Refining secondary lead

Several sources of refined secondary lead with higher purity standards, produced specifically for the manufacture of VRLA designs, are now available. Typical purity standards are shown in Table 5.1. 

Refining secondary lead is not as complex as refining primary lead. The low levels of bismuth and silver contained in the product, as shown in Table 15.2, are generally below the specification limits required for most lead alloys and do not require removal. As mentioned above, the processes to remove these elements from lead are quite complex and there are no eeonomie incentives to recover them, as the levels are far too low. 

The U.S. is the world s largest recycler of lead scrap and is able to meet about 72% of its total refined lead production needs from scrap recycling. The secondary lead industry consists of 16 companies that operate 23 battery breakers-smelters with capacities of between 10,000 and 120,000 t/yr five smaller operations with capacities between 6000 and 10,000 t/yr and 15 smaller plants that produce mainly specialty alloys for solders, brass and bronze ingots, and miscellaneous uses. 

Litharge and the other lead oxides that are used in the production of glasses and ceramics are obtained primarily through the oxidation of refined (purified) metallic lead. Because metallic lead does not occur naturally in large quantities, it must be extracted from either primary sources (mineral ores) or secondary sources (recycled materials such as lead-acid batteries and cathode ray tubes). The processing required to refine metallic lead can be broken down into three major steps, as seen in Fig. 3 ... 

Primary and secondary sources of lead exist in the United States and throughout the world [29], U.S. mine production of lead in concentrate is approximately 450,000-500,000 metric tons per year, which represents approximately 15% of the world production. Other countries with significant mine production of lead include Australia, Canada, China, Mexico, and Peru. Refining of secondary lead is dominated by the U.S. production, although other major sources include Canada, China, France, Germany, Italy, Peru, Spain, and the United Kingdom. In the United States, approximately 79% of the current lead refinery production is derived from secondary sources. Worldwide, secondary sources... 

Due to the bypassing of some of the refining stages, secondary lead alloys can have an elevated level of impurities, particularly in antimonial alloys. 

To close the recycling loop, the majority of the production from secondary lead producers returns to the battery manufacturer as alloys and soft lead. At present, secondary producers experience no problems in achieving the purity requirements for most automotive battery alloys, particularly those that are antimony-based. The increased purity requirement in VRLA batteries will, however, make the refining stages more critical. 

Modern industry practice can be extremely effective in limiting lead emissions from recycling facilities. Facility emissions have been a cause of historic concern, with speculation that increased use of lead-acid batteries in electric and/or hybrid electric vehicles might result in unacceptable levels of lead contamination. For example. Lave et al. [23] estimated that emissions to water and air associated with primary lead production, secondary lead production, and battery prodnction were 4, 2, and 1%, respectively, of the total amount of lead processed. In contrast, Socolow and Thomas [24] estimated that secondary smelting and refining were associated with system losses of up to only 0.01% of material processed. 

Refined lead is produced from both primary and secondary sources. Primary lead is that produced from mined ores, whilst secondary lead results from recycled materials such as battery plates and lead pipes. Recycled lead currently accounts for 14% of the world s production of refined lead (Table 1.2, cf. Table 1.1). The consumption of lead is concentrated primarily in only eight countries (Table 1.3). Storage batteries currently account for about half of the refined lead consumption in the western world (Table 1.4), whilst the production of tetraalkyllead, a petrol additive which reduces engine knock, accounts for about 10% of consumption. 

Metallic scrap is one significant source and can be pnrchased by the smelter or refinery at prices reflecting a nominal discount to the prevailing LME price for refined lead. However, the bulk of secondary lead is derived from the processing of recycled scrap lead-acid batteries. The trade is very localised with no general standard terms and the cost to the secondary smelter often simply reflects the cost of collection of scrap batteries. 

Electrolysis of lead fluosilicate solutions is well established for lead refining by the Betts process, as detailed in Chapter 13. The principal advantage is the ability to produce a dense cathode deposit rather than a powder deposit. The process has largely been examined for the treatment of secondary lead materials, which are converted either into lead carbonate or PbO from mixed sulfate-oxide residues, and are then leached in fluosiUcic acid. The US Bureau of Mines developed an approach along these lines as an extension of the Betts electrorefining process to electrowinning (Cole, Lee and Paulson, 1981). This approach was also developed and applied on a commercial scale by RSR Corporation in the USA (Prengaman and McDonald, 1990). 

The standard approach has been to use thin lead starter sheets for the cathode and to melt the total cathode after removal from the cell. The alternative approach is to use stainless steel cathodes and strip the deposited lead from the starting cathode. The latter has been applied more recently in secondary lead refining using fluoroborate electrolytes (Olper, 1998). There must be a balance between the requirements for producing starter sheets and eqnipment required for cathode stripping. 

Other refining technologies, such as hydrometallurgical or aqueous processes, using chemical treatment or solvent extraction and electrolysis, are still in the development phase in the primary sector. They have made some inroads in secondary lead recovery, however, and are discussed in Chapter 6. 

Raw material costs are probably the single most important cost item for smelters. They normally account for as much as 30-40 per cent of total operating costs at both primary and secondary lead plants, but are likely to be proportionately more significant at the latter. Plant location is a crucial influence, as is the particular range of feed that can be processed by each smelter. Raw material costs are also closely linked to the price of refined metal. 

Many primary and secondary lead producers offer a range of products in addition to refined metal, but the degree of product differentiation and value-added is generally limited. These may include various lead alloys, chemicals, composite materials and semi-fabricated (rolled, cast or extruded) goods. Although some refiners may also be involved in the manufacture of intermediate or end-use lead products (like cable sheathing, proprietary chemicals. 

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