Refining and alloying of lead

Once bullion lead has been recovered via the various primary and secondary smelting operations, it must undergo a refining process to remove impurities. Bullion 

Analyses of bullion lead from primary and secondary sources are given in Table 15.2. The data show that the main impurities found in secondary lead are the major constituents of the lead alloys used in the construction of the battery, namely, antimony, tin, arsenic, and copper, whilst minor contaminants include nickel, cadmium, sulfur, bismuth, and silver. 

Analysis of primary lead reveals higher impurity levels, particularly for valuable elements such as silver and gold. The removal and recovery of these elements is an important and valuable process in primary smelting. 

Two methods of lead refining — the fire refining pyrometallurgical and electrolytic methods — are well established throughout the world. The choice of method depends on the impurity content of the bullion (particularly for primary operations) and on important economic considerations. 

The last part of the de-silverizing proeess is the removal of excess zinc from the lead bullion. This can be achieved in numerous ways, such as chlorination and oxidation, but the accepted practice by major primary smelters is vacuum distillation of the zinc from the bullion. The zinc-rich lead is heated to 600°C, and a vacuum is applied. Zinc distils from the lead and deposits in a solid crystalline state on a 

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