On the Electrowinning of Zinc from Alkaline Zincate Solutions

Abstract

The cathode current efficiency for the electrowinning of zinc was determined under different conditions of alkali concentration (2-8M), current density (10-40 mA. cm-2), and temperature (30-75~ Some remarkably high values of current efficiency were observed especially at 75~ A possible mechanism involving the discharge of monovalent complex ions is suggested. The effect of two tetra-alkyl ammonium salts TAS(a) and TAS(b) was investigated. The tetra-alkyl ammonium hydroxide, TAS(a) was found more suitable than the tetra-alkyl ammonium ethoxide, TAS (b). The morphology of zinc deposits was inspected by the scanning electronmicroscope; these were mainly spongy deposits. The cell voltage was measured and the energy consumption was calculated and was found to decrease with the increase of temperature. The total energy kWh/kg of deposited zinc from an additive-free solution at 75~ was 1.253 kWh/kg. In the presence of 0.37 rag/1 TAS(a), a further reduction was observed. The energy consumption amounted to 1.180 kWh/kg at the same temperature. The current density for maximum efficiency was 20 mA/cm 2. * Electrochemical Society Student Member.

Electrodeposition of zinc from sodium zincate/hydroxide electrolytes in a spouted bed electrode

“…deposited zinc, and some surface porosity is evident thereafThese results are close to those obtained in short-term runs ter; Figure 16 (c) and (d) show this porous surface for a with the Berkeley synthetic electrolyte (Figures 9, 10, and particle at 52 hours at greater magnifications. The hexagonal 11), and the micrographs of the deposit were similar to those platelets characteristic of zinc electrodeposits are seen at the obtained from synthetic electrolyte. Microprobe analysis of highest magnification.…”

“…The cell consisted of There have been many investigations of the deposition of zinc from alkaline electrolytes onto more conventional a cathode chamber (space for particles 22 mm thick), which contained a draft tube (15 mm width) and the spouted bed electrodes. For example, Afifi et al [11] have examined the deposition of zinc from alkaline electrolytes onto planar of zinc particles (750 to 850 g, usually of 1.45-mm cut wire particles from Abrasive Materials Inc. (Hillsdale, MI); 0.4-mm zinc cut wire particles used in some experiments were from Platt Bros. & Co. (Waterbury, CT)), plus a 1.6-mmthick copper current feeder to make contact with the particles. The cathode chamber was separated from the anode chamber by a diaphragm.…”

Zinc regeneration in rechargeable zinc-air fuel cells—A review

“…The initial ZnO precipitates are normally loose, but then they tend to agglomerate and thicken over time, eventually form a compact layer causing conductivity problems at electrode surface. Previously, various negative electrodes, such as Zn plate, sheet, cylinder, strip, or Zn amalgam, were applied to study zinc deposition from zincate solutions or Zn/ZnO phase equilibria in the Zn/ZnO system [26][27][28][29][30][31][32]. A porous electrode made of spherical 0.2-cm-sized zinc particles was also tested to study the electro-winning of zinc with simultaneous hydrogen evolution [33].…”

“…Tetra-alkyl ammonium hydroxide and tetra-alkyl ammonium ethoxide were tested. The former was proven to provide a better effect than the latter at deposition temperatures above 30°C because it enhances or catalyzes Zn deposition from a mono-valent zinc complex [27].…”

“…Despić et al [31] also found out that the chemical dissociation of the intermediate univalent complex in between the two electrochemical steps expressed by reactions (27) and (29) acts as the rate-determining step, and the overall reaction order is 2 with respect to both OH -and…”