Lead electrowinning

The use of fluoborate for lead electrowinning from both secondary and primary sources has been developed by Engitec SpA in Italy and is known as the FLUOBOR process (Olper, 1998). 

A novel approach in treating paste in order to provide feed for a paste lead electrowinning process is proposed by Engitec, in which all lead containing salts are converted into PbS by using anaerobic bacteria. This follows the successful commercial application of sulfate reducing bacteria to treat smelter waste waters for the separation and recovery of heavy metals as sulfides. Reactions are as in Equations 10.9 to 10.11 ... 

Gonzalez-Dominguez, J A, Kirby, R C and Heim, H, 1995. An evaluation of lead electrowinning in HjSiFg -PbSiFg electrolytes, in Proceedings Zinc and Lead 95 Symposium, Sendai, pp 713-721. 

The electrowinning process developed by Ginatta (34) has been purchased by M.A. Industries (Atlanta, Georgia), and the process is available for licensing (qv). MA Industries have also developed a process to upgrade the polypropylene chips from the battery breaking operation to pellets for use by the plastics industry. Additionally, East Penn (Lyons Station, Pennsylvania), has developed a solvent-extraction process to purify the spent acid from lead—acid batteries and use the purified acid in battery production (35). 

Anodes. Lead—antimony (6—10 wt %) alloys containing 0.5—1.0 wt % arsenic have been used widely as anodes in copper, nickel, and chromium electrowinning and metal plating processes. Lead—antimony anodes have high strength and develop a corrosion-resistant protective layer of lead dioxide during use. Lead—antimony anodes are resistant to passivation when the current is frequendy intermpted. 

Lea.dAnodes. A principal use for lead—calcium—tin alloys is lead anodes for electrowinning. The lead—calcium anodes form a hard, adherent lead dioxide layer during use, resist corrosion, and gready reduce lead contamination of the cathode. Anodes produced from cast lead—calcium (0.03—0.09 wt %) alloys have a tendency to warp owing to low mechanical strength and casting defects. 

Electrowinning from Aqueous Solutions. Electrowinriing is the recovery of a metal by electrochemical reduction of one of its compounds dissolved in a suitable electrolyte. Various types of solutions can be used, but sulfuric acid and sulfate solutions are preferred because these are less corrosive than others and the reagents are fairly cheap. From an electrochemical viewpoint, the high mobiUty of the hydrogen ion leads to high conductivity and low ohmic losses, and the sulfate ion is electrochemicaHy inert under normal conditions. 

Adding teUurium to lead and to lead aUoyed with sUver and arsenic improves the creep strength and the charging capacity of storage battery electrodes (see Batteries). These aUoys have also been suggested for use as insoluble anodes in electrowinning. 

The ease with which the ferrous ion can be oxidized to a ferric ion in the electrowinning cell furthers this reaction. Attack on the copper is most apparent at the solution line, where it results in corrosion of the loops supporting the cathodes, leading to dropped cathodes. 

In the most common hydrometallurgical process for zinc manufacturing, the ore is leached with sulfuric acid to extract the lead/zinc. These processes can operate at atmospheric pressure or as pressure leach circuits. Lead/zinc is recovered from solution by electrowinning, a process similar to electrolytic refining. The process most commonly used for low-grade deposits is heap leaching. Imperial smelting is also used for zinc ores. 

In the field of electrowinning and electrorefining of metals, titanium has an advantage as a cathode, upon which copper particularly can be deposited with finely balanced adhesion that allows the electrodeposited metal to strip easily when required. Titanium anodes are also being employed as a replacement for lead or graphite in the production of electrolytic manganese dioxide. 

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... 

Lead-cobalt anodes used for electrowinning of zinc from sulfate solutions were investigated by Rashkov et al. [404]. 

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