Rotary-Kiln Process

a process for treatment of the polymetallic by-products of metallurgical production (the slags of lead, copper, and tin production, the solid residues of zinc production [cakes], and so on) in order to extract valuable metals. The by-products to be treated are mixed with pulverized carbonaceous fuel (coke, anthracite, and others) to 35-45 percent of the charge by weight and are heated to 1200°-1300° C in a rotating horizontal tube furnace (known as a rotary kiln). The lead and zinc are reduced from the oxides, distilled, and in the form of a vapor are oxidized again by atmospheric oxygen and carbon dioxide. The reconstituted metal oxides are carried out of the furnace by the gases and collected in dust traps. The so-called sublimates thus obtained represent a product that is rich in volatile metals, which are recovered in subsequent processing. The nonvolatile metals (copper, nickel, and others) remain in the solid product of the rotary-kiln process (clinker). The charge should remain in a loose or friable state during the process. The clinker is concentrated, recovering the excess fuel, which is used again for the process. The copper-enriched product is sent to copper-smelting plants.