In most of the world other than the U.S., 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.