Refining of Secondary Lead

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. 

Some refining of secondary bullion is required for the removal of antimony, arsenic, copper and tin. This is usually done in kettles using standard pyrometaUmgical refining techniques, but is far less extensive than for primary lead. 

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 lead-bearing components ate released from the case and other nordead-containing parts, followed by the smelting of the battery plates, and refinement to pure lead or specification alloys. The trend toward battery grid alloys having Httle or no antimony, increases the abiHty of a recovery process to produce soft lead (refined). As requited in the production of primary lead, each step in the secondary operations must meet the environmental standards for lead concentration in ait (see Air pollution Lead compounds, industrial toxicology). 

By-Product and Secondary Antimony. Antimony is often found associated with lead ores. The smelting and refining of these ores yield antimony-hearing flue, baghouse, and CottreH dusts, drosses, and slags. These materials may be treated to recover elemental antimony or antimonial lead from which antimony oxide or sodium antimonate may be produced. 

The SIC code of the battery plant is 3691 (storage batteries) the SIC code for the smelter is 3341 (secondary smelting and refining of non-ferrous metals). A lead oxide production plant located adjacent to the battery plant, on the same property, also falls under SIC code 3691. 

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 ... 

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. 

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. 

With this method, the refining process takes place in open kettles, usually quite large, heated by a direct flame underneath. Plants producing lead from spent batteries prefer this process because the investment and direct costs are lower and there is a small quantity of secondary metals. Refining can be performed either continuously or in batches, according to the production requirement of the plant. 

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