Y. Stefanov

Insoluble anodes used in hydrometallurgy. Part I. Corrosion resistance of lead and lead alloy anodes

A literature review on the corrosion resistance of Pb and Pb alloy anodes used in hydrometallurgy is presented. Data from many authors show that Pb alloys that contain Ag, Co or Tl are the most resistant. The increased corrosion resistance of these anodes is explained by the decreased current density and the decreased potential of the lead component of the alloy due to the higher conductivity of the alloying metals as compared with that of lead. As a result, a greater part of the current is distributed on the alloying metal in spite of its high positive potential.

Lead–cobalt anodes for electrowinning of zinc from sulphate electrolytes

Abstract A new anodic lead–cobalt (Pb–Co) 0.5–6% (by weight) material for electrowinning of zinc from sulphuric acid electrolytes has been obtained. The properties of Pb–Co alloys anodes, based on an entirely different principal were studied by means of electrochemical methods. The results obtained were compared with those from lead–silver (Pb–Ag) anodes with a 1% Ag content as used in industry. It is established that above 0.5% Co, the corrosion resistance of the new anodes is better and at Co content of 3% the anodic overpotential is about 0.08–0.1 V lower than that of Pb–Ag (1%) alloy. The anodic layer of the Pb–Co anodes—dense and tightly attached to the surface—consisted of β-PbO 2 , MnO 2 and PbSO 4 .

Developing and studying the properties of Pb–TiO2 alloy coated lead composite anodes for zinc electrowinning

Abstract A new anodic material for zinc electrowinning from sulphate electrolytes has been developed. This is a lead–titanium alloy coated lead composite electrode containing titanium nanoparticles. The titanium is present in the lead matrix as n-type TiO2. It has been established that the optimal content of the Ti in the composite coatings is about 0·5 wt-%. The behaviour of the lead–titanium anodes during the zinc electrowinning has been studied by means of galvanostatic polarisation investigations. The depolarising of the anodic reaction at lead–titanium composite electrodes is attributed to the increased anode area during continued polarisation. The processes occurring on the lead–titanium anodes during zinc electrowinning have been studied by cyclic voltammetry. The surface morphology of the composite lead–titanium electrodes was investigated by scanning electron microscopy.

Electroextraction of zinc from sulphate electrolytes containing antimony ions and hydroxyethylated-butyne-2-diol-1,4: Part 3. The influence of manganese ions and a divided cell

Abstract By means of cyclic voltammetry, the influence of manganese ions on zinc electroextraction from pure sulphate electrolyte and electrolytes, containing antimony ions and hydroxyethylated-butyne-2-diol-1,4 (EAA), has been studied. It was established that manganese ions (5 g L −1 ) have a negligible effect on the zinc deposition from a pure electrolyte. The separation of electrode compartments by a cation exchange membrane leads to an increase of the amount of deposited zinc. This is due to the prevention of the diffusion to the cathode of MnO 4 − ions and other oxidized products, which decrease the amount of deposited zinc and enhance the deleterious influence of antimony ions. It was proved that the organic additive EAA inhibits the process of zinc redissolution taking place in the presence of antimony ions and the inhibition is stronger when the electrode compartments are separated with a diaphragm.

Investigations of new anodic materials for zinc electrowinning

Abstract A new group of anodic materials and lead–silver alloys, produced in various ways, used as anodes for zinc electrowinning have been investigated. The new anodic materials are composite coatings, deposited on lead–calcium rolled substrates, consisting of a lead matrix and a cobalt–titanium phase. The cobalt and titanium are present in the lead matrix as CoTiO3 nanoparticles. The behaviour of lead–cobalt–titanium anodes during zinc electrowinning was studied by means of galvanostatic polarisation investigations. The processes, occurring on the anodes during zinc electrowinning, have been studied by cyclic voltammetry. The surface morphology of the composite electrodes was investigated by scanning electron microscopy. It has been established that the anodic potentials of the composite electrodes investigated are negligibly higher than those of the classical lead–silver alloy. It has been shown by cyclic voltammetry that the curves of the new electrodes possess the same characteristic peaks as those of pure lead electrode.

Electroextraction of zinc from sulphate electrolytes containing antimony and hydroxyethylated-butine-2-diol-1,4: Part 2: Deposition on a specpure aluminium cathode

Abstract The electroextraction of zinc on a specpure aluminium cathode from sulphate electrolytes containing antimony and hydroxyethylated-butyne-2-diol-1,4 (EAA) has been studied. It was established that the process of reverse zinc dissolution in the presence of antimony ions starts from the very beginning of electrolysis. It is found that the inhibitory effect of the additive on the zinc redissolution manifests itself immediately after the start of electrolysis. The inhibitor concentration of 1.0 ml L −1 results in an increase in the amount of deposited metal twice and in an increase of zinc current efficiency from 30% up to 80%.

Mechanism of the reverse dissolution of zinc in the presence of nickel

Cyclic voltammetry and impedance measurements were used to investigate the influence of an additive, triethyl-benzyl-ammonium chloride, on the kinetics of zinc deposition in acidic sulphate electrolytes containing Niu2+ ions able to induce the reverse dissolution of zinc deposits. It is shown that the adsorbed additive inhibits both the nucleation and growth of zinc deposits. By competing with the formation of a nickel-containing surface compound responsible for a stimulation of hydrogen evolution, the additive adsorption also inhibits hydrogen evolution and thereby stabilizes the galvanostatic deposition of zinc.

Electrochemical behaviour of lead alloys as anodes in zinc electrowinning

Abstract The electrochemical and corrosion properties of the ternary and quaternary lead alloys Pb–0·18Ag–0·012Co, Pb–0·2Ag–0·06Sn–0·03Co, and Pb–0·2Ag–0·12Sn–0·06Co (wt-%) have been investigated. The formation of oxide layers on the surface of these alloys was traced by cyclic voltammetric methods and the composition of the anodic oxide layers was determined by X-ray and SEM analyses. The cobalt inclusions reduce the anodic polarisation and improve the corrosion resistance of the alloy. The Pb–0·2Ag–0·12Sn–0·06Co alloy displays electrochemical and corrosion properties similar to those of Pb–1Ag and can be used as a substitute for the latter as a material for anodes in the electrowinning of zinc from sulphate electrolytes.

Electro-extraction of zinc from sulphate electrolytes containing antimony and hydroxyethylated-butyne-2-diol-1,4. Part 1: Deposition on an aluminium cathode containing iron impurities

Abstract By means of cyclic voltammetry, the initial stages of zinc deposition from sulphate solutions, in the presence of antimony ions and an organic inhibitor of zinc redissolution, were studied. It was found that the redissolution of the zinc deposit, due to the presence of the antimony ions, is more intense when the deposition is carried out without the separation of the cathodic from the anodic compartment. The organic additive — hydroxyethylated-butyne-2-diol-1,4 (EAA) — inhibits the redissolution process and restores the characteristic zinc morphology.

Blocking of harmful effect of bismuth ions during electroextraction of zinc from sulphate electrolytes

Abstract Binary and ternary (Pb–Bi and Pb–Ag–Bi) cast and rolled alloys have been investigated. These alloys are intended for use as anodes in the electroextraction (electrowinning) of zinc from sulphate electrolytes. Characterisation of the alloys has been performed by means of quantitative inductively coupled plasma atomic emission spectroscopy (ICP-AES). This analytical technique has also been employed to determine the quantity of dissolved bismuth in the sulphate electrolytes. The electrochemical behaviour of the investigated alloys has been evaluated by galvanostatic studies and their surface morphology has been examined by scanning electron microscopy. It has been established that addition of inhibitors and complexants leads to an increase of the current efficiency of zinc electrowinning and blocks significantly the harmful effect of bismuth ions on the reaction of zinc deposition.