Lead-bearing materials

Miscellaneous. Where a copper refinery is adjacent to a lead (qv) plant it is feasible to recover the selenium in slimes by smelting them in conjunction with lead-bearing materials. Utilizing the lower temperatures needed to melt lead, the selenium is volatilized from a lead bath or cupel blown with air. The selenium is recovered from flue dust and fume by scmbbing. This is the process used by Union Miniere at its Hoboken plant in Belgium. 

Lead intake in mammals is caused by both food ingestion and inhaled air containing lead-bearing particles and aerosols. The latter pathway is a two-stage process the deposition of very small lead-bearing materials in the lungs and then the absorption of the metal which ultimately enters the bloodstream. 

The high lead and arsenic fume produced was collected from the balloon flue, spray cooler and baghouse and was roasted in the Tsumeb arsenic plant to reduce the arsenic levels in the fume and to produce arsenic trioxide as a separate product. In due course this fvime was to be smelted in a separate lead campaign, together with other lead bearing materials, to produce bullion in a similar manner to that previously established. 

Sodium—lead alloys that contain other metals, eg, the alkaline-earth metals, are hard even at high temperatures, and are thus suitable as beating metals. Tempered lead, for example, is a beating alloy that contains 1.3 wt % sodium, 0.12 wt % antimony, 0.08 wt % tin, and the remainder lead. The German BahnmetaH, which was used ia axle beatings on railroad engines and cars, contains 0.6 wt % sodium, 0.04 wt % lithium, 0.6 wt % calcium, and the remainder lead, and has a Brinell hardness of 34 (see Bearing MATERIALS). 

Other Metals. Tellurium has been added to copper-base, lead-base, and tin-base bearing aUoys. In babbit-type aUoys, teUurium controls the stmcture and improves uniformity and fatigue resistance by restraining the tendency to segregation (see Bearing Materials). 

Arsenic added ia amounts of 0.1—3% improves the properties of lead-base babbitt alloys used for beatings (see Bearing materials). Arsenic (up to 0.75%), has been added to type metal to increase hardness and castabiUty (21). Addition of arsenic (0.1%) produces a desirable fine-grain effect in electrotype metal without appreciably affecting the hardness or ductihty. Arsenic (0.5—2%) improves the sphericity of lead ammunition. Automotive body solder of the composition 92% Pb, 5.0% Sb, and 2.5% Sn, contains 0.50% arsenic (see Solders and brazing alloys). 

Some other bearing materials find extensive use for which production volume is less well defined. EiHed plastics such as nylon, acetal resin, PTEE, and phenoHcs are formed and molded into bearings in a wide variety of mechanical stmctures. Tin, lead, and bronze alloys are used for oil-film bearings in heavy industrial and power generating equipment, frequently in custom bearings manufactured directly as machine components. 

The dross is removed and fed into a dross furnace for recovery of the nonlead mineral values. To enhance copper recovery, dressed lead bullion is treated by adding sulfur-bearing materials, zinc, and/or aluminum, lowering the copper content to approximately 0.01%. 

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