Electrowinning, zinc

Systems for evaluating electrolytes for metal electrowinning have been developed and are being used commercially in zinc production (96). Computerized mathematical models of zinc electrowinning cells have been developed and vaUdated by comparison with experimental data taken from pilot-plant cells (97). 

D. R. Fosnacht andT. J. O Keefe, The Effects of Certain Impurities and their Interactions on Zinc Electrowinning, Metal Trans. B, Vol. 14B, p. 645,1983. 

Zinc electrowinning takes place in an electrolytic cell and involves running an electric current from a lead-silver alloy anode through the aqueous zinc solution. This process charges the suspended zinc and forces it to deposit onto an aluminum cathode (a plate with an opposite charge) that is immersed in the solution. Every 24 to 48 h, each cell is shut down, the zinc-coated cathodes removed and rinsed, and the zinc mechanically stripped from the aluminum plates. The zinc concentrate is then melted and cast into ingots, and is often as high as 99.995% pure. 

Zinc electrowinning Zinc in a sulfuric acid/ aqueous solution, lead-silver alloy anodes, aluminum cathodes, barium carbonate, or strontium, colloidal additives... 

Zinc electrowinning requires high electrolyte purity.186 Cementation with powdered zinc to remove heavy metals such as Cd, Hg, and Pb, and other precipitation techniques are most... 

Figure 8. Effect of glue addition on current efficiency (12) of zinc electrowinning for antimony-containing solutions ((A) 0.0 mg/L Sb (B) 0.04 mg/L Sb and (C)...

Figure 10. Current efficiency for zinc electrowinning vs. cobalt concentration for prepared electrolytes (4) containing 65 g/L Zn and 100 g/L H1SOi T = 45°C, current density = 40 mA/cm2 (A) 0.0 ppb Sb (B) 28 ppb Sb...

Metallic impurities complicated zinc electrowinning [361-368] from acidic sulfate solutions and can adversely affect the cathodic current efficiency, cell potential, power consumption, deposit quality, and the overall polarization behavior of the cathode. 

MacKinnon and coworkers [391-393] have studied a number of organic compounds as additives and have shown that tetrabutylammonium chloride improves surface morphology and current efficiency during zinc electrowinning from acidic chloride solutions. A similar influence was observed using other tetraalkylammo-nium compounds as additives [371, 374, 375, 394],... 

The effect of antimony, germanium, and nickel ions, and the organic additives on the zinc electrowinning from sulfuric acid electrolytes was also studied by Ivanov [400]. 

Also, the influence of aluminum sulfate, animal glue, and an extract of horse-chestnut nuts on zinc electrowiiming from a weak acidic sulfate electrolyte prepared from an industrial waste product was investigated [401]. The use of additives mixture has a beneficial effect on zinc electrowinning and results in smooth, slightly bright zinc deposits. 

The zinc electrowinning was also studied in alkaline solutions [405-407]. 

The concentrated solution of zinc(II) sulfate produced in this way forms the feed to the zinc electrowinning stage, and the regenerated D2EHPA is recycled to extraction. 

See also - Leclanche cell, -> Zn2+/Zn electrodes, -> Zn2+/Zn(Hg) electrodes, -> zinc-air batteries (cell), -> zinc-carbon cell, -> zinc electrowinning. 

Cadmium production is often connected with zinc production. The impure cadmium metal produced in the purification of zinc electrowinning electrolyte is dissolved in 150 g L-1 sulfuric acid solution and electrowon in a process similar to that for zinc. The impure metals that would disturb electrowinning, for example, Cu, Ni, As, are removed by cementation with impure cadmium. The solution is neutralized with lime. The electrolyte contains 140-180 gL-1 Cd, 30-40gL x Zn, some chlorides, and animal glue as additives. The electrolysis is done using... 

A. Siegmund, D. Prengaman, Zinc electrowinning using novel rolled Pb-Ag-Ca anodes, Hydrometallurgy 2003 5th International Symposium, Honoring Professor Ian M. Ritchie, Minerals, Metals and Materials Society (TMS), Vancouver, Canada, 2003, pp. 1279-1288. 

The influence of orthophenylene diamine and sodium lignin sulfonate on zinc electrowinning from industrial zinc electrolyte was studied [399]. A very negative effect of orthophenylene diamine on current efficiency was found. 

ABC extractants were found to possess attractive properties with regard to salt extraction. Extraction is efficient and selective. Compared with liquid cation exchangers, ABC extractants are less sensitive to acidity in the aqueous phase and extract alkali and alkaline earth metals better. Both the cation and the anion are extracted therefore, no acid or base addition is required for pH adjustment or for stripping. Extraction is reversible and provides for back-extraction of the extracted salt by water. Several potential applications of ABC extractants in salt extraction were studied, including MgCb recovery from concentrated seawater [2,4,5,7], separation of LiCI [6], removal of Fe from AlCl solutions [14,23], and recovery of ZnSO from zinc electrowinning bleeds [21]. 

Acid-containing wastes are produced in many industries. Thus, in leaching of minerals, in regeneration of cation exchangers, and in metal surface treatment, only a part of the acid is utilized (due to the reduced activity at the lower acid concentration). The acids plus salts comprising aqueous solutions formed in these operations as well as in others (e.g., zinc electrowinning) are neutralized in most cases and disposed of. Efficient separation and recovery of the acid values is more beneficial, as it would save on acid and base consumption, reduce discharge of solution or solids, and enable recovery of other valuable components (e.g., metal values) from the deacidified solutions. 

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