® 301 extract with thiourea–hydrazine–sodium hydroxide solution

The stripping of copper from the organic extract of bis(2,4,4-trimethylpentyl) phosphinodithioic acid, CYANEX® 301, using an aqueous mixture of thiourea, hydrazine and sodium hydroxide has been investigated. The optimal concentrations of the aqueous solution were found to be 1.0 M, 5 × 10^− 2 M and 5.0 M, respectively which led to 95% stripping of copper from CYANEX 301 with concomitant regeneration of the extractant. The characterization of the stripped copper product was done using a combination of microanalyses, cyclic voltammetry and X-ray diffractometry (XRD). The product was made up of two non-stoichiometric copper sulfides, Cu_xS with x = 1.60 and 1.77. Cu_1.60S was the major product. Hydrazine appears to play the role of reducing the disulfide species of CYANEX 301, R₂P(S)S–S(S)PR₂, formed during the extraction step, back into CYANEX 301, whereas thiourea provides a source of sulfur in the formation of the stripping products.     

Dissolution of bornite in sulfuric acid using oxygen as oxidant

Leaching of natural bornite in a sulfuric acid solution with oxygen as oxidant was investigated using the parameters: temperature, particle size, initial concentration of ferrous, ferric and cupric ions, and using microscopic, X-ray and electronprobe microanalysis to characterize the reaction products. Additionally, stirring rate, pH and P_O2 were varied. Dissolution curves for percent copper extracted as a function of time were sigmoidal in shape with three distinct periods of reaction: induction, autocatalytic and post-autocatalytic which levelled off at 28% dissolution of copper. The length of the induction period was not reproducible, causing the dissolution curves to be shifted with respect to time. The dissolution curves in the autocatalytic and post-autocatalytic regions were reproducible, and this property was utilized to treat much of the kinetic data. The iron dissolution curves had four dissolution regions. An initial small but rapid release of iron to solution preceded the three periods just given for copper dissolution. Aside from this initial iron release, the iron and copper dissolution curves were almost identical.Stirring rate had no effect on dissolution of copper above 400 min^?1 nor did oxygen flow rate in the range 20–40 cm³/min. Dissolution rate was slightly dependent on oxygen partial pressure for P_O2 < 0.67. Hydrogen ion concentration had no effect except that sufficient acid was required to prevent hydrolysis and precipitation of iron salts.The dissolution rate was directly dependent on the reciprocal of particle diameter indicating possible surface chemical reaction control, but the activation energy of 35.9 kJ/mol (8.58 kcal/mol) for the autocatalytic region of copper dissolution is slightly too small for that, though not unreasonable. Initial addition of Fe²⁺ had a rather complex effect and markedly enhanced dissolution of copper, as also did initial addition of Fe³⁺. Microscopic analysis showed nuclei of two new phases, covellite and Cu₃FeS₄, in the induction region. The new phases grow rapidly in the autocatalytic stage, which is controlled by nuclei formation and chemical reaction. The post-autocatalytic region is characterized by complete transformation of bornite into covellite on the particle surfaces and Cu₃FeS₄ as an internal product with an X-ray spectrum very similar to that of chalcopyrite. The post-autocatalytic region is controlled by autocatalytic growth of newly formed phases. Further reaction beyond the autocatalytic region (percent copper dissolution > 28%) occurs so slowly with oxygen as oxidant that it was not studied.The rate of copper dissolution appears to be controlled by the rate of iron dissolution. Using that and the other experimental evidence a mechanism for reaction is proposed in which iron-deficient bornite, Cu₅Fe_?S₄, is formed on the surface by initial preferential iron dissolution. Labile Cu⁺ diffuses into this from Cu₅Fe_?SO₄ and unreacted bornite to produce CuS on the surface. Depletion of labile Cu⁺ ions from Cu₅FeS₄ produces Cu₃FeS₄ in the interior of the mineral particles.     

Evaluation of zinc sulfate electrolytes by cyclic voltammetry and electron microscopy

A cyclic voltammetric technique has been developed for approximating the quantities of active chemical species present in zinc sulfate electrolytes. The experimental apparatus consisted of a Pyrex “H” cell, an aluminum cathode encased in a Teflon holder, a carbon anode and a mercurous sulfate reference electrode. Voltammograms were obtained using industrial, purified neutral leach solution (Cominco Ltd., Trail, BC) acidified to give a final concentration of 0.77 M Zn⁺⁺ and 1 M H₂SO⁴. The polarization curves were then evaluated and used as reference standards to compare with results obtained when various organic and inorganic additions were made. The deposit morphologies obtained for short-time cathodic cycles were also studied with the aid of a Scanning Electron Microscope. Changes in concentrations of glue in the 5 to 10 ppm range and of antimony in the 5 to 10 ppb range were detected using the techniques described.     

Effect of added cobalt ion on electro-deposition of copper from sulfate bath using graphite and Pb–Sb anodes

Effect of added Co²⁺(aq) on copper electro-deposition was studied using Pb–Sb and graphite anodes and a stainless steel cathode. The presence of added Co²⁺(aq) in the electrolyte solution was found to decrease the anode and the cathode 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) and cyclic voltammetry (CV) were used to study the influence of added Co²⁺(aq) on the anodic and the cathodic processes in a copper sulfate-sulfuric acid electrolyte. The oxygen-evolution potential is depolarised at lower current densities (≤ 150 A/m²) and attains saturation at [Co²⁺]_o ? 600 ppm; whilst at higher current densities (≥ 300 A/m²) it is depolarised with [Co²⁺]_o ≥ 300 ppm. The presence of Co²⁺ promoted the deposit of a smoother and brighter copper cathode as measured by surface reflectivity. X-ray diffraction (XRD) showed that added Co²⁺ changed the preferred crystal orientations of the copper deposits. Scanning electron microscopy (SEM) indicated that the surface morphology of the copper deposited in the presence of added Co²⁺ has well-defined grains. Analysis of cathode copper deposits found negligible cobalt.     

Effects of ionic liquid additive [BMIM]HSO4 on copper electro-deposition from acidic sulfate electrolyte

The effect of a new ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ on the kinetics of copper electro-deposition from acidic sulfate solution was investigated by cyclic voltammetry, polarization and electrochemical impedance measurements and compared with those exerted by the conventional additive, thiourea. Results from cyclic voltammetry and kinetic parameters such as Tafel slope, transfer coefficient and exchange current density obtained from Tafel plots, indicated that [BMIM]HSO₄ had a pronounced inhibiting effect on Cu²⁺ electro-reduction and led to more leveled and fine-grained cathodic deposits. In addition, [BMIM]HSO₄ was found to inhibit the charge transfer and slightly change the copper electro-deposition mechanism compared to the absence of additives. Data obtained from X-ray diffraction spectra revealed that the presence of these additives did not change the crystal structure of the electro-deposited copper but strongly affected the crystallographic orientation of the crystal planes.     

Formation of complex compounds of univalent copper at the Cu<Superscript>0</Superscript>-Cu<Superscript>2+</Superscript> interphase boundary in chloride solutions

Kinetics and a mechanism of formation of compounds of univalent copper at the interphase boundary Cu⁰-Cu²⁺ in the solution containing excess chlorine anions are investigated by the spectrophotometry method. It is shown that the [CuCl₂]^? and [CuCl₃]^2? complex anions are formed during the contact of metal copper with the Cu²⁺ ions. The former ones are characterized by the appearance of the band in the region of 233 nm in the spectra of electron absorption, and the latters ones—in the region of 273 nm. The dependence of intensity of absorption bands on the contact time of the Cu²⁺ ions with copper is used to estimate the kinetic parameters of formation and oxidation of the [CuCl₂]^? and [CuCl₃]^2? ions. A thickness of the reaction layer, in which they are formed, is determined. The formation of the Cu(I) compounds during the contact interaction of copper with the Cu²⁺ ions is confirmed by the results of electrochemical investigations. The mechanism of cathode reduction of copper-containing compounds on a copper electrode is suggested.     

铜电解液物理化学性质之四:电解液中Cu2+的扩散系数

在铜电解过程中，Cu^2 的扩散系数不仅影响阳极的溶解和阴极的沉积特性，而且还影响着阴、阳极的极化情况。本文对铜电解液中Cu^2 的扩散系数的研究方法、研究情况等进行了比较和综述。     

Cathodic copper deposition at 65 °C in the absence and presence of Bi3+ and Sb3+ additives in acidified CuSO4 aqueous solutions

An electrochemical study by cyclic voltammetry and potentiostatic pulse method of the cathodic deposition of copper on polycrystalline copper electrode was carried out in acidic aqueous copper sulfate solution. Comparative electrochemical investigations were performed in electrolytes in the absence and presence of Bi³⁺ and Sb³⁺ ions. All experiments were performed at 65 °C. For bulk copper deposition, the results indicate that in the presence or absence of additive ions, the charge transfer at the Cu/Cu²⁺ electrode occurs in two consecutive one-electron steps, with Cu⁺ being formed as an intermediate. The addition of Bi³⁺ to the electrolyte retarded the copper deposition process, while the introduction of Sb³⁺ caused a depolarization effect. The kinetic studies in the potential range which characterizes the deposition of bismuth show that this reaction takes placevia a stepwise electron transfer mechanism. In the case of antimony-containing electrolyte, the cathodic reduction was found to proceedvia a two-electron transfer pathway. The presence of Sb³⁺ and Bi³⁺ in potentiostatic studies shows that the additive ions behave in a manner consistent with that observed by cyclic voltammetry. The nucleation and growth of bulk copper deposition appears to occurvia aninstantaneous three-dimensional (3-D) nucleation and growth mechanism. However, in the presence of Bi³⁺ or Sb³⁺, copper is deposited by aprogressive 3-D nucleation and growth pattern. X-ray photoelectron spectroscopic surface analyses revealed strong incorporation of both antimony and bismuth within the copper deposit.