Effect of nickel in zinc electrowinning under periodical reverse current

Massé, Normand; Piron, D. L.

doi:10.1007/bf01008874

Cited by 5 publications

(3 citation statements)

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“…at Oz dp=0 at ar --K--~i ~z ar -0 at Or z = 0, r > r0 [12] r 2 + z2~ oo [13] at z=O,r<ro [14] r = 0 for all z [15] where r is the potential at a given point and K is the conductivity of electrolyte.…”

Section: ~J0mentioning

confidence: 99%

“…r 2 + z2~ oo [13] at z=O,r<ro [14] r = 0 for all z [15] where r is the potential at a given point and K is the conductivity of electrolyte. face, and concentration overpotential within the masstransfer region, which can be expressed as follows…”

Section: ~J0mentioning

confidence: 99%

“…In addition, it was demonstrated that the PCR technique can decrease the energy consumption due to the low anodic overpotential at the lead electrode in the electrowinning of zinc in acidic media (11) and increase the current efficiency of zinc electrodeposition in the presence of 5 mg/1 of lead (12). Mass6 and Piron (13) also showed that the beneficial effect of PCR in zinc electrowinning remained even in the presence of nickel.…”

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Time‐Averaged Current Distribution for a Rotating‐Disk Electrode under Periodic Current Reversal Conditions

Jeong

Lee

Sohn

1992

J. Electrochem. Soc.

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The time-averaged current distribution over the surface of a rotating-disk electrode is calculated under conditions of periodic current reversal by simultaneously solving the transient-convective-diffusion equation and Laplace's equation. The calculated results compare well with experiments performed using the copper/copper sulfate system. The grid search technique is used to determine the optimum plating conditions in terms of uniform thickness of electrodeposits by varying the duty factor and the ratio of anodic to cathodic current density.Pulsed current (PC) technology has long been used in electroplating industries due to the improvements in the quality of electrodeposits, and its characteristics are well described in the monograph by Puippe and Leaman (1). But the current distribution over the electrode surface in pulse plating is generally less uniform than that in dc plating. Recently, Wan and Cheh (2) developed a mathematical model of the pulse plating of copper for the case below the limiting current density condition and calculated the tertiary current distribution on a rotating-disk electrode. Also Chin et al. (3), computed the secondary current distribution on a planar electrode neglecting the mass-transfer effect. They showed that the nonuniform ohmic potential drop in the solution outside the diffusion layer contributed to the nonuniform current distribution.In order to minimize the nonuniformity of thickness distribution, organic additives as well as periodic current reversal (PCR) technique has been practiced in plating industries largely based on empiricism. The organic additives which act as levelers or brighteners generally tend to increase the polarization resistance, leading to an increase in throwing power (4). Popov et al. (5) showed that the macrothrowing power was considerably better with a PCR than with a PC. Also Granato and Sobral (6) found that dendritic growth of gold was not observed even at high current density in electrorefining with PCR technique.Fedkiw and Brouns (7) developed a mathematical model of PCR plating on a planar electrode with an assumption of steady state. Recently, Pesco and Cheh (8,9) presented a simulation of plated through-holes, and compared the current distribution between dc, PC, and PCR. They indicated that plating with PCR appeared to be a promising technique to obtain more uniibrm metal-thickness distribution at low current densities. In addition, it was demonstrated that the PCR technique can decrease the energy consumption due to the low anodic overpotential at the lead electrode in the electrowinning of zinc in acidic media (11) and increase the current efficiency of zinc electrodeposition in the presence of 5 mg/1 of lead (12). Mass6 and Piron (13) also showed that the beneficial effect of PCR in zinc electrowinning remained even in the presence of nickel.In this study, a mathematical model to describe the current distribution on the rotating-disk electrode under periodic reversal conditions is presented with experimental confirmations followed by obt...

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confidence: 99%

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Time‐Averaged Current Distribution for a Rotating‐Disk Electrode under Periodic Current Reversal Conditions

Jeong

Lee

Sohn

1992

J. Electrochem. Soc.

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Electrodeposition of Zinc and Zinc Alloys

Winand¹

2010

Modern Electroplating

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Zinc has a standard reversible potential [À0.76 V/standard hydrogen electrode (SHE)] that is more negative than that of iron (Fe/Fe 2 þ -0.44V/SHE). For this reason zinc is used for sacrificial cathodic protection of steel against corrosion.According to Fischer [1], in metal electrodeposition, zinc can be considered as an intermediate metal, giving rise to medium values of overpotentials due to secondary inhibition resulting from adsorbed hydrolized species.In acid sulfate solutions without an organic additive, BR metallographic cross-sectional structures are obtained (BR: basis reproduction; coherent deposits with coarse crystals whose diameter increases with the deposit thickness; see Fig. 10.1). In chloride electrolytes, even coarser grains are observed, because of the more activating character of chloride ions against sulfate ions [2] and despite the complex formation in solution [3, p. 464]. In cyanide baths, on the other hand, much finer grains are obtained, and the deposits pertain to the FT (field-oriented texture: coherent deposits, with elongated crystals perpendicular to the substrate, with almost constant diameter throughout the deposit thickness) or UD types (UD: unoriented dispersion type; coherent deposit, with small crystals showing three-dimensional nucleation to occur all the time during electrodeposition). Figure 10.2 shows a deposit obtained in a cyanide solution without an organic additive: the structure is initially FT, but it becomes progressively bad. Going from a cyanide bath to a noncyanide alkaline bath should result in still worse deposits because electrolyte complexation decreases [3] and exchange current density increases [4, pp. 528-543].Accordingly, when rather thick deposits are needed and/or if a bright surface is required, organic additives are always present at high concentration (1 g L À1 or more). This always occurs in barrel-and-rack plating of small pieces of equipment, because the local current densities will vary over a wide range. For continuous plating on steel sheets or wires, constant current density and rather good hydrodynamic control may be achieved over the whole cathodic surface, and organic additives are not so much in use.Whatever the pH, zinc is always more negative than hydrogen [5]. In electrolytes where zinc is complexed, its standard reversible potential is still more negative; for instance, for cyanide baths, the reversible potential for reactionin alkaline solution is À1.26 V/SHE [6]. Consequently hydrogen evolution occurs at the cathode as a competitor to zinc deposition, resulting in a decrease of current efficiency and eventually in some atomic hydrogen diffusion into the substrate.Finally, in industrial processes electrolytic plating is an alternative to hot-dip galvanizing. Both processes have advantages and disadvantages. Continual technological improvements make it difficult to conclude in favor of one process over the other. However, hot dip always includes some surface alloying by diffusion, and the deposit thickness is less easily controlled th...

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