The electrochemical behaviour of copper in alkaline solutions containing sodium sulphide

The electrochemical behaviour of copper in NaHCO₃ solution (pH 9) and NaOH solutions (pH 14) in the presence of sodium sulphide (10^–3 to 5×10^–2m) was investigated by using rotating disc electrode and rotating ring-disc techniques, triangular potential scanning voltammetry and potentiostatic steps. When the potential increases from –1.2V upwards, copper sulphide layers are firstly formed at potentials close to the equilibrium potentials of the Cu/Cu₂S and Cu/CuS reversible electrodes. When the potential exceeds 0.0 V (NHE), the copper oxide layer is electroformed. Pitting corrosion of copper is observed at potentials greater than –0.3 V. The charateristics of copper pitting are also determined through SEM optical microscopy and EDAX analysis. There are two main effects in the presence of sodium sulphide, namely, the delay in the cuprous oxide formation by the presence of the previously formed copper sulphide layer and the remarkable increase of copper electrodissolution when the potential exceeds the cuprous oxide electroformation threshold potential. These results are interpreted on the basis of a complex structured anodic sulphide layer and on a weakening of the metal-metal bond by the presence of adsorbed sulphur on the copper surface.     

The inhibiting effect of 3-methyl 1,2,4-triazole 5-thione on corrosion of copper in 3% NaCl in presence of sulphide

The effect of sulphide addition to the corrosion of copper in 3% NaCl was studied. The concentration of sulphide was remained rather low, up to 10 ppm. The effect of sulphide to copper corrosion is controversial in the literature and worth to verify by means of various experimental techniques. The polarization curves, plotted from a potential close to the open circuit one to negative or to positive direction indicated a decrease of corrosion current density, explained in the literature by the protective effect of CuS. In contrast, a quartz crystal microbalance, with electro-deposited copper indicated the increase of corrosion rate with increasing sulphide ion concentration. The EIS measurements showed also an acceleration of corrosion rate by addition of sulphide ions in sodium chloride solution. It is concluded that the presence of sulphide ions in the seawater accelerates the corrosion of copper. To protect the copper structure from the corrosion in presence of sulphide as pollutants, the anticorrosion effect of a new molecule, 3-methyl 1,2,4-triazole 5-thione was examined. The action of this molecule results in the reduction of the both anodic and cathodic current density, and its inhibiting efficiency reached a value of 90% at the concentration of 10 mM.     

Investigation of the surface oxidation of bornite by linear potential sweep voltammetry and X-ray photoelectron spectroscopy

The products of surface oxidation of a natural sample of the copper iron sulphide mineral, bornite, have been determined from analysis of linear potential sweep voltammograms and from X-ray photoelectron spectroscopic examination of the oxidized layer. Anodic oxidation of bornite in alkaline media results initially in the formation of an iron(III) oxide/hydroxide and an iron-free copper sulphide of stoichiometry Cu₅S₄. The latter species is oxidized further at higher potentials to form a copper sulphide of lower copper content and cupric hydroxide. Air oxidation involves the first of these two steps. In acid solution, anodic oxidation yields iron(II) ions rather than an iron oxide in the first stage and copper(II) ions in the second. Sulphate and elemental sulphur are not formed under the experimental conditions investigated.     

Corrosion and passivity of copper in solutions containing sodium sulphide. Analysis of potentiostatic current transients

The electrochemical behaviour of copper electrodes in NaOH solutions with the addition of Na₂S was studied through the analysis of current transients under constant potential and complementary voltammetric and scanning electron microscopy data including energy dispersive X-ray analysis.The overall process can be described by the following three stages. The first stage corresponds to the nucleation and growth of a complex copper sulphide layer at potential values close to the equilibrium potentials of the Cu/Cu₂S and Cu/CuS reversible electrodes. The second stage is related to the rupture of the copper sulphide film at potentials more positive than a certain critical value leading to pitting corrosion of copper metal and yielding a poorly protective copper sulphide layer. The third stage occurs in the copper oxide electroformation range, where the presence of copper sulphide accelerates the electrodissolution of the base metal and copper oxide hinders the sulphidization processes. The current transients of each stage are interpreted through a model based on the nucleation and growth mechanism.     

Comparative study of copper behaviour in bicarbonate and phosphate aqueous solutions and effect of chloride ions

Copper oxidation in aqueous solutions of pH 8 showed some differences in the presence of bicarbonate and phosphate ions. The bicarbonate ions did not interfere with Cu₂O film formation but the Cu²⁺ ions were stabilized by the complexing action of CO _2– ³ anions. In phosphate solutions, copper dissolved in the range of potentials associated with the Cu(I) oxidation state and the Cu(II) compound on the surface resulted in an extensive passivation region. In both solutions, a higher ion concentration caused an increase in the anodic current, suggesting that the copper ions were stabilized by the complexing action of the electrolyte. The copper oxidation current in a bicarbonate solution was higher than that observed in a phosphate solution of the same concentration. The thickness of the Cu(II) film rather than the Cu(I) layer appears to be the important factor related to the stability of the passive layer on the copper surface. The shift in the breakdown potential toward more positive values indicates that both bicarbonate and phosphate ions inhibit localized corrosion due to the presence of chloride ions. Their protective effect depends on the concentration of each anion, although the concentration of chloride ions necessary for pitting is larger in phosphate solutions than in bicarbonate solutions. In both solutions, long-term immersion of copper under anodic polarization results in the precipitation of a protective coating.     

Copper electrodeposition from an acidic plating bath containing accelerating and inhibiting organic additives

Copper electrodeposition on copper from still plating solutions of different compositions was investigated utilising electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and scanning electron microscopy (SEM). An acid copper sulphate plating base solution was employed either with or without sodium chloride in the presence of a single additive, either polyethylene glycol (PEG) or 3-mercapto-2-propanesulphonic acid (MPSA), and their mixture. Thallium underpotential deposition/anodic stripping was employed to determine the adsorption capability of additives on copper. In the absence of chloride ions, MPSA shows a moderate adsorption on copper, whereas PEG is slightly adsorbed. At low cathodic overpotentials, the simultaneous presence of MPSA and chloride ions accelerates copper electrodeposition through the formation of an MPSA-chloride ion complex in the solution, particularly for about 220 μM sodium chloride. The reverse effect occurs in PEG-sodium chloride plating solutions. In this case, from EIS data the formation of a film that interferes with copper electrodeposition can be inferred. At higher cathodic overpotentials, when copper electrodeposition is under mass transport control, the cathode coverage by a PEG-copper chloride-mediated film becomes either partially or completely detached as the concentration of chloride ions at the negatively charged copper surface diminishes. The copper cathode grain topography at the μm scale depends on the cathodic overpotential, plating solution composition and average current density. Available data about the solution constituents and their adsorption on copper make it possible to propose a likely complex mechanism to understand copper electrodeposition from these media, including the accelerating effect of MPSA and the dynamics of PEG-copper chloride complex adsorbate interfering with the surface mobility of depositing copper ad-ions/ad-atoms.     

Silver Recovery from Dilute Aqueous Solutions Using Semi‐Batch RF‐Pertraction

Silver recovery from dilute nitrate solution was studied by using a rotating film‐pertraction technique in a semi‐continuous mode. Tri‐isobutylphosphine sulphide (TIBPS) dissolved in kerosene was used as a carrier and an aqueous ammonia solution as a stripping phase. A high transfer flux of silver ions during the pertraction process was observed. It was shown that the selectivity of silver transport through the TIBPS‐containing liquid membrane provides an excellent separation of silver from other metals such as copper, nickel, and iron presented in the treated solutions.     

Advances and future prospects in copper electrowinning

In recent years research on the electrowinning of copper has led to a number of significant advances. These developments include improved mass transfer and higher current density operation through air sparging, reduced anode overvoltage in the conventional cell as a result of cobalt(II) addition to the electrolyte or the use of alternative types of anodes, and the production of high quality cathodes in the electrowinning of copper from solvent extraction strip liquor. The fluidized-bed cathode offers the possibility of continuous electrowinning as well as the direct electrowinning of copper from dilute solutions. The problem of high power consumption may find its solution in the adoption of an alternate anode reaction or in the electrowinning of copper (I) electrolytes. Noteworthy is the development of unique electrowinning cells in conjunction with the hydrometallurgical treatment of copper concentrates. These cells utilize cuprous or ferrous anodic oxidation with the resulting cupric or ferric ions being active lixiviants of sulphide copper minerals. The numerous advances combined with the increasing tonnage of copper being produced by the electrowinning route ensure an interesting and promising future for this process.     

The effect of pulsed reverse current on the polarization behaviour of acid copper plating solutions containing organic additives

The polarization behaviour of acid copper solutions containing polyethers, sulphopropyl sulphides and chloride ions was studied using both direct and pulsed reverse current. The effect of these additives on the rest potentials of copper foils immersed in the electrolyte was also studied. Polyethers were found to have an inhibiting effect on the deposition of copper whereas the sulphopropyl sulphides produced a stimulating (i.e. depolarizing) effect. Chloride ion concentration was found to have an influence on the adsorption characteristics of the polyether. The use of pulsed reverse current in solutions containing both polyether and sulphopropyl sulphide was found to inhibit the adsorption/diffusion of the sulphopropyl sulphide at the cathode surface. Thus at higher current densities, above 2 A dm^–2, the inihibiting effect of the polyether produced a shift in the cathodic polarization potential to more negative values as compared with an equivalent current density using direct current. At lower current densities, below 2 A dm^–2, the depolarization effect of the sulphopropyl sulphide was still effective. This effect of pulsed current on additive containing solutions can improve dramatically the metal distribution in low current density areas on plated items. This was illustrated by plating Hull cell panels using both pulsed and direct current.     

Dissolved-Air Flotation of Metal Ions

Abstract

Metal ions (copper, nickel, zinc, and ferric ions) were separated from dilute aqueous solutions by dissolved-air flotation. The ions were either precipitated as sulfides or floated (as ions) by xanthates. Copper and nickel were selectively separated; promising results were obtained with single, binary, and ternary mixtures. The effect of several parameters (solution pH, addition of chemical reagents at varying concentrations, and the presence of other ions) on the removal of ions was studied. The collectorless flotation of copper ions was also investigated.     

Selective removal of copper ions from aqueous solutions using modified silica beads impregnated with LIX 84

Silica beads immobilized with 2‐hydroxy‐5‐nonylacetophenoneoxime (LIX 84) were prepared after silica surface modification by γ‐aminopropyltriethoxysilane (SB‐L). Batch and packed‐column tests were conducted to evaluate the metal ion removal capabilities of the prepared adsorbent. Equilibrium isotherms of the SB‐L with aqueous solutions containing copper ions were obtained. In addition, the kinetic performances for copper ion removal from aqueous solutions were investigated. The results showed that the amount of extraction increases with solution pH in the range between 1.5 and 5. The selectivity was also experimentally investigated, these results showed that the SB‐L adsorbed copper ions selectively in the presence of other metal ions such as Ni²⁺, Co²⁺, Zn²⁺, Cd²⁺, Ca²⁺ and Mg²⁺. From the regeneration experiments, it was found that the copper ions adsorbed at the SB‐L surface were recovered by acidic solutions. The recovery ratios were between 78% and 90%, depending on the types of acidic solutions. The results showed that the SB‐L prepared may be used for the selective extraction of copper ions from aqueous solutions. © 1999 Society of Chemical Industry     

Oxidation of hydrosulphide ions on gold Part I: A cyclic voltammetry study

The results of an investigation to determine the mechanism(s) of oxidation of sulphide ions on a gold electrode are discussed. The cyclic voltammetry results are presented in Part I and characterization results after various electrochemical pretreatments are to follow in Part II. The cyclic voltammetry studies show that several stages are involved in oxidation of sulphide ions to form elemental sulphur. Initially, sulphide ions undergo underpotential deposition to form chemisorbed sulphur as isolated atoms. As oxidation proceeds, a monolayer of chemisorbed atoms is formed which reacts with sulphide ions in solution to form polysulphides at higher potentials. As the potential for oxidation is further increased elemental sulphur is produced. The reduction of polysulphide to hydrosulphide ions occurs by a 2-electron transfer process whereas the reduction of elemental sulphur occurs by a l-electron transfer process. The latter reaction involves the formation of an activated complex which is a relatively slow process.     

Cementation-induced recovery of self-assembled ultrafine copper powders from spent etching solutions of printed circuit boards

Ultrafine copper powders have been recovered from spent etching solutions of printed circuit boards by cementation on helical-form iron scrap chips. The tested solution is an ammoniacal copper solution containing 135 g/l copper with minor impurities. The influences of contact time, temperature, pH, initial copper concentration and Fe stoichiometry on the yield, purity and grain size and shape of the precipitated copper powders were studied. Ultrafine self-assembled copper nanocubes with high purity of about > 99% was obtained at temperature 25 °C, time 20 min, pH 2, Fe stoichiometry 1X and initial copper concentration 20 g/l Cu. It was proposed that the precipitation of copper from the solution involved two main processes: (1) adsorption of copper ions on the surface of the iron chips due to the iron oxides present on it and (2) cementation of copper ions onto the metallic iron contained in the chips. Scrap iron chips is seen to be an effective material for copper powder recovery from spent etching solutions in a pure and fine form.     

Solvent extraction of metals from chloride solutions

A review is presented of a series of investigations into the extraction of copper, iron, zinc and cadmium into kerosene solutions of Lix or Kelex reagents from aqueous solutions containing chloride ions. The effects of chloride ions on the extraction of copper and iron were smaller than might have been expected to result from the formation of inextractable metal chlorocomplexes, and the extractants retained their selective properties. Extraction with Kelex 100 from chloride solution increased the separation between zinc and cadmium, in comparison with sulphate solutions.     

Cathodic processes in the leaching and electrochemistry of covellite in mixed sulfate–chloride media

The cathodic processes that occur on a covellite (CuS) surface in mixed sulfate–chloride solutions in the absence and presence of copper(II) ions have been studied using potentiostatic transients and cyclic voltammetry at rotating disk electrodes in the potential range 0.3–0.7 V (versus SHE). This range is relevant to the oxidative leaching of this copper mineral in sulfate and chloride lixiviants. Variations in the concentrations of sulfate and chloride ions had a small effect on the cathodic reduction of covellite in the potential range of 0.5–0.3 V, although the presence of chloride ion resulted in a significant increase in the anodic current on the reverse sweep. On the other hand, addition of copper(II) ions resulted in enhanced cathodic currents and subsequent anodic currents in both sulfate and chloride solutions due to reduction of covellite to an undefined reduced copper sulfide species. Reduction of copper(II) to copper(I) ions becomes the preferred cathodic reaction as the concentration of chloride ions increases, becoming mass transport controlled at a rotating disc electrode at potentials below about 0.4 V. Potentiostatic measurements at potentials negative to the mixed potential in acidic chloride solutions have shown that reduction of copper(II) ions is reversible and have been used to estimate the rate of oxidative dissolution of the mineral which value agrees reasonably well with previously reported leaching rates under similar conditions. Reduction of dissolved oxygen has been found to be very much slower that that of copper(II) ions under ambient conditions.     

The interaction of pyrite with solutions containing silver ions

Linear potential sweep voltammetry and X-ray photoelectron spectroscopy have been used to determine the products of the interaction of pyrite with sulphuric acid solutions containing silver ions. Silver sulphide was found to be the principal product for all reaction times. Initially, some sulphur excess (metal deficiency) in the sulphide lattice was associated with the formation of silver sulphide. The presence of elemental silver in addition to silver sulphide after extended reaction times was evident from the characteristics of voltammograms. This elemental silver was not detected by electron spectroscopy because it was formed as crystallites occupying only a very small area of the surface of the silver sulphide-covered pyrite. Silver sulphide was the only surface silver species present on a pyrite surface during acid iron(III) leaching; elemental sulphur was also identified on such surfaces.     

Electrochemical formation of mackinawite in alkaline sulphide solutions

The growth of mackinawite, an iron-rich sulphide, on an iron electrode at constant potential in alkaline sulphide solutions is preceded by the fast growth of a thin imperfect film of magnetite. Nucleation of mackinawite patches on the electrode starts at fault sites in the oxide film and the rate of coverage is controlled by the rate of oxide removal. Sulphide film formation occurs when the proton concentration at the fault site is high enough to reduce the local concentration of OH⁻ significantly. The protons are released when sulphide ions are oxidised yielding polysulphide species and an elemental sulphur deposit. The mackinawite films are highly stressed and crack readily. This leads to substantial currents on the sulphide covered surface.     

Influence of anion adsorption on the action of inhibitors on the acid corrosion of iron and cobalt

It has been shown by the method of current/potential (i/) curves and by differential capacitance measurements that the chemisorption of halogen anions from H₂SO₄ solutions on cobalt leads, as in the case of iron, to an increase in the overvoltage of the cathodic reaction of hydrogen-ion discharge and of the anodic reaction of metal ionization. Due to a positive charge of the cobalt surface in H₂SO₄ solutions, organic cations are poorly adsorbed and ineffective as inhibitors, but in the presence of halogen anions their adsorption increases and they exert an additional inhibitive effect upon the above reactions, although less pronounced than in the case of iron.

Hydrogen sulphide accelerates the electrochemical reactions occurring on iron and cobalt electrodes. In small concentration in acid solutions, it increases the adsorption of organic bases, which become effective inhibitors. This leads to the disappearance of the accelerating effect of hydrogen sulphide. The distortion of the anodic i/ curves (decrease in the slope in the case of inhibitors and increase in the case of stimulators) is connected with the finite rate of the establishment of adsorption equilibrium and with the removal of the adsorbed organic substance together with the ionized metal atoms. A hypothesis is advanced that the acceleration of the anodic reaction of iron and cobalt ionization in the presence of hydrogen sulphide is due to the formation of a surface catalyst from the chemisorbed HS⁻ ions and the metal atoms.     

脂肪酸-聚醚胺-CO2相行为及萃取性能研究

研究了脂肪酸-聚醚胺-水络合溶剂在CO₂触发开关作用下的相分离行为、开关性能及萃取水溶液中铜离子效能。通过辛酸-癸酸、辛酸-月桂酸、癸酸-月桂酸3种憎水性低共熔溶剂DES和辛酸、癸酸与聚醚胺D230水溶液配伍构建了系列开关型溶剂,并考察了不同脂肪酸与不同浓度聚醚胺D230水溶液配伍形成均相溶液的CO₂响应性能。实验发现,聚醚胺D230水溶液质量分数为10%、13%和15%时,极性逆转导致体系的相行为变化有所不同。借助脂肪酸-聚醚胺-水络合溶剂,实现了脂肪酸DES均相萃取水溶液中铜离子以及与水相的非均相分离萃取模式。实验结果表明,质量分数10%聚醚胺D230水溶液与脂肪酸组合具有良好的CO₂开关相行为,癸酸-月桂酸DES萃取铜离子的效果最佳。实验表明铜离子萃取率达到92.7%。     

Separation of Silver(I) and Copper(II) from Aqueous Solutions by Transport through Polymer Inclusion Membranes with Cyanex 471X

In this work the selective transport of silver(I) and copper(II) ions from aqueous nitrate(V) solutions by transport through polymer inclusion membrane (PIM) has been studied. The membrane consisted of cellulose triacatate (CTA) as the polymeric support, o-nitrophenyl pentyl ether (ONPPE) as the plasticizer and Cyanex 471X (triisobutylphosphine sulphide) as the ion carrier. Ag(I) ions were effectively removed from the source phase by transport through PIM into 0.01 M Na₂S₂O₃ as the receiving phase. The influence of membrane composition on the transport of silver(I) ions has been evaluated.