Lead silver anodes

Lead silicochromates Lead-silver Lead-silver alloys Lead-silver anodes... 

Zinc is extracted from the purified solution in cells using lead/silver alloy anodes and aluminum cathodes at a current density of 38-60 amperes/square foot (400-650 amperes/square meter) The product is normally SHG zinc, particularly if strontium carbonate is added and/or lead/silver anodes of greater than 0.596 silver content are used. After deposition of 24 to 72 horns, the cathodes are removed from the cells and the zinc is stripped by automatic machines in modem plants, melted, and cast for market. The move to automated handling of large cathodes was a major factor in lowering the overall labor requirement in producing zinc. 

Lead contamination of the cathodes in zinc electrowinning is minimized by the formation of a stable protective coating of Pb02 on the surface of the anode. The formation of the stable Pb02 layer is a slow process on the normally utilized lead-silver anodes. Lead-calcium-silver alloys, investigated and applied in the past, also showed a very slow rate of formation of the protective Pb02 layer. 

Lead-silver anodes have been used for many years for zinc electrowinning. The anodes are produced by casting a lead - 0.5-1.0% silver alloy into a mold containing a copper bus bar and having the anode shape. The anodes have been produced in flat, ribbed, or perforated designs for the body of the anode. 

Lead-silver anode (Pb with 0.25 0.75 wt.% Ag) with a copper core... 

Anode material (+) Lead-silver anode (99Pb-lAg) Lead-silver anode (99Pb-l... 

Electrowinning of zinc is from sulphuric acid leach. The solution is purified from more noble metals by two methods one is to add scrap iron, oxidize it to the ferric state which is precipitated, carrying down many impurities. The other method is to add zinc dust, thus precipitating the more noble metals. Cadmium, as well as other metals, are usually recovered at this stage. The electrolysis is between lead-silver anodes and aluminium cathodes the product is generally 99-9% pure. 

Crude lead contains traces of a number of metals. The desilvering of lead is considered later under silver (Chapter 14). Other metallic impurities are removed by remelting under controlled conditions when arsenic and antimony form a scum of lead(II) arsenate and antimonate on the surface while copper forms an infusible alloy which also takes up any sulphur, and also appears on the surface. The removal of bismuth, a valuable by-product, from lead is accomplished by making the crude lead the anode in an electrolytic bath consisting of a solution of lead in fluorosilicic acid. Gelatin is added so that a smooth coherent deposit of lead is obtained on the pure lead cathode when the current is passed. The impurities here (i.e. all other metals) form a sludge in the electrolytic bath and are not deposited on the cathode. 

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

Lead-silver is primarily used in seawater and strong chloride-containing electrolytes. PbAg anodes are particularly suitable for use on ships and in steel-water constructions, especially as they are relatively insensitive to mechanical stresses. The original alloy developed by Morgan [8,9] consists of 1% Ag and 6% Sb, with the remainder Pb. It is represented as alloy 1 in Table 7-2. A similar alloy developed by Applegate [10] has 2% Ag and the remainder Pb. Another alloy... 

Mine, F., Ogaia, Y., Yasuda, M. Consumption of Lead-silver Alloy Anodes in Sulfuric Acid, B. Electrochem., 4, 61-65 (1988)... 

Barnard, K. N., Christie, G. L. and Gage, D. G. Service Experience with Lead Silver Alloy Anodes in Cathodic Protection of Ships , Corrosion, 15, 11, 581-586 (1959) Peplow, D. B. and Shreir, L. L. Lead/Platinum Electrodes for Marine Applications , Corr. Tech. Apr. (1984)... 

Co-axial anodes These are copper-cored anodes of lead silver, platinised titanium and platinised niobium. 

It should be remembered that a minimum current density is necessary to ensure passivation of the anode and that anodes operating below this current density may experience rapid consumption rates. A minimum value of 32-3 Amis quoted by Barnard et The consumption rate of lead silver is high in the initial stages of operation as can be seen from Table 10.18. However, the rate in seawater, taken over an extended period, is generally taken as 0 06 kg A y . 

Electrorefining has been used for the purification of many common as well as reactive metals. It has been seen that the emf or the potential required for such a process is usually small because the energy needed for the reduction of the ionic species at the cathode is almost equal to that released by the oxidation of the crude metal at the anode. Some metals, such as copper, nickel, lead, silver, gold, etc., are refined by using aqueous electrolytes whereas molten salt electrolytes are necessary for the refining of reactive metals such as aluminum,... 

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... 

Note Most process operations are accomplished without the use of process water No wastewater characterization data available Anode production (zinc, mercury, TSS, oil, and grease) Cathode production (copper, chromium, zinc, lead, silver, nickel, mercury, and TSS)... 

The original process used aqueous tetraethylammonium ethylsulfate as the electrolyte, a lead cathode, and a lead-silver alloy anode. The Mark II process, commercialized in the mid-1970s, uses an emulsion of acrylonitrile in aqueous sodium phosphate containing a salt of the hexamethylene-bis-(ethyldibutylammonium) cation. The process was invented in 1959 by M. M. Baizer at Monsanto Corporation, St. Louis, MO. It was commercialized in 1965 and has been continuously improved ever since. The process is also operated in Japan by Asahi Chemical Industry Company. In 1990, the world production of adiponitrile by this process was over 200,000 tonnes per year. 

Lead-calcium-silver anodes, 74 777 Lead-calcium-tin alloys, 74 775-776 Lead carbonates, 74 794-795 Lead chalcogenides, 79 157 Lead chloride, 74 785 Lead chromate... 

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