Zinc Electrolyte Research Articles

ChemInform Abstract: EFFECTS OF CADMIUM IMPURITIES ON THE ELECTROWINNING OF ZINC

AbstractDer Einfluß von Cd auf die Stromausb.

Effects of Cadmium Impurities on the Electrowinning of Zinc

A study was carried out on the effect of cadmium, a major impurity in commercial zinc electrolytes, on the zinc plating current efficiency in acid sulfate baths. The synthetic electrolyte (200 g · dm−3 Zn++ and 0–100 mg · dm−3Cd++) was continuously circulated through the electrolysis cell. The electrolysis was carried out with a current density of 480–490 A · m−2 at 37°C. Hydrogen overpotential, potential sweep, atomic absorption, x‐ray diffraction, and electron microscopy were used to determine the effect of cadmium on the behavior of the zinc plate. The results indicate that cadmium may either increase or decrease the zinc plating current efficiency. For Cd++ less than 20 mg · dm−3, increasing cadmium concentrations in the electrolyte reduce the hydrogen overpotential and the zinc plating current efficiency. For Cd++greater than 20 mg · dm−3, increasing cadmium concentrations cause a refinement in the structure of the zinc plate with subsequent increase in the hydrogen overpotential and in the zinc plating current efficiency. The incorporation of cadmium into the zinc plate neither significantly alters the crystal orientation of the deposit nor alters the hydrogen evolution mechanism.

Influence of oxygen reduction in the electrowinning of zinc

The electrodeposition of zinc from an acid zinc sulphate electrolyte similar to those used in commercial zinc electrowinning has been studied at a rotating aluminium cathode. The presence of dissolved oxygen is shown to lower the current efficiency for zinc deposition, and the influence of current density, rotation speed, and oxygen concentration indicates that the mass-transfer-controlled electrochemical reduction of oxygen is responsible. The mass-transport parameters of oxygen in the zinc electrolyte are deduced from voltammetric studies on carbon, aluminium, and platinum cathodes. The influence of dissolved oxygen on current efficiency in a practical electrowinning cell is estimated to be in the order of 1%, with the main uncertainties being in the mass-transfer coefficients and in possible oxygen supersaturation.

Pitting of zinc in leclanche and related electrolytesII. Mode of growth of pits and rate of propagation

The nucleation and growth of pits on battery zinc alloy electrodes in commercial (standard) Leclanché and related electrolytes has been studied quantitatively using both potentiodynamic and potentiostatic techniques. Pit numbers, volumes, surface areas and distributions have been determined by optical microscopy. The effect on pitting kinetics of pH, NH + 4 ions and various anions: Br −, Cl −, ClO − 4 and SO 2− 4, has also been investigated. A theory is provided which acts as a basis for interpreting the observed time dependence of the pitting current density at constant potential and deviations of the real system from the idealized model are discussed.

Current photoresponse of an electrolyte–zinc selenide junction

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The structures of zinc electrodeposits formed at low current densities

An examination of zinc electrodeposits formed at low current densities, mainly from alkaline zincate electrolytes but also from pyrophosphate, cyanide and acid sulphate baths, showed that the structures depend more on the cathode potentials than on current densities. Similar structures were formed at the same potentials but at different current densities, varied by changing temperature and making organic additions to the baths. The forms of the deposits are consistent with mechanisms which change from growth along close-packed crystal directions at low overpotentials to random growth at large overpotentials.

Recent Progress in Bright Plating from Zincate Electrolytes

SummaryRecent progress in the development and commercial application of decorative electroplating from zincate solutions is reviewed. New organic additives are described and an explanation of their role in the zincate solution put forward. Detailed results show the variation of cathode current density with solution temperature and other operating variables. Results showing the similarity of the deposit distribution from zincate solutions to that obtained when using cyanide electrolytes are given. The organic contents of various zinc deposits are compared. Results of salt spray testing show the excellent performance obtainable from zincate deposits.

The effect of cadmium on zinc deposit structures obtained from high purity industrial acid sulphate electrolyte

The effect of cadmium on cathodic zinc crystal growth was studied in high purity industrial electrolyte, with and without additives, in an attempt to establish a correlation between morphology, polarization and the extent of cadmium contamination. Cadmium additions to acid zinc sulphate electrolyte did not have a significant effect on the zinc deposit orientation but did substantially refine the deposit grain size. The refinement in deposit grain size is directly related to the level of cadmium in the zinc deposits. Cadmium, in combination with glue and optimum amounts of glue and antimony, also reduced the deposit grain size: the preferred deposit orientation remained (1 1 2) with a slight tendency to (1 0 1) at high glue concentrations. Cadmium in combination with antimony resulted in an increased depolarization of zinc deposition and a basal (0 0 2) deposit orientation. Lead additions to zinc electrolyte containing cadmium resulted in increased deposition overpotentials and intermediate to vertical deposit orientations.

The electrode behaviour of zinc in ternary alkaline electrolytes stabilized by silicate

The vapour pressure of alkaline solutions has been measured using a modified version of the Ramsay and Young method. The addition of potassium fluoride to 3 molar potassium hydroxide containing 0.15 molar potassium silicate lowers the vapour pressure to that of 8 molar potassium hydroxide. The ternary mixture of fluoride/hydroxide/silicate may be suitable for application in primary zinc/air cells, as the previously reported slurry region is still observed with this electrolyte. The limitations of this mixed electrolyte are discussed.

The electrode behaviour of zinc in ternary alkaline electrolytes stabilized by silicate

The vapour pressure of alkaline solutions has been measured using a modified version of the Ramsay and Young method. The addition of potassium fluoride to 3 molar potassium hydroxide containing 0.15 molar potassium silicate lowers the vapour pressure to that of 8 molar potassium hydroxide. The ternary mixture of fluoride/hydroxide/silicate may be suitable for application in primary zinc/air cells, as the previously reported slurry region is still observed with this electrolyte. The limitations of this mixed electrolyte are discussed.

The effect of foreign atoms on the properties of electrolytic zinc powders

Kinetic and morphological studies have been made of the deposition of zinc powder on steel substrate, from pure alkaline zincate electrolytes and with small amounts of lead and tin ions in the electrolyte. The rate of co-deposition of hydrogen has been followed volumetrically and the current efficiency of zinc deposition calculated as a function of potential.

A meter for measuring the quality of zinc electrolytes

T.R. Ingraham was Head of Extraction, Metallurgy Research Section, Mines Branch and is now Director, Technology Develop~ ment Branch (Air), Environmental Protection Service, Department of the Environment. R.C. Kerby is a Scientific Officer with the Extraction Metallurgy Research Section, Mines Branch, Department of Energy, Mines and Resources~ Ottawa. The successful electrolytic production of zinc is dependent on several factors, one of which is the concentration of harmful impurities in the zinc electrolyte. (1) The concentration of impurities must be kept below some predetermined level or excessive amounts of hydrogen will be evolved during electrodeposition, with a consequent loss in current efficiency and a decrease in the quality of the zinc electrodeposit. (2) To keep the current efficiency of zinc electrodeposition at an economically acceptable level, many electrolytic zinc plants depend on the judgment of experienced operators and, to a lesser extent, on daily measurements of the concentration of certain impurities. The developmen t of a reliable method of automatically measuring and controlling the quality of zinc electrolyte would be of some advantage to the electrolytic zinc industry. Several methods.involving some degree of automation have been tested with varying degrees of sucess. (3-9) However, none of the methods has gained .wide acceptance with the electrolytic zinc industry. Three basic methods have been used to measure the current efficiency of zinc electrolysis. The earliest method was to compare the weight of zinc actually deposited with the amount expected from the quantity of electricity consumed: (10) this method ~oes not lend itself to the automatic measurement and control of zinc' electrolyte quality because the results are known only at the end of the electrolysis. Several groups have developed methods which involve the electrodeposition and anodic dissolution of zinc from a sample of the electrolyte under carefully controlled conditions. (3-5) The ratio of the current required for anodic dissolution to that required for cathodic deposi, tion was used as an indication of the current efficiency of the process. The method has been used for controlling zinc electrolyte quality. Most electrolytic zinc plants control the quality of the zinc electrolyte by continuously analyzing for certain metallic impurities such as iron, cadmium, lead, copper, and nickel. (1) This method presumes that when the concentration of these impurities is kept below certain levels, all other .. harmful impurities are likely to have also been removed during the purification process. Several methods of automatically analyzing samples of the zinc electrolyte have been developed. They involve instrumental techniques such as spectrophotometric analysis (6) and automatic titrations. (7) These methods have the disadvantages of (a) not measuring all the metallic impurities in the zinc electrolyte which could be harmful to zinc electrolysis and (b) not providing data on the cumulative effects of metallic impurities on the current efficiency of zinc electrolysis. A direct method of measuring the

A meter for measuring the quality of zinc electrolytes

A meter for measuring the quality of zinc electrolytes

Anodic Behaviour of Zinc in Potassium Hydroxide Solution: II.* Horizontal Anodes in Electrolytes Containing Zn(II)

Equilibrium solubility data for ZnO in KOH are reported for KOH concentraiions up to 14M.Results of passivation time determination for horizontally orientated zinc anodes In alkaline zincate electrolytes are reported. These results are correlated in the form: (i–i1) tp½ = k, where k and i1 depend on [Zn(II)], [OH−] and temperature. Passivation occurs when the [Zn(II)] at the anode is equivalent to the [OH−] of the electrolyte.Overpotential–current density relationships indicate that the charge-transfer reactIon is complicated.

亜鉛電解における浮遊物質の挙動に関する研究 (第2報)

It has been generally considered that major substances suspended in zinc electrolyte are lead compounds such as PbO2, PbO, PbSO4, Pb and manganese dioxide particles. The experiments, were -made on various properties of these particles in the solution, i. e., the variations of coagulation, electrophoresis, settling rate of suspension, pH value etc. From theabove experiments, it was considered that lead peroxide particles, which aremost harmful in zinc deposit, are positively charged by absorbing hydrogen ion in zinc electrolyte, and deposited on the cathode with zinc by the electrophoresis, but this hydrogenion is exchanged by the presence of manganese dioxide particle and the deposition of lead peroxide on the cathode is prevented.Next, the preventive phenomenon to deposit of lead peroxide particle on the cathode was compared with regard to manganese dioxide and ion exchange resins. From this experimental results, it was considered that the properties of manganese dioxide particle has a, selective ion exchange to hydrogen ion on lead peroxide particle.

Study of a.c. polarographs of copper and zinc in ammonium chloride and ammonium hydroxide electrolytes.

Study of a.c. polarographs of copper and zinc in ammonium chloride and ammonium hydroxide electrolytes.

亜鉛電解における脱落過酸化鉛の挙動に関する研究

The layer of lead peroxide is formed on the anode during the electrodeposition of zinc. It was separated mechanically from anode and suspended in the zinc electrolyte. The variation of lead peroxide particle suspended in the electrolyte and the effects of various lead compounds such as lead oxide, lead sulphate formed by this decomposition to the zinc deposit was investigated.These results are as follows.(1) Lead peroxide is suspended in cohesive state by the cathodic reduction, but lead oxide or lead sulphate is in dispersive state in the electrolyte.(2) Lead peroxide is decomposed easily by the cathodic reduction, it is converted from yellow lead oxide to lead sulphate. This decomposition increases with the rise of temperature and the presence of cobalt ion in the electrolyte.(3) On the presence of lead peroxide, it is deposited mechanically with zinc and we obtained a loosely adherent sponge deposit. The current efficiency of zinc is much lower. Cathodic potential becomes more positive. The content of lead in, deposited zinc is high. These results are accelerated with. an increase of temperature or the presence of cobalt ion in the electrolyte.(4) On the presence of lead oxide or lead sulphate, when alone in the electrolyte, there are much less effect than that of lead peroxide to the zinc deposit. Zinc is obtained in a smooth deposit. The current efficiency of zinc is high. The content of lead in deposited zinc is lower than the case of lead peroxide. Cathodic potential becomes more negative.The effect on the variation of temperature is small. The effect of cobalt ion in the electrolyte is prevented.

The Caustic Electrolytic‐Zinc Process

Zinc is extracted from oxidized ores with solution, and the zincate electrolyte is purified with zinc powder and lime. The zinc is recovered electrolytically as “flake” powder consisting of pinnate crystals. At 12.9 amp/dm2 (120 amp/ft2) about 1.5 kw hr/lb of zinc is required. Many types of oxidized ores have been tested in the laboratory and some pilot‐plant work has been done; the process appears to be feasible.

Effect of Impurities in Zinc Electrolyte on the Electrodiposition of Zinc. X

Effect of Impurities in Zinc Electrolyte on the Electrodiposition of Zinc. X

Effect of Impurities in Zinc Electrolyte on the Electrodeposition of Zinc. XI

Effect of Impurities in Zinc Electrolyte on the Electrodeposition of Zinc. XI