Lead-Smelting Processes The major smelting processes to recycle lead scrap involve the use of blast furnaces, short rotary furnaces, long rotary kilns, reverberatory furnaces, electric furnaces, and top-blown rotary furnaces.
For many years blast furnaces were the primary furnace for recycling lead. Blast furnaces are used to recycle slag, dross, and residues from other processes. Blast furnaces require metallurgical coke, produce large volumes of gas that must be filtered, require a special charge, require afterburners to burn carbon monoxide contained in off-gases, and produce slag and matte that, in some cases, may be considered hazardous materials. Blast furnaces produce a bullion that is high in antimony; this bullion can be readily refined into lead-antimony alloys.
In most of the world rotary furnaces (long, short, and top blown) have replaced blast furnaces as the major smelting vessels for lead recycling. Rotary furnaces are very versatile. They can accept virtually any type of lead-bearing feed material, including battery scrap, dust, dross, scrap lead, and sludge. Rotary furnaces can use any carbon source such as coal, coke, or ebonite as reducing agent, and they can use a variety of fuels, such as oil, coal, or gas. Because they are batch furnaces, rotary furnaces can be operated in stages to produce low-impurity bullion for refining to pure lead, or they can completely reduce the charge to recover all metal values for production of lead-antimony alloys. Rotary furnaces generally use Na2CO3 and iron as fluxes, which produce a fluid, low-melting slag.